JP2001223155A - Photolithography method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photolithography process in which a contact aperture is set small. SOLUTION: In this photolithography method, two line patterns of different line/interval mask are crossed with each other. Consequently, since a contact aperture pattern is formed, an outline of the desired contact aperture is formed on a negative resist. Since the pitch between line and interval mask can be controlled accurately, the limit size of contact aperture (CD) becomes small. Accordingly, difficulty to raise the integration density of device can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photolithography process for manufacturing a semiconductor device.
In particular, the present invention relates to a photolithography process for reducing the size of a contact window.

[0002]

2. Description of the Related Art Semiconductor processes include diffusion, etching,
It is divided into four basic processes including thin film formation and photolithography. In the photolithography process, the pattern is transferred from the mask to the wafer,
This includes preparing an etched pattern that has been prepared or providing an excellent implantation pattern in a thin film process. Therefore, the quality of photolithography controls the quality of the entire semiconductor process.

In a photolithography process, an exposure apparatus defines parameters such as resolution (R) and wavelength (λ), and the relationship can be expressed as described above. R = K ₁ λ / NA where K ₁ is a constant related to the photoresist material and processing conditions, and NA is a value indicating the numerical aperture of the projection lens system. It is understood from the above equations that better resolution of the exposure apparatus is possible when using short wavelength light sources. In addition, good resolution of the exposure apparatus becomes possible when the NA of the exposure apparatus is larger. In order to transfer the pattern onto the photoresist layer completely accurately, the pattern projected by the exposure device must have a certain depth of focus (DO
F) must be included. That is, it is necessary to maintain a uniform focus throughout the photoresist, regardless of the surface edge or wafer edge adjacent to the photolens layer. Generally, the DOF of an exposure apparatus can be represented by the following equation. DOF = K ₂ λ / (NA) ²

In order to increase the DOF of the exposure apparatus, a longer wavelength light and a smaller NA are required for the projection lens system.
And the result would be against resolution requirements.

As the degree of integration and mask pattern density of integrated circuits (ICs) increase, the pitch of word lines, bit lines, doped regions or capacitors becomes smaller. Therefore, it is necessary to transfer a more precise pattern by improving the resolution of the exposure apparatus. However, when the resolution of the exposure apparatus is improved, DOF is usually lost. On the other hand, if the DOF is improved and an excellent pattern transfer effect is obtained, the resolution will be reduced.

As semiconductor processes enter deep sub-micron size technology, photolithographic processes become more difficult in controlling DOF and resolution, which also reduces the life of equipment for photolithographic processes. Various attempts to solve the above-mentioned problems have been proposed, but require many special photolithography processes and averaging processes, and increase manufacturing costs.

In semiconductor technology, increasing the degree of integration is a goal that many people are trying to achieve, and many top-level engineers are involved in the development of processes that involve reducing line widths. ing. Photolithography is one important step in the process technology developed to achieve smaller critical dimensions (CD) and higher integration. On the other hand, the choice of projection light source and depth of focus (DOF) limits the resolution of photolithography.

[0008] Exposure resolution and DOF are two important indicators of the quality of a photolithographic process. Because it requires a higher resolution to increase the semiconductor integration, there solution includes the use of a light source such as K _r F lasers emitting ultraviolet light acts as a projection light source. The resolution is improved by using a K _r F laser, but on the other hand the DOF is more limited and the process window is narrower. Therefore, in order to obtain good resolution, a photolithography technique using a phase shift mask (PSM) is used.

[0009]

The basic theory of PSM involves adding a phase shifter layer on a regular mask,
The phase shifter layer interferes during the exposure to improve the resolution of the pattern image projected on the wafer. The advantage of using PSM is that exposure resolution can be improved by modifying the mask without using another new light source. Generally, there are two types of PSMs, including a strong PSM and a weak PSM.

In the manufacture of a strong PSM, particles are poured into a portion of the quartz substrate at the opening during etching, and these particles form a pump on the quartz plate. When light passes through the quartz substrate in the opening, problems such as phase defects occur. Several etching steps are required to improve the phase defect by reducing the size of the particles. As a result, the number of photolithography steps increases, the manufacturing cost increases, and the number of cycles increases.

Further, since the surface of the quartz substrate at the opening formed by etching is not flat, light scattering occurs, and after passing through the opening, the light intensity is not uniform. When using strong PSM in the photolithography process,
The non-uniform light intensity results in an asymmetric photoresist pattern, which makes the size accuracy of the semiconductor device more inaccurate. In addition, there are design, manufacturing and maintenance issues associated with using a strong PSM.

On the other hand, when transferring a pattern using a weak PSM, a side lobe effect occurs when the opening patterns are extremely close to each other. This side lobe effect is caused by the interference of the first-order diffracted light in the nearby form, and the light intensity above the photoresist corresponding to the edge of the opening is further increased. Will be done. As a result, the corresponding portions of the photoresist are dissolved. The thickness of the photoresist becomes thin. Therefore, the capability of preventing the etching is reduced, and problems such as mis-etching and a decrease in the conductivity of the interconnect portion occur in subsequent processes.

In order to reduce the side lobe effect, it is necessary to reduce the exposure, but there is a possibility that the exposure is insufficient. On the other hand, when the exposure amount is considerable, a side lobe effect occurs around the opening. Therefore, it is difficult to solve two problems in this process at the same time.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a photolithography process for reducing the size of a contact opening. Line patterns having different lengths and widths are exposed using two different line / spacing masks and cross each other to form a pattern of contact openings. The pattern is projected onto the substrate by exposure, and the critical dimension (CD) of the contact opening is reduced without using complex masks and special exposure techniques.

Patterning a contact opening in a conventional manner using a single mask is more than forming a contact opening using a line / space mask under the same K ₁ value, ie, the same resolution. Because of the difficulty, a better photolithography process for forming the contact openings is realized. This process is
The method includes a step of preparing a wafer on which a negative resist is formed, and a step of projecting a first pattern image of a first line / space mask on the negative resist. The same exposure process is repeated to project a second pattern image of the second line / interval mask on the negative resist, and the first pattern image and the second pattern image intersect with each other to form a negative pattern on the negative resist. A contact opening pattern is formed. Then, after the wafer is developed, the contour of the contact opening is formed in the negative resist.

As described in detail herein, the present invention provides a method for reducing the size of a contact opening in which pattern images having different lengths and widths intersect each other to form a pattern of contact openings. An object of the present invention is to realize a photolithography method for reducing the size. The pattern is transferred to a predetermined substrate using a predetermined light source. The process includes forming a first pattern using a first mask in a parallel line configuration and forming a second pattern using a second mask in a parallel line configuration. . Intersecting images of the first and second patterns are:
The substrate on which the negative type photoresist is coated is repeatedly exposed. Next, the substrate is developed to form the desired contact opening contours in the negative resist.

According to a first aspect of the present invention, there is provided a photolithography method in which line patterns formed by two line / interval masks cross each other to obtain a desired pattern of contact openings. This method can replace the conventional photolithography process of forming a pattern of wafer contact openings coated with a positive resist, increasing the process window and reducing the size of the contact openings.

In another aspect of the invention, the line patterns of two different line / interval masks cross each other after repeated exposure. As a result, a pattern of the contact opening is formed, so that a desired contour of the contact opening is formed on the negative resist layer. Since the pitch between line / spacing masks can be precisely controlled, the critical dimension (CD) of the contact openings is reduced. Therefore,
According to the present invention, a photolithography method for reducing the size of a contact opening can eliminate processing difficulties and limitations when the degree of device integration increases.

[0019]

DETAILED DESCRIPTION OF THE INVENTION The present invention can be applied to a mask used for exposing a negative resist,
A part of the negative resist remaining after the development corresponds to a transparent region on the mask.

FIG. 1 shows a contact opening pattern, and FIGS. 2A and 2B show a first line / space mask and a second line / space mask, respectively, for forming the contact opening pattern of FIG.

A mask is a tool for transferring a circuit pattern in a photolithography process, and plays an important role in an integrated circuit (IC) process. The mask body is made of a planarized transparent material, and the pattern for the semiconductor device at each level is formed by coating a transparent substrate with a mask layer.

Referring to FIGS. 1, 2A and 2B, a typical mask is formed of a transparent substrate 200 made of glass or quartz, and a mask layer 202 for forming a pattern is formed on the transparent substrate 200. Since the mask layer 202 is made of a material such as chromium (Cr) and has a thickness of about several hundred degrees, the portion of the transparent substrate covered with the mask layer 202 does not transmit any light. Mask layer 20
The method of forming 2 (opaque region) includes covering the transparent substrate 200 with a metal layer, and subsequently patterning the metal layer to expose a part of the transparent substrate 200 (transparent region). As a result, the first line / space mask 203 shown in FIG. 2A is formed, and the mask layer 202 (opaque region) and the exposed region (transparent region) of the transparent substrate 200 are parallel to the first line / space mask 203. Line shape is formed.

Next, a mask layer 2 for forming another pattern
04 is formed on another transparent substrate 200 made of glass or quartz. The mask layer 204 is made of a material such as chromium (Cr) and has a thickness of about several hundred degrees.
The portion of the transparent substrate 200 covered by the mask layer 204 does not transmit any light. A method of forming the mask layer 204 (opaque region) is to cover the transparent substrate 200 with a metal layer, and then pattern the metal layer to form the transparent substrate 200.
Exposing a portion of the surface (transparent region). As a result, a second line / spacing mask 205 shown in FIG. 2B is formed, and the mask layer 202 includes the (opaque region) and the transparent substrate 2.
The exposed areas (transparent areas) of 00 form a parallel line form of the first line / interval mask 205.

Next, the first line / spacing mask 202 is exposed to expose the first resist on the negative resist on the wafer 100.
The pattern image of the line / interval mask 202 is projected. The same exposure process is repeated for the second line / interval mask 204, and the pattern image of the second line / interval mask 204 is projected on the negative resist on the wafer 100. Since the first pattern image intersects the second pattern image, the desired contact opening pattern 102 shown in FIG. 1 is formed on the upper 100 negative resist.

Third, a flow chart illustrating a photolithography process for reducing the size of a contact opening according to a preferred embodiment of the present invention. 4A to 4
D is a diagram and a sectional view showing a photolithography process for reducing the size of the contact opening according to the preferred embodiment of the present invention.

Referring to FIG. 3 and FIGS. 4A to 4D, a wafer 400 on which a negative resist is formed is prepared (step 300). First line / space mask 20
3 is used to project a first pattern image onto a negative resist coated wafer 400 to form a first pattern in which vertical exposure regions 402 and vertical photoresist regions 404 parallel to each other are alternated. (Step 302). This is shown in FIG. 4B. In this case, the vertical exposure region 402 corresponds to an exposed portion (transparent region) of the transparent substrate 200, and the vertical photoresist region 404 is the first photoresist region 404.
Corresponds to the mask layer 202 (opaque region) of the line / interval mask 203.

A second line / space mask 205 is used to project a second image onto a negative resist coated wafer 400. The second pattern is formed as alternating laterally exposed regions 406 and laterally photoresist regions 408, which are parallel to each other (step 304). This is shown in FIG. 4C. In this case, the laterally exposed area 406 is the transparent substrate 200
The lateral photoresist region 408 corresponds to the mask layer 202 (opaque region) of the second line / spacing mask 205.

After the repeated exposure, the first pattern and the second
Therefore, a desired pattern of the contact opening is formed on the negative resist. That is, the area where the vertical resist area overlaps with the vertical resist area becomes the exposed area 410 that will later form a contact opening. In the present invention, the pitch between the first line / spacing mask and the second line / spacing mask and their size are determined by dimensions including the length and width of the desired contact opening.

The negative resist on which the contact opening pattern has been printed is subjected to a developing step. 4C
A block-shaped resist pattern 412 having the shape of a contact opening shown in FIG. Next, the negative resist in the exposed region 410 is removed to form a contact opening region 414.

In the present invention, the line patterns of the two line / interval masks intersect each other to obtain a desired pattern of contact openings on the negative resist layer. Also, the first line / interval mask and the second line / interval
The pitch between the spacing mask and its size can be determined by the length and width of the desired contact opening, and can therefore be adjusted according to the intention of the designer. Thus, the present invention not only increases the process window, but also reduces the critical dimension (CD) of the contact opening by precisely controlling the pitch between the line / space masks.

The integration of devices in the semiconductor industry as a whole is 0.
Whether the line width reaches 15 μm or less is determined by the development of process technology. To satisfy the need for such development, various methods such as optical proximity correction (OPC), phase shift mask (PSM) off-axis illumination (OAI), and the like have been proposed.

In the present invention, in addition to forming the line / space mask by the usual method, the line / space mask is formed by using a strong PSM or a weak PSM to further improve the resolution of the exposure apparatus. As a result, the CD of the contact opening becomes smaller.

Further, errors occurring during pattern transfer must not be ignored. The reason for this is that errors caused by the sequential processes after the exposure step cause problems such as mis-etching and a decrease in the conductivity of the interconnects. Therefore,
When the proximity pattern is generally transferred, the original pattern is subjected to optical proximity correction before being used as a mask pattern.

In this case, the reason for performing the OPC is to increase the process window and to reduce the occurrence of CD errors due to proximity effects that affect the accuracy of the CD projected on the wafer.

This proximity effect will be briefly described below. When light passes through the mask and is projected onto the wafer, optical distortion occurs due to light deflection and scattering. On the other hand, light reflected from the wafer substrate passes through the photoresist and causes interference. As a result, the actual exposure amount on the photoresist layer changes due to repeated exposure. This effect becomes more pronounced as the CD in the process becomes smaller, especially when the CD is very close to the wavelength of the light source.

Due to light scattering and light deflection caused by the projection light, the corners of the photoresist are rounded and the size of the photoresist is reduced. In addition, there are other possible pattern distortions not shown here. . For example, if the pattern has a very high density or if the pattern deviates from its original position,
The patterns converge together. A general method for solving the above-mentioned problem is to correct the pattern distortion by increasing a step region or an edge near a corner. As a result, a pattern close to the expected pattern is obtained.

Therefore, the two line / interval masks are
A larger process window and a more precise pattern can be obtained by correcting with C.

In addition, the two line / spacing masks can be exposed by conventional exposure methods or by new techniques using off-axis illumination (OAI). Since the OAI improves the angle of incidence, the two line / space masks can be exposed by tilting the incident light at a more appropriate angle without using another new light source. As a result, a more accurate pattern can be obtained because the focus is improved and the resolution of the exposure apparatus is increased.

To summarize the above, the present invention repeats two different line / spacing masks to achieve the purpose of forming the desired pattern of contact openings on the negative resist and reducing the size of the contact openings. It relates to crossing line patterns after exposure.

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope or spirit of the invention. From this point of view, it is to be understood that the present invention includes various changes and modifications that fall within the scope of the appended claims.

[Brief description of the drawings]

FIG. 1 is a diagram showing a pattern of a contact opening.

FIG. 2 is a diagram showing first and second line / spacing masks for forming a contact opening pattern of FIG. 1;

FIG. 3 is a flowchart of a photolithography process for reducing the size of a contact opening according to a preferred embodiment of the present invention.

FIG. 4A illustrates a photolithography method for reducing the size of a contact opening according to a preferred embodiment of the present invention. FIG. 3B illustrates a photolithography method for reducing the size of a contact opening according to a preferred embodiment of the present invention. C illustrates a photolithography method for reducing the size of a contact opening according to a preferred embodiment of the present invention. D illustrates a photolithographic method for reducing the size of a contact opening according to a preferred embodiment of the present invention.

[Explanation of symbols]

 200 Transparent substrate 202, 204 Mask layer 203 First line / space mask 205 Second line / space mask 410 Exposure area 414 Contact opening area

Claims (20)

[Claims] 1. A photolithography method for reducing the size of a contact window, comprising: providing a wafer coated with a negative resist; exposing a first line / interval mask to a first line / interval mask;
Projecting a first pattern of an interval mask onto the negative resist; exposing a second line / interval mask to a second line / interval;
The second pattern of the interval mask is projected on the negative resist on which the first pattern is formed, and the overlapping pattern formed by the first pattern and the second pattern forms a contact opening pattern on the negative resist. A photolithography method comprising: forming; and developing the negative resist to expose a contact opening defined by the contact opening pattern. 2. The photolithography method according to claim 1, wherein the first pattern has a line shape in which transparent regions and opaque regions are alternately formed in parallel with each other. 3. The photolithography method according to claim 2, wherein the transparent region is a part of a transparent substrate that is not covered by a mask layer. 4. The photolithography method according to claim 3, wherein said mask layer includes a chromium layer. 5. The photolithography method according to claim 2, wherein the opaque region is a part of a transparent substrate covered by a mask layer. 6. The photolithography method according to claim 1, wherein the second pattern has a line shape in which transparent regions and opaque regions are alternately formed in parallel with each other. 7. The photolithography method according to claim 6, wherein the transparent region is a part of a transparent substrate that is not covered by a mask layer. 8. The photolithography method according to claim 7, wherein the mask layer includes a chromium layer. 9. The photolithography method according to claim 6, wherein said opaque region is a part of a transparent substrate covered by a mask layer. 10. The photolithography method according to claim 1, wherein the first pattern crosses a second pattern to form a contact opening pattern. 11. The photolithography method according to claim 1, wherein the pitch of the first mask and the pitch of the second mask determine the size of a contact opening. 12. The photolithography method according to claim 1, wherein the size of the first mask and the size of the second mask determine the size of a contact opening. 13. A photolithographic method for defining a contact opening pattern applicable to a wafer coated with a negative resist, comprising exposing a first mask and exposing a first pattern of the first mask. Projecting the second pattern on the negative resist, exposing a second mask, projecting a second pattern of the second mask onto the negative resist on which the first pattern is formed, and A photolithography method comprising: a step of forming a contact opening pattern in a negative resist with an overlapped pattern formed by a second pattern; and a step of developing a negative resist having the contact opening pattern. 14. The photolithography method according to claim 13, wherein the first mask includes a line / space mask in which transparent regions and opaque regions are alternately formed in parallel with each other. 15. The photolithography method according to claim 13, wherein the second mask includes a line / space mask in which transparent regions and opaque regions are alternately formed in parallel with each other. 16. The photolithography method according to claim 13, wherein the first pattern crosses a second pattern to form a contact opening pattern. 17. The photolithography method according to claim 16, wherein the first pattern has a vertical line shape. 18. The photolithography method according to claim 16, wherein the second pattern has a horizontal line shape. 19. The photolithography method according to claim 13, wherein the pitch of the first mask and the pitch of the second mask determine the length and width of a contact opening. 20. The photolithography method according to claim 13, wherein the size of the first mask and the size of the second mask determine the length and width of the contact opening.