JPH02241019A - X-ray mask blanks, x-ray mask structure body, x-ray aligner and x-ray exposure method - Google Patents

Abstract

PURPOSE:To obtain a suitable X-ray mask blanks excellent in alignment property and dimensional accuracy by setting the thickness variation rate of the X-ray transmitting region of an X-ray transmitting film in a range, and forming an antireflection film relieving the reflectivity variation of alignment light caused by the thickness variation of the transmitting film, on the both surfaces of the transmitting region. CONSTITUTION:An X-ray mask blanks are constituted of an X-ray transmitting film 2 to retain an X-ray absorber 4 and a retaining frame to retain the absorber 4. The thickness variation rate of an X-ray transmitting region of the X-ray transmitting film 2 is in the range of 0.5-5%. On both surfaces of the region, an antireflection film 3 to relieve the reflectivity variation of alignment light caused by the thickness variation of the transmitting film 2 is formed. For example, on a silicon substrate 1, a silicon carbide film 2 is formed by plasma CVD method; an etching protection film composed of silicon oxide is formed on the periphery of the rear of the silicon substrate 1; the substrate 1 is back-etched, and then the protecting film is eliminated. By sputtering method, silicon oxide is deposited to be 0.146mum+ or -10% thick on the surface and the rear, thereby forming the antireflection film 3 and obtaining the X-ray mask blanks.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to semiconductor manufacturing equipment, particularly X-ray mask blanks with excellent alignment properties between an X-ray mask and an exposed material, an X-ray mask structure, and an X-ray exposure device. The present invention relates to an apparatus and an X-ray exposure method.

(Prior Art) In recent years, with the increasing density and speed of semiconductor integrated circuits, the pattern line width of integrated circuits has tended to be reduced by 70% in about three years.

With the further integration of large-capacity memory elements (for example, 4M DRAM), devices with a capacity of 16 Mbit and the like have come to be designed on a 0.5 μm rule. For this reason, printing devices are required to have even higher performance, and high performance such that the minimum line width that can be transferred is 0.5 μm or less is beginning to be required. Therefore, the wavelength of the exposure light source is in the X-ray region (7 to 1
An X-ray exposure device that uses the light of four people is being developed.

The X-ray exposure apparatus has an X-ray generation source (X-
ray), an exposure chamber 10, a wafer chuck 16 that fixes an exposed material 15 such as a silicon wafer in a predetermined position, and a mask chuck 1 that fixes an X-ray mask 14 in a predetermined position.
2, an alignment light source, an alignment detection section 13, etc. as main elements.

For example, as shown in FIG. 4, the mask structure used in these X-ray exposure devices is made of a silicon compound of about 2 μm, particularly silicon nitride, silicon carbide, polyamide, etc., deposited on a silicon wafer 1 by chemical vapor deposition or the like. A film 2 made of silicon or the like is formed so as to have a slight tensile stress (FIG. 4a). Next, membrane 2
An absorber pattern 4 is formed on the surface of the silicon wafer 1 using a material that absorbs X-rays well, such as gold (Fig. 4b), and then the necessary area (an area for transmitting X-rays) is formed from the back side of the silicon wafer 1. When removed by etching, a mask in which the inorganic thin film 2 is held under tension on the silicon wafer 1 is obtained. However, in this state, the silicon wafer 1 is thin and has low strength, making it inconvenient for handling and practical use.Therefore, as shown in FIG. 4C, the reinforcing body 5 may be bonded with an adhesive 6 for use.

(Problem to be solved by the invention) As the X-ray transparent film that holds the absorber of the X-ray mask as described above, inorganic films such as silicon carbide, silicon nitride, and polysilicon are close to the silicon substrate that serves as the holding frame. It is considered promising because of its high coefficient of thermal expansion. The thinner these X-ray transmitting membranes are, the better from the standpoint of X-ray transmittance, but on the contrary, the thicker the better from the standpoint of mechanical strength. In consideration of both of these performances, a film having a thickness of about 2 μm has conventionally been used in many cases.

In addition, if these X-ray transparent films have uneven film thickness in their X-ray transparent region, intensity unevenness will occur in the transmitted X-rays.
Although it is desirable that the film has a uniform thickness, the intensity unevenness of the transmitted X-rays is also caused by the unevenness of the thickness of the reflecting mirror and Be window of the device, so the intensity unevenness of the transmitted X-rays should be within 3.5%. It is necessary to keep it to

However, for these silicon carbide films, silicon nitride films, polysilicon films, etc., prior to X-ray exposure, a semiconductor laser (for example, 8,300 laser beams) is incident at an angle of, for example, 17.5@ to align the mask. Up to about 55% if
(silicon carbide), approximately 36% (silicon nitride), and approximately 76% (polysilicon), and the transmitted X-ray intensity unevenness is 3.5%.
Even if the film is within %, the reflectance will vary greatly due to slight differences in film thickness, so lower the S/N ratio of the alignment light,
There is a problem that alignment efficiency is poor.

Further, depending on the arrangement of the alignment detection section, detection may be hindered by reflected light.

Therefore, an object of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide an X-ray mask blank, an X-ray mask structure, an X-ray exposure apparatus, and an X-ray exposure method that have excellent alignment properties, are appropriate, and have excellent dimensional accuracy.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention provides an X-ray mask blank consisting of an X-ray transparent film for holding an X-ray absorber and a holding frame for holding the same, in which the thickness variation rate of the X-ray transparent area of the X-ray transparent film is is within the range of 0.5% to 5%, and an antireflection film is formed on both sides of the above region to alleviate changes in the reflectance of alignment light due to changes in the thickness of the transmitting film. The present invention provides blanks, an X-ray mask structure, an X-ray exposure apparatus, and an X-ray exposure method using these mask blanks.

(Function) The thickness variation rate of the xa transmission region of the X-ray transmission film is set within the range of 0.5% to 5%, and the alignment light is reflected on both sides of the X-ray transmission region due to the thickness variation of the transmission film. By forming an anti-reflection film that alleviates the rate fluctuation, the intensity unevenness of transmitted X-rays is suppressed to within 3.5%, and the reflectance for alignment light and the rate of change in reflectance due to thickness changes are reduced, making alignment X with excellent properties, regularity, and dimensional accuracy
Line exposure is achieved.

(Example) The present invention will be explained in more detail with reference to embodiments shown in the drawings below.

Example 1 FIG. 1 is a sectional view of the manufacturing process of an X-ray mask blank and an X-ray mask structure of the present invention.

First, the silicon substrate 1 was set in a plasma CVD chamber, the back pressure was reduced to 2 x 10-' Torr, and then 10 sc of silane gas diluted to 10% with hydrogen was applied.
(2) and methane gas 10105e were supplied through a hole drilled in the lower electrode. The temperature of the substrate 1 was heated to 650° C., and a high frequency power of 50 W was applied at a pressure of 5×10 Torr to form a silicon carbide film 2 on the substrate 1 (FIG. 1a).

Next, an etching protective film made of silicon oxide is formed around the back surface of the silicon substrate 1, and the substrate 1 is back-etched with a mixed solution of pyrocatechol: ethylenediamine: water = 4:46.4:49.6, and then etched with fluoroethylene diamine. The silicon oxide protective film was removed with a mixture of acid and ammonium fluoride = 1:1, as shown in Figure 1 (
A mask blank as shown in b) was formed.

The thickness of the X-ray transparent film 2 in the X-ray transparent region of this blank is 1.96 to 2.04 μm, and the maximum is 0.08 μm.
It had thickness unevenness of m. The intensity unevenness of transmitted X-rays caused by the uneven thickness of this film was 2.1%.

FIG. 5 is a simplified diagram of the X-ray exposure apparatus of the present invention, and 10 is an exposure chamber. 11 is the Be window port, 2
0 is an exhaust port, and the exposure chamber 10 is B e
f It is isolated from the X-ray generation source, and the chamber can be exposed in any conditions such as air, vacuum, He atmosphere, etc.

12 is a mask stage, 13 is an alignment detection section, 1
4 is a mask, 15 is a wafer, 16 is a wafer chuck, 1
Reference numeral 7 designates a Unihachi stage, 18 represents an X-axis stage drive motor, and 19 represents a Y-axis guide.

When the mask 14 is attracted to the mask stage 12, it is mechanically set in a certain direction using a positioning bin or an orientation flat. Wafer 1
5 is similarly set on the wafer chuck 16, and then the relative positional relationship between the mask 14 and the wafer 15 is determined by instructions from the alignment detection section 13, and then exposed to X-rays.

The mask blanks are placed in the exposure chamber 10 as described above.
and a semiconductor laser (83°) with an incident angle of 17.5°.
00 people) Using alignment light, mask (blanks)
When aligning 14 and wafer 15, the reflectance varied greatly from 27.5% to 55% depending on the location.
It was difficult to keep the S/N ratio of alignment light constant.

Next, silicon oxide was deposited to a thickness of 0.146 μm±10% on both the front and back surfaces of the mask blank by sputtering to form an antireflection film 3, thereby obtaining an X-ray mask blank of the present invention.

When the blank was attached to an X-ray exposure device in the same manner as above and the reflectance of the alignment light was measured in the same manner, the reflectance and its fluctuation range depending on the location were 0.1% to 6.3%.
The alignment accuracy has been improved. Furthermore, noise on the alignment detection section due to reflection of alignment light has also been significantly reduced. In addition, the final X-ray transparent membrane (2+3
) The maximum intensity distribution of transmitted X-rays was 3.35%.

Alternatively, the reinforcing body 5 may be bonded with an adhesive 6 as shown in FIG. 1(e).

Example 2 FIG. 2 is a sectional view of the manufacturing process of the mask structure of the present invention.

In Example 1, the thickness unevenness of silicon carbide film 2 is at most 0.
．． 08 μm, and the intensity unevenness of transmitted X-rays is about 3.5%, but even with this level of thickness unevenness (O, Oa μm), the reflectance of the alignment light is, for example, at wavelengths 8, 3.
00 people, 27.5 with alignment light with an incident angle of 17.5°
It varies from % to 55%.

Therefore, a silicon nitride film with a thickness of 0.105 μm ± 10% was previously formed on the surface of the silicon substrate 1 as an antireflection film 3 by magnetron sputtering, and then a silicon carbide film was further formed on the surface under the same conditions as in Example 1. 2 and then further form a silicon nitride film as an antireflection film 3 on the surface thereof in the same manner as described above (FIG. 2a).

Next, an etching protection film is formed on the back surface of the substrate 1, and the substrate is removed by back etching with a 30% by weight caustic potassium solution (Fig. 2b).Furthermore, a tantalum film is formed on the surface, and this is dry etched to remove the etching film. A radiation absorber pattern 4 was formed to obtain an X-ray mask structure of the present invention (FIG. 2C).

When the X-ray mask was set in the exposure chamber 10 as described above and alignment was performed using a semiconductor laser (8,300 people) alignment light with an incident angle of 17.5°, the reflectance and its variation range depending on location were 0. .1% to 18
．． The alignment accuracy has improved to within 5%.

Furthermore, noise on the alignment detection section due to reflection of alignment light has also been significantly reduced. In addition, the final X-ray transparent membrane (
The intensity distribution of transmitted X-rays in 2◆3) was 2.6% at maximum.

Example 3 FIG. 3 is a sectional view of the manufacturing process of the mask structure of the present invention.

As in Example 2, a polyimide film having a thickness of 0.620 μm±3% was formed on the silicon substrate 1 by a coating method as an antireflection film 3 for reducing reflectance.

The substrate l having the anti-reflection film 3 was set in a magnetron sputtering device, and after the back pressure was reduced to 2×10-” Torr, argon gas was flowed for 30 seconds and the pressure was increased to 5.
X 10 "" Torr, high frequency power of 100 W was applied to the silicon nitride target, and after the discharge was sufficiently stabilized, the shutter was opened to form a silicon carbide film 2 on the substrate 1.

The thickness of this silicon carbide film 2 is from 1.98 μm to 2.02 μm.
m, and has a maximum thickness unevenness of 0.04 μm (note that a silicon carbide film with the same thickness unevenness without forming a polyimide film has a wavelength of 8.300 nm and an incident angle of 17.5
It has reflectance unevenness from 46% to 55% at @).

Furthermore, a polyimide film having a thickness of 0.620 μm±3% was formed as an antireflection film 3 on the surface of the silicon carbide film 2 by the same coating method as described above (FIG. 3a).

Next, a tungsten film is formed on the surface, and an X-ray absorber pattern 4 is formed by dry etching (Fig. 3b).Finally, an etching protection film is formed on the back surface of the substrate.
By back etching and removing a part of the substrate,
A line mask structure was obtained (Figure 3c).

When the X-ray mask was set in the exposure chamber 10 as described above and alignment was performed using a semiconductor laser (8,300 people) alignment light with an incident angle of 17.5@, the reflectance and its variation range depending on location were 0. % to 3.0%
The alignment accuracy has been improved. or,
Noise on the alignment detection unit due to reflection of alignment light has also been significantly reduced. Also, the final X-ray transmission 1! !
The maximum intensity distribution of the (2+3) transmitted X-rays was 1.6%.

Furthermore, the formation of the polyimide film improves the strength of the entire mask, making it easier to handle.

Example 4 First, a silicon substrate 1 was set in a plasma CVD chamber, and after the back pressure was reduced to 2 x 10-'Torr, silane gas diluted to 10% with hydrogen was applied for 5 seconds.
m and ammonia gas for 20 sec+a were supplied through a hole made in the lower electrode. The temperature of the substrate 1 was heated to 250° C., and a high frequency power of 50 W was applied using a pressure cuff at 5×10 −3 Torr to form a film of silicon nitride WA2 on the substrate 1 (FIG. 1a).

Next, a mask blank was created by back-etching the substrate in the same manner as in Example 1 (Fig. 1b).The film thickness of this blank was between 1.96 μm and 2.04 μm, and the intensity of transmitted X-rays was The unevenness was 2.3%, but the wavelength was 8.
The reflectance for alignment light of 30 OA and an incident angle of 17.5° varied from 21% to 36% depending on the location.

After forming the X-ray absorber pattern 4 made of gold on the film 2,
Both sides of membrane 2 are made of silicon oxide and have a thickness of 0.146 μm±1.
A 0% antireflection film 3 was formed by vapor deposition.

When the X-ray mask was aligned as described above, the reflectance and its fluctuation range depending on the location were from 0% to 1.1.
%, improving alignment accuracy. or,
Noise on the alignment detection unit due to reflection of alignment light has also been significantly reduced. In addition, the final X-ray transparent membrane (2◆
The maximum intensity distribution of the transmitted X-rays in 3) was 3.5%.

Example 5 First, a silicon substrate 1 was set in a magnetron sputtering device, and after reducing the back pressure to 2 x 10-'Torr, argon gas was flowed at a rate of 30 sec to a pressure of 5 x 10-' Torr.
' Torr, high frequency power too was applied to the silicon nitride target, and after the discharge was sufficiently stabilized, the shutter was opened and a silicon nitride film 2 was formed on the substrate 1 (Fig. 1a) e Next, the same as in Example 1 A mask blank was prepared by back-etching the substrate (FIG. 1b). The film thickness of this blank is between 1.98 μm and 2.24 μm, and the reflectance for alignment light with a wavelength of 8,300 and an incident angle of 17.5° is 30% to 36.1% depending on the location.
It varied between.

When a 2.5% polyimide film of 0.620 μm thickness was formed on both sides of the film 2 of the mask blank by a coating method and alignment was performed in the same manner, the reflectance and its fluctuation range depending on location were 3.1%. It decreased from 13.2% to 13.2%.
Alignment accuracy has been improved. Furthermore, noise on the alignment detection section due to reflection of alignment light has also been significantly reduced.

Moreover, the intensity distribution of the transmitted X-rays of the final X-ray transmitting membrane (2+3) was 1.6% at the maximum.

In addition, the elastic limit is larger than in the case of silicon nitride alone,
The overall strength of the mask has been improved, making it easier to handle.

Example 6 Same as Example 3, but the X-ray transparent film is formed from polysilicon.

First, a silicon nitride film with a thickness of 0.105 μm±10% was formed on the surface of a silicon substrate 1 as an antireflection film 3 by magnetron sputtering, and then a back pressure of 2×10 −′ was applied in a pyrolytic CVD apparatus. After pulling down to Torr, silane gas diluted to 10% with hydrogen was flowed for 50 sec, the pressure was set to 0.3 to 0.5 Torr, and the substrate 1
was heated to a temperature of 600 to 650° C., and a polysilicon film 2 was formed on the substrate 1.

The thickness of this polysilicon film is from 1.95 μm to 2.05 μm.
When measured using only a similarly formed polysilicon film, the intensity unevenness of transmitted X-rays was 2.2%.
Met. The reflectance for alignment light with a wavelength of 8,300 and an angle of incidence of 17.5° varies from 4% to 76, depending on the location.
It varied widely between %.

Further, an antireflection film 3 made of silicon nitride and having a thickness of 0.105 μm±10% was formed in the same manner as described above (Fig. 3a).
).

Furthermore, a tungsten film is formed on the surface and this is dry etched to form the pattern 4 of the X-ray absorber.
), an etching protection film was further formed on the back surface of the substrate 1, and back etching was performed to obtain the X-ray mask structure of the present invention (FIG. 3d).

When alignment was performed in the same manner as described above using this mask blank, the reflectance and its fluctuation range depending on location were in the range of 0% to 5.2%, and the alignment accuracy was improved. Furthermore, noise on the alignment detection section due to reflection of alignment light has also been significantly reduced. In addition, the intensity distribution of the final X-ray transmitting membrane (2÷3) of the transmitted membrane X-rays is 3.
It was 4%.

Example 7 A substrate was prepared in the same manner as in Example 5! A mask blank is prepared by forming a film of silicon nitride 2 on top, and the thickness of the silicon nitride film 2 is reduced to 1.
．． The thickness was between 96 and 2.04 μm. The intensity unevenness of transmitted X-rays through this membrane was 2.3%.

When alignment was performed in the same manner as above using a He-No laser (6328 people) and alignment light with an incident angle of 20@, the reflectance varied greatly from 12.0% to 37% depending on the location.

Next, as the anti-reflection film 3, silicon oxide was coated with a thickness of 0.11 μm±10
When the silicon nitride film 2 was sputter-deposited to a thickness of 1.5% on both sides and aligned in the same manner, the reflectance and its variation ranged from 0% to 1.5%.

Further, the intensity distribution of the transmitted X-rays due to the thickness unevenness of the final X-ray transmitting film (2+3) was 3.2%.

Although the present invention has been described above using specific examples, the present invention is not limited to these examples. That is, the mask blank, mask structure, X-ray exposure apparatus, and exposure method of the present invention have no other features except that the thickness variation rate of the X-ray transmitting film of the mask is defined and an antireflection film is formed on both surfaces thereof. Any of the configurations may be a conventionally known configuration and is not limited to the above embodiment.

In particular, in order to maximize the effects of the present invention, it is necessary to reduce the thickness variation rate of the X-ray transmitting film and the intensity unevenness of transmitted X-rays by 3.5%.
In order to keep it within the range of 0.5 to 5% in the line-transmissive region, it is necessary to keep it within the range of 0.5 to 5%. Thickness variation rate 0.5%
It is difficult in practice to reduce the intensity of transmitted X-rays to less than 3.5%, and if the variation rate exceeds 5%, it is not economically appropriate. It becomes difficult.

Incidentally, the rate of variation in thickness referred to in the present invention is a value calculated by the following formula.

T: average value of the thickness of the X-ray transparent membrane Δt = film thickness unevenness of the X-ray transparent membrane (maximum film thickness - minimum film thickness) In addition, the thickness of the X-ray transparent film in the present invention varies depending on the material used, so there is no general rule. However, in terms of X-ray transmittance, the thickness is preferably such that the X-ray transmittance is 30 to 85%, more preferably 50 to 85%.

Regarding the anti-reflection film, as long as it is formed from a material with a refractive index lower than that of the X-ray transmission film, in addition to the above-mentioned examples, for example, an anti-reflection film of silicon carbide or silicon oxide may be used on an X-ray transmission film of polysilicon film. etc. can be used similarly.

Further, the optimum thickness of these antireflection films depends on the material thereof, the wavelength and incidence angle of the alignment light, and can be determined as follows.

Alignment light wavelength: λ Incident angle of alignment light: θ.

Incident angle in anti-reflection film: 01 Refractive index of anti-reflection film: n.

Optimal thickness of anti-reflection film: If d is an integer 2 m, then from Bragg's formula, 2n, d, cosθI = (m+H)λ-(1)Sn
From the equation of e l l, sin θ. = n, sin θI - (2) From (1) and (2), the optimal thickness of the anti-reflection film is defined by the above formula, but ±
Even if there is a film thickness unevenness of about 10%, it exhibits sufficient effectiveness as an antireflection film.

Further, m may be an integer, but if m is too large, the antireflection film will become thick and the X-ray transmittance will decrease, so m is preferably about 0.1.2.3.

(Effects) As described above, according to the present invention, the thickness variation rate of the X-ray transparent region of the X-ray transparent membrane is within the range of 0.5% to 5%, and
By forming an anti-reflection film on both sides of the X-ray transmitting region to reduce changes in the reflectance of the alignment light due to changes in the thickness of the transmitting film, the unevenness of the intensity of the transmitted X-rays can be suppressed to within 3.5%, while the The reflectance and its rate of change in reflectance due to changes in thickness are reduced, and X-ray exposure with excellent alignment and appropriate dimensional accuracy is realized.

Further, although the anti-reflection coating is effective even on one side, the effect is even greater when it is coated on both sides. Furthermore, it is also possible to reduce the rate of variation in the alignment light reflectance when wavelength variation (approximately ±100) occurs in the alignment light.

[Brief explanation of drawings]

1 to 3 are cross-sectional views of the X-ray mask manufacturing process according to the present invention, FIG. 4 is a cross-sectional view of the conventional X-ray mask manufacturing process, and FIG. 5 is a cross-sectional view of the X-ray mask manufacturing process according to the present invention. FIG. 2 is a simplified diagram of the device. 1: Silicon substrate 2: X-ray transmission film 3: Anti-reflection film 4: X-ray absorber 5: Reinforcement body 6: Adhesive 10: Exposure chamber 11: Be window boat 12: Mask stage 13: Alignment detection section 14: Mask 15: Wafer 16: Wafer chuck 17: Wafer stage 18: X-axis stage drive motor 19: Y-axis guide 20: Exhaust boat Figure 1 Figure 2 Figure 5

Claims (4)

[Claims] (1) In an X-ray mask blank consisting of an X-ray transparent film for holding an X-ray absorber and a holding frame for holding the same, the thickness variation rate of the X-ray transparent area of the X-ray transparent film is 0. 5
% to 5%, and is characterized in that an antireflection film is formed on both sides of the above region to alleviate changes in reflectance of alignment light due to changes in the thickness of the transmitting film. (2) In an X-ray mask structure consisting of an X-ray absorber, an X-ray transparent membrane for holding the absorber, and a holding frame for holding these, the thickness of the X-ray transparent area of the X-ray transparent membrane. The variation rate is within the range of 0.5% to 5%, and an antireflection film is formed on both sides of the above region to alleviate changes in reflectance of the alignment light due to changes in the thickness of the transparent film.
line mask. (3) An X-ray generator including an X-ray generation source, an exposure chamber, a means for fixing the exposed material in a predetermined position, a means for fixing an X-ray mask in a predetermined position, an alignment light source, and an alignment detection section.
In the radiation exposure apparatus, the X-ray mask includes an X-ray absorber, an X-ray transparent film for holding the absorber, and a holding frame for holding these, and the X-ray mask includes an X-ray transparent area of the X-ray transparent film. An X-ray mask that has a thickness variation rate within the range of 0.5% to 5% and has an anti-reflection film formed on both sides of the above region to alleviate changes in the reflectance of the alignment light due to changes in the thickness of the transmission film. An X-ray exposure device characterized by the following. (4) In an X-ray exposure method in which an X-ray mask is stacked on the surface of a material to be exposed, the X-ray mask is aligned using alignment light, and X-rays are exposed through the mask, the X-ray mask is made of an X-ray absorber. and an X-ray transparent membrane for holding the absorber, and a holding frame for holding these, and the thickness variation rate of the X-ray transparent area of the X-ray transparent membrane is within the range of 0.5% to 5%. An X-ray exposure method characterized in that the X-ray mask is an X-ray mask in which an anti-reflection film is formed on both sides of the region to alleviate changes in the reflectance of alignment light due to changes in the thickness of the transmission film.