JPH05326378A - Manufacture of x-ray mask structure - Google Patents

Abstract

PURPOSE:To prevent a fluctuation in the film stress of an X-ray transmitting film when an X-ray mask substrate is bonded to an X-ray mask reinforcement body. CONSTITUTION:In a method of manufacturing an X-ray mask structure which is formed by bonding an X-ray mask substrate 2 composed of a silicon wafer to an X-ray mask reinforcement body 4 composed of a silicon plate, a face which is opposite to the face, on which an X-ray transmitting face 1 has been formed, of the X-ray mask substrate 2 is bonded to the X-ray mask reinforcement body 4 at the film formation temperature or lower or the annealing temperature or lower of the X-ray transmitting film 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an X-ray mask structure, and more particularly to a method of manufacturing a mask structure for X-ray lithography which is free from warpage and distortion and which enables highly accurate lithography.

[0002]

2. Description of the Related Art Regarding the lithography technique for semiconductor devices, the X-ray lithography technique is regarded as promising along with the miniaturization of pattern formation. The mask used in this X-ray lithography is as shown in FIG. An X-ray mask substrate 2 as a holding frame for the X-ray transparent film 1, an X-ray absorber 3 formed in a desired pattern on the X-ray transparent film 1, and reinforcement for reinforcing the holding frame. The one consisting of the body 4 is used.

This X-ray transparent film is generally made of a light metal having a small X-ray absorption coefficient, such as boron nitride (BN), silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC). Inorganic thin film with a thickness of 10 μm or less, X
The X-ray absorbing film 3 is made of a heavy metal such as gold (Au), tungsten (W), tantalum (Ta), etc. that absorbs a large amount of X-rays. In order to maintain the morphology, it is essential to have a tensile stress of 5 × 10 ^{6 to} 5 × 10 ⁹ dynes / cm ² , and this X-ray transmission film 1 has an X-ray absorber 3 Since it supports, it is also called an X-ray absorber support (membrane) or an X-ray transmission membrane.

The X-ray permeable film holding frame 2 has a flat surface and is a mirror surface, and since it can be anisotropically etched with an alkaline solution, a silicon wafer is usually used. Has a diameter of 2 to 4 inches and a thickness of 300 to 2,000 μm. In this X-ray lithography mask, an X-ray transmission film 1 is formed on the mirror surface of this silicon wafer, an X-ray absorber 3 is formed on the film, and then alkali etching is performed from the opposite surface of the silicon wafer to perform X-ray lithography. The X-ray permeable membrane is formed by making the permeable membrane 1 into a membrane state. In this case, the unetched region corresponding to the periphery of the membrane 6 becomes the X-ray permeable membrane holding frame 2, but the X-ray absorber 3 is formed by the X-ray permeable membrane. It may be performed after forming the membrane.

Since the silicon wafer as the holding frame 2 for the X-ray permeable film is easily broken and has insufficient strength,
It is necessary to reinforce the periphery of the holding frame with the reinforcing body 4. Borosilicate glass (trade name Pyrex glass), which has a thermal expansion coefficient relatively equal to that of a general silicon wafer, is used as the reinforcing body, and the holding frame 2 and the reinforcing body 4 are usually fixed by using an adhesive. Are combined in a way that

However, when the holding frame and the reinforcing body are bonded to each other via an adhesive, an epoxy adhesive having a large adhesive strength is required to bond the holding frame and the reinforcing body with an adhesive strength that does not cause peeling. The adhesive layer thickness of 30-100 μm
And need to. As a result, there is a disadvantage in that the parallelism between the holding frame and the reinforcing body after adhesion cannot be set to a level not more than several μm, which is the parallelism of the mask required as an X-ray mask. In addition, the thermal expansion coefficient of the silicon wafer as the holding frame material and that of the borosilicate glass as the reinforcement are different.Since the silicon wafer is 2.4 × 10 ⁶ , the borosilicate glass is 3.5 × 10 ^6. Disadvantage that strain easily occurs due to temperature change.

Therefore, regarding this, a borosilicate glass as a reinforcing body is used as a silicon single crystal plate which is the same material as the holding frame, and a silicon single crystal as a silicon wafer as a holding frame is subjected to heat treatment at high temperature. A method of direct bonding has been proposed (see Japanese Patent Laid-Open No. 2-162714), but in this case, in order to obtain an adhesive strength that can withstand practical use, it is necessary to maintain a high temperature of 900 ° C or higher, preferably 1,000 ° C or higher.
Since it is necessary to perform heat treatment for 30 minutes or more, preferably 1 hour or more, the internal stress of the X-ray transparent film and the X-ray absorber formed on the surface changes, and not only the pattern distortion and damage, It has the disadvantage that the X-ray permeable membrane is destroyed.

Further, in this case, a silicon wafer serving as a holding frame and a silicon single crystal plate having a hollowed central portion serving as a reinforcing body are joined by preheat treatment, and then the X-ray transmitting film and the X-ray absorber are attached. Although a method of bonding can be considered, it is still disadvantageous that the bonded body is likely to warp and the surface of the silicon wafer is easily roughened when the heat treatment is performed at a high temperature for a long time. There is also the disadvantage that a device for

[0009]

Therefore, the present inventors have proposed an X-ray mask structure comprising an X-ray transmissive film holding frame, an X-ray transmissive film, an X-ray absorber and a reinforcing member for reinforcing the holding frame, A method has been proposed in which an X-ray transparent film holding frame made of silicon single crystal and a silicon single crystal reinforcing body are bonded via a silicon oxide film (see Japanese Patent Laid-Open No. 3-219207). According to the above, the advantage that bonding can be performed at a relatively low temperature is given, but for this, an X-ray mask substrate (usually a silicon wafer is used) having a pre-formed X-ray transparent film is formed, and X-ray mask reinforcement is used. If the temperature at which the body is bonded via silicon oxide is higher than the temperature at which the X-ray transparent film is formed, there arises a problem that the film application of the X-ray transparent film fluctuates. Exposed to a temperature higher than that during film formation If tend to fluctuate stress side tensile film stress by annealing effect.

Further, in order to obtain an X-ray permeable membrane, the film stress is 5 × 10 ^{8 to} 5 × 10 ^{9 as described above.}
Since maintaining a tensile stress of dyne / cm ² is essential, a membrane can be obtained if the film stress of the X-ray transparent film fluctuates outside the desired stress range in the next bonding step. Disappear. Although a method of forming an X-ray transparent film after joining the X-ray mask substrate and the X-ray mask reinforcing body can be considered for this, in this case, the amount of warpage of the X-ray mask substrate can be measured. Since it is difficult, the stress cannot be obtained from the warp amount, and the stress of the formed X-ray transparent film cannot be accurately measured.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing an X-ray mask structure which solves the above disadvantages and drawbacks, and it is an X-ray mask substrate made of a silicon wafer and an X made of a silicon plate. In a method of manufacturing an X-ray mask structure obtained by joining a line mask reinforcement with
The X-ray mask substrate and the surface opposite to the surface on which the X-ray transparent film is formed
It is characterized in that the line mask reinforcing material is bonded at a temperature not higher than the film forming temperature of the X-ray transparent film or not higher than the annealing temperature.

That is, the inventors of the present invention prevent the film stress of the X-ray transparent film in the X-ray mask structure obtained by bonding the X-ray mask substrate and the X-ray mask reinforcing member from changing due to the heat treatment at the time of bonding. As a result of various studies on the method, the surface of the X-ray mask substrate opposite to the surface on which the X-ray transparent film is formed and the X-ray mask reinforcing agent are kept at a temperature below the deposition temperature of the X-ray transparent film or below the annealing temperature. The present invention has been completed by finding that the stress of the X-ray transparent film does not fluctuate when bonded.
This will be described in more detail below.

[0013]

The present invention relates to a method for manufacturing an X-ray mask structure, which is an X-ray mask structure manufacturing method for bonding an X-ray mask substrate and an X-ray mask reinforcing member. According to this, the surface opposite to the surface on which the X-ray transmission film is formed and the X-ray mask reinforcing agent are bonded at a temperature not higher than the film formation temperature of the X-ray transmission film or not higher than the annealing temperature. Since the stress of the X-ray transparent film does not change, the yield of the membrane is improved.

The X-ray mask structure of the present invention is made by joining an X-ray mask substrate and an X-ray mask reinforcement. The X-ray mask substrate as the X-ray transparent film holding frame constituting the X-ray mask structure of the present invention is made of a silicon wafer made of a silicon single crystal. There is no particular limitation on the size or thickness of this product, but in general, the diameter is 2
~ 4 inches, this thickness is 2,000 μm
In the above case, it takes a long time to carry out back etching in a later step, so that the thickness is preferably 300 to 2,000 μm, but it is preferable that the crystal orientation is (100) because alkali etching is performed.

Further, this has a X-ray transmission film formed on its surface, and since this X-ray transmission film needs to be smooth and have a uniform film thickness, it is a mirror surface. However, it is desirable that the opposite surface is also a mirror surface because the silicon oxide film described later is thinly and uniformly formed on this surface.

Further, the X-ray mask reinforcement constituting the X-ray mask structure of the present invention is made of a silicon single crystal plate, which is larger in size than the X-ray mask substrate described above. Therefore, it is generally in the shape of a circle or square having a size of 5 to 8 inches, and has a thickness of 3 to 10 mm, preferably 5 to 7 mm. If the surface of the silicon single crystal as the reinforcing member is rough, it will be necessary to thicken the silicon oxide film described later, and as a result, distortion is likely to occur, so mirror finishing is preferable.

It is necessary that this reinforcing member has a larger area than the area where the membrane of the X-ray permeable membrane is formed, and this hollowed area may have a round shape or a square shape. Since the membrane size of the X-ray permeable membrane is a circle with a diameter of 20 to 30 mm or a square shape with one side of 20 to 30 mm, it is necessary to make it larger than these sizes. Or 1
It should be a square with a side of 40 mm.

The X-ray mask structure of the present invention is one in which an X-ray mask substrate made of this silicon wafer and an X-ray mask reinforcement made of a silicon single-bonded plate are joined, and the silicon surface and the silicon surface are heated. To join by
A temperature of 1,000 ° C or higher is required, but for this, a silicon oxide film (SiO ₂ film) is placed between the silicon surfaces.
Since they can be joined at a temperature of 300 to 400 ° C. or higher, it is preferable to interpose a silicon oxide film.

This silicon oxide film is formed on the X-ray mask substrate side,
The silicon oxide film may be installed on either side of the X-ray mask reinforcement, but it may be installed on both sides. However, since it is desirable to avoid heat treatment of the X-ray mask substrate as much as possible, this silicon oxide film is used as an X-ray mask reinforcement. It is advisable to install it only on the silicon single crystal plate side and heat this.

This silicon oxide film is formed by heating the silicon surface of the X-ray mask substrate or the X-ray mask reinforcement to a temperature of 800 ° C. or higher in the presence of oxygen to oxidize it, or by a known CVD method for this silicon surface. Method, sputtering method SiO ₂
A film may be formed, but the thickness of this silicon oxide film is 10
〜10,000Å, preferably 100〜5,000 Å.

As described above, the method of manufacturing the X-ray mask structure according to the present invention comprises forming the X-ray transparent film of the X-ray mask substrate, the surface opposite to the molding surface, and the X-ray mask reinforcing member to form the X-ray transparent film. Although the bonding is performed at a temperature below the film temperature or below the annealing temperature, the film forming temperature of the X-ray transparent film is 1,000 to 1,500 ° C. when the CVD method is used, and 200 to when the sputtering method is used. 1,000 ℃ In the sputter method, the film is formed at a relatively low temperature, but since the film is annealed at a constant temperature in order to control the film forming stress to a constant value, it is necessary to perform it at a temperature equal to or lower than the annealing temperature.

That is, when the X-ray transparent film formed on the X-ray mask substrate is a film formed by the CVD method,
The bonding temperature may be 1,000 ° C or lower, for example, 600 to 800 ° C. In the case of the sputtering method, a film is formed in a compressed state at a temperature of 200 ° C or lower and then annealed at 800 ° C or lower. In the method of the present invention, the joining temperature in this case is lower than the annealing temperature. Therefore, after adjusting the desired tensile stress, the joining is performed at a temperature of 800 ° C. or lower, for example, 600 ° C.

In the method of manufacturing an X-ray mask structure according to the present invention, the X-ray mask substrate and the X-ray mask reinforcement are bonded to each other by forming the above-mentioned silicon oxide film on them and / or by applying a predetermined amount of them. After stacking them in the same position and fixing them so that they will not shift, at a specified temperature for 1 hour to 20
The heat treatment may be performed under vacuum or normal pressure for 3 hours to 8 hours.

[0024]

EXAMPLES Examples and comparative examples of the present invention will be given below.
The adhesiveness and suitability for membrane formation in the examples are the results of judgment based on the following criteria. (Adhesiveness) Tensile strength of 10 kg was applied between the silicon wafer for the holding frame and the silicon single crystal as the reinforcing member by a tensile tester, and the case of not peeling was defined as “good”, and the case of peeling was defined as “poor”. (Appropriate for membrane formation) An alkali etching protective film (BN film) is provided on the joint surface of the X-ray transparent film holding frame, BN in the portion that becomes the membrane region is removed, and the exposed silicon surface is alkali-etched to become a membrane. At this time, those having good membranes are regarded as good for proper membrane formation, and those not having good membranes are regarded as poor membrane formation.

Examples 1 to 12 X-ray mask substrates made of double-side polished silicon wafers having a diameter of 3 inches and a thickness of 600 μm and a crystal orientation of (100) to be used as a frame for holding an X-ray transparent film are shown in Table 1. An X-ray transparent film made of SiC, Si ₃ N ₄ or SiCN _x having a thickness of 1.0 μm was formed by the above film forming method.

Next, the crystal orientation is (100) and one side is 100 m.
We made an X-ray mask reinforcement with a 55 mm diameter hole in the center of a double-sided, square-shaped silicon single crystal with a thickness of 5 mm and a temperature of 1,000 ° C in an oxygen atmosphere of 1 atm.
The surface was oxidized for 2 hours to form a 1,000 Å thick silicon oxide film on the polished surface.

Next, the silicon wafer serving as the X-ray transparent film holding frame and the silicon single crystal serving as the X-ray mask reinforcing member provided with the silicon oxide film are opposite to the X-ray transparent film forming surface of the silicon wafer. Superposed so that the polished surface, which is the surface, and the silicon oxide film of the reinforcing body overlap,
A bonding body of a silicon wafer and a silicon single crystal as a reinforcing body was produced by pressure bonding under vacuum at the bonding temperature shown in Table 1 for 3 hours, and the adhesiveness of this bonding body was examined. The following results were obtained.

With respect to this bonded body, a BN film as an alkali etching protective film was formed to a thickness of 0.5 μm on the bonded surface of the X-ray transparent film holding frame by plasma CVD.
CF the BN film in the square area of 25 mm on each side that becomes the membrane area.
After removing by dry etching with a ₄ / O ₂ mixed gas, the exposed silicon surface was removed by alkali etching, and the suitability for membrane formation at this time was examined. The results shown in Table 2 were obtained.

Comparative Examples 1 to 4 On an X-ray mask substrate made of the same silicon wafer as that used in the examples, the film forming method and the film forming conditions shown in Table 1 were set to 1.0 μm thick Si ₃ N ₄ , SiC. An X-ray mask reinforcement having a silicon oxide film obtained in the same manner as in the example was superposed thereon in the same manner as in the example, and shown in Table 1 under vacuum. When a bonded body was produced by performing pressure bonding treatment at the bonding temperature for 3 hours, and the adhesiveness and membrane-forming suitability of this bonded body were examined, the results shown in Table 2 were obtained.

[0030]

[Table 1]

[Table 2]

[0031]

The present invention relates to a method of manufacturing an X-ray mask structure, which is, as described above, manufactured by bonding an X-ray mask substrate and an X-ray mask reinforcement. In the method, the surface of the X-ray mask substrate opposite to the surface on which the X-ray transmission film is formed and the X-ray mask reinforcement are bonded at a temperature not higher than the film formation temperature of the X-ray transmission film or not higher than the annealing temperature. This provides the advantage that the stress of the X-ray transparent film does not fluctuate and the suitability for membrane formation is improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an X-ray mask structure.

[Explanation of symbols]

1 ... X-ray transparent film, 2 ... X-ray transparent film holding frame, 3 ... X-ray absorber, 4 ... X-ray mask reinforcement, 5 ... BN film,
6 ... Membrane, 7 ... Silicon oxide film.

Front page continued (72) Inventor Yoshihiro Kubota 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory

Claims (3)

[Claims] 1. A method of manufacturing an X-ray mask structure, which comprises bonding an X-ray mask substrate made of a silicon wafer and an X-ray mask reinforcement made of a silicon plate, to form an X-ray transparent film of the X-ray mask substrate. A method for manufacturing an X-ray mask structure, characterized in that the opposite surface of the surface and the X-ray mask reinforcement are bonded at a temperature not higher than the film formation temperature of the X-ray transparent film or not higher than the annealing temperature. 2. The method of manufacturing an X-ray mask structure according to claim 1, wherein the X-ray mask substrate and the X-ray mask reinforcing member are bonded together via a silicon oxide film. 3. The method of manufacturing an X-ray mask structure according to claim 2, wherein the silicon oxide film is formed on the X-ray mask reinforcing body.