KR19980067571A - Dummy cells in the reticle to prevent poor focus - Google Patents

Abstract

The present invention relates to a dummy cell of a reticle for preventing focus failure to adjust to an optimal focus state by detecting a focus state and a degree of misalignment at various points within one shot formed on a wafer and taking appropriate measures based on this.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dummy cell of a reticle for preventing focus failure to detect a focus state of various points within one shot and to optimally adjust a focus condition. In addition, an object of the present invention is to provide a dummy cell of the reticle for preventing the focus failure to accurately check whether a mismatch occurs in one shot using the SEM.

To achieve this purpose, the dummy cell of the reticle for preventing the focus failure has a scribe brain corresponding to each of the edges and the center point of one shot, and the dummy cell for detecting the focus state and mismatch in one shot and the position of the shot. Characterized by the minimum design rule in the region of the. According to this configuration, it is possible to prevent the focus failure in one shot by checking the focus state and the degree of matching from the dummy cells in one shot formed on the wafer, and it is possible to accurately determine whether mismatch occurs by the SEM.

Description

Dummy cells in the reticle to prevent poor focus

The present invention relates to a stepper reticle, and more particularly, to detect the focus state and the degree of mismatch at various points within one shot actually formed on the wafer and to take appropriate measures based on the optimum focus. The present invention relates to a dummy cell of a reticle for preventing focus failure to be adjusted to a state.

As is generally known, the reduced projection exposure method is a method represented by a stepper marketed by GCA of USA. This method uses a reticle in which one pattern or a plurality of patterns of an integrated circuit chip enlarged by 10 times are formed. This pattern is scaled down and stepped onto the photo-coated wafer, and once one shot is exposed, the wafer is moved for exposure of the next shot on an interferometrically controlled XY table. do. This approach is slightly lower in throughput, but advantageous for large chips because it depends on the number of repetitive transfers over the wafer. Nowadays, since the resolution of 1 micrometer level and the matching precision of about 0.3 micrometer are acquired using a positive photosensitive film, it is mainly used for forming a fine pattern.

On the other hand, it is very important to detect the occurrence of mismatch in the photo process, the following three methods have been mainly used.

The first method is to match the mask to the wafer while the operator checks the vernier key pattern of the mask through a microscope. This has a disadvantage in that it is difficult to detect precise mismatches and it is difficult to form all the edge points within one shot because the area of the vernier key is large.

The second method is to numerically indicate the degree of shift of the pattern due to mismatch between the mask and wafer using a mask and a KLA device having a KLA key formed at each edge of one shot. It has the disadvantage of low accuracy at severe steps.

The third method is to detect the occurrence of mismatch through the SEM. If it is difficult to check the accuracy of mismatch by KLA, the overlay of the previous step pattern and the current step pattern is overlaid. ) And detect CD (critical dimension) to detect mismatch.

Currently, the first and second methods are mainly used. In the case of matching using these methods, if the focus of the center point and the edge points of one shot is not equal to each other, the shot edge focus often occurs poorly. do.

Conventionally, in the case of a DRAM or an SRAM device having a cell structure of a repeating pattern in order to prevent the occurrence of such focus failure, as shown in FIG. 1, an area for an integrated circuit chip in the center of the reticle 10 ( The focus of the same cell pattern located at the upper left and right support points (a) and (b) of 11) and the lower left and right support points (c) and (d) of the region 13 for the integrated circuit chip. I have checked and focused.

However, devices such as logic, microcomputers, and ASICs are multi-chips in which a number of different devices exist in one shot, but the edges (a), (b), (c), and (d) of FIG. ), It is difficult to find patterns of the same size and shape. When the optimum focus conditions of the edge points are difficult to meet, the focus of the edge points is not constant. For example, when the integrated circuit chip of the region 11 is determined to be good, the integrated circuit chip of the region 13 is determined to be defective. Occurs frequently.

In addition, when confirming whether mismatch occurred using SEM, the pattern of mismatched state was not seen except the specific step of the area | regions 11 and 13, and it was not able to confirm whether a mismatch occurred correctly.

In addition, devices such as logic, microcomputers, and ASICs have been difficult to find defect points and difficult to determine how stable the current process is.

Accordingly, it is an object of the present invention to provide a dummy cell of a reticle for preventing focus failure to detect a focus state of various points within one shot and to optimally adjust a focus condition.

In addition, the present invention is to provide a dummy cell of the reticle for preventing the focus failure to accurately check whether the mismatch occurs in one shot using the SEM.

1 is an internal layout view showing a conventional stepper reticle.

2 is a layout view showing a dummy cell of the reticle for preventing focus failure according to the present invention.

3 is an exemplary view illustrating a dummy cell of FIG. 2.

4 is an exemplary view illustrating a matching state between a previous step and a current step pattern using the pattern for matching of FIG. 3.

Explanation of symbols on the main parts of the drawing

Reference Signs List 10 reticle 11, 13: area for integrated circuit chip 15: scribe line 20: reticle 21: dummy cell 23: area for checking focus 25: area for checking matching 26a: pattern of previous step 26b: current step Pattern 27: area for checking the position of the dummy cell

To achieve this purpose, the dummy cell of the reticle for preventing the focus failure has a scribe brain corresponding to each of the edges and the center point of one shot, and the dummy cell for detecting the focus state and mismatch in one shot and the position of the shot. Characterized by the minimum design rule in the region of the. According to this configuration, it is possible to prevent the focus failure in one shot by checking the focus state in the dummy cells in one shot formed on the wafer by adjusting the optimal focus condition to be applied to the next photo process, and also in the same shot. SEM can accurately check whether the previous step and the current step pattern have mismatch.

Hereinafter, a dummy cell of a reticle for preventing focus failure according to the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals are given to the same parts as the conventional parts.

2 is a layout view showing a dummy cell of a reticle for preventing focus failure according to the present invention, Figure 3 is an exemplary view showing a dummy cell of FIG.

As shown in FIG. 2, the reticle 20 is formed in the scribe line 15 so that the dummy cells 21 are positioned at each edge portion and the center portion of one shot. In addition, as shown in FIG. 3, the dummy cell 21 may include a region 23 in which a predetermined pattern (not shown) is formed to check a focus state, and a region 25 in which a pattern 26 to confirm mismatch is formed. ) And a region 27 in which a pattern (not shown) for confirming the position of the dummy cell 21 is formed.

The operation of the dummy cell of the reticle for preventing the focus failure configured as described above is as follows.

First, a photoresist film (not shown) is coated on the surface of the wafer (not shown) where the previous step is completed, and then exposed to the wafer (not shown) by step and repeat one by one using the reticle 20 of FIG. 2. Subsequently, the exposed photosensitive film is developed to form a desired pattern.

In this case, a scribe line 15 is formed around the regions 11 and 13 for the integrated circuit chip, and the scribe lines adjacent to the upper left and right support points a and b of the region 11 are formed. Dummy cells 21 are formed at the points of the line 15, and dummy cells 21 are formed at the points of the scribe line 15 adjacent to the lower left and right support points c and d of the region 13. 21 are formed respectively, and the dummy cell 21 is formed at the point of the scribe line adjacent to the center point e.

Here, as shown in FIG. 3, the dummy cell 21 is an area 23 for confirming a focus state, an area 25 for confirming mismatch, and an area 27 for confirming the position of the dummy cell. Is formed.

Region 25 is formed with a pattern 26a of the previous step, with a cross-shaped blank area at the center, and a pattern 26b of the current step, located crosswise in the cross-shaped blank area, as shown in FIG. In the region 27, a predetermined mark indicating the position of the dummy cell is formed.

Then, the operator checks the patterns formed on the wafer through the SEM monitor in the inspection step of the photo process. If this is described in more detail as follows.

The area 23 of each dummy cell 21 is checked to determine whether the focus in one shot is uniform. At this time, when the defective focus state of the region 11 or region 13 is confirmed, a line fail phenomenon in which only the integrated circuit chips of the region 11 become defective by applying appropriate measures to the following process is performed. You can prevent it.

In addition, when the pattern size of the region 23 is the same as the pattern size of the regions 11 and 13 and is preferably formed with a minimum design rule, when a defect such as a bridge or notching occurs, It occurs earlier in the region 23 than in the regions 11 and 13. Therefore, since the failure of the integrated circuit chip can be detected at an early stage, it is not necessary to check whether the defects of many patterns in the regions 11 and 13 are actually performed when the process is actually performed. It is desirable to inspect the patterns of the regions 11 and 13 precisely.

The degree of registration made by the KLA device, which is the main matching device in the photo process, is measured again by SEM to confirm the degree of mismatch of the actual pattern of the center point and the edge support point in one shot. That is, the degree of mismatch can be measured from the area 25 of each dummy cell on the same wafer to monitor the match by KLA.

For example, the spacing between the left end of the pattern 26a of the previous step and the pattern 26b of the current step is A, and the spacing between the right end of the pattern 26a and the right end of the pattern 26b is B. In this case, the degree of X-axis mismatch is given by (AB) / 2. And if the spacing between the lower end of the pattern 26a and the lower end of the pattern 26b is C, and the spacing between the upper end of the pattern 26a and the upper end of the pattern 26b is D, the Y-axis mismatch The degree is given by (CD) / 2. The A, B, C, D may be changed depending on the film quality and process conditions. When the degree of mismatch of the X and Y axes is a positive value, it is a positive mismatch state, and when the degree of mismatch of the X and Y axes is a negative value, it is a negative mismatch state.

Then, the pattern of the area 27 (not shown), for example, letters, arrows, or other patterns can be confirmed by SEM to quickly find where the corresponding dummy cell is located in one shot.

That is, when the pattern is identified as UL (upper left), the dummy cell is located at the upper left edge of one shot adjacent to the edge support point a, and when the pattern is identified as UR (upper right), the edge If there is a corresponding dummy cell at the support point of the upper right side of one shot adjacent to the point (b), and if the pattern is found to be LL (lower left), it is located at the support point of the lower left of the one shot adjacent to the support point c. If there is a corresponding dummy cell and the pattern is identified as LR (lower right), the dummy cell is present at the lower left edge of one shot adjacent to the edge d, and if the pattern is identified as CC, This means that the dummy cell is located at the center point of one shot adjacent to the center point e.

On the other hand, the dummy cell 21 is not limited to five edge points but may be formed at more points, and also the edge points a, b, and c of the regions 11 and 13. It may be formed at (d) and the central point (e).

As described above, the dummy cell of the reticle for preventing the focus failure according to the present invention is formed at the center point of each shot and each of the supporting points, so as to detect the focus state in the one shot actually formed on the wafer by SEM and appropriately. An action can be taken to enable an optimal focus state that makes the focus within one shot uniform. In addition, it is possible to confirm the degree of mismatch of the actual pattern of the center point and the edge point within one shot by detecting the matched degree of the matched by the KLA device, which is the main matching device, again and again. do. Then, the dummy cell can be checked at which point of one shot.

Therefore, the present invention can improve the reliability of the photo process by maintaining a good focus state of the center point and each of the edge points within one shot and good matching of the previous step and the current step.

Claims (9)

In the reticle for stepper, The dummy cell of the reticle for preventing focus failure, characterized in that a plurality of dummy cells each having a pattern for detecting a focus state within one shot are formed in a predetermined region of the reticle. The dummy cell of the reticle of claim 1, wherein the dummy cells each have a pattern for detecting matching. The dummy cell of the reticle according to claim 1, wherein the dummy cells each have a pattern for checking its position. The dummy cell of the reticle according to claim 2, wherein the dummy cells each have a pattern for checking its position. The dummy cell of a reticle according to any one of claims 1 to 4, wherein the dummy cells are formed in an area for an integrated circuit chip in the one shot. The dummy cell of the reticle according to any one of claims 1 to 4, wherein the dummy cells are formed in a scrabble line in the one shot. 7. The dummy cell of the reticle of claim 6, wherein the dummy cells are formed at points of a scrabble line corresponding to edge and center points in the one shot. The dummy cell of the reticle according to claim 1, wherein the pattern of the dummy cell is formed to a minimum size of the design rule of the reticle. The dummy cell of the reticle according to claim 1, wherein the pattern of the dummy cell is smaller than a minimum size of the design rule of the reticle.