JP2647232B2 - Phase shift mask and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift mask used for manufacturing an LSI and a method for manufacturing the same, and more particularly, to a phase shift mask which is easy to inspect and correct for defects and has good controllability, and a phase shift mask therefor. It relates to a manufacturing method.

[Prior Art] Conventionally, an optical lithography technique for forming a desired LSI pattern by reducing an enlarged pattern on a photomask on a wafer and repeatedly forming an image is well known.

FIG. 2 is a principle view showing an exposure method by a conventional photolithography technique using the above-described reduction optical type optical stepper, wherein the upper part shows a side cross-sectional shape of the photomask, and the middle part shows the light passing through the photomask. The electric field intensity and the lower part are the light intensity on the wafer irradiated with the photomask transmitted light.

In the figure, (1) is a glass substrate serving as a transparent substrate of a photomask, and (2) is a Mo substrate formed on the glass substrate (1).
This is an opaque mask pattern made of Si (molybdenum silicon) or the like. The material of the mask pattern (2) may be any other material that can sufficiently block light used in photolithography, for example, g-line, i-line, excimer laser, and the like.

When light (for example, the i-line) is irradiated through a photomask including the glass substrate (1) and the mask pattern (2), the electric field of the light transmitted through the photomask has a pulse-like intensity distribution having the same polarity. Becomes Therefore, when a pattern transfer with a resolution equal to or less than the resolution limit R [μm] of the photolithography is performed, as shown in the figure, the light intensity irradiated on the wafer is transmitted around the edge of the mask pattern (2).
The result is a gentle interference waveform. In other words, the electric field of the light transmitted through the photomask has a spatially separated waveform, but the light intensity on the wafer overlaps with the adjacent light, so that the pattern cannot be resolved.

By the way, the resolution limit R that contributes to the pattern density is expressed by the following equation. The smaller the resolution limit R, the higher the resolution.

R = k ₁ · λ / NA where k ₁ is a constant depending on the resist process, and can be reduced to about 0.5. Λ is the wavelength of light used for exposure, and NA is the numerical aperture of the lens.

From the equation, it can be seen that the resolution limit R becomes smaller (that is, the resolution becomes higher) when the constant k ₁ and the wavelength λ are reduced and the numerical aperture NA of the lens is increased. At present, the i-line (λ = 0.36
5 μm), an optical stepper having a numerical aperture NA of 0.5 is realized, and the value of the constant k ₁ can be reduced to 0.5, so that the value of the resolution limit R is 0.4 [μm ]].

In order to obtain a smaller resolution limit R, the wavelength λ may be further shortened or the numerical aperture NA may be increased, but the design of the light source and the lens becomes technically difficult. Further, the depth of focus δ practically related to the resolution is represented by the following.

δ = λ / [2 (NA) ² ] Accordingly, as is clear from the equation, when the wavelength λ is reduced and the numerical aperture NA is increased to reduce the resolution limit R, the depth of focus δ is also reduced, and eventually the resolution is increased. However, there is a problem that the temperature is lowered.

In order to solve such a problem, an exposure method using a phase shift mask has been conventionally proposed as follows.

FIG. 3 shows, for example, JP-A-57-62052 and
FIG. 1 is a principle diagram showing an improved exposure method using a photolithography technique described in Japanese Patent Application Laid-Open No. 8-17344.

In the figure, reference numeral (3) denotes a phase shifter made of a transparent material such as SiO ₂ , and is disposed between every two adjacent mask patterns (2) (light transmitting portions). Phase shifter (3)
Has a function of shifting the phase of transmitted light by 180 °.

When a phase shift mask as shown in FIG. 3 is used, the electric field intensity distribution of the light transmitted through the phase shift mask has an inverted pulse shape as shown in FIG.

Therefore, when projecting with the same optical system as in the case of FIG. 2,
The light intensity on the wafer has a separated pattern waveform as shown in the figure, because the light intensity is canceled out at the portion where the pattern images are adjacently overlapped.

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

However, the configuration of the phase shift mask of FIG. 3 can be easily applied to periodic patterns such as line and space patterns, but the light intensity on the wafer can be reduced for arbitrary patterns. It cannot be completely separated and is difficult to apply.

In order to solve this problem, there has been proposed an exposure method using a phase shift mask which can be applied to an arbitrary pattern and can be easily realized from the viewpoint of manufacturing.

FIG. 4 is a principle diagram showing an exposure method using a further improved conventional self-aligned phase shift mask described in, for example, "IEDM Conference" in 1989.

In this case, the phase shifter (3) is formed so as to be mounted on the upper surface of 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 inverted, and the light intensity formed on the wafer is reliably separated irrespective of the pattern arrangement as shown in the figure.

Next, referring to the process chart shown in the sectional view of FIG.
A method of manufacturing the conventional phase shift mask shown in FIG. 4 will be described.

First, as shown in step (a), a mask pattern (2) and a material film of a phase shifter (3) are laminated on a glass substrate (1), and a resist pattern (4) is further formed on the phase shifter (3). To form

Subsequently, as in step (b), a mask pattern (2) and a phase shifter (3) having a shape corresponding to the resist pattern (4) are formed by etching, and the resist pattern (4) is removed.

Next, as in the step (c), isotropic etching for processing only the mask pattern (2) is performed, and the width of only the mask pattern (2) is made smaller than that of the phase shifter (3). Thereby, a mask pattern (2) having a phase shifter (3) as shown in FIG. 4 is formed on the glass substrate (1).

The phase shift mask thus formed is subjected to step (b)
Or, after (c), a defect inspection such as a chipped pattern is performed. However, in the isotropic etching in the step (c), the processing accuracy tends to vary due to foreign substances and the like existing between the mask pattern (2) and the phase shifter (3), and the controllability is poor. Therefore, there are many factors of manufacturing variation, and the reliability of defect inspection and repair is poor.

[Problems to be Solved by the Invention] As described above, the conventional phase shift mask and the method for manufacturing the same are such that only the mask pattern (2) is isotropic after etching the mask pattern (2) and the phase shifter (3). In addition, there is a problem that it is difficult to inspect and correct defects and that controllability of processing accuracy, which must be strictly controlled, is poor due to the nature etching.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a phase shift mask which can be easily inspected and corrected for defects and has good controllability and a method of manufacturing the same.

[MEANS FOR SOLVING THE PROBLEMS] A method for manufacturing a phase shift mask according to claim 1 of the present invention includes a step of forming a mask pattern of MoSi on a transparent substrate, and a step of oxidizing the mask pattern to form a mask. Forming a phase shifter made of MoSi oxide at the periphery of the pattern.

The phase shift mask according to claim 2 of the present invention includes a transparent substrate, a mask pattern formed on the transparent substrate, and a Mo pattern formed around the mask pattern.
And a phase shifter made of Si oxide.

In the method for manufacturing a phase shift mask according to claim 1 of the present invention, after a complete mask pattern of MoSi is formed on a transparent substrate, the peripheral portion of the mask pattern is oxidized over the front surface, and the MoSi is oxidized. The phase shifter made of the oxide of is formed with high precision and uniformity.

Further, in the phase shift mask according to claim 2 of the present invention, the electric field intensity of the transmitted light is inverted by a phase shifter made of an oxide of MoSi formed on the periphery of the mask pattern, and the phase shift mask is formed on the wafer. The light intensity at the edge of the pattern is canceled to improve the resolution.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a phase shift mask and a method for manufacturing the same according to an embodiment of the present invention, in which (1) to (4) are the same as those described above.

First, in step (a), a material film to be a mask pattern (2) is formed on a glass substrate (1), and a resist pattern (4) is formed on the mask pattern (2).

Subsequently, in the step (b), the mask pattern (2) is etched in a shape according to the resist pattern (4) to remove the resist pattern (4).

Next, in the step (c), the mask pattern (2) is oxidized to form a phase shifter (3) having a uniform thickness on the entire peripheral portion of the mask pattern (2).

In this case, the pattern defect inspection and correction are performed after the step (b), whereby a complete mask pattern (2) according to the required accuracy is formed.

Further, the thickness of the phase shifter (3) formed in the step (c) can be easily controlled by controlling the oxidation time, and there is no possibility that a defect occurs in the phase shifter (3). It is not necessary to perform the inspection after (c).

Thus, as shown in FIG. 1 (c), the glass substrate (1)
A phase shift mask on which a predetermined mask pattern (2) and a phase shifter (3) that uniformly covers the periphery of the mask pattern (2) are formed is completed.

The material of the mask pattern (2) may be any material that can sufficiently block light (g-line, i-line, excimer laser, etc.) used in photolithography and becomes transparent after oxidation. It is desirable to use excellent MoSi.

In addition, when the thermal oxidation treatment is used as in the above-described embodiment, the controllability of the oxide film thickness serving as the phase shifter (3) can be further improved, and the high-precision phase shifter (3) can be formed. .

[Effects of the Invention] As described above, according to the first aspect of the present invention, a step of forming a MoSi mask pattern on a transparent substrate, and a step of oxidizing the mask pattern to form a MoSi Forming a phase shifter made of an oxide of the above, after forming a complete mask pattern on the transparent substrate, oxidize the entire periphery of the mask pattern to form the phase shifter with high precision and uniformity Therefore, there is an effect that a method of manufacturing a phase shift mask that can be easily inspected and corrected and has good controllability can be obtained.

According to the second aspect of the present invention, a transparent substrate, a mask pattern formed on the transparent substrate, and a phase shifter made of an oxide of MoSi formed around the mask pattern are provided. The phase shifter at the periphery of the mask pattern inverts the electric field intensity of the transmitted light, thereby canceling the light intensity at the edge of the pattern on the wafer to improve the resolution, making defect inspection and repair easy. In addition, a phase shift mask having good controllability can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a phase shift mask and a method of manufacturing the same according to an embodiment of the present invention in a sectional view, FIG. 2 is a principle view showing a conventional exposure method by photolithography, and FIG. FIG. 4 is a principle view showing an exposure method by photolithography, FIG. 4 is a principle view showing a further improved conventional photolithography exposure method, and FIG. 5 is a sectional view showing a method of manufacturing the phase shift mask in FIG. FIG. (1)... Glass substrate (transparent substrate) (2)... Mask pattern (3)... Phase shifter In the drawings, the same symbols indicate the same or corresponding parts.

Claims (2)

(57) [Claims] 1. A phase forming method comprising: forming a MoSi mask pattern on a transparent substrate; and oxidizing the mask pattern to form a phase shifter made of MoSi oxide around the mask pattern. Shift mask manufacturing method. 2. A phase shift mask comprising: a transparent substrate; a mask pattern formed on the transparent substrate; and a phase shifter made of MoSi oxide formed around the mask pattern.