JPH06104287A - Formation of gate electrode - Google Patents

Abstract

PURPOSE:To provide a method for forming a gate electrode by which the gate electrode having a gate length shorter than a specified value can be manufactured at low cost and with good throughput. CONSTITUTION:A first photoresist film 2, an insulating film 3 and a second photoresist film 4 are formed in this order on a semiconductor substrate 1. Then, an area of a width of D is exposed and developed to open an upper layer gate pattern 4a. After that, the insulating film 3 is etched to expose a soluble area 2a of the first photoresist film 2. Then, CF4 plasma is cast aslant on the soluble area 2a to make a part of the soluble area 2a unsoluble. Then, development is conducted to open a lower layer gate pattern 5 of a opening width of (d).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a gate electrode. Specifically, the present invention relates to a method of forming a gate electrode in a field effect transistor.

[0002]

BACKGROUND ART A mushroom type gate electrode having a gate length of 0.2 μm and a small gate resistance has been put into practical use in order to improve the performance of GaAs-MESFETs.

FIGS. 3A to 3D show a conventional method of forming a gate electrode. In this gate electrode forming method, as shown in FIG. 3A, a low-sensitivity first photoresist film 32 and a high-sensitivity second photoresist film 33 are sequentially laminated on a semiconductor substrate 31. After that, a strong electron beam (EB) is scanned in the central region of the gate electrode formation region having a width d (for example, 0.2 μm) by using an electron beam exposure apparatus. The portions 32 and 33 having the width d are exposed. Then, a weak electron beam is scanned over the entire width D (for example, 0.5 μm) of the gate electrode formation region to form the second photoresist film 3
Only 3 is exposed over the width D.

Next, this is developed and the photoresist films 32 and 33 in the exposed portions are removed. As shown in FIG.
As shown in, the gate pattern 34 is opened in the photoresist films 32 and 33. After performing recess etching,
When the gate metal 35 is vapor-deposited on the entire surface, a mushroom type gate electrode 35a having a lower width d and an upper width D is formed in the gate pattern 34, as shown in FIG. Finally, the unnecessary resist films 32 and 33 are lifted off to complete the mushroom type gate electrode 35a [FIG. 3 (d)].

[0005]

However, in the conventional method of forming the gate electrode, the photoresist film 32, 33 is exposed by scanning the electron beam over the entire exposed area, but the resolution is good, but Poor throughput,
Further, the electron beam exposure apparatus has a problem that the apparatus cost is high.

According to the usual photolithography method,
Although the equipment cost can be reduced and the throughput can be improved, the resolution is poor and the gate length is 0.5μ because the wavelength of the ultraviolet light used for exposure is longer than the wavelength of the electron beam.
It is difficult to form a gate electrode of m or less.

The present invention has been made in view of the drawbacks of the above conventional examples, and an object thereof is to form a gate electrode having a gate length of 0.5 μm or less with an inexpensive device and at a high throughput. It is to provide a method of forming a gate electrode that can be formed.

[0008]

A method of forming a gate electrode according to the present invention comprises a first photoresist film, a spacer layer and a second photoresist film, which are soluble on at least a gate electrode formation region on a semiconductor substrate. And a step of forming a first gate pattern in the second photoresist film by a photolithography method, etching the spacer layer to form a space below the opening, and A step of insolubilizing a plasma irradiation region of the first photoresist film with a developing solution by obliquely irradiating the first photoresist film with anisotropic plasma using the photoresist film as a mask; The soluble region of the second photoresist film is removed, a second gate pattern is opened in the first photoresist film, and the second gate pattern is opened. It is characterized by comprising a step of forming a gate electrode by depositing a gate metal on the surface of the semiconductor substrate through preparative pattern.

[0009]

In the method of forming a gate electrode of the present invention, anisotropic plasma is obliquely irradiated by using a second photoresist film having a first gate pattern opened by a photolithography method as a mask. Since a part of the soluble region of the first photoresist film is insolubilized, a soluble region having a width smaller than that of the first gate pattern, that is, the second gate pattern can be formed in the first photoresist film. . Therefore, a second gate pattern having a lower limit of 0.5 μm or less, for example, about 0.2 μm in the photolithography method can be opened, and a gate electrode having a gate length of about 0.2 μm can be formed.

Further, in the photolithography method used here, an inexpensive ultraviolet exposure apparatus is used without using an expensive electron beam exposure apparatus as in the conventional example, so that the apparatus cost can be reduced. . Further, instead of scanning the area to be exposed with the electron beam as in the conventional example, the ultraviolet rays are collectively radiated through the mask to perform the exposure, so that the throughput can be improved.

[0011]

EXAMPLE FIG. 1 (a) (b) (c) (d) (e) and FIG.
2 shows a method of forming a gate electrode according to an embodiment of the present invention.
You In the method of forming the gate electrode, first, as shown in FIG.
As shown in (a), the semiconductor substrate 1 (for example, GaAs
Forming a positive type first photoresist film 2 on the substrate)
And then SiO 2 by sputtering or low temperature CVD X membrane or
SiN_XForm an insulating film (spacer layer) 3 such as a film
Then, a positive type second photoresist film 4 is formed.
It Here, the first photoresist film 2 is the second photoresist film.
A resist film having a higher sensitivity than the resist film 4 is used.

The thickness T of the first photoresist film 2
_Since the height of the lower portion of the gate electrode 7 described later is determined by ₁ , the value is set to a predetermined value (for example, T ₁ = 2000Å). The thickness T ₂ and the thickness T ₃ of the second photoresist film 4 of insulating film 3 is a gate length d of the gate electrode 7 to be described later
A predetermined value (for example, T ₂ = 4000Å,
It is set to T ₃ = 3000Å).

Then, the surface is covered with a photomask having an opening having a width D, and the gate electrode formation region of the semiconductor substrate 1 is irradiated with ultraviolet rays to expose the first and second photoresist films 2 and 4, This is developed to open a gate pattern 4a in the upper layer of the width D in the second photoresist film 4. At this time, the region 2a of the width D of the first photoresist film 2 which is irradiated with ultraviolet rays has been modified to be soluble in the developing solution, but is not removed by the development because it is covered with the insulating film 3. The opening width D of the gate pattern 4a in the upper layer is set to 0.5 μm which is the lower limit that can be formed with good reproducibility by a photolithography method using ultraviolet rays, for example.

Next, isotropic etching is performed, for example, by a wet etching method through the upper layer gate pattern 4a, and as shown in FIG. 1B, the insulating film 3 below and near the upper layer gate pattern 4a is etched. It is removed and the space 3a is formed.

Next, as shown in FIGS. 1 (c) and 2,
For example, in a reactive ion etching apparatus equipped with parallel plate electrodes, the semiconductor substrate 1 is used as an electrode at a constant angle θ.
It is set at an angle (for example, 25 degrees), low-pressure carbon fluoride (CF ₄ ) gas is introduced to cause discharge, and anisotropic CF ₄ plasma is irradiated. The CF ₄ plasma is used not only for the second photoresist film 4 on the surface but also for the upper gate pattern 4a.
Through the first photoresist film 2 through CF
_{4 The} entire second photoresist film 4 irradiated with plasma and the partial region 2b of the first photoresist film 2 are denatured and become insoluble in the developing solution.

At this time, if the semiconductor substrate 1 is not tilted, C
When the F ₄ plasma is vertically irradiated, the CF ₄ plasma is irradiated through the upper gate pattern 4a over the entire width D of the soluble region 2a of the first photoresist film 2. However, the CF ₄ plasma is irradiated by the upper gate. Pattern 4a
Since the irradiation is performed obliquely from the first photoresist film 2, the soluble region 2a of the first photoresist film 2 has a width d _p =
CF ₄ plasma is applied only to the region of D- (T ₂ + T ₃ ) tan θ to insolubilize it. Here, the angle θ is the width d _p
Is set to 0 or more and D / 2 or less.

Next, the semiconductor substrate 1 is set to be tilted by the same angle θ in the opposite direction, and anisotropic CF ₄ plasma is similarly irradiated. As a result, the portions of the width d _p at both ends of the soluble region 2a of the first photoresist film 2 become insoluble, and the central portion of the width d = D−2d _p remains soluble. This width d can be freely changed from 0 to D by changing the angle θ of CF ₄ plasma irradiation within an appropriate range. Since the gate length of the mushroom type gate electrode 7 described later is determined by this width d, it is set to a predetermined width (for example, 0.2 μm).

However, when this is developed, the region 2a soluble in the developing solution is removed, and as shown in FIG. 1 (d),
The gate pattern 5 below the opening width d is opened in the first photoresist film 2. After that, wet etching is performed to very thinly remove the surface of the semiconductor substrate 1 exposed from the lower gate pattern 5 to form a recess region 6.

Finally, the upper and lower gate patterns 4
Gate metal (eg Ti / Pt / A) through a and 5
u) is vapor-deposited by, for example, a vacuum vapor deposition method to remove unnecessary photoresist films 2 and 4 and the like, and a mushroom gate having a width D of the upper portion, a width d of the lower portion, and a height T ₁ of the lower portion by the lift-off method. The electrode 7 is completed [FIG. 1 (e)].

[0020]

According to the method of forming a gate electrode of the present invention, it is possible to open a gate pattern having an opening width (for example, about 0.2 μm) narrower than that of a gate pattern which can be opened by photolithography. A gate electrode having a gate length of about 0.2 μm can be formed.

Further, unlike the conventional example, an expensive electron beam exposure apparatus is not used, but an inexpensive ultraviolet exposure apparatus is used, so that the apparatus cost can be reduced.

Since the exposure area is not scanned with an electron beam as in the conventional example, but is irradiated with ultraviolet rays all at once,
Throughput can be improved.

Since the gate length is determined by the opening width of the first gate pattern, the film thickness of the second photoresist film and the insulating film, and the angle of plasma irradiation, the gate length can be uniformly formed on the entire wafer.

Further, since the opening of the gate pattern is formed by the developing solution, there is an advantage that the semiconductor substrate is not damaged.

[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.

FIG. 2 is a cross-sectional view showing a plasma processing step of the same.

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

[Explanation of symbols]

 1 semiconductor substrate 2 first photoresist film 2a soluble region 2b insoluble region 3 insulating film (spacer layer) 4 second photoresist film 4a upper layer gate pattern 5 lower layer gate pattern 7 mushroom type gate electrode

Claims (1)

[Claims] 1. A first photoresist film in which at least the vicinity of a gate electrode formation region is soluble on a semiconductor substrate,
Stacking a spacer layer and a second photoresist film, and opening a first gate pattern in the second photoresist film by a photolithography method, and etching the spacer layer to form a space below the opening. Forming step, and by irradiating the first photoresist film with anisotropic plasma obliquely using the second photoresist film as a mask, the plasma irradiation region of the first photoresist film is exposed to the developing solution. And insolubilizing the first photoresist film by removing the soluble region of the first photoresist film to open a second gate pattern in the first photoresist film, and through the second gate pattern to the surface of the semiconductor substrate. Forming a gate electrode by depositing a gate metal.