JPH06104285A - Formation of gate electrode - Google Patents

Abstract

PURPOSE:To form a short gate length and small gate resistance mushroom- shaped gate electrode with good reproducibility and good throughput at low cost. CONSTITUTION:A gate pattern 2a is opened in an opening width D by photolithography on a photo resist film 2 formed on a semiconductor substrate 1. After that, it is baked at a temperature higher than an ordinary post baking temperature to cause the photoresist film 2 on both sides of the gate pattern 2a to flow and then to make the opening width (d) of the gate pattern 2a smaller than D. Then, a mushroom-shaped gate electrode 5 is formed in this gate pattern 2a and nearby.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for forming a gate electrode. Specifically, the present invention relates to a method for forming a fine gate electrode in a semiconductor device (for example, MESFET).

[0002]

BACKGROUND ART AND ITS PROBLEMS Conventionally, MESFET (me
In tal-semiconductor FET), the miniaturization of the gate electrode is being promoted, and a gate electrode having a gate length of 0.5 μm or less is required.

On the other hand, on the other hand, when the gate length of the gate electrode is reduced, especially when the gate length is 0.5 μm or less, the gate resistance increases excessively, so that the noise characteristic of the MESFET deteriorates.

As a method for solving this problem, a method of making the cross section of the gate electrode a mushroom type has been proposed. This is intended to reduce the gate resistance while making the gate length finer by making the upper width of the gate electrode larger than the lower width (gate length). As a method for forming the mushroom type gate electrode, there are an exposure method using ultraviolet rays (photolithography method) and an exposure method using an electron beam or the like.

FIG. 3 shows a method of forming a mushroom type gate electrode by photolithography. In this method, first, two layers of photoresist films 32 and 33 having different etching characteristics and exposure characteristics are formed on a semiconductor substrate 31.
And a photomask 34 having an opening width equal to the gate length.
The upper and lower photoresist films 32 and 33 are exposed to ultraviolet light by using [FIG. 3 (a)], and the upper photoresist film 33 is exposed to ultraviolet light using a photomask (not shown) having a wide opening. Perform exposure. After that, by developing, the opening width d in the lower photoresist film 32 is increased.
Is equal to the gate length, and the opening width W in the upper photoresist film 33 is larger than d (W> d) (FIG. 3B). Then, a gate metal is vapor-deposited on the entire surface, and the photoresist films 32 and 33 are peeled and removed. By the lift-off method, a mushroom type gate electrode 36 having a gate length d and an electrode width W as shown in FIG. 3C is obtained. .

In the method of forming the mushroom type gate electrode by the photolithography method, since it is covered with the photomask 34 and is collectively exposed to ultraviolet rays, the throughput is good, but when the gate length becomes small, the resolution becomes poor, If the gate length is 0.5 μm or less, there is a problem that it cannot be manufactured with good reproducibility.

Next, FIG. 4 shows a method of forming a mushroom type gate electrode by an electron beam exposure method. In this method, the photoresist film 37 formed on the semiconductor substrate 31 is scanned along the gate pattern with an electron beam whose energy intensity is adjusted so as to reach the surface of the semiconductor substrate 31, and the width of d is drawn. After that, as shown in FIG. 4A, an electron beam whose intensity is adjusted so as not to reach the surface of the semiconductor substrate 31 is scanned along the gate pattern to draw a width W (> d) [FIG. (B)]. When this is developed, an opening 35 having a lower width d and an upper width W is formed.
Is opened in the photoresist film 37 [FIG. 4 (c)], and the mushroom type gate electrode 36 is formed by the lift-off method [FIG. 4 (d)].

FIG. 5 shows a method of forming a mushroom type gate electrode by the focused ion beam exposure method. In this method, a range of width d is drawn on the photoresist film 38 formed on the semiconductor substrate 31 with a Be ion beam having an intensity reaching the surface of the semiconductor substrate 31 [FIG.
(A)], width W (> d) with a Si ion beam of the same intensity
The range is drawn [Fig. 5 (b)]. At this time, since the mass of Si ions is larger than that of Be ions, the Si ion beam does not reach the surface of the semiconductor substrate 31. When this is developed, the photoresist film 38 has a lower width d,
An opening 35 having an upper width W is formed [FIG. 5 (c)]. After that, when the gate metal is deposited by the lift-off method,
A mushroom type gate electrode 36 is formed [FIG.
(D)].

According to the exposure method using an electron beam or a focused ion beam, since the wavelength of the beam is shorter than the wavelength of ultraviolet rays, the resolution is good, but the focused beam is scanned to directly draw the gate pattern. Therefore, the throughput is poor and the exposure apparatus is expensive, resulting in a high cost.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of conventional examples, and an object of the present invention is to reduce the gate length by a photolithography method and to reduce the gate resistance. It is to provide a method for forming a small gate electrode.

[0011]

A method of forming a gate electrode according to the present invention comprises a step of opening a gate pattern in a photoresist film formed on a semiconductor substrate by a photolithography method, and a gate pattern of the photoresist film by heating. Flowing both sides, narrowing the gate length of the gate pattern by the flow, and projecting from the surface of the semiconductor substrate exposed from the gate pattern to the upper surface of the photoresist film, the upper width is smaller than the gate length of the lower surface. And a step of forming an enlarged gate electrode.

[0012]

In the method of forming a gate electrode according to the present invention, after the gate pattern is opened in the photoresist film by the photolithography method, both sides of the photoresist film are caused to flow by heating. Therefore, the gate pattern by the photolithography method is used. It is possible to obtain a gate pattern narrower than the opening width of. As a result, it is possible to form a gate electrode having a gate length even shorter than the minute gate length achievable by the conventional photolithography method.

For example, when a gate pattern having a width of 0.5 μm is opened in the photoresist film by the photolithography method and then the photoresist film is flowed, the pattern becomes 0.5 μm.
A gate pattern width narrower than m can be obtained, and a photolithography method can achieve a gate length shorter than 0.5 μm, which is said to be the limit of the gate length. In particular, according to this method, it has become possible to reproducibly form a mushroom type gate electrode having a gate length of quarter micron.

Since the gate electrode having a minute gate length can be formed by the photolithography method in this manner, an expensive exposure apparatus unlike the electron beam exposure method and the focused ion beam exposure method is not required, and the throughput is improved. Also, the gate electrode having a small gate length can be formed at low cost.

[0015]

1A to 1E show a method of forming a gate electrode according to an embodiment of the present invention. This is the step of forming the gate electrode in the MESFET, and the semiconductor substrate 1 shown in FIG.
Source and drain regions, gate regions, etc. (none of which are shown) are formed on the As substrate. First, as shown in FIG. 1A, a positive photoresist solution (for example, AZ1350) is applied on a semiconductor substrate 1 to form a photoresist film 2, which is then covered with a photomask and exposed to ultraviolet light. After development, the photoresist film 2 has a width D larger than the intended gate length (for example, the design width is 0.5 μm which is the limit of the ultraviolet exposure method; D = 0.
The gate pattern 2a of 5 μm) is opened.

Next, as shown in FIG. 1B, the photoresist film 2 is caused to flow by heating at a temperature higher than the normal post-baking temperature (for example, about 140 ° C.) to perform post-baking. When the photoresist film 2 is flowed,
Since the photoresist film 2 flows toward the gate pattern 2a, the opening width D of the gate pattern 2a becomes narrower by the amount of the flow, and the opening width d that determines the gate length of the gate electrode.
(<D; for example, d = 0.25 μm) is obtained.

Next, a positive photoresist solution is applied to the entire surface again to form a photoresist film 3. After the surface of the photoresist film 3 is cured by treatment with chlorobenzene or the like, it is exposed to ultraviolet light through a photomask, developed to open the electrode pattern 3a, and the electrode pattern 3a opens the gate pattern 2a of the photoresist film 2. And its periphery are exposed [FIG. 1 (c)]. At this time, since the surface of the photoresist film 3 is hardened before development, the vicinity of the surface of the photoresist film 3 is less soluble in the developing solution than the inside. Therefore, when developed, the electrode pattern 3a opens slightly larger in the inside than in the vicinity of the surface of the photoresist film 3, and an eaves portion 3b is formed near the surface.
The distance W between the eaves 3b determines the width of the gate electrode and is larger than the opening width d of the photoresist film 2. Since the lower photoresist film 2 is subjected to high temperature treatment during the flow, it does not dissolve in the developing solution.

Thereafter, as shown in FIG. 1D, a gate metal (for example, Ti / Pt / Au or Ti / Al) 4 is vapor-deposited on the photoresist film 3 by a vacuum vapor deposition method or the like. At this time, in the gate pattern 2a and the electrode pattern 3a, the lower width is equal to the opening width d of the gate pattern 2a, and the upper width is the electrode width W of the electrode pattern 3a.
To form a mushroom-type gate electrode 5.
Finally, when the photoresist films 2 and 3 are stripped and removed by a stripping solution, the mushroom type gate electrode 5 is formed on the substrate 1 by the lift-off method [FIG. 1 (e)].

In the method of the present invention, first, a gate pattern 2a having an opening width D (for example, D = 0.5 μm) which can be formed with good reproducibility even by a photolithography method is formed,
Next, since the photoresist film 2 in the vicinity of the gate pattern 1a is heated to reduce the gate length, the heating temperature and the flow length of the photoresist film 2 are checked in advance to obtain a desired opening width d. (For example, d = 0.25
.mu.m) can be formed with good reproducibility, and the mushroom type gate electrode 5 having a gate length equal to the opening width D can be formed. Therefore, the mushroom type gate electrode 5 having a gate length d of 0.5 μm or less can be formed with good reproducibility by using a photolithography method which is inexpensive in device and has a high throughput.

2A to 2F show a method of forming a gate electrode according to another embodiment of the present invention. First, FIG. 2 (a)
As shown in FIG. 3, a positive photoresist solution (for example, AZ1350) is applied on the semiconductor substrate 1 to form a photoresist film 2, and a gate pattern 2a having an opening width D is opened in the photoresist film 2 by an ultraviolet exposure method. .

Next, as shown in FIG. 2B, the photoresist film 2 is heated at a temperature higher than the normal post-baking temperature (for example, about 140 ° C.), and the photoresist film 2 is caused to flow so that the gate is formed. The pattern 2a is narrowed to the opening width d.

After that, as shown in FIG. 2C, a gate metal 6 (for example, Ti / Pt / Au or Ti / Al) is formed on the photoresist film 2 so as to cover the entire surface.
Vapor deposition.

Then, as shown in FIG. 2D, a photoresist film 7 is formed on the gate metal 6, and the photoresist film 7 is formed with a width W (> d) by photolithography.
Patterning so that After this, for example, CCl
The gate metal 6 in a portion not covered with the photoresist film 7 is removed by reactive ion etching using ₂ F ₂ gas to form a mushroom type gate electrode 8 having a desired shape [FIG. 2 (e)].

Finally, the photoresist films 2 and 7 are stripped with a stripping solution.
Then, a mushroom type gate electrode 8 having a lower width substantially equal to the gate length d of the gate pattern 2a and an upper width equal to the width W of the photoresist film 7 is formed on the substrate 1.

[0025]

According to the present invention, the photolithography method enables the formation of a gate electrode having a gate length much shorter than the minute gate length achievable by the conventional photolithography method. It becomes possible to form a mushroom type gate electrode having a gate length of quarter micron with high reproducibility, which could not be achieved by the photolithography method.

Further, unlike the electron beam exposure method and the focused ion beam exposure method, an expensive exposure apparatus is not required, throughput is improved, and a mushroom gate electrode having a small gate length can be formed at low cost.

Therefore, according to the present invention, a mushroom type gate electrode having an extremely short gate length and a small gate resistance can be manufactured at low cost, and high performance of a semiconductor device can be achieved.

[Brief description of drawings]

1A, 1B, 1C, 1D, and 1E are cross-sectional views showing a method of forming a gate electrode according to an embodiment of the present invention.

2 (a), (b), (c), (d), (e), and (f) are cross-sectional views showing a method for forming a gate electrode according to another embodiment of the present invention.

3A, 3B and 3C are cross-sectional views showing a method of forming a gate electrode according to a conventional example.

4 (a), (b), (c) and (d) are cross-sectional views showing another method of forming a gate electrode according to a conventional example.

5A, 5B, 5C, and 5D are cross-sectional views showing another conventional method of forming a gate electrode.

[Explanation of symbols]

 1 semiconductor substrate 2 photoresist film 2a gate pattern 5,8 mushroom type gate electrode

Claims (1)

[Claims] 1. A step of opening a gate pattern in a photoresist film formed on a semiconductor substrate by a photolithography method, and heating both sides of the gate pattern of the photoresist film to flow, and the flow causes a gate length of the gate pattern. And a step of forming a gate electrode whose upper width is larger than the gate length of the lower surface so as to project from the surface of the semiconductor substrate exposed from the gate pattern to the upper surface of the photoresist film. A method for forming a gate electrode, comprising: