JPH04190353A - Photomask and its manufacture - Google Patents

Abstract

PURPOSE:To certainly have a light shading part of a photomask stuck to a resist recessed part even in the case when a territory to make a non-exposed part is at the recessed part by providing the recessed part with a depth enough to make the light shading part to be protruded enough to stick it to a non- exposed scheduled territory of a resist membrane. CONSTITUTION:A photomask 30 is selectively provided with a chrome film, for example, as a light shading material on a quartz glass substrate 31, for example, as a light shading substrate, a light shading part 33 is constituted at a part where the chrome film is provided and a light transmission part 35 is constituted at a part where the chrome film is not provided, and simultaneously, there is a recessed part 35a formed by way of removing a part of the glass substrate itself at a part corresponding to the light transmission part 35 of the glass substrate 31 and a recessed part 35a of a depth t2 enough to make the light shading part 33 to be protruded enough to stick it to a non-exposed scheduled territory of a resist membrane. In this case, the light shading part 33 is protruded enough to make contact with a part to make a non-exposed part of a resist recessed part. Consequently, it is possible to secure favourable sticking of both of them.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a photomask used in a contact exposure method and a method for manufacturing the same, and particularly relates to a photomask used in a contact exposure method, and in particular, to a photomask used in a contact exposure method. This is a dispute regarding a photomask suitable for use in exposing images and a method for manufacturing the same.

(Prior art) The exposure method (currently called the contact exposure method), in which a photomask is brought into close contact with a resist film for exposure, can virtually eliminate diffraction of the light transmitted through the photomask, making it possible to form fine patterns. It is widely used in the manufacturing field.

When this exposure method is applied to the formation of a recessed gate electrode of an inverted structure HEMT, the process is, for example, as follows. FIGS. 4(A) to 4(E) are process diagrams for explaining the process. All are shown as schematic cross-sectional views.

First, semiconductor layers such as a buffer layer, a carrier supply layer, and a channel layer (these semiconductor layers are collectively indicated by 13 in the figure) are formed on a GaAs substrate 11 (FIG. 4(A)).
.

Next, an element isolation region (not shown) is formed on this sample, and an ohmic electrode 11ii15 is formed (fourth
Figure (B)).

Next, after a negative resist 17 is applied onto this sample, a photomask 19 whose gate electrode formation area is set as a light shielding part 19a is closely attached to this resist 17 (1
Figure 14 (C)). In addition, in FIG. 4(C), 19b is the base of the photomask and is made of quartz glass.

Next, this sample is exposed to light and developed to obtain a resist pattern 21 having an opening in the area where the gate is to be formed.

Next, this sample is etched to form a recess 23 in the portion of the semiconductor layer 13 exposed from the resist batten.
is formed (Fig. 4(D)).

Next, apply a gate electrode forming material (not shown) to the entire surface of this sample.
is formed, and then by removing the resist pattern 21, the gate electrode forming material portion thereon is removed (lifted off). As a result, a gate electrode 25 is formed within the recess 23 (FIG. 4(E)).

Here, the photomask 19 used in the above-mentioned exposure process is a glass substrate 19 as shown in a plan view in FIG.
A light shielding portion 19a made of a chromium film having a thickness t1 of approximately 800λ is provided on the portion b.

(Problem to be Solved by the Invention) However, if there are irregularities on the substrate to be patterned, in the above example, if there are irregularities consisting of the semiconductor layer 13 and the ohmic electrode 15, this substrate When a resist is applied, its surface becomes uneven. The level difference due to such unevenness is generally at least 1o.
It is more than ooA. On the other hand, in conventional photomasks, although the light-shielding part has a convex shape equal to the thickness of the chromium film, the purpose of this is to shield light, and the height of the light-shielding part is at most a few. Since this photomask is fixed in contact with the convex portion of the resist, as shown in FIG. 4(C), exposure is performed in a state where the light shielding portion 19a, which should originally be in close contact with the resist, is not in close contact with the resist. There was a problem with this.

If exposure is performed in a state where there is a gap between the resist and the light-shielding portion of the photomask, accurate patterning becomes difficult because the light transmitted through the photomask is diffracted.

In particular, the gate length of the field effect transistor is 0.25 μm.
If the resist is shortened to a certain extent, the portion of the resist that should be the gate button portion (unexposed portion when using a negative resist) is exposed, and therefore, there may be cases where no opening can be formed at all.

The present invention has been made in view of the above points, and an object of the present invention is to apply a resist to an exposed object having irregularities and to attach a photomask to the resist, so that the area to be left unexposed is It is an object of the present invention to provide a photomask that can reliably bring a light-shielding part of a photomask into close contact with a resist recess even when the photomask is located in a recess, and a method for easily manufacturing the same.

(Means for Solving the Problem) In order to achieve this object, according to the first invention of this application, a light-shielding material is selectively provided on a light-transmitting substrate to form a light-shielding portion and a light-transmitting portion. In a photomask for contact exposure method, a concave part is formed by removing the substrate part itself in the part corresponding to the light transmitting part of the light transmitting substrate, and the light shielding part is brought into close contact with the unexposed area of the resist film. It is characterized in that it is provided with a recessed portion having a depth that can be drawn into a shape that can be drawn.

Further, according to the second invention of this application, in manufacturing the photomask of the first invention, the above-mentioned recessed portion is formed by using the light-shielding material of the above-mentioned light-shielding part as a mask and removing the portion of the substrate that is not covered with the mask. It is characterized by being formed with.

In carrying out the second invention, it is preferable that the substrate portion be removed by anisotropic etching. This is because it is possible to prevent the substrate portion under the light-shielding material from being side-etched.

(Function) According to the configuration of the photomask of the first invention of this application, the light-shielding portion has a diameter that contacts the portion of the resist recess that is desired to be unexposed, so that good adhesion between the two is ensured. It turns out.

Further, according to the second invention of this application, the light shielding part itself is used as a mask and the substrate portion is removed to form four parts, so that the light shielding part has a convex shape like a self-alignment.

Furthermore, if the film thickness of the light-shielding material constituting the light-shielding part is made thicker and the light-shielding part is brought into contact with the recessed part of the resist, the convex part cannot be made too high due to the stress of the chromium film that constitutes the light-shielding part. However, in the case of the second invention, by making the light transmitting part concave, the light shielding part is made convex as a result, so that the degree of protrusion of the light shielding part can be increased.

(Examples) Hereinafter, examples of the photomask and the method for manufacturing the same of the present invention will be described with reference to the drawings.

Note that the figures used in the following explanation schematically show the dimensions, shapes, and arrangement relationships of each component to the extent that these inventions can be understood. Further, these embodiments are examples in which the invention is applied to a photomask used in the HEMT manufacturing process described using FIG. 4.

(Explanation of the structure of the photomask) Fig. 1 is a cross-sectional view for explaining the structure of the photomask of the example, and shows an SEM of the photomask manufactured by the manufacturing method described later.
This is a reproduction of a photograph.

The photomask 30 of this embodiment is made by selectively providing, for example, a chromium film as a light-shielding material on, for example, a quartz glass substrate 31 (hereinafter referred to as glass substrate 31) as a light-transmitting substrate.
The part where the chromium film is provided constitutes a light shielding part; the part where 33 is not provided constitutes a light transmitting part 35, and the glass substrate part itself is removed from the part of the glass substrate 31 that corresponds to the light transmitting part 35. The formed concave fa35a and the light shielding part 33
A concave portion 35a having a depth t2 and having a diameter t2 that can be brought into close contact with an unexposed area of the resist film is formed.

FIG. 2 shows a new front view of the photomask 30 of this embodiment used in an exposure step in the HEMT manufacturing process.

The light shielding portion 33 of the photomask 30 corresponds to the concave portion 1 of the resist 17.
It can be seen that it comes to adhere well to 7a.

<Description of photomask manufacturing method> Next, the second invention will be described in detail using an example of manufacturing the photomask 30 of the above-described embodiment. Figure 3 (A) and (B)
) is a process diagram for explaining the process. All are shown in cross-sectional views.

First, a chromium film is selectively provided on the glass substrate 31 (selectively on the portion corresponding to the gate electrode portion) using a conventionally known film forming method and photoetching technique to shield light s33.
is formed, and the other area is used as a light transmitting part 35 (third
Figure (A)). In this example, the thickness of the chromium film is 7.
It is set to 30A. Further, the dimension corresponding to the gate length of the light shielding portion 33 is set to 0.8 μm.

Next, a portion of the glass substrate 31 other than the light shielding portion 33 is removed to a predetermined depth. This removal is carried out using a suitable etching method using the chromium film that constitutes the light shielding part 33 as a mask, but in order to prevent the part of the substrate under the light shielding part 33 from being side-etched, it is etched in the thickness direction of the substrate. It is preferable to use anisotropic etching in which etching proceeds selectively. This etching is performed by, for example, RIE (Reactive Ion Etching) using SFa gas.
) can be done. With this etching,
Since the portion of the glass substrate 31 other than the light shielding portion 33 is removed, the photomask of the invention is obtained (FIG. 3(B)).
.

The etching rate of the glass substrate 31 during this etching was 190 A/min. After carrying out this etching for 4 minutes, the sample was observed with a scanning electron R machine gun, and it was found that the step (t2°) between the light transmitting part 35 and the light shielding part 33 (FIG. 3 CB) was 1500A, indicating that the chromium It was found that the step difference 730A is approximately twice as large as the step difference 730A in the case of only the membrane.

Although the embodiments of each invention of this application have been described above, these inventions are not limited to the above-mentioned embodiments.

For example, the embodiments described above describe each invention of this application as HEM
Although the present invention was applied to the case of forming a T gate electrode, it is clear that these inventions can be widely applied to cases where a resist having irregularities is exposed by a contact exposure method.

Moreover, although a negative resist was used in the above-mentioned embodiments, it is clear that the same effects as in the embodiments can be obtained by patterning a positive resist.

Further, in the second invention, the method of anisotropically removing the portion of the glass substrate other than the light-transmitting portion is not limited to the method using SF or gas, but may be any other suitable method.

(Effects of the Invention) As is clear from the above description, according to the photomask of the first invention of this application, the light shielding portion has a diameter that contacts the portion of the resist recess that is desired to be an unexposed portion. , good adhesion between the two can be ensured. Therefore, resist patterning can be performed more accurately than before.

Further, according to the second invention of this application, the light shielding part itself is used as a mask, the substrate portion is removed, and a concave part is formed to make the light shielding part convex in a self-aligned manner. Therefore, the light-shielding portion can be formed into a convex shape accurately and easily.

Also, in this second invention, by making the light transmitting part concave, the light shielding part is made convex, so when the thickness of the chromium film constituting the light shielding part is increased to make the light shielding part convex. Than,
The degree of protrusion of the light shielding part can be increased. Therefore, it is also effective for exposing resist films with large irregularities.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a photomask of an example. FIG. 2 is a sectional view showing how the photomask of the example is used. 3(A) and (B) are diagrams for explaining the photomask manufacturing method, FIGS. 4(A) to (E) are process diagrams for explaining the conventional technology, and FIG. 9J5 is a conventional photomask FIG. 2 is a diagram for explaining the problem. 30: Photomask of Example 31: Transparent substrate, 33: Light shielding part 35: Light transmitting part, 35a: Recessed part. Patent Applicant: Oki Electric Industry Co., Ltd. Figure 1: Cross-sectional view showing how the photomask of the embodiment is used Figure 2: Hill Whistle 3 for explaining the photomask production method Process diagram for explaining the technology Figure 4: Process diagram for explaining the conventional technology Figure 5 for explaining the problems of conventional photomasks

Claims (2)

[Claims] (1) In a photomask for contact exposure method, in which a light-shielding part and a light-transmitting part are formed by selectively providing a light-shielding material on a light-transmitting substrate, in the part of the light-transmitting substrate corresponding to the light-transmitting part, A photomask comprising a recess formed by removing the substrate portion itself, the recess having a depth that can be convex enough to bring the light shielding part into close contact with an unexposed area of the resist film. (2) In manufacturing the photomask according to claim 1, the recess is formed by using a light-shielding material of the light-shielding portion as a mask and removing a portion of the substrate not covered by the mask. manufacturing method.