JP3032262B2 - X-ray mask manufacturing method - Google Patents

Description

Description: Object of the Invention (Industrial application field) The present invention relates to a method for manufacturing an X-ray exposure mask (hereinafter referred to as X-ray mask), and particularly to an X-ray mask support or X-ray transmission. It relates to the joining of a conductive thin film to a reinforcing frame.

(Prior Art) In recent years, as the demand for higher density and higher integration of semiconductor integrated circuits has increased, research and development of a lithography technique for forming a pattern on a photosensitive agent has been rapid among fine processing techniques for circuit patterns. Showing progress.

At present, photolithography technology using light as an exposure medium is the mainstream in mass production lines, but it is approaching the limit of resolution, and as an alternative to this photolithography technology, X-rays whose resolution is dramatically improved in principle R & D of lithography technology is making rapid progress.

In the X-ray lithography, unlike an exposure method using light, a technique of transferring a predetermined pattern in a reduced size has not been put to practical use at present. For this reason, in the X-ray exposure, an X-ray exposure mask on which a predetermined pattern is formed and a sample are held in parallel at an interval of about 10 μm, and X-rays are irradiated through the X-ray mask to thereby expose the surface of the exposure target. A 1: 1 transfer method for forming a transfer pattern is adopted.

In this 1: 1 transfer method, since the dimensional accuracy and positional accuracy of the pattern of the X-ray mask directly become the device accuracy,
1/10 of the minimum line width of the device in the line mask pattern
Dimensional accuracy and positional accuracy are required. Also, since SOR light (synchrotron radiation) is the preferred X-ray source, the X-ray mask must have a structure that does not damage strong X-rays. Furthermore, in the situation where the line width of the device starts from 0.5 μm and goes to 0.1 μm of the next generation, the aspect ratio of the cross section of the pattern of the X-ray mask increases, so that various manufacturing difficulties increase.

As described above, in order to realize X-ray lithography,
The development of the structure and manufacturing method of the X-ray mask is the most important key.

An X-ray mask generally has the following structure. That is, a thin film made of an X-ray transmissive material having a particularly low X-ray absorptance is formed on a ring-shaped mask support, and a mask pattern made of a material having a high X-ray absorptivity is formed on the X-ray transmissive thin film. (X-ray absorber pattern). Here, the mask support is used to support the X-ray transparent thin film in order to reinforce that the X-ray transparent thin film is extremely thin and has low mechanical strength.

Further, a reinforcing frame is further provided on the back side of the mask support,
There has also been proposed a method of preventing the mask support from being deformed by the tensile stress of the X-ray transparent thin film.

Incidentally, this X-ray exposure mask has conventionally been manufactured by a method as shown in FIGS. 3 (a) to 3 (f).

First, a third CVD process was performed at a substrate temperature of 1200 ° C.
As shown in FIG. 1A, a 2.7 μm thick SiC film 2 is formed on a Si substrate 1. Under these conditions, a SiC film having a polycrystalline structure and an internal stress of 3 × 10 ⁹ dyn / cm ² was obtained. Next, Si
An SiC film 3 is also formed on the back side of the substrate 1. Here, the SiC film 2 is used as an X-ray transparent thin film. The X-ray transparent thin film transmits X-rays and emits alignment light (visible,
It is required that the film be a self-supporting film having excellent transparency to infrared rays and having a tensile stress. At present, BN, Si, SiC, Ti and the like have been reported as this material.

Next, as shown in FIG. 3 (b), after selectively removing the central part of the SiC film 3 on the back side, a W film 4 is formed on the SiC film 2 on the front side as an X-ray absorber. The X-ray absorber is required to have a large X-ray absorption coefficient at an exposure wavelength, a low internal stress, and easy fine processing. At present, Au, Ta, W, WNx and the like have been reported as such materials. Regarding the internal stress of the X-ray absorber, 1 ×
It is essential that the stress be as low as about 10 ⁸ dyn / cm ² , and the deposition is performed by controlling the internal stress by a sputtering method capable of controlling the stress.

Next, as shown in FIG. 3 (c), after a resist 5 for electron beam lithography is applied on the W film 4 by sputtering, a pattern is drawn by electron beam lithography, and a desired pattern is formed on the resist 5. Form.

Next, as shown in FIG. 3D, the W film 4 is selectively etched by a dry etching method using the resist 5 as a mask to obtain an X-ray absorber pattern.

Then, as shown in FIG. 3 (e), the SiC film 3 on the back surface is used as a mask by a wet etching method such as KOH or the like.
The substrate 1 is etched.

Finally, a ring-shaped reinforcing frame 6 made of Pyrex glass is bonded to the silicon substrate 1 with an epoxy adhesive 7 as shown in FIG.

 An X-ray mask is manufactured through the above steps.

In such an X-ray mask manufacturing process, it is a big problem that the displacement of the X-ray absorber pattern is likely to occur when the last reinforcing frame is bonded (Oki et al .:
Proceedings of the Second Microprocess Conference (p94).
This misalignment can be caused by the difference in thermal expansion coefficient between the mask support and the reinforcing frame, the stress generated between the reinforcing frame of the mask support due to the volume change when the adhesive solidifies, and the uniform adhesive force over the entire bonding surface. Is difficult to obtain.

Therefore a thickness of 2 mm to 5 with strength that does not require a reinforcing frame
Although it has been proposed to use a silicon substrate of 0.2 mm as a mask support (Sano et al., Proceedings of the 33rd Annual Conference of the Allied Physics-related Lectures, P324), the time required for backside etching is enormous. Not practical. Further, there is a disadvantage that the stress of the X-ray absorber or the X-ray transparent thin film cannot be measured.

In order to solve such a drawback, the present inventors made the bonding surface between the X-ray mask support and the reinforcing frame or the X-ray transparent thin film a mirror surface, and set the X-ray mask support and the reinforcing frame or the X-ray transparent thin film. Have been proposed by direct bonding without using an adhesive (Japanese Patent Application No. 1-312193).

According to this method, the X-ray mask support can be bonded to the reinforcing frame or the X-ray transparent thin film without any change in the volume of the adhesive or the distortion of the mask due to the uneven adhesive force. For this reason, it is possible to prevent the occurrence of displacement of the X-ray absorber pattern, and successfully form a highly accurate X-ray mask.

In this method, an X-ray absorber thin film pattern is formed in the steps shown in FIGS. 3 (a) to 3 (e) as described above, and the silicon substrate whose surface is polished after the shape processing of the Si substrate is performed. After the silicon substrate 1 as a mask support is treated with dilute hydrofluoric acid, the reinforcing frame is made of dilute hydrofluoric acid and then directly joined. Bonding is performed in a vacuum to prevent air from remaining on the bonding surface, and heat treatment is performed to obtain bonding strength, thereby completing the bonding.

The X-ray mask formed by the above steps can reduce the displacement of the in-plane pattern in the mask. That is, if the same silicon is used for the mask support and the reinforcing frame, the problem due to the difference in thermal expansion coefficient is eliminated, and since the adhesive is not used, the volume of the mask support changes due to the solidification of the adhesive. Since there is no problem such as the stress generated between the metal and the reinforcing frame and the difficulty in obtaining a uniform adhesive force over the entire adhesive surface, it is considered that the pattern accuracy is remarkably improved.

As described above, a high-precision X-ray mask has been successfully formed by adopting the direct bonding method. However, as a next problem, a decrease in yield is a factor preventing practical use. In other words, the joints may be peeled off during ultrasonic cleaning.
The problem is that only a small yield can be obtained.

In order to investigate the cause, a cross section of the bonding surface was observed using a transmission electron microscope. As a result, when polishing the joint surface,
It has been found that a ground layer having a thickness of about 50 nm mixed with an abrasive is formed on the surface of the joint surface, thereby reducing the adhesive strength.

(Problems to be Solved by the Invention) As described above, in the X-ray mask manufacturing process, it is a major problem that the displacement of the X-ray absorber pattern is likely to occur at the time of bonding the last reinforcing frame. I have.

Further, the X-ray mask formed by the direct bonding method can prevent positional displacement and has high accuracy, but when polishing the bonding surface, the thickness of the mixed surface of the abrasive formed on the bonding surface is high.
The crushed layer of about 50 nm caused a decrease in the adhesive strength, which caused a decrease in the yield.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent a decrease in adhesive force when a reinforcing frame is joined to a mask support or an X-ray permeable thin film, and to improve the production yield of an X-ray mask.

[Constitution of the Invention] (Means for Solving the Problems) In order to achieve the above object, the invention according to claim 1 includes an X-ray transparent thin film forming step of forming an X-ray transparent thin film on a mask support. An X-ray absorber thin film forming step of forming an X-ray absorber thin film on the X-ray transparent thin film; an X-ray absorber thin film pattern forming step of patterning the X-ray absorber thin film into a desired shape; A bonding step of bonding a reinforcing frame to the mask support or the X-ray permeable thin film, wherein the mask support, the X-ray permeable thin film, and the reinforcing frame are preceded by the bonding step. A surface treatment step of performing chemical dry etching or reactive ion etching on at least one bonding surface is provided, and the bonding step is performed by direct bonding.

(Operation) In the present invention, before bonding the reinforcing frame to the mask support or the X-ray permeable thin film, the bonding surface is subjected to chemical dry etching or reactive ion etching to remove a crushed layer to make a clean surface. By the addition, the crushed layer on the bonding surface is removed by chemical dry etching or reactive ion etching, and the bonding is performed in a good surface state, so that the yield is improved.

(Example) Example 1 Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In this method, an X-ray absorber thin film pattern is formed after attaching a reinforcing frame to an X-ray mask support.

First, a 3-inch Si substrate with a plane orientation (111) and a thickness of 600 μm polished on both sides was placed on a SiC-coated graphite susceptor using a high-frequency heating LPCVD apparatus. At 1100 ° C, HC1 gas was used. The natural oxide film and heavy metal contaminants present on the Si substrate were removed by subjecting the Si substrate to gas phase etching. This allows Si
The surface mask cleaning process of the substrate is completed.

Next, as shown in FIG. 1 (a), silane (SiH ₄ ) as a Si raw material, acetylene (C ₂ H ₂ ) as a C raw material, and hydrogen (H ₂ ) as a carrier gas are supplied to supply a substrate temperature of 11.
At 00 ° C., a 2 μm thick SiC film 12 is deposited on the Si substrate 11, and a 0.5 μm thick SiO ₂ film 13 is deposited on the back surface of the Si substrate 11 by LPCVD using silane and oxygen. An opening of 20 mmφ was provided at the center of the SiO ₂ film 13 by lithography technology.

Next, as shown in FIG.
Sputtering W film 14 on SiC film 12 by 0.5μm
Deposited. The sputtering power was 1 kW, and the gas pressure was 3 mTorr at which the stress was 0 on the low pressure side where a W film having a high density could be formed. The stress of the W film thus formed was measured from the warpage of the Si substrate 11, and as a result, 3 × 10 ⁸ N / m
^{Was 2} . Next, Ar ions were implanted into the W film 14 at an energy of 180 keV at a dose of 3 × 10 ¹⁵ atoms / cm ² to reduce the stress of the W film to zero.

Next, as shown in FIG. 1 (c), the reinforcing frame 15 made of silicon coated with the SiO ₂ film and the silicon substrate 11 as a mask support are mirror-polished, and the atomic They were bonded (direct bonding) in vacuum by force and fixed.
Then, the adhesive strength is ensured through a heat treatment at 400 ° C. for 3 minutes.

Next, as shown in FIG. 1 (d), a 0.6 μm thick CMS (chloromethylated polystyrene) is applied as an electron beam resist 16 on the W film 14 and baked at 150 ° C. in an N ₂ atmosphere. After the solvent in the electron beam resist 16 is removed, the resist 16 is drawn at a dose of 150 μC / cm ² by electron beam lithography using a variable shaped beam with an acceleration voltage of 50 KeV to form a desired pattern (minimum line width 0.2 μm).
m) was formed.

Next, as shown in FIG. 1 (e), the W film 14 is anisotropically etched by ECR plasma etching with SF ₆ + 10% O ₂ , a gas pressure of 5 mTorr and a microwave power of 200 W using the resist 16 as a mask. Patterned.

Then, as shown in FIG. 1 (f), the Si substrate 21 was etched using the SiO ₂ film 13 as a mask to form an opening of 20 mmφ.

In the above-described embodiment, the example in which the joining between the reinforcing frame and the mask support is performed by direct joining has been described. However, the present invention is also applicable to joining via an adhesive, and this case is particularly effective.

Further, in the above embodiment, W was used as the X-ray absorber, but the present invention is not limited to this, and Ta, its nitride or carbide, Au or the like can be used.

Also, the X-ray transparent thin film is not limited to SiC, and SiN _x , BN, boron-doped Si, or the like can be used.

Further, the reinforcing frame is not limited to silicon, but may be a silicon compound or glass such as Pyrex glass.

In addition, prior to direct bonding, the bonded surface after polishing is CDE
(Chemical dry etching) method or RIE (Reactive Ion Etching) method to remove the crushed layer on the surface and then join the surfaces is more effective.

As described above, by attaching the reinforcing frame to the X-ray mask support and then forming the X-absorber pattern, a high-precision X-ray mask can be obtained without causing displacement during joining of the reinforcing frame. be able to.

In addition, various modifications can be made without departing from the scope of the present invention.

Embodiment 2 Next, a second embodiment of the present invention will be described.

In this example, prior to direct bonding between the X-ray mask support and the reinforcing frame, the bonded surface after polishing is treated by RIE (reactive ion etching) to remove the crushed layer and then bond.

First, using a high-frequency heating LPCVD system, SiC
A 3-inch Si substrate 21 with a plane orientation (111) that has been polished on both sides is placed on a graphite susceptor coated with, and the Si substrate is subjected to gas-phase etching with HC1 gas at 1100 ° C. The existing native oxide and heavy metal contaminants were removed. Thereby, the surface mask cleaning treatment of the Si substrate is completed.

Next, as shown in FIG. 2 (a), trichlorosilane (SiHC1 ₃₎ as the Si raw material, propane as C material (C
₃ H _8), at a substrate temperature of 1100 ° C. by supplying the gas of hydrogen (H ₂₎ is used as a carrier gas, 1.0 micron a SiC film 22 on the Si substrate 21
After depositing a 0.5 μm SiC film 23 on the back surface of the Si substrate 21 under the same conditions as those described above, an opening of 20 mmφ is provided at the center of the SiC film 23 by ordinary photolithography technology. Was.

Next, as shown in FIG.
Sputtering device W film 24 on SiC film 22 0.5μm
Deposited. The sputtering power was 1 kW, and the gas pressure was 3 mTorr at which the stress was 0 on the low pressure side where a W film having a high density could be formed. As a result of measuring the stress of the W film thus formed from the warpage of the silicon substrate 21, 3 ×
It was 10 ⁷ N / m ² .

Subsequently, Ar ions are applied to the W film 24 at an energy of 180 ke.
V was implanted at a dose of 3 × 10 ¹⁵ atoms / cm ² to reduce the stress of the W film 24 to zero.

Next, as shown in FIG. 2C, the back surface of the Si substrate 21 was etched with a mixed solution of HF / HNO _{3 using} the opening of the SiC film 23 as a mask.

Next, as shown in FIG. 2 (d), a 0.6 μm-thick CMS (chloromethylated polystyrene) is applied as an electron beam resist 25 on the W film 24 and baked at 150 ° C. in an N ₂ atmosphere. After removing the solvent in the electron beam resist 25, the resist 25 is drawn at a dose of 150 μC / cm ² by electron beam lithography using a variable shaped beam with an acceleration voltage of 50 KeV to obtain a desired pattern (minimum line width 0.2 μm).
m) was formed.

Then, as shown in FIG. 2 (e), the W film 24 is patterned by anisotropic etching using a resist 25 as a mask with SF ₆ + 10% O ₂ , a gas pressure of 5 mTorr and a microwave power of 200 W by ECR type plasma etching. did. And CF
_After the mask SiC on the back surface was removed by reactive ion etching using _four gases, the front surface was polished, and the crushed layer generated by this polishing was removed using an RIE apparatus. At this time, CF ₄ + O ₂ was used as an etching gas, and the applied power was 200 W.

Next, the surface of the reinforcing frame 26 made of silicon was polished, and a crushed layer generated by the polishing was removed using an RIE apparatus. At this time, CF ₄ + O ₂ was used as an etching gas, and the applied power was 200 W.

Then, the bonding surface of the reinforcing frame 26 and the silicon substrate 21 as a mask support was treated with dilute hydrofluoric acid, and then directly bonded. Bonding was performed in a vacuum to prevent air from remaining on the bonding surface.

Finally, heat treatment was performed at 400 ° C. for 3 minutes. The heat treatment is performed here to increase the adhesive strength.

The yield of peeling of the reinforcing frame of the X-ray mask formed by the above steps was 93%. Incidentally, the yield by the conventional method was 70%.

As described above, according to the method of the present invention, the bonding surface of the X-ray mask support and the reinforcing frame is previously etched to remove the crushed layer and obtain a clean surface, and then the direct bonding is performed. It is considered that the strength was greatly increased and peeling was prevented.

In this embodiment, both the mask support and the reinforcing frame are etched, but either one may be used. The etching method may be not only the RIE method but also a CDE method using CF ₄ or CF ₄ + O ₂ as an etching gas.

Note that the present invention is not limited to the above-described embodiments. For example, the X-ray absorber thin film is not limited to W,
Ta, Mo and their nitrides and carbides can also be used. Using SiC film as an X-ray transparent film but, SiN _X, B
An N, boron doped Si substrate can be used.

Furthermore, the reinforcing frame is not limited to silicon,
A glass such as a silicon compound or Pyrex glass may be used.

In the above embodiment, the direct joining of the mask support and the reinforcing frame has been described. However, the present invention is also applicable to the case where the reinforcing frame is joined to the X-ray transparent thin film.

In addition, various modifications can be made without departing from the scope of the present invention.

〔The invention's effect〕

As described above, in the present invention, before bonding the reinforcing frame to the mask support or the X-ray transparent thin film, the bonding surface is subjected to chemical dry etching or reactive ion etching to remove the crushed layer and clean the surface. By obtaining the surface, there is no separation and the yield is improved.

[Brief description of the drawings]

1 (a) to 1 (f) are views showing a manufacturing process of an X-ray mask according to a first embodiment of the present invention, and FIGS. 2 (a) to 2 (f) are drawings of the present invention. FIGS. 3 (a) to 3 (f) are views showing a manufacturing process of the X-ray mask of the second embodiment, and FIGS. 3 (a) to 3 (f) are diagrams showing the manufacturing process of the conventional X-ray mask. 1,11,21 ... Silicon substrate, 2,12,13,22,23 ... X-ray transparent film, 4,14,24 ... X-ray absorbing film pattern, 5,16,25 ... CMS
Resist, 6,15,26 ... Reinforcing frame, 7 ... Adhesive.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 1/16

Claims (1)

(57) [Claims] 1. An X-ray transparent thin film forming step of forming an X-ray transparent thin film on a mask support, and an X-ray absorber thin film forming step of forming an X-ray absorber thin film on the X-ray transparent thin film X for patterning the X-ray absorber thin film into a desired shape.
In a method for manufacturing an X-ray mask, comprising: a step of forming a line absorber thin film pattern; and a step of joining a reinforcing frame to the mask support or the X-ray transparent thin film, prior to the joining step, the mask support, An X-ray mask comprising: a surface treatment step of performing chemical dry etching or reactive ion etching on at least one bonding surface of the X-ray transparent thin film and the reinforcing frame; and the bonding step is performed by direct bonding. Production method.