CN1378102A - Method for reducing optical proximity effect - Google Patents

Abstract

The invention relates to a method for correcting optical proximity effect, which cuts a master mask into a plurality of sub-masks according to different densities, gives conditions such as aperture and exposure energy to the ideal critical dimension which can be achieved by the sub-masks under each density, and then exposes the photoresist through the sub-masks in sequence, thereby achieving the purpose of transferring a mask pattern onto the photoresist layer faithfully, not only improving the problems caused by the proximity effect, but also not limiting the line width of the element pattern to be reduced, and having great development potential.

Description

Methods to Reduce Optical Proximity Effect

The present invention relates to an optical correction method, in particular to an optical correction method capable of improving the problem of circuit pattern distortion caused by optical proximity effect (OPE).

The design and manufacturing technology of semiconductor integrated circuits has made great progress in recent years. The size of components continues to shrink as the chip density of products continues to increase. In order to meet the needs of miniaturization, photoetching technology has adopted i-line or deep ultraviolet light ( deep UV (DUV) range of optical systems; and when the design rule of circuit components approaches the wavelength of the light source used in the exposure machine, the optical proximity effect will gradually appear, not only causing the circuit pattern transferred to the wafer Distortion, and therefore consumes most of the critical dimension tolerance (criticaldimensiontolerance), making the process more difficult.

The so-called optical proximity effect refers to the uneven distribution of exposure dose in the photoresist due to the effects of reflection, refraction, or diffraction after the light source irradiates the mask pattern during the photoetching process, resulting in distortion of the developed circuit pattern. Please refer to FIG. 1 , which shows a photomask pattern and the pattern that is transferred to the photoresist after the general exposure etching process; as shown in the figure, due to the influence of scattered light, the end of the circuit pattern 10 is also exposed, so it is developed The resulting photoresist pattern 12 cannot match the circuit pattern 10 on the photomask, thus affecting the properties of the circuit components.

In general, the remedy for proximity effects is at least partially offset by masking the feature pattern in the opposite direction of the expected distortion. That is, a line that is likely to become too narrow can be designed in advance to have a larger width than it actually does, and so on. As shown in FIG. 2, a hammerhead 24 is added to the end of the above-mentioned mask pattern 20. Since the area of the mask pattern 20 increases, the loss caused by scattered light can be compensated, thereby avoiding pattern transfer distortion. An expected photoresist pattern 22 is formed. The data of a photomask pattern suitable for the photoetching process is stored as a computer data file, and the correction data for the proximity effect can also be stored there, and appropriate corrections are made directly when the photomask is made and the pattern is read and written.

In addition, by adjusting optical parameters such as numerical aperture, light source coherence, and exposure, or changing the contrast value of the photoresist, it is beneficial for the pattern of the photoresist to reach the critical size after exposure. (critical dimension, CD) ideal range to reduce the impact of the optical proximity effect.

However, with the increasing development of the semiconductor industry, the line width of the components also tends to shrink with the increase of the density. This is not only a major limitation for the aforementioned optical proximity effect compensation method, because the The mask pattern correction system has a certain limit, and not all graphics under all line widths can be reversely compensated for the mask; therefore, the integration of components is likely to stagnate due to the ineffective pattern transfer effect of the mask. As a result, the development of the semiconductor industry has reached a limit.

In addition, due to the different densities of wiring distribution on a single silicon chip, it is difficult to adjust the critical dimension (CD) of dense and sparse areas to achieve an ideal value by optically adjusting the same parameters.

In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method of optical correction, which can improve the optical proximity effect (OPE) without using the compensation of the mask pattern in the opposite direction, thus allowing the line width to shrink without It will affect the development of the industry; and the critical dimensions of each region can be adjusted optically according to their needs (such as aperture, exposure time, exposure amount...etc.), which is beneficial to the progress of photoetching technology.

In order to accomplish the purpose of the present invention, the present invention provides a method for optical correction, which firstly sets the specifications by the component design department according to the design rule (design rule), then designs the pattern on the photomask according to the compactness of the component arrangement, and then These patterns are respectively manufactured on multiple photomasks, and the density of the patterns on the same photomask is similar. Afterwards, these photomasks are exposed sequentially to transfer the required circuit pattern to the photomask. Block on.

In order to achieve the present invention, another method of optical correction is provided. After the component design department sets the specifications according to the design rule (design rule), the pattern on the photomask is designed according to the compactness of the component arrangement, and then the original The mask (hereinafter referred to as the mother mask) is divided into multiple sub-masks, and the density of the pattern on the same sub-mask is similar; after that, exposure is performed through the sub-masks in sequence step, so that the pattern of the master mask can be transferred to the photoresist.

It should be noted here that the above-mentioned method of exposing each (sub) mask is carried out separately under the optical conditions allowed by the components at various densities at the same time, so the line width of the formed components does not vary. will be constrained and have an appropriate critical dimension.

In order to make the above-mentioned purposes, features, and advantages of the present invention more comprehensible, a preferred embodiment is specifically cited below, together with the accompanying drawings, as follows:

A brief description of the attached drawings:

Figure 1 shows the situation of photoresist pattern distortion caused by optical proximity effect;

Fig. 2 shows the known reticle reverse pattern compensation and the standard pattern transfer situation it presents;

3A and 3B respectively show the master mask with dense and uniform circuit patterns provided by the embodiment of the present invention and the situation of cutting it into sub-masks;

4A and 4B respectively show the pattern transfer situation produced on the positive and negative photoresists along the A-A, B-B, and C-C cut planes in FIG. 3B;

5A and 5B respectively show the comparison of the intensity of light energy projected by sub-masks 301, 302, and 303 for forming images on positive and negative photoresists;

FIG. 6A shows the distribution of measured CD change values after exposure through the sub-masks 301, 302, and 303 under different apertures;

FIG. 6B shows the distribution of measured CD change values after exposure through the sub-masks 301, 302, and 303 under different degrees of light coherence; and

FIG. 6C shows the distribution of measured CD change values after exposure through the masks 301 , 302 , and 303 under different light energy intensities.

Description of figure number

10~line pattern 12~photoresist pattern

20~Reticle pattern 22~Resist pattern

24~Hammer line 30~Master mask

301, 302, 303~ sub-mask 32~ line pattern

321, 322, 323~ sub-line graphics

Example

Please refer to Figures 3A and 3B to understand the correction method of the present invention in more detail; firstly, after the component design department sets the specifications according to the design rules, the pattern on the photomask is designed according to the density of the component arrangement, After that, it is possible to choose whether to provide a master mask; for example, a master mask 30 is provided first, as shown in FIG. 3A , and a plurality of circuit patterns 32 are formed on the master mask 30 . Next, the master mask 30 is divided into multiple sub-masks according to the density of the circuit patterns, and those with similar pattern densities are located on the same sub-mask. For example, referring to FIG. 3B , the master mask 30 is divided into three sub-masks 301, 302, and 303 according to the density of the circuit pattern, and the sub-circuit pattern 321 located on each sub-mask 301, 302, and 303 The densities of , 322, and 323 are dense, medium, and sparse, respectively. Please note here that if there is no step of providing the master photomask at the beginning, the component design department can also design the circuit pattern according to the density of the component arrangement, and then directly manufacture the designed circuit pattern on the sub-photos respectively. On the cover 301, 302, 303, its condition is as shown in Fig. 3B. In this embodiment, the step of providing a master photomask is taken as an example, but this description does not limit the protection scope of the patent application. In addition, for the convenience of description, the number of sub-masks described in this embodiment is 3 as an example, and their sizes are the same. Make adjustments for the application.

Next, the steps of sequentially exposing the sub-masks 301, 302, and 303 include adjusting the machine’s aperture, light energy intensity, and other parameters for the density of the three patterns to obtain each mask pattern. The most ideal critical dimension (CD) value; please refer to Figure 4A, 4B, which is the pattern transfer through the sub-reticle pattern 321, 322, 323 of Figure 3B; as Figure 4A, it is along A-A, B-B respectively , and the pattern shown on the positive photoresist (not labeled) of the C-C cut plane, and Fig. 4B is also the pattern shown on the negative photoresist along the A-A, B-B, and C-C cut planes.

For the adjustment of the above-mentioned parameters, please refer to FIGS. 5A and 5B , which show the comparison of light energy received by the sub-masks 301 , 302 , and 303 for forming images on the positive and negative photoresists respectively. That is, when exposing each photomask, the energy conditions can be adjusted separately; for example, if the pattern of photomask 301 is to be imaged on a positive photoresist, then when the photomask 301 is exposed, the 5A can be selected. The energy distribution curve of the photomask 301 in the figure specifies the energy to obtain ideal exposure results.

Please refer to FIG. 6A, which shows the distribution of CD change values measured after exposure through the sub-masks 301, 302, and 303 under different apertures; When 301 performs the exposure action, it can be selected to be adjusted to correspond to the closest ideal CD value; its aperture size A ₃₀₁ ; and when the exposure action is performed through the mask 302, the aperture aperture can be adjusted to be A ₃₀₂ ; the mask 303 The aperture aperture is selected to be adjusted to A ₃₀₃ .

Please refer to FIG. 6B, which shows the distribution of CD change values measured after exposure through the sub-masks 301, 302, and 303 under different light densities; When the mask 301 performs the exposure operation, it can be adjusted to the optical density S ₃₀₁ corresponding to the closest ideal CD value; and when the exposure operation is performed through the mask 302, the optical density can be adjusted to S ₃₀₂ ; The light density when exposed through the mask 303 is adjusted to S ₃₀₃ .

Please refer to FIG. 6C, which shows the distribution of CD change values measured after exposure through the mask 301, 302, and 303 under different light energy intensities; When 301 performs the exposure operation, it can be selected to be adjusted to the light energy intensity E ₃₀₁ corresponding to the closest ideal CD value; and when the exposure operation is performed through the mask 302, the light energy intensity can be adjusted to E ₃₀₂ ; The light energy intensity when the mask 303 is exposed is selected to be adjusted to E ₃₀₃ .

According to the optical calibration method of the present invention, it utilizes cutting a master mask into multiple sub-masks according to the density (or directly fabricating circuit patterns with different densities on multiple sub-masks) , and then give a specific condition (such as aperture aperture, exposure energy, etc.) for the ideal critical dimension that can be achieved by the sub-reticle for each density level, and then sequentially pass through the sub-masks to process the photoresist The action of exposure, thus achieving the purpose of faithfully transferring a mask pattern to the photoresist layer, which not only improves the problems caused by the proximity effect, but this improvement method is not limited by the increasingly reduced component patterns Line width, great potential for development.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection shall prevail as defined in the appended claims in combination with the specification and drawings.

Claims (7)

1. one kind is reduced the optical proximity effect method, is applicable to the component design of the density degree of distinguishing line pattern, comprises the following steps:

A plurality of light shields are provided; And

This line pattern is formed on these light shields, and pattern density degree fellow is positioned at on a slice light shield.

2. the method for claim 1, wherein also comprise a light source is provided.

3. method as claimed in claim 2 wherein, also comprises a photoresistance is provided, so that the pattern of these light shields can be transferred on this photoresistance in regular turn because of follow-up exposure actions.

4. method as claimed in claim 3 wherein, is to utilize this light source to see through this sub-light shield in regular turn this photoresistance to be exposed.

5. method as claimed in claim 4, wherein, the live width that this photoresistance can provide according to each sub-light shield in the rayed amount in when exposure and set different values.

6. one kind is reduced the optical proximity effect method, comprises the following steps:

One original layout case is provided;

Density degree according to circuit is divided into a plurality of sub-line patterns with this original layout case;

Form the sub-light shield of multi-disc according to this sub-line pattern, and pattern density degree fellow is positioned on the same slice, thin piece light shield;

One light source is provided; And

The pattern of this sub-light shield provides a photoresistance, so that can be transferred on this photoresistance in regular turn because of follow-up exposure actions.

7. method as claimed in claim 6, wherein, the live width that this photoresistance can provide according to each sub-light shield in the rayed amount in when exposure and set different values.

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