KR100742969B1 - A fabrication method for a photo mask - Google Patents

Abstract

A photomask manufacturing method is provided to effectively correct a pattern distortion phenomenon by using an effect of OPC for repeated patterns of a cell transistor. A design pattern is recognized, and then the design pattern is oversized(S110). Light intensity is measured by using the oversized design pattern to detect a vulnerable point of a reference level or below(S120). The oversized design pattern is returned to an original design pattern by under sizing the pattern(S130). The design pattern is corrected by an effect of OPC(Optical Proximity Correction)(S140), and then a mask pattern is formed in the design pattern corrected by the OPC(S150).

Description

Photomask manufacturing method {a fabrication method for a photo mask}

1 is a plan view showing a memory cell, that is, an SRAM cell portion of a conventional semiconductor mask;

FIG. 2 is a diagram of overlapping three optical image contours simultaneously confirming a resolution limit on a mask drawing for a first and second unit cells by applying an OPC simulation program for quantitative analysis of a conventional pattern connection failure. FIG.

3 is a view illustrating a contour image according to light intensity obtained by simulating cell patterns of FIG. 2 in areas A, d, and B; FIG.

Figure 4 is a flow chart showing a photomask manufacturing process according to the present invention.

FIG. 5A illustrates a first unit cell and a second unit cell of an SRAM cell in a photomask fabrication process according to the present invention. FIG.

5B is a diagram illustrating oversizing the first unit cell and the second unit cell.

5C is a contour image according to light intensities of the first and second unit cells oversized in FIG. 5B.

FIG. 5D shows that the pattern bridge generation region is detected through the contour image of FIG. 5C. FIG.

<Description of Signs of Major Parts of Drawings>

211: first unit cell 213: second unit cell

211a: first oversizing unit cell 213a: second oversizing unit cell

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor photomask, and more particularly, a photo mask capable of effectively compensating for a pattern distortion phenomenon due to an optical proximity effect on a repetitive pattern of a semiconductor cell transistor and making accurate line width manufacturing. It relates to a manufacturing method.

The patterning technique of the photomask has a close influence on the accuracy of the actual pattern formed on the semiconductor substrate. In particular, when the degree of integration of the semiconductor pattern is very high, there is insufficient space for inserting an optical proximity correction (OPC) pattern, and a line width bridge between patterns occurs unlike the lithography original exposure intention, It is bad.

Semiconductor photolithography technology can precisely control the amount of light emitted from the photomask by elaborating the design of the photomask. In order to elaborate the design of the photomask, an optical proximity compensation (OPC) technique or a phase shifting mask technique has been introduced, and various methods for minimizing light distortion caused by the shape of the pattern drawn on the mask have been introduced. Sought. In particular, the development of a chemically amplified resist having excellent photosensitivity to light having an ultraviolet light (wavelength of 248 nm or 194 nm) has introduced practical technologies that can further increase the resolution. Auxiliary pattern formation technique (also known as a dummy pattern) that controls the proximity effect also contributes to the improvement of the resolution.

In general, the photomask is formed of light blocking patterns by a light blocking material such as chromium (Cr) on the light transmissive substrate.

In the photomask, a memory cell region and a logic device region form one chip. The memory cell has a regular pattern and a relatively short length. Its shape is irregular and its length is relatively long.

1 is a plan view showing a memory cell, that is, an SRAM cell portion of a conventional semiconductor mask.

As shown in FIG. 1, the SRAM cells have regular patterns of cell patterns 111 and 113, and upper and lower portions of each cell pattern 111 and 113 are formed of NMOS cells and PMOS cells having a minimum line width of 0.18 μm. .

In this case, the adjacent unit SRAM cells are referred to as a first unit cell 111 and a second unit cell 113.

The closest distance between the first unit cell 111 and the second unit cell 113 is d, and the closer the distance between the first and second unit cells 111 and 113 is, the poorer the pattern due to the optical proximity effect is. Easy to occur

FIG. 2 simultaneously shows three optical image contours 120a, 120b, and 120c for applying a OPC simulation program for quantitative analysis of pattern linkage defects to identify resolution limits on mask plots for first and second unit cells. This is an overlapping drawing.

3 is a diagram illustrating a contour 120 image according to light intensity obtained by simulating the cell patterns of FIG. 2 in areas A, d, and B. Referring to FIG.

In FIG. 3, the X axis represents a distance (nm) and the Y axis represents a normalized light intensity.

In this case, when the reference light intensity level is about 0.4 and the light intensity peak value of the contour image 120 is insufficient energy or the depth of focus becomes worse than the reference light intensity, the first unit cell 111 and the second unit cell 113 ) Bridge phenomenon (T) that is attached to each other is generated.

In particular, the density and the step of the SRAM cell are relatively higher than that of the logic device, so that the line width bias of the SRAM cell is relatively increased, which causes the relative decrease of the cell line width of the SRAM cell. .

The present invention provides a method of manufacturing a photomask that predicts the occurrence of pattern bridges between adjacent patterns in advance to increase design accuracy when changing a design, prevents pattern bridges of unit cells, and maintains cell line width uniformly. The purpose.

In order to achieve the above object, a photomask manufacturing method according to the present invention includes the steps of recognizing a design pattern; Oversizing the design pattern; Detecting a weak point below a reference level by measuring light intensity with the oversized design pattern; Undersizing the oversized design pattern to return to the original design pattern; OPC compensating the design pattern; And forming a mask pattern with the OPC-compensated design pattern.

The design pattern is characterized in that the SRAM cell pattern.

The oversizing range of the design pattern is selected from 10% to 40% of the original design pattern and is enlarged.

The separation range between the design patterns is selected and secured from 20% to 60% of the separation distance between the original design pattern.

The method may further include changing a design to remove a weak point from the design pattern.

Hereinafter, a method of manufacturing a photomask according to the present invention will be described in detail with reference to the accompanying drawings.

4 is a flowchart showing a photomask fabrication process according to the present invention.

FIG. 5A illustrates a first unit cell and a second unit cell of an SRAM cell in a photomask fabrication process according to the present invention, and FIG. 5B illustrates an oversizing of the first unit cell and the second unit cell. 5C is a contour image according to light intensities of the first unit cell and the second unit cell oversized in FIG. 5B, and FIG. 5D is a view showing that the pattern bridge generation region is detected through the contour image of FIG. 5C. .

First, a design DB is input to recognize first and second unit cells 211 and 213 patterns, and the first and second unit cells 211 and 213 are oversized to form virtual first and second oversizing unit cells ( Steps 211a and 211b are performed (S100 and S110).

When the closest distances of the first and second unit cells 211 and 213 are d, the closest distances of the first and second oversizing unit cells 211a and 211b are dm when the first and second unit cells are oversized. Dm is smaller than d.

For example, about 20% of the sizes of the first and second unit cells 211 and 213 may be oversized, and the oversizing ratio may be variously performed depending on the size of the pattern and whether or not a pattern bridge occurs. .

The oversizing range of the first and second unit cells 211 and 213 may be extended to 10% to 40% of the original design pattern.

As such, in order to predict a weak point where the pattern bridge may occur in the first and second unit cells 211 and 213, it is necessary to perform a sizing operation to increase the cell line width of the SRAM cell before OPC compensation.

Subsequently, as shown in FIGS. 5C and 5D, the optical image contour for checking the resolution limits on the A, d, and B area mask drawings for the oversized first and second oversizing unit cells 211a and 213a is shown. contours 400 are shown graphically.

In this graph, the X axis represents distance (nm) and the Y axis represents normalized light intensity.

In this case, the first unit cell 211 including the region A is a light blocking region, and the second unit cell 213 including the region B is also a light blocking region, and the first unit cell 211 and the first unit cell 211 are formed. The distance d between the two unit cells 213 is a portion through which light is transmitted.

However, when the reference light intensity level for forming the first and second unit cells 211 and 213 having a good pattern is about 0.4, the light intensity peak value of the contour image is insufficient energy or the depth of focus is higher than the reference light intensity. When the peak value of the light intensity level is reduced to about 0.35, a bridge phenomenon occurs in which the first unit cell 211 and the second unit cell 213 adhere to each other during pattern formation.

Therefore, when the optical contour image is measured below the reference level by performing an optical image contour with the oversized first and second oversizing unit cells 211a and 213a, it may be recognized as a potential weak point (S120). ).

In particular, the density and step height of SRAM cells are relatively higher than that of logic devices, and the line width bias of SRAM cells is relatively increased, resulting in a relative decrease in cell line width of SRAM cells. It is easy to generate a pattern bridge when forming a pattern by making a mask afterwards, but it is possible to design change or modify this part later by detecting a weak point by using an oversized cell pattern. It is possible to detect a defective position quickly.

After detecting the weak point of failure generation (X) in the first and second unit cells, a pattern undersizing step is performed to return the first and second unit cell patterns to their original state (S130).

After the pattern undersizing, OPC compensation is performed to fabricate a mask (S140 and S150).

Here, the step of modifying the design may be further performed to correct the weak point (X).

As described above, a design error can be easily detected by detecting a defect-prone point X such as a pattern bridge / pinch through pattern oversizing, and a light intensity amplification effect can be obtained.

As mentioned above, the present invention has been described in detail through specific examples, which are intended to describe the present invention in detail, and the method for manufacturing a mask according to the present invention is not limited thereto, and it is common in the art within the technical spirit of the present invention. It is obvious that modifications and improvements are possible by the knowledgeable.

According to the mask manufacturing method of the present invention as described above, by detecting the weak point of defect occurrence between the adjacent patterns through the oversizing of the pattern, it is easy to find the design error to increase the accuracy when modifying the design, pattern bridge or pinch Even when such a defect occurs, there is an effect that can easily find the location of the failure.

Claims (5)

Recognizing a design pattern; Oversizing the design pattern; Detecting a weak point below a reference level by measuring light intensity with the oversized design pattern; Undersizing the oversized design pattern to return to the original design pattern; OPC compensating the design pattern; And forming a mask pattern with the OPC-compensated design pattern. The method of claim 1, And the design pattern is an SRAM cell pattern. The method of claim 1, The oversizing range of the design pattern is selected from 10% to 40% of the original design pattern to enlarge the photomask manufacturing method. The method of claim 1, The separation range between the design pattern is selected from 20% to 60% of the separation distance between the circular design pattern is secured to be secured. The method of claim 1, And changing the design so that the weak point is removed from the design pattern.

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