JPS6348042B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a follow-up focus device, and more particularly to a follow-up focus device in an exposure apparatus that can improve the alignment accuracy between a photomask and a wafer arranged in the exposure apparatus.

In a conventional exposure apparatus, the following steps are used to align a photomask and a wafer that are placed one on top of the other using a microscope, and then perform printing.
That is, the photomask and the wafer are separated by a distance of 20 to 40 μm, and in this state, either the photomask or the wafer is moved in the horizontal direction for alignment. Next, the wafer is brought into close contact with or close to the photomask. At this point, the accuracy of alignment is checked, that is, it is checked whether proper alignment is being performed. If the result of this check is desirable, exposure is performed. If the results of this check are not as desired, the photomask and wafer should be replaced as before.
The same operation is repeated with a distance of ~40 μm.

By the way, when the photomask and the wafer are separated by 20 to 40 μm, the objective lens of the microscope cannot be focused on the photomask and the wafer at the same time. For this reason, an operation is performed to focus on a wafer with low contrast or to a position midway between the wafer and the photomask. However, in this case, sharp images of the photomask and the wafer cannot be obtained at the same time, making it difficult to achieve accurate alignment. Therefore, in order to improve the alignment accuracy, it is necessary to check the alignment accuracy when the photomask and wafer are close to each other or in close contact with each other, and to repeat the alignment operation several times when the photomask and the wafer are separated by 20 to 40 μm. Therefore, this method is time consuming and inefficient, and the number of times the photomask and wafer come into contact increases, resulting in a problem that the photomask and wafer are easily damaged.

In addition, when aligning the photomask and wafer manually, that is, when humans do it, assuming there are no time constraints, the focus can be finely adjusted each time, and within the resolution of the eye. alignment is possible. However, there are naturally limits to the accuracy of this alignment.

On the other hand, when aligning automatically by photoelectrically detecting the patterns on the photomask and wafer, the focus is fixed in the conventional technology, which makes it difficult to obtain a sharp image as described above. Accuracy was limited. When performing automatic positioning in this way, conventional attempts have been made to focus on the photomask and wafer by using an objective lens with a deep focal depth or illumination; Since a lens cannot be used, there is a limit to the resolution, and in the end it was not possible to improve the alignment accuracy.

In this way, with conventional technology, if the focus is not accurate or the resolution of the imaging optical system is low, the signal-to-noise ratio of the photoelectrically detected signal of a low-contrast wafer is poor, and it is difficult to improve alignment accuracy. Not only is this not possible, but there are also problems in that automatic positioning may become impossible or incorrect positioning may occur.

The present invention has been made in view of the actual state of the prior art described above, and its purpose is to improve the accuracy of alignment between a photomask and a wafer, and to improve the ability to detect a wafer pattern. It is an object of the present invention to provide a tracking focus device in an exposure apparatus that can improve the yield of semiconductors.

In order to achieve this object, the present invention provides an exposure apparatus that is equipped with a microscope that photoelectrically detects an image of an alignment pattern between a mask and a wafer, and performs printing by matching the patterns of the mask and wafer that are arranged one above the other. In this tracking focusing device, upper and lower leaf springs that support a wafer chuck holding a wafer on a wafer block are deformed by a pressurizing means, and the wafer is brought into contact with or close to a mask held by a mask holding means. wafer moving means for vertically moving the wafer to a state and a gap forming state, and a displacement meter that detects the amount of movement of the wafer chuck from a reference position where the wafer is brought into contact with the mask by activating the pressurizing means of the wafer moving means. a movement amount/signal conversion means for converting the amount of movement of the wafer into an electric signal and outputting the electric signal based on an electric signal obtained from the wafer, and aligning the position of the objective lens of the microscope with the reference position, which is the pattern surface on the mask. The microscope is moved downward from the focused state by an amount equal to the amount of movement obtained from the movement amount/signal conversion means, and the microscope aligns the images of the alignment pattern on the wafer surface in the close state and gap forming state. This is a follow-up focus device for an exposure apparatus, characterized in that it is equipped with objective lens moving means for controlling photoelectric detection in a focused state.

Hereinafter, the tracking focus device of the present invention will be explained in detail based on the drawings. Figures 1 and 2 are explanatory diagrams showing an embodiment of the present invention. In particular, Figure 1 is a configuration diagram showing a wafer moving means and an objective lens moving means, and Figure 2 is a diagram showing a configuration of a wafer moving amount to an electrical signal. FIG. 2 is a block diagram showing movement amount/signal converting means for outputting a signal.

In FIG. 1, 1 is a photomask held by mask holding means, 2 is a wafer disposed below the photomask 1, and 3 is a wafer chuck for holding the wafer 2. In FIG. 4 is a chuck cylinder on which the spherical seat of the wafer chuck 3 is placed; 5 is an upper plate spring attached to the upper side of the chuck cylinder 4; and 6 is a lower plate spring attached to the lower side of the chuck cylinder 4. The chuck cylinder 4 is supported by the upper leaf spring 5 and the lower leaf spring 6. Further, the upper leaf spring 5 and the lower leaf spring 6 are attached to the chuck block 15. Chuck block 15 is called
It is configured to be movable in the XY horizontal direction and the θ tilt direction. One chamber 32 is formed by the lower leaf spring 6, the lower surface 30 of the chuck cylinder 4, and the flat surface 31 of the chuck block 15.
A guide hole 33 provided in the chuck block 15 communicates with this chamber 32. The above-mentioned wafer chuck 3, chuck cylinder 4, upper plate spring 5, lower plate spring 6, and chuck block 15 constitute wafer moving means for moving the wafer 2 in the optical axis direction of the microscope, that is, in the direction of arrow 34.

In the wafer moving means constructed as described above, when the pressure p flowing from the guide hole 33 of the chuck block 15 increases as shown by the arrow 35, the lower plate spring 6 is bent, the chamber 32 expands, and the chuck cylinder 4 moves upward, and at the same time, the wafer 2 held in the wafer chuck 3 moves in a direction closer to the photomask 1. Also, when the pressure p decreases,
By the opposite action, the chuck cylinder 4 moves downward and the wafer 2 similarly moves away from the photomask 1.

Further, 14 is a pulse motor driven by a pulse signal, 13 is a pinion fixed to the output shaft of the pulse motor 14, 12 is a gear that meshes with this pinion 13, and 11 is a screw shaft fixed below this gear 12. . 8 is an objective lens of the microscope; 9 is a coil spring that is attached to the upper part of the objective lens 8 and urges the objective lens 8 downward; 10 is a lever, and this lever 10 is rotatable about a fulcrum 36; One end is in contact with the tip of the screw shaft 11, and the other end is in contact with a protrusion provided on a cylindrical body constituting the objective lens 8. These pulse motor 14, pinion 1
3, the gear 12, the screw shaft 11, and the lever 10 constitute an objective lens moving means for moving the objective lens.

In the objective lens moving means configured in this way, the pinion 13 and gear 12 are rotated by the rotation of the pulse motor 14, and the screw shaft 11 is moved up and down. Then, the lever 10 rotates in response to the vertical movement of the screw shaft 11, thereby moving the objective lens 8 in the optical axis direction as shown by an arrow 37. Note that since a coil spring 9 is attached to the objective lens 8, breakage is effectively prevented during movement.

Reference numeral 7 denotes a displacement meter probe, which is always in contact with the upper surface 38 of a notch provided in the middle of the chuck cylinder 4. This displacement meter probe 7 is connected to a displacement meter circuit 16 shown in FIG.
In FIG. 2, 17 is a pressure gauge circuit, 18 is a contact position detection circuit, 19 is a contact position storage circuit, 20 is an up-down counter, 21 is a pulse motor drive circuit, and 22 is a central control circuit. Note that the pulse motor drive circuit 21 is connected to the pulse motor 14 shown in FIG. The above-mentioned displacement meter probe 7, circuits 16, 17, 18, 1
9, 21, 22 and up/down counter 20
constitutes a movement amount/signal conversion means that detects the amount of movement of the wafer 2 in the optical axis direction of the microscope, converts this movement amount into an electrical signal, and outputs the electric signal. The operation of this movement amount/signal conversion means will be described later.

Next, the operation of moving the objective lens 8 to follow the movement of the chuck cylinder 4, that is, the movement of the wafer 2 in the optical axis direction of the microscope, so that the objective lens 8 is always focused on the wafer 2 will be explained. First, the focus of the objective lens 8 is set in advance on the S plane, which is the pattern forming surface of the photomask 1. Then, a new wafer 2 to be aligned is placed on the wafer chuck 3, the pressure p is increased, the chuck cylinder 4 is moved upward, and the wafer 2 is placed on the photomask 1.
contact with. This contact position can be detected because the amount of movement of the chuck cylinder 4 is no longer proportional to the increase in pressure, and the amount of movement becomes minute. The contact position memory circuit 19 uses this as a reference position.
Then, when the photomask 1 and wafer 2 are separated for alignment, the vertical movement amount of the wafer 2, that is, the difference between the vertical movement amount of the chuck cylinder 4 and the reference position is determined.
According to this difference, a pulse signal is generated as described later, and the pulse motor 14 is driven to move the objective lens 8. Then, with the wafer 2 separated from the photomask 1, positioning is performed by moving the chuck block 15 in the horizontal direction. Upon completion of this positioning, the pressure p is increased and the chuck cylinder 4 is raised to move the wafer 2. An operation is performed to bring the wafer 2 close to the photomask 1 (a state in which the wafer 2 and the photomask 1 are brought close to each other until the distance between them is about 2 μm). At this time, the chuck cylinder 4 is supported by the upper leaf spring 5 and the lower leaf spring 6, but does not rise directly upward, but rises in a slightly meandering manner. For this reason, the alignment state described above cannot be maintained as it is. Furthermore, since the objective lens 8 is focused on the wafer 2, the positioning accuracy is not sufficient when the wafer 2 is separated from the photomask 1 (gap formation state).
Therefore, it is necessary to move the chuck block 15 in the horizontal direction again while bringing the wafer 2 close to the photomask 1 for alignment. At this time, since the wafer 2 is only about 2 μm away from the photomask 1, the photomask 1 is also brought into focus to a degree sufficient for practical use, and highly accurate positioning can be achieved. Thereafter, an operation is performed to bring the wafer 2 into close contact with the photomask 1, but the amount of rise of the chuck cylinder 4 at this time is extremely small, and it is possible to minimize the influence of the meandering of the chuck cylinder 4 on the alignment accuracy. can.

The contact position between the photomask 1 and the wafer 2 described above is determined by the contact position detection circuit 18 based on the output signal of the displacement meter circuit 16 and the output signal of the pressure gauge circuit 17, and is converted into a digital quantity and stored in the contact position storage circuit 19. It is stored as a reference value (reference position). When the chuck cylinder 4 moves in the vertical direction, the displacement meter circuit 16 passes through the displacement meter probe 7.
The central control circuit 22 receives this signal, converts it into a digital value, and calculates the difference from the reference value of the contact position storage circuit 19, that is, the distance between the photomask 1 and the wafer 2. The up-down counter 20 is reset in advance to "0" when the objective lens 8 is brought into focus on the S plane of the photomask 1. The central control circuit 22 checks the difference with the above reference value and the contents of the up-down counter 20, and if there is a difference, it issues one pulse signal and inputs it to the pulse motor drive circuit 21 and the up-down counter 20. . This pulse signal causes the pulse motor drive circuit 21 to rotate the pulse motor 14 by one pulse. The rotation direction of the pulse motor 14 is such that the objective lens 8 moves in the same direction as the chuck cylinder 4.
At the same time, the up-down counter 20 counts up or down in accordance with a predetermined rotation direction and counting direction. The central control circuit 22 determines that the distance between the photomask 1 and the wafer 2 matches the value of the up-down counter, that is, the amount of movement of the objective lens 8 from the reference position where the objective lens 8 is focused on the S surface of the photomask 1. When the pulse stops generating. Therefore, the objective lens 8 also stops moving. In this way, the objective lens 8 can be automatically moved following the vertical movement of the chuck cylinder 4, that is, the movement of the wafer 2.

In addition to the above-mentioned movement amount/signal conversion means, the displacement meter circuit 16 is configured to emit one pulse signal per unit movement amount and a signal for discriminating the movement direction, and the pulse motor drive circuit 21 is configured to emit one pulse signal per unit movement amount. When input, the objective lens 8 is moved by the same amount as the unit movement amount, and the pulse signal and direction discrimination signal output from the displacement meter circuit 16 are directly input to the pulse motor drive circuit 21. Even in this case, the same follow-up control as described above can be performed. The movement/signal converting means constructed in this manner has a simpler construction than the one described above, and is therefore economically advantageous.

As described above, the tracking focus device of the present invention includes a wafer moving means for moving the wafer in the optical axis direction of the microscope, a moving amount/signal converting means for converting the wafer moving amount into an electrical signal and outputting the electrical signal, and Since the objective lens moving means for moving the objective lens based on the above-described structure is provided, remarkable effects as listed below can be achieved.

In the past, fine focus adjustments were made repeatedly every time a new wafer was loaded onto the wafer chuck, but this complication is alleviated and the number of man-hours required for alignment work is reduced.

Even during alignment, a sharp image of the wafer pattern can be obtained when the wafer is brought into close contact with the photomask, so alignment accuracy is significantly improved.

Objective lenses with higher resolution than those used in conventional fixed-focus devices can be used. Therefore, from this point of view as well, a sharp image with good contrast can be obtained, which is especially convenient for observing patterns with low contrast.

Because of this, a detection signal with a good signal-to-noise ratio can be obtained, making it possible to automatically align wafers with extremely low contrast, which was previously impossible.

Improved yield by improving alignment accuracy,
It is also possible to improve yield through automation.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams showing an embodiment of the present invention. In particular, Figure 1 is a configuration diagram showing a wafer moving means and an objective lens moving means, and Figure 2 is a diagram showing a configuration of a wafer moving amount to an electrical signal. FIG. 2 is a block diagram showing movement amount/signal converting means for outputting a signal. 1...Photomask, 2...Wafer, 3...Wafer chuck, 4...Chuck cylinder, 5...Upper plate spring, 6...Lower plate spring, 7...Displacement meter probe, 8...Objective lens, 9 ...Coil spring, 10
... Lever, 11 ... Screw shaft, 12 ... Gear, 1
3...Pinion, 14...Pulse motor, 15...
...Chuck block, 16...Displacement meter circuit, 17
... Pressure gauge circuit, 18 ... Contact position detection circuit, 19 ... Contact position memory circuit, 20 ...
Up-down counter, 21...Pulse motor drive circuit, 22...Central control circuit.

Claims (1)

[Claims] 1. The wafer is held in a follow-up focusing device of an exposure device that is equipped with a microscope that photoelectrically detects the image of the alignment pattern between the mask and wafer, and performs printing by matching the patterns of the overlapping mask and wafer. The upper and lower leaf springs that support the wafer chuck on the wafer block are deformed by a pressurizing means, and the wafer is vertically brought into contact with, in close proximity to, and in a gap-forming state with respect to the mask held by the mask holding means. a wafer moving means for moving;
Converting the amount of movement of the wafer into an electric signal based on an electric signal obtained from a displacement meter that detects the amount of movement of the wafer chuck from a reference position where the pressurizing means of the wafer moving means is activated to bring the wafer into contact with the mask. The movement amount/signal conversion means outputs the output from the movement amount/signal conversion means from a state where the objective lens of the microscope is focused on the reference position, which is the pattern surface on the mask. objective lens moving means for controlling the microscope to photoelectrically detect an image of the alignment pattern on the wafer surface in the focused state in the close state and gap forming state by moving the objective lens downward by the same amount as the moving amount by which the microscope is in the close state and in the gap forming state. A tracking focus device in an exposure apparatus, characterized in that: