JPH0345526B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention applies to
The present invention relates to a method for manufacturing a line exposure mask.

Since the X-ray exposure method uses soft X-rays with short wavelengths as a pattern transfer medium, it is possible to transfer fine patterns all at once with high precision using proximity exposure.
For this reason, it has the advantage that the mask is less likely to become contaminated and that highly accurate mask positioning is possible. On the other hand, in X-ray exposure equipment using an electron beam excitation type X-ray source, soft X-rays generated radially from a point light source are used as a pattern transfer medium, so warping and distortion of the mask and wafer may occur in the transferred pattern. It also has the problem of greatly affecting positional shift and blurring. However, increasing the diameter of wafers is also essential for increasing the productivity and yield of semiconductor devices. For this reason, conventionally, a large-diameter X-ray exposure mask (hereinafter referred to as a plastic mask) with a thin film of plastic such as Mylar, Kabuton, polyimide, or Parylene-N as a support layer for the transferred pattern is used to perform contact exposure. Attempts have been made to transfer to large diameter wafers.

However, to date, these plastic masks have problems such as changes in the dimensions of the plastic thin film over time, changes in dimensions due to fluctuations in temperature and humidity, and distortion that occurs when the plastic thin film that is in close contact with the wafer is separated during use. Therefore, it is extremely difficult to overlay and expose ultrafine patterns of around 1 μm or less with the desired precision.

On the other hand, as shown in Fig. 1, a desired transfer pattern 1 made of a heavy metal such as Au that absorbs X-rays well
1 is a thin film 1 made of an inorganic material with high soft X-ray transmittance such as Si, Si ₃ N ₄ , SiO ₂ , SiC, BN, Al ₂ O ₃ etc.
The development of an X-ray exposure mask (hereinafter referred to as an inorganic mask) having a structure in which the thin film 12 is reinforced and supported by a Si frame 14 formed by selectively etching and removing the thin film 12 using a protective film 13 is also actively being developed. It is. Such inorganic masks generally have almost no change in dimensions over time, and small variations in dimensions due to changes in temperature or humidity, so they are suitable for manufacturing VLSIs and the like that require extremely high-precision alignment.

The disadvantage of inorganic masks is that the thin film 12 and the Si
The stress acting on the interface with the frame 14 causes warping, and the mechanical strength is lower than that of a plastic mask, so it is still difficult to expose large diameter wafers all at once. However, the above-mentioned problems when exposing a large-diameter wafer can be solved by employing a step-and-rebeat exposure method using an inorganic mask with a relatively small diameter and high flatness. This is because by doing this, the mask area can be small, and the small dimensions of the mask reduce warping, and furthermore, the decrease in mask pitch accuracy due to changes in temperature and humidity is kept to a minimum. Furthermore, since the spacing and parallelism between the X-ray exposure mask and the wafer can be finely adjusted for each exposure step, highly accurate alignment is possible regardless of the diameter of the wafer.

Furthermore, when considering the case of manufacturing an X-ray exposure mask for such a step-and-rebeat method, the number of patterns drawn is also large when forming patterns on the X-ray exposure mask using fine pattern drawing technology such as electron beam exposure technology. , you can even enjoy the advantage that it becomes easier because it requires less.

Now, let's take a look back at the problems with conventional inorganic masks that attempted to achieve large apertures. For example, as can be seen from the schematic cross-sectional view in Figure 1, X
In order to form the Si frame 14 that forms the line-transmissive area and reinforces and supports the thin film 12, first the transfer pattern 1 is
The surface on which 1 was formed is provided with means to protect it from being etched or damaged, and then
It is customary to selectively etch away areas not covered with the protective film 13 from the back surface of the Si substrate.
In this case, it takes approximately one hour to apply means to protect the surface of each mask, and further five to six hours to selectively etch the back surface. Although an inorganic mask is an excellent transfer mask having many advantages as described above, its poor productivity is still a problem. Generally, to make a device such as a MOS transistor, it is necessary to use at least 5 to 6 masks, or about 10 masks as a set.If you include the spare mask, the number of masks required and the manufacturing required. Time has become a huge amount.

In addition, in the conventional method of manufacturing an X-ray exposure mask,
In the process of forming X-ray transparent thin films and protective films against anisotropic etchants, there are variations in film thickness and film quality for each Si substrate, so the amount of warping of the X-ray exposure mask substrate may vary. There is also the problem that the pitch accuracy is lowered due to variations in the temperature and the fixing state of the substrate during the electron beam exposure process.

The present invention solves the problems in manufacturing such inorganic masks and provides a method for simultaneously producing a large number of X-ray exposure masks. explain. Figure 2a
to FIG. 2F are schematic cross-sectional views sequentially showing the main manufacturing steps of an X-ray exposure mask according to an embodiment of the present invention. In Figure 2 a,
21 is a Si single crystal plate, and at least one surface is mirror-polished (hereinafter, the mirror-polished surface will be referred to as the surface,
(The surface that does not necessarily require mirror polishing is called the back surface.)

In the following, this embodiment will be described on the assumption that the surface of 21 is a {100} plane. Therefore, hereinafter, they will be specifically referred to as crystal planes and crystal axes, but these are based on the assumption that the surface of 21 is {100}, and are not essential conditions for the present invention. Other combinations are of course possible. On the back side of the Si single crystal substrate 21
A thin film 22 made of one of Si ₃ N ₄ , SiO ₂ or SiC, or a composite film thereof is deposited by a method such as a CVD method, a sputtering method, or a thermal oxidation method. Next, as shown in FIG. 2B, a predetermined region of the thin film 22 is etched away using, for example, a conventional optical exposure technique, to form a pattern 22' consisting of a portion of the thin film. At this time, the pattern 22' is preferably formed parallel to the <110> direction of the Si single crystal substrate 21. The openings 23 and 24 formed by etching away a part of the thin film 22 are
3 corresponds to an area where a desired transfer pattern will be formed, and the latter 24 is for etching away a part of the Si single crystal substrate 21 in a later process to divide it into a plurality of X-ray exposure masks. corresponds to the scribe line. However, the groove width of the opening 24 is 2 (t-100) x (tan54.7°) ^-1 μm when the thickness of the Si single crystal substrate is tμm.
m
It is desirable that the value is between 2(t-10)×(tan54.7°) ^-1 μm. Next, as shown in FIG. 2C, Si ₃ N ₄ , SiO ₂ , SiC,
A thin film 25 made of a material that transmits X-rays well, such as BN or Al ₂ O ₃ , is formed using a method such as a CVD method, a sputtering method, or an ion vapor deposition method. Furthermore, as shown in FIG. 2d, a desired transfer pattern 26 is formed on the surface of the thin film 25 using a method such as an electron beam exposure technique, an ion beam exposure technique, or a deep ultraviolet exposure technique. Formed with heavy metals. Hereinafter, the pattern 26 will be referred to as an X-ray absorber pattern. in this case,
The X-ray absorber pattern 26 is formed in a region corresponding to the opening region 23.

Thereafter, while protecting the X-ray absorber pattern using an arbitrary jig, a part of the Si single crystal substrate 21 is etched using an anisotropic etchant such as a potassium hydroxide aqueous solution or hydrazine hydrate. The opening 23 and the etched groove 24' are removed as shown in FIG. 2e.
form. At this time, since the anisotropic etchant has a high etching rate for the {100} plane of the Si single crystal substrate and a low etching rate for the {111} plane, the thin film pattern 22' is previously etched onto the Si single crystal substrate as described above. If the opening region 23' and the opening groove are formed parallel to the <110> direction of 21, a {111} plane will appear on the side surface of the Si single crystal substrate 21' surrounding the opening region 23' and the opening groove 24'. The angle formed by the {111} plane is equal to the angle 54.7° between the {100} plane and the {111} plane. Therefore, as described above, the width of the opening area 24 is estimated in advance.
2(t-100)×corresponding to the thickness tμm of the Si single crystal plate
(tan54.7゜) ^-1 μm to 2 (t-10) x (tan54.7゜)
^-1μm
If the etched groove 24' is formed within the range of
It is formed in a range of approximately (t-100) μm to (t-10) μm. Therefore, in the region of the etched groove 24', the thickness of the Si single crystal substrate 21' is approximately 10 μm.
m to 100 μm, and since the etched grooves are previously formed parallel to the <110> direction, after the etching process using the anisotropic etching solution, the second etching groove is
As shown in FIG. f, the mask can be easily divided manually into a plurality of rectangular plate-shaped X-ray exposure masks with the etched groove 24' as a boundary. In other words, according to the method provided by the present invention, the etching process of the Si substrate of the X-ray exposure mask, which conventionally required a lot of time, can be significantly shortened, and the productivity of inorganic masks with excellent dimensional accuracy can be improved. This will make a major contribution. In general, in an inorganic mask, the thin film 25, which serves as a support layer for the transferred pattern, is formed to a thickness of several μm or less at most in consideration of the transmittance of soft X-rays. It is extremely difficult to divide the Si single crystal substrate 21' using a cutting machine without damaging the thin film 25 and the X-ray absorber pattern 26. Furthermore, according to the manufacturing method of the present invention, a large number of X-ray exposure mask substrates can be obtained from the same Si substrate at the same time, which reduces the pitch accuracy between different masks, which is a big problem in conventional X-ray exposure masks. will be significantly improved. This effect holds true both between masks at the same level (for example, wiring level) and between masks at different levels (for example, LOCOS and wiring level).

FIG. 3 is a schematic plan view of an X-ray exposure mask shown to explain the embodiment of the present invention in more detail. FIG. 2e corresponds to a cross-sectional view taken along line A-A' in the figure, viewed from the direction of the arrow. In FIG. 3, 31 is a Si substrate having a {100} plane as its surface, and 32 is an orientation flat showing the <110> direction. Rectangular area 33 indicated by a broken line
2 is an opening region formed by selectively etching a predetermined region of the Si single crystal substrate 31 using an anisotropic etchant, and corresponds to 23' in FIG. A film that transmits X-rays well is formed in advance in each opening region 33, and a desired X-ray absorber pattern is formed in advance on the thin film. The X-ray absorber pattern can be formed at different mask levels in each of the opening regions 33, or it is also possible to repeatedly form a pattern at the same mask level. In either case, for example, a pattern forming process using electron beam exposure technology has the advantage that the mask substrate only needs to be installed in the apparatus once. In FIG. 3, a two-dot chain line 34 is an etched groove formed by etching away a portion of the Si single crystal substrate 31 using an anisotropic etchant, and is indicated by 24' in FIG. corresponds to a portion. The shape of this etched groove is determined by the number of main planes of the Si single-crystal substrate, the number of side faces of the etched groove, and the direction of the etched groove. Become. In the above example, {100
As a result of selecting the {111} plane}, the {111} plane, and the <110> direction, a rectangular shape is obtained, and these selections can be made appropriately in consideration of the etching solution.
An example was given earlier when setting the width of the etched groove 24.
The value of 54.7° has the character of being a constant determined crystallographically by setting these conditions.

A state in which the Si crystal substrate 31 of FIG. 4 is divided into individual X-ray exposure masks with the etched groove 34 as a boundary is shown. In FIG. 4, 41 is the X-ray transparent thin film 33.
This is a reinforcing support frame formed of a part of the Si single crystal substrate 31 for reinforcing and supporting the Si single crystal substrate 31.

As described above, according to the present invention, multiple X-ray exposure masks can be manufactured at once, so the productivity of high-precision X-ray exposure masks using a Si single crystal substrate is significantly improved compared to conventional methods. This is particularly effective in the production of step-and-repeat X-ray exposure masks.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a conventional inorganic mask using a Si substrate. Each of FIGS. 2a to 2f is a schematic cross-sectional view showing the main steps of a method for manufacturing an X-ray exposure mask according to an embodiment of the present invention, and FIG. Si showing examples
FIG. 4 is a schematic plan view of a single crystal substrate, and FIG. 4 is a schematic plan view of a single X-ray exposure mask obtained by the manufacturing method of the present invention. In the figure, each number indicates the following. 11, 26...X-ray absorber pattern, 1
2, 25... X-ray transparent thin film, 13, 22'...
Protective film, 21, 31...{100}Si single crystal substrate,
14, 21', 41... Reinforcement support beams formed from a part of the Si single crystal substrate, 23', 33... Etched grooves formed by etching away a part of the Si single crystal substrate.

Claims (1)

[Claims] 1. A step of forming an X-ray transparent thin film on one surface of the Si single crystal substrate, a step of forming an X-ray absorber pattern made of heavy metal on the thin film, and a step of forming an X-ray absorber pattern on the other surface of the Si single crystal substrate. A step of forming a thin film made of one of Si ₃ N ₄ , SiO ₂ or SiC, or a composite film of these, and patterning this thin film into a desired shape, and using the patterned thin film as a protective film. a plurality of opening regions in which a portion of the single crystal substrate is etched away using an anisotropic etchant to expose the back surface of the X-ray transparent thin film; and a V-shape arranged to surround the opening regions; 1. A method for manufacturing an X-ray exposure mask, comprising the steps of: simultaneously forming an etched groove having a cross section; and dividing the mask into a plurality of X-ray exposure masks using the etched groove as a boundary.