JPS6237530B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an X-ray exposure mask having a highly accurate metal absorber pattern used in the manufacture of semiconductor devices.

First, a conventional technique related to absorber pattern formation for an X-ray exposure mask will be explained with reference to FIG. 1, and the problems to be solved will be clarified. FIG. 1 shows two typical examples of conventional absorber pattern forming methods.

In conventional example (1), a metal such as Ti, Cr, Mo, etc. is deposited on a so-called mask substrate layer 2 of SiO ₂ , Si ₃ N ₄ , etc. that covers the surface of a substrate 1 made of a semiconductor crystal such as Si. After depositing a first layer 3 consisting of a metal absorber such as Au, a second layer 4 consisting of a metal absorber such as Au, and a third layer 5 consisting of a metal such as Ti, Cr, Mo, etc., A photoresist film or an electron beam resist film 6 is applied to the metal film 5, and a desired pattern is baked onto the resist film 6 to form a resist pattern 6 on the metal film 5, as shown at a-1 in FIG. Next, a-2
As shown in FIG. 2, holes are formed in the metal film 5 by a plasma etching method using a well-known Freon gas such as CF ₄ using the resist pattern 6 as a mask. After forming holes in the metal film 4 by ion etching or sputter etching, as shown in a-3, the metal film 5 and metal film 3 are etched by plasma etching using a chlorine gas such as CCl ₂ F ₂ .
By removing unnecessary portions, a desired metal absorber pattern 4 as shown in FIG. 1A-4 is obtained on the mask substrate layer 2.

In conventional example (2), after depositing the metal film 3 and the metal film 4 on the mask substrate layer 2 covering the surface of the semiconductor substrate 1, the first layer is deposited on the surface in the same manner as described above. As shown in FIG. b-1, a resist pattern 6 is formed. Next, as shown in b-2, a metal film 5 is deposited by vacuum evaporation or sputtering using this resist pattern 6 as a mask, and then a known lift-off method is used to deposit the resist pattern 6 and its top. The unnecessary metal film 5 is removed to obtain an inverted pattern as shown in b-3. Further, using this metal film pattern 5 as a mask, holes are formed in the metal film 4 by an ion etching method or a sputter etching method as shown in b-4, and then a plasma treatment using a chlorine gas such as CCl ₂ F ₂ is performed. The metal film 5 and unnecessary portions of the metal film 3 are removed by etching, and a first layer is etched onto the mask substrate layer 2.
A metal absorber pattern 4 having an inverted form of the desired pattern as shown in FIG. b-5 is obtained.

As described above, in the conventional absorber pattern forming method in which holes are formed in the metal absorber 4 by ion etching or sputter etching using the metal film pattern 5 as a mask, the film thickness of the absorber pattern is
If it is up to about 0.1 μm, there is no problem. However, the absorber pattern of an X-ray exposure mask is generally 0.4 μm thick in order to obtain a high contrast ratio.
If it is necessary to have a film as thick as above, and considering the blurring of the transferred pattern due to X-rays, the inclination angle θ of the side surface of the pattern is required to be close to 90°.
Furthermore, since mask patterns are transferred in a one-to-one correspondence, very strict requirements are placed on pattern accuracy and uniformity. In contrast, conventional methods meet the standards imposed on absorber patterns for X-ray exposure masks, that is, absorbers with fine pattern dimensions of around 1 μm can be produced with pattern accuracy and uniformity of ±10% or less. High ethifactor (Tanθ). It was extremely difficult to form a pattern with this.

The reason for this is, first, that the metal film 5 is required as a masking material for the absorber pattern, and that it is necessary to make holes in this metal film 5 by either the plasma etching method or the lift-off method. . The so-called plasma etching method is
This is a method in which _CF4 gas, etc. is turned into plasma by high-frequency discharge, and the layer to be processed is made to react with the plasma gas to be gasified.In principle, this is a chemical etching method, and since the etching action is not directional, it is difficult to undercut by side etching. The occurrence of cuts is unavoidable, and the difference in pattern conversion (deviation in pattern width) is very large (±0.3 to ±0.5 μm). Furthermore, the etching uniformity was poor at ±10% on a 2-inch diameter wafer.
Furthermore, impurities in the metal film, the size of crystal grains, etc. tend to cause uneven etching and deterioration in quality of the pattern shape, cross-sectional shape, etc. Furthermore, in the lift-off method, the thickness of the metal film 5 is limited by the thickness of the resist pattern 6, and is generally said to be 20% or less of the resist film thickness. Moreover, the heat effect during vapor deposition of the metal film 5 causes deformation and deterioration of the resist film, degrading the quality of the metal film pattern 5. To avoid this, lowering the vapor deposition temperature reduces the adhesion of the metal film 5. There is a problem. On the other hand, as seen in electron beam resists, resists are generally
There are limitations on heat resistance, film thickness, etc., and therefore there are severe restrictions on manufacturing, such as the thickness of the metal film and the conditions for forming it.

Second, when forming the absorber pattern 4 by ion etching or sputter etching, the metal film 5 itself, which serves as a mask, is also etched. Therefore, the pattern width deviation is determined by the ratio of the etching speed V ₂ of the workpiece metal to the etching speed V ₁ of the mask material V ₂ /V ₁
When V ₂ /V ₁ > 1, the pattern width reduction rate (on one side) is approximately 4 times the mask material etch rate.
Double. Furthermore, the etching factor (tanθ) is almost determined by the etching speed ratio V ₂ /V ₁ ,
It is very small when V ₂ /V ₁ <1, and increases discontinuously when V ₂ /V ₁ >1, but in the conventional method, the limit is etch factor: 2.75 and pattern inclination angle θ: about 70°. , is a well-known fact. Also, the uniformity of etching is ±5 to ±10 on a 2-inch diameter wafer.
%, and furthermore, the pattern accuracy decreases due to variations in pattern width, etch depth (film thickness), etc. due to changes in the etch step (amount) due to re-adhesion of the etched mask material to the etched surface. There are also problems, and there are many obstacles to forming fine, highly accurate, and highly uniform absorber patterns.

Further, the conventional X-ray exposure mask manufactured by the above method has the problem that the absorber pattern is susceptible to mechanical damage due to cleaning etc. during use, making it difficult to maintain accuracy.

The present invention solves the above-mentioned problems of the conventional technology, makes it possible to form a metal absorber pattern with a film thickness of 0.4 μm or more on a semiconductor substrate with high precision and a high tilt angle, and prevents mechanical damage during use. It is an object of the present invention to provide a method for manufacturing an X-ray exposure mask that can appropriately protect a metal absorber pattern from.

A feature of the present invention is that a spacer film of 0.4 μm or more in thickness made of an isotropic inorganic compound or a heat-resistant organic material is formed on an arbitrary base film provided on a semiconductor substrate, and a Using a metal film pattern formed by any method as a mask, holes are opened using a plasma/sputter combined etching method.
Thereafter, a thick metal film made of a metal absorber is deposited by any method to a thickness equal to or less than that of the spacer film pattern, and the metal film pattern and metal thickness are By removing unnecessary parts of the film, a desired metal absorber pattern is formed on the semiconductor substrate,
After removing the spacer film pattern left on the semiconductor substrate until it has a film thickness almost equal to that of the metal absorber pattern, the entire surface of the spacer film pattern and the metal absorber pattern is covered with a protective film, The metal absorber pattern is embedded in a spacer film, and the spacer film is used to reinforce the metal absorber pattern.

_{The plasma} sputter composite etching method was recently developed by the present inventors, and _it
A mixed gas (mixing ratio 5:1 to 12:1, pressure 10 ^-2 to ^{10 -1} Torr) of Freon gas such as C ₂ H ₂ and hydrocarbon gas such as C ₂ H ₄ is placed between parallel electrodes. The material is turned into plasma by high-frequency discharge, and the processing is performed by a combined action of sputter etching by colliding the positive ions of the plasma gas with the layer to be processed placed near the cathode, and chemical etching due to the reactivity of the plasma gas. This plasma etching method is non-directional, whereas known plasma etching methods are non-directional.
The sputter composite etching method has strong directivity in the etching action, has less undercuts due to side etching, and can obtain a processed surface with excellent pattern accuracy, uniformity, and etching pattern. In contrast to using an inert gas such as Ar, this plasma
The sputter composite etching method uses excited F,
Because it involves a chemical etching effect in which gas atoms such as C and H react with the layer to be processed and gasify it,
There is little variation in pattern width, etching depth, etc. due to re-deposition of the etched material, and there is no deterioration in pattern accuracy due to re-deposition. (Please refer to the specification of Japanese Patent Application No. 51-30966 filed by Mr.

The material for forming the spacer film is SiO ₂ ,
In addition to isotropic inorganic compounds such as Si ₃ N ₄ and PSG (phosphorus glass), heat resistance that does not cause deformation or alteration at the deposition temperature (200 to 300°C) of the metal film pattern formed on the spacer film Organic materials such as polyimide, parylene, etc. can also be used. When a plasma-sputter composite etching method is applied to a spacer film made of these materials, the etching speed is about 100% compared to the etching speed of the metal film pattern that serves as a mask.
It is 10 times larger, which not only makes it possible to minimize the deviation in pattern width due to etching of the mask itself, but also makes it easy to obtain a high side inclination angle of 80° or more for the spacer film pattern. - The characteristics of the sputter composite etching method can be fully utilized. Therefore, by depositing a thick metal film between these spacer film patterns, a metal absorber pattern with high precision and a high tilt angle that fully satisfies the standards required for X-ray exposure masks can be easily realized. be able to.

A metal such as Ti, V, TiO ₂ , V ₂ O ₅ or a compound thereof is used for the metal film serving as a mask for the spacer film pattern. In the present invention, plasma-sputter composite etching is mainly applied to opening holes in a spacer film, but if this method is also applied to opening holes in a metal film pattern formed on a spacer film, it will be possible to use other known etching methods. A more accurate mask pattern can be obtained than with the method described above.

The base film on the semiconductor substrate serves as a stopper film to prevent damage to the substrate during etching of the spacer film, and is made of a metal film such as polycrystalline Si, Ti, V, Cr, Mo, or the like.

The unnecessary thick metal film deposited on the spacer film pattern can be removed by a known lift-off method. At this time, the spacer film pattern is left on the semiconductor substrate and the metal thick film pattern is embedded in the spacer film, and the spacer film is used to reinforce the metal thick film pattern.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 is a sectional view for explaining the process of forming a metal absorber pattern of an X-ray exposure mask according to the present invention.

As shown in Figure 2 c-1, the surface of a substrate 1 made of semiconductor crystal such as Si is covered with a mask substrate layer 2 of SiO ₂ , Si ₃ , N ₄ etc., and a composite material is deposited on this mask substrate layer 2. Polycrystalline Si, which becomes a stopper film for etching,
A base film 7 of Ti, V, Cr, Mo, etc. is deposited to a thickness of about 500 to 1000 Å by vacuum evaporation or sputtering. On this base film 7, SiO ₂ , Si ₃ N ₄ ,
A spacer film 8 made of an isotropic inorganic compound such as PSG (phosphorus glass) or a heat-resistant organic material such as polyimide is deposited by sputtering or the like, and Ti, V, etc. Films made of metals such as Ti, O ₂ , V ₂ O ₅ or their compounds (hereinafter simply referred to as metal films)
5 is deposited by sputtering or the like. Next, a photoresist film or an electron beam resist film 6 is applied on the surface of the metal film 5, and patterned by a well-known method to form a resist pattern 6 as shown in c-2. Next, a hole is formed in the metal film 5 as shown in c-3 using a plasma sputter composite etching method, and then, using the metal film pattern 5 as a mask, a plasma sputter composite etching method is used to etch c-4. As shown in FIG. 2, holes are formed in the spacer film 8. Thereafter, the exposed portions of the metal film 5 and base film 7 remaining on the spacer film 8 are removed by a known plasma etching method using a chlorine gas such as CCl ₂ F ₂ . c-5 shows this state. next,
As shown in c-6, M ₀ , Ag, which has a large contact potential difference with a different metal as the base film of the metal absorber,
Metal film 9 such as Ti, Cr, etc. and as a metal absorber
After depositing a thick metal film 4 such as Au by sputtering or the like, use an etching solution that forms local batteries due to the contact potential difference and increases the side etching of the underlying film to form a spacer film pattern as shown in c-7. Only unnecessary portions of the metal film 9 and the thick metal film 4 are removed by lift-off, leaving only the metal film 8, thereby forming a desired metal absorber pattern 4 on the substrate. At this time, if the spacer film 8 is also removed using an etching solution that etches the spacer film 8 itself, as shown in c-8, it will remain on the substrate as in the conventional X-ray exposure mask. The metal absorber pattern 4 becomes susceptible to mechanical damage.

FIG. 3 is a sectional view showing an example of a process for obtaining an inverted pattern of the pattern obtained in the process of FIG. 2.

FIG. 3 d-1 shows that a base film 7, a spacer film 8, and a metal film 5 are deposited on a mask substrate layer 2 covering the surface of a semiconductor substrate 1, and then a metal film 5 is deposited.
A resist pattern 6 is shown formed on the top by a well-known method. Next, as shown in d-2,
High etch resistance against plasma/spatter composite etching using resist pattern 6 as a mask
After depositing the metal film 10 of Cr, Al, Au, etc., the resist pattern 6 and unnecessary metal film 10 thereon are removed by a known lift-off method, and the d-
3. Obtain an inverted pattern of the desired pattern as shown in 3. Next, using this metal film pattern 10 as a mask, holes are formed in the metal film 5 as shown in d-4 by a plasma-sputter composite etching method, and then etched using a known plasma etching method using chlorine-based gas or a chemical etching solution. As shown in d-5, only the unnecessary metal film 10 on the metal film 5 is removed. By using the metal film pattern 5 thus obtained as a mask and proceeding with the steps from c-4 onward in Figure 2, a metal absorber pattern in the form of an inverted version of the desired pattern can be obtained on the substrate. .

FIG. 4 is a cross-sectional view showing another example of the process for obtaining an inverted pattern.

As shown in FIG. 4e-1, a base film 7 and a spacer film 8 are deposited on the mask substrate layer 2, and a resist pattern 6 is formed on the surface of the spacer film 8 by a known method. Next, using this resist pattern 6 as a mask, as shown in e-2, a metal film 5 is deposited, and then the resist pattern 6 and unnecessary metal film 5 thereon are removed using a known lift-off method. Then, an inverted pattern of the desired pattern as shown in e-3 is obtained. This metal film pattern 5
By proceeding with the steps from c-4 onward in FIG. 2 using this method, a metal absorber pattern having an inverted form of the desired pattern can be formed on the substrate.

FIG. 5 is a sectional view showing a part of the manufacturing process of the absorber pattern embedded mask.

After going through the steps in Figure 2 c-2 to c-6, Figure 5 f
1, a spacer film pattern 8 and a metal absorber pattern 4 are formed on the mask substrate layer 2. Next, the spacer film pattern 8 is removed until it has a film thickness approximately equal to that of the metal absorber pattern 4 using a plasma sputter combined etching method or a chemical etching solution that etches only the spacer film. After that, over the entire surface of the metal absorber pattern 4 and the spacer film pattern 8,
Covering with a transparent protective film 11 having high chemical resistance such as a Si ₃ N ₄ film by CVD method or sputtering method or a parylene film by spin coating method, and using spacer film pattern 8 as a part of the mask substrate layer, As shown in f-3, the desired metal absorber pattern 4 embedded in the mask substrate layer is obtained. By using such an embedded type, the mask can be prevented from being damaged and can be cleaned.

Next, an example of the construction conditions and experimental results of plasma/sputter composite etching when forming a metal absorber pattern according to the present invention will be shown.

Construction conditions Gas used: C ₂ F ₆ + C ₂ H ₄ (mixing ratio 12:1) Pressure: 3 × 10 ^-2 Torr High frequency output: 200 W Frequency: 13.56 MHZ Electrode spacing: 35 mm (sample placed on the cathode) Experimental results Product pattern width shift amount: 0.1 μm or less Etching uniformity: ±5% or less/2 inch wafer Pattern side inclination angle (θ): 80° or more Etching factor (tanθ): 5.6 or more As is clear from the above description, the present invention According to the film thickness required for an X-ray exposure mask is 0.4μm
The above-mentioned fine metal absorber pattern can be formed with high precision, high quality (tilt angle of 80° or more), and with good yield, and the resulting X-ray exposure mask has a metal absorber pattern with a spacer film. It is embedded inside and the entire surface is covered with a protective film, so
The major advantage is that the metal absorber pattern will not be damaged by friction during use of the mask, which will not impair precision, and that it will be easy to handle.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a metal absorber pattern forming process according to a conventional method, FIG. 2 is an explanatory diagram of an embodiment of a metal absorber pattern forming process according to the present invention, and FIGS. FIG. 5 is a process explanatory diagram for obtaining an inverted pattern of the pattern obtained in the process, and FIG. 5 is an explanatory diagram showing an example of manufacturing an absorber pattern embedded type X-ray exposure mask according to the present invention. Explanation of symbols, 1... Semiconductor substrate, 2... Mask substrate layer, 4... Metal thick film, 5... Metal film for etching mask, 6... Resist film, 7... Base film for etching stopper, 8 ...Spacer film, 9...
Base film for lift-off, 10...Metal film for inverted pattern mask, 11...Protective film.

Claims (1)

[Scope of Claims] 1.
A method for producing an X-ray exposure mask, the method comprising obtaining a radiation exposure mask. (A) Arbitrary base film and film thickness 0.4μm on semiconductor substrate
A step of forming a spacer film made of the above-described isotropic inorganic compound or heat-resistant organic compound. (B) A step of forming a metal film pattern on the spacer film. (C) Sputter etching by turning a mixed gas of Freon gas and hydrocarbon gas into plasma by high-frequency discharge, and causing positive ions of the plasma gas to collide with the layer to be processed placed near the cathode, and the plasma gas A step of forming a spacer film pattern by opening holes in the spacer film using the metal film pattern as a mask by a combined effect with chemical etching due to the reactivity of etching. (D) A step of depositing a metal thick film made of a metal absorber between and on the spacer film pattern to a thickness equal to or less than that of the spacer film pattern. (E) A step of removing unnecessary portions of the metal film pattern and thick metal film on top of the spacer film pattern while leaving the spacer film pattern to form a desired metal absorber pattern. (F) After removing the spacer film pattern left on the semiconductor substrate until the film thickness is approximately the same as that of the metal absorber pattern, the entire surface of the spacer film pattern and metal absorber pattern is covered with a protective film. The process of doing.