JPH06282066A - Substrate for phase shift photomask and its production - Google Patents

Abstract

PURPOSE:To easily produce the phase shift photomask having the improved controllability of a phase shift angle by sticking a thin-film optical crystalline material layer consisting of an oxide or fluoride to a substrate. CONSTITUTION:This substrate for the phase shift photomask is constituted by sticking the thin-film optical crystalline material layer 2b onto the substrate 1. More specifically, an unpolished optical crystalline material 2a sliced to about <=1mm thickness is subjected to smooth polishing and washing and is stuck onto the substrate 1 sufficiently washed after plane polishing by sticking the smoothly polished surfaces of both to each other without using adhesives, etc. The resulted substrate 3a is annealed and is ground and polished, by which the phase shift photomask substrate 3 stuck with the thin-film optical crystalline material 2b on the substrate 1 is obtd. Sufficient overetching with the substrate 3b is possible under dry etching conditions of SOG (coated glass). The accurate control of the phase shift angle is executable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift photomask used for manufacturing high density integrated circuits such as LSI and VLSI, and a substrate for phase shift photomask for manufacturing this photomask (phase shift photomask. Blank).

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs are manufactured by a lithographic process, and a photomask used at that time is disclosed in JP-A-58-1.
A reticle of a new concept called a phase shift photomask has been proposed, as disclosed in Japanese Patent No. 73744, Japanese Patent Publication No. 62-59296, and the like. Phase shift lithography using a phase shift photomask is a technique for improving the resolution and contrast of a projected image as compared with a conventional photomask by manipulating the phase of light transmitted through a reticle.

In phase shift lithography, high precision control of the phase shift angle is required in order to improve the resolution and contrast of the projected image at the time of transfer. The phase shift angle is determined by the film thickness and the refractive index of the shifter pattern, and in particular, the control of the film thickness is a big problem in manufacturing the phase shift photomask.

For the etching of the shifter layer, a dry etching method, which is excellent in high precision microfabrication, is used.
The most reliable method for controlling the film thickness of the shifter pattern is
Select a shifter and underlayer material that does not increase the etching rate ratio (selection ratio) of the shifter layer and the underlayer, and perform dry etching for a specific time longer than the time when the shifter layer will be completely removed, that is, ， It is to over-etch. By doing so, a uniform etching depth can be obtained over the entire surface of the substrate.
In addition, overetching may be necessary to adjust the pattern cross-sectional shape.

However, for example, when quartz is used as the underlayer for the glass substrate and commercially available coated glass (SOG; for example, Accuglass 211S manufactured by Allied Signal Co.) is used as the shifter material, the dry etching selection ratio is Only about 1.5 to 2.0 can be obtained,
Even if the minimum necessary over-etching is performed, the glass substrate is etched to such an extent that the phase shift angle is affected. Therefore, in order to accurately control the phase shift angle, it is indispensable to provide a so-called etching stopper layer, which is made of a material having a sufficiently large etching selection ratio with the shifter layer, on the glass substrate.

[0006] As an example of what plays such a role as an etching stopper layer, for example, Japanese Patent Publication No. 61-6166.
No. 4, a transparent conductive film mainly composed of tin oxide, SPIE Vol. 59 of 1463 (1991)
Thin films of oxides or fluorides such as aluminum oxide films and magnesium fluoride films as shown on page 5 are known.

[0007]

However, the transparent conductive film mainly composed of tin oxide has a small transmittance for a wavelength of 350 nm or less, and there is a problem that it cannot be used for exposure in this wavelength range. Further, even when the exposure wavelength is the i-line (365 nm) of a mercury lamp, there are the following problems. That is, the transparent conductive film mainly composed of tin oxide is
It does not have sufficient resistance to dry etching of G and is etched at a rate of about 1.5 nm / min under normal dry etching conditions (etching selection ratio with SOG is about 20). Therefore, the etching stopper layer mainly composed of tin oxide can prevent the quartz substrate from being etched, but the etching stopper layer is reduced in thickness during the above-described overetching.

However, since tin oxide has a large refractive index of approximately 2.0 at the i-line wavelength, the film loss during dry etching causes a phase angle difference. In general, light having a wavelength λ that has passed through a medium having a refractive index n and a film thickness d has a phase angle shift of 2π (n−1) d / λ [rad] as compared with the case of passing through air having the same optical path length. According to this, in the i-line, a film thickness reduction of 1 nm causes a phase angle shift of about 1 degree, and a phase angle shift of as much as 1.5 degrees occurs per minute of overetching, thus forming an accurate phase shifter. Will be difficult. Further, in an actual dry etching apparatus, when the etching rate has a distribution in the substrate, this distribution produces a film thickness distribution of the etching stopper layer mainly composed of tin oxide, and therefore, a phase angle distribution in the substrate is obtained. There is also the problem that it will occur.

On the other hand, optical crystal materials such as aluminum oxide, magnesium oxide, and magnesium fluoride have sufficient transmittance in the i-line region as well as around 200 nm, and the functions required for the SOG dry etching stopper. Attention has been paid to satisfying the above conditions, and practical application has been attempted by two methods: forming a thin film of the above material on a quartz substrate and using it as an etching stopper layer, or using the above optical crystal material as it is as a substrate. However, in the above case, since the characteristics of these materials largely depend on their crystallinity, impurities, etc., a film having sufficient characteristics by the conventional thin film deposition technology (vacuum evaporation method, sputtering method, CVD method, etc.) Was not obtained. If the substrate is heated sufficiently during the film formation, the film characteristics may be improved, but there is a problem that the substrate cannot be heated because the substrate warps.
Further, in the above case, there was no optical crystal material having the same mechanical strength, workability, i-line transparency and cost as compared with the quartz substrate.

For example, taking aluminum oxide as an example,
Single crystal white sapphire wafer is SOG
No film loss occurs during dry etching, and chemicals (acid,
There is no problem with resistance to alkali, organic solvent, etc.). However, when an aluminum oxide thin film is formed on a quartz substrate by a sputtering method, only a film that easily dissolves in acid or alkali can be obtained. In addition, the white sapphire wafer has weaker mechanical strength than the quartz substrate, and handling of photomasks using this substrate is limited. Also,
Since the transmittance for i-line is slightly inferior to that of the quartz substrate, the plate thickness is limited, and problems such as warpage occur. Furthermore, it is also disadvantageous in terms of price compared to quartz substrates. Therefore, aluminum oxide could not be put to practical use as a dry etching stopper for a phase shift photomask. Similarly, magnesium fluoride and magnesium oxide cannot be put to practical use, and the etching stopper mainly composed of tin oxide, which cannot obtain an accurate phase shift angle, is unavoidably used at present. In view of the above problems, the problem to be solved by the present invention is to find a substrate for a phase shift photomask having an etching stopper layer for SOG dry etching capable of realizing an accurate phase shift angle, and a manufacturing method thereof.

[0011]

That is, the means of the present invention is to provide a thin film optical crystal material layer 2b made of an oxide or a fluoride.
Is a substrate for a phase shift photomask, which is bonded to the substrate 1. Thin film optical crystal material layer 2b made of oxide or fluoride
Is a substrate for a phase shift photomask as described above, which is made of a single crystal. Thin film optical crystal material layer 2b made of oxide or fluoride
Is the etching stopper layer for dry etching of the phase shifter layer formed on the thin film optical crystal material layer 2b.

The phase shift photomask substrate as described above, wherein the oxide is aluminum oxide or magnesium oxide. In the phase shift photomask substrate described above, the fluoride is magnesium fluoride. The phase shift photomask substrate described above, characterized in that the material of the substrate 1 is quartz.

Further, the substrate 1 and the thin film optical crystal material layer 2b
The method for producing a substrate for a phase shift photomask as described above, characterized in that the bonding with and is bonded on the surfaces of both materials that have been smooth-polished.

The present invention will be described below with reference to the drawings. FIG. 1 is a process diagram illustrating an example of a method for manufacturing a phase shift photomask substrate of the present invention. FIG. 1 (a) shows the first process, in which a photomask substrate material substrate 1 and an unpolished optical crystal are shown. This is a bonding step with the material layer 2a. (For information on this kind of bonding or joining technology, please refer to the monthly Semiconduct
or world 11992.12 P.I. 90-96) After performing smooth polishing, the unpolished optical crystal material layer 2a sliced to a thickness of about 1 mm or less is subjected to smooth polishing / cleaning on the sufficiently cleaned substrate 1. Both smooth polished surfaces are bonded together at room temperature without using an adhesive or the like. It is desirable to perform this work in a dust-free environment. At this time, if necessary, in order to increase the bonding strength, a film having excellent adhesion to the substrate 1 such as silicon oxide is previously formed on the bonding surface side of the unpolished optical crystal material layer 2a. It is also possible to previously form a film of aluminum oxide, magnesium fluoride or the like on the bonding surface side of the substrate 1.

It is also possible to bond them in a liquid such as water or to bond them while applying pressure. In order to prevent generation of voids due to degassing on the bonding surface, it is possible to degas the bonding surface by heating, vacuuming or the like in advance. Of course, it is also possible to perform the bonding operation itself in a vacuum chamber. further,
It is also possible to increase the bonding strength by controlling the temperature during bonding.

If the required unpolished optical crystal material layer 2a is obtained only by the above steps, the next step may be omitted, but if a stronger bonding force is required, the second step may be omitted. Proceed to. The second step is a step of annealing the unpolished bonded substrate 3a obtained in the first step. The atmosphere, temperature, heating time, etc. at this time are determined by the material, but in general, if the heating temperature is lower than the appropriate temperature or the heating time is shorter than the appropriate time, the bonding interface If the binding strength is insufficient and conversely the heating temperature is higher than the appropriate temperature or the heating time is longer than the appropriate time,
The material of the substrate 1 or the unpolished bonded substrate 3a is easily broken.

The third step is a grinding / polishing step, as shown in FIG. 1 (b). This process has two purposes.
That is, the flatness and flatness of the substrate 1 are processed to a level required for a phase shift photomask, and in particular, the unpolished optical crystal material layer 2a does not have sufficient transparency with respect to the exposure wavelength. In this case, it is necessary to reduce this layer to the required film thickness. However, it is required that the optical crystal material is left at least on the surface of the substrate 1 and that the transmittance for the exposure wavelength is uniform over the entire substrate 1.

FIG. 2 is a process chart for explaining another example of the method for manufacturing the phase shift photomask substrate of the present invention.
(a) is the required thickness in the above example of FIG.
FIG. 2B shows a state before laminating the unpolished optical crystal material layer 2a by grinding and polishing. As shown in FIG. 2B, the final phase shift photomask substrate 3b is formed by the same method as in FIG. Obtainable.

After the above steps are completed, a substrate 3b for a phase shift photomask in which a thin film optical crystal material layer 2b having an arbitrary thickness is bonded on a quartz substrate 1 is obtained. Here, the lower limit of the thickness of the thin film optical crystal material layer 2b is at least the minimum thickness that functions as an etching stopper, and the upper limit is the transmittance of the entire substrate 1 with respect to the exposure wavelength required at the time of exposure. It is the thickness at which the transmittance is not reached.

In the thus obtained substrate 3b for a phase shift photomask, the thin film optical crystal material layer 2b is scarcely thinned under the dry etching condition of SOG, so that sufficient overetching is possible and the accuracy is high. Phase shift angle control is possible. Further, since the thin film optical crystal material layer 2b has a strong resistance to chemicals (acid, alkali, organic solvent, etc.) during the patterning process and cleaning, it can be processed into a phase shift photomask without any problem. In the above, the thin film optical crystal material layer 2b
Although the case of using it as an etching stopper layer for dry etching of SOG has been described, it can be used as an etching stopper layer for SOG wet etching and as an etching stopper layer for a silicon oxide shifter formed by a sputtering method or a chemical vapor deposition method. It can also be used.

It is also possible to use the thin film optical crystal material layer 2b laminated by the same method as a shifter layer. That is, the thin film optical crystal material layer 2b processed in advance to a thickness required as a phase shifter is attached, or the unpolished optical crystal material layer 2a thicker than the required thickness is attached and then ground. A shifter layer can be obtained by processing to a desired thickness in the polishing step.

[0022]

EXAMPLES The present invention will be specifically described below with reference to examples. (Embodiment 1) As shown in FIG. 2, a thin film optical crystal material layer 2b, which is a 6 × 6 inch white sapphire (aluminum oxide single crystal) plate sliced to a thickness of about 500 μm and optically polished on both sides, and Same size, thickness 0.2
Substrate 1 for 5 inches, flatness 2 μm, ultra-high purity synthetic quartz photomask substrate 1 in 200 ° C. oven (air atmosphere)
Bake dehydration for 5 minutes. Next, the thin film optical crystal material layer 2b
Place the (white sapphire plate) on the surface of the quartz substrate 1,
They are combined to form a phase shift photomask substrate 3b. This work should be done in a clean room so as not to trap dust. Next, this phase shift photomask substrate 3b
Is fired in a firing furnace at 500 ° C. (air atmosphere) for 1 hour. As a result, the coupling strength becomes the strength required for the phase shift photomask substrate.

The phase shift photomask substrate 3b thus obtained has a transmittance of, for example, i-line of a mercury lamp of about 85% when air is 100%, and a transmittance of krypton fluoride excimer laser light. Also becomes about 80%, which has the transparency required for a substrate for a phase shift photomask. The mechanical strength of the substrate is
Since it is obtained by the quartz substrate 1, there is no problem.

The phase shift photomask substrate 3b described above.
Resist pattern (a commercially available resist having sufficient resistance to SOG dry etching conditions; for example, positive type UV resist THM manufactured by Tokyo Ohka Kogyo Co., Ltd.).
Rip-1800 was used) and an etching test was performed under the following conditions. Etching condition Device: DEM-451 (using Rf plasma) manufactured by Nichiden Anelva Gas: Carbon tetrafluoride 90% + oxygen 10%; total 20 cc
/ Min Pressure: 5 pascals Power: 100 watts Time: 1 hour (Over etching is 2 in normal process)
0 minutes or less After completion of the test, the resist was peeled off and the step was measured with a surface roughness meter “Dec Tuck 8000” (manufactured by Veeco), and no step was confirmed. Further, even if the surface is observed with a projector (sener), the thin film optical crystal material layer 2b
No patterning was observed. From the above, it is considered that the phase shift photomask substrate 3b has sufficient resistance to the SOG dry etching conditions.

Next, the phase shift photomask substrate 3b
Was examined for chemical resistance. Mixed acid (80 ° C) of concentrated sulfuric acid (90%) + concentrated nitric acid (10%) used for cleaning photomasks
The film loss was examined when the film was dipped in water (120 minutes or more), but no film loss was observed as a result of the above-mentioned check using a surface roughness meter and a floodlight. Similarly, it was found to have sufficient resistance to various developing solutions, stripping solutions, and etching solutions used in the manufacturing process of phase shift photomasks, and it can be used as a substrate for phase shift photomasks.

(Embodiment 2) The thin film optical crystal material layer 2b is used in which the white sapphire (aluminum oxide single crystal) plate of the embodiment 1 is replaced with a magnesium oxide single crystal plate and a magnesium fluoride single crystal plate, respectively. In addition, the same test was performed under the same conditions and the above-mentioned confirmation tests were performed. As a result, the same results as in Example 1 were obtained, and it was found that the substrate can be used as a substrate for a phase shift photomask.

(Embodiment 3) Next, an example in which the thin film optical crystal material layer 2b of the phase shift photomask substrate 1 of the present invention is used as a shifter layer will be described. The thin film optical crystal material layer 2b, which is a white sapphire (aluminum oxide single crystal) plate, obtained by the same method as in Example 1 is ground and polished to have a thickness which serves as a phase shifter layer for the exposure wavelength. Processed into. At this time, the final film thickness adjustment is performed by etching with H ₃ PO ₄ + H ₂ SO ₄ mixed acid (150 ° C.), and the film thickness is evaluated with an optical film thickness meter (Dainippon Screen Lambda Ace). It was Then, chromium that will become the light-shielding film is formed by the sputtering method, and white sapphire (aluminum oxide single crystal) is formed.
A lower shifter type phase shift photomask blank having a film as a shifter layer was obtained. The patterning of this blank shifter layer was performed using H ₃ PO ₄ + H
It can be performed with ₂ SO ₄ mixed acid (150 ° C.), and at this time, the chromium mask and the quartz substrate 1 are hardly etched, and high-precision phase angle control is possible.

[0028]

The substrate for a phase shift photomask of the present invention uses a thin film optical crystal material layer as an etching stopper layer for dry etching of SOG, and when the phase shift photomask is formed, the shifter layer is dry-etched. Since the etching stopper layer is hardly etched, it is easier to produce a phase shift photomask with improved controllability of the phase shift angle as compared with the case where a material mainly containing tin oxide is used as the etching stopper layer. Also, the thin film optical crystal material layer can be used as a shifter layer.

[Brief description of drawings]

FIG. 1 is a process chart illustrating an example of a method for manufacturing a phase shift photomask substrate of the present invention.

FIG. 2 is a process drawing explaining another example of the method for manufacturing the substrate for phase shift photomask of the present invention.

[Explanation of symbols]

 1 Substrate 2a Unpolished Optical Crystal Material Layer 2b Thin Film Optical Crystal Material Layer 3a Unpolished Bonded Substrate 3b Phase Shift Photomask Substrate

Claims (7)

[Claims] 1. A substrate for a phase shift photomask, characterized in that a thin film optical crystal material layer (2b) made of an oxide or a fluoride is bonded to a substrate (1). 2. The substrate for phase shift photomask according to claim 1, wherein the thin film optical crystal material layer (2b) made of oxide or fluoride is made of single crystal. 3. A thin film optical crystal material layer (2b) made of an oxide or a fluoride is an etching stopper layer for dry etching of a phase shifter layer formed on the thin film optical crystal material layer (2b). Claim 1 characterized by the above.
The phase shift photomask substrate described. 4. The substrate for a phase shift photomask according to claim 1, wherein the oxide is aluminum oxide or magnesium oxide. 5. The substrate for phase shift photomask according to claim 1, wherein the fluoride is magnesium fluoride. 6. The substrate for a phase shift photomask according to claim 1, wherein the material of the substrate (1) is quartz. 7. A substrate (1) and a thin film optical crystal material layer (2)
2. The method for manufacturing a substrate for a phase shift photomask according to claim 1, wherein the bonding with b) is bonded on the surfaces of both materials which have been smooth-polished.