JP7828476B2 - Wafer Inspection Equipment - Google Patents

Description

The present invention relates to an inspection device for inspecting wafers.

In the semiconductor manufacturing process, the presence of foreign matter on substrates such as semiconductor wafers can cause defects such as poor wiring insulation and short circuits. These foreign matter can come in a variety of forms, including those generated by moving parts such as transport devices, those generated by the human body, those generated by reactions caused by process gases within processing equipment, and those contaminated with chemicals or materials.

Therefore, by using wafer inspection equipment to detect and manage foreign matter on wafer surfaces, we are able to monitor and control the dust generation status of each manufacturing device and the cleanliness of each process, thereby improving product quality and yield. Foreign matter inspection methods involve irradiating the wafer surface with light such as a laser beam and detecting the scattered light from foreign matter, thereby detecting the size and attachment position of the foreign matter, and acquiring this information as unique information for each wafer.

Wafer holding devices are used during inspection. Wafer holding methods can be broadly divided into backside suction and backside non-contact methods. Backside suction methods use an air intake port on a flat table to suction the backside of the wafer. This means that the backside of the wafer comes into contact with the table and is fixed in place. On the other hand, backside non-contact methods hold only the outer periphery of the wafer and fix it to the table. Backside suction methods are primarily used for wafers with patterns formed on them. Backside non-contact methods are used for wafers before patterns are formed, i.e., bare wafers. Backside non-contact wafer inspection devices, in particular, are used for wafer shipping inspections at manufacturing manufacturers and wafer acceptance inspections at process manufacturers, so they are required to not only prevent foreign matter from adhering to wafers, but also to improve the reproducibility and accuracy of foreign matter detection.

One method for improving the accuracy of detecting foreign particles on wafers is to improve the flatness of the wafer. When a wafer is fixed flat in an inspection device, there is no significant deformation (e.g., warpage) in the wafer, which improves the accuracy of detecting foreign particles. An example of conventional technology for improving wafer flatness is described in Patent Document 1.

The inspection device described in Patent Document 1 includes a chuck with a ring-shaped rim that conforms to the wafer's shape and on which the wafer is placed, and a ring-shaped air gap forming portion disposed on the surface of the chuck. The internal space surrounded by the wafer, chuck, and rim is maintained at a predetermined pressure distribution by gas supplied into the internal space, constantly forming a predetermined air gap between the air gap forming portion and the wafer, correcting wafer flexure and warpage. The inspection device in Patent Document 1 also includes a height position control portion that detects height information near the corrected wafer inspection point and drives an elevation drive mechanism to control the vertical movement position of the inspection point that could not be fully corrected, thereby controlling the wafer's inspection surface to a predetermined height position.

JP 2009-168479 A

Conventional wafer inspection devices have not necessarily satisfied users with their ability to maintain wafer flatness with a simple configuration. For example, the inspection device described in Patent Document 1 ensures wafer flatness by applying gas pressure to the backside of the wafer and dynamically controlling the wafer surface. Because this control is performed in real time on a wafer rotating at high speed during inspection, the control circuitry becomes large. Furthermore, correcting wafer warpage deviation to zero requires addressing the second- and third-order components of rotation warpage, necessitating complex control. Furthermore, the proximity of the correction drive frequency to the wafer's natural frequency can cause self-excited vibration of the wafer, potentially deteriorating wafer flatness.

The object of the present invention is to provide a wafer inspection device that can hold a wafer flat with a simple configuration.

A wafer inspection device according to the present invention includes a rotatable wafer chuck on which a wafer can be placed. The wafer chuck includes an air supply port that supplies air to the backside of the wafer, an air exhaust port that exhausts the air, a clamping mechanism that holds the wafer, and multiple annular protrusions that protrude upward. If the wafer chuck were not equipped with the annular protrusions, the pressure distribution between the wafer and the wafer in the radial direction of the wafer chuck when the wafer chuck rotates is expressed by a high-order function of the radial position. The annular protrusions are shaped so that when the wafer chuck rotates and the air is supplied, the value of the pressure loss caused by the annular protrusions is equal to or greater than the pressure value in the pressure distribution expressed by the high-order function at the same radial position at which the pressure loss value was applied.

The present invention provides a wafer inspection device that can hold a wafer flat with a simple configuration.

1 is a schematic diagram showing a configuration of a wafer inspection device according to a first embodiment of the present invention; FIG. 2 is a perspective view showing a wafer chuck. 2B is an enlarged view of the central portion of the wafer chuck taken along the line AA in FIG. 2A. 2B is an enlarged view of the clamp mechanism and its vicinity taken along the line AA in FIG. 2A. FIG. 2 is a view of the wafer chuck on which the wafer is placed, viewed from above the wafer. FIG. 3B is a cross-sectional view taken along the line BB in FIG. 3A. FIG. 10 is a diagram illustrating the concept of correction pressure. 10A and 10B are diagrams illustrating a correction method using a correction pressure when a plurality of ribs are arranged on a wafer chuck. 10 is a graph showing the change in pressure loss caused by the rib when the distance between the wafer and the rib is changed. FIG. 10 is a diagram showing the positional relationship between the wafer chuck and the optical system immediately after the wafer is placed on the wafer chuck. FIG. 10 is a diagram showing a state in which the measurement position of the height sensor coincides with the center of the wafer due to linear movement of the wafer chuck. FIG. 10 is a diagram showing the wafer chuck moved to a position where the rotation center of the wafer chuck coincides with the geometric center of the optical measurement unit. 10 is a flowchart showing the operation of the wafer inspection device in the second embodiment. 10A and 10B are diagrams illustrating the pressure distribution of the correction air when the wafer chuck described in the first embodiment is used and the pressure distribution of the correction air when a conventional wafer chuck is used. FIG. 10 is a diagram showing the measurement results of the average height in the circumferential direction of the wafer at each position in the radial direction of the wafer. FIG. 10 is a diagram showing the analysis results obtained by examining, by fluid-structure coupled analysis, the change in the radial flatness of the wafer relative to the amount of correction air when a downwardly convex deformed wafer is placed on the wafer chuck of Example 1. FIG. 10 is a diagram showing the analysis results obtained by examining, by fluid-structure coupled analysis, the change in the flatness in the radial direction of the wafer relative to the amount of correction air when an upwardly convex deformed wafer is placed on the wafer chuck of Example 1. FIG. 10 is a diagram showing the results of comparing the radial shape of a wafer with a downward convex deformation obtained by fluid-structure interaction analysis with the shape before the deformation was corrected. FIG. 10 is a diagram showing the results of comparing the radial shape of a wafer obtained by fluid-structure interaction analysis with the shape before the deformation was corrected for an upwardly convex deformed wafer.

The wafer inspection device of the present invention ejects air onto the back surface (lower surface) of the wafer to generate pressure, which corrects the wafer's deformation (or flatness), thereby keeping the wafer flat. In the wafer inspection device of the present invention, the wafer chuck on which the wafer is placed is equipped with an annular protrusion that corrects the wafer's deformation (or flatness), and the shape of the annular protrusion is determined based on the appropriate distribution of the corrective pressure generated between the wafer and the wafer chuck by air, allowing the wafer to be kept flat efficiently with a simple configuration.

In this invention, wafer flatness is an index showing whether a wafer is flat. Wafer flatness is expressed, for example, as the height distance between the top and bottom positions of a wafer that has been deformed due to warping or other reasons when placed on a wafer inspection device. A wafer being flat means that the flatness of the wafer falls within a predetermined range.

Below, a wafer inspection device according to an embodiment of the present invention will be described with reference to the drawings.

A wafer inspection device according to a first embodiment of the present invention will be described. In the wafer inspection device according to this embodiment, the shape of annular protrusions (hereinafter referred to as "ribs") that correct wafer deformation (or flatness) is determined based on the appropriate distribution of radial correction pressure on the wafer chuck. The shape of the ribs includes the size of the ribs (for example, the protruding height and the width, which is the radial length).

Figure 1 is a schematic diagram showing the configuration of a wafer inspection apparatus 10 according to this embodiment. The wafer inspection apparatus 10 mainly comprises a wafer introduction section 11 for introducing a wafer 205 from outside, a transport mechanism 12 for transporting the wafer 205, an inspection chamber 13 for inspecting the wafer 205, and a control section 14 for overall control of the wafer inspection apparatus 10. The wafer inspection apparatus 10 is installed in a space where cleanliness is maintained to prevent foreign matter from adhering to the wafer 205.

The inspection chamber 13 includes an optical measurement unit 131 that optically measures foreign particles on the wafer 205, a wafer chuck 200 on which the wafer 205 is placed, a motor 132 that rotates the wafer chuck 200, and a linear movement unit 133 that linearly moves the motor 132 and the wafer chuck 200. The optical measurement unit 131 is fixed in position. Therefore, the wafer 205 placed on the wafer chuck 200 rotates with the rotation of the wafer chuck 200, and changes position with the linear movement of the wafer chuck 200, allowing the optical measurement unit 131 to measure the position and size of foreign particles present on the surface.

In the following, the directions along the surface (wafer surface) of the wafer 205 placed on the wafer chuck 200 are referred to as the XY direction or horizontal direction, and the direction perpendicular to the wafer surface is referred to as the Z direction or vertical direction. The rotation axis of the motor 132 faces the Z direction. The wafer chuck 200 and the wafer 205 placed on the wafer chuck 200 rotate around the Z direction (vertical direction) as their rotation axis and move linearly in the XY direction (horizontal direction). Furthermore, the radial direction and circumferential direction refer to the radial direction and circumferential direction of the wafer chuck 200 (or the wafer 205 placed on the wafer chuck 200). The inside in the radial direction (center side) is referred to as the inner peripheral side, and the outside in the radial direction is referred to as the outer peripheral side. The outer peripheral part is the part on the outside in the radial direction.

The wafer 205 is loaded into the wafer introduction section 11 while stored in a cassette (not shown). The wafer 205 is then removed from the cassette by the transport mechanism 12 and moved to the inspection chamber 13. The wafer 205 moved to the inspection chamber 13 by the transport mechanism 12 is placed on the wafer chuck 200.

Figure 2A is a perspective view showing wafer chuck 200. In Figure 2A, wafer 205 placed on wafer chuck 200 is removed from wafer chuck 200, and wafer chuck 200 is shown in a transparent view.

The wafer 205 is placed on top of the wafer chuck 200. That is, the wafer 205 is placed in a position opposite to the direction in which gravity acts (the direction of gravity) relative to the wafer chuck 200.

The wafer chuck 200 comprises a wafer chuck base 201, a wafer support 202, an air supply port 204, an air exhaust port 203, a clamping mechanism 206, and multiple ribs 2011. The wafer chuck 200 is capable of placing a wafer 205 thereon and is rotatable around the Z direction (vertical direction) as the rotation axis. The wafer chuck 200 may comprise multiple clamping mechanisms 206.

The wafer chuck base 201 is the main body (base) of the wafer chuck 200.

The wafer support portion 202 is ring-shaped and vertically supports the outer peripheral surface of the wafer 205. As described below, the wafer support portion 202 has multiple contact portions 202a that are in contact with the wafer 205, and multiple non-contact portions 202b that do not come into contact with the wafer 205 and have a gap between them.

The air supply port 204 is an opening that supplies air (correction air) to the back surface (lower surface) of the wafer 205 to correct deformation (or flatness) of the wafer 205, and is located in the center of the wafer chuck 200.

The air exhaust port 203 is composed of the non-contact portion 202b and exhausts the correction air supplied to the back surface of the wafer 205 to the outside of the wafer chuck 200.

The clamping mechanism 206 is a mechanism that holds the wafer 205.

The rib 2011 is an annular protrusion provided on the surface of the wafer chuck 200 facing the wafer 205, and protrudes upward from the wafer chuck base 201. Multiple ribs 2011 are arranged concentrically around the rotation axis of the wafer chuck 200.

The wafer 205 placed on the wafer chuck 200 is held by a clamping mechanism 206 to prevent it from falling off the wafer chuck 200. Furthermore, the wafer 205 placed on the wafer chuck 200 will partially sink under its own weight due to the action of gravity, resulting in deformation such as warping and making it less flat (i.e., reducing flatness). Therefore, in the wafer inspection device 10 of this embodiment, air (correction air) is ejected from the air supply port 204 onto the back surface of the wafer 205 to generate pressure, thereby preventing the wafer 205 from sinking under its own weight and correcting the deformation (or flatness) of the wafer 205. Correction of the flatness of the wafer 205 will be explained later.

The wafer chuck 200 holding the wafer 205 whose flatness has been improved in the above manner is rotated by the motor 132 and moved linearly by the linear movement part 133 in a direction perpendicular to the rotation axis of the motor 132 so that the optical measurement part 131 can measure any foreign matter present on the surface of the wafer 205.

The control unit 14 rotates and moves the wafer chuck 200 holding the wafer 205 as described above, maps the size and position of foreign particles over the entire surface of the wafer 205, and records the data obtained from this mapping as foreign particle data for the wafer 205.

After the foreign matter measurement has been completed, the wafer 205 is released from the clamping mechanism 206 and is transported by the transport mechanism 12 from the wafer chuck 200 to the wafer introduction section 11, where it is placed in a cassette.

The wafer inspection device 10 repeats the above operations to inspect all wafers 205 contained in the cassette in the wafer introduction section 11 for foreign matter.

Next, we will explain the clamping mechanism 206 and the operation of the clamping mechanism 206 to hold the wafer 205.

Figure 2B is an enlarged view of the central portion of the wafer chuck 200 at the A-A cross section in Figure 2A. Figure 2C is an enlarged view of the clamp mechanism 206 and its vicinity at the A-A cross section in Figure 2A. In Figures 2B and 2C, the directions of the black and white arrows indicate the movement direction of each part. The black arrow indicates the movement direction of the part when the clamp mechanism 206 holds the wafer 205. The white arrow indicates the movement direction of the part when the clamp mechanism 206 releases its hold on the wafer 205.

The clamping mechanism 206 is provided on the wafer chuck 200, which rotates the wafer 205, and includes a cam 211, a bearing 213, a bearing holder 214, a compression spring 215, a rod 216, a link 217, a holder 218, and a holder claw 219.

The cam 211 is installed in the center of the wafer chuck base 201 and is attached to an air cylinder 212 that moves vertically (Z direction), and moves vertically.

Bearing 213 contacts cam 211 and converts the vertical movement of cam 211 into radial (XY) movement.

The bearing holder 214 holds the bearing 213 and is connected to the compression spring 215.

The compression spring 215 is connected to the bearing holder 214 and the rod 216 and is radially expandable and contractible.

The rod 216 is connected to a compression spring 215 and can move radially relative to the bearing holder 214 by the expansion and contraction of the compression spring 215.

Link 217 connects rod 216 and retaining portion 218, and when rod 216 moves radially, it displaces retaining portion 218 circumferentially.

The holding portion 218 is rotatable around the dashed line in Figure 2C and holds the holding claws 219. The direction of the rotation axis of the holding portion 218 is the Z direction (a direction perpendicular to the surface of the wafer 205). The link 217 and the holding claws 219 are attached to the holding portion 218 in positions symmetrical about the rotation axis.

The holding claws 219 are attached to the holding portion 218, and can move as the holding portion 218 rotates, bringing them into contact with the wafer 205. The direction of movement of the holding claws 219 is the XY direction (directions along the surface of the wafer 205). The clamping mechanism 206 holds the wafer 205 when the holding claws 219 come into contact with the wafer 205, and releases the wafer 205 when the holding claws 219 no longer contact the wafer 205. It is also preferable that the holding claws 219 be rotatable relative to the holding portion 218. The direction of the rotation axis of the holding claws 219 can be, for example, the Z direction. In other words, the holding claws 219 can rotate laterally (rotation in the direction along the surface of the wafer 205).

The clamping mechanism 206 operates by the movement of air supplied to the air cylinder 212. For example, when the air cylinder 212 operates by air and the cam 211 moves upward, the holding claws 219 move radially away from the wafer 205 and no longer come into contact with the wafer 205. In the clamping mechanism 206, the mechanisms excluding the air cylinder 212 and cam 211 are arranged symmetrically with respect to the central axis of the wafer chuck 200. The number of clamping mechanisms 206 excluding the air cylinder 212 and cam 211 is determined taking into consideration the holding force generated by the clamping mechanism 206 and the holding force required for the clamping mechanism 206.

The operation of the clamping mechanism 206 is described below.

After the wafer 205 is transported to the inspection chamber 13 by the transport mechanism 12, as shown in FIG. 2B, air is supplied to the air cylinder 212, causing the cam 211 to move upward and the rod 216 to move inward (in the direction of the white arrow in FIG. 2B). When the rod 216 moves inward, the link 217 moves inward in response to the movement of the rod 216, as shown in FIG. 2C. This causes the holding portion 218 to rotate, and the holding claws 219, which are positioned symmetrically to the link 217 around the rotation axis, are displaced outward (in the direction of the white arrow in FIG. 2C). This displacement causes the holding claws 219 to move outward beyond the outer edge of the wafer 205. In this way, the holding claws 219 of the wafer chuck 200 open outward, and the wafer chuck 200 is ready to load the wafer 205.

Then, the transport mechanism 12 places the wafer 205 on the wafer support 202 arranged on the wafer chuck 200. Once the wafer 205 has been placed, the transport mechanism 12 exits the inspection chamber 13.

After the transport mechanism 12 exits, the clamping mechanism 206 stops supplying air to the air cylinder 212. This causes the cam 211 to move downward, moving the rod 216 toward the outer periphery (in the direction of the black arrow in Figure 2B). As the rod 216 moves toward the outer periphery, the holding portion 218 rotates, displacing the holding claws 219 toward the inner periphery (in the direction of the black arrow in Figure 2C). This displacement causes the holding claws 219 to come into contact with the outer periphery of the wafer 205, generating a holding force. During this operation, the bearing holding portion 214, compression spring 215, and rod 216 move toward the outer periphery together until the holding claws 219 come into contact with the outer periphery of the wafer 205.

After the holding claws 219 contact the wafer 205, the rod 216 stops moving, but the bearing holder 214 continues to move toward the outer periphery until the movement of the cam 211 finishes. This movement of the bearing holder 214 reduces the relative distance between the bearing holder 214 and the rod 216, causing the compression spring 215 to compress. The compression spring 215 then generates a spring force due to a reaction force, which is transmitted to the holding claws 219.

In this way, the spring force of the compression spring 215 becomes the holding force with which the holding claws 219 hold the wafer 205 in the X and Y directions (directions along the surface of the wafer 205). The spring force of the compression spring 215 is determined by the ratio of the distance from the center of rotation (fulcrum) of the holding portion 218 to the joint (point of force) between the link 217 and the rod 216, to the distance from this center of rotation to the holding claws 219 (point of action). In this way, the holding claws 219 of the wafer chuck 200 come into contact with the wafer 205 and hold the wafer 205.

It is preferable that the holding claws 219 are detachable from the holding portion 218. If the holding claws 219 are detachable, when the holding claws 219 become worn, they can be reattached to the holding portion 218 so that the surface of the holding claws 219 that contacts the wafer 205 is different from before (so that it becomes a new surface). In this way, worn holding claws 219 can be reused, thereby extending the life of the holding claws 219.

The shape of the holding claws 219 can be determined arbitrarily, and can be, for example, cylindrical or rectangular. The holding claws 219 are fitted into the holding portion 218, for example. If the holding claws 219 are cylindrical, the surface of the holding claws 219 that contacts the wafer 205 can be set arbitrarily, thereby further extending the life of the holding claws 219. If the holding claws 219 are rectangular, this has the advantage of preventing the holding claws 219 from rotating at the fitting portion with the holding portion 218, allowing the clamping mechanism 206 to hold the wafer 205 more securely. The shape of the holding claws 219 can be determined, for example, taking into consideration the strength of the fit between the holding claws 219 and the holding portion 218.

In this embodiment, the holding claw 219 is described as rotating laterally (the direction of the rotation axis is in the Z direction), but the holding claw 219 may also rotate vertically (the direction of the rotation axis is perpendicular to the Z direction).

The holding force of the clamp mechanism 206 will now be explained. The functions required for the clamp mechanism 206 to hold the wafer 205 are primarily the alignment function when the wafer 205 is placed, the function to prevent slippage when rotation begins, and the function to resist centrifugal force caused by eccentricity of the wafer 205 during steady rotation. The alignment function when the wafer 205 is placed is provided by static holding force. This is the holding force generated by the compression spring 215 of the clamp mechanism 206. Regarding the anti-slip function and the function to resist centrifugal force, the centrifugal force generated by each component of the clamp mechanism 206 is added to the holding force, so this centrifugal force must also be taken into consideration. At the start of rotation, a holding force greater than the inertial force that tries to bring the wafer 205 to a standstill is required. During steady rotation, a holding force greater than the centrifugal force calculated by adding up the eccentricity, mass, and rotation speed of the wafer 205 is required. The holding force that resists these forces can be adjusted by adjusting the shape and mass of components such as the bearing 213, bearing holder 214, rod 216, and link 217.

We will now explain the multiple ribs 2011 provided on the wafer chuck 200. The ribs 2011 are annular protrusions that correct deformation (or flatness) of the wafer 205.

Figure 3A is a view of the wafer chuck 200 with the wafer 205 placed on it, viewed from above the wafer 205 (in the +Z direction). Figure 3B is a view of the B-B cross section in Figure 3A. In Figure 3B, the arrows indicate the flow of correction air (air for correcting deformation (or flatness) of the wafer 205).

As mentioned above, the wafer chuck 200 on which the wafer 205 is placed supplies corrective air from the air supply port 204 to the back surface (lower surface) of the wafer 205 to correct deformation of the wafer 205 and hold the wafer 205 flat. As already mentioned, the wafer 205 is held on the wafer chuck 200 by the holding force of the holding claws 219 of the clamping mechanism 206.

As shown in Figure 3A, the wafer support portion 202 of the wafer chuck 200 has a contact portion 202a, which is the portion with which the wafer 205 actually comes into contact, and a non-contact portion 202b, which does not come into contact with the wafer 205 and has a gap between it and the wafer 205.

As shown in FIG. 3B, the correction air flows into the wafer chuck 200 through the air supply port 204, flows radially outward through the gap between the backside of the wafer 205 and the wafer chuck base 201, and is discharged to the outside of the wafer chuck 200 through the non-contact portion 202b (air discharge port 203) of the wafer support portion 202. In order to efficiently correct deformation of the wafer 205 and ensure flatness using the correction air, the wafer chuck 200 is provided with multiple ribs 2011 on the surface facing the wafer 205. As described above, the ribs 2011 are annular protrusions and are installed on the wafer chuck base 201 in a concentric circle around the rotation axis of the wafer chuck 200.

Here, we will explain the concept of correcting the deformation (or flatness) of the wafer 205 by the pressure that the correction air applies to the wafer 205. Hereinafter, the pressure that the correction air applies to the wafer 205 to correct the deformation of the wafer 205 will be referred to as the correction pressure. The correction pressure is the pressure generated between the wafer 205 and the wafer chuck 200 by the correction air.

Figure 4A is a diagram illustrating the concept of corrective pressure. Figure 4A schematically shows three types of pressure distributions between the wafer 205 and the wafer chuck 200 in the radial direction when the wafer chuck 200 rotates. The left part of Figure 4A shows the pressure distribution in the wafer chuck 200 when no ribs 2011 are provided and no corrective air is supplied (pressure distribution without ribs). The center part of Figure 4A shows the distribution of corrective pressure generated by the ribs 2011 (pressure distribution with ribs). The right part of Figure 4A shows the pressure distribution (total pressure distribution) obtained by combining the pressure distribution without ribs and the pressure distribution with ribs. The total pressure distribution is the pressure distribution in the wafer chuck 200 when ribs 2011 are provided and corrective air is supplied. The cross between the left and center diagrams of Figure 4A represents the combination of the pressure distributions.

The idea behind the corrective pressure applied to wafer 205 is to generate a corrective pressure (pressure due to rib 2011) using rib 2011 for the pressure distribution without ribs, as shown in Figure 4A, and then apply the total pressure distribution obtained by combining the two to wafer 205. In other words, the pressure distribution without ribs is corrected by the pressure distribution due to ribs to obtain the total pressure distribution.

When a wafer chuck 200 without ribs 2011 rotates with a wafer 205 placed on it, the centrifugal force of the rotation generates a force that expels air from the space between the wafer 205 and the wafer chuck 200. This results in a pressure distribution in which the pressure at the center of the wafer chuck 200 becomes the maximum negative pressure (pressure lower than atmospheric pressure) and the pressure at the outermost periphery of the wafer chuck 200 becomes atmospheric pressure (pressure distribution without ribs in Figure 4A). In other words, in the pressure distribution without ribs, the pressure increases from the center of the wafer chuck 200 toward the periphery (as the radial position r of the wafer chuck 200 increases).

The pressure distribution without ribs is basically a distribution in which the pressure is expressed as the square of the radial position r of the wafer chuck 200 (the radial position r of the wafer chuck 200 has its origin at the position of the rotation axis of the wafer chuck 200). However, considering that correction air is supplied to the center of the wafer chuck 200, this pressure distribution is one in which the pressure can be approximated by a function of the cube of the radial position r of the wafer chuck 200. Using a higher-order function can more accurately represent the pressure distribution.

In this embodiment, fluid analysis is used in advance to obtain the pressure distribution without ribs when the wafer chuck 200 rotates, and an approximate curve representing this pressure distribution is prepared. The approximate curve representing the pressure distribution without ribs is a curve expressed as a higher-order function of the radial position r of the wafer chuck 200, and is obtained by performing fluid analysis on a model of the wafer chuck 200 with the wafer 205 placed thereon, under the conditions that no correction air is supplied to the wafer chuck 200 and the wafer chuck 200 does not have ribs 2011. Any existing method can be used for the fluid analysis.

In this embodiment, the approximate curve obtained in this manner, i.e., the curve expressed as a higher-order function of the radial position r of the wafer chuck 200, is treated as a pressure distribution without ribs.

In this embodiment, the shape of the rib 2011 is determined so that when the wafer chuck 200 rotates and correction air is supplied, the pressure loss caused by the rib 2011 can cancel out the pressure in the pressure distribution without the rib. Specifically, the shape of the rib 2011 is determined so that, in the radial direction, the shape of the distribution of pressure loss caused by the rib 2011 when correction air is supplied is approximately the same as the shape of the pressure distribution without the rib (Figure 4A). In other words, the shape of the rib 2011 is determined so that, in the radial direction, the increase in pressure loss (increase in the amount of pressure reduction) in the pressure distribution with the rib (Figure 4A) is approximately the same as the increase in pressure in the pressure distribution without the rib.

As shown in the left diagram of Figure 4A, in the pressure distribution without ribs, the pressure increases from the center of the wafer chuck 200 toward the outer periphery (as the radial position r of the wafer chuck 200 increases). Also, as shown in the central diagram of Figure 4A, in the pressure distribution with ribs, the pressure loss caused by the ribs 2011 increases from the center of the wafer chuck 200 toward the outer periphery. The pressure loss caused by the ribs 2011 is pressure that compensates for deformation of the wafer 205. The shape of the ribs 2011 is determined so that the pressure distribution caused by the ribs cancels out the pressure distribution without the ribs.

As described above, the shape of the rib 2011 is such that, in the radial pressure distribution of the wafer chuck 200, the pressure loss caused by the rib 2011 is approximately equal to the pressure in the wafer chuck 200 that does not include the rib 2011. However, the shape of the rib 2011 may also be such that, in the radial pressure distribution of the wafer chuck 200, the magnitude of the pressure loss caused by the rib 2011 is equal to or greater than the pressure in the wafer chuck 200 that does not include the rib 2011. In other words, the shape of the rib 2011 may be such that the value (magnitude) of the pressure loss caused by the rib 2011 is equal to or greater than the value of the pressure in the wafer chuck 200 that does not include the rib 2011 at the same radial position where this pressure loss value was applied (equal to or greater than the pressure value in the pressure distribution expressed as a higher-order function of the radial position r). If the pressure loss caused by the rib 2011 is equal to or greater than the pressure in the wafer chuck 200 that does not include the rib 2011, sinking of the wafer 205 under its own weight can be more effectively prevented.

First, we will explain the shape and pressure loss of one rib 2011. The pressure loss ΔP caused by the rib 2011 is expressed by the well-known formulas (1) to (3).

Here, ξ is the pressure loss coefficient, l is the width of the rib 2011, h is the distance between the wafer 205 and the rib 2011, ρ is the density of the correction air, v is the flow velocity of the correction air between the wafer 205 and the rib 2011, Re is the Reynolds number, and ν is the dynamic viscosity coefficient of the correction air. The width of the rib 2011 is the radial length of the rib 2011.

As shown in Equation 1, when a narrow portion, i.e., a rib 2011, is provided between the wafer chuck 200 and the wafer 205, a pressure loss ΔP is generated by the rib 2011. From the relationships shown in Equations (1) to (3), the smaller the Reynolds number Re, i.e., the smaller the gap h between the wafer 205 and the rib 2011, or the smaller the flow velocity v of the correction air, the greater the pressure loss ΔP generated by the rib 2011. Furthermore, from Equation (1), the larger the width l of the rib 2011, the greater the pressure loss ΔP. Therefore, the gap h between the wafer 205 and the rib 2011, the flow velocity v of the correction air between the wafer 205 and the rib 2011, and the width l of the rib 2011 are parameters that determine the magnitude of the pressure loss ΔP.

Figure 5 is a graph showing the change in pressure loss ΔP caused by the rib 2011 when the distance h between the wafer 205 and the rib 2011 is changed. The graph in Figure 5 can be obtained from equations (1) to (3).

As can be seen from equation (2), the pressure loss ΔP changes significantly at the boundary of the distance h where the Reynolds number Re is 2000. In other words, by setting the distance h so that the correction air is a laminar flow when the Reynolds number Re is 2000 or less, the pressure loss ΔP due to the rib 2011, i.e., the pressure to correct deformation of the wafer 205, can be effectively generated. As can be seen from Figure 5, when the distance h is less than a predetermined value h0, the pressure loss ΔP can be increased. In other words, when the protruding height of the rib 2011 is greater than a predetermined value, the pressure loss ΔP can be increased.

In addition, since the correction air is a laminar flow between the wafer 205 and the rib 2011, it rotates together with the wafer chuck 200 and flows radially at a speed according to the pressure of the correction air flowing in from the air supply port 204. Therefore, the correction air is not affected by the centrifugal force caused by the rotation of the wafer chuck 200. Therefore, there is no need to consider negative pressure where the rib 2011 is installed.

The results of a detailed study of the relationship between pressure loss ΔP and spacing h are described below. Assuming that the wafer 205 has a radius of 150 mm and a rotation speed of 50 Hz, the spacing h at which the Reynolds number Re is 2000 or less was determined. The relationship between pressure loss ΔP and spacing h is shown in Figure 5. It was found that if the spacing h is 0.5 mm or less, the correction air becomes a laminar flow over the entire area of the wafer 205. In other words, the spacing h (predetermined value h0) at which the Reynolds number Re is 2000 or less is 0.5 mm or less. On the other hand, to prevent the wafer 205 from contacting the rib 2011, the minimum value of spacing h must be 0.1 mm. From the above, it is preferable that the spacing h between the wafer 205 and the rib 2011 be 0.1 mm or more and 0.5 mm or less.

Next, we will explain the concept of the distance h between the wafer 205 and the ribs 2011 when the wafer chuck 200 has multiple ribs 2011.

The wafer 205 is held by the wafer chuck 200 with its outer periphery supported by the wafer support portion 202. Therefore, when the wafer 205 is initially placed on the wafer chuck 200, it sinks at its center due to its own weight, causing the center to become concave and deformed. For this reason, the rib 2011 must be shaped so as not to come into contact with the wafer 205. The sinking of the wafer 205 due to its own weight reaches its maximum value at the center of the wafer 205, which is approximately 0.1 mm. Considering the variation in deformation of the wafer 205, it is desirable that the spacing h at the center of the wafer 205 be approximately 0.5 mm.

To efficiently obtain the pressure loss ΔP due to the ribs 2011, it is desirable that the spacing h be smaller at the outer periphery of the wafer chuck 200 than at the center, i.e., that the protruding heights of the multiple ribs 2011 are different from one another and greater at the outer periphery than at the center of the wafer chuck 200. Furthermore, it is even more desirable that the spacing h become smaller from the center to the outer periphery of the wafer chuck 200, i.e., that the protruding height of the ribs 2011 become greater from the center to the outer periphery of the wafer chuck 200.

The pressure distribution to be corrected (the pressure distribution without ribs shown in FIG. 4A) is a distribution in which the pressure at the center of the wafer chuck 200 is the maximum negative pressure and the pressure at the outermost periphery of the wafer chuck 200 is atmospheric pressure, and is a curve expressed as a high-order function of the radial position r of the wafer chuck 200. Therefore, in order for the pressure distribution with the ribs (FIG. 4) to cancel out the pressure distribution without the ribs (i.e., for the value (magnitude) of the pressure loss caused by the ribs 2011 to be equal to or greater than the pressure value in the wafer chuck 200 without the ribs 2011 at the same radial position where this pressure loss value was applied), the pressure loss must be greater at the outer periphery than at the center of the wafer chuck 200. Therefore, it is desirable for the protruding height of the ribs 2011 to be greater at the outer periphery than at the center of the wafer chuck 200, and it is even more desirable for the protruding height of the ribs 2011 to increase from the center to the outer periphery of the wafer chuck 200.

The protruding height of the ribs 2011 does not have to increase monotonically from the center to the outer periphery of the wafer chuck 200. In other words, among the multiple ribs 2011 arranged in the radial direction, there may be a rib 2011 that has a greater protruding height than two adjacent ribs 2011 on the inner and outer periphery sides. Of course, the protruding height of the rib 2011 is a height that prevents the rib 2011 from coming into contact with the wafer 205.

The flow velocity v of the correction air between the wafer 205 and the rib 2011 is the flow velocity at the radial center of the rib 2011. The flow rate of the correction air (the product of the area of the air supply port 204 and the flow velocity v) is constant. Therefore, the flow rate of the correction air is determined in advance as a constant, and the flow velocity v can be determined by determining the area through which the correction air passes at the radial center of the rib 2011 from the spacing h.

Next, we will explain how to set the pressure distribution when multiple ribs 2011 are placed on the wafer chuck 200.

Figure 4B is a diagram explaining a correction method using a correction pressure when multiple ribs 2011 are arranged on the wafer chuck 200. Figure 4B shows the pressure distribution without ribs and the distribution of the correction pressure (pressure distribution with ribs) in the radial direction of the wafer chuck 200. As an example, the pressure distribution without ribs is expressed as a cubic function of the radial position r.

Let M be the number of ribs 2011, and each rib 2011 be identified by a subscript n (n = 1 to M) that increases from the outer periphery toward the center. Let ΔPxn be the pressure loss value due to each rib 2011, and let P(xn) be the pressure loss value at radial position xn of the nth rib 2011 counting from the outer periphery.

When multiple ribs 2011 are arranged on the wafer chuck 200, the pressure at the radial position xn of interest increases by the sum of the pressure losses caused by the ribs 2011 located further outward than this position xn. In other words, the distribution of the corrected pressure is expressed by equation (4).

Here, P(xN) is the pressure loss value at radial position xN of the Nth rib 2011 counting from the outer periphery, and N is the order of the rib 2011 counting from the outer periphery.

After specifying the distance h between the wafer 205 and the ribs 2011 to a certain extent, the ribs 2011 are placed on the outermost periphery of the wafer chuck 200 to determine the pressure loss ΔPx1. Then, sequentially from the outer periphery to the center, the pressure loss ΔPxn of each rib 2011 is adjusted by changing the radial position xn of each rib 2011. Then, the width l of each rib 2011 and the number of ribs 2011 are adjusted so that the shape of the corrected pressure distribution (the distribution of pressure loss caused by the ribs 2011) roughly matches the shape of the pressure distribution without the ribs. If these shapes do not match sufficiently, the distance h between the wafer 205 and the ribs 2011 is adjusted. In this way, the ribs 2011 are adjusted from the outer periphery to the center of the wafer chuck 200, and the pressure losses caused by the ribs 2011 are added up to obtain the corrected pressure distribution.

The compensation pressure distribution obtained in this manner is used to compensate for the pressure distribution without ribs. During this adjustment routine, the compensation pressure distribution must be constantly referenced so that the pressure curve without ribs and the compensation pressure curve roughly match. After the wafer 205 is placed on the wafer chuck 200 configured in this manner, the flatness of the wafer 205 is finally adjusted using compensation air.

As described above, the wafer inspection device 10 of this embodiment can hold the wafer 205 flat with a simple configuration, thereby improving the accuracy of detecting foreign matter present on the surface of the wafer 205.

We will now describe Example 2 of the present invention. In this example, using the wafer inspection device 10 according to Example 1, the flatness of the wafer 205 is measured by a sensor, and corrective air is supplied based on the measured flatness, thereby keeping the wafer 205 flat.

Figure 6A shows the positional relationship between the wafer chuck 200 and the optical system immediately after the wafer 205 is placed on the wafer chuck 200. The position of the wafer chuck 200 is the wafer receiving position.

The wafer inspection device 10 includes a height sensor 301, an amplifier 302, a data processing unit 303, and an air control unit 304.

The height sensor 301 measures the height position of the wafer 205 placed on the wafer chuck 200. Hereinafter, the height position of the wafer 205 will be referred to as the height of the wafer 205. The installation position of the height sensor 301 is directly above a line that passes through the center of the wafer 205 and extends in the direction of linear movement of the wafer chuck 200 when the transport mechanism 12 places the wafer 205 on the wafer chuck 200 (i.e., when the position of the wafer chuck 200 is the wafer receiving position), and is directly above the outer periphery of the wafer 205.

The amplifier 302 amplifies the signal output by the height sensor 301.

The data processing unit 303 receives the signal output by the height sensor 301 from the amplifier 302, processes this signal (the measurement value of the height sensor 301), and outputs the processed result to the air control unit 304. Through this processing, the data processing unit 303 supplies corrected air to the wafer chuck 200 using the air control unit 304.

The air control unit 304 is provided in the wafer chuck 200 and supplies corrected air to the wafer chuck 200 based on instructions from the data processing unit 303.

The operation of the wafer inspection device 10 in this embodiment will be described.

Figure 7 is a flowchart showing the operation of the wafer inspection device 10 in this embodiment.

In step S71, the wafer chuck 200 is placed at the wafer receiving position with the wafer 205 and holds the wafer 205 with the clamping mechanism 206 (Figure 6A).

In step S72, the wafer chuck 200 begins to rotate. At this time, as shown in FIG. 6A, the geometric center of the optical measurement unit 131, which optically measures foreign particles on the wafer 205, is separated from the center of rotation of the wafer chuck 200.

In step S73, the height sensor 301 measures the height of the outer periphery of the wafer 205 while the wafer 205 makes one rotation. The data processing unit 303 averages the heights of the outer periphery of the wafer 205 measured by the height sensor 301 while the wafer 205 makes one rotation, and calculates the average value of the height of the outer periphery of the wafer 205. This average value becomes the reference value.

In step S74, the wafer chuck 200 moves linearly while rotating the wafer 205 to a position where the center of rotation of the wafer chuck 200 coincides with the geometric center of the optical measurement unit 131. During this linear movement, the measurement position of the height sensor 301 coincides with the center of the wafer 205.

Figure 6B shows the state in which the measurement position of the height sensor 301 coincides with the center of the wafer 205 due to linear movement of the wafer chuck 200.

In step S75 of FIG. 7, the height sensor 301 measures the height of the wafer 205 when the measurement position of the height sensor 301 coincides with the center of the wafer 205 while the wafer chuck 200 is moving. In other words, the height sensor 301 measures the height of the center of the wafer 205 while the wafer 205 is rotating.

In step S76, the data processing unit 303 calculates the difference between a reference value, which is the average height of the outer periphery of the wafer 205, and the height of the center of the wafer 205.

In step S77, the data processing unit 303 supplies an amount of correction air corresponding to the calculated height difference to the wafer chuck 200 via the air control unit 304. Specifically, the data processing unit 303 supplies an amount of correction air to the wafer chuck 200 that reduces the height difference (preferably to zero) so that the wafer 205 is held flat. The data processing unit 303 can determine the amount of correction air that reduces (or reduces to zero) the height difference, for example, by feedback processing.

The operations from step S73 to step S77 are performed while the wafer chuck 200 is rotating, before the wafer inspection device 10 starts inspecting the wafer 205. Because the response delay when supplying correction air is less than one second, the supply of correction air in step S77 can be performed almost immediately after measuring the height of the wafer 205 in step S75.

In step S78, the wafer inspection device 10 begins inspecting the surface of the wafer 205 using the optical measurement unit 131. Once the supply of correction air in step S77 has ended and the wafer chuck 200 has moved linearly to a position where the center of rotation of the wafer chuck 200 coincides with the geometric center of the optical measurement unit 131, the wafer inspection device 10 begins inspecting the surface of the wafer 205.

Figure 6C shows the wafer chuck 200 moved to a position where the center of rotation of the wafer chuck 200 coincides with the geometric center of the optical measurement unit 131. In the state shown in Figure 6C, the wafer inspection device 10 inspects the surface of the wafer 205.

In the operation of the flowchart shown in Figure 7, the wafer inspection device 10 determines the amount of correction air to be supplied using the difference between two values: the average height of the outer periphery of the wafer 205 and the height of the center of the wafer 205, while the wafer chuck 200 is rotating. This allows the configuration of the data processing unit 303 to be simplified, and the response speed is fast, allowing the wafer 205 to be kept flat without affecting throughput.

The relationship between the amount of correction air and the difference between the height of the outer periphery and the height of the center of the wafer 205 can also be determined by experimentation or other means and recorded in advance in a table. The data processing unit 303 can save this table, and in step S77 of Figure 7, the amount of correction air that will reduce (or eliminate) the height difference can be determined from this table. The data processing unit 303 supplies the amount of correction air determined from the table to the wafer chuck 200. Using such a table allows the wafer 205 to be held flat more quickly.

Next, to evaluate the validity of the method of measuring the height of the wafer 205 and supplying corrective air, corrective air was manually supplied using this method, and the radial flatness of the wafer 205 was evaluated. The flatness of the wafer 205 was compared when using the wafer chuck 200 described in Example 1 and when using a conventional wafer chuck. Note that with the conventional wafer chuck, the protruding height of the rib (the distance h between the wafer 205 and the rib) and the width l of the rib are constant.

Figure 8 is a diagram schematically showing the pressure distribution of the correction air when using the wafer chuck 200 described in Example 1 (pressure distribution of the example) and the pressure distribution of the correction air when using a conventional wafer chuck (conventional pressure distribution). The left diagram of Figure 8 shows the pressure distribution of the example, and the right diagram of Figure 8 shows the conventional pressure distribution. The pressure distribution of the correction air corresponds to the total pressure distribution shown in the right part of Figure 4A.

In the conventional pressure distribution, the pressure drops at the radial center position. In the pressure distribution of the embodiment, the pressure drop at the radial center position seen in the conventional pressure distribution is eliminated, confirming the effect of rib 2011 in improving the pressure distribution.

In addition, the wafer chuck was pre-adjusted so that the variation in height of the multiple contact portions 202a of the wafer support portion 202 was approximately 8 μm, and the circumferential flatness of the outermost periphery of the wafer 205 (the distance between the top and bottom positions of the wafer 205) was 11 μm. The rib 2011 described in Example 1 was placed on the thus-adjusted wafer chuck to form the wafer chuck 200 described in Example 1, and a conventional rib was placed to form a conventional wafer chuck. The correction air was adjusted according to the flowchart shown in Figure 7. That is, the height of the outer periphery of the wafer 205 was measured and the average value was calculated, and then the height at the center of the wafer 205 was measured. The amount of correction air was manually adjusted so that the difference between these values was as small as possible, approaching zero.

Figure 9 shows the measurement results of the average circumferential height (height displacement) of wafer 205 at each radial position of wafer 205. Figure 9 shows the measurement results when using wafer chuck 200 described in Example 1 (Example) and when using a conventional wafer chuck (Conventional).

The curve obtained from the measurement results in Figure 9 is a curve representing the height of the wafer 205 in the radial direction, i.e., a curve representing the deformation of the wafer 205, and is influenced by the structure of the rib 2011. The overall trend of these curves is the same between the Example and the conventional example. However, the maximum difference in height, which indicates the flatness of the wafer 205, is 25.5 μm in the conventional example and 12.5 μm in the Example. In other words, in the Example, the flatness of the wafer 205 has improved to about half of that of the conventional example.

Furthermore, the time required to manually adjust the correction air was less than one minute. When the correction air is adjusted automatically as described in Example 1, the correction air adjustment can be completed within the time it takes to start up the rotation of the wafer chuck 200 (approximately a few seconds).

The measurement results shown in Figure 9 confirm that the structure of the rib 2011 in the embodiment improves the flatness of the wafer 205, and that the wafer 205 can be held efficiently.

In the wafer chuck 200 described in Example 1, the pressure distribution of the correction air is axially symmetric with respect to the rotation axis of the wafer chuck 200. Therefore, in the wafer chuck 200 of Example 1, improved flatness can be expected when the wafer chuck 200 holds a wafer 205 that has been deformed axially symmetrically, for example, a wafer 205 whose central portion has been deformed into a concave or convex shape before inspection.

A coupled analysis of fluid and structure was therefore performed to study how to improve (correct) the flatness of the deformed wafer 205. The deformation of the wafer 205 used in the study simulated deformation due to sinking under its own weight, with the deformation being greatest at the center, and the maximum deformation amount was 73 μm at the center. The deformed wafer 205 has a downwardly convex shape. This model of wafer 205 was turned upside down, and a model of wafer 205 with an upwardly convex shape was also created. In other words, two types of deformed wafer 205 models were created: one with a downwardly convex shape and one with an upwardly convex shape.

For the analysis system in which these wafers 205 were placed on the wafer chuck 200, the pressure on the backside of the wafer 205 due to the corrected air was first obtained through fluid analysis, and this pressure was reflected in the boundary conditions of the structural analysis to determine the radial shape of the wafer 205 through structural analysis.The maximum value of the deformation of the wafer 205 in the radial direction (the distance between the top and bottom positions) was evaluated as the flatness.

In the following, a wafer 205 that has been deformed into a downwardly convex shape will be referred to as a downwardly convex deformed wafer, and a wafer 205 that has been deformed into an upwardly convex shape will be referred to as an upwardly convex deformed wafer.

Figures 10A and 10B show the analysis results obtained by fluid-structure coupled analysis of the change in radial flatness of a wafer relative to the amount of correction air when a downwardly convexly deformed wafer is placed on the wafer chuck 200 of Example 1, and when an upwardly convexly deformed wafer is placed on the wafer chuck 200. Figure 10A shows the results for a downwardly convexly deformed wafer, and Figure 10B shows the results for an upwardly convexly deformed wafer.

The flatness of the downward-convex deformed wafer and the upward-convex deformed wafer changed depending on the amount of correction air, and a minimum value of flatness was obtained for each. The minimum deformation amount (flatness) was 10 μm for the downward-convex deformed wafer and 5 μm for the upward-convex deformed wafer, indicating that deformation could be corrected for both types of deformed wafer.

Figures 10C and 10D show the results of comparing the radial shape of the wafer obtained by fluid-structure interaction analysis with the shape before the deformation was corrected (before correction air was supplied). Figure 10C shows the results for a downwardly convexly deformed wafer, and Figure 10D shows the results for an upwardly convexly deformed wafer. In Figures 10C and 10D, the wafer height (height position) relative to the radial position of the wafer is shown as the radial shape of the wafer, with the wafer height obtained by fluid-structure interaction analysis shown by a solid line and the wafer height before the deformation was corrected shown by a dashed line.

The results obtained from the fluid-structure interaction analysis showed that for both the downward convex deformed wafer and the upward convex deformed wafer, the wafer height was approximately equal at the center (where the radius is 0 mm) and the outer periphery (where the radius is 150 mm). This indicates that the wafer height adjustment method used in this example made the wafer flat, and therefore this method is valid.

From the above, it can be seen that, if the deformation of the wafer 205 is axially symmetric, by using the wafer chuck 200 described in Example 1, it is possible to ensure a certain degree of flatness even for a wafer 205 that was deformed before inspection. As described above, the wafer inspection device 10 according to this embodiment, as also described in Example 1, can hold the wafer 205 flat with a simple configuration and can improve the accuracy of detecting foreign matter present on the surface of the wafer 205.

The present invention is not limited to the above-described examples, and various modifications are possible. For example, the above-described examples have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to embodiments that include all of the described configurations. It is also possible to replace part of the configuration of one example with the configuration of another example. It is also possible to add the configuration of another example to the configuration of one example. It is also possible to delete part of the configuration of each example, or to add or replace other configurations.

10...wafer inspection device, 11...wafer introduction section, 12...transport mechanism, 13...inspection chamber, 14...control section, 131...optical measurement section, 132...motor, 133...linear movement section, 200...wafer chuck, 201...wafer chuck base, 202...wafer support section, 202a...contact section, 202b...non-contact section, 203...air exhaust port, 204...air supply port, 205...wafer, 206...clamping mechanism, 211...cam, 212...air cylinder, 213...bearing, 214...bearing holder, 215...compression spring, 216...rod, 217...link, 218...holder, 219...holding claw, 301...height sensor, 302...amplifier, 303...data processing section, 304...air control section, 2011...rib.

Claims (6)

a rotatable wafer chuck on which a wafer can be placed,
the wafer chuck includes an air supply port that supplies air to the back surface of the wafer, an air discharge port that discharges the air, a clamping mechanism that holds the wafer, and a plurality of annular protrusions that protrude upward;
the wafer chuck does not include the annular protrusion, and when the wafer chuck rotates, a pressure distribution between the wafer and the wafer in a radial direction of the wafer chuck is expressed by a high-order function of position in the radial direction;
the annular protrusion has a shape such that a value of pressure loss caused by the annular protrusion when the wafer chuck is rotated and the air is supplied is equal to or greater than a value of the pressure in the pressure distribution expressed by the higher-order function at the same position in the radial direction as the position at which the value of the pressure loss was given.
A wafer inspection device characterized by: The plurality of annular protrusions have different heights.
The wafer inspection device according to claim 1 . the height of the plurality of annular protrusions increases from the center of the wafer chuck toward the outer periphery thereof;
The wafer inspection device according to claim 1 . The plurality of annular protrusions include an annular protrusion having a height greater than that of the annular protrusions adjacent to each other in both radial directions.
The wafer inspection device according to claim 1 . a height sensor for measuring the position of the wafer placed on the wafer chuck in the height direction;
a data processing unit;
an air control unit for supplying the air to the wafer chuck;
the height sensor measures the height of the outer periphery of the wafer while the wafer makes one rotation, and measures the height of the center of the wafer while the wafer is rotating;
the data processing unit calculates an average value by averaging the heights of the outer periphery of the wafer measured by the height sensor, and calculates a difference between the average value and the height of the center of the wafer measured by the height sensor;
the data processing unit supplies the amount of air corresponding to the difference to the wafer chuck by the air control unit;
The wafer inspection device according to claim 1 . the data processing unit stores a table recording the relationship between the amount of air to be supplied to the wafer chuck and the difference between the height of the outer periphery of the wafer and the height of the center, and obtains from the table the amount of air that reduces the difference between the average value and the height of the center of the wafer, and supplies the obtained amount of air to the wafer chuck.
6. The wafer inspection device according to claim 5.