JPS6352141A - Photomask - Google Patents

Abstract

PURPOSE:To obtain a sharp mask superior in durability and high in precision by laminating on a substrate 3 layers composed of 2 thin film layers made of chromium oxide and nitride and an intermediate thin chromium film layer sandwiched between both, and rendering their etching speeds same. CONSTITUTION:The sharp mask superior in durability and high in precision is obtained with high productivity without forming level differences in the sections of the layers 8, 7, and 8 due to undercutting of one of them by successively laminating on the transparent substrate 6 the 30-40nm thick composite film layer 8 made of a mixture of chromium oxide and chromium nitride, on this layer the 40-100nm thick chromium film layer 7, and on this layer, again the same mixture film layer 8 same in thickness by sputtering or the like without taking it out in the air and then, patterning this surface, because the films 8 and the films 7 have been formed so as to be same as each other in the etching speed.

Description

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

Photomasks, which are the original plates for repeatedly and accurately printing extremely fine circuit images on semiconductor wafers, include emulsion masks that use inexpensive high-resolution drying plates, and chrome masks that are highly durable hard masks. There are masks, single-sided low-reflection chrome masks, double-sided low-reflection chrome masks, silicone masks, etc.

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, although this multilayer 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, 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. 1. Normally, the etching rate of the chromium oxide layer is several times slower than that of the chromium layer.
For this reason, in the case of a two-layer structured single-sided low-reflection chrome mask and a three-layer structured double-sided low-reflection chrome mask, as shown in FIG. 1 (a) and (b), the topmost chromium oxide layer 1
Since the etch rate of the lower chromium layer 2 is faster, the amount of undercut of the chromium layer 2 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 speed changes greatly in the middle of the film, the entire back side is likely to be etched non-uniformly, resulting in loss of image sharpness, and 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 intended use of high-precision transfer, and is particularly difficult to use in the manufacture of advanced semiconductor devices such as VLSIs. 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. In addition, significant changes in the conditions may impair the basic properties of a photomask such as film strength and chemical resistance, or significantly reduce productivity. For example, When a chromium oxide film is formed by a sputtering method, 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, to form a film in this intermediate oxidation state, the control of sputtering conditions is very fixed and reproducibility is poor.In addition, if the degree of oxidation is too low, the refractive index will increase and the original antireflection effect will be impaired. It ends up.

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. By comparing these facts, we have arrived at 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 in that it has a structure in which a mixed composition film of chromium oxide and chromium nitride as an antireflection layer is laminated on a layer consisting of 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 double-sided low-reflection chrome mask according to the present invention. Film thickness 300~40
A mixed composition film 8 of chromium oxide and chromium nitride is provided,
Then, on top of that, a chromium film 7 with a thickness of 400 to 1000 people is applied.
A mixed composition film 8 of chromium oxide and chromium nitride having the same film thickness is provided thereon again, and this laminated film is patterned.

The composition ratio of the mixed composition film depends on the film creation conditions, but if the interlayer is expressed as Cr x N y Oz, usually x = 1
゜'/ =0.1~0.3. A range of z = 0.8 to 1.4 is suitable. In reality, the optimum x etching speed for each film is matched according to the film creation equipment and creation conditions.
y.

It is necessary to select a value of 2. The method for producing the above film is C.
Sputtering method using a target with composition of r, N 0□, reactive sputtering method using N2 gas, 0□ gas atmosphere, vacuum evaporation method using Crx N y Oz sample, using N2 gas + Oz gas atmosphere -) It is possible to apply reactive vapor deposition methods, etc., each with an optimal x
, y, z values, it is possible to produce a multilayer mask blank in the same way, without even venting to the atmosphere.

The pattern formation 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 general etching liquids, It is possible to obtain a highly durable, sharp, and high-precision mask without the occurrence of 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 film with a mixed composition of chromium oxide and chromium nitride was first formed to a thickness of 400 mm on a quartz glass substrate whose surface had been thoroughly polished by an inert sputtering method using a mixed composition of argon gas, chromium oxide, and chromium nitride. establish. Next, a chromium film was deposited to a thickness of 500 mm using an inert sputtering method using argon gas and a chromium target, and then a chromium oxide and chromium nitride mixed composition film was deposited on top of it using the same method as the first layer. 300 people were trained to obtain double-sided low-reflection chrome mask blanks.

The argon gas pressure during the deposition of the mixed composition films of the first and third layers was 2 x 10-'' Torr, the substrate-target distance was 5a1, the sputtering speed was 70 people/min, and the target composition was CrxN02. as x:y:z=l
:0.2:1.2.

Furthermore, the argon gas pressure during the formation of the second fiCr film was 8
The distance between the substrate and the target layer was 5 dll, and the sputtering rate was 120 people/min. The surface reflectance of the thus obtained mask blank was 5% for the Hg-g line, and the back surface reflectance was 5% for the Hg-g line. Reflectance is 10% for Hg-e line
Met.

The obtained mask blank was plate-made by a well-known photolithography process to obtain a very sharp image with a minimum line width of 0.8-. 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(NO3)s: ceric ammonium nitrate 65g HCQO4: perchloric acid 43ccH20
: A liquid consisting of 1000cc of deionized water,
The liquid temperature was 20° C. and the etching time was 40 seconds.

This photomask was washed with 300W ultrasonic water for 10 minutes.
Furthermore, a high-pressure water washing process of 2000 psi for 2 minutes was performed using an Ultratic plate cleaner, but no abnormalities were observed in the image quality, and high-precision images could be repeatedly transferred onto the wafer. .

As is clear from the above description, according to the present invention, it is possible to obtain a photomask that is more durable than conventional ones and is capable of forming highly accurate images.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional schematic diagram of a conventional multilayer photomask, FIG. 2 is a plan view showing the shape of an image edge of a conventional multilayer photomask, and FIG. 3 is a partial cross-section of a multilayer photomask according to the present invention. It is a schematic diagram. 6...Transparent substrate 7...Chromium film 8...Chromium oxide film Attorney Junnosuke NakamuraFigure 1 (Q) (b) Figure 2Figure 3

Claims (1)

[Claims] 1. A photomask comprising a patterned multilayer light-shielding film in which a first thin film layer, a second thin film layer, and a third thin film layer are sequentially arranged on a transparent substrate, wherein the second thin film The layer is made of chromium, and the first thin film layer and the third thin film layer have two main components, chromium oxide and chromium nitride,
and the etching rate of the first thin film layer and the second thin film layer.
A photomask characterized in that the chromium oxide and chromium nitride are blended so that the etching rates of the thin film layer and the third thin film layer are the same.