JPH0298147A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To simplify the formation of a T-shaped electrode by employing a photomask in which a shielding thin film varying in light permeability with thickness for forming an opening and a shielding thin film formed with a large opening are laminated. CONSTITUTION:A shielding thin film 2 varying in light permeability with thickness having an opening 3 of width lg and thickness T1 is formed on a transparent substrate 1. Then, a shielding thin film 4 having an opening of larger width lT than the width lg is laminated to form a photomask 10. On the other hand, a semiconductor substrate 11 is coated with positive type photoresist 12. Then, a mask 10 is superposed on the resist 12 with the substrate 1 disposed above, and radiated with an ultraviolet ray 15, and a T-shaped opening 13 is obtained at the resist 2. Subsequently, a metal electrode 14' is formed by a vacuum depositing, etc. Then, the electrode 14' on the resist 12 is removed together with the resist 12, and a T-shaped electrode 14 is formed. Thus, the resist of one layer is exposed at once to form a T-shaped electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of forming a mask for forming electrodes in a field effect semiconductor device.

[Conventional technology]

In recent years, advances in semiconductor devices have been remarkable, and their operating functions are increasingly required to be faster.Semiconductor devices that operate at ultra-high speeds adopt element structures that minimize the electron mobility distance inside the semiconductor. There is a need to. A typical example is a field effect semiconductor device using a T-type electrode.

First, the process of forming this T-type i-pole will be explained with reference to FIG.

In FIG. 8(a), 0.2 μm is placed on the semiconductor substrate 11.
A low-sensitivity positive resist 12a of about m.

Furthermore, a high-sensitivity positive resist 12b having a thickness of about 0.5 μm is formed thereon. These two layers of resist are processed with the same developer. Next, as shown in Figure 8(b),
Infrared rays 15 are irradiated to desired positions to expose the high-sensitivity positive resist 12b and the low-sensitivity positive resist 12a. When developed after exposure, the upper layer high-sensitivity positive resist 12b is easily dissolved in the developer, while the lower layer low-sensitivity positive resist 12a is less soluble than the high-sensitivity positive resist 12b, but , a resist pattern such as a T-shaped opening 13 as shown in FIG. 8(e) is formed. Next, as shown in FIG. 8(d), an electrode metal 14' having a thickness of about 0.6 μm is formed by vacuum evaporation or the like. Finally, as shown in FIG. 8(e), a high-sensitivity positive resist 12b is applied.
The entire semiconductor substrate 11 is immersed in a chemical solution that dissolves the low-sensitivity positive resist 12a, and then the high-sensitivity positive resist 12b is dissolved.
The upper electrode metal 14' is also removed to form a T-shaped electrode 14.

FIG. 9 is a cross-sectional view showing the main steps of a method for forming a photoresist profile with arbitrary steps in a conventional photolithography process for a GaAsFET device.

In the photolithography process of the GaAsFET device in this conventional example, first, a source electrode 33. After forming the drain electrode 8i34, photolithography is performed to form the gate 'M, a pattern. That is, first, the first layer of photoresist 35a is applied, and then the first layer of photoresist 35a is applied.
A second layer of photoresist 35b having higher sensitivity than H is applied. Thereafter, the exposed portion 3 is exposed using a mask 37 for patterning the second layer of photoresist 35b.
5b' is exposed (FIG. 9(a)).

(b)). Next, the exposed portion 35a' of the first layer photoresist 35a is exposed using a mask 38 with a thinner pattern than the mask 37 for exposure of the second layer photoresist 35b (9th layer photoresist 35b). Figure (C)). After that, the first and second layer photoresists 35a and 3 are developed.
The exposed portions 35a and 35b' of 5b are removed to form a T-shaped pattern on the photoresist profile (FIG. 9(d)).

In addition, without using the optical exposure method using a photomask as described above, after coating the photoresists 35a and 35b, the EB
A similar pattern can be formed by pattern formation using (electron beam) exposure.

By using the mask thus formed, a T-shaped electrode can be formed.

(Problems to be Solved by the Invention) In the conventional method of forming the T-shaped electrode 14 as shown in FIG.
The use of photoresist layers 35a and 35b complicates the pattern formation process, and the electron beam irradiation technique must be sequentially applied to each desired pattern, resulting in low throughput. Ta.

In addition, in the method of forming a photomask as shown in FIG. 9, since the photoresists 35a and 35b are formed into two layers, the photoresist is thick and has variations in thickness, making it difficult to form fine patterns. There was a problem.

Furthermore, in order to perform mask alignment of the fine pattern twice,
The method of forming the pattern was difficult because it caused pattern pitch deviations and the like.

In addition, when using EB exposure to improve pattern accuracy, the pattern accuracy becomes higher, but there are problems in that the equipment is expensive and the pattern formation time per sheet is poor, making it difficult to mass-produce. .

The present invention has been made to solve these problems, and an object of the present invention is to provide a method for forming a photomask that is simple and can form electrodes with high precision.

[Means to solve the problem]

The method for manufacturing a semiconductor device according to claim (1) of the present invention includes a transparent thin film having a desired opening formed on a transparent substrate, and a transparent thin film having a thickness such that an opening larger than the opening is formed on a transparent substrate. forming a photomask for forming a T-shaped electrode in which a pattern with a T-shaped opening cross section is formed on the transparent substrate by sequentially laminating light-shielding thin films that change the amount of transmitted light accordingly;
A T-type electrode is formed using this photomask.

Further, in the method for manufacturing a semiconductor device according to claim (2) of the present invention, the etching depth of the light-shielding thin film of a photomask including a transparent substrate and a light-shielding thin film is changed, and a required number of the light-shielding thin films are etched. Steps are provided, and this photomask is used to form an electrode having a required number of steps.

[Effect]

In the invention described in claim (1) of the invention, a transparent thin film in which a desired opening is formed on a transparent substrate and a light-shielding thin film in which an opening larger than the opening is formed are sequentially formed on a transparent substrate. Laminated to form a photomask for forming a T-shaped electrode in which a pattern with a T-shaped opening cross section is formed on a transparent substrate,
Since the T-shaped electrode is formed using this photomask, the amount of light that the photoresist on the semiconductor substrate receives varies depending on the desired position due to the effect of the transparent thin film that constitutes the photomask, and the amount of light that the photoresist on the semiconductor substrate receives varies depending on the desired position. Since the cross-sectional shape of the resist is obtained, a desired T-shaped electrode can be obtained by forming an electrode metal thereon and removing the photoresist.

In addition, in the invention described in claim (2) of this invention, since the required number of steps are provided in the light-shielding thin film of the photomask for photolithography, light can be transmitted to the photoresist in one exposure. The amount of irradiation changes depending on the step part of the light-shielding thin film, and it is possible to form a photomask in which the required number of step patterns are accurately formed in the profile of the -layer photoresist. An electrode having a step difference of .

〔Example〕

FIG. 1 is a sectional view showing a photomask 10 for forming a T-type electrode according to the first aspect of the present invention. In this figure, 1
2 is a transparent substrate, and 2 is Au203. which transmits infrared rays. CaO
The transparent thin film has an opening 3 having an opening width of .degree. C. and a thickness of T1. 4 is a light-shielding thin film made of Cr or the like that does not transmit infrared rays, and has an opening 5 with an opening width of 1A. These opening widths JZ.

A T-shaped opening is formed by the opening 3 having an opening width of .degree. C. and the opening 5 having an opening width of .degree.

Here, when the T-shaped opening is irradiated with infrared rays, the opening width J21. The infrared rays of I2 are transmitted through the opening 3 with the thickness T1, and the infrared rays of I2 are transmitted through the opening 5 with the opening width (l 1 □)/211 mm I2, and since the thickness I2>TI, the amount of infrared transmission is If >I2, and the intensity of infrared rays, that is, the irradiation amount, is obtained depending on the thickness of the transparent thin film 2.

FIGS. 2(a) to 2(d) are cross-sectional views showing the manufacturing process of a photomask for forming a T-type electrode according to the present invention. In FIG. 2, the same reference numerals as in FIG. 1 indicate the same parts, and 6 is a photoresist formed on the light-shielding thin film 4. In FIG.

First, as shown in FIG. 2(a), a 1□ opening is formed in the light-shielding thin film 4 to form a resist pattern, and then, as shown in FIG. 2(b), Cr, etc. are etched by wet etching. The light-shielding thin film 4 is etched to an opening width 17 to form an opening 5. Next, as shown in FIG. 2(C), dry etching is performed to obtain an AJI of 20. , a transparent thin film 2 made of CaO or the like is etched to form an opening 3 having the width of the opening. Finally, by removing the photoresist 6 with a soluble chemical solution, a T-shaped electrode having an opening width ℃1 and a T-shaped opening consisting of AT openings 3 and 5 is formed, as shown in FIG. 2(d). A photomask 10 for formation is obtained. Figure 3(a)-(d)
FIG. 2 is a cross-sectional view showing another manufacturing process of a photomask for forming a T-type electrode according to the present invention. The formation of this photomask is
First, as shown in FIG. 3(a), the photoresist 6 is heated at 1°C.
Next, as shown in FIG. 3(b), a resist pattern with an opening of 200° C. is formed, leaving a thickness of T1 on the transparent thin film 2 made of AJ2203° CaO, etc. A light-shielding thin film 4 such as A203, a light-transmitting thin film 2 such as CaO, etc.
Dry etching. Next, as shown in FIG. 3(C), the light-shielding thin film 4 made of Cr or the like is wet-etched to the opening width IT. Finally, as shown in FIG. 3(d), the photoresist 6 is removed with a soluble chemical to form a T-shaped electrode having a T-shaped opening consisting of an opening width 11 and a JZT opening 3.5. A photomask 10 is obtained.

The method for forming a T-type electrode of the present invention utilizes the characteristics of a positive resist.
An example of a method for forming a T-shaped electrode using the following will be described.

FIGS. 4(a) to 4(e) are process cross-sectional views showing one embodiment of the method for forming a T-type electrode of the present invention. In this diagram,
10 is a photomask for forming a T-type electrode according to the present invention;
11 is a semiconductor substrate; 12 is a positive photoresist coated on the semiconductor substrate 11; 13 is a T-shaped opening formed in the positive photoresist 12; 14;
is a T-type electrode, 14' is an electrode metal, and 15 is an infrared ray.

First, as shown in FIG. 4(a), a positive type photoresist 12 is applied onto a semiconductor substrate 11. As shown in FIG. Next, Figure 4 (b
), a transparent substrate 1 according to the present invention is placed on a positive photoresist 12. A photomask 10 for forming a T-shaped electrode consisting of an infrared-transmitting thin film 2 and a light-shielding thin film 4 is stacked with the transparent substrate 1 facing upward, and infrared rays 15 are irradiated. By irradiating the infrared rays 15, the positive type photoresist 12 is irradiated with the infrared rays 15 of II>I2 depending on the difference between the thicknesses T1 and I2 of the transparent thin film 2. Thereafter, by performing a development process, a T-shaped opening 13 is obtained in the positive photoresist 12, as shown in FIG. 4(C). Next, as shown in FIG. 4(d), the electrode metal 1 is formed by vacuum evaporation or the like.
4' is formed.

Finally, the entire semiconductor substrate 11 is immersed in a chemical solution that dissolves the positive photoresist 12, and the electrode metal 14' on the positive photoresist 12 is also removed, as shown in FIG.
A T-shaped electrode 14 is formed as in e).

In the above embodiment, the opening width Il, the thickness T1. Although the opening width of the light-shielding thin film 3 is set to 0.degree. C., it can be arbitrarily selected depending on the desired shape. For example, the thickness of the transparent thin film 2 may be T, =O.

Further, in the above embodiments, a positive type photoresist is described, but the same effect can be obtained with a negative type photoresist by inverting the photomask for forming the T-type electrode to a negative type mask.

Further, in the above embodiment, the T-shaped electrode 14 is connected to the semiconductor substrate 11.
Although the case where the semiconductor substrate is formed on the semiconductor substrate is described above, it can also be applied to a case where a recess structure is formed by etching the semiconductor substrate.

FIG. 5 is a diagram showing a photomask for photolithography according to the second invention of the present invention, in which a light-transmitting thin film (glass portion) 21a
and the photomask 2 from the light-shielding thin film (metal part) 21b.
1 is configured. This photomask 21 is formed by changing the thickness of the light-transmitting portion of the light-shielding thin film 21b in multiple stages (in this embodiment, two stages) by changing the etching amount, and the thickness is set to 1.
．． It is set at 12.

Next, with reference to FIGS. 6 and 7, the main part of the process of forming electrodes of a GaAsFET element using the photomask 21 shown in FIG. 5 will be explained.

First, as shown in FIG. 6(a), a source electrode 33 and a drain electrode 34 are formed at predetermined positions on the active layer 32 of the semiconductor substrate 31. Next, for photolithography, a photoresist 35 is applied onto the semiconductor substrate 31 using a spinner or the like. Thereafter, as shown in FIG. 6(b), using the photomask 21 shown in FIG.
They are stacked one on top of the other, and exposed to form a pattern. At this time, the thickness of the light-shielding thin film 21b of the photomask 21 is 1. ．． 12, the light-shielding thin film 21
Since the amount of light transmitted through the thin t1 portion of b is greater than the thick t2 portion of the light-shielding thin film 21b, the photoresist 35
In this case, the t1 portion is more deeply exposed than the t2 portion. 35
a' indicates the exposed portion. Next, development is performed to remove the exposed portion 35a' of the photoresist 35, thereby forming the sixth
As shown in Figure (C), a pattern having arbitrary steps is formed in the resist profile.

Next, a method for forming a gate electrode using the pattern formed by the method shown in FIG. 6 will be described with reference to FIG.

Using the pattern obtained in FIG. 6(C) as a mask, a recess for forming a gate electrode is formed by etching.
7(a)), then a gate metal 36' is formed by vapor deposition or the like (FIG. 7(b)), and then unnecessary portions are removed by a lift-off method. As a result, a fine gate electrode 36 having a large gate cross-sectional area and low gate resistance is formed.

In the above embodiment, the thickness of the light-shielding thin film 21b of the photomask 21 is set to 1. ．． Although a photomask having a step difference of two steps as shown in FIG. Moreover, t+ and t2 are arbitrary thicknesses, and the thickness of the light-shielding thin film 21b of 1 may be zero.

Further, in the above embodiment, a positive type photoresist in which the exposed area is melted by development is used, but a negative type photoresist in which the unexposed area is melted by development, and a ( A negative mask) may also be used.

〔Effect of the invention〕

As explained above, the invention described in claim (1) of the present invention provides a light-transmitting thin film in which a desired opening is formed on a transparent substrate, and a light-shielding thin film in which an opening larger than the opening is formed on a transparent substrate. A photomask for forming a T-shaped electrode, in which a pattern with a T-shaped opening cross section was formed on a transparent substrate, was formed by sequentially laminating the thin films, and this photomask was used to form a T-shaped electrode. A T-type 1i pole can be formed by exposing one layer of resist all at once in the exposure process. Therefore, the electrode forming process is simplified and processing capacity is further improved.

In addition, the invention described in claim 2 of this invention provides an arbitrary number of steps in the light-transmitting thin film of a photomask for photolithography consisting of a light-transmitting thin film and a light-shielding thin film. By using this photomask, arbitrary steps can be formed in the profile of the photoresist by one optical exposure, so there is no pattern shift that is likely to occur with conventional methods, and a highly accurate pattern can be easily formed.

Moreover, since it does not use expensive equipment like EB for exposure,
Patterns can be formed at low cost. Therefore, by using this photomask, it is possible to form an electrode having a required number of steps.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view illustrating a photomask for forming a T-type electrode according to the first invention of the present invention and the amount of infrared rays irradiated in this photomask, and FIG. 2 is a cross-sectional view showing the formation of a T-type electrode according to the first invention of the present invention. 3 is a sectional view showing an embodiment of the manufacturing process of a photomask according to the present invention, and FIG. 4 is a sectional view showing an example of the manufacturing process of a photomask according to the present invention. FIG. 5 is a cross-sectional view showing an example of the process of forming a T-type electrode using a photomask for forming a T-type electrode, and FIG. 5 is a cross-sectional view of a photomask according to the second aspect of the present invention.
6 and 7 are main part cross-sectional views showing the process of forming an electrode using the photomask shown in FIG. 5, FIG. 8 is a cross-sectional view showing the process of forming a conventional T-shaped electrode, and FIG. Conventional GaAsFE
FIG. 3 is a cross-sectional view of a main part showing a step of forming an electrode of a T element. In the figure, 1 is a transparent substrate, 2 is a transparent thin film, 3 is an opening, 4 is a light-shielding thin film, 5 is an opening, 10 is a photomask for forming a T-shaped electrode, 11 is a semiconductor substrate, and 12 is a positive 13 is a T-shaped opening, 14 is a T-shaped electrode, 14' is an electrode metal, 15 is an infrared ray, 21 is a photomask, 21a is a transparent thin film, 21b is a light-shielding thin film, 31
is a semiconductor substrate, 32 is an active layer, 33 is a source electrode, 34
35 is a drain electrode, 35 is a photoresist, 35a is an exposed portion, and 36 is a gate electrode. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent: Masuo Oiwa (2 others) Photomask for Q/T type 4th line --) 1 prisoner i Figure 5b

Claims (2)

[Claims] (1) A transparent thin film in which a desired opening is formed on a transparent substrate, and a light-shielding thin film in which the amount of transmitted light is changed according to the thickness, in which a gateway larger than the opening is formed, are sequentially laminated, A pattern with a T-shaped opening cross section is formed on the transparent substrate to form a photomask for forming a T-shaped electrode, and this photomask is placed on a photoresist coated on a semiconductor substrate with the transparent substrate facing upward. After patterning the photoresist into a T-shaped opening cross section by exposing the photoresist to light through the photomask, an electrode metal is formed on the entire surface, and then unnecessary electrode metal is removed together with the photoresist. 1. A method of manufacturing a semiconductor device, comprising forming a T-shaped electrode. (2) It consists of a light-transmitting thin film that transmits light and a light-shielding thin film portion that changes the amount of transmitted light depending on the thickness, and a pattern is formed by adding a required number of steps in the thickness direction of the light-transmitting thin film. This photomask is placed on a photoresist coated on a semiconductor substrate with the transparent thin film facing upward, and the photoresist is opened by exposing it to light through the photomask. After patterning so that the cross section has a required number of steps, an electrode metal is formed on the entire surface, and then unnecessary electrode metal is removed together with the photoresist to form an electrode having a required number of steps. A method for manufacturing a semiconductor device.