JP3324005B2 - Phase shift photomask substrate and method of manufacturing the same - Google Patents

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 LSIs and VLSIs, and a phase shift photomask substrate (phase shift photomask) for manufacturing the photomask. Blank).

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs are manufactured by a lithography process.
No. 73744, Japanese Patent Publication No. 62-59296, etc., a reticle based on a new concept of a phase shift photomask has been proposed. 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 passing through a reticle.

In phase shift lithography, high-precision control of the phase shift angle is required to improve the resolution and contrast of a 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. In particular, controlling the film thickness is a major problem in manufacturing a phase shift photomask.

[0004] For etching the shifter layer, a dry etching method which is excellent in high-precision fine processing is used.
The most reliable way to control the shifter pattern film thickness is
Select a shifter and an underlayer material in which the etching rate ratio (selectivity) between the shifter layer and the underlayer is large, and dry-etch for a specific time longer than the time when the shifter layer will be completely removed, that is, , Over-etching. By doing so, a uniform etching depth can be obtained over the entire substrate surface.
In addition, over-etching may be required to adjust the pattern cross-sectional shape.

However, for example, when quartz is used as a base layer for a glass substrate and commercially available coated glass (SOG; for example, Accuglass 211S manufactured by Allied Signal Inc.) is used as a shifter material, the selectivity of dry etching is as follows. Approximately only 1.5-2.0 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 essential to provide a so-called etching stopper layer made of a material having a sufficiently large etching selectivity with the shifter layer on the glass substrate.

[0006] Such an etching stopper layer is described in, for example, Japanese Patent Publication No. 61-6166.
4, a transparent conductive film mainly composed of tin oxide, SPIE Vol. 59 of 1463 (1991)
Oxide or fluoride thin films such as an aluminum oxide film and a magnesium fluoride film as shown on page 5 are known.

[0007]

However, the transparent conductive film mainly composed of tin oxide has a low transmittance at a wavelength of 350 nm or less, and cannot be used for exposure in this wavelength region. Even when the exposure wavelength is the i-line (365 nm) of a mercury lamp, the following problems are encountered. That is, the transparent conductive film mainly composed of tin oxide is made of SO
G is not sufficiently resistant to dry etching, and is etched at a rate of about 1.5 nm / min under ordinary dry etching conditions (etching selectivity with SOG is about 20). For this reason, the etching stopper layer mainly composed of tin oxide can be prevented from being etched to the quartz substrate, but the film thickness of the etching stopper layer is reduced during the above-mentioned over-etching.

[0008] However, since tin oxide has a refractive index of about 2.0 at the wavelength of the i-line, a decrease in film thickness during dry etching causes a phase angle difference. In general, light of wavelength λ that has passed through a medium having a refractive index of n and a thickness of d has a phase angle shifted by 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 case of 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 1.5 degrees occurs per minute of overetching, thereby forming an accurate phase shifter. Becomes difficult. Also, if the etching rate in the actual dry etching apparatus has a distribution in the substrate, this distribution produces a thickness distribution of the etching stopper layer mainly composed of tin oxide, and therefore, the phase angle distribution in the substrate is reduced. 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 not only in the i-line region but also in the vicinity of 200 nm, and have the functions required for the SOG dry etching stopper. Attention has been paid to satisfying the above conditions, and practical use has been attempted in two ways: forming a thin film of the above-mentioned material on a quartz substrate and using it as an etching stopper layer, or using the above-mentioned optical crystal material as it is as a substrate. However, in the above case, the properties of these materials greatly depend on their crystallinity, impurities, and the like, and therefore, a film having sufficient properties with conventional thin film forming techniques (vacuum deposition, sputtering, CVD, etc.). Was not obtained. If the substrate is sufficiently heated during film formation, the film characteristics may be improved, but there is a drawback that the substrate cannot be heated due to warpage or the like.
In addition, in the above case, there is no optical crystal material having the same mechanical strength, workability, i-ray transmittance, and cost as compared with the quartz substrate.

For example, taking aluminum oxide as an example,
The single crystal white sapphire wafer is SOG
During dry etching, no film loss occurs, and chemicals (acids,
Resistance to alkalis, organic solvents, 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 an acid or an alkali can be obtained. Further, the mechanical strength of a white sapphire wafer is lower than that of a quartz substrate, and handling of a photomask using the substrate as a substrate is limited. Also,
Since the transmittance for the i-line is slightly inferior to that of the quartz substrate, the thickness is also limited, and problems such as warpage also occur. Further, it is disadvantageous in price as compared with the quartz substrate. Therefore, aluminum oxide could not be put to practical use as a dry etching stopper for a phase shift photomask. Similarly, at present, magnesium fluoride and magnesium oxide cannot be put to practical use, and at present, an etching stopper mainly composed of tin oxide, which cannot provide an accurate phase shift angle, is unavoidably used. An object of the present invention is to provide a phase shift photomask substrate having an SOG dry etching etching stopper layer capable of realizing an accurate phase shift angle and a method of manufacturing the same in view of the above problems.

[0011]

That is, the means of the present invention combines the smooth polished surfaces of both materials without using an adhesive to form a thin-film optical crystal material layer 2b made of oxide or fluoride. A phase shift photomask substrate, which is bonded to a substrate 1. The phase shift photomask substrate as described above, wherein the thin film optical crystal material layer 2b made of an oxide or a fluoride is made of a single crystal. The thin film optical crystal material layer 2b made of an oxide or a fluoride is
The phase shift photomask substrate described above, which is an etching stopper layer at the time of dry etching of a phase shifter layer formed thereon.

The above-mentioned substrate for a phase shift photomask, wherein the oxide is aluminum oxide or magnesium oxide. The phase shift photomask substrate according to the above, wherein the fluoride is magnesium fluoride. The substrate for a phase shift photomask described above, wherein the material of the substrate 1 is quartz.

A substrate 1 and a thin-film optical crystal material layer 2b
The method of manufacturing a substrate for a phase shift photomask as described above, wherein the bonding is performed on both surfaces of the material that have been polished smoothly.

The present invention will be described below with reference to the drawings. FIG. 1 is a process chart for explaining an example of a method for manufacturing a phase shift photomask substrate according to the present invention. FIG. 1 (a) shows a first process, in which a photomask substrate material substrate 1 and an unpolished optical crystal are shown. This is a step of bonding with the material layer 2a. (For information on this type of bonding or joining technology, see Monthly Semiconductor
or world 1992.12 P.R. After smooth polishing, the unpolished optical crystal material layer 2a sliced to a thickness of about 1 mm or less is smooth-polished and cleaned on the sufficiently cleaned substrate 1. The two smooth polished surfaces are bonded together at room temperature without using an adhesive or the like. This work is desirably performed in a dust-free environment. At this time, if necessary, a film having excellent adhesion to the substrate 1 such as silicon oxide is formed on the bonding surface side of the unpolished optical crystal material layer 2a in advance to increase the bonding strength. It is also possible to form a film of aluminum oxide, magnesium fluoride, or the like on the bonding surface side of the substrate 1 in advance.

Further, the bonding may be performed in a liquid such as water, or may be performed while applying pressure. In order to prevent generation of voids due to degassing on the bonding surface, degassing of the bonding surface may be performed in advance by heating, vacuuming, or the like. Of course, the bonding operation itself can be performed in a vacuum chamber. further,
By controlling the temperature at the time of bonding, the bonding force can be increased.

If the required unpolished optical crystal material layer 2a can be obtained only by the above steps, the next step can be omitted. However, if a stronger bonding force is required, the second step is required. 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 If the bonding strength is insufficient and 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 and polishing step as shown in FIG. This step has two purposes.
That is, the flatness and flatness of the substrate 1 are processed to a level required as a phase shift photomask, and in particular, the unpolished optical crystal material layer 2a does not have sufficient transparency to the exposure wavelength. In this case, this layer is cut to a required thickness. However, it is required that the optical crystal material remains on at least the surface of the substrate 1 and that the transmittance with respect to the exposure wavelength is uniform over the entire substrate 1.

FIG. 2 is a process chart for explaining another example of a method for manufacturing a substrate for a phase shift photomask according to the present invention.
(a) in the above example of FIG.
FIG. 2B shows a state before the unpolished optical crystal material layer 2a is ground and polished, and 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 serving as an etching stopper, and the upper limit is that the transmittance of the entire substrate 1 with respect to the exposure wavelength is required at the time of exposure. This is the thickness that does not reach the transmittance.

In the phase shift photomask substrate 3b obtained in this manner, the thin film optical crystal material layer 2b hardly loses its thickness under dry etching conditions of SOG, so that it is possible to perform sufficient overetching with high accuracy. Phase shift angle control can be performed. Further, since the thin film optical crystal material layer 2b has strong resistance to chemicals (acids, alkalis, organic solvents, 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 is
Has been described as being used as an etching stopper layer for dry etching of silicon oxide. However, it can be used as an etching stopper layer for wet etching of SOG, or 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 bonded in the same manner as a shifter layer. That is, a thin film optical crystal material layer 2b processed in advance to a thickness required as a phase shifter is bonded, or an unpolished optical crystal material layer 2a thicker than the required thickness is bonded, followed by grinding. By processing to a desired thickness in the polishing step, a shifter layer can be obtained.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to embodiments. Example 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
An ultra-high-purity synthetic quartz photomask substrate 1 having a 5-inch flatness of 2 μm was placed in a 200 ° C. oven (air atmosphere).
Dehydrate bake for 5 minutes. Next, the thin-film optical crystal material layer 2b
(White sapphire plate) on the surface of the quartz substrate 1,
This is combined with the substrate 3b for a phase shift photomask. This work is performed in a clean room so that dust and the like are not interposed. Next, the 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 as a phase shift photomask substrate.

The thus obtained substrate 3b for a phase shift photomask has, for example, a transmittance for i-line of a mercury lamp of about 85% when air is 100%, and a transmittance for krypton fluoride excimer laser light. Is also about 80%, which is the transmittance required for a phase shift photomask substrate. The mechanical strength of the substrate is
There is no problem because it can be obtained from the quartz substrate 1.

The above-mentioned substrate 3b for phase shift photomask
In order to examine the resistance to SOG dry etching conditions, a resist pattern (a commercially available resist having sufficient resistance to SOG dry etching conditions; for example, a positive UV resist THM manufactured by Tokyo Ohka Kogyo Co., Ltd.)
Rip-1800) and an etching test was performed under the following conditions. Etching conditions Apparatus: DEM-451 manufactured by Nidec Anelva (using Rf plasma) Gas: 90% carbon tetrafluoride + 10% oxygen; total 20 cc
/ Min Pressure: 5 Pascal Power: 100 Watts Time: 1 hour
0 minutes or less After completion of the test, the resist was peeled off, and the level difference was measured with a surface roughness meter “Deck Tack 8000” (manufactured by Beco). As a result, no level difference was confirmed. In addition, even if the surface is observed with a light projector (sener), the thin-film optical crystal material layer 2b
Was not observed at all. From the above, it is considered that the resistance of the phase shift photomask substrate 3b to the SOG dry etching condition is sufficient.

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 photomask cleaning
When the film was immersed in the sample (120 minutes or more), the film was reduced. As a result of checking with a surface roughness meter and a light projector, no film reduction was observed. Similarly, it has been found that it has sufficient resistance to various developing solutions, stripping solutions, and etching solutions used in the manufacturing process of the phase shift photomask and can be used as a substrate for the phase shift photomask.

(Example 2) A thin film optical crystal material layer 2b obtained by replacing the white sapphire (aluminum oxide single crystal) plate of Example 1 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 confirmation tests were performed. As a result, the same results as in Example 1 were obtained, and it was found that the film could 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 substrate 1 for a phase shift photomask of the present invention is used as a shifter layer will be described. A 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 a thickness serving as a phase shifter layer for the exposure wavelength. Processed to. The final adjustment of the film thickness at this time is performed by etching with a mixed acid of H ₃ PO ₄ + H ₂ SO ₄ (150 ° C.), and the evaluation of the film thickness is performed by an optical film thickness meter (Lambda Ace manufactured by Dainippon Screen). Was. Next, chromium, which is used as a light-shielding film, is formed by a sputtering method, and white sapphire (aluminum oxide single crystal)
A lower shifter type phase shift photomask blank using the film as a shifter layer was obtained. The patterning of the shifter layer of this blank is performed using H ₃ PO ₄ + H with chromium as a mask.
₂ SO ₄ can be carried out by mixed acid (0.99 ° C.), when the chromium mask and the quartz substrate 1 was possible hardly etched, a highly accurate phase angle control.

[0028]

The substrate for a phase shift photomask according to the present invention is characterized in that, when a thin film optical crystal material layer is used as an etching stopper layer for dry etching of SOG, when a phase shift photomask is formed, the shifter layer is subjected to dry etching. Since the etching stopper layer is hardly etched, it becomes easier to form a phase shift photomask with improved controllability of the phase shift angle as compared with a case where a material mainly composed of tin oxide is used as the etching stopper layer. Further, a thin film optical crystal material layer can be used as a shifter layer.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 Reference Signs List 1 substrate 2a unpolished optical crystal material layer 2b thin film optical crystal material layer 3a unpolished bonded substrate 3b substrate for phase shift photomask

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-126630 (JP, A) JP-A-4-361259 (JP, A) JP-A-3-78747 (JP, A) JP-A-61- 173249 (JP, A) JP-A-4-68352 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (7)

(57) [Claims] 1. A smooth polished surface of both materials is joined together without using an adhesive, and a thin-film optical crystal material layer (2b) made of an oxide or a fluoride is bonded to a substrate (1). A substrate for a phase shift photomask, comprising: 2. The phase shift photomask substrate according to claim 1, wherein the thin film optical crystal material layer made of oxide or fluoride is made of a single crystal. 3. A thin film optical crystal material layer (2b) made of an oxide or a fluoride serves as an etching stopper layer in dry etching of a phase shifter layer formed on the thin film optical crystal material layer (2b). 2. The method according to claim 1, wherein
The substrate for a phase shift photomask according to the above. 4. The substrate for a phase shift photomask according to claim 1, wherein the oxide is aluminum oxide or magnesium oxide. 5. The phase shift photomask substrate 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 the step (b) is performed on both surfaces of the material that have been smooth-polished. "