JPS5923105B2 - Manufacturing method for soft X-ray exposure mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a mask for soft X-ray exposure, and particularly provides a method for manufacturing a mask for soft X-ray exposure that does not cause mask displacement and enables manufacturing of a large-area mask. It is.

Conventionally, optical plate-making technology has been used to manufacture semiconductor integrated circuit devices.

However, the resolution ability of optical plate-making technology is limited by interference and diffraction effects that are directly related to the wavelength of the light used, and the minimum line width that can be stably reproduced is about 2 μm. A scanning electron beam exposure method and an X-ray exposure method have been developed to overcome this limitation of resolution by light. However, the former method takes time to perform exposure by sequentially scanning an electron beam, and although it is used for manufacturing a master mask, it is not economical to directly expose a semiconductor substrate. On the other hand, a technique called an X-ray transfer method that uses soft X-rays with a wavelength of several angstroms instead of light is cheaper and more economical than the scanning electron beam method. A mask for soft X-rays consists of a mask material and a thin film that supports the mask material and transmits the soft X-rays. The thickness of this mask material is limited by the technique of patterning the mask material, and the thickness is up to about 0.5 microns, assuming a minimum line width of 1 micron. On the other hand, the thickness of a thin film that transmits soft X-rays is approximately 10 μm at most, depending on the wave length of the X-rays and the material of the thin film. Conventionally, silicon or organic films have been used as thin films that transmit X-rays.

Although organic films facilitate the manufacture of large-area masks, they have the fatal drawback of causing "mask misalignment" due to the difference in thermal expansion coefficient between the film and the silicon of the semiconductor substrate. This is because the accuracy of the mask cannot be maintained unless temperature control is performed not only during transfer but also during the mask manufacturing process. On the other hand, in the case of a silicon thin film, since it is made of the same material as the substrate, there is no problem with the above-mentioned "mask misalignment," but since it is more fragile than an organic film, it is easy to make a mask for a small area, but it is difficult to make a mask for a large area. Previously '5 was considered difficult.

An example of manufacturing a mask using a silicon thin film is shown in cross-sectional views in FIGS. 1 and 2. In this method, a silicon substrate is partially thinned and this part is used as a mask. 1 in the figure is a silicon substrate, and a layer 2 containing a high concentration of boron is grown on this 1 main surface by diffusion or epitaxial growth. Then, the mask material 3 is formed.

Next, when etching is performed from the back side using an alkaline solution, the silicon layer 2 containing a high concentration of boron is more difficult to etch than the silicon substrate, so the silicon substrate is etched from the exposed side, resulting in the result as shown in FIG. However, this method does not have perfect selectivity, and in liquid phase etching, as shown in Figure 3, the etching rate is fast at the edge portions, forming grooves (arrows in the figure) and sometimes forming holes, and also causing variations in etching. The area where the etching occurs occupies a considerable portion, which reduces the effective area of the mask, and has the disadvantage that the etched surface is not uniform. This invention was made to eliminate the above-mentioned conventional drawbacks.
In order to manufacture a soft X-ray exposure mask with a relatively large area using a silicon thin film, the outline of the process is to form a lattice pattern on the exposed parts of the first epitaxial growth layer formed on the silicon substrate that are not covered around the substrate periphery. This is achieved by increasing the strength of the mask by increasing the strength of the mask, and by dividing the selective etching of the silicon into two stages to improve the selectivity and improve the surface uniformity.

Next, embodiments of this invention will be described.

In Figure 4, the impurity concentration is 1018 particles/Cc or less, the diameter is 75
Pilgrimage, 600μ thick n-type (100) silicon wafer 1
1, the impurity concentration was reduced to 1 x 1020 pieces/5CC at 1170°C by hydrogen reduction of trichlorosilane (SiHCl3).
A first epitaxial layer 12 having a thickness of 35 microns was formed containing boron.

Next, by thermal decomposition of monosilane (SiH4),
The thickness is 3.8 including 8 x 1014 pieces/Cc of boron at °C.
A second epitaxial layer 13 of μ was laminated. A chromium layer 14 having a thickness of 150× was then deposited by vacuum evaporation in an example. This is to facilitate the subsequent application of gold plating. Next, a desired resist pattern 15 with a thickness of 0.8 μm is formed by scanning electron beam exposure, and using this as a mask, a gold layer 16 with a thickness of 0.5 μm is selectively deposited. After removal, the result will be as shown in FIG. The impurity concentrations exemplified for each of the first and second epitaxial layers 12 and 13 are based on the etching rate of the first epitaxial layer, the first epitaxial layer, and the second epitaxial layer with respect to the silicon substrate. State 10:
This is to increase the impurity concentration to 1,200:1, and the impurity concentration of the first epitaxial layer is 2×1019/Cc.
As mentioned above, the impurity concentration of the second epitaxial layer is 5×10
It is preferable that the number is 15 pieces/Cc or less.

Next, as shown in FIG. 6, a protective film 17 against the silicon etching solution is applied to the surface subjected to the above treatment, and the exposed principal surface of the silicon wafer (the principal surface opposite to the principal surface subjected to the above treatment) is applied.
Leaving the peripheral edge 18 of 5 mI wide, the capacitance ratio is given by the following formula: HF:HN
O3=3:97・・・・・・・・・・・・・・・・・・
・・・・・・400μ thick with silicone etching solution 1
was removed.

Next, as shown in Fig. 7, the peripheral part was covered with a protective film having a width of 711 mm and a mixture of ethylenediamine:water:pyrocatechol:17 and 0:8.
The silicon wafer 11 was etched with a silicon etching solution having a composition of 0:39...2 to form a stepped surface 18' of the silicon substrate.

This etching solution having composition 2 has a selectivity of 15:1 in terms of the impurity concentration ratio between the wafer 11 and the first epitaxial layer 12. Then, by means of well-known photoetching, a width of 400
A lattice-shaped resist of μ is applied, and the peripheral part is covered with a protective film with a width of 9 μ. HF:HNO3:CH3COOH=1:3:8
. . . Selective etching of the first epitaxially grown layer is achieved in an etching solution having a composition of 3.

That is, as shown in FIG.
3, 23..., and arranged an example of carbon (O electrode 24 and platinum (Pt) electrode 25 in the liquid, making the carbon electrode 24 positive and the platinum electrode 25 negative, so that the electrode potential at both ends was 40 mV.
This is accomplished by a selective etching method in which hydrogen peroxide (H2O2) is introduced in a controlled manner from the hydrogen peroxide inlet 26. The etching solution having this composition has a selectivity of 200:1 in terms of the impurity concentration ratio between the first epitaxial layer 12 and the second epitaxial layer 13 mentioned above. The surface roughness of the second epitaxial layer 13 after etching the first epitaxial layer 12 is an excellent smooth surface of 1000X, and compared to the thickness of this layer of 3.8μ, the transmission of X-rays is reduced. can be completely ignored. Etching of the wafer 11 and the first epitaxial layer 12 was performed by rotating the wafer at 40 revolutions per minute and rotating at 20 revolutions per minute. This is effective for obtaining surface uniformity. Further, in the selective etching of the first epitaxial layer 12, the selectivity decreases to 30:1 unless the wafer is rotated. Next, the protective film 17 was removed to obtain an X-ray exposure mask as shown in FIG. This mask covers the first epitaxial layer 12.
The portions left in the grid form become the reinforcing portions of the mask. When aluminum was irradiated with soft X-rays having a wavelength of 8.34λ using the mask formed as described above, an extremely good pattern could be obtained.

That is, according to the method for manufacturing a soft X-ray exposure mask of the present invention, it is easy to form a soft X-ray exposure mask made of thin silicon that is strong and has a highly smooth exposure surface. , it is possible to manufacture a mask with excellent resolution performance, and it has the remarkable advantage that a dense and fine pattern can be formed.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views for explaining a conventional method of manufacturing a mask for soft X-ray exposure, and FIG. 3 is a cross-sectional view for explaining the drawbacks of a conventional mask for soft X-ray exposure and its manufacturing method. 4 to 7 are cross-sectional views illustrating the manufacturing method of a soft X-ray exposure mask according to an embodiment of the present invention in the order of steps, and FIG. 8 is a diagram showing the etching of the second epitaxial growth layer. FIG. 11... Silicon wafer, 12... First epitaxial layer, 13... Second epitaxial layer, 14, 16... Metal layer, 17...
...Protective film, 18... Wafer periphery, 2
1... Etching solution, 22... Etching container, 23... Silicon wafer (at the stage of etching the first epitaxial growth layer), 24...
...Carbon electrode, 25...Platinum electrode, 26.
...Hydrogen peroxide injection port.

Claims (1)

[Claims] 1 Boron impurity concentration is 2×10^1^9 on one main surface of a silicon substrate with an impurity concentration of 10^1^8 pieces/cc or less
forming a first epitaxial growth layer having an impurity concentration of 5×10^1^5 impurities/cc or less on the first epitaxial growth layer; forming a metal mask pattern layer that does not allow soft X-rays to pass through the second epitaxial growth layer through a metal layer that is compatible with the second epitaxial growth layer, and excluding the periphery of the other principal surface of the silicon substrate; Etching with an etchant having a composition ratio of ethylenediamine, water, and pitecatechol of 17 cc: 8 cc: 3 g, and etching the exposed portion of the first epitaxial growth layer that is not covered with the peripheral edge of the silicon substrate with hydrofluoric acid, nitric acid, and acetic acid. A method for manufacturing a mask for soft X-ray exposure, comprising the step of selectively etching with an etchant having a composition ratio of 1:3:8 to selectively leave a portion where a mask pattern layer is not formed.