JPH0618274B2 - Method of manufacturing Schottky barrier semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high breakdown voltage Schottky barrier semiconductor device.

2. Description of the Related Art Schottky barrier diodes are widely used in high-frequency rectifier circuits and the like, taking advantage of good high-speed response (high-speed switching characteristics) and low power loss. But,
In the Schottky barrier diode, a phenomenon in which the peripheral breakdown voltage (breakdown voltage around the Schottky barrier) is significantly lower than the bulk breakdown voltage (breakdown voltage in the central portion of the Schottky barrier) is recognized, and therefore a high breakdown voltage is obtained. Is difficult.

As one of methods for improving the peripheral breakdown voltage, Japanese Patent Laid-Open No. 62-
As shown in Japanese Patent No. 45172, there is known a high breakdown voltage structure in which a Schottky barrier and a semiconductor region therebelow are surrounded by a semi-insulating semiconductor region. A Schottky barrier diode having this high breakdown voltage structure will be described with reference to FIG. The illustrated Schottky barrier diode is n ⁺
There is a semiconductor substrate 1 made of GaAs (gallium arsenide) in which an n-type region 3 is formed on a n-type region 2, and He (helium), H (hydrogen), B (boron), etc. are ionized in the n-type region 3. By implanting, the semi-insulating semiconductor region 4 is formed. The semi-insulating semiconductor region 4 is formed in a ring shape in plan view. A barrier electrode 5 made of an Al (aluminum) layer is formed on the upper surface of the n-type region 3a surrounded by the semi-insulating semiconductor region 4.
And a Schottky barrier which is a rectifying junction is formed between the barrier electrode 5 and the n-type region 3a. On the lower surface of the n ^{+ -type} region 2, an ohmic electrode 6 in which an Au layer is superposed on an alloy layer of Au (gold) and Ge (germanium) is formed. In this Schottky barrier diode, when a reverse voltage is applied, the spread of the depletion layer is limited by the semi-insulating semiconductor region 4, so that the electric field concentration around the Schottky barrier is alleviated, and a considerably large breakdown voltage is expected. it can. It is considered that the semi-insulating semiconductor region 4 is made of the same semiconductor material as that of the n-type region 3 and is formed without stress concentration around the Schottky barrier, which is also a factor in improving the breakdown voltage. Note that the notation of “semi-insulating semiconductor region” contradicts the terms “semi-insulating” and “semiconductor”, but as used in this specification as a general term, “consisting of semiconductor materials and A high resistance region having a semi-insulating property ". The semi-insulating semiconductor region is formed by implanting ions such as H into the semiconductor substrate material. It has been confirmed by experiments that this semi-insulating semiconductor region is effective in increasing the breakdown voltage.

By the way, when the Schottky barrier diode shown in FIG. 4 is manufactured as shown in Japanese Patent Laid-Open No. 62-45172, a method is known in which ion implantation is carried out using the barrier electrode 5 to be left finally as a mask. When this method is carried out, a silicon oxide film 7 is formed on the barrier electrode 5 as shown in FIG. 5, and the silicon oxide film 7 and the barrier electrode 5 are n He is ion-implanted into the shaped region 3 to form the semi-insulating semiconductor region 4. According to this method, the silicon oxide film 7 and the barrier electrode 5 are used as a mask at the time of ion implantation, and the barrier electrode 5 can be left as it is after the ion implantation, so that the mask effect is sure and the peripheral area is simplified by the simplified manufacturing process. A Schottky barrier diode having a high breakdown voltage can be obtained.

SUMMARY OF THE INVENTION However, the Schottky barrier diode manufactured by the above-described method has a fact that desired breakdown voltage characteristics cannot be obtained. This is because the overlapping portion between the peripheral edge portion of the barrier electrode 5 and the inner peripheral edge portion of the semi-insulating semiconductor region 4 is not formed with a sufficient width when seen in a plan view. That is, when the peripheral portion of the barrier electrode 5 is enlarged and the barrier layer 5 is formed by selectively removing the Al layer formed on the entire surface by photoetching as shown in FIG. By directional etching, an eave-shaped protrusion 7a is formed on the silicon oxide film 7. Therefore, the implantation amount of He is reduced in the n-type region 3 below the eave-shaped protrusion 7a. Although the behavior of the ion beam is complicated at the tip of the eave-shaped protrusion 7a due to the scattering of the ion beam, it is presumed that the semi-insulating semiconductor region 4 having the shape as illustrated is formed. Although it is difficult to grasp the exact shape of the semi-insulating semiconductor region 4, the barrier electrode 5 and the semi-insulating semiconductor region 4 when viewed two-dimensionally are difficult.
It is a fact that the overlapping part of is hardly formed or is slightly formed even if it is formed. In this case, the effect of increasing the withstand voltage by the semi-insulating semiconductor region 4 is not sufficiently exerted, and the withstand voltage is reduced as compared with the case where the overlapping portion is sufficient as shown in FIG.

If the ions are implanted using only the barrier electrode 5 as a mask without forming the silicon oxide film 7, the above-mentioned problems caused by the eave-shaped protrusion 7a can be solved. However, since the range (reaching depth) of the implanted ions into the Al layer is about the same as the range into the n-type region 3, the ion must be formed thickly, for example, with a film thickness of 4 μm or more. Since a part of the above penetrates the barrier electrode 5, a sufficient masking effect cannot be obtained. If the barrier electrode 5 is thickened so as to obtain a sufficient masking effect,
The accuracy of the photoetching is lowered, and the pattern of the barrier electrode 5 is broken, which causes the breakdown voltage to be lowered.

Therefore, an object of the present invention is to provide an improved method of manufacturing a Schottky barrier semiconductor device capable of improving the peripheral breakdown voltage of a high breakdown voltage structure including a semi-insulating semiconductor region.

Means for Solving the Problems A method of manufacturing a Schottky barrier semiconductor device according to the present invention includes a relatively thick electrode layer made of a substance that forms a Schottky barrier between itself and a semiconductor region, and surrounding and surrounding the electrode layer. A step of forming a relatively thin thin layer made of a substance that forms a Schottky barrier with the semiconductor region on one main surface of the semiconductor region; and an electrode layer or a film formed on the electrode layer as a mask. Forming a semi-insulating semiconductor region adjacent to the lower part of the thin layer so as to surround the semiconductor region under the electrode layer by implanting ions into the semiconductor region through the layer; Forming an insulating film covering the upper surface of the thin layer.

Since the thin layer, which can be regarded as the working auxiliary barrier electrode, and the semi-insulating semiconductor region can be formed with an overlapping portion having a sufficient width, the breakdown voltage characteristic is not deteriorated and the characteristic is not unstable. In addition, the surface of the semi-insulating semiconductor region is double-coated with a thin layer and an insulating film, and in particular, the thin layer forms a Schottky barrier with the semiconductor region and stabilizes the surface state. Even if the semiconducting property remains near the surface of the conductive semiconductor region, no problem occurs and the instability of the property does not occur.

Example Hereinafter, a method of manufacturing a high breakdown voltage Schottky barrier diode for electric power, which is an example of the present invention, will be described with reference to FIGS. 1 and 2.

First, as shown in FIG. 1A, a semiconductor substrate 11 made of GaAs (gallium arsenide) is prepared. Semiconductor substrate 1
1 is a semiconductor in which an n-type region 13 having an impurity concentration of 2 × 10 ¹⁵ cm ⁻³ and a thickness of about 15 μm is epitaxially grown on an n ^{+ -type} region 12 having an impurity concentration of 2 × 10 ¹⁸ cm ⁻³ and a thickness of about 300 μm. Has an area.

Next, as shown in FIG. 1B, Ti (titanium) and Al are continuously vacuum-deposited on the upper surface of the semiconductor substrate 11 to form a Ti thin layer 14 and an Al layer 15. The thickness of the Ti thin layer 14 is extremely thin, about 100 Å (0.01 μm). Al layer 15
Has a thickness of about 2 μm. Further, a total of Au (gold) and Ge (germanium) and Au are continuously vacuum-deposited on the back surface of the semiconductor substrate 11 to form the ohmic electrode 16. After that, plasma CVD (Chemical Vapor Deposition)
Thus, a silicon oxide film 17 having a thickness of about 1 μm is formed on the upper surface of the Al layer 15.

Then, as shown in FIG.
The thin layer 14, the Al layer 15, and the silicon oxide film 17 of i are removed by photoetching, and Ti on the element peripheral side is further removed.
The thin layer 14 of Al and the Al layer 15 are removed by photoetching, and the thin layers 14a and 14b of Ti and the Al layer 1 are formed as shown in the figure.
5a and the silicon oxide film 17a are left. Ti layer 14a,
Both 14b and the Al layer 15a are metal layers forming a Schottky barrier between the n-type region 13 which is a semiconductor region. However, since the Ti thin layer 14a is extremely thin, the Ti thin layer 14a is formed.
It is not clear how is involved in the formation of the Schottky barrier. Here, the Al layer 15a and the Ti thin layer 14a thereunder are collectively referred to as a main barrier electrode 18 which constitutes an electrode layer. In this case, the Ti thin layer 14b forms a Schottky barrier between itself and the n-type region 13, and
It has a function of stabilizing the surface state of the shaped region 13, and can be called an auxiliary barrier electrode. Since the Ti thin layer 14b is extremely thin, the sheet resistance is about 400Ω / □.
It is a resistance layer. Next, as schematically shown by an arrow 19, He (helium) is multiply ion-implanted into the entire upper surface of the semiconductor substrate 11 while changing the acceleration voltage. As a result, H
The GaAs crystal lattice is disturbed by the ion implantation of e, and a ring-shaped semi-insulating semiconductor region 20 is formed in a plan view so as to surround the n-type region 13a immediately below the Al layer 15a. He
Does not reach the n-type region 13 in the portion masked by the silicon oxide film 17a and the main barrier electrode 18. However, since the Ti thin layer 14b is extremely thin,
In the portion not masked by the silicon oxide film 17a,
He is simply implanted through the thin layer 14b of Ti into the n-type region 13. As a result, the semi-insulating semiconductor region 20
Are formed to a depth of about 2.5 μm. The semi-insulating semiconductor region 20 is a high resistance layer close to an insulator having a specific resistance of 10 ⁷ to 10 ⁹ Ω-cm. As shown in an enlarged view of the peripheral portion of the main barrier electrode 18 in FIG. 2, the peripheral portion of the silicon oxide film 17a forms an eave-shaped protrusion 17b protruding from the peripheral portion of the main n-type region 18. Since it is difficult to accurately grasp the shape of the semi-insulating semiconductor region 20, the shape shown is an expected figure. However, the thin Ti layer 14b serving as an auxiliary barrier electrode for the main barrier electrode 18 is formed in the semi-insulating semiconductor region 2
It is formed of an overlapping portion having a width sufficient for 0.

Further, as shown in FIG. 1D, the silicon oxide film 17
After removing a by etching, plasma CVD or light C
The silicon oxide film is coated on the upper surface of the semiconductor substrate 11 by VD, and the silicon oxide film 2 is subjected to a photoetching process.
1 is formed. Further, Ti and Au are formed on the upper surface of the semiconductor substrate 11.
Are continuously vacuum-deposited, and an external connection electrode 22 is formed through a photoetching process to complete a Schottky barrier diode chip. A Schottky barrier serving as a main current path is formed between the main barrier electrode 18 and the n-type region 13, the main barrier electrode 18 side is the anode, and the ohmic electrode 16 side is the cathode.

The Schottky barrier diode manufactured in this way obtained a high breakdown voltage of about 210V. In some cases, a breakdown voltage of about 230 V, which is almost equal to the bulk breakdown voltage, was obtained. The reliability test also gave good results. On the other hand, when the thin Ti layer 14b is removed by etching and He ions are implanted when the semi-insulating semiconductor region 20 is formed, the peripheral portion 22a of the connection electrode 22 is exposed through the silicon oxide film 21. It works as a general field plate, but withstands about 15
It was 0V. Particularly, in this case, the silicon oxide film 21
Due to the influence of the film quality of the protective film and the forming conditions due to the above, the variation of the withstand voltage is large, and the withstand voltage is likely to decrease even in the reliability test. In the structure in which the Ti thin layer 14b is removed and the semi-insulating semiconductor region 20 is not formed (structure in which no measure against high breakdown voltage is taken), the breakdown voltage is about 60V.

The thin layer 14b of Ti is considered to act as a field plate in the portion extending above the semi-insulating semiconductor region 20, but the detailed mechanism is unknown.
However, it has the following features. Ti thin layer 14b is n
When formed on the surface of the n-type region 13, the n-type region 13
A Schottky barrier is formed between and, and the surface state of the n-type region 13 is stabilized. Therefore, even if the semiconducting properties remain near the surface of the semi-insulating semiconductor region 20, there is no problem. Further, since the Ti thin layer 14b is a field plate that does not have an insulating layer such as a silicon oxide film interposed therebetween, the action of forming a depletion layer therebelow is very large, and the material (type of material) forming the insulating layer is large. Instability of characteristics due to impurities, interface states, etc.) does not occur.

Modifications The present invention is not limited to the embodiments, and various modifications can be made within the scope of the spirit thereof.

For example, as a thin layer corresponding to the Ti thin layer 14b, a titanium oxide thin layer 23 formed by oxidizing the Ti thin layer 14b may be used as shown in FIG. in this case,
The thin layer 23 of titanium oxide is similar to the thin layer 14b of Ti,
It has a function of forming a Schottky barrier with the n-type region 13 and stabilizing the surface state of the n-type region 13. Titanium oxide is a high resistance layer with a sheet resistance of about 100 MΩ / □. The main barrier electrode 18 is a thin Ti layer 1 on the outer periphery.
This is due to only the Al layer 15a except the portion 4c.

From the viewpoints of excellent adhesion to the semiconductor region, surface stabilization effect, and influence on the semiconductor surface due to the field plate structure, a thin layer of Ti or titanium oxide (TiOx) is used as a thin layer.
Thin layers are preferred. However, as long as it is a substance that forms a Schottky barrier with the n-type region 13 and allows the implanted ions to easily pass therethrough, a Ta (tantalum) thin layer, a tantalum oxide (TaOx) thin layer, and the like other than those described above are used. A substance can be used. The thickness of the thin layer is 10-1000Å in order to pass the ions and minimize the stress generation.
It is desirable to select 20 to 300Å.

The present invention is particularly effective when a film such as a silicon oxide film 17a is formed on the electrode layer corresponding to the main barrier electrode 18 and the electrode layer and the film are combined and used as a mask for ion implantation. . However, even when ion implantation is performed with a mask of an electrode layer made of a metal having a large masking effect alone, it is effective as a method of improving the instability of the withstand voltage characteristics due to a small overlap between the electrode layer and the semi-insulating semiconductor region. Note that, after the ion implantation, the periphery of the electrode layer may be slightly removed by etching to intentionally separate the main barrier electrode 18 from the semi-insulating semiconductor region.

Further, the present invention is suitable for a semiconductor device using a III-V group compound semiconductor such as GaAs, AlGaAs (aluminum gallium arsenide), GaP (gallium phosphide), InP (indium phosphide), but other It can also be applied to a semiconductor device using a compound semiconductor or Si (silicon).

According to the present invention, in the method of manufacturing a Schottky barrier semiconductor device in which a semi-insulating semiconductor region is formed by ion implantation and the breakdown voltage is increased, the barrier electrode forming the Schottky barrier is also used as a mask for ion implantation. It becomes possible to manufacture a high breakdown voltage Schottky barrier semiconductor device with a high manufacturing yield.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a Schottky barrier diode showing an embodiment of the present invention. FIG. 1 (A) is a sectional view of a semiconductor substrate, FIG. 1 (B) is a thin layer of Ti on the upper surface of the semiconductor substrate, A
a cross-sectional view showing a state in which an I-layer and a silicon oxide film are formed,
FIG. 1 (C) is a sectional view showing the step of ion implantation, FIG. 1 (D) is a sectional view showing a state in which a silicon oxide film and an electrode for external connection are formed, and FIG. 2 is FIG. 1 (C). A partial sectional view showing an enlarged peripheral portion of the main barrier electrode in the step of
FIG. 3 is a sectional view of a Schottky barrier diode showing another embodiment of the present invention, FIG. 4 is a sectional view of a conventional Schottky barrier diode, and FIG. 5 shows an ion implantation process in manufacturing a conventional Schottky barrier diode. The sectional view shown in FIG. 6 is a partial sectional view showing an enlarged peripheral portion of the barrier electrode in FIG. 13, 13a ... n type region (semiconductor region), 14a ... T
i thin layer, 14b ... Ti thin layer (thin layer), 18 ... main barrier electrode (electrode layer), 20 ... semi-insulating semiconductor region,

Claims (1)

[Claims] 1. A relatively thick electrode layer made of a substance forming a Schottky barrier with a semiconductor region, and a substance forming a Schottky barrier with the semiconductor region adjacently surrounding the electrode layer. Forming a relatively thin thin layer on one main surface of the semiconductor region, and passing the thin layer to the semiconductor region by using the electrode layer or a coating formed on the electrode layer as a mask. Implanting ions to form a semi-insulating semiconductor region adjacently below the thin layer so as to surround the semiconductor region under the electrode layer, and a part of the electrode layer and the thin layer A method of manufacturing a Schottky barrier semiconductor device, comprising: forming an insulating film covering an upper surface of the Schottky barrier semiconductor device.