JPH04316047A - Phase shift mask - Google Patents

Abstract

PURPOSE:To enhance the precision of pattern transfer to a semiconductor wafer by always uniformizing intensity of light passing through the phase shift mask. CONSTITUTION:The recessed part 5 is formed on the bottom side of a glass substrate 1 at the position just opposite to the position on which the shifter film 4 is formed and the depth t2 of the recessed part 5 is set so as to equalize the intensity of the light transmitted through only the glass substrate 1 as thick as t0 almost to that of the light transmitted through the shifter film 4 and the t1 thick glass substrate 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift mask used in the manufacture of semiconductor integrated circuits.

0002

2. Description of the Related Art In recent years, as the degree of integration of semiconductor integrated circuits has improved, there has been a tendency for transfer patterns to be transferred onto semiconductor wafers to become even finer. Therefore, when transferring a pattern onto a semiconductor wafer, sufficient resolution may not be obtained by simply using a normal photomask. In other words, a normal photomask is made by forming a light-shielding film on a glass substrate, but when using such a photomask, the finer the pattern, the more
Due to the light diffraction effect, light also enters the light-blocking area, resulting in so-called light fog, resulting in a problem of reduced contrast.

[0003] In order to solve these problems and increase resolution and depth of focus, a phase shift mask has been provided in which the phase of light passing through the mask is controlled.

This phase shift mask is, for example, shown in FIG.
As shown in FIG. 2, a light shielding film 2 made of a thin metal film such as Cr is patterned on a glass substrate 1 made of synthetic quartz or the like, and a light shielding film 2 is formed on a glass substrate 1 made of synthetic quartz or the like. S which shifts the phase of the light passing through this light transmission window 3
A shifter film 4 made of iO2 or the like is arranged.

When pattern transfer is performed on a semiconductor wafer, this phase shift mask is applied, and as shown in FIG. 2, while the semiconductor wafer is placed above the phase shift mask, light is emitted from the bottom side of the phase shift mask. irradiate. Then, the phase of the light that sequentially passes through the glass substrate 1 and the shifter film 4 and the light that passes only through the glass substrate 1 is reversed by 180 degrees, and therefore the boundary between the two (the light shielding film 2
The intensity of the light becomes zero at the area where the image is formed, and the contrast is improved.

[0006]

[Problems to be Solved by the Invention] In the conventional phase shift mask shown in FIG. was not taken into consideration. Therefore, in the prior art, the glass substrate 1 always has a constant thickness t regardless of the presence or absence of the shifter film 4.
It was formed to be 1.

Therefore, compared to the light that passes through only the glass substrate 1, the light that passes through the glass substrate 1 and the shifter film 4 sequentially is absorbed and attenuated by the amount that passes through the shifter film 4, and its intensity is lower. As a result, the effect of phase control by the phase shift mask cannot be fully exhibited, and the accuracy of pattern transfer is still insufficient.

[0008]

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and the intensity of light transmitted through a phase shift mask is always uniform regardless of the presence or absence of a shifter film. In this way, the accuracy of pattern transfer to a semiconductor wafer is further improved.

Therefore, in the present invention, a light-shielding film is patterned on the glass substrate, and the phase of the light passing through the light-transmitting window is changed at required locations within the light-transmitting window that are not covered with the light-shielding film. In a phase shift mask in which a shifting shifter film is arranged, a recess is formed on the bottom side of the glass substrate that faces the location where the shifter film is formed, and the depth of this recess is such that light passes through only the glass substrate and exits. The intensity of the light and the light transmitted through the glass substrate and the shifter film and emitted are set to be approximately equal in intensity.

0010

[Operation] In the above structure, since the light-transmitting part of the glass substrate corresponding to the location where the shifter film is formed has a thin wall thickness, the intensity of the light transmitted therethrough becomes uniform over the entire surface of the phase shift mask, and the intensity of the light transmitted through this part becomes uniform over the entire surface of the phase shift mask. Pattern transfer accuracy is improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a phase shift mask according to an embodiment of the present invention, and parts corresponding to those of the conventional example shown in FIG. 2 are given the same reference numerals.

In FIG. 1, reference numeral 1 indicates a glass substrate, 2 a light shielding film, 3 a light transmitting window, and 4 a shifter film.

A feature of this embodiment is that a concave portion 5 is formed on the bottom side of the glass substrate 1 opposite to the location where the shifter film 4 is formed. The thickness t1 of the light transmitting portion is the shifter film 4.
It is thinner than the thickness t0 of the light transmitting portion of the glass substrate 1 corresponding to the non-forming portion.

The depth t2 of the recess 5 is set such that the intensity of the light that passes through only the glass substrate 1 and is emitted is approximately equal to the intensity of the light that passes through the glass substrate 1 and the shifter film 4 and is emitted. It is set.

For example, if the light transmittance of the portion of the glass substrate 1 where the shifter film 4 is not formed is 90%, and the light transmittance of the shifter film 4 is 95%, then the glass substrate 1 corresponding to the portion where the shifter film 4 is formed If the thickness t1 is made approximately half of the thickness t0 of the other part, the transmittance of the glass substrate 4 in that part is 95%.
As a result, the combined light transmittance of the shifter film 3 and the glass substrate 1 becomes 90%, which is the same as the light transmittance of the glass substrate 1 in the area where the shifter film 1 is not formed.

Naturally, in this case as well, the depth of the recess 5 is set so as to make the light intensity uniform, and at the same time, the light transmitted through only the glass substrate 1 and emitted is separated from the glass substrate 1 and the shifter film 4. The phase of the transmitted and emitted light is 1
It is necessary to determine the thickness of the shifter film 4 so that it is reversed by 80 degrees.

Note that, for example, when the resist pattern for forming the shifter film 4 is positive, the recess 5 is formed by etching using a resist pattern that has a negative relationship with the resist pattern.

[0018]

According to the present invention, regardless of the presence or absence of a shifter film, the intensity of light transmitted over the entire surface of the phase shift mask becomes uniform, and the accuracy of pattern transfer to a semiconductor wafer is improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a phase shift mask according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a phase shift mask according to a conventional example.

[Explanation of symbols]

1 Glass substrate 2. Light shielding film 3. Light transmission window 4 Shifter membrane 5 Recess

Claims (1)

[Claims] 1. A light-shielding film is patterned on a glass substrate, and a shifter film is provided at required locations within the light-transmitting window that is not covered with the light-shielding film to shift the phase of light passing through the light-transmitting window. In the phase shift mask where is placed,
A concave portion is formed on the bottom side of the glass substrate facing the location where the shifter film is formed, and the depth of the concave portion is determined such that the light that passes through only the glass substrate and is emitted, and the light that passes through the glass substrate and the shifter film and is emitted. A phase shift mask characterized in that the intensity of light is set to be approximately equal to that of light.