JPH0997790A - Forming method of oxide film and semiconductor device provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming an oxide film thicker than one formed through LOCOS method without increasing crystal defects and the like in it and to lessen a semiconductor device further in stray capacitance by the use of the above oxide film. SOLUTION: An oxide film and a nitride film are deposited on a semiconductor substrate 11, an opening is provided in the oxide film and the nitride film, and a stripe-like deep groove is provided by etching the substrate 11 through the opening, the side face of the groove is oxidized, whereby a stripe-like part of the substrate is oxidized to from an oxide film 18 as thick as the depth of the groove. This semiconductor device is equipped with the thick oxide film 18 on the underside of a bonding pad 16.

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 an oxide film and a semiconductor device using the oxide film, and particularly to forming a thick oxide film suitable for reducing stray capacitance of electrode wiring in a super high frequency transistor or the like. The present invention relates to a method and a semiconductor device using the oxide film.

[0002]

2. Description of the Related Art In high frequency transistors, especially ultra high frequency transistors operating above the GHz band, PG
In order to improve high frequency characteristics such as (POWER GAIN) characteristics, it is required to reduce the stray capacitance of electrode wiring. In particular, since the area directly under the electrode of the bonding pad is large, it is necessary to reduce the capacitance. Therefore, in the ultra-high frequency transistor and the like, the floating capacitance is reduced by increasing the film thickness of the oxide film immediately below the bonding pad by the LOCOS method or the shallow etching LOCOS method. Further, a multi-layer electrode wiring structure is adopted to reduce the area of the first layer electrode portion having a large stray capacitance and to enlarge the area of the second layer electrode portion having a relatively small stray capacitance.

However, when a thick oxide film is formed by the LOCOS method, there are problems that defects increase due to increase in bird's beag and defects due to long oxidation time at high temperature, and that thick oxide film causes problems. There is a problem that the steps increase. Considering these problems, the film thickness of the oxide film that can be used in the present invention for the ultra-high frequency transistor is limited to about 12,000Å.

Even if the shallow etching LOCOS method is used, the step difference can be reduced, but the film thickness is similarly increased due to the increase of defects due to the increase of bird's beag or the increase of defects due to the increase of oxidation time. 12,000
The limit was about 0Å. Further, when the multilayer electrode wiring structure is used, the number of steps is increased, and it is preferable to use the nitride film in terms of the denseness of the interlayer insulating film. However, since the nitride film has a high dielectric constant, the same thickness of oxide film is used. The stray capacitance is larger than the membrane,
It is necessary to increase the film thickness.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is a method for forming an oxide film, which is thicker than the conventional LOCOS method without increasing crystal defects and the like. Another object of the present invention is to provide a semiconductor device in which stray capacitance is further reduced by using the oxide film.

[0006]

According to the method for forming an oxide film of the present invention, an oxide film and a nitride film are deposited on a semiconductor substrate, an opening is provided in the oxide film and the nitride film, and the substrate is opened from the opening. To form deep stripe-shaped grooves by etching
By oxidizing the side surface of the deep groove, the stripe-shaped substrate portion is oxidized to form an oxide film having a thickness corresponding to the depth of the groove.

Further, the semiconductor device of the present invention is characterized in that the oxide film formed by the above-mentioned forming method is provided at least on the lower surface of the bonding pad.

[0008]

According to the above-described method for forming an oxide film of the present invention, a stripe-shaped deep groove is formed in a silicon substrate, and the side surface of the deep groove is oxidized to stripe the stripe portion from both sides. It is possible to oxidize the entire structure, and the groove portion can be completely filled with the oxide film by the oxide film growing from the side surface of the stripe. As a result, an oxide film having a thickness corresponding to the depth of the stripe groove can be formed under the oxidation condition by the normal LOCOS method, and the oxide film having a thickness that is about 2-3 times thicker than that by the normal LOCOS method can be formed. A film can be formed.

A semiconductor device having such a thick oxide film has a thickness of at least 2-3 μm on the lower surface of the bonding pad.
By providing a thick oxide film, the stray capacitance in the electrode wiring portion can be significantly reduced. As a result, high frequency characteristics can be significantly improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. The same reference numerals in the drawings indicate the same or corresponding parts.

FIG. 1 is a pattern diagram of an ultra high frequency transistor according to an embodiment of the present invention. FIG. 2 shows a partial cross-sectional structure of the ultra high frequency transistor shown in FIG. An active region including an emitter region 13 and a base region 12 is provided on the semiconductor chip 11, a wiring electrode 14 is connected to the emitter region 13, and a wiring electrode 15 is provided in the base region 12.
Is connected. Each wiring electrode communicates with the bonding pads 16 and 17, and is connected to the lead terminal of the semiconductor package by a bonding wire (not shown). LOC is provided on the lower surfaces of the bonding pads 16 and 17.
Thicker than the field oxide film 20 formed by the OS method,
It is provided with oxide films 18 and 19 described in detail below.

The thick oxide films 18 and 19 are formed by depositing an extremely thin oxide film and a nitride film on a silicon semiconductor substrate, forming openings in the oxide film and the nitride film, and etching the substrate through the openings. Is a thick oxide film region formed by forming a deep groove of the stripe and oxidizing the side surface of the deep groove. Therefore, this thick oxide film region 18,
Reference numeral 19 is an oxide film having a thickness corresponding to the depth of the groove, and the LOC is formed without generating crystal defects or thermal strain in the semiconductor substrate.
An insulating film region thicker than the field oxide film 20 formed by the OS method can be obtained. In particular, the stray capacitance on the lower surface of the bonding pad can be significantly reduced.

3 to 6 show various stripe-shaped deep groove patterns formed by etching a silicon semiconductor substrate. Reference numeral 21 indicates a stripe portion that remains without etching the silicon substrate, and reference numeral 22 indicates a groove portion where the silicon substrate is removed by etching. In the present embodiment, the width of each of the stripe portion 21 and the etched groove portion 22 is about 1 μm, and the groove depth is about 2 μm. Strictly speaking, the ratio of the growth rate of the oxide film toward the inside of the silicon substrate to the growth rate of the outside toward the silicon substrate is 0.9 / 1.1. Therefore, by setting the ratio of the width S of the groove portion to the width L of the stripe portion to L / S = 0.9 μm / 1.1 μm, when the stripe portion is just oxidized from both sides, The part is just filled with an oxide film that grows outward.

FIG. 3 shows a stripe pattern formed in a ring shape. It is possible to form such an annular groove having a width of about 1 μ in the entire lower surface of the bonding pad and then oxidize the groove-side surface to make the entire stripe-formed area a thick oxide film area. it can. Similarly, FIG. 4 shows a case where the stripe pattern is formed in a square band shape. FIG. 5 shows a case where the stripe pattern is formed in a strip shape. FIG. 7 shows a case where the stripe pattern is formed in a cell mesh shape. In addition, the stripe pattern is such that when the stripe portion is just oxidized from both sides, the groove is just filled with the oxide film,
As long as the dimensional ratio is sufficient, various modifications other than those shown in FIGS. 3 and 6 are possible.

Next, a method for forming a thick oxide film will be described with reference to FIGS. As shown in FIG.
First, a thin oxide film 25 is deposited on the silicon semiconductor substrate 11, and a nitride film 26 is similarly deposited by vapor phase growth. The thickness of the oxide film is about 500Å, but the thickness of the nitride film is 1000Å
The degree is preferred. Next, as shown in FIG. 8, a non-doped oxide film 27 is similarly deposited thereon by vapor phase growth.
The thickness is preferably 2000 to 3000Å.

Next, resist patterning is performed. First, a photoresist 28 is applied on the entire surface, and is exposed and developed according to the mask having the stripe pattern shown in FIGS. 3 and 6 described above to form the resist pattern 28 shown in FIG. In this embodiment, the width of the resist pattern and the width of the opening are 1.1 /, respectively.
It is about 0.9 μm. Then, the resist pattern 28
Using the as a mask, the non-doped oxide film 27, the silicon nitride film 26, and the oxide film 25 are dry-etched. And
The photoresist film 28 is removed. This stage is shown in FIG.

Then, using the non-doped silicon oxide film 27 as a mask, the silicon semiconductor substrate 11 is anisotropically etched to form a groove 22 having a depth of about 2 μm. At this stage, the stripe portion 21 and the groove portion 22 are formed on the silicon semiconductor substrate 11. This is shown in FIG. Next, oxidation is started with the oxide film 27 removed (see FIG. 12) or with the oxide film left (see FIG. 11). These nitride films and the like are removed after the oxidation is completed.

Then, the silicon substrate formed in a stripe shape is oxidized under the same wet oxidation condition as the LOCOS method. Oxidation gradually progresses from the surface of the stripe 21, spreads inside the stripe 21, and an oxide film grows also on the groove 22 side, and the width of the groove portion 22 gradually narrows as shown in FIG. Then, as the oxidation further progresses, as shown in FIG. 14, the stripe portion 21 is just oxidized from both sides, and the groove portion 22 is completely filled, so that the thick oxide film 1 is formed.
8 and 19 are formed. The thick oxide films 18 and 19 are
It can be formed flat with almost no step difference from its peripheral portion.
Therefore, the electrode wiring can be easily formed.

In manufacturing the ultra high frequency transistor, the oxide film having a thickness of about 2 .mu.m described above is first formed on the portion where the bonding pad is arranged. Then the normal LOCOS
A field oxide film is formed by the method. Then, base and emitter diffusion regions are formed in the active region.
Next, a wiring electrode material is deposited by sputtering or the like, and a wiring electrode including a bonding pad is formed by resist patterning.

The field oxide film may be formed simultaneously with the formation of the thick oxide film of the present invention by using the nitride film used for forming the stripe pattern.
According to such a manufacturing process, the semiconductor device having the thick oxide film of the present invention can be manufactured only by increasing the number of processes for forming the groove portion of the stripe pattern.

In the above description of the embodiment, the width of the stripe portion and the groove portion is about 1 μm, but the width of the stripe portion and the groove portion are made narrower by the progress of the fine processing technology. Furthermore, the oxidation time can be shortened, and problems such as the occurrence of crystal defects can be reduced.

Further, in the above-mentioned embodiment, the example of etching the silicon substrate using the non-doped oxide film as a mask has been described. However, the etching when the silicon nitride film / oxide film is etched is carried out using the resist as a mask. But of course it is good.

Further, in the above-described embodiment, only the bonding pad portion is formed of the thick oxide film of the present invention, but the thick oxide film of the present invention may be formed over the entire lower portion of the electrode wiring or the entire chip except the active region. . By doing so, the surface of the chip is flattened and the steps are eliminated, so that the electrode wiring of the fine pattern is facilitated.

[0024]

As described above, according to the method for forming a thick oxide film of the present invention, the required oxide film thickness can be obtained by controlling the depth of the groove in the stripe portion. In this embodiment, the oxidation condition at this time may be an oxidation time at the time of 12000Å growth by the normal LOCOS method, and the generation of crystal defects due to the oxidation at a high temperature for a long time is similar to that in the normal LOCOS oxidation method. Can be suppressed to

Further, according to the method for forming a thick oxide film of the present invention, since oxidation proceeds from the surface of the stripe portion toward the surface of the substrate, there is almost no bulging growth in the direction of the upper surface of the substrate. Therefore, by using the oxidation method of the present invention, a thick oxide film can be formed on a surface which is almost flat with respect to the periphery thereof.

Further, in the semiconductor device such as an ultra-high frequency transistor using a thick oxide film of the present invention, the above-mentioned thick oxide film is used under the bonding pad portion having a relatively large area, whereby the stray capacitance of the electrode wiring is reduced. Can be significantly reduced, and high frequency characteristics such as power gain characteristics can be improved. Further, since the oxide film having a flat surface and a sufficient thickness can be obtained, the electrode wiring has a single-layer structure, and the manufacturing process can be simplified.

Further, when the field region other than directly under the bonding pad is obtained by the usual LOCOS oxidation method,
Sufficient high-frequency characteristics can be obtained when the oxide film thickness in the field region is about half the conventional thickness. Therefore, it is possible to reduce the oxidation time, the temperature, and the like, and it is possible to suppress the occurrence of crystal defects and the like due to bird's beag. In general, according to the present invention, it becomes possible to manufacture an ultra high frequency transistor or the like having a high frequency characteristic improved by providing a thick oxide film with higher quality.

[Brief description of drawings]

FIG. 1 is a pattern diagram of an ultra high frequency transistor chip according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of the ultra high frequency transistor in FIG.

FIG. 3 is an explanatory diagram of an annular stripe pattern according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of a square striped stripe pattern according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram of a striped stripe pattern according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram of a cell mesh-shaped stripe pattern before oxidation according to an embodiment of the present invention.

FIG. 7 is an explanatory diagram of a process of forming a thick oxide film according to an embodiment of the present invention.

FIG. 8 is an explanatory diagram of a process of forming a thick oxide film according to an embodiment of the present invention.

FIG. 9 is an explanatory diagram of a process of forming a thick oxide film according to an embodiment of the present invention.

FIG. 10 is an explanatory diagram of a process of forming a thick oxide film according to an embodiment of the present invention.

FIG. 11 is an explanatory diagram of a process of forming a thick oxide film according to an embodiment of the present invention.

FIG. 12 is an explanatory diagram of a process of forming a thick oxide film according to an embodiment of the present invention.

FIG. 13 is an explanatory diagram of a process of forming a thick oxide film according to an embodiment of the present invention.

FIG. 14 is an explanatory diagram of a process of forming a thick oxide film according to an embodiment of the present invention.

Claims (2)

[Claims] 1. A semiconductor substrate is coated with an oxide film and a nitride film, openings are formed in the oxide film and the nitride film, and the substrate is etched through the openings to form deep stripe grooves. A method for forming an oxide film, characterized in that the side surface of the deep groove is oxidized to oxidize the stripe-shaped substrate portion to form an oxide film having a thickness corresponding to the depth of the groove. 2. A semiconductor device comprising the thick oxide film according to claim 1 on at least a lower surface of a bonding pad.