JPH01214859A - Mask - Google Patents

Abstract

PURPOSE:To reduce the variance of dimensions due to ghost or flare by forming a multilayered film whose reflectance is minimum for the wavelength of excimer laser light. CONSTITUTION:A light shielding film 3 consisting of a chromium film and a low reflection film 4 consisting of a chromium oxide film are formed on a translucent substrate 2 consisting of quartz by the sputtering method or the CVD method. The film thickness of the film 4 is selected in accordance with the classification of excimer laser light used for exposure. An electron beam resist pattern is formed on the film 4 and selectively etched to form a light shielding pattern 5 consisting of films 3 and 4. Thus, a mask where the reflectance of the surface of the pattern 5 is minimum for the wavelength of excimer laser light is obtained. The pattern may consist of three layers, namely, a low reflection film, a light shielding film, and another low reflection layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a mask, and is a technique that is particularly effective when applied to a mask when excimer laser light is used as exposure light.

[Conventional technology]

Japanese Patent Application Laid-Open No. 61-80820 describes a reticle used in a reduction projection exposure apparatus that transfers a pattern onto a wafer in the wafer process in the manufacturing process of semiconductor devices.
It is stated in the No.

The outline is as follows.

In other words, with the miniaturization of semiconductor device patterns, reduction projection exposure equipment with high resolution and high overlay accuracy has become the mainstream pattern transfer equipment, but ghosts and flares caused by reflected light in the optical system have become common. The occurrence of transfer defects such as these is becoming more and more noticeable. In particular, it has been recognized that the influence of light reflection from the front and back surfaces of the light-shielding pattern made of the metal thin film of the reticle is significant. Therefore, as a countermeasure against the transfer failure, a low-reflection film is provided on the surface of the light-shielding pattern so that the reflectance from the front and back surfaces of the light-shielding pattern of the reticle is in the range of 0 to 30%.

[Problem that the invention sought to solve]

It is known that light reflection from the reticle used in reduction projection exposure equipment affects dimensional variations due to transfer defects such as ghosts and flares, and this effect becomes more pronounced as patterns become finer. .

In order to eliminate the influence of this light reflection, the G
The thickness of the low-reflection film was adjusted so that the reflectance of the light-shielding pattern surface of the reticle was 20% or less at 11ne (wavelength: 436 nm).

By the way, with the miniaturization of semiconductor device patterns, the wavelength of light used for pattern transfer to semiconductor wafers is shifting from the 436 nm of the G11ne currently used to an even shorter wavelength in order to improve resolution. be. One of them is excimer laser, which has a wavelength of 248 nm.
A KrF excimer laser with a wavelength of 282 nm, a XeCl excimer laser with a wavelength of 308 nm, and an XeF excimer laser with a wavelength of 351 nm are being considered. In addition, in mask blanks having a one-dimensional multilayer film with a two- to three-layer film structure, which is the substrate of the reticle used in the current reduction projection exposure apparatus that uses G11ne as the exposure light, the reflectance of G11ne is about a few percent. However, in the case of the excimer laser mentioned above, the reflectance is about 20%, and when the excimer laser light is used as the exposure light, dimensional variations due to transfer defects such as ghosts and flares are increased due to the effect of miniaturization of dimensions. It is thought that it will become noticeable.

As mentioned above, the reflectance of excimer laser light is about 20% in the current reticle substrate, which has a light-shielding multilayer film with a two- to three-layer film structure, and the reflectance of excimer laser light is about 20%. The inventors of the present invention have conducted extensive studies and discovered that there is a problem in pattern transfer using a reduced projection exposure apparatus, in which dimensional variations due to transfer defects such as ghosts and flares become noticeable, and the present invention was developed to solve this problem. I did it.

An object of the present invention is to provide a mask that can reduce dimensional variations caused by transfer defects such as ghosts and flares in pattern transfer by a projection exposure apparatus using excimer laser light as exposure light.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

In this specification, except for special uses, the definition of a mask includes a photomask having a light-shielding pattern of the same size as the transferred pattern used in a projection exposure device, and a photomask having a light-shielding pattern multiple times the size used in a reduction projection exposure device. A reticle having a transparent pattern, the photomask, and a mask blank that is a starting material for manufacturing the reticle are collectively referred to as a mask.

[Means to solve the problem]

Representative inventions* among the inventions disclosed in this application
A brief explanation of i is as follows.

That is, in a mask when excimer laser light is used as exposure light, a light-shielding film, a low reflection film, or a low reflection film, which is laminated from the light-transmitting substrate side on one main surface of a light-transmitting substrate, -Light film.

The thickness of the low-reflection film is adjusted so that the reflectance from the light-shielding multilayer film having a 2- to 3-layer structure consisting of the low-reflection film becomes minimum at the wavelength of the exci-laser light.

[Effect]

According to the above means, the intensity of the reflected light can be reduced by causing the reflected light at the interface between the low reflection film and the light shielding film to interfere with the reflected light at the interface between the low reflection film and the air or the quartz substrate. Therefore, it is possible to reduce the reflectance from the light-shielding multilayer film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described below along with an embodiment in which the present invention is applied to a droplet used in a reduction projection exposure apparatus using excimer laser light as exposure light.

〔Example〕

1 to 3 are diagrams for explaining a reticle used in a reduction projection exposure apparatus using an excimer laser as an exposure light, which is an embodiment of the present invention. Figure 1 is a cross-sectional view of a reticle having a light shielding pattern with a two-layer structure of a chromium film and a chromium oxide film from the quartz substrate side, and Figure 8g2 is a drawing showing the reflection characteristics of a mask blank having a film with the same structure as the reticle. It is. Further, FIG. 3 is a drawing showing an optical system of an excimer laser reduction projection exposure apparatus.

As shown in FIG. 3, the reduction projection exposure apparatus 12 that uses an excimer laser as exposure light reflects excimer laser light from an excimer laser light source 13 through a reflecting mirror 14, a scanning lens 15,
The pattern of the reticle 1 is irradiated onto a condenser lens 17 via the scanning mirror 16 and the scanning lens 15, and converted into parallel light by the condenser lens 17. It is configured to form a reduced image on the surface of the wafer 19.

The reticle 1 used in the above-mentioned excimer laser reduction projection exposure apparatus 12 has a light-shielding pattern that is multiple times, for example, five times as large as the pattern transferred onto the semiconductor wafer 19, and has a transparent pattern as shown in FIG. On one main surface of the optical quartz substrate 2, from the quartz substrate 2 side, a chromium film 3 with a thickness of about 800A as a light-shielding film and a chromium oxide film 4 with a predetermined thickness as a semi-transparent low reflection film are formed. The light-shielding pattern 5 having a predetermined shape and having a two-layer film structure is arranged in a predetermined arrangement. That is, a chromium oxide film 4 of a predetermined thickness, which is a semi-transparent, low-reflection film, is laminated on the surface of a chromium film 30 of about 800A, which is an NFT film.

Here, the thickness of the chromium film 3, which is a light-shielding film, has a light transmittance of about ]/1000, and is set to about 800A in order to have sufficient light-shielding properties. What is the thickness of the chromium oxide film 4? ! The reflectance from the surface of the original pattern 5 is set to be minimal. The reflectance varies depending on the wavelength of the excimer laser light,
For example, in the case of a KrF excimer laser with a wavelength of 248 nm, 1
In the case of a KeBr excimer laser with a 20A brightness and a wavelength of 282 nm and a KeCl excimer laser with a wavelength of 308 nm, it is set to about 160A, respectively, and in the case of a XeF excimer laser beam with a wavelength of 351 nm, it is set to about 200A. At this time, the reflectance from the surface of the light shielding pattern 5 is approximately 3 to 5%, which is extremely small. Therefore, the reflected light (2) from the surface of the reduction lens of the reduction optical system 18 and the reflected light (2) from the surface of the semiconductor wafer 19 in FIG. ! Dimensional variations caused by transfer defects such as ghosts and flares caused by reflection on the surface of the original pattern 50 are suppressed.

Next, the effect of reducing the reflectance of the low reflection film made of the chromium oxide film 4 in the reticle 1 having the above structure will be described. Since the low-reflection film made of the chromium oxide film 4 is semi-transparent, the reflected lights (2) and (2) from the reduction lens of the reduction optical system 18 and the surface of the semiconductor wafer 190 in FIG. 3 reach the light-shielding pattern 5 of the reticle 1. In this case, the reflected light from the light shielding pattern 5 is reflected light from the interface between the chromium film 3 and the chromium oxide film 4 due to the different refractive indexes of the chromium M3 of the light shielding pattern 5, the chromium oxide film 4, and the air. and reflected light from the interface between the chromium oxide film 4 and air. On this occasion,
The light reflected from the interface between the chromium film 3 and the chromium oxide film 4 and the light reflected from the interface between the chromium oxide film 4 and air interfere and weaken each other, thereby reducing the light reflected from the surface of the light shielding pattern 5. is now possible. That is, the reflectance of the light shielding pattern 50 is reduced by interference between the light reflected from the interface between the chromium film 3 and the chromium oxide film 4 and the light reflected from the interface between the chromium oxide film 4 and air. Since the reflectance is reduced by the above action, the reflectance of the surface of the light shielding pattern 5 depends on the thickness of the chromium oxide film 4 and the wavelength of the excimer laser beam. FIG. 2 shows the wavelength dispersion of this reflectance and the film thickness dependence of the chromium oxide film 4.

The figure shows a mask blank with the same film structure as reticle 1, by varying the thickness of the chromium oxide film, which is a low reflection film, and measuring the dependence of reflectance on light wavelength using a Hitachi spectrometer model 124. It is a drawing showing the obtained reflectance characteristic curves 6 to 11. As shown in FIG. 2, the wavelength range in which the reflectance from the mask blank becomes minimum differs depending on the thickness of the chromium oxide film, which is a semi-transparent low-reflection film. For example, K at a wavelength of 248 nm
In the case of rF excimer laser, the reflectance becomes minimum between the reflectance characteristic curve i@7 for a chromium oxide film thickness of 60A and the reflectance characteristic curve i@7 for a chromium oxide film thickness of 60A. ing.

Further, in the case of the X e Br excimer laser with a wavelength of 282 nm and the XeCl excimer laser with a wavelength of 308 nm, the reflectance becomes minimum at about 160 A, which is the chromium oxide film thickness of the reflectance characteristic curve 7. Also, the wavelength is 351 nm
In the case of the XeF excimer laser, the reflectance becomes minimum at about 200 A, which is the chromium oxide film thickness of reflectance characteristic curve 8. The reflectance of each is extremely small (approximately 5%).For the above reasons, in the excimer laser reduction projection exposure apparatus 12, the K
When the rF excimer laser is used as the exposure source, when the film thickness of the chromium oxide film 4 of the light shielding pattern 5 of the reticle 1 is about 120A, and when the exposure light is an XeBr excimer laser with a wavelength of 282 nm and a XeCl excimer laser with a wavelength of 308 nm, the oxidation The thickness of the chromium film 4 is about 160A, the wavelength is 351
When the exposure light is a XeF excimer laser with a wavelength of 1.5 nm and the thickness of the chromium oxide film 4 is set to about 200 A, the reflectance becomes minimal at about 5%, and dimensional variations due to transfer defects such as ghosts and flares are suppressed. It has become so.

Next, a method for manufacturing the reticle 1 having the above structure will be described. First, a sputtering process is performed on one main surface of a transparent quartz substrate 2.
A chromium film 3 of about 800A is deposited by the tcvn method. A chromium oxide film 4 of a predetermined thickness is deposited thereon in a similar manner. The predetermined film thickness is set here because the optimal film thickness of the chromium oxide film 4 differs depending on the wavelength of the excimer laser light used for exposure light. For example, in the case of a KrF excimer laser with a wavelength of 248 nm, it is about 120λ,
eBr excimer laser and X e with a wavelength of 308 nm
For Cl excimer laser, 16OAa degree, wavelength 351
In the case of a nm XeF excimer laser, a chromium oxide film 4 of about 200 A is deposited. Next, although not shown, an electron beam resist of a predetermined thickness is applied to the entire surface, and an electron beam resist pattern of a predetermined shape is formed by electron beam lithography. Next, selective etching is performed using the electron beam resist pattern as a mask, and after etching, the electron beam resist pattern serving as a mask is removed by oxygen plasma treatment, etc., to form a light-shielding pattern of a predetermined shape made of the chromium film 3 and the chromium oxide film 4. form 5.

As described above, this embodiment uses a two-layer film consisting of a chromium film 3 as a light-shielding film and a chromium oxide film 4 as a low-reflection film in a reticle l used in a reduction projection exposure apparatus 12 that uses excimer laser light as exposure light. It is characterized in that the thickness of the low reflection film is adjusted so that the reflectance of the surface of the light shielding pattern 5 of the structure becomes minimum at the wavelength of the excimer laser light. The functions and effects obtained from the above embodiments can be briefly described as follows.

1) In a reticle used in a reduction projection exposure device that uses excimer laser light as exposure light, a chromium film, which is a light-shielding film, and a chromium oxide film, which is a low-reflection film, are formed on one main surface of a transparent quartz substrate. By adjusting the film thickness of the chromium oxide film in the light-shielding pattern of the two-layer film structure, the light reflected from the interface between the chromium film and the acid fluorium film and the light reflected from the interface between the chromium oxide film and air can be adjusted. make the interference effect of
Since the reflectance of the excimer laser light from the surface of the light shielding pattern can be adjusted to be minimal, it is possible to suppress dimensional variations due to transfer defects such as ghosts and flares.

2) Also, by adjusting the thickness of the chromium oxide film so that the reflectance from the continuous light pattern surface is minimal,
Changes in reflectance due to changes in the thickness of the chromium oxide film can be reduced, and dimensional variations caused by transfer defects such as ghosts and flares can be stably suppressed.

3) As described in 1) and 2) above, it is possible to more easily suppress intra-chip dimensional variations due to transfer defects such as ghosts and flares, thereby improving the quality and yield of semiconductor devices.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor. For example, the thickness of the low-reflection film is adjusted so that the reflectance on the surface of the light-shielding pattern is minimal, but the reflectance does not necessarily have to be minimal, but is sufficient to suppress dimensional variations. Just adjust it accordingly.

In addition, the light shielding pattern has a two-layer film structure consisting of a chromium film, which is an S light film, and a chromium oxide film, which is a low reflection film, in order from the quartz substrate side. Low reflective film.

A three-layer film structure consisting of a light-shielding film and a low-reflection film may also be used. In this case, the reflectance of excimer laser light can be effectively reduced on both sides of the light-shielding pattern. In addition, the light-shielding film is formed of a chromium film and the low-reflection film is formed of a chromium oxide film, but the S-light film may be any continuous light metal thin film, and the low-reflection film is a semi-transparent metal thin film. Anything is fine. For example, the light-shielding film and the low-reflection film can be made of a filtering or semi-transparent film made of molybdenum (Mo), titanium (Ti), tungsten (W), tankle (Ta), and their oxides, nitrides, or silicides. may be formed.

“ In the above explanation, the invention made by the present inventor was mainly applied to a reticle used in an excimer laser reduction projection exposure apparatus, which is the field of application in which the invention was made, and a mask blank, which is the material thereof. The present invention is not limited to this, and can be applied to photomasks used in projection exposure apparatuses. It can also be applied to techniques for reducing reflectance from semiconductor substrates and substrates on which various thin film tubes are deposited on the semiconductor substrates.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, in a mask using excimer laser light as exposure light, a light-shielding film, a low-reflection film, or a low-reflection film, which is laminated on one main surface of a light-transmitting substrate from the light-transmitting substrate side, +1! By adjusting the film thickness of the low-reflection film of a light-shielding multilayer film with a two- to three-layer film structure consisting of an original film and a low-reflection film, the light reflected at the interface between the light-shielding film and the low-reflection film and the low-reflection film can be reduced. The reflectance from the front and back surfaces of the light-shielding multilayer film increases by making the interference effect between the air and the light reflected from the interface with the light-transmitting substrate significant.
Since the wavelength of the excimer laser light can be controlled to be minimal, it is possible to suppress dimensional variations due to transfer defects such as ghosts and flares.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a reticle having an S original pattern consisting of a chromium film and a chromium oxide film, Fig. 2 is a drawing showing the reflection characteristics of a chrome blank having a film with the same structure as the reticle, and Fig. 3 is an excimer laser The optical system of the reduction projection exposure apparatus shows rI! It is Jf. DESCRIPTION OF SYMBOLS 1... Reticle, 2... Quartz substrate, 3... Chrome film, 4... Chrome oxide film, 5... Light shielding pattern, 6
~11...Reflectance characteristic curve, 12...Excimer laser reduction projection exposure device, 13...Excimer laser light source,
14... Reflection mirror, 15... Scanning lens, 16.
...Scanning mirror, 17...Condenser lens, 18.
...Reducing optical system, 19...Cow conductor. Figure 1 Figure 2 Figure 3/':I

Claims (1)

[Claims] 1. In a mask when excimer laser light is used as exposure light, a light-shielding film laminated from the light-transmitting substrate side on one main surface of a light-transmitting substrate, and a low reflection film. The invention is characterized in that the reflectance from a light-shielding multilayer film having a two- to three-layer film structure consisting of a film, a low-reflection film, a light-shielding film, and a low-reflection film is minimized at the wavelength of the excimer laser light. mask. 2. The mask according to claim 1, wherein the optimum film thickness of the low reflection film of the light-shielding multilayer film varies depending on the wavelength of the excimer laser beam. 3. The mask according to claim 1, wherein the light-transmitting substrate is a quartz substrate. 4. The mask according to claim 1, wherein the light shielding film is a chromium film. 5. The mask according to claim 1, wherein the low reflection film is a chromium oxide film.