CN1208691C - Method of Transferring Graphics - Google Patents

Abstract

A method for transferring pattern is to transfer the pattern from the photo mask to the photoresist layer on the surface of the wafer by two-stage exposure. The first stage is to expose the photoresist layer in the area to be patterned with the first light source energy and the first mask to change the material property of the photoresist layer. The first mask includes a first pattern. In the second stage, a second photomask containing a second pattern is used, and a second light source energy is used for exposing the photoresist layer on the area to be patterned. The second photomask comprises a second pattern which is distributed irregularly or regularly. And finally, after development, if the used photoresist layer is a positive photoresist layer, removing the twice-exposed photoresist layer, and if the used photoresist layer is a negative photoresist layer, retaining the twice-exposed photoresist layer to form a required pattern. The first light source energy and the second light source energy are both less than the developing critical value of the photoresist layer, and the first light source energy plus the second light source energy must be greater than or equal to the developing critical value of the photoresist layer.

Description

Method of Transferring Graphics

technical field

The invention relates to a method for transferring patterns, in particular to a method for successfully transferring patterns from a photomask to a photoresist layer on a wafer surface by means of two-stage exposure.

Background technique

When the density of integrated circuits (ICs) continues to expand, the only way to keep the chip area the same, or even shrink, to continuously reduce the unit cost of the circuit, is to continuously reduce the circuit design specification (design). rule). When reducing the size, the biggest bottleneck encountered is the yellow light lithography technology. Unless yellow light lithography imaging can be gradually reduced, the development of integrated circuit technology will suffer the fate of stagnation.

Photolithography in the production of integrated circuits converts a large number of electronic components and circuits into a tiny chip layer by layer, each layer has a mask, relying on the principle of optical imaging, The light is imaged on the surface of the wafer through the mask and the lens. The surface of the wafer must have a substance like a photographic film, which belongs to a photosensitive colloidal compound (photoresist). The pattern of the photomask is transferred to the wafer one by one. Therefore, the photomask, photoresist, photoresist coating and developing equipment, and alignment and exposure optical system are all necessary conditions in the lithography imaging process. With the progress of the integrated circuit industry, the components that need to be accommodated in the chip continue to grow by multiples, resulting in the continuous shrinking of the line width, making the continuous search for new materials, the development of technology that breaks through the optical bottleneck, etc. challenge.

In addition, because the photoresist material of lithography imaging is a light-sensitive substance, if it is exposed to ordinary light, it will change, and the work of fixing the image cannot be done well. It must be done in a darkroom, just like the processing of photographic negatives. Lithographic imaging also needs to be limited to a special environment, generally under yellow light, so it is commonly called a yellow light room. Due to the complexity of integrated circuits and their widths below microns (μm; 10 ^-6 m), they must be manufactured in a dust-free clean room. In the process of lithography, the requirements for cleanliness are more stringent, because any dust particles , may cause component defects due to imaging, making the circuit blurred.

Modern sub-micron integrated circuit manufacturing technology has extremely strict requirements for line width control. From a more microscopic perspective or a more rigorous definition, the requirements for line width control should be extended to any graphics and graphics in the chip. The size requirements of any corner, that is, taking into account the "Fidelity" of the wafer pattern to the corresponding pattern of the mask. The "aerial image" before the resist layer is usually not as "perfect" as the pattern on the mask. This defect is generally called optical proximity effect (OPE). Graphics interact with each other due to light diffraction. In addition to distorting the graphics, it also makes the processing window smaller. If the graphics distortion is unavoidable, in order to ensure that the graphics on the chip meet the designer's needs, Then it may be considered to perform graphic correction on the mask graphic according to a certain rule, and use additional graphics to compensate or reduce the distortion of the graphic. This technology is called optical proximity correction (OPC).

Referring to FIG. 1 , this is a schematic diagram of the optical approximation effect. Although lithography technology has entered the deep sub-micron field, when faced with processing similar to the one-micron square pattern 10, it is inevitable that round corners will appear at the corners of the final photoresist pattern, which makes the micron square pattern 10 is easily distorted into a circle 15 due to the optical approximation effect after conventional exposure and development processing. The size of the micron square pattern 10 is about less than or equal to 1 micron square. This is due to the intersection of the diffracted light from the edge in the X direction and the edge in the Y direction. As the size becomes smaller, the exposure ratio between the corner and the edge increases relatively, and the rounded corner becomes more obvious. In order to solve this problem, the simplest solution is to "push out" the corner shading pattern (see Figure 2), that is, to extend the corners of the micron square shading pattern outward to reduce the overexposure of the corners, or it can be Simply imagine it with the concept of graphic "compensation", that is, the known result is rounded corners, so an additional protruding figure 20 (usually a smaller square) is placed in advance to compensate, so that the micron square figure 10 is in the After the traditional exposure and development processing, a square figure 25 is still formed. The placed compensation pattern is also called "serif". The size and position of it depends on the processing parameters.

Of course, the pattern of the integrated circuit mask is not so simple in reality. Generally, the optical characteristics of two types of patterns including repetitive patterns (memory products) and arbitrary patterns (peripheral circuit or logic products) are different. However, when correcting the optical approximation effect, two things should be considered: ( 1) The distance between two adjacent different graphics (points); (2) The local area density of the graphics. Especially when considering the regional density of the pattern, the influence on both lithographic imaging and plasma etching should be considered at the same time. Therefore, using the optical approximation effect correction method will make the lithography process more complicated and reduce the efficiency of the process operation. However, when using the optical approximation effect correction method, it is necessary to add graphics extending from the corners on the mask, which easily increases the production cost. Using the optical approximation effect correction method must go through quite complicated considerations and steps. Although this improvement method has corrected the optical approximation effect, it still cannot accurately display the graphics to be formed. Therefore, the dimensional accuracy after graphics conversion cannot meet the requirements of semiconductor manufacturing. The demand for line width is shrinking day by day.

Contents of the invention

An object of the present invention is to provide a method for successfully transferring patterns from a photomask to a photoresist layer on a wafer surface by means of two-stage exposure, so as to improve the accuracy of the pattern size during pattern transfer and simplify the steps required for production. , Accelerate the efficiency of processing operations and reduce the production costs of production operations.

In order to achieve the above object, the method for transferring patterns according to one aspect of the present invention is characterized in that it includes the following steps: providing a wafer, which includes a photoresist layer; using a first light source energy and a first photomask irradiation portion The photoresist layer, wherein the first photomask includes a first light-transmitting region and the energy of the first light source is less than a development threshold of the photoresist layer; and a second light source energy and a second photomask are used Part of the photoresist layer is irradiated, wherein the second mask includes a second light-transmitting region, part of the second light-transmitting region and part of the first light-transmitting region overlap each other, and the energy of the second light source is less than The developing critical value of the photoresist layer, and the numerical value of the first light source energy plus the second light source energy reaches above the developing critical value of the photoresist layer.

According to another aspect of the method of pattern transfer of the present invention, it is characterized in that the method includes: providing a wafer, the wafer includes a photoresist layer; installing the wafer on an exposure machine, wherein the exposure machine includes a light source; installing a first A photomask is placed on the exposure machine, wherein the first photomask includes a first light-transmitting area and a first pattern, and a range of the first pattern is larger than a required area to be formed on the photoresist layer. A range of graphics; use a first light source energy to irradiate part of the photoresist layer to perform a first-stage exposure process; remove the first photomask; install a second photomask on the exposure machine, wherein the first photomask The second photomask includes a second light-transmitting area and a second pattern, the second pattern is selected from one of regular distribution and irregular distribution patterns, and the range of the second pattern is larger than that to be formed on the photoresist layer In the range of the required pattern, part of the second light transmission area and part of the first light transmission area overlap each other; a second light source is used to irradiate part of the photoresist layer, wherein the second light source The value of energy plus the energy of the first light source reaches above the development threshold of the photoresist layer; and removing part of the photoresist layer to form the desired pattern on the wafer with part of the photoresist layer.

The invention can improve the accuracy of graphic size during graphic transfer, simplify the steps required for production, accelerate the efficiency of processing operation, and reduce the production cost of processing operation.

Description of drawings

Fig. 1 is the schematic diagram of optical approximation effect;

Fig. 2 is the schematic diagram of optical approximation effect correction method;

3 is a top view of a semiconductor element;

4 is a schematic diagram of an irregular pattern to be formed on the photoresist layer;

5 is a schematic diagram of a first photomask;

6 is a schematic diagram of a second photomask;

Fig. 7 is a schematic diagram of overlapping the first photomask and the second photomask; and

FIG. 8 is a schematic diagram of forming a photoresist layer on a wafer by using the exposure method of the present invention.

Detailed ways

Some embodiments of the invention are described in detail below. However, the present invention can be widely implemented in other embodiments besides the detailed description, and the scope of the present invention is not limited by it, but by the patent scope defined by the claims.

Referring to FIG. 3 , this is a top view of a semiconductor device. The semiconductor device includes several word lines (word lines) 100 and several bit lines (bit lines) 110 . In order to make the semiconductor device generate "0" and "1" signals, some areas 120 of several word lines 100 are usually removed by lithography and etching, so that the word lines are disconnected to achieve the semiconductor device. Component functional requirements. If the positions to be removed on the several word lines 100 cannot be accurately located during the lithography process, then in the subsequent etching process, the desired removal may not be completely removed on the word lines to be removed. part, or etched to the bit line, which affects the performance and quality of the semiconductor device.

For general lithography, if the distance between the light-transmitting area and the opaque area on the mask is equal, and the regional density of the light-transmitting area or the opaque area on the mask is relatively consistent, then the exposure After that, the accuracy of transferring the pattern from the mask to the photoresist layer is high. However, as the volume of semiconductor elements becomes smaller and smaller, the processing width becomes smaller and smaller, and the functions of semiconductor elements themselves become more and more, so the circuits in the semiconductor elements become more and more complicated, and on the photomask The pattern of the photomask also becomes complicated, which leads to a very large regional density difference between the light-transmitting area and the opaque area on the mask.

The method of the invention can be used to smoothly transfer the pattern on the photomask to the photoresist layer, so as to avoid the occurrence of optical approximation effect. Therefore, the pattern on the mask can be a regularly distributed pattern or an irregularly distributed pattern. The following description is only an embodiment of the present invention, which is for pattern transfer of irregularly distributed patterns, but does not limit the scope of the present invention. Referring to FIG. 4 , this is the pattern distribution situation on a mask. The photomask 200 is used to form a photoresist layer on partial areas of several bit lines and several word lines, so as to remove partial areas of several bit lines in the subsequent etching process, so that semiconductor elements can be produced. "0" and "1" signals. Therefore, the mask 200 includes several light-transmitting regions 210 and opaque regions. If these light-transmitting regions 210 correspond to the wafer, they represent the regions to be removed on several bit lines. Since the functions of the semiconductor elements tend to be more complicated, the light-transmitting regions 210 on the mask 200 are relatively more complicated, and become an irregular distribution pattern.

For the irregular distribution patterns with large regional density differences, it is very difficult to successfully transfer the pattern on the photomask to the photoresist layer by using the traditional one-time exposure method. If the parameters of the exposure instrument are adjusted for the area with low regional density, the pattern with low regional density on the mask will be successfully transferred to the photoresist layer after exposure and development. However, for the pattern with higher regional density on the mask, during the exposure process, due to the defect of optical approximation effect or overexposure, after the development process, all the patterns will be tangled together. Unable to successfully transfer the desired pattern from the mask to the photoresist layer. If the parameters of the exposure instrument are adjusted for the areas with relatively high regional density, the patterns with relatively high regional density on the mask will be successfully transferred to the photoresist layer after exposure and development. However, for the pattern with low regional density on the photomask, during the exposure process, the pattern with low regional density will not be able to be smoothly formed on the photoresist layer after the development process due to insufficient exposure. , so that all the graphics on the mask cannot be successfully transferred to the photoresist layer. If you want to divide the area with high area density and the area with low area density into two steps of exposure, the first problem you will encounter is how to limit the size of the area density, and the second is that the positioning accuracy of these two masks is very demanding. High, it is easy to cause the failure of lithography processing due to the problem of mask positioning. Therefore, an optical approximation effect correction method must be used to completely transfer the pattern on the mask to the photoresist layer. However, the optical approximation effect correction method tends to complicate the processing and tend to reduce the efficiency of the processing operation and increase the cost of the processing operation. Therefore, the method of the present invention must be adopted to successfully and accurately transfer the pattern on the photomask to the photoresist layer by means of two-stage exposure.

If the lithography process intends to transfer an irregularly distributed pattern (as shown in Figure 4) from the mask to the photoresist layer, in order to remove part of the digital word line in the subsequent etching process, the semiconductor element will produce "0" and When the signal is "1", a chip must first be provided, which at least includes word lines and bit lines, and both word lines and bit lines contain a photoresist layer. The photoresist layer is different for processing requirements. However, a positive photoresist layer is used in this process. Next, the wafer is fixed on the exposure machine, and the first photomask 300 (shown in FIG. 5 ) is installed on the exposure machine. After positioning and calibration procedures, the photoresist layer on the wafer is subjected to the first photoresist layer using the energy of the first light source. One-stage exposure processing. The first mask at least includes a first light-transmitting area 310 and a first light-impermeable area. The first light-transmitting region 310 on the first mask is the region of the word line on the semiconductor device. The energy of the first light source is less than the critical value for developing the photoresist layer. Generally, the range of the first light-transmitting region 310 is larger than the range of the pattern to be formed on the photoresist layer.

Next, the first photomask 300 is taken off from the exposure machine, and the second photomask 400 (shown in FIG. 6 ) is installed on the exposure machine. The photoresist layer undergoes the second stage of exposure processing. The second mask includes a second transparent area 410 and a second opaque area. The second light-transmitting area 410 on the second photomask is an irregular distribution pattern to be formed on the photoresist layer. Generally, the range of the second light-transmitting region 410 is larger than the range of the pattern to be formed on the photoresist layer. However, in order to cooperate with the operation of the processing and improve the operation efficiency of the processing, the irregular distribution pattern contained in the second mask is usually similar to the irregular distribution pattern to be formed on the photoresist layer, and the patterns of the two do not necessarily have to be completely same. The energy of the second light source is less than the critical value for developing the photoresist layer. The energy of the first light source plus the energy of the second light source must be greater than or equal to the critical value for developing the photoresist layer. In the present invention, the types of light sources used for the energy of the first light source and the energy of the second light source are not limited, and the types of light sources used are usually determined by the requirements of processing, such as: dipole ray, deep ultraviolet (deep ultra ray) -violet ray), or off-axis light, etc. Usually, the energy of the first light source is greater than the energy of the second light source, so as to obtain a better pattern transfer result. However, depending on the processing requirements, sometimes the energy of the first light source will be smaller than the energy of the second light source to meet the processing requirements.

Finally, the wafer is removed from the exposure machine, and the unnecessary photoresist layer is removed by using a developer, and the required pattern is left on the wafer surface for subsequent processing steps. The photoresist layer is a chemical film whose characteristic is that it will produce chemical changes after exposure. If the photoresist layer is a positive photoresist layer, the exposed part of the positive photoresist layer will be removed by the developer during the subsequent developing process to leave a part of the unexposed positive photoresist layer. If the photoresist layer is a negative photoresist layer, the unexposed part of the negative photoresist layer will be removed by the developer during the subsequent developing process to leave a part of the exposed positive photoresist layer. During the exposure process of the photoresist layer, the light energy used must reach a value above a certain value, and then the photoresist layer will display the desired pattern on the photomask after the exposure and development process. When the light energy used in the exposure process is lower than a certain value, even though the photoresist layer has undergone the exposure process, after development, the photoresist layer still cannot show the desired pattern on the photomask. This value is generally referred to as the critical value for photoresist development. The photoresist layers of different materials have different development thresholds.

After using the first photomask 300 and the energy of the first light source to perform the first-stage exposure process on the photoresist layer on the word line, although the energy of the first light source used is lower than the development threshold of the photoresist layer, resulting in characters The photoresist layer on the line still cannot be developed and the pattern of the first mask is successfully transferred. However, the chemical properties of the exposed photoresist layer on the word line have been changed by the energy of the first light source. After using the second photomask 400 and the energy of the second light source to expose the photoresist layer on the part of the word line in the second stage, part of the area only affected by the energy of the second light source, because the energy of the second light source is less than that of the photoresist layer developed Therefore, it is still impossible to develop and successfully transfer the pattern of the second mask. Because the energy of the light source has an accumulative effect in the photoresist layer, when the energy of the first light source plus the energy of the second light source is greater than or equal to the critical value of the development of the photoresist layer, the part of the photoresist layer on the word line will be affected by the second light source at the same time. Affected by the energy of a light source and the energy of a second light source, there is sufficient kinetic energy to undergo a chemical change. Because the photoresist layer used in this embodiment is a positive photoresist layer, after the subsequent development process, part of the photoresist layer irradiated by the energy of the first light source and the energy of the second light source will be removed by the developer. Smoothly transfer the pattern from the second mask to the photoresist layer. Next, etching can be performed to remove part of the word line, so that the semiconductor device can generate "0" and "1" signals after completion.

Referring to FIG. 7 , it is a schematic diagram of overlapping the first mask and the second mask at the same reference point. The overlapping portion 700 of the first light transmission area 310 of the first mask and the second light transmission area 410 of the second mask is the area on the photoresist layer that simultaneously receives the energy of the first light source and the energy of the second light source . Referring to FIG. 8 , this is a schematic diagram of forming a photoresist layer on a wafer by using the exposure method of the present invention. The chip includes word lines 800 and bit lines 810 . In order to achieve the purpose of the present invention to remove some parts of the digital word line 800, a positive photoresist is used in this embodiment. After developing, the area 820 of the photoresist layer receiving the energy of the first light source and the energy of the second light source can be accurately removed, and the subsequent etching step can be smoothly performed.

In another embodiment, if desired ions are to be implanted in certain parts of the digital word lines and the digital bit lines, a negative photoresist layer can be used as the material of the photoresist layer. When the exposure method of the present invention is used to expose and develop the photoresist layer in two stages, the area of the photoresist layer that receives the energy of the first light source and the energy of the second light source at the same time can be accurately left, and the area to be implanted The photoresist layer on the region of the ions can be removed precisely so that the subsequent ion implantation process can be carried out smoothly.

According to the above-mentioned embodiments, the present invention provides a method for successfully transferring patterns from a photomask to a photoresist layer on a wafer surface by means of two-stage exposure. The first stage is to expose the photoresist layer on the area to be patterned with a first light source energy and a first photomask to change the material properties of the photoresist layer. The first mask contains the first pattern. The second stage is to use a second photomask containing the second pattern, and use a second light source energy to expose the photoresist layer on the area where the pattern is to be formed. The second mask includes a second pattern with irregular distribution or a regular distribution. After the final development step, if the photoresist used is a positive photoresist, the photoresist after two exposure steps will be removed, and if the photoresist used is a negative photoresist, it will be removed after two exposures. The photoresist layer in the exposure step will remain to form the required pattern, which is convenient for subsequent etching or doping processing. Both the energy of the first light source and the energy of the second light source are less than the development threshold of the photoresist layer, and the energy of the first light source plus the energy of the second light source must be greater than or equal to the development threshold of the photoresist layer. The invention can improve the accuracy of the figure size when the figure is transferred and simplify the steps required for the manufacturing process. The present invention can also speed up the efficiency of processing operations, and can also reduce the production costs of processing operations.

The above description is only a preferred embodiment of the present invention, and this embodiment is only used for illustration and not for limiting the patent scope of the present invention. Changes can still be made and implemented within the scope of not departing from the essence of the present invention, and these changes should still belong to the scope of the present invention. Accordingly, the scope of the present invention is defined by the claims.

Claims (10)

1. A method for transferring graphics, characterized in that, comprising the following steps: providing a wafer comprising a photoresist layer; Using a first light source energy and a first photomask to irradiate part of the photoresist layer, wherein the first photomask includes a first light-transmitting region and the first light source energy is less than a development threshold of the photoresist layer value; and Use a second light source energy and a second photomask to irradiate part of the photoresist layer, wherein the second photomask includes a second light-transmitting region, part of the second light-transmitting region and part of the first light-transmitting region The transparent regions overlap each other, the energy of the second light source is less than the development threshold of the photoresist layer, and the value of the energy of the first light source plus the energy of the second light source is above the development threshold of the photoresist layer. 2. The method for transferring graphics as claimed in claim 1, wherein the energy of the first light source is greater than the energy of the second light source. 3. The method for transferring graphics as claimed in claim 1, wherein the energy of the second light source is greater than the energy of the first light source. 4. The method for transfer figure as claimed in claim 1, is characterized in that, comprises the following steps: mounting the wafer on an exposure machine, wherein the exposure machine includes a light source; and Part of the photoresist layer is removed to form a desired pattern on the wafer using part of the photoresist layer. 5. The method for transferring patterns as claimed in claim 4, wherein said first mask comprises a first pattern. 6. The method for transferring graphics as claimed in claim 5, wherein the range of the first graphics is larger than the required graphics. 7. The method for transferring patterns as claimed in claim 4, wherein said second mask comprises a second pattern. 8. The method for transferring graphics as claimed in claim 7, wherein said second graphics are regularly distributed graphics. 9. The method for transferring graphics as claimed in claim 7, wherein said second graphics are irregularly distributed graphics. 10. A method for transferring graphics, characterized in that the method comprises: providing a wafer comprising a photoresist layer; mounting the wafer on an exposure machine, wherein the exposure machine includes a light source; Install a first photomask on the exposure machine, wherein the first photomask includes a first light-transmitting area and a first pattern, and a range of the first pattern is larger than a desired pattern formed on the photoresist layer a range of desired graphics; irradiating a portion of the photoresist layer with energy from a first light source to perform a first-stage exposure process; removing the first mask; Install a second photomask on the exposure machine, wherein said second photomask includes a second light-transmitting area and a second pattern, the second pattern is selected from one of the patterns of regular distribution and irregular distribution and the said second photomask The range of the second pattern is larger than the range of the desired pattern to be formed on the photoresist layer, and part of the second light-transmitting region overlaps with part of the first light-transmitting region; Irradiating a portion of the photoresist layer with energy from a second light source, wherein the value of the energy from the second light source plus the energy from the first light source reaches above the development threshold of the photoresist layer; and removing part of the photoresist layer to form the desired pattern on the wafer with part of the photoresist layer.

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