JPH0125220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a step and repeat direct exposure apparatus for repeatedly exposing a semiconductor wafer to a pattern of circuits or devices on a reticle. The present invention also relates to a direct exposure apparatus in which alignment targets are placed on the wafer at each circuit location during an initial masking operation. During subsequent masking operations, image alignment is performed by viewing the reticle alignment pattern and the image of the alignment target on the wafer through an image exposure lens.

In the production of integrated circuits and individual semiconductor devices,
Many identical devices, ie, identical circuits, are simultaneously fabricated on one semiconductor wafer. The wafer is usually silicon and has a diameter of about 7.6 to 12.7 cm.
(3 to 5 inches). Depending on the dimensions of the devices or circuits, 50 or more, 100 or more devices can be fabricated on a single wafer. Once the manufacturing operation is complete, the wafer is scribed and cut along the scribe lines to yield separate chips containing individual devices or circuits.
The chips are packaged separately and manufactured.

A number of sequential process operations are performed on each wafer. The number and type of these steps vary depending on the type of device being manufactured. For example, various manufacturing processes are used to create circuits including bipolar transistors, metal gate field effect transistors, silicon gate field effect transistors, C-MOS (complementary metal-oxide-semiconductor) devices, etc. . However, what all of these manufacturing methods have in common is that they require photographic techniques to define specific areas within each circuit to be fabricated. During manufacturing, at least 3 times and at most
Each wafer is subjected to 12 such "masking" operations using photographic techniques.

For example, we will discuss how to make a very simple metal gate field effect transistor (FET).
First, a silicon wafer is coated with a relatively thick field oxide of silicon dioxide. A photosensitive photoresist material is coated over this oxide layer.
This photoresist layer is illuminated through a first photomask to define the areas where the individual FETs are to be made. The exposed and developed photoresist layer is
It functions as a thinning layer for selectively etching away the field oxide in the region where the FET is to be formed.

A thin gate oxide layer is then grown directly on the silicon substrate in those exposed areas.
Another photoresist step using a second photomask is used to define the source and drain locations of each FET. Holes are drilled into the thin gate oxide layer at locations defined by this source-drain mask. Dopants are diffused through the holes to form the source and drain. This diffusion operation takes place at high temperatures, typically on the order of 1100°C. At the same time, oxide grows to fill the source and drain holes.

A third photomask is then used to define the location of the metal gate electrode for each FET, the location of the metal contacts to the source and drain regions, and the location of the bond pads.

A thick oxide is then deposited over the entire surface of the device to provide a protective coating. Finally, a fourth photomask is used to define where to remove the deposited oxide and expose the junction pads for the gate, source, and drain of the FET. The oxide is etched away at defined locations to expose the metal pad areas.
Electrical connection lines are bonded to these metal pad areas.

Thus, four photographic masks are used in this simple example. It is of paramount importance that each subsequent mask be properly aligned with the circuit or device pattern formed in the previous masking step. This alignment is important for proper operation of the finished device. for example,
In the FET manufacturing method described above, the positioning of the third mask used to define the location of the metal gate electrode is very important. The gate region must be properly positioned above the gate oxide between the source hole and the drain hole. Misalignment can cause the gate electrode to overlap the source or drain, causing the FET
The performance of the device is degraded or worse, resulting in a gate-to-source or drain short, which makes the device inoperable.

The problem of mask misalignment becomes more important as the density of individual components in each integrated circuit increases. In order to create integrated circuits with large numbers of components, each component must be made extremely small.
Modern integrated circuits may require device spacing as narrow as 2 microns. Such fine resolution requires extremely small alignment errors of subsequent photographic masks during manufacture. In fact, the degree to which such sequential alignment can be achieved is one of the major factors limiting the number of devices per square centimeter, or density, that can be achieved in large scale integrated circuits.

The method described above was for the fabrication of a single FET device. In practice, multiple devices or circuits, each containing a large number of individual devices, are fabricated on a single wafer. To create this, each photographic mask conventionally comprised a glass plate containing multiple identical pattern images in locations corresponding to multiple devices or circuits being fabricated on a single wafer. For example, if 50 identical circuits are to be made on a wafer, arranged in 5 rows with 10 circuits per row, each mask will fit exactly into the corresponding 5-by-10 array. placed in
It will contain 50 identical patterns.

The actual exposure of the wafer to be processed is performed as follows. The wafer is placed on a holder or table provided under a binocular microscope. The mask or reticle itself (ie, the glass plate on which a number of photographic images are formed) is positioned in a holder directly above the wafer and below the microscope. A worker looks at the wafer and mask through a microscope and moves the table or mask holder until they are aligned. The entire wafer is then simultaneously exposed through the mask using a single high intensity light source. That is, the wafer is simultaneously exposed to all individual patterns located on the mask.

There are certain alignment problems inherent in this method.
One of these occurs during the fabrication of the mask itself. Mask fabrication is typically accomplished by repeatedly exposing an enlarged pattern for one (or several) devices to be fabricated on a wafer. The individual patterns are sequentially exposed to each array location on the mask. For example, one or more images may be slightly off-column or twisted relative to the rows or columns of other images on the same mask. If this happens, even if the alignment between the other masks used during device fabrication and the wafer is perfect, the misalignment of a certain pattern on this individual mask may result. This will result in a defective device.

Even if the individual images within the mask array can be perfectly positioned, misregistration can occur during the exposure process. For example, by using only one or two reference points near the center or near the edge of the wafer and mask, the operator can align the mask to the wafer. For example, if the mask is slightly twisted relative to the wafer, such that the mask is turned so slightly that its centerline is no longer perfectly parallel to the wafer's centerline, the operator can correct this deviation. Sometimes you don't notice. For example, if a worker is looking only near the center of the mask and wafer, the mask and wafer may appear to be aligned within the microscope's limited field of view. Furthermore, even if the mask misalignment is very small at the periphery of the wafer,
The position may be misaligned enough to cause a misalignment sufficient to impair operation of the device.

There are other problems as well. This occurs as a result of thermal cycling of the wafer itself during the manufacturing process. For example, in the method described above, the diffusion of the source and drain regions is carried out at very high temperatures. Normally,
The wafer is exposed to processes such as going from room temperature to elevated temperature and then back to room temperature. This thermal cycle may cause the wafer itself to warp irregularly.
As a result, even if the mask is perfect, the image produced on a wafer whose mask is warped may be misaligned with the pattern formed during processing performed before the wafer warped.

Many of these misregistrations are eliminated by a device that eliminates masks with many images. Instead, a reticle containing a pattern corresponding to one or at most a few circuits or devices to be formed on the wafer is used to directly expose the wafer itself. That is, each masking operation does not use one mask containing many images, but rather a reticle containing one pattern is used to repeat all the devices, or circuits, to be formed on the wafer, one at a time. It is used for sequential exposure. In such a direct exposure apparatus, a reticle is attached to a projection camera provided on a table that holds a wafer. One device or circuit on the wafer is aligned under the camera and exposure to that circuit is made through the reticle.
The wafer is then stepped to the next circuit location, for example by appropriately moving the stage in the row or column direction. The next circuit is then exposed through the reticle. This operation is repeated for each device, ie, each circuit, on the wafer.

This direct exposure wafer stepping technique eliminates all misalignment problems associated with fabricating masks with many images and using them to simultaneously expose all circuits at once. . This technique also has the advantage that the dimensions of the reticle used to expose the image can be much larger (eg, 5 or 10 times) larger than the actual dimensions of the circuit being created. This is in contrast to multiple image masking techniques, where each image has a one-to-one dimensional relationship to the devices or circuits on the wafer. Using such enlarged patterns via optical reduction techniques to perform exposures on the wafer provides the opportunity to produce images of smaller dimensions than can be achieved by one-to-one masking operations.

However, direct exposure wafer advancement devices also have some problems. These problems are primarily related to the alignment of the reticle image with the previously exposed pattern on the wafer. In conventional equipment, only one alignment operation is performed for each masking operation, regardless of how many individual reticle exposures are performed. Before or during the initial masking operation, a pair of alignment targets are attached to each side of the wafer. A high-precision table transfer system, which typically uses laser interferometers to control movement, is then used to step the wafer to each array position during subsequent exposure operations.
For the next masking operation and each subsequent masking operation, an indirect off-axis method is used to initially align the wafer with the new reticle.

To accomplish this, each reticle is provided with a pair of reference targets. These targets are first used to manually align the reticle in the off-axis portion of the camera. The wafers are then placed on the wafer stage and separately aligned to the same off-axis reference of the camera. As successive individual exposures are made, proper positioning of the stage is determined by mechanical
- Depends on the reliability of the Y drive. Individual alignment of each circuit with respect to the camera and reticle is not performed or possible. The alignment depends entirely on the degree to which the platform can be controlled by the platform positioning device. There is ample opportunity for positioning errors to occur.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved direct exposure step and repeat image generator that overcomes the disadvantages of the prior art.

Another object of the present invention is to provide a direct exposure apparatus in which the reticle and target are aligned through the optical system of the camera.

Still another object of the present invention is to provide an apparatus in which individual alignment targets can be provided at each separate circuit location on the wafer and individual alignment can be performed at each array location prior to exposure. That's true.

These and other purposes are a "single lens repeater" that aligns an image of a reticle pattern with a previous exposure pattern on a semiconductor wafer using the same camera lens system used to make the exposure. This is achieved by providing Exposures are repeated and sequentially performed at successive array locations on the wafer, with suitable wafer stepping equipment being used to move the wafer between each exposure.

This device consists of a camera that projects a reduced image of the circuit pattern contained in the reticle directly onto the semiconductor wafer. During the initial masking operation, a reticle containing the circuit pattern and alignment targets is used. A wafer stepping mechanism is used to step the wafer through the array of positions. At each location, a camera exposes the wafer to an image of the reticle's circuit pattern and alignment target.

After the appropriate wafer processing steps have been performed, the wafer is returned to the apparatus of the present invention for subsequent masking operations with a second reticle. The second reticle includes another circuit pattern and alignment pattern. The shape of the alignment pattern is complementary to the shape of the previously exposed alignment target at each array location on the wafer. The wafer stepping mechanism re-moves the wafer in steps to the same array position originally used. Each array location can be performed using an alignment target on the wafer, an alignment pattern on a second reticle, and the same camera lens system used to make each exposure.

To this end, a low intensity, narrow beam light source is used to illuminate the alignment target contained in the wafer. Appropriate viewing optics, typically including a beam splitter, a microscope lens system, and a television camera, combine the virtual image of the wafer alignment target projected by the camera lens with the alignment pattern contained on the reticle. used for viewing. A pedestal holding the wafer can be used to perfectly align the virtual image of the target with the alignment pattern. If this is done, a conventional camera light source is used to expose the image of the circuit pattern of the second reticle onto the wafer. This exposure is precisely overlaid with circuitry previously exposed on the wafer.

Disclosed herein is an apparatus for pre-aligning a wafer under a camera before stepwise iterations are performed. This pre-alignment system uses air gauges to locate opposing edges of the wafer. A perpendicular centerline of the wafer is defined from the opposing edges of the wafer. Equipped with a unique mounting device. In this mounting device,
The wafer support platform can be rotated about its vertical axis without linear movement along the X-Y axes of the support table. With this configuration, rotational errors in preliminary alignment of the wafer can be precisely corrected.

The air gauge can be used simultaneously with the spherical air bearing support to bring the wafer platform parallel to a portion of the wafer surface and a reference plane through the camera. By establishing such parallelism, focusing errors and depth of field errors due to wafer warpage or non-uniform thickness can be eliminated.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

The apparatus 10 shown in FIG. 1 is for directly and repeatedly exposing each portion of a semiconductor wafer 11 (FIG. 2) to an image contained in a reticle 12 (FIG. 3) or 13 (FIG. 4). used for. As will be explained later with reference to FIG. 5, the alignment of each new image with the pattern previously formed on wafer 11 is performed using the same camera optics used for direct exposure of each reticle image. This is done by system 14.

The device 10 rests on a heavy granite block 15 held by three supports 16. Due to the large weight of the block 15, external vibrations do not affect the device 10.
A cassette 17 containing wafers to be exposed is placed in the load/unload module 18. One wafer at a time is removed from the cassette 17 and transported onto a set of O-ring belts 19 to a pre-alignment station 20. In the preliminary alignment section 20, the wafer 11 is placed on the spindle 2.
Mechanically centered on 0'. The wafer 11 is held on the spindle 20' by vacuum. Thereafter, the spindle 20' is rotated until the flat edge 11f (FIG. 2) of the wafer 11 is oriented in a predetermined direction.
is rotated. Wafer 11 is then said to be "pre-aligned."

Next, the pre-aligned wafer 11 is transferred to the spindle 20' by the vacuum chuck of the feeding mechanism 21.
be lifted up from The feeding mechanism 21 includes a stand 23 used to support the wafer during exposure work.
The wafer 11 is moved along the rail 22 until the wafer 11 is on top (FIG. 7). The wafer 11 is then lowered from the transport mechanism 21 onto the table, where it is again fixed in position by vacuum.

The platform 23 can be moved along two orthogonal axes X, Y by means of a precision X-Y drive 24. A conventional laser interferometer 25 is used in conjunction with the drive 24 to provide very precise X-Y positioning of the platform 23. After the wafer 11 is completely exposed, the feeding mechanism 2 is used to take the wafer 11 out of the stage 23 and send it to the O-ring belt 19.
1 is used. O-ring belt 19 is attached to wafer 1
1 into another cassette 17'. Exposed wafers are automatically stacked in this cassette 17'.

When the wafer 11 is placed on the stage 23, stepwise direct exposure is repeatedly performed. This exposure is
This is done with suitable reticles 12, 13 mounted on a reticle holder 28 which is pivotally mounted on a support 29 near the top of the device 10. Several reticles 12, 13 can be pre-placed in corresponding holes 28' of the reticle holder 28 and rotated into position within the camera 30 as required.

Camera 30 (FIGS. 1 and 5) includes a generally cylindrical camera body 31 that is vertically mounted. This camera body 31 has reticles 12 and 13.
The wafer 11 includes suitable optics 14 for focusing an image of the pattern onto the wafer 11, which is mounted on a pedestal 23. The optical system 14 itself is known and utilizes one or more lenses to perform the required focusing function. To expose the photoresist coated on the wafer 11, a high intensity exposure lamp 32, typically 4360 Å, is used as a light source.

By providing camera alignment marks 33, 33' on each reticle 12, 13, the reticle can be automatically aligned with the camera optical system 14. A suitable mechanism (not shown) provided in the housing 34 is used to detect the marks 33, 33' and to position the reticle 12, 13 accurately relative to the optical system of the camera 30.・
The movement of at least one of the holder 28 and the support 29 can be controlled.

As mentioned above, each wafer 11 undergoes a series of device fabrication steps. Some of these processes require separate masking and pattern exposure steps. A reticle 12 (FIG. 3) is used during the initial masking operation. Only this reticle includes a cross-shaped alignment target 35. The image of this target 35 is exposed onto the wafer 11 at the same time as the pattern 36 contained in the same reticle 12 is exposed.

Using stepwise and iterative direct exposure operations, multiple images of pattern 36 and cross-shaped alignment targets 35 are created in the desired array 37 on wafer 11.
(Fig. 2). To this end, the platform 23 is initially positioned at an arbitrary location below the camera 30. A first exposure is made through the reticle 12 using an exposure lamp 32, and the reticle pattern 36
An image 36-1 of the cross-shaped alignment target 35 and an image 35-1 of the cross-shaped alignment target 35 are generated on the wafer 11. A drive system 24 is then used in conjunction with a laser interferometer 25 to move the stage 23 a distance along at least one of the X and Y axes to a new position for exposing the next image. For example, pattern image 36
-2 and the wafer 11 along the Y axis only until the next new position where the target image 35-2 is exposed.
can be moved. Similarly, until a complete pattern array 37 is completed, the wafer 1
1 is repeatedly stepped and exposed. When this is completed, the wafer 11 is transferred from the table 23 to the module 1.
7'.

After the appropriate semiconductor processing steps have been performed, the wafer 11 is transferred to the apparatus 10 for subsequent masking operations.
be returned to. The next masking operation uses reticle 13 (FIG. 4) having alignment pattern 40. This alignment pattern 40 is the reticle 1
Advantageously, the shape is complementary to the shape of the alignment target 35 of No. 2. In the illustrated embodiment, pattern 40 is comprised of four L-shaped elements 40' arranged to form an open cross-shaped area 40'' that corresponds to the shape of alignment target 35.
Reticle 13 also includes a new pattern 41. This pattern 41 is different from the pattern 36, but the first
Each image 36- generated using the reticle 12 of
1, 36-2, etc., onto the wafer 11 so as to be properly aligned.

To do this, the reticle 13 is placed in the holder 28
is attached to and positioned within the camera 30. Marks 33' are used to align reticle 13 with camera optics 14. A pedestal 23 containing a wafer 11 with a previously exposed array 37 is positioned such that one previously exposed image (eg, image 36-1) is below the camera 30. How to do this is explained below.

The image of pattern 40 and previously exposed alignment target 35 is then used to perfectly align the image of reticle pattern 41 with the previously exposed image of pattern 36. . For this purpose, the image 35-1' (sixth
) is viewed directly through the camera optics 14. The stand 23 is appropriately moved so that the virtual image 35-1 is correctly aligned with the alignment pattern 40 of the reticle 13. When the desired alignment is achieved, the aligned overlapping pattern 40 and virtual image target 35-1' appear as shown in FIG. 6 when viewed through camera optics 14. When this alignment is achieved, the exposure lamp 32 is turned on to expose the image of the pattern 41 onto the wafer 11. Then the stand 23 is on the X axis and Y axis
It is moved along at least one of the axes to the next image position and the exposure operation is repeated there.

In order to facilitate this positioning work, the positioning target 3 is
A low-intensity light source 42 for illuminating the light 5-1 is provided (FIG. 5). The light source 42 has a sufficiently low brightness so that the photoresist coated on the wafer 11 is not exposed too strongly. The wavelengths of light sources 32 and 42 can be the same. Light 4 from light source 42
3 passes through the beam splitter 44 and the pattern 40 of the reticle 13, and illuminates the target 35-1. An image of target 35-1 is applied to the surface of reticle 13 by reduction lens 14. The image of the alignment target 35-1 and the pattern 40 are captured by the optical system 49.
, the beam splitter 44 , the prism 45 , and the television camera 46 .
The television camera 46 is attached to the housing 4 of FIG.
Included in 7. The television camera 46 can be combined with an optical system 48 of a microscope.
Once the alignment is done, the television camera 4
The image displayed by the television screen (not shown) associated with 6 will be as shown in FIG.

After each image of pattern 41 has been exposed onto one pattern, such as previously exposed patterns 36-1, 36-2, stage 23 is moved such that the next pattern in array 37 is in the exposure position. and wafer 11
A driving device 24 and a laser interferometer 25 are used to move the
is used. The direction and distance of movement from step to step correspond, respectively, to the direction of movement and distance used to advance wafer 11 when the first array is exposed from reticle 12. In each step, the corresponding targets 35-1,
A pattern image such as 35-2 (for example, a virtual image 35-
1') can be viewed using a light source 42 and a television camera 46. In order to allow the operator to precisely adjust the position of platform 23 to achieve perfect alignment of the target (as shown in FIG. It can be used in combination with the laser interferometer 25. Perfect alignment of the targets can be achieved in array 37 for each individual exposure. Alternatively, if the positioning performance of drive 24 and interferometer 25 is sufficiently accurate, it is preferable to perform a visual re-alignment at each position.
It only needs to be done once, twice or several times for each row or column of 7. Providing individual alignment targets 35-1, 35-2, etc. at each array location provides an opportunity for individual alignment for each exposure.

Camera optics typically have a very shallow depth of focus. If the thickness of the wafer 11 is not uniform, the wafer 1
1 may be in focus while the image generated by camera 30 is in focus on one portion of the camera 30, while the image generated on another portion may be out of focus.
In such cases, the full performance of the device 10 for precise alignment and high resolution may be lost. This problem is solved by a wafer flattening device (FIG. 7). This problem can be caused by the wafer itself having a wedge-shaped cross section, or by warping of the wafer during processing.

Referring to FIG. 7, the stand 23 is a movable table 50.
including. This table interferes with the drive device 24 25
is driven along the X and Y axes. The interconnection between table 50 and drive 24 is conventional. A stationary base 51 of a spherical air bearing mechanism 52 for a platform 53 rests on the table 50. platform 53
is attached to a generally hemispherical bearing 55 with bolts 54. Bearing 55 is received within a hemispherical recessed upper surface 56 of base 51 .

A series of annular grooves 57, 58, 59 form the surface 5 of the bearing.
Formed on top of 6. Groove 57 communicates with connector 61 via passage 60 in base 51 . Connector 64 is connected to a vacuum. The groove 58 is the base 51
It is communicated with the atmosphere through a vent hole 62 passing through it. With this configuration, the connector 6
When a vacuum is applied through 1, the vacuum holds bearing 55 and platform 53 in position with respect to the base. Vacuum passageway 60 also communicates with passageway 63 and, via bearing 55 and platform 53, with one or more holes provided in the top surface of platform 53 below wafer 11'. With this configuration, the connector 6
The same vacuum applied to wafer 11 holds wafer 11' on top of platform 53. In another embodiment, the wafer holding vacuum can be provided separately from the vacuum used to secure each half of the two air bearing halves.

Groove 59 communicates with connector 65 via passage 64 . Connector 65 is attached to a source of compressed air or other gas. Normally, a vacuum is continuously applied to connector 61. When it becomes necessary to reorient platform 53, pressurized gas is supplied to connector 65. Due to the pressure of this gas applied to the inner surface of the base 51 through the groove 59, the vacuum "holding force" is broken and an air support for the bearing 55 is created. As a result, bearing 55 and platform 53 can be positioned with respect to base 51 by applying very little force to platform 53 or wafer 11'. Once the platform 53 is in the desired orientation, the supply of pressurized gas to the connector 65 is cut off and the bearing 55 is immediately fixed to the base 51 by the vacuum force.

This air bearing support mechanism 52 is connected to the camera body 3.
This is used to facilitate making the upper surface 11T of the wafer 11' parallel to a certain reference plane, such as the surface of the lower end portion 31L of the wafer 11'.

To this end, a plurality (typically three) of air ducts 68, 68' are included in the camera body 31. Those air ducts are connected to the camera body 31.
Advantageously, they are arranged at intervals of, for example, 120 degrees on the periphery of the. A source of compressed air or other compressed gas (not shown) is connected to the upper ends of the ducts 68, 68'. Air jet 69, 69'
A portion of the air flows through the ducts 68, 6 so as to form a
8' exits from the open lower end portions 68a, 68a'. The air pressure inside each duct is determined by the camera body 3.
A corresponding pressure sensor 7 provided in 1
It can be detected by 0.70'.

In order to align the wafer 11' in parallel,
Compressed air is supplied to connector 65 so that platform 53 and wafer 11' can move freely over spherical air bearing mechanism 52. after that,
The camera body 31 is lowered toward the wafer 11' while supplying compressed air to the ducts 68, 68'. Air jet 6 blown out from the duct
9,69' connects wafer 11' and platform 5.
Force is applied to 3. Surface 11T of wafer 11'
are not parallel to the lower surface 31L of the camera body 31, the forces exerted by each air jet 69, 69' will be unequal. As a result, air jet 6
The unequal forces cause wafer 11' and platform 53 to move relative to spherical air bearing mechanism 52 until an equilibrium condition is achieved in which the forces applied by 9 and 69' are equal. This equilibrium state occurs when the distance between the open lower ends 68a, 68a' of the duct and the surface 11T of the wafer 11' becomes equal.
That is, this occurs when the front surface 11T of the wafer 11' becomes parallel to the lower surface 31L of the camera body 31.
This equilibrium condition is determined by the sensors 70, 70' detecting that the back pressures in the ducts 68, 68' have become equal. In appropriate response to this equal backpressure condition, a control circuit (not shown) cuts off the compressed air being supplied to connector 65. As a result, the air bearing 55 is immediately fixed by the vacuum applied to the base 51, so that the platform 53 and the wafer 11' are fixed at the desired position where the upper surface 11T of the wafer 11' and the lower surface 31L of the camera body 31 are parallel. be done.

The parts of FIG. 7 are not drawn to relative scale, and the wedge-shaped cross-section of wafer 11' is exaggerated. Furthermore, the diameter of the camera body 31 is actually sufficiently smaller than the diameter of the wafer 11'. Therefore, parallel alignment is performed over a relatively smaller area of wafer 11' than shown in FIG. Parallel alignment can be performed before each exposure, or it can be performed only once or several times between step movements across the wafer 11 and repeated exposures.

The apparatus shown in FIG. 7, a series of air jets similarly used at various physical locations, can also be used to provide very precise focusing of the camera 30 after the parallel alignment described above. can. Air jets 69, 69' and back pressure sensors 70, 70' are also used to accomplish this focusing.

Accurate focusing occurs when the camera optical system 14 is a precise distance away from the top surface 11T of the wafer. At this interval, a certain back pressure is applied to the sensor 70,
It is located at 70'. Focusing can be accomplished by gradually lowering the camera body 31 toward the wafer 11' while monitoring the back pressure level with the sensors 70, 70'. This back pressure increases as the camera body is lowered. When a predetermined back pressure corresponding to the correct focal length is detected, the lowering of the camera body 31 is stopped. This achieves correct focusing.
This focusing operation is performed each time an individual exposure is made in array 37.

The air jet back pressure detector or "air gauge" described above in connection with the operation of keeping the surface of the wafer parallel to the bottom surface of the camera body and the adjustment of focus automatically and precisely pre-positions the wafer 11. It can also be used for specific purposes. As described above, before performing the first exposure using the reticle 13, preliminary alignment of the wafer 11 is performed,
Wafer 11 is placed in a position where image 40 (FIG. 6) is very close to alignment target 35-1 on wafer 11. Once wafer 11 is properly pre-aligned, alignment target 35-1 appears within the field of view of television camera 46. However, since this field of view is very narrow (usually about 0.051 cm (0.002 inch) square), it is necessary to ensure that alignment target 35-1 appears within the field of view of television camera 46. requires accurate preliminary alignment.
Furthermore, it is important that the orientation of the wafer 11 on the table 23 is correct. For example, it is important that the trajectories of the alignment targets 35-1, 35-2, etc. be parallel to the X and Y axes of the drive device 24.
This is necessary because as the wafer 11 is stepped along at least one of the X and Y axes during successive exposures, each successive target 35-2, 35-3, etc. This is to make it appear in the field of view of the television camera 46.

As mentioned above, the flat edge 11 of the wafer 11
Preliminary alignment of f is performed at a station 20 that is previously aligned. Thus, when the wafer 11 is placed on the platform 23, the flat edge 11f is generally aligned with one of the axes of the drive 24 (usually the X-axis). Next, one of the air jets (eg, air jet 69 and pressure sensor 70) in camera body 31 is used to determine the center of wafer 11. This technique is shown in FIG.

First, the platform 23 is moved parallel to the Y-axis until the air jet 69 is placed along any direct line 75 parallel to the X-axis and away from the horizontal centerline 76 of wafer 11. Next, the edges 75L, 7 of the wafer 11
The drive device 24 is used to move the platform 23 parallel to the X-axis 73 until 5R is detected. For example, table 23 is first moved to the right so that straight line 75 is the path of air jet 69 to the moving wafer (see FIG. 9). When the edge 75L of the wafer 11 is reached, the back pressure detected by the sensor 70 immediately decreases. Sensor 70 then sends a corresponding signal to a computer (not shown) which, together with laser interferometer 25, determines the reference position of the edge of wafer 11 along straight line 75. Next, turn the stand 23 in the opposite direction, i.e.
In the diagram, move it to the left. The air jet 69 and sensor 70 are then used to detect the position of the opposite edge 75R of the wafer 11. Once those two positions are known, the corresponding length along the straight line 75 (i.e., the distance between the edge points 75L and 75R) is divided (by computer) into two to determine the position of the midpoint 75c of the straight line 75. do.

This measurement is performed using a different straight line 77 parallel to the straight line 75,
78 as many times as possible. As a result, a set of points 75c, 77c, and 78c are determined. The average position of those points defines the vertical centerline 79 of wafer 11. This method also eliminates errors that may occur due to the presence of defects along the edge of wafer 11 where any of the straight lines 75, 77, 78 intersect.

The same operation is then performed in the vertical direction to define the centerline 76. To this end, the platform 23 is moved to a position where the air jet 69 lies along a vertical line 81 (FIG. 9) that does not intersect the flat edge 11f of the wafer 11.
is moved parallel to the X-axis 73. Then move platform 23 to Y
Points 81T and 81B where the straight line 81 intersects the "top" and "bottom" of the wafer 11 by moving parallel to the axis only
In order to determine the air jet 69 and the sensor 70
Use. In addition, a computer and a laser interferometer 2
5 are combined and measured, and the center 81c of the straight line 81 is calculated.

This operation is repeated for one or more vertical lines 82, etc., to obtain other center points 82c. The position of the horizontal center line 76 is determined by these points 81c and 82c. The intersection 83 of centerlines 76, 79 defines the center of wafer 11. That is, in this way, the correct position of the center point 83 is determined with respect to arbitrary reference points for the X-axis 73 and the Y-axis 74. With respect to this center point 83, the drive device 24
and interferometer 25 determine the position of table 23.

While performing the first masking operation on wafer 11 using reticle 12, array 37 (second
The stepwise and iterative positioning operation for determining the center point 83 and the center lines 76, 79 determined in accordance with the procedure described with reference to FIG. It is carried out as follows. but,
In order to eliminate rotational errors that may occur in the positioning of the wafer 11, it is advisable to perform additional preliminary alignments as shown in numbers 10 and 11 for subsequent masking operations using the reticle 13.

Once reticle 13 is in place, the center of wafer 11 is determined as described above. If there is a rotational error, the determined center line 76,
79 is the alignment target 35 of array 37.
-1, 35-2, etc. are no longer parallel to the X-axis and Y-axis, which are the reference targets. To correct this rotational error, a certain alignment target 35-C (FIG. 10) near the centerline of wafer 11 is directly below camera 30 and aligned with alignment target 35-C of alignment target 40. The drive device 24 initially drives the wafer 11 until it is in a coincident position. Since this target 35-C is close to the center 83 of wafer 11, target 35-C should appear within the field of view of television camera 46 even with significant rotational positioning errors of the wafer.

The operator then operates the drive device 24 using a suitable operating rod (not shown) and moves the platform 23 along the X axis until the alignment target 35-C approximately matches the image of the pattern 40 on the reticle 13. 73
and Y-axis 74. At this time, the worker presses a button (not shown) to display the target 35-C on the computer.
This position can be recorded.

Next, the platform 23 is moved along the X or Y axis to the predicted position of another alignment target 35-D that is further away from the center 83 of the wafer. Assuming that there is a rotational error, the relationship between the image of the target 40 and the alignment target 35 will be as shown in FIG. The operator then operates the operating rod again to move the platform 23 along the X and Y axes until the target 35-D is in the center of the image of the target 40. The new position of the wafer at that time is also entered into the computer.

By repeating this operation, the correction of at least one of the X-axis and Y-axis necessary to align the targets 35-C, 35-D, etc. at each point can be made in the positioning of the wafer 11. It will be clear that the resulting rotational error θ is directly indicated. After calculating the error θ by trigonometry,
The base 51 and the platform 53 supporting the wafer 11 are arranged at a corresponding angle φ with respect to the center of the wafer.
The mechanism shown in FIG. 8 can be used to rotate by. This eliminates wafer rotational position errors.

In order to correct this error φ, the base 51 is mounted on the table 50 in such a way that the base 51 can be rotated by a minute angle without moving along the X and Y axes. To this end, a cylindrical recess 85 is provided on the underside of the base 51, into which the ends 86a of three flexible arms 86-1, 86-2, 86-3 are mounted. The outer ends of the arms 86 are connected to the table 50 by fittings 87. Each arm 86 extends through a respective slot 88 and through the cylindrical lower wall of base 51. A sturdy arm 89 extends outwardly from the base 51.

With this configuration, when the outer end 89a of the arm 89 is moved to the left or right in FIG.
Rotates around the vertical central axis of 1. This rotational movement is possible due to the deflection of all arms 86. However, arm 86 prevents base 51 from moving laterally relative to table 50 (ie, parallel to the X or Y axis). A pure rotational correction is therefore performed.

Motion is transmitted to arm 89 by motor 91. This motor rotates a shaft 92 having a threaded portion 93. The end of this shaft is journalled to a bearing 94 mounted on the table 50.

The shaft 92 is screwed into a screw hole provided at one end of the arm 95. The other end of arm 95 is attached to connecting arm 97 by a flexible joint 96. This arm 97 is connected to the outer end 89a of arm 89 by another flexible joint 98. Arm 95 is pivotally connected to table 50 by a fitting 99 which is pivotally connected thereto with a flexure joint 100.

With such a configuration, when the motor 91 is rotated in one direction (for example, clockwise), the threaded portion 93 of the shaft 92 rotates the arm 95 about the joint 100, thereby causing the arm 97 to rotate. A leftward or rightward movement is transmitted to the arm 89 through the arm 89. As a result, base 51 and platform 53 are rotated into corresponding angular orientations. Further, when the motor 91 is rotated in the opposite direction to the above, the base 51 is correspondingly rotated in the opposite direction to the above. An encoder 101 connected to the shaft 92 indicates the amount of rotation of the motor 91. Therefore, an output signal indicating the rotation angle of the base 51 is generated.

The motor 91 can be automatically controlled by a computer (not shown) used as described above to determine the rotational position error θ of the wafer 11. When the motor 91 is rotated, the encoder 101
provides a signal indicating the amount of rotation transmitted to the base 51 to the computer. In response to this signal, the motor 91 can be appropriately stopped when the desired correction angle θ is reached. In this way, wafer 1
The rotation angle in the first position can be automatically corrected with high accuracy.

When this rotational position error is corrected, the wafer 11
The effective center lines 76 and 79 of the table 23 are the X-axis 73 and Y
parallel to the axis 74, and all alignment targets 35-1, 35-2, etc.
Correct alignment with the axis is obvious. Therefore, during this stepwise iterative operation, array 37
When the wafer 11 is stepped at the same distance and in the same orientation as was used during the initial exposure operation of the wafer 11 to make the image (FIG. 2), in each case the pattern image 40a is aligned with the corresponding alignment target. 35-
1, 35-2, etc. If necessary, small corrections can be made manually using the control wand. Perfect alignment of the image of pattern 41 from reticle 13 with previously exposed images 36-1, 36-2, etc. is performed for every array position.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a stepping and repeating apparatus of the present invention used for direct exposure of semiconductor wafers; FIG.
FIG. 3 is a plan view of a wafer being exposed using the apparatus shown in FIG. A plan view of a reticle containing the first image exposed onto a wafer; FIG. 4 shows a complementary target used to align the target image previously exposed onto a wafer using the reticle shown in FIG. 3; 5 is a schematic diagram of the image alignment system used in the apparatus of FIG. 1, and FIG. 6 is a plan view of a reticle used in subsequent processing steps, FIG. 7 is a schematic diagram of a virtual image of the wafer alignment target superimposed on the alignment pattern of the reticle, FIG. 7 is a cross-sectional view of the wafer support table and wafer surface parallel alignment device used in the apparatus of FIG. 1, and FIG. FIG. 7 is a schematic diagram of the rotating drive mechanism of the table; FIGS. 9 and 10 are schematic diagrams showing wafer stepping and preliminary alignment of the wafer before repeated exposure; FIG.
Figure 6 shows the situation during preliminary alignment.
FIG. 10... Device of the present invention, 12, 13... Reticle, 14... Camera optical system, 23... Stand, 24
...X-Y drive device, 28 ... Reticle holder,
30...Camera, 31...Camera body, 32...
...Light source, 33, 33'...Positioning mark, 3
5, 42... Alignment target, 40... Alignment pattern, 44... Beam splitter, 50
... table, 51 ... base, 52 ... spherical air bearing support, 53 ... platform.

Claims (1)

[Scope of Claims] 1. A positioning device for an exposure device that exposes a predetermined pattern image on a semiconductor wafer, comprising: a table on which the semiconductor wafer is placed; and a table that moves this table along orthogonal X and Y axes. a drive means; an air jet means attached to the body of the camera and including a first sensor for blowing a jet of pressurized air toward the wafer and detecting back pressure of the blown air; means for moving the platform parallel to one of the orthogonal axes and measuring the change in back pressure of the blown air as the air jet moves across opposite ends of the wafer. control means for detecting a position of the opposing edge of the wafer along the one axis and determining a first centerline position of the wafer from the edge; The air jet means includes a plurality of air jets spaced apart from each other and each having a corresponding back pressure sensor, and the table further includes a platform for supporting the semiconductor wafer, and the platform further includes a platform for supporting the semiconductor wafer. , is supported on an air bearing so as to be rotatable under the pressure applied to the wafer by the plurality of air jets, and a part of the surface of the wafer is parallel to a reference plane of the camera, and the back pressure is A semiconductor device comprising fixing means for fixing the air bearing so as to prevent rotation of the platform and the wafer when all back pressures detected by the sensors become equal. Positioning device for wafer exposure equipment. 2. The camera is configured to expose a pattern image from a reticle onto the wafer, and the control means moves the wafer mounted on the platform drive to an array of preselected positions with respect to the camera. 2. The positioning device for a semiconductor wafer exposure apparatus according to claim 1, wherein the camera moves stepwise so that the pattern image is exposed onto the wafer at each of the positions. 3. The wafer has a first circuit pattern and an array of patterns previously exposed by a first reticle that includes an alignment target in an area adjacent to each first circuit pattern and has a surface coated with photoresist. and the camera has a shape complementary to the second circuit pattern and the alignment target, and when correctly overlapped, the first circuit pattern and the second circuit pattern are connected to each other. illuminating the alignment target area on the wafer with light of low intensity that does not expose the photoresist from a second reticle containing an alignment pattern configured to accurately overlap; an alignment view element for simultaneously viewing the alignment pattern of the second reticle and an image of the alignment target; 3. The positioning device for a semiconductor wafer exposure apparatus according to claim 2, wherein the positioning device is configured to move the table on which the wafer is placed so that the wafer is placed on the wafer. 4. The viewing element includes a beam splitter and a viewing optics for viewing the light polarized by the beam splitter, and the first light source is configured to avoid intense exposure of the photosensitive material on the semiconductor wafer. the first light source has a luminance sufficiently low to match the wavelength of the first light source, and the light from the first light source is transmitted through a portion of the reticle that includes the alignment pattern. , configured to advance toward the wafer through the beam splitter, and reflected light from the wafer forms an image of the target on a reticle and is polarized through the beam splitter. A positioning device for a semiconductor wafer exposure apparatus according to claim 3. 5. The positioning device for a semiconductor wafer exposure apparatus according to claim 3, wherein the viewing element includes a television camera arranged to receive light from the viewing optical system. . 6. In an exposure method using a step-and-repeat method in which a desired circuit pattern is sequentially exposed while aligning a semiconductor wafer with a reticle using the same lens system used for exposing the circuit pattern, using a first reticle having a circuit pattern of a first exposure step of stepping the semiconductor wafer by a distance to form a first array of circuit pattern images on the semiconductor wafer; and moving the exposed wafer parallel to one of orthogonal axes while moving the stage. , by blowing a pressurized air jet toward the wafer and detecting changes in the back pressure of the blown air as the air jet moves across opposite ends of the wafer. a centerline locating step of detecting a position of the opposing edges of the wafer along an axis of the wafer and determining a first centerline position of the wafer from the edge; A jet of air is blown onto the semiconductor wafer so that a part of the surface of the wafer becomes parallel to the reference plane of the camera, and the back pressure is detected by a back pressure sensor disposed corresponding to each air jet. a rotational positioning step of preventing rotation of the table and the wafer when all back pressures are equal; and a second reticle having a second circuit pattern and a second alignment target in place of the first reticle; while irradiating only the peripheral area of the first alignment target formed on the semiconductor wafer in the first exposure step with low-intensity light that does not expose the resist on the wafer;
an alignment step of observing through the lens system and finely adjusting the position of the semiconductor wafer so that the first alignment target on the semiconductor wafer overlaps a second alignment pattern; The aligned semiconductor wafer is sequentially exposed to light through the second reticle using the lens system, and the semiconductor wafer is advanced each time it is exposed to form an image of a second circuit pattern row. A method for exposing a semiconductor wafer, comprising a second exposure step. 7. The semiconductor wafer exposure method according to claim 6, wherein the low-intensity light used in the alignment step is configured to have the same wavelength as the light used in the exposure step.