JPH03211880A - Forming method for schottky junction - Google Patents

Abstract

PURPOSE:To form a Schottky junction having thermal stability, large barrier height and small leakage current by heat treating the junction at 500 deg.C or higher in inert gas. CONSTITUTION:A heat resistant first metal layer for forming a Schottky barrier, an intermediate metal layer made of nitride of heat resistant metal, and a high conductivity second metal layer are sequentially laminated, and then heat- treated at 500 deg.C or higher in a nonoxidative gas atmosphere. That is, in the junction, Schottky metal is formed of an intermediate layer made of nitride of heat resistant metal such as TaN between a first metal layer formed of heat resistant metal for forming the barrier such as Ta and a second metal layer made of metal having excellent conductivity such as Al. Thus, mutual diffusion of the Ta and GaAs is limited only to a boundary, the diffusion is suppressed, and a thermally stable Schottky barrier is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for forming a Schottky junction between metal and gallium arsenide (GaAs) in the manufacture of semiconductor devices.

(Conventional technology) Recently, Ga
Research and development of device-related technologies such as As and InP are actively underway. One of these device-related technologies is a technique for forming a good Schottky junction. Schottky junction formation techniques have been advanced particularly in connection with the development of GaAs devices.

Conventionally, 80 has been mainly used as a Schottky gate electrode metal for GaAs devices, such as FETs, because of its good bonding properties, good processability, good electrical conductivity, and low cost.

However, with recent demands for higher performance and higher reliability for FETs, various drawbacks have been discovered in AQ/GaAs Schottky junctions, and improvements in the junction characteristics have been made.

Improvement is required. For example, AQ has a low melting point of 660°C and is highly reactive, so the reaction between AQ and GaAs proceeds even at a relatively low temperature of about 200°C, for example, Al2G
Unstable compounds such as aAs are formed. As a result, the Schottky barrier height φB decreases, resulting in an increase in leakage current or an increase in the n value, which is an indicator of the quality of rectification. Changes in φB and n value appear as changes in drain saturation current, forward rising voltage, pinch-off voltage, etc. in FET characteristics.

Various measures have been taken to improve the above drawbacks.

For example, attempts have been made to use AQ/Ti in place of Al2, but even in this case a reaction occurs between Ti and GaAs, and fluctuations in FET characteristics cannot be avoided.

The inventors have investigated the stability of AQ/Ta/GaAs junctions, but even in this junction, φB due to interdiffusion between Ta and GaAs and other factors
It was not possible to suppress the fluctuations. Generally, interdiffusion between metal and semiconductor is considered to be a cause of Schottky barrier deterioration.

(Problems to be Solved by the Invention) As mentioned above, in conventional Schottky junctions such as Aρ/GaAs, the Schottky barrier properties tend to deteriorate due to the progress of interfacial reactions, and the barrier height increases accordingly. This often has drawbacks that are undesirable for device applications, such as a decrease in φB and an increase in the n value.

An object of the present invention is to provide a method for forming a Schottky junction that improves the above-mentioned drawbacks and exhibits thermally stable characteristics.

[Structure of the invention]

(Means for Solving the Problems) A method for forming a Schottky junction according to the present invention includes a heat-resistant first metal layer that forms a Schottky barrier on the main surface of a gallium arsenide substrate, and a heat-resistant metal nitride. The method is characterized by comprising a step of sequentially laminating and forming an intermediate metal layer and a highly conductive second metal layer, and then a step of performing heat treatment at 500° C. or higher in a non-oxidizing gas atmosphere.

(Function) In the Schottky junction according to the present invention, the Schottky metal is a heat-resistant metal such as Ta that forms the Schottky barrier.
As a result, an intermediate layer made of a heat-resistant metal nitride, such as TaN, is formed between the first metal layer made of a highly conductive metal such as AQ, and the second metal layer made of a highly conductive metal such as AQ.
The interdiffusion between a and GaAs is limited only to the interface, and as a result, diffusion is significantly suppressed compared to the conventional method, and a thermally stable Schottky barrier is realized.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

n-GaA with carrier concentration 2 x 10” tyi-3
The carrier concentration on the s substrate is 5 x 10"cm-",
A GaAs wafer on which an epitaxial layer (hereinafter abbreviated as shrimp layer) with a thickness of 0.5 Ia was grown was boiled in HCR, washed with water, and dried. The GaAs wafer was housed in a Pelger of a vapor deposition device, and a back pressure inside the Pelger was set to 5×
A Ta layer with a thickness of ~2,000 layers is formed on the shrimp layer by an electron beam method at 10-7 Torr. Next, the GaA
The S wafer is housed in a DC sputtering apparatus, and a TaN layer is formed on the Ta layer to a thickness of 100 to 300 ml by a 5-reactive sputtering method. The sputtering conditions for the TaN layer are to use a mixed gas of nitrogen and argon, and the partial pressure of nitrogen gas/partial pressure of argon gas! 0.03゜ total gas pressure ~ 3 x 10-'' Torr, applied DC voltage 3 ν, ion current -0.2 ■A 0
Then, 13,000 AQ layers were deposited on the TaN layer using a resistance heating method under a back pressure of I x 10''Torr;
A Schottky junction was formed.

G with Schottky junction formed in this way
The aAs wafer was housed in a heat treatment furnace and heat treated in an argon gas stream using m degrees and time as parameters.

Figure 1 shows AQ/TaN/T fabricated using the above method.
a /GaAs Schottky junction junction characteristic values (φB,
It is a figure showing the relationship between n) and heat treatment temperature. The heat treatment time is 10 minutes. For reference, the characteristics of an All/Ta layer GaAs junction manufactured using the conventional method using the same process as the present invention except for the TaN layer formation process are shown below.
As can be seen from FIG. 1, the AQ layer of the present invention, the TaN layer T
The φB and n values of the a/GaAs junction are 500-600'
For heat treatment at C, each has a nearly constant value ~0.86
eV and −1.08, and the value of φB is increased by ~0.03 V compared to the case without heat treatment. φ
An increase in B leads to a decrease in junction leakage current. This shows that the AQ/TaN/Ta/GaAs junction of the present invention is thermally stable and effective in reducing leakage current. In contrast, the conventional AQ/Ta
In the /GaAs junction, both the φB and n values vary with respect to temperatures of 1500° C. or higher, and cannot be said to be stable. The effects of the present invention are also clear from the results shown in FIG. 2, which explains the dependence of φB and n values on heat treatment time. As shown in Figure 3, the heat treatment temperature is 500°C or less, for example 400°C.
In the heat treatment, both the bonding according to the present invention and the conventional bonding,
φB gradually decreases with time, indicating that stabilization of the bond cannot be expected with heat treatment at this temperature.

Note that the heat treatment time is preferably about 10 minutes; if the heat treatment time is longer than that, it may adversely affect other steps of device manufacturing. Furthermore, if the heat treatment is too short, the effect of heat treatment will not be effective.

Further, in the embodiment, Ta is used as the first metal layer.

Although the combination of AQ as the second metal layer and TaN as the intermediate layer has been described, as the first metal layer,
Mo, Zr, etc., as the second metal layer, Au, Ag
, Cu, etc., intermediate layer, WN, VN, NbN,
Similar effects can be expected when ZrN or the like is also used.

〔Effect of the invention〕

As described above, according to the present invention, when depositing metal on a GaAs substrate to form a metal/semiconductor Schottky junction, the first metal layer made of a heat-resistant metal forming a Schottky barrier and the An electrically conductive intermediate layer made of a heat-resistant metal nitride is interposed between the second metal layer laminated on the Schottky junction, and the Schottky junction is heat-treated at a temperature of 500°C or higher in an inert gas. By performing this, it is possible to form a Schottky junction that is thermally stable, has a large barrier height, and therefore has a small leakage current, compared to the case where the heat treatment is not performed.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between heat treatment temperature and barrier height φB and n value for Schottky junctions, Figure 2 is a diagram showing the relationship between heat treatment time, barrier height φB and n value for Schottky junctions, FIG. 3 is a diagram showing the relationship between Schottky junction heat treatment time and barrier height φB. In each case, O relates to the present invention and X relates to each Schottky junction of the conventional example.

Claims (1)

[Claims] A step of sequentially laminating and forming a heat-resistant first metal layer forming a Schottky barrier, an intermediate metal layer made of a heat-resistant metal nitride, and a highly conductive second metal layer on the main surface of the gallium arsenide substrate; , and then heat treatment at 500° C. or higher in a non-oxidizing gas atmosphere.