JPH04299514A - Method for manufacturing a mask for X-ray lithography - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing a mask for X-ray lithography, and in particular to a method for uniformly forming an alkali etching protective film to improve the yield of a membrane and to form a membrane into a predetermined shape. The present invention relates to a method for manufacturing an X-ray lithography mask.

0002

BACKGROUND OF THE INVENTION With the miniaturization of pattern formation in semiconductor devices, X-ray lithography is seen as a promising lithography technique. Therefore, this X-ray lithography mask is made by providing an X-ray transparent film on the surface of a silicon substrate, creating an X-ray absorber on this surface as necessary, and then removing the opposite side of the substrate. The entire surface is coated with boron nitride, silicon nitride, etc. using a method such as plasma CVD to create an alkaline etching protective film, and the central part of this protective film is dry etched with CF4 gas to partially remove this film. It is manufactured by adding an alkaline solution to the removed portion and performing alkaline etching to remove the silicon substrate and form the X-ray transparent film into a membrane.

[0003] However, the X-ray lithography mask used in this X-ray lithography is said to have an X-ray absorber formed in a desired shape on the surface of an X-ray transparent film, which is reinforced with a support. However, since this X-ray transparent membrane supports an X-ray absorber, it is also called an X-ray support (membrane) or an X-ray transparent membrane.

This X-ray transparent film is generally made of boron nitride (
BN), silicon nitride (Si3 N4), silicon carbide (
It is a thin film of 10 μm or less of inorganic material made of light elements with small X-ray absorption coefficients such as SiC), and X-ray absorbers include gold (Au), tungsten (W), and tantalum (SiC).
It is said to be made of an inorganic substance made of heavy metals with a large X-ray absorption coefficient such as Ta), but this X-ray transparent membrane has a thickness of 5 x 108 to 5 x 1 in order to maintain its thin film form.
It is essential that the material has a tensile stress of 0.09 dynes/cm2.

However, since this X-ray transparent film has tensile stress, the substrate on which the X-ray transparent film is formed is subjected to shear stress, and as a result, warpage occurs in the substrate. That is, for example, if a 3-inch silicon wafer with crystal orientation (100) and thickness t (μm) is used as a substrate, a tensile stress of 1×109 dynes/cm2 is applied to the substrate.
When an X-ray transparent film with a thickness of 2.0 μm is formed, the amount of warpage d (μm) of the substrate is expressed as d=36.5×105/t2, and this amount of warpage is equal to 2 of the thickness of the substrate. is inversely proportional to the power.

Therefore, the thickness of the substrate should be reduced to 0.5 mm (5 mm).
00μm), the amount of warpage at this time is d=14.5μ
m, and the thickness of the substrate is 1.0 mm (1,000 μm)
Then, the amount of warpage in this case is d = 3.6μm, and if the thickness of the substrate is 2.0mm (2,000μm), the amount of warpage is d = 0.9, and as the substrate becomes thicker, the amount of warpage decreases rapidly. However, for X-ray lithography masks, the line width of the absorber pattern is required to be 0.2 to 0.4 μm, so in order to obtain a highly accurate mask, the substrate of the X-ray mask must have no warpage. Since it is important to have a surface as flat as possible, it is advantageous for this substrate to have a large thickness to reduce warpage.

However, when the substrate is made thicker, a disadvantage arises in that the step of removing a predetermined region on the opposite side to the surface on which the X-ray transparent film is formed (hereinafter this step is abbreviated as a back etching step) takes a long time. For example, if a silicon substrate with crystal orientation (100) is used as the substrate and a 20% potassium hydroxide aqueous solution is used as the etching solution, the back etching process at 90°C will take 8 to 10 hours for a silicon substrate with a thickness of 1 mm. In the case of a silicon substrate with a thickness of 2 mm, 15 to 20 hours are required, and if this back etching process takes longer, an X-ray transparent film and an X-ray absorber pattern are formed on its surface. In this case, the damage to the X-ray absorber pattern increases, and as a result, troubles such as distortion and breakage are more likely to occur.

[0008]

[Problem to be Solved by the Invention] Therefore, in order to shorten the time of this back-etching process, a method has been considered in which the area to be back-etched is thinned in advance by a mechanical processing method such as grinding. However, if you simply perform normal grinding, the surface after processing will be rough and the protective film for alkaline etching will not be formed uniformly, and as a result, the thin part of the protective film for alkaline etching will be removed during the back etching process. Since the membrane is locally etched by the alkaline etching agent, there are disadvantages in that the membrane is damaged or the shape of the membrane is not in a predetermined shape.

[0009]

[Means for Solving the Problems] The present invention relates to a method for manufacturing an X-ray lithography mask that solves these disadvantages. In a method of manufacturing an X-ray lithography mask by forming an X-ray absorber pattern on a substrate and then removing a region of a silicon substrate on the opposite side of an X-ray transparent film, the silicon substrate is removed in a region including the removed region on the back surface. It is characterized in that a thinning process is performed in advance, and then a surface flattening process is performed so that the surface roughness of the processed surface is 1,000 Å or less in terms of center line average roughness (Ra). be.

[0010] That is, the present inventors have conducted various studies to develop a method for manufacturing an X-ray lithography mask that can improve the membrane yield after alkali etching and can form a membrane into a predetermined shape. , The substrate used here is subjected to a thinning process in advance on the back side of the area including the removed area, and then the surface roughness of the processed surface is flattened so that the center line average roughness is 1,000 Å or less. The inventors have completed the present invention by discovering that this object can be achieved by This will be explained in further detail below.

[0011]

[Operation] The present invention relates to a method for manufacturing a mask for X-ray lithography, and the gist of this invention is to perform a thinning process in advance on the removal area on the back side of a silicon substrate, and then flatten the processed surface. It is something to do.

The production of the X-ray lithography mask itself in the present invention involves forming an X-ray transparent film made of boron nitride, silicon nitride, silicon carbide, etc. on a silicon substrate, and coating the surface with gold, tungsten, tantalum, etc. After forming an X-ray absorber consisting of the This is done using a known method in which the silicon is partially removed by dry etching, and then the silicon is removed by alkali etching in this area to create a membrane.

However, as mentioned above, the silicon substrate used here is warped due to the tensile stress of the X-ray transparent film, but the thicker it is, the more advantageous it is in terms of reducing this warping. The silicon substrate used in the
mm or more, preferably 2 to 5 mm. In addition, after forming an X-ray transparent film and an X-ray absorber on the surface of this product, the area opposite to the X-ray transparent film is removed, but if this is thick, a long time is required for alkaline etching. Therefore, it is processed to become a thin film in advance.

This thinning process may be carried out using a known processing machine such as a lathe, milling machine, or grinding machine, but from the viewpoint of dimensional accuracy and smoothness of the finished surface, it is necessary to use a grinding wheel at high speed. It is preferable to use a rotating grinder. However, this grinding is usually done with a coarse grindstone that uses hard and large abrasive grains with a high degree of bonding, but this results in a large surface roughness, and if left as it is, it will not be possible to grind it on this surface. The alkaline etching protective film made of boron nitride, silicon nitride, silicon carbide, etc. does not uniformly cover this surface, and the thin part of this coating is etched with the alkaline etching solution, making it difficult to use as a protective film. This ground surface is then required to be flattened as it becomes free of grain.

This flattening process uses abrasive grains that are softer and smaller in particle size than the abrasive used in the above-mentioned thinning process, for example,
Grinding can be done using a fine whetstone with a small grain size that uses abrasive grains with a grain size of 700 to 2,000, but the surface roughness due to this flattening treatment is equal to the center line average roughness specified in JIS B0601 ( Ra) must be 1,000 Å or less, preferably 500 Å or less.

[0016] Furthermore, the center line average roughness (Ra) of the surface of the silicon substrate that has been thinned with the above-mentioned abrasive is 3,000.
Since the thickness is ~8,000 Å, the alkaline etching protective film formed on this by chemical CVD or the like becomes non-uniform, but the surface of the silicon substrate after this planarization treatment is as described above. so that its center line average roughness is 1
,000 Å or less, especially 500 Å or less, so that the alkali etching protective film can be made uniform, and therefore, according to this, dry etching with CF4 and etching removal of silicon with an alkaline etching solution can be performed as specified. This gives the advantage that membranes can be obtained in a high yield and in a predetermined shape.

[0017] In the present invention, the thickness of the starting material is 1 m.
A silicon substrate having a thickness of more than m, preferably 2 to 5 mm, is made thinner by the above-described thinning treatment and planarization treatment. However, although the thinner this thickness is, the shorter the alkali etching time is, the thickness is preferably 1 mm or less, preferably 0
．． What is necessary is just to set it to 1-0.5 mm.

[0018]

[Examples] Next, examples of the present invention and comparative examples will be given. Examples 1 to 4, Comparative Examples 1 to 2 One side of a double-sided polished silicon wafer with a diameter of 3 inches, a thickness of 3 mm, and a crystal orientation (100) was given a tensile strength of 1.5 x 109 dynes/cm2 by high-frequency magnetron sputtering. A silicon carbide coating with a thickness of 1.0 μm was formed.

Further, a circular area with a diameter of 40 mm in the center of the opposite side of this silicon wafer was ground with a universal grinder using a grindstone made of diamond abrasive grains of No. 280 to a depth of 2.4 mm. A counterbore was provided, and a counterbore with a depth of 0.1 mm was provided using a universal grinder using a grindstone made of diamond abrasive grains with a grain size of #700 to #2,000 as shown in Table 1. When the centerline average roughness (Ra) of the processed surface was measured using Surfcorder SE-30C (trade name, manufactured by Kosaka Institute), the results shown in Table 1 were obtained.

[0020]

[Table 1]

[0021] Next, the entire surface of the silicon wafer that has been subjected to the thinning process and planarization process is subjected to plasma CVD.
A boron nitride film with a thickness of 0.5 μm is formed using the method, and an alkaline etching protective film is formed thereon.
The boron nitride film in this area was removed by dry etching using a gas to expose the silicon surface in this area.

Next, a 20% aqueous potassium hydroxide solution as an alkaline etching solution was poured onto the exposed silicon surface, and alkali etching was performed at 90° C. for 5 hours to remove the silicon and form a silicon carbide membrane. , a membrane with a normal shape of 2.5×2.5 mm was obtained.

However, for comparison, when the planarization process in the example was carried out using a diamond grindstone with a grain size of 500 and 360 degrees as shown in Table 1, in this case, the center of the obtained silicon wafer surface Line average roughness (Ra
) is 1,240 Å, 2,150 Å as shown in Table 1.
An alkaline etching protective film made of silicon carbide was made on this, but it became non-uniform, and the membrane obtained by dry etching with CF4 gas and alkali etching was as shown in Table 2. None of them had straight parts, making them incompletely circular.

[0024]

[Table 2]

[0025]

The present invention relates to a method for manufacturing an X-ray lithography mask, and as described above, after forming an X-ray transmitting film on a silicon substrate and an X-ray absorbing pattern on the surface thereof, In a method of manufacturing an X-ray lithography mask by removing a region of a silicon substrate on the opposite side to the radiation-transmitting film, the substrate is processed to thin the film in advance in the region including the removed region on the back side, and then the processed surface is thinned. The surface is flattened so that the center line average roughness (Ra) of the surface is 1,000 Å or less.

If the silicon plate used here is treated in this way, the surface of the silicon substrate in the region where the back surface is removed will be extremely flat, and the alkali etching protective film provided on the silicon substrate will be Since it can be made uniform, subsequent dry etching using CF4 gas and etching removal of silicon using an alkaline etching solution can be performed as specified, and therefore the desired membrane can be obtained with high yield. Moreover, it has the advantage that it can be obtained in a predetermined shape.

Claims (2)

[Claims] Claim 1: After forming an X-ray transparent film on a silicon substrate and further forming an X-ray absorber pattern on its surface,
The region of the silicon substrate opposite to the X-ray transparent film is removed and
In a method for manufacturing a mask for line lithography, the silicon substrate is processed in advance to form a thin film in the region including the removed region on the back surface, and then the surface roughness of the processed surface is adjusted to the center line average roughness (Ra). X, characterized in that the surface is flattened so that the thickness is 1,000 Å or less
A method for manufacturing a mask for line lithography. 2. The method of manufacturing an X-ray lithography mask according to claim 1, wherein the silicon substrate has a thickness of 1.0 mm or more, and the thickness of the thinned region is less than 1.0 mm.