JPH0147007B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an exposure method for printing a predetermined pattern on a substrate such as a silicon wafer, bubble wafer, ceramic substrate, printed circuit board, etc., specifically a pattern formed by a photographic technique such as a photomask or reticle. and devices.

For example, in order to form an LSI pattern on a wafer, it is common to apply photoresist on the LSI wafer and expose the wafer to a photomask pattern to expose the photoresist.

This process is called photolithography, and includes contact type (exposes the mask and wafer in close contact with each other), close-range type (exposes the mask and wafer with a distance of several microns to several tens of microns), and projection type (exposes the pattern on the mask onto the wafer). ).

FIG. 1 is a diagram showing a schematic configuration of a projection type exposure apparatus, which is an example of an exposure apparatus. On the surface of mask 1,
A pattern 2 indicated by an arrow in the figure is imaged and printed onto a wafer 4 by exposure light 3 through a mirror optical system consisting of a concave mirror M ₁ , a convex mirror M ₂ and a plane mirror M ₃ . Reference numeral 5 indicates an imaging pattern.
The carriage 6 carrying the wafer 4 and the mask 1 scans back and forth as indicated by arrow A in the figure, and the mask pattern 2 is transferred onto the wafer 4 in accordance with the scanning. In addition, so that the wafer 4 can be attracted to the upper surface,
The wafer chuck 7 forms an air passage in which porous holes arranged on the upper surface are connected to holes 8 on the lower surface.
The hole 8 communicates with a vacuum generator (not shown) via a pipe indicated by an arrow 9. FIGS. 2a and 2b are an enlarged sectional view and a plan view of the wafer 4 placed on the wafer chuck 7, respectively.
In FIG. 2b, the flatness of the wafer 4 is shown by contour lines 10, which in this example indicate that it is formed into an upwardly protruding spherical shape. As shown in Figure 2a,
If the surface of the wafer 4 does not match the imaging plane 12 of the optical system, even if you try to transfer the line pattern 13 (see FIG. 2b), the image will only be focused on the wafer surface 11 within the depth of focus. Only a portion of the line pattern 13 is transferred. The depth of focus of the imaging plane 12 is determined by the resolution of the optical system required for transfer, and the depth of focus at the resolution required to transfer a line width of 3 μm is ±5 μm. If this depth of focus is divided into mask setting errors, etc., the allowable depth of focus on the wafer side is ±3 μm. Further, if the line width to be transferred is 2 μm, the depth of focus on the wafer side is allowed to be ±2 μm. On the other hand, the flatness of the wafer surface 11 adsorbed onto the flat chuck surface 15 is usually ±4 μm or more, and some flatness is ±10 μm or more, resulting in a decrease in yield. On the other hand, it is extremely difficult to improve the flatness of the wafer itself.

Therefore, in order to image and print a mask pattern on a wafer with poor flatness, a method of focusing on the wafer surface 11 can be considered. Referring to Figure 3,
The printing of a circuit pattern onto a wafer by focusing will be explained. Wafer 4 is shown in Figure 2 a and b.
Similarly, it is assumed to have a spherical shape that protrudes upward, and the depth of focus is defined as two contour lines 10. When scanning in the direction of the arrow in the printing range W1 without focusing, the circuit pattern is printed only within a ring-shaped area with a width R ₀ corresponding to the depth of focus. Next, in the same range W1, range W1
When scanning while focusing along the center of R ₁
Burned within the range of . Next, in the narrow burning range W ₃ ,
In the figure, if you scan in the vertical direction three times while adjusting the focus, you can print within the range _R3 . From the above explanation, it will be understood that the yield is best if the exposure is performed in parts. However, if the pattern is divided into three times, the throughput will be reduced to 1/3, resulting in a large loss, and it will be extremely difficult to connect patterns between printing areas, making it difficult to achieve high-precision pattern printing. Further, it requires complicated mechanisms and operations for detecting the focal position, adjusting the focal plane, etc., is expensive, and has the disadvantage that maintenance is difficult and troublesome.

The above explanation has been made using LSI as an example, but the same discussion can be made in the case of other substrates (magnetic bubble substrate, thick film, thin film circuit board, printed circuit board).

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to form an image over the exposed area by deforming the substrate surface without horizontally shifting the substrate with respect to the chuck body under any conditions. An object of the present invention is to provide an exposure method and apparatus that improves the yield of semiconductors, magnetic bubbles, thick film/thin film circuits, and printed circuit boards by uniformly exposing the light to a surface.

That is, in order to achieve the above object, the present invention
A measurement process of measuring the amount of deformation of the exposed surface of the substrate, and a flexible plate formed to suction and hold almost the entire back surface of the substrate opposite to the exposed surface of the substrate at multiple locations, each independently. Each of the plurality of vertical displacement generating means installed to generate vertical displacement is driven based on the amount of deformation of the exposed surface of the substrate measured in the above measurement step, and force is applied to the flexible plate from the back side. At the same time, the exposed surface of the substrate is deformed by deforming the substrate, which is adsorbed and held on almost the entire surface of the flexible plate, following the deformation of the flexible plate. An exposure method characterized by comprising a control step of positioning the image plane, and an exposure step of exposing and printing a predetermined pattern on a substrate whose exposure surface has been deformed by the control step, and the present invention also provides an exposure method. , a measuring means for measuring the amount of deformation of the exposed surface of the substrate, a flexible plate formed to suction and hold almost the entire back surface of the substrate opposite to the exposed surface of the substrate, and each independently at multiple locations. a chuck having a plurality of vertical displacement generating means that partially deforms the flexible plate by engaging with the back surface of the flexible plate and slightly moving the flexible plate in the vertical direction; Based on the measured amount of deformation of the exposed surface of the substrate,
Each vertical displacement generating means of the chuck is driven to apply force to the flexible plate from the back side to deform the flexible plate, and the chuck is held by suction over almost the entire surface of the flexible plate. A control means for deforming the substrate by making a flexible plate follow the deformation and positioning the exposed surface of the substrate on the imaging plane, and exposing and printing a predetermined circuit pattern on the substrate whose exposed surface has been deformed by the control means. This is an exposure apparatus characterized by comprising an exposure means.

The present invention will be specifically described below based on embodiments shown in the drawings. FIG. 4 shows the overall schematic structure of the exposure apparatus of the present invention. That is, 4 is a substrate called a wafer,
Reference numeral 16 denotes a substrate flattening chuck, which has the function of correcting "undulations" and "warpage" of the substrate 4. Further, the substrate flattening chuck 16 is positioned and attached by a positioning means (not shown) to the carriage 6 supported so as to be able to reciprocate and slide on the base 22 from the substrate flattening position A to the exposure/printing position L. 17
is a device for measuring the flatness of the surface of the substrate 4 installed at the substrate flattening position A. The flatness information of the surface of the substrate 4 obtained by the flatness measuring device 17 at the substrate flattening position A is fed back to the substrate flattening chuck 16 to make the surface of the substrate 4 horizontal and flat. After the above operations, the substrate 4 and the substrate flattening chuck 16 are moved and set in the exposure apparatus. At this position, there is a device 21 for exposing the pattern on the photomask, and the pattern is exposed on the substrate 4. More specifically, this exposure apparatus includes a substrate flattening chuck 16 having one or more displacement generating devices for flattening the substrate 4, which is a wafer, with respect to the main body 38, a flatness measuring device 17, a controller 18 for the displacement generating device, It consists of a carriage 6 on which the substrate 4 and mask 1 are placed and scanned, a cartridge 19 that stores the substrate 4 before and after printing, a transport mechanism 20 between the cartridge 19 and the substrate flattening chuck 16, an exposure optical system 21, and a base 22. A substrate 4 such as a wafer is set from a cartridge 19 onto a substrate flattening chuck 16 which has been flattened in advance by a transport mechanism 20, and a flatness measurement device 17 detects the flatness of the substrate 4, and a controller 18 detects the flatness of the substrate 4. is calculated and the displacement generating device of each divided portion of the flattening chuck 16 is moved by the necessary amount to make the substrate 4 into the required shape, that is, in this case, flattened. Next, the flatness is checked with the flatness measuring device 17, and if it is not within the standard range, the displacement generator is slightly moved up and down a predetermined number of times to repeat the deformation operation of the wafer, and after the flatness is within the standard range, the exposure optical Move the carriage 6 under the system 21 and print the pattern of the mask 1.
The substrate such as a wafer that has been baked is transferred to a transport mechanism 20.
It enters the printing cartridge 19. Repeat the above steps until there are no more unbaked boards left. Here, it is preferable that the deformed shape of the substrate 4 matches the imaging plane of the mask surface pattern at the time of printing. However, in the exposure apparatus, the imaging plane of the mask surface pattern is made flat, and if it is sufficiently flat for the required accuracy, it is sufficient to make it flat. Although not shown in the figure, when aligning with the mask image plane, a means for detecting the mask image plane in advance is required. This can be done by detecting the image formation of the mask pattern on the substrate 4 through the exposure optical system 21 while moving the displacement generating device 16. In addition, a simple method is to detect the flatness of the mask, find out the deviation from the image formation position when it is flat, and use the flatness of the wafer surface and several reference points on the wafer to determine the deviation that was previously determined. Another possible method is to match the image formation position.

Figure 5 a, b, c, d are substrate planarization chuck 1
This shows the principle of 6. When the convex lens-shaped substrate 4 shown in a is sucked into a conventional flat vacuum chuck 23 as shown in b, the upper surface 11 of the substrate becomes convex. Here, the upper surface 11 of the substrate can be flattened by suctioning with the chuck 24, which can be selected in any shape depending on the thickness of the substrate as shown in c. The force that deforms the substrate is, in this example, the force of the atmospheric pressure 25 generated by the vacuum force of the chuck pressing the substrate against the chuck. Other possible deforming forces include electrostatic force, adhesive force, force due to contact with the upper surface 11 of the substrate, and force applied around the substrate. Although the deformation of the substrate is arbitrary, it is determined by the deformation curve of the substrate determined by the elastic deformation coefficient of the substrate and the deformation force, and a small deformation force 26 such as d
In some cases, it may not follow the chuck. For example, in the case of wafers, the amount of deformation in most substrates is 10μ.
Since it has a simple shape that can be approximated by a quadratic curve within ±2 μm, deformation due to atmospheric pressure is sufficient.

In order to further explain the principle of the present invention, FIGS. 6a and 6b are a plan view and a sectional view showing a substrate flattening device that flattens a convex lens-shaped substrate by moving each divided portion up and down. be. As shown in b, a motor 33 is attached to each of the grids divided as shown in a.
A gear 34 and a vertical displacement generating device 35 formed by a feed screw constitute one set of vertical displacement generating devices 36, and each group includes an independent vertical displacement generating device 36, a gap detector 37 corresponding to each vertical displacement generating device 36, and a vertical displacement generating device 36. Calculate the values of the chuck body 38 which incorporates the device 36 and sucks the substrate 4, the piping 8 that communicates with vacuum piping (not shown in this figure) to create a vacuum inside the chuck body, and the full gap detector 37. and a controller 3 that determines the vertical amount of each vertical displacement generator mechanism 36.
9, a driver 40 for driving each motor 33;

The substrate 4 is vacuum-suctioned and the vertical displacement generator 36
The substrate surface 11 corresponding to each vertical displacement generating device 36 can be moved up and down following the tip of the vertical displacement generating device 36.
After detecting the flatness of the top surface 11 of the board, each motor 33 rotates based on the amount of correction, and the rotational movement decelerated by the reduction gear 34 is transferred to the upper and lower frames 35 by the feed screw.
Raise and lower. If the motor 36 is a DC motor, a sufficient reduction gear ratio of 10,000 to 100,000 is required, but in the case of a pulse motor, it is sufficient to control the upper and lower pieces 2 in units of about 0.5 μm, and a large gear ratio is required. does not require. Also, for DC motors, detector 3
It is easy to control the vertical amount in a closed loop using a motor 7, but it is possible to control in an open loop with a pulse motor. However, pulse motors are larger than DC motors and have the disadvantage of generating heat even when stopped. In either case, it is necessary to eliminate bumpiness and play, or to keep it to a controllable value even if it occurs.

That is, the upper surface of the substrate flattening chuck consists of one or more pieces 35, and each piece can be moved up and down by a small distance independently by a displacement generator 36. The chuck body 38 has a circular shape around the periphery.
A flange portion having a rectangular or nearly rectangular shape is provided, and the substrate 4 is mounted on the flange portion of the main body and the displacement generator 36 . Further, a vacuum hole 8 and a tube are connected to this, and this tube is connected to a vacuum source 9.

As described above, while the entire substrate 8 is sucked downward in a vacuum, the flatness of each piece 13 is fed back to the displacement generator 36 from the flatness measurement device 17 at the position of the substrate corresponding to each piece 13, and the flatness is transferred upward and downward. By driving a small distance in the direction of
For example, even if the substrate has irregularities, warps, or undulations, or if foreign matter is present between the substrate and the frame, the surface of the substrate can be flattened.

In addition to the screw connected to the motor, the vertical displacement generating device 36 may be an electrostrictive element, a magnetostrictive element, a thermal deformation element, a mechanism using a magnet, a mechanism using a fluid, a fine deformation mechanism using a lever, or a combination thereof. If the substrate is a wafer, the stroke must be 30 μm, the positioning accuracy must be ±1 μm or more, the deformation speed must be faster than that of a throughput, and it must be stable during printing.

In addition, there are two methods for measuring the flatness of a substrate: one method uses a single measuring element to measure several points serially, and the other uses multiple measuring elements and measures several points in parallel. You could think so.

In any case, it is essential to measure the flatness of the surface of the substrate 4 at a position corresponding to the top 35 using these measuring devices and measuring methods.

Next, the exposure position (b) will be explained. The exposure equipment installed at this exposure position includes a contact type exposure equipment that exposes the photomask and the substrate in close contact with each other, and a contact type exposure equipment that exposes the photomask and the substrate in close contact with each other. There is an apparatus that exposes a pattern by irradiating exposure means such as X-rays. Another exposure apparatus is a projection type exposure apparatus shown in FIG.
By imaging the pattern 5 on the substrate 4
A pattern is exposed on top.

The shape of the top is as shown in FIGS.
Multiple concentric segmental divisions 44, parallel divisions 45, combinations of concentric and radial divisions 46, etc.
Various methods are possible.

Next, an embodiment of the substrate flattening apparatus according to the present invention will be described. That is, as shown in FIG. 8, a thin plate (flexible plate) 47 is pasted on the top of the displacement generator 36 that has been divided into a plurality of pieces and on the upper surface of the periphery of the chuck body 38. There is. As other displacement generating means 15, a substrate (flexible plate) 47 whose periphery is attached and fixed to the upper surface of the periphery of the chuck body 38 by adjusting the vacuum pressure of each chamber divided into a plurality of chambers. It is also possible to transform it into a diaphragm shape. Note that 48 is a hole for holding the substrate 4 on the thin plate (flexible plate) 47 by suction. In this way, the periphery of the thin plate 47 is held and fixed around the upper surface of the chuck body 38, and when each displacement generating means 36 is driven and a force is applied to a local part of the thin plate 47 to deform it, the entire thin plate 47 is held and fixed around the upper surface of the chuck body 38. 3
8, the alignment state is maintained, and exposure of a circuit pattern with high precision can be realized.

Further, the substrate surface flatness measuring device 17 includes a contact type and a non-contact type. Contact types include dial gauges, and non-contact types include air micrometers, electromagnetic measuring instruments, capacitance measuring instruments, optical measuring instruments, and various other means.

As described above, according to the present embodiment, after being subjected to various heat treatments, for example, "warpage" and "waviness" of about 100 μm usually occur.
The flattening of LSI wafers, which conventionally could only be about ±15 to 20 μm, can be reduced to about ±1 μm.

If a pattern is exposed to light on a substrate that has been flattened and made horizontal in this way, it will be uniformly exposed over the entire surface.
It is possible to form fine patterns of 1 to 2 μm,
For example, if the substrate is a wafer, the yield of LSI can be greatly improved.

As explained above, according to the present invention, each of the plurality of vertical displacement generating means installed to independently generate vertical displacement at a plurality of locations is driven, and the back surface of the substrate is covered almost entirely. Exposure of the substrate by deforming a flexible plate formed to be held by suction and deforming the substrate, which is held by suction over almost the entire surface of the flexible plate, following the deformation of the flexible plate. Since the surface is positioned at the image formation plane, even if the substrate is warped, it can be moved smoothly without damaging the substrate while it remains horizontally stationary with respect to the chuck body, that is, the alignment is maintained. Practical effects that allow the exposed surface of the substrate to match the imaging surface with high precision by deforming, allowing exposure printing of fine circuit patterns with high resolution and greatly improving product yield. be effective.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram showing a projection exposure apparatus, which is an example of a conventional exposure apparatus, Figures 2a and b are diagrams illustrating the relationship between wafer flatness and image formation, and Figure 3 is a diagram illustrating the relationship between wafer flatness and image formation. FIG. 4 is a schematic configuration diagram showing an embodiment of the exposure apparatus according to the present invention, and FIG. 5 a, b, c, and d are diagrams for explaining exposure. Figure 6a is a cross-sectional view of a part of the device for deforming the substrate at the substrate flattening position, and Figure 6b is a front view of Figure 6a. Cross-sectional view, Figure 7 a, b, c,
d, e, and f are diagrams showing the arrangement of the top and vertical displacement generator shown in Figure 6, respectively, and Figure 8a is the same as Figure 6a.
FIG. 8b is a sectional view taken along the line C--C in FIG. 8a, and FIG. 9 is an embodiment of the exposure device installed at the exposure position. It is a schematic diagram showing a projection type. Explanation of symbols 4... Substrate (wafer), 6... Carriage, 16... Substrate flattening chuck, 17... Flatness measuring device, 18... Controller, 19... Cartridge, 20... Transport mechanism, 21... Exposure optical system (exposure device) , 36...Vertical displacement generator.

Claims (1)

[Claims] 1. A measuring step for measuring the amount of deformation of the exposed surface of the substrate, and a flexible plate formed to suction and hold almost the entire back surface of the substrate opposite to the exposed surface of the substrate. The flexibility is achieved by driving each of the plurality of vertical displacement generating means installed to independently generate vertical displacement at a plurality of locations based on the amount of deformation of the exposed surface of the substrate measured in the above measurement process. A force is applied to the plate from the back side to deform the flexible plate, and the substrate, which is suctioned and held on almost the entire surface of the flexible plate, is deformed to follow the deformation of the flexible plate. An exposure method comprising: a control step of positioning the exposed surface of the substrate on an image forming surface; and an exposure step of exposing and printing a predetermined pattern on the substrate whose exposed surface has been deformed by the controlling step. . 2. A measurement process of measuring the amount of deformation of the exposed surface of the substrate, and forming the back surface of the substrate opposite to the exposed surface of the substrate to be suctioned and held over almost the entire surface, and holding and fixing the periphery around the chuck body. Each of the plurality of vertical displacement generating means installed to independently generate vertical displacement of the flexible plate at a plurality of locations is determined based on the amount of deformation of the exposed surface of the substrate measured in the above measurement process. A force is applied to the flexible plate from the back side based on the periphery held and fixed to the chuck main body by driving to deform the flexible plate and to apply force to the flexible plate over almost the entire surface thereof. a control step in which the substrate held by suction is deformed to follow the deformation of the flexible plate, and the exposed surface of the substrate is positioned on the imaging plane; 1. An exposure method comprising: an exposure step of exposing and printing a predetermined pattern. 3 A measuring means for measuring the amount of deformation of the exposed surface of the substrate, a flexible plate formed to suction and hold almost the entire back surface of the substrate opposite to the exposed surface of the substrate, and each independently at multiple locations. a chuck having a plurality of vertical displacement generating means that partially deforms the flexible plate by engaging with the back surface of the flexible plate and slightly moving the flexible plate in the vertical direction; Based on the measured amount of deformation of the exposed surface of the substrate,
Each vertical displacement generating means of the chuck is driven to apply force to the flexible plate from the back side to deform the flexible plate, and the chuck is held by suction over almost the entire surface of the flexible plate. A control means for deforming the substrate to follow the deformation of the flexible plate and positioning the exposed surface of the substrate on the imaging plane, and exposing and printing a predetermined circuit pattern on the substrate whose exposed surface has been deformed by the control means. 1. An exposure apparatus comprising an exposure means. 4. A measuring means for measuring the amount of deformation of the exposed surface of the substrate, a flexible plate formed to suction and hold almost the entire back surface of the substrate opposite to the exposed surface of the substrate, and the flexible plate. A chuck body for holding and fixing the periphery of the plate; and a chuck body provided within the chuck body, each of which independently engages the back surface of the flexible plate at a plurality of locations and moves the flexible plate slightly in the vertical direction. A chuck having a plurality of vertical displacement generating means for partially deforming the chuck, and driving each vertical displacement generating means of the chuck based on the amount of deformation of the exposed surface of the substrate measured by the measuring means to generate the chuck. A force is applied from the back side to a flexible plate whose periphery is held and fixed to the main body to deform the flexible plate and flex the substrate which is suctioned and held by this flexible plate over almost the entire surface. a control means for deforming the substrate to imitate the deformation of the magnetic plate, and positioning the exposed surface of the substrate on an imaging plane; and an exposure means for exposing and printing a predetermined circuit pattern on the substrate whose exposed surface has been deformed by the control means. An exposure device characterized by comprising: