JPH0141246B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an exposure apparatus that controls the amount of deviation of mask dimensions from design values by adjusting exposure time so that the dimensions of a photoresist after development become equal to the design dimensions. [Technical Field of the Invention] Conventionally, negative type photoresists have been mainly used in photolithography processes. However, with the recent trend toward ultra-high integration, photolithography technology with a resolution of 2 to 3 μm has come to be required, and negative-type photoresists are being replaced by positive-type photoresists. Also,
As resolution dimensions have become finer, photomasks have also changed from conventional emulsion-type ones to so-called hard masks made of metals and their oxides. The reason why photomasks are being replaced by hard masks is that conventional emulsion-type masks do not have good resolution and dimensional accuracy. As described above, as patterns become finer, higher resolution and dimensional accuracy are required. Currently, the accuracy of masks used in the photolithography process is approximately ±0.2 to ±0.5 μm (value of 3σ). Furthermore, as patterns become finer, it is natural that the transfer accuracy, that is, the accuracy when transferring from the photomask to the photoresist coated on the semiconductor substrate, must be as accurate as the accuracy of the mask itself. ing. [Problems in the Background Art] However, in the photolithography process, especially in the process of transferring a pattern onto a resist using a completed mask, the precision of the mask is transferred directly onto the photoresist, so no matter how accurate it is, Even if it is transferred, it will not be as accurate as a mask. In reality, it's a little worse than this. Here, if the total transfer accuracy when transferring the photomask pattern to the photoresist is σ _tptal , then σ _tptal = (σ _nask ² + σ _tra ² ) ^1/2 where σ _nask is the mask accuracy and σ _tra is the transfer accuracy. It is. In this way, the overall transfer accuracy is determined by the mask accuracy and the transfer accuracy, but conventionally, even if the mask accuracy is improved, if the transfer accuracy is poor, the overall transfer accuracy is deteriorated. Causes of such deterioration of transfer accuracy include variations in the illuminance of the mask aligner, variations in the developer, and variations in the resist film thickness. [Object of the invention] This invention was made in view of the above points,
The purpose of this is to improve transfer accuracy by adjusting the exposure time to eliminate the effects of changes in mask aligner illuminance, developer changes, resist film thickness, etc. that affect mask transfer accuracy, and improve overall transfer accuracy. The object of the present invention is to provide an exposure apparatus that can be improved. [Summary of the Invention] Overall transfer accuracy is improved by adjusting the exposure time to an optimal time to eliminate the effects of changes in mask aligner illuminance, developer changes, resist film thickness, etc. that affect mask transfer accuracy. Improving. [Embodiment of the Invention] An exposure apparatus according to an embodiment of the invention will be described below with reference to the drawings. As shown in FIG.
2, in the case of exposure and development using mask 12
Let _W be the pattern size of
is expressed as the following equation. This situation is shown in Figure 2. ΔW=A(lnE _i −B) (1) Here, the constants A and B are parameters that change due to fluctuations in the developer in the photolithography process and fluctuations in the coating film thickness. Here, as mentioned above, ΔW
= W _DEV − W _MASK . Since we want to obtain the same value as the design value of the mask as the dimension after development, we substitute the design value of the mask as W _DEV and the average value of the actually completed mask dimensions as W _MASK . Here, if we transform the first equation, E _i =EXP(B+(W _DEV -W _WASK )/A)...(2) Here, the exposure energy E _i is the product of the illuminance I and the exposure time t. Therefore, when calculating the exposure time t by modifying the second equation, t=EXP[B-lnI+(W _DEV -W _MASK )/A]...(3) As shown in the third equation, the dimensions after development and The deviation ΔW from the mask design value can be corrected by appropriately adjusting the exposure time. That is, by determining the process parameters A and B of the photolithography process experimentally, it is possible to eliminate the effects of variations in the developer and coating film thickness in the lithography process. Next, a case in which process parameters A and B are calculated will be specifically explained. The case of calculating the process parameters A and B of the SiO ₂ film will be explained. First, a silicon wafer is heat-treated in an oxidizing atmosphere at 1,100°C to form a silicon oxide film with a thickness of about 5,000 Å. Next, a positive type photoresist is applied on the silicon oxide film to a thickness of about 1.5 μm using a spin coater, and then heat treated on a hot plate at 105° C. for 90 seconds. Next, this wafer is exposed using an exposure device using a hard mask with a 30 μm cutout pattern and varying the exposure time. (The illumination intensity at this time is 502 mW/cm ² .) Thereafter, after developing with a spray type photoresist developer, the developed dimensions are measured using a micrometer. The experimental results obtained at this time are shown in FIG. In this case, pattern dimensions with different exposure energies are obtained by changing the exposure time. Parameters A and B are calculated below using the least squares method. As a result, A
= 0.64, B = 9.63. By the way, parameters can be similarly calculated not only for SiO ₂ but also for Si ₃ N ₄ , polysilicon, Al, etc. The situation is shown in the table below.

〔Effect of the invention〕

As detailed above, according to the present invention, the effects of fluctuations in mask aligner illumination, resist film thickness, etc. that affect mask transfer accuracy are eliminated by adjusting the exposure time, so an exposure device with high transfer accuracy can be used. can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between a photoresist and a mask, FIG. 2 is a diagram showing exposure energy and pattern dimensions, and FIG. 3 is a diagram showing an exposure apparatus according to an embodiment of the present invention. 211, 212...mask aligner, 25...
Shutter, 27...Wafer, 281,282...
Shutter drive circuit, 31...mask size measuring device,
32... Development size measuring device.

Claims (1)

[Claims] 1 Shutter drive circuit that controls the opening and closing of the shutter that adjusts the exposure time and the mask dimension W
A mask dimension measuring means for measuring MASK, a developed dimension measuring means for measuring the developed dimension W DEV of the photoresist, a process parameter measuring means for calculating process parameters A and B, and a mask dimension measuring means for measuring the mask dimension measuring means. Dimensions of mask W
Based on MASK, the photoresist dimension W DEV measured by the developed dimension measuring means, the process parameters A, B, and illumination intensity, the exposure time t = EXP [B -lnI+(W DEV-W
MASK)/A];
An exposure apparatus comprising means for driving the shutter drive circuit based on the exposure time t calculated by the exposure time calculation means.