JPS631740B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an X-ray exposure mask.

The X-ray exposure process is characterized by the fact that there is no generation of secondary electrons or scattering due to dust, which are problems in conventional electron beam exposure processes, and that a fine resist pattern with a high aspect ratio can be obtained.

FIG. 1 is a diagram showing the principle of an X-ray exposure apparatus.

That is, the X-ray exposure apparatus is basically divided into an X-ray generation chamber 1 and a sample chamber 2, and both chambers are separated by a beryllium window 3, so that the X-ray generation chamber 1 is always kept at a high vacuum. This prevents the target 4 from getting dirty.

In the figure, in an X-ray generation chamber 1, an electron beam 6 generated from an electron gun 5 collides with a target 4, and X-rays 7 are generated from the target 4. Then, the X that entered the sample chamber 2 through the beryllium window 3
The rays 7 pass through an X-ray exposure mask 8 and are selectively irradiated onto an X-ray resist 10 deposited on a substrate 9 to be processed.

Here, the X-ray exposure mask 8 consists of a frame 21, a membrane (support film) 22, and an X-ray absorber 23, as shown in detail in FIG.

Conventionally, a rigid thin film such as silicon (Si) or silicon nitride (Si ₃ N ₄ ) has been used as the membrane 22. However, when exposure processing is performed using membranes made of these rigid thin films, if the substrate to be processed warps due to heat treatment during the manufacturing process,
The mask and the substrate to be transferred did not come into complete contact with each other, making it impossible to perform accurate exposure processing.

Therefore, it was proposed to use a plastic film such as polyimide as the membrane.
This structure has the advantage that not only can the mask and the substrate to be processed be brought into perfect contact with each other, but also optical alignment can be performed because the plastic film is transparent.

The frame of such an X-ray exposure mask having a membrane made of plastic film is generally made of stainless steel or pyrex glass.

However, although stainless steel has good processing accuracy, it has a thermal expansion coefficient of 10 × 10 ^-6 /℃, and when performing exposure processing on a silicon substrate (thermal expansion coefficient of 2 × 10 ^-6 /℃), which is the substrate to be processed. , the temperature difference is large, and there is a temperature difference between the time of manufacturing the X-ray exposure mask by electron beam exposure and the time of X-ray exposure processing using the X-ray exposure mask, or if there is a long-term X-ray exposure. If a temperature change occurs at times, a positional shift occurs between the X-ray exposure mask and the substrate to be processed, which is inappropriate in terms of microfabrication. For example, when performing exposure processing on a silicon (Si) substrate with a diameter of 100 [mm], if the temperature difference during the processing is 2 [°C], the maximum positional deviation will reach about 1.6 [μm].

Also, Pyrex glass has a coefficient of thermal expansion of 3.
×10 ^-6 /℃, which is close to silicon, but it has the disadvantage that it is difficult to increase its own processing accuracy.

Therefore, if silicon, which is the transfer target substrate material, is used as the frame material, the transfer deviation due to the temperature difference can be reduced to zero.

By the way, the thickness of the silicon frame used in conventional X-ray masks is usually 76 [mm] in diameter and 300 to 400 [μm].
The thickness is about 600 [μm] with a diameter of 100 [mm]. This is because ordinary LSI manufacturing wafers are used as is, and the thinner the silicon, the shorter the etching time for the silicon.

However, even if the membrane is stretched with uniform tension in a plastic mask made of polyimide or the like, the tension is large, causing deformation of the frame and impairing the pitch accuracy of the absorber pattern. In addition, if there is non-uniform polyimide film thickness or non-uniform temperature within the surface of the film-forming substrate during heat treatment for polyimide formation, the tension distribution will not be uniform and complex deformation will occur in the frame. The disadvantage is that the pitch accuracy of the absorber pattern deteriorates.

One way to solve this problem is to make the silicon frame as thick as possible, but increasing the thickness poses the following two problems.

One is that silicon backside etching takes a long time. If the silicon thickness is 3 mm, the etching rate of potassium hydroxide (KOH) solution or ethylenediamine-pyrocatechol mixture is very slow at approximately 1 μm/min, so it would take 50 hours.

In addition, in the case of a hydrofluoric acid-nitric acid-acetic acid mixture, the etching rate changes depending on the composition, liquid rotation speed, and liquid temperature, but if it is fast, it will be about 10 [μm/min], and the etching time will be as short as about 5 hours. However, there is another problem.

Figure 3a shows the state before etching the back side of the silicon during the manufacturing process of the mask for X-ray exposure.
A sample in which a polyimide film 32 is formed on a silicon substrate 31 having a thickness of ~600 [μm] is sealed with an O-ring 33 so that the etching solution does not enter the outer periphery that remains as a frame.

Figure b shows the state when etching is completed, and when the silicon thickness is about 600 [μm], the O-ring 33
The amount of side etching in the vicinity is small, the sealing state by the O-ring 33 is maintained, and the frame 34 remains.

However, if the silicone is thick, the airtight state cannot be maintained. FIG. 4a shows a thick silicon substrate 4
This is a state in which a sample with a polyimide film 42 formed thereon is sealed with an O-ring 43 before silicon etching.

Figure b shows the state after the etching of the central part is completed, and the side etching amount is large because the silicon substrate is thick, and even with the elasticity of the O-ring, it cannot be sealed, and the etching liquid penetrates into the frame part 44.
I also end up etching myself. Furthermore, if the etching is uneven and thick silicon remains in the form of islands, the polyimide film 42, which is several μm thick, may break due to its weight.

The present invention aims to eliminate the drawbacks of conventional X-ray exposure masks and to provide an X-ray exposure mask that can perform exposure processing with higher precision.

The present invention also provides a manufacturing method that can easily form the X-ray exposure mask.

Therefore, according to the present invention, there is provided an X-ray exposure mask characterized by having a frame having a thickness of 1 mm or more and having the same coefficient of thermal expansion as the substrate to be processed.

Further, according to the present invention, a silicon film forming substrate made of the same material as the substrate to be processed and having a thickness of 1 mm or more is prepared, and the area other than the area that will become the frame is scraped off from the back surface of the substrate by ultrasonic processing or the like. An X-ray method comprising the step of reducing the thickness of the region substrate, forming a membrane and an X-ray absorber pattern, and then removing the film-forming substrate other than the frame by chemical etching or the like from the back side of the substrate. A method of manufacturing an exposure mask is provided.

That is, according to the present invention, an X-ray exposure mask that can prevent deformation of the frame due to membrane tension by increasing the frame thickness and increase the dimensional accuracy of the mask pattern, and such an X-ray exposure mask can be easily manufactured. A method for manufacturing an X-ray mask is provided.

Next, the present invention will be explained in detail using examples.

A specific embodiment of the present invention will be described in more detail with reference to the manufacturing process shown in FIG.

In this example, polyimide was used as the plastic material for the membrane, and silicon (Si) was used as the mask frame material.

First, as shown in FIG. 5a, a film-forming substrate 51 made of silicon and having a thickness of 1 mm or more is prepared.

Next, as shown in FIG. 5B, the region 53 of the film-forming substrate 51 other than the region 52 that will become the frame is removed from the back surface to make it thinner. The thickness should be such that it can be easily selectively etched and still maintain mechanical strength during the subsequent polyamic acid spin coating step, for example, 300 to 600 μm. Silicon is a very hard material, and it is difficult to process it using normal machining methods, such as thinning only the center part while leaving the frame part intact.In this example, we used ultrasonic processing, which is easy to process. .

Next, as shown in FIG.
Polyamic acid was spin-coated to a thickness of about 2 to 5 μm on the surface not subjected to the etching treatment, and then heat treated to form a polyimide film 54.

Next, as shown in FIG. d, the frame 52
The edges are sealed with an O-ring 55, and the thin silicone portion 53 at the center is etched and removed. At this time, as shown in FIG. 5E, since thin silicon is etched, the amount of side etching is small, and the O-ring 55 maintains a tight seal, so that the frame portion is not etched. Figure f shows the state in which etching has been completed.

Next, an electron beam resist layer is formed on one surface of the polyimide film 54, and a desired pattern is exposed to the electron beam resist to form a developed pattern 56. This state is shown in FIG. 5g.

Thereafter, a film 57 of an X-ray absorber such as gold (Au) is selectively formed on the surface of the polyimide film not covered by the resist pattern 55 by a lift-off method, plating method, etc., and then the resist 56 is peeled off. This state is shown in FIG. 5h.

As a result, an X-ray exposure mask according to the present invention having the structure shown in FIG. 5h is completed.

Further, as an application of the present invention, a part of the silicon 61 of a thick silicon substrate is selectively removed by ultrasonic processing as shown in the plan view and cross-sectional view of FIGS. silicon 67
Leave a thick layer. Thereafter, a polyimide film 64 is formed in the same manner as in FIG. 5c, and then backside etching is performed to remove the thin silicon portion. In this case, the silicon lattice (ribs) 67 are etched by the thickness of the thin silicon portion 63, but are left as shown in FIG. 6c.

This rib 67 serves as mechanical reinforcement for the thin polyimide film 64.

As described above, according to the present invention, by using silicon, which is the material of the transferred substrate, as the frame material, it is possible to reduce transfer deviation due to temperature differences to zero, and it is possible to eliminate transfer deviation due to temperature differences, and also to prevent polyimide films having uneven tension. Also, it is possible to easily manufacture an X-ray exposure mask having an absorber pattern with good pitch accuracy without frame deformation.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the general structure of an X-ray exposure device, FIG. 2 is a sectional view showing the general structure of an X-ray exposure mask used in the X-ray exposure device,
FIG. 3 is a process sectional view showing the conventional backside etching process for a thin silicon substrate, FIG. 4 is a process sectional view showing the backside etching process for a thick silicon substrate, and FIG.
The figure is a cross-sectional view showing the manufacturing process of an X-ray exposure mask according to the present invention, and FIG. 6 is a plan view and a cross-sectional view of a ribbed X-ray exposure mask as an application of the present invention. In FIG. 5, 51...thick silicon substrate, 5
2...Frame part, 53...Thin silicon substrate part, 5
4... Polyimide film, 55... 0 ring, 56... Electron beam resist pattern, 57... X-ray absorber.

Claims (1)

[Scope of Claims] 1. Prepare a film-forming substrate with a thickness of 1 mm or more and having almost the same coefficient of thermal expansion as the substrate to be processed, and cover the area other than the area that will become the frame of the mask on one side of the substrate. After selectively removing from the main surface to make the region thin, an X-ray absorber support film is formed on the other main surface of the substrate, and then an etching process is performed from one main surface of the substrate to form the frame. 1. A method for manufacturing an X-ray exposure mask, comprising the step of removing other film-forming substrates.