JPS5896737A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make patterns with high dimensional accuracy, by a method wherein oxide film portions are formed on an Si substrate by utilizing a Si3N4 mask to decrease the difference in level, a photo-resist is applied on an oxide film after the mask was removed, and then, exposing, developing, and etching processes are performed. CONSTITUTION:Thermal oxide film portion 2a are formed on an Si substrate 1 by applying an Si3N4 mask 21 so that lower portions of the thermal oxide film portions 2a are buried in the substrate and the difference in level is decreased. The mask 21 is then removed, and the substrate 1 is covered by an oxide thin film 26. Then, a photo- resist film 3 is applied thereon and a glass mask 4 is further applied on the film 3 tightly. Ultraviolet rays 5 are irradiated onto the mask 4 to print and develop patterns 6 thereon. The oxide film 26 with printed and developed patterns 6 thereon are etched to form the patterns 6. By the above structure, the difference in level is decreased to about 60% as compared with the conventional method, even when the thickness of the oxide film portion 2a, which is directly under the external wiring region, is increased. Accordingly, patterns with high dimensional accuracy in conformity with the design are formed readily, since there occurs not so much overexposure at printing time as that in the conventional method, thus, the resolution is not decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and in particular to a method for improving resolution by printing on stepped portions of an oxide film.

Generally, in a semiconductor device 9, for example, a high frequency transistor, it is advantageous to design the oxide film directly under the external electrode wiring area such as the bonding pad 9 to be as thick as possible in order to improve the high frequency characteristics. The thicker the oxide film becomes, the larger the oxide layer step becomes, making it difficult to pattern the active region. In other words, conventionally, a diffusion region of a different conductivity with a higher concentration than the base region is formed directly under the opening of the base ohmic contact in a pattern of the same size as the opening to lower the base resistance. This diffusion region is usually designed into a fine pattern, and the finer the pattern, the thinner the oxide film must be. The film thickness needs to be as thick as possible.

In order to satisfy both of these requirements, recent high-frequency transistors have an oxide film (2a) on the semiconductor substrate (1) corresponding to the external electrode wiring area, as shown in FIGS. 1(a) and (b). A thin oxide film (2b) corresponding to the active region is formed thereon.

Further, in order to form the diffusion region in this state, as shown in FIG. 1(b), a photoresist film (3) is used.

Normally, an 0MR83 resist is applied, a glass mask (4) is placed on top of the resist, and then, for example, ultraviolet light (5) is irradiated to perform baking. Here, (1) is the pattern dimension provided on the glass mask (4). Mask alignment equipment that irradiates ultraviolet rays through a glass mask generally includes a contact exposure method and a projection exposure method, but the former is used for semiconductor devices such as high-frequency transistors, where printing is focused on resolution. A mask alignment device based on this method is used. However, even when using this device, the ultraviolet rays (5) used for printing are not perfectly parallel rays, so if the adhesion between the glass mask and the photoresist is poor, the printing will inevitably result in a decrease in resolution. As mentioned above, if the oxide film level difference is large, the adhesion will naturally deteriorate, making it impossible to obtain a pattern as designed. That is, FIG. 1(c) shows a pattern (6) for forming a diffusion region obtained after the above-mentioned baking through steps such as development, oxide film etching, and photoresist removal.

The design dimensions of this diffusion region are the pattern dimensions (1) of the glass mask (4), but the dimensions (11) of the pattern (6) obtained here are due to the close contact due to the oxide film step etc. As the power decreases and exposure fog occurs, the dimensions become quite small (l>11), and when the dimension standard unit becomes around 1 μm, it is no longer possible to resolve, and in this state, the diffusion directly below the base ohmic contact mentioned earlier. This made it impossible to form a region.

This invention was made to improve these conventional drawbacks, and an embodiment of the method for manufacturing a semiconductor device according to the invention will be described below with reference to FIGS. 2(a) to 2f). Explain in detail.

FIGS. 2(a) to 2(g) show the method of this embodiment in the order of steps. In this embodiment method, a nitride film (21) is first formed on a semiconductor substrate (1), and then a photoresist film (3) is left on the nitride film (21) in a portion corresponding to the active region formation portion. In the same figure (a), using the photoresist film (3) in parentheses as a mask, the nitride film (21) other than the active region forming area is partially selectively etched by dry process technology such as plasma etching. ((b) in the same figure).

Then, thermal oxidation is performed in this state. Namely.

When thermally oxidized leaving the nitride film (21), the nitride film (21)
In other words, oxygen is not supplied to the active region formation area and oxidation does not proceed, but other parts, in this case the external electrode wiring area formation area, do not have the nitride film (21) and oxidation does not occur. progresses, a thick oxide film (2a) is formed (FIG. 2(c)), and then an unnecessary nitride film (21) is left behind.
) is removed as appropriate ((d) in the same figure).

However, in this case, as is clear from the same figure (d),
The oxide film (2a) will be formed at the interface (force) of the silicon substrate (1), on the inside and outside of the substrate (1), and if its thickness is, for example, 1o, oooA. , in the conventional case described above, this thickness is 10.0OOA.
However, in this example, 4. is normally applied to the inside of the substrate. oooi, outward 6. ooooo
The oxide film is oxidized by a degree of X, and the oxide film step difference here is about 6,000λ, that is, about X of the conventional one.

Next, as mentioned above, in order to improve the high-frequency characteristics of a high-frequency transistor, a diffusion region with a higher concentration than the base region is formed in a pattern of about the same size just below the base ohmic opening. For the purpose of lowering the base resistance, an oxide film (2b
) is formed ((C) in the same figure). Furthermore, a photoresist film (3) is formed on this oxide film (2b) in the same manner as before.
and apply a glass mask (4) on it,
Baking is performed by irradiating ultraviolet rays (5) with a mask alignment device ((f) in the same figure), and then through processes such as development, oxide film etching, and photoresist removal, a pattern (6) for forming a diffusion region is obtained. (Figure (g)). The dimensions of the pattern (6) obtained here are as follows:
The pattern size (4) is almost the same as the pattern size (1) set in 4). That is, there is a relationship of at least (l>4<It>).

Therefore, in the case of the method of this embodiment, even if the oxide film directly under the external electrode wiring area is formed thickly, the high-frequency transistor formed in this way has a fine pattern because the oxide film step is about 60% of the conventional one. It is easy to form and can achieve high performance.

Although the above embodiments have been described with respect to the manufacture of high-frequency transistors, it is of course applicable to the manufacture of other semiconductor devices such as integrated circuits.

As detailed above, according to the method of the present invention, even if the thickness of the oxide film directly under the external electrode wiring area is the same as in the conventional method, the difference in level between the oxide film and the active region forming area can be made sufficiently small. In addition, even when forming the ultra-fine pattern 7 by printing, there is no conventional practice that any exposure causes blurring, and it is easy to form a pattern according to the designed value.

[Brief explanation of drawings]

1(a) to C) are cross-sectional views illustrating the manufacturing process of a high-frequency transistor according to a conventional example, and FIGS. 2(a) to 2(g) show manufacturing of a high-frequency transistor using an embodiment of the method of the present invention. 0 (1)...Semiconductor substrate, (2a), (zb)...
・Oxide film, (21)...Nitride film, (3)...Photoresist film, (4)...Glass mask, (5)...
...Ultraviolet light, (6)...pattern. Agent Makoto Kuzuno (1 other person) Figure 1 Figure 2 Figure 2 Figure 1

Claims (1)

[Claims] a step of selectively forming a nitride film on a portion corresponding to the formation of an active region on a semiconductor substrate; and a step of thermally oxidizing the nitride film to form a thick oxide film in a portion of the external electrode wiring region other than the active region formation portion. , removing the remaining nitride film;
A process of forming a thin oxide film on these, then coating a photoresist film on these, baking a glass mask in close contact with the film, developing, etching the oxide film, and removing the photoresist, and then forming a pattern on the thin oxide film. 1. A method of manufacturing a semiconductor device, comprising the step of forming an opening.