JPS6352142A - Photomask - Google Patents

Abstract

PURPOSE:To obtain a sharp mask superior in durability and high in precision by laminating on a substrate, 2 layers composed of 2 thin film layers made of chromium oxide and nitride and a thin chromium film layer, and rendering their etching speeds same. CONSTITUTION:The mask superior in durability and high in precision and capable of forming an image without forming level differences in the sections of the layers due to undercutting of one of them by successively laminating on the transparent substrate 6 the 50-100nm thick light-shading chromium film layer 7, and the 20-40nm thick reflection-preventing film layer 8 made of a mixture of chromium oxide and chromium nitride, and controlled in the etching speed same as the layer 7, and then, patterning this surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photomask and a photomask substrate used for manufacturing semiconductor devices, ICs, LSIs, etc.

As a photomask, which is the original plate for printing extremely fine circuit images etc. onto wafers such as semiconductors with high precision, there are emulsion masks that use inexpensive high-resolution drying plates, as well as highly durable hard masks. Examples include chrome masks, single-sided low-reflection chrome masks, double-sided low-reflection chrome masks, and silicone masks.

Generally, hard masks with excellent resolution are used for high-precision applications, but single-layer chrome masks have a high surface reflectance, which tends to cause multiple reflections between the mask and the wafer. To prevent this, we use a single-sided low-reflection chrome mask with an anti-reflection layer made of chromium oxide on the front surface, and a double-sided low-reflection chrome mask with an anti-reflection layer on the back side for automatic mask aligner operation. It is used as a multilayer mask.

By the way, as mentioned above, this multilayer structure mask has advantages such as a wide exposure latitude when printing patterns on a wafer and the ability to operate a Kasbar type auto aligner, but on the other hand, it cannot be used as a mask itself. When forming an image, it is difficult to create a mask with superior image quality and durability compared to a single-layer chrome mask.

Specifically, when etching and patterning the light shielding layer of the multilayer structure using a well-known photolithography process, the etching rate of the chromium layer and the chromium oxide layer laminated on the top or bottom surface of the chromium layer is slow. This is due to different factors. In normal cases, the etching rate of the chromium oxide layer is several times slower than that of the chromium layer.
For this reason, we used a two-layer single-sided low-reflection chrome mask and a 3M
In the case of a structured double-sided low-reflection chromium mask, as shown in FIG. 1 (a) and (b), the uppermost chromium oxide layer 1
Since the etch rate of the lower chromium layer 2 is faster, the amount of undercut of chromium M2 becomes larger, creating a step in the cross-sectional shape between the two layers, and creating an eaves made of the chromium oxide layer around the image. Become. In the figure, 3 is a transparent substrate.

On the other hand, since the etching rate changes greatly in the middle of the film, the entire film is likely to be etched non-uniformly, resulting in loss of image sharpness. For example, as shown in FIG. The reason why it is easy to cause stickiness and worm-shaped edges, and the formation of eaves around the pattern is a big problem is that this eave is a film several hundred thick that protrudes from the pattern edges and is extremely fragile. The reason is that it is easy to use. In reality, sagging occurs during various cleaning processes during mask manufacture or use, and during adhesion and peeling from the resist surface during transfer, resulting in discontinuous clinging and insect-like edges around the image.

The above phenomenon is contrary to the original use of high-precision transfer, and in particular, rotation is used in the manufacture of advanced semiconductor devices such as VLSI. On the other hand, creating an eaves around the mask pattern also means that the optical density gradient of the image edge becomes gentle from a microscopic perspective, and the dimensional values at the time of transfer are easily affected by exposure conditions, resulting in poor accuracy. It may also cause a decline.

The usual method to solve these problems is to use fundamentally different methods for forming the chromium film and chromium oxide film. For example, the underlying chromium film is formed by sputtering. In this method, the upper chromium oxide film is formed by vacuum evaporation. This is because the etching rate of a chromium oxide layer obtained by vacuum deposition is faster than that of a chromium oxide film formed by sputtering, and is close to the etching rate of a chromium film formed by sputtering. The reason for this difference in etching rate is unknown, but it is believed that sputtering films are generally denser, whereas vapor deposited films are sparser and easier to obtain with a low degree of oxidation. Seem.

Regardless of this method, if a chromium layer and a chromium oxide layer are laminated using only the normal sputtering method or only the vapor deposition method, the etching rate of the chromium oxide layer is relatively slower than that of the chromium layer as described above. , which will cause overhangs and bumps.

The serious disadvantage of the above-mentioned combination of sputtering and vacuum evaporation is that, first, after the sputtering film is formed, it is taken out of the vacuum and then the evaporated films are laminated again in the vacuum evaporation apparatus. Productivity is extremely low due to the process. Furthermore, in terms of quality, since an oxide film is formed again on a chromium film that has been exposed to the atmosphere, the reproducibility of the film properties of the oxide film deteriorates, and after forming the lower chromium film, the vacuum of the equipment is removed. When the pressure is returned to atmospheric pressure, there is a high probability that dust will be sucked in and adhere to the chromium film, and pinholes are likely to occur in the upper layer chromium oxide film. There are problems such as an increase in the quality instability associated with this.

Of course, it is possible to change the density and degree of oxidation of the film to some extent by changing the film forming conditions by sputtering, vacuum evaporation, etc., and thereby change the etching rate of the film to some extent, but the range is very limited. Moreover, a significant change in the conditions will impair the basic properties of a photomask, such as film strength and chemical resistance, or significantly reduce productivity. For example, when forming a chromium oxide film by sputtering, if a chromium oxide film with a low degree of oxidation is formed by controlling the oxygen partial pressure of the atmosphere, an etching rate closer to that of a chromium film can be obtained.

However, it is very difficult to control the sputtering conditions to form a film in this intermediate oxidation state, resulting in poor reproducibility.Additionally, if the degree of oxidation is too low, the refractive index will increase and the original antireflection effect will be lost. I'll get lost.

The formation of films in the intermediate oxidation state is even more difficult to control in the case of reactive deposition.

In order to solve the above-mentioned problems in the conventional technology, the present inventor investigated various materials to replace the chromium oxide film as an antireflection layer that does not impair the characteristics of the conventional chrome mask.
As a result of research, the above problems can be solved by laminating a mixed composition film of chromium nitride and chromium oxide on a chromium film as an antireflection layer, and a mask with significantly superior characteristics and high productivity can be obtained. This discovery led to the present invention.

The reason for this is that the etching rate of a chromium nitride film is faster than that of a chromium oxide film, and by appropriately changing the composition ratio of chromium oxide and chromium nitride, the etching rate can be varied over a fairly wide range. This is because it becomes possible to control.

This mixed composition film of chromium oxide and chromium nitride has almost the same chemical resistance and optical properties as the conventionally used chromium oxide film, and is free from the above-mentioned problems and is highly durable. Accurate images can be achieved.

As described above, the photomask substrate of the present invention is characterized by having a structure in which a mixed composition film of chromium oxide and chromium nitride as an antireflection layer is laminated on a chromium film as a light shielding layer. be.

Further, the photomask of the present invention is characterized in that the above-described laminated film on a transparent substrate is provided in a patterned manner.

The present invention will be explained in more detail below.

FIG. 3 is a schematic diagram showing the cross-sectional structure of a single-sided low-reflection chrome mask according to the present invention. A light-shielding layer 7 is usually formed with a film thickness of 5 on a transparent substrate 6 made of soda lime glass, borosilicate glass, quartz glass, sapphire, etc. with a smooth surface.
A chromium oxide film with a thickness of 200 to 1000 and a mixed composition of chromium nitride was provided thereon as an antireflection layer 8, and this laminated film was patterned. It is something.

The composition ratio of the mixed composition film depends on the film creation conditions, but if the interlayer is expressed as CrxNyOz, usually x = 1° y = 0
．． 1-0.3. A range of z = 0.8 to 1.4 is suitable. In reality, it is necessary to select the optimal value of X+y*Z that matches the etching rate of each film in accordance with the film forming apparatus and forming conditions. The method for producing the above film is Cr x
Sputtering method using a target with a composition of N y Oz, N2 gas 10! It is possible to apply a reactive sputtering method using a gas atmosphere, a vacuum evaporation method using a Cr x N y OZ sample, a reactive evaporation method using an N2 gas or O2 gas atmosphere, etc., and each method can achieve the optimal X+
By selecting the yrZ value, it is possible to produce a multilayer mask blank in the same way without venting even -degrees into the atmosphere.

The pattern production method is the same as that of normal photolithography or electron beam lithography. In the former method, if etching is performed using perchloric acid and ceric ammonium nitrate, or other common etching solutions, the above-mentioned process can be achieved. It is possible to obtain a sharp, high-precision mask that is highly durable and does not have bulges, stickiness, cracks, etc. Furthermore, even after the obtained mask was subjected to ultrasonic cleaning, scrubber cleaning with a rotating brush, and high-pressure water cleaning, there was no change in image quality, and no damage to the image edges was observed even after repeated transfer to wafers. do not have.

The present invention will be explained in detail below using examples.

Example A chromium layer was first formed to a thickness of 500 mm by an inert sputtering method using argon gas and a chromium target on a soda lime glass substrate whose surface had been polished sufficiently smooth. Using a chromium nitride mixed composition target, a chromium oxide and chromium nitride mixed composition film was deposited to a thickness of 300 mm by sputtering to obtain a single-sided low-reflection chromium mask blank.

The gas pressure during the formation of the first layer chromium film is lXl0-”T o
The distance between the rre substrate and the target was 5a11, and the sputtering speed was 100 people/min.

In addition, the gas pressure during film formation of the second layer thermal composition film is the same < I
Xl0-”Torr, distance between substrate and target is 5a
1. Target composition is CrxNyOz, x:y:z=
1: 0.3: 1.3. Sputtering speed is 4
It was 0 people/min.

The obtained mask blank was plated by a well-known photolithography process to obtain a very sharp image with a minimum line width of 1.0-. The photoresist used in the photolithography process was AZ-1350 (
(manufactured by Silapray), the film thickness is 0.5-, and the etching solution for the chromium film and mixed composition film is (NH4)2Ce(N03): ceric ammonium nitrate 65 g HCI204: perchloric acid 43ccH,
O: A solution consisting of 1000 cc of deionized water, the solution temperature was 20° C., and the etching time was 40 seconds.

The photomask thus obtained was washed with high pressure water using a plate cleaner manufactured by Ultratic, but no change in image quality was observed. The water pressure at this time was 2000 psi and the washing time was 2 minutes.

As is clear from the above explanation, the present invention has superior durability compared to conventional products.

A photomask capable of forming highly accurate images can be obtained.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional schematic diagram of a conventional multilayer structure photomask, FIG. 2 is a plan view showing the shape of an image edge of a conventional multilayer structure photomask, and FIG. 3 is a multilayer structure photomask of the present invention. FIG. 2 is a schematic partial cross-sectional view of a mask. 6...Transparent substrate 7...Chromium film 8...
chromium oxide film

Claims (1)

[Claims] 1. A photomask equipped with a patterned multilayer light shielding film consisting of a first thin film layer and a second thin film layer formed on a transparent substrate, the first thin film layer being made of chromium, The second thin film layer has two main components, chromium oxide and chromium nitride, and the oxidation layer is formed so that the etching rate of the first thin film layer and the etching rate of the second thin film layer are the same. A photomask characterized by a combination of chromium and chromium nitride.