JPH046557A - Method for forming phase shifting mask - Google Patents

Abstract

PURPOSE:To obtain a phase shifting mask easy in inspection and correction of defects and good in controllability by forming an opaque mask pattern on a transparent substrate and oxidizing the mask pattern to form the phase shifter uniform in thickness around the mask pattern. CONSTITUTION:A resist pattern 4 is formed on the material film to be formed into the mask pattern 2, and this film is etched by using the resist pattern 4 as a mask to form the mask pattern 2, and the resist pattern 4 is removed. Then, the pattern 2 is oxidized to form the phase shifter 3 on the whole surface of the circumference of the pattern 2, thus permitting inspection and correction of defects to be facilitated and the obtained phase shifting mask to be good in controllability by oxidizing the whole surface of the mask pattern after forming the perfect mask pattern.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for creating a phase shift mask used in the manufacture of LSI, and in particular a method for creating a phase shift mask that is easy to inspect and repair defects and has good controllability. It is related to.

[Prior Art] Conventionally, the optical phosphorography technique is well known in which an enlarged pattern on a photomask is reduced and repeatedly imaged on a wafer to form a desired LSI pattern.

FIG. 2 is a principle diagram showing an exposure method using a conventional optical lithography technique using a reduction optical type optical stepper as described above.

In the figure, (1) is the glass substrate that becomes the transparent substrate of the photomask, and (2) is the C formed on the glass substrate (1).
It is an opaque mask pattern made of R, MoSi, Si, etc. The material of the mask pattern (2) may be any material as long as it can sufficiently block light used in optical lithography, such as g-line, ili, excimer laser, etc.

Such a glass substrate (1) and mask pattern (2)
When light is irradiated through a photomask made of the above, the electric field of the light on the mask pattern (2) becomes a pulse-like intensity distribution of the same polarity. Therefore, the resolution limit R[
μm] or less, as shown in the figure,
The light intensity irradiated onto the wafer is determined by the mask pattern (2)
Since the light wraps around the edges of the frame, the interference waveform becomes smooth.

In other words, the electric field of the light transmitted through the mask pattern (2) becomes spatially separated waveforms, but the light intensity on the wafer overlaps with adjacent light, making it impossible to resolve the pattern. become unable.

By the way, the resolution limit R contributing to the pattern density is expressed as R=kl·λ/NA, and the smaller the resolution limit R, the higher the resolution. However, ni+ is a constant that depends on the resist process, and can be lowered to about 0.5. Further, λ is the wavelength of light used for exposure, and NA is the numerical aperture of the lens.

From the above equation, it can be seen that by decreasing the constant + and the wavelength λ and increasing the numerical aperture NA of the lens, the resolution limit R becomes smaller (that is, the resolution becomes higher).

Currently, using i-line (λ = 0.365 μm), numerical aperture N
An optical stepper with a value of A of 0.5 has been realized, and it is possible to reduce the value of 1 to 0.5 in the constant, so the value of the resolution limit R is about 0.4 [μm] It can be made as small as

In order to obtain a resolution limit R smaller than this, the wavelength λ may be further shortened or the numerical aperture NA may be increased, but this makes it technically difficult to design the light source and lens. Also, since the depth of focus δ is expressed as δ-λ/[2(NA)2], there is a problem that if the resolution limit R is reduced, the depth of focus δ is also reduced, resulting in a lower resolution. .

In order to solve these problems, an exposure method using a phase shift mask has been proposed as described below.

FIG. 3 is a principle diagram showing an exposure method using an improved conventional optical lithography technique, which is described in, for example, Japanese Patent Laid-Open No. 57-62052 and Japanese Patent Laid-Open No. 58-173744.

In the figure, (3) is a phase shifter made of a transparent material such as 5i02, and the rWI of the adjacent mask pattern (2)
The 0 phase shifters (3) arranged every other (light transmitting part) have a function of shifting the phase of the transmitted light by 180°.

According to the phase shift mask shown in FIG. 3, the mask pattern (
The intensity distribution of the electric field of the light transmitted through 2) has an inverted pulse shape as shown in the figure because the phase is alternately inverted.

Therefore, when projecting with the same optical system as in the case of Fig. 2, the light intensity on the wafer is canceled out in the areas where the pattern images overlap, so that the light intensity on the wafer is different from the separated pattern waveform as shown in the figure. Become.

According to the method shown in FIG. 3, the resolution is higher than that shown in FIG. 2, and experimentally, the minimum resolution pattern width can be reduced to about half.

However, although the configuration of the phase shift mask shown in FIG. It is difficult to apply because it cannot be completely separated.

In order to solve this problem, a method has been proposed that is applicable to any pattern and is easily realized from a manufacturing standpoint.

FIG. 4 is a principle diagram showing a further improved exposure method using a phase shift mask using a conventional self-aligning method, which was described in, for example, the 1989 rIEDM Conference.

In this case, the phase shifter (3) is connected to the mask pattern (2).
It is formed on the mask pattern (2) and has a wider pattern width than the mask pattern (2).

As a result, the phase of the light near the edge of the mask pattern (2) is reversed, and the light intensity imaged on the wafer is reliably separated, as shown, regardless of the pattern arrangement.

Next, with reference to FIG. 5, a method for creating the conventional phase shift mask shown in FIG. 4 will be described.

First, as in step (a), the mask pattern (2) and the material f: 4M of the phase shifter (3) are laminated on the glass substrate (1), and then the resist pattern ( 4) Form.

Next, as in step (b), a resist pattern (4) is formed.
Mask pattern (2) and phase shifter (
3) is formed by etching, and a resist pattern (4) is formed by etching.
) to remove.

Next, as in step (C), isotropic etching is performed to process only the mask pattern (2), so that the width of only the mask pattern (2) is made smaller than that of the phase shifter (3). As a result, a mask pattern (2) having a phase shifter (3) as shown in FIG. 4 is formed.

The thus formed phase shifter mask is inspected for defects such as pattern defects after step (b) or (c). However, in the isotropic etching of step (c),
Processing accuracy tends to vary due to foreign matter existing between the mask pattern (2) and the phase shifter (3), and controllability is poor.Therefore, there are many factors causing variations in manufacturing, and reliability of defect inspection and correction is poor.

[Problems to be Solved by the Invention] As described above, in the conventional method for creating a phase shift mask, after etching the mask pattern (2) and the phase shifter (3), only the mask pattern (2) is made isotropic. Because it is etched, it is difficult to inspect and correct defects, and
There was a problem in that the controllability of machining accuracy, which should be strictly controlled, was poor.

The present invention was made to solve the above-mentioned problems, and aims to provide a method for manufacturing a phase shift mask that allows easy defect inspection and correction and has good controllability.

[Means for Solving the Problems] A method for producing a phase shift mask according to the present invention includes a step of forming an opaque mask pattern on a transparent substrate and oxidizing the mask pattern to uniformly form the periphery of the mask pattern. The method includes a step of forming a phase shifter having a thickness of .

[Operation] In the present invention, after forming a complete mask pattern, the entire peripheral portion of the mask pattern is oxidized to form a phase shifter.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a process diagram showing one embodiment of the present invention, (1) to
(4) is similar to the above.

First, in step (a>), a resist pattern (4) is formed on a material film that will become a mask pattern (2).

Subsequently, in step (b), a resist pattern (4) is formed.
The mask pattern (2) is etched in a shape according to the following, and the resist pattern (4) is removed.

Next, the mask pattern (2) is oxidized to form a phase shifter (
3) Form.

In this case, pattern defect inspection and correction, etc. are performed in step (b).
This is followed by forming a complete mask pattern (2) that meets the required accuracy.

Furthermore, the thickness of the phase shifter (3) formed in step (c) can be easily controlled by controlling the oxidation treatment time, and there is no possibility of defects occurring in the phase shifter (3).
There is no need to perform an inspection after step (c).

The material for the mask pattern (2) may be light used in optical lithography (g-line, i@-excimer laser, etc.).
Any material can be used as long as it can sufficiently block the oxidation and become transparent after oxidation, and the above-mentioned Cr, MoSi, Si, etc. can be used.

Further, if thermal oxidation treatment is used, the controllability of the oxide film thickness that becomes the phase shifter (3) can be further improved, and a highly accurate phase shifter (3) can be formed.

[Effects of the Invention] As described above, according to the present invention, by forming an opaque mask pattern on a transparent substrate and oxidizing the mask pattern, a phase shifter having a uniform thickness can be formed around the periphery of the mask pattern. Since the mask pattern is completely oxidized after forming a complete mask pattern, it is possible to obtain a method for manufacturing a phase shift mask that is easy to inspect and correct defects and has good controllability. be.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing an embodiment of the present invention, FIG. 2 is a principle diagram showing a conventional exposure method using photolithography, and FIG. 3 is a principle diagram showing an improved conventional exposure method using photolithography. FIG. 4 is a principle diagram showing a further improved conventional exposure method using photolithography, and FIG. 5 is a process diagram showing a method for producing the phase shift mask shown in FIG. 4. (1)...Glass substrate (transparent substrate) (2)...Mask pattern (3)...Phase shifter In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A phase shift mask comprising: forming an opaque mask pattern on a transparent substrate; and oxidizing the mask pattern to form a phase shifter with a uniform thickness around the mask pattern. How to make.