JPS6322454B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a chuck device for transferring and baking a mask pattern onto a substrate.

Semiconductor integrated circuits are becoming smaller year by year, and projection type aligners are becoming mainstream instead of conventional contact type aligners. Since a projection aligner projects and prints a mask pattern onto a wafer, if the flatness of the wear surface adsorbed to the wafer chuck is poor, the pattern will not be printed in areas that are out of the focal plane. do not have. The requirements for flatness of the wafer surface are more stringent as the pattern becomes finer.

FIG. 1 is a schematic diagram of a conventional projection type aligner manufactured by Cobilt. A pattern 2 on the surface of the mask 1, indicated by an arrow in the figure, is formed by a concave mirror due to the exposure light 3.
An image is formed and printed onto the wafer 5 via a mirror optical system consisting of a convex mirror M ₁ , a convex mirror M ₂ and a plane mirror M ₃ . Reference numeral 7 indicates an imaging pattern. The carriage 8 carrying the wafer 5 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 5 in accordance with the scanning.
In order to attract the wafer 5 to the upper surface, the wafer chuck 9 forms an air passage in which the holes arranged on the upper surface are connected to the holes 9a on the lower surface. The hole 9a communicates with a vacuum generator (not shown) via a pipe indicated by an arrow 10. FIGS. 2a and 2b are an enlarged sectional view and a plan view of the wafer 5 placed on the wafer chuck 9, respectively. In FIG. 2b, the flatness of the wafer 5 is shown by contour lines 11, which in this example shows that it is formed into a spherical shape that projects upward. As shown in FIG. 2a, the surface 12 of the wafer 5 is the imaging plane 1 of the optical system.
If there is no match for 3, line pattern 14
Even if an attempt is made to transfer the line pattern 14 (see FIG. 2b), the image is only formed on the wafer surface 12 within the depth of focus, so only a portion of the line pattern 14 is transferred. The depth of focus of the imaging plane 13 is determined by the resolution of the optical system, and to transfer a line width of 3 μm, the depth of focus at the resolution required is ±5 μm. The smaller the line width to be transferred, the higher the resolution is required and the shallower the depth of focus becomes. For a line width of 2 μm, a depth of focus of ±3 μm or less is required. On the other hand, the flatness of the wafer surface 12 adsorbed onto the flat chuck surface 16 is usually ±2 μm or more, and increases as the integrated circuit manufacturing process progresses, sometimes exceeding ±10 μm, which reduces the yield. was causing a decline in In addition, the cause of the deterioration of flatness is often unknown, and it is difficult to expect much improvement in flatness.

Therefore, in order to image and print a mask pattern on a wafer with poor flatness, a method of focusing on the wafer surface 12 can be considered. Referring to Figure 3,
The creation of a wafer circuit by focusing will be explained. The wafer 5 has a spherical shape projecting upward as in FIGS. 2a and 2b, and the depth of focus is defined by two contour lines 11. When scanning in the direction of the arrow in the printing range W ₁ 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, if you scan in the same range W ₁ while focusing, the image will be printed in the range R ₁ . next,
If the image is scanned in the narrow printing range W ₃ while focusing three times in the vertical direction in the figure, printing will be done in the range R ₃ . From the above explanation, it will be understood that the yield is best if the exposure is carried out in parts. However, if the process is divided into three times, the throughput will be reduced to 1/3, resulting in a large loss.
Further, it requires complicated operations for detecting the focal point position, adjusting the focal plane, etc., is expensive, and has the disadvantage that maintenance work for repair and inspection is difficult and troublesome.

SUMMARY OF THE INVENTION An object of the present invention is to provide a chuck device which eliminates the above-mentioned drawbacks and is capable of transferring and printing a mask pattern with high precision.

In order to achieve this object, the present invention provides a plurality of replacement chucks capable of adsorbing substrates and having different degrees of flatness, a chuck magazine that stores these chucks, and a system that selectively stores the replacement chucks in a predetermined manner. a chuck base that attracts the chuck in position; a vacuum generator that causes the replacement chuck and the chuck base to perform a suction action; and a detection means that detects the flatness of the substrate;
A selection means for selecting an optimal replacement chuck based on a signal from the detection means, and a transport means for transporting an optimal replacement chuck from the chuck magazine to the chuck base based on the signal from the selection means, and detects the shape of the board. , the wafer surface is flattened by selecting a replacement chuck having a substantially complementary shape to the substrate shape, transporting it to a predetermined position, and adsorbing the substrate to the replacement chuck. .

The illustrated embodiment will be described in detail below. FIG. 4 shows an example of a wafer chuck device according to the present invention, which includes a chuck magazine 21 that stores a plurality of replacement chucks 20, and a chuck magazine 21 that transports the replacement chucks 20 from the chuck magazine 21 to the chuck base 2.
chuck handling mechanism 23 for transporting the chuck to 2 and returning it to the original position after use; motor 24a, 2;
4b; a transport means consisting of a controller 25, etc.; a wafer magazine 27 for storing wafers before baking; a wafer loader/unloader 26 for selectively placing or removing wafers from the wafer magazine 27 at a predetermined position; and a chuck moving table 28; Pulse motor 29: Detection section 30 for detecting the flatness of the wafer on the chuck; Detection means consisting of a detection signal input circuit 31; Chuck selection circuit 3 for selecting a replacement chuck having a shape substantially complementary to the shape of the wafer.
2; It is constituted by a selection means consisting of the overall control mechanism 33.

More specifically, a plurality of replacement chucks are available, one with a flat top surface (34) and one with an upwardly concave top surface with different radii of curvature (20), all of which have a stepped cylindrical shape. I am doing it. The chuck magazine 21 is provided with grooves 21a that open toward the chuck handling mechanism 23 in equal numbers to the number of replacement chucks, and the width of the grooves 21a is such that the small diameter portion of the replacement chuck can slide therein. ing. The chuck handling mechanism 23 includes two arms 23a that grip and open and close the replacement chuck 20, and a first arm 23a that swingably supports the arms 23a in a substantially right-angled range indicated by arrow B in the figure.
A supporting member 23b, a second supporting member 23c that supports the first supporting member 23b in the direction of arrow C, that is, the replacement chuck 20 can be freely inserted and removed along the groove 21a by driving the motor 24a, and the second supporting member 23c. It consists of a motor 24b, etc., which enables the member 23c to reciprocate in the direction of arrow D, that is, along the arrangement direction of the replacement chucks 20. On the other hand, the chuck moving table 28 is driven by the pulse motor 28 to move in the direction of arrow E, that is, parallel to the direction of arrow C, and attaches the chuck base 22 thereto. The upper part of the chuck base 22 has a complementary shape to the stepped portion of the replacement chuck 20, 34, and is adapted to fit tightly with the chuck, as shown in FIG. The wafer 5 can be sucked through the air holes provided in the replacement chucks 20 and 34. The detecting section 30 detects the surface height of the wafer 5 in synchronization with the moving position of the chuck moving table 28, and inputs the detected surface height to the detection signal input circuit 31. Check selection circuit 32
performs the calculation described later using the detection signal,
A signal for selecting a replacement chuck most suitable for the wafer 5 is commanded to the transfer means.

Now, the operation of the wafer chuck device of the present invention will be explained.

First, a flat chuck 34 is selected from the chuck magazine 21 and fitted onto the chuck base 22 attached to the chuck moving table 28. Operations during this time are performed by pressing an operation button (not shown) to operate the selection means and conveyance means. Next, the wafer 5 is taken out from the wafer magazine 27, placed on the chuck base 22, and sucked through the vacuum generator. Then, while controlling the pulse motor 29,
The wafer 5 on the chuck moving table 28 is scanned, and the flatness of the entire surface of the wafer is input to the detection signal input circuit 31 in synchronization with the moving position of the table 28.
This data is expressed, for example, as Wφ(x, y) in the case of an upwardly protruding type as shown in FIG. 6a, and as shown in FIG. The value at each intersection on the mesh 35, which is perpendicular to the y direction, is recorded. In the chuck selection circuit 32, replacement chucks 20a (FIG. 6b) and 20b (FIG. 6c) are selected.
Flatness data of the surface C ₁ (x, y) and C ₂ (x,
y), the flatness of the wafers 12a and 12b when the wafer 5 is vacuum-suctioned into these chucks is calculated based on the following formula.

W _f1 (x, y) = Wφ (x, y) + C ₁ (x, y) W _f2 (x, y) = Wφ (x, y) + C ₂ (x, y) Focus from W _f1 and W _f2 The area S _F within the depth (W _F1 to _{W F2} ) is calculated using the following formula. In other words, S _F =‖(x _i , y _i ) | W _F1 ≦W _f (x _i , y _i )≦W _F2
x _i , y _i ‖ Substitute W _f1 , W _f2 and Wφ into this equation and select the replacement chuck with the largest value of _SF .

As a result, if the flat chuck 34 has the maximum _SF value, the wafer 5 attracted to the flat chuck 34 is subjected to an exposure printing operation by an exposure section (not shown). The exposed and baked wafer 5 is
It is removed from the flat chuck 34 by means not shown. Next, in FIG. 4, the wafer magazine 27
Take out a new wafer 5 from the flat chuck 3.
Place it on 4. Next, the detection signal input circuit 3
1 and chuck selection circuit 32, if it is determined that, as a result of calculation, the chuck showing the maximum S _F value is, for example, the replacement chuck 20a, the wafer 5
is removed from the flat chuck 34, and the flat chuck 34 is returned to the vacant position 34A of the chuck magazine 21 by the conveying means, and a replacement chuck 20a is tightly fitted onto the chuck base 22 in its place. . Next, the wafer 5 is placed on the replacement chuck 20a, the flatness of the wafer is checked by the detection section 30, and the exposure section performs exposure and printing. If the confirmation by the detection unit 30 does not match the calculation result, a chuck for replacement is reselected based on the new detected value. If this kind of rework is repeated several times or if there are abnormal values,
The operation of the device is stopped to notify the operator that exposure is not possible.

In this embodiment, the number of exchange chucks is three including the flat chuck, and this number is set depending on the flatness of the wafer. Furthermore, the detection mesh interval should be similarly set based on the wafer flatness. Furthermore, the detection unit 30 includes a non-contact type detector (air micro, capacitance type, ultrasonic type, optical type,
(eddy current type, etc.) may be used in parallel, or may be scanned at high speed. Furthermore, if the flatness is determined by the wafer production process, there is no need for flatness detection of the wafer surface 12 (FIG. 6a) and calculations for selecting the optimum exchange chuck.
All you need to do is determine and calculate the optimal evaluation function taking into account the depth of focus and process yield, and it is also possible to use a system that places the chuck on the optimal exchange chuck from the beginning without exchanging the exchange chuck and the flat chuck. good.

As described above, according to the present invention, it is possible to improve the degree of image formation and realize highly accurate transfer printing.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a conventional projection aligner, Figures 2a and b are diagrams explaining the relationship between wafer flatness and image formation, Figure 3 is a diagram explaining divided exposure, and Figure 4 is a diagram explaining the relationship between wafer flatness and image formation. Figure 5 is a configuration diagram of an embodiment of the present invention.
The figure is a sectional view of the wafer chuck part applied to the above embodiment, Figures 6a, b and c are diagrams explaining the flatness of the wafer surface on each chuck, and Figure 7 is a diagram illustrating the flatness of the wafer surface. It is a figure explaining a detection mesh. 2...Pattern on mask, 5...Wafer, 2
0, 20a, 20b...replacement chuck, 21...
...Chuck Magazine, 22...Chuck Base,
23... Chuck handling mechanism, 30... Detection section, 32... Chuck selection circuit, 34... Flat chuck.

Claims (1)

[Claims] 1. A substrate on which the mask pattern is projected and imaged,
a plurality of replacement chucks capable of adsorbing the substrate and having different flatness; a chuck magazine for storing these chucks; and a chuck base for selectively adsorbing the replacement chucks at predetermined positions;
a vacuum generator for performing an adsorption action on the replacement chuck and the chuck base; a detection means for detecting the flatness of the substrate; a selection means for selecting an optimal replacement chuck based on a signal from the detection means; A chuck device comprising a conveying means for conveying an optimal replacement chuck from the chuck magazine to the chuck base in response to a signal.