JP3118957B2 - Electrode formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode forming method particularly for forming an ohmic electrode on an n-type compound semiconductor.

[0002]

2. Description of the Related Art As an ohmic metal of a compound semiconductor, particularly an ohmic metal for an n-type GaAs-based semiconductor substrate, an Au-Ge based metal, for example, Au / A
u-Ge and Ni / Au / Ni / Au-Ge are used. Particularly, in the case of a GaAs-based semiconductor, a good ohmic contact cannot be obtained only by contact with a metal. Therefore, by applying a metal and then performing an alloying reaction by a heat treatment such as heating at 450 ° C. for several minutes, for example, Try to get ohmic contact.

As a method of forming the metal, a resistance heating type or electron beam heating type vapor deposition apparatus, a sputtering apparatus, or the like is used. At this time, in order to easily proceed with the alloying reaction, it is desired that the reaction is likely to occur at a temperature as low as possible. In the case of Au and Ge, an alloy exists, and its melting point is lower than that of Au and Ge itself, and it is known that it changes depending on the composition ratio. Among these, the lowest melting point is when Ge is 12% by weight, and the melting point is 361 ° C. For this reason, an Au-Ge alloy containing 12% by weight of Ge is usually used as an evaporation source or a sputtering target in forming an ohmic metal.

When such an Au—Ge alloy is deposited by a vapor deposition apparatus, the melting points of Au and Ge are as follows.
e is shifted to 959 ° C., the weight composition ratio of Ge is 1
Even when a 2% alloy is used, the composition ratio varies depending on the film thickness, and it is difficult to always deposit an Au-Ge alloy having a constant composition ratio.

Therefore, in general, a resistance heating method is adopted in film formation in a vapor deposition apparatus, and Au-Ge equivalent to a film thickness is put into a heater, and the material is vapor-deposited to keep the composition ratio constant. I have. However, even in this case,
It is also difficult to keep the composition ratio completely constant because it is difficult to control the film thickness or metal remains on a part of the heater, that is, a part with a low temperature.

When a sputtering apparatus is used during film formation,
However, due to differences in sputtering efficiency, Au and G
It is difficult to accurately control the composition and film thickness of e. Yo
Therefore, when the ohmic metal is formed by these methods,
Since the composition ratio of metal cannot be sufficiently controlled,
Contact resistance of 1 × 10^-6~ 3 × 10^-6Ω · cm
^TwoAnd fluctuate greatly.

An increase in ohmic contact resistance leads to an increase in resistance of a field effect transistor (FET).
In recent years, as the performance of FETs has improved, the specific gravity of the source resistance in the performance has increased. Therefore, the fluctuation of the ohmic contact resistance greatly contributes to the performance of the FET, and the stability of the ohmic contact resistance is a serious problem.

In order to solve these problems, Si-based materials other than Au-Ge-based alloys as ohmic metals,
Various ohmic metal materials such as Ge-based and In-based materials have been studied, but no alloy material capable of stably obtaining low contact resistance as compared with Au-Ge-based materials has not been obtained.

[0009]

According to the present invention, an Au-Ge alloy can be used as an ohmic metal for an n-type compound semiconductor to stably control the respective composition ratios.
An object of the present invention is to form an electrode having uniform contact resistance with no variation in characteristics with good reproducibility.

[0010]

According to the electrode forming method of the present invention, at least Au is deposited on a compound semiconductor.
Ni and Ge layers are laminated and deposited on Au.
The composition ratio of u, Ni, and Ge is set to 50 to 7 for the Au concentration.
0 atomic%, and the Ge concentration is 1/3 to 1% of the Ni concentration.
It is formed as 0.7 atomic%.

Further, according to the electrode forming method of the present invention, in the above-mentioned electrode forming method, Ni is deposited on the compound semiconductor substrate by several nm.
After the deposition, Au, Ni and Ge are deposited in the above-described composition ratio.

[0012]

As described above, in the present invention, in forming an electrode, each layer of Au, Ni, and Ge is independently applied to each other to form a laminated structure. Was formed while controlling the composition ratio stably with good reproducibility.

That is, as described above, in forming the conventional electrode part, the Au-Ge alloy ohmic metal is formed using the Au-Ge alloy as it is as an evaporation source or a sputtering target. It is difficult to control with good reproducibility. Thus, Au-Ge
The alloy is used because its melting point is low and the reaction occurs smoothly, and a low contact resistance is obtained. Therefore, good contact resistance cannot be obtained only by forming each of them in a laminated structure so that the composition can be easily controlled.

On the other hand, in the present invention, Au, Ge and Ni are used.
As described above, and the composition ratios thereof are selected such that Au is 50 to 70 atomic% and the Ge concentration is 1/3 to 0.7 atomic% of the Ni concentration. Ohmic metal contact resistance is 1 × 10 ^-6 Ω
-It could be about cm ² and uniform characteristics could be obtained.

In particular, by depositing Ni on a compound semiconductor and then depositing Au, Ni and Ge at the above-mentioned composition ratio, the composition ratio can be similarly controlled stably and uniform characteristics can be obtained. Electrodes having good reproducibility.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.
I will tell. In this example, the sample is semi-insulating, L
Using a GaAs substrate by EC (liquid sealing pulling method),
Silicon is applied to this GaAs substrate at an energy of 150 keV.
Ion⁺To 3 × 10 ¹³cm^-2With the dose of
Perform on-implantation, heat-treat at 840 ° C for 30 minutes, n-type
A compound semiconductor was formed.

As a film forming apparatus, a resistance heating type vapor deposition apparatus was used. In addition, the present invention can be applied to any device capable of forming a multilayer film such as an electron gun type vapor deposition device or a sputtering device. As a heat treatment apparatus, a hot plate type heating furnace is used, and as a gas atmosphere, H ₂ 4%
However, other general electric furnaces, infrared alloy furnaces and the like can be used as the heat treatment apparatus, and the gas atmosphere can be H ₂ gas, N ₂ gas, H ₂ gas, or the like.
The same effect can be obtained by using a _2- N ₂ mixed gas or the like.

With such a device and sample, first, A
The thickness of each of u, Ge and Ni is set to 140n for Au.
While keeping m and Ge constant at 39 nm and Ni at 43 nm, the order of film formation of each layer was changed to form an ohmic metal, and a heat treatment at 400 to 500 ° C. was performed to measure a change in contact resistance. In this case, Au is 59 atomic%, Ge is 13
Atomic% and Ni correspond to a composition ratio of 28 atomic%. The result is shown in FIG.

In FIG. 1, a solid line A indicates that Au, Ge, and Ni are laminated and deposited on a GaAs substrate in the order of Ni / Ge.
/ Au / GaAs, the solid line B is Ge / Ni / Au / GaAs, and the solid line C is Ge /
Au / Ni / GaAs, solid line D is Au / Ge / Ni / G
aAs, solid line E is Au / Ni / Ge / GaAs, solid line F
Is Ni / Au / Ge / GaAs, and solid line G is Ni / Ge /
The case of a laminated structure of Au / Ge / GaAs is shown respectively. As can be seen from the results, on the GaAs substrate, the case where the solid line A is applied in the order of Au, Ge and Ni , or the case where the solid line B is applied in the order of Au, Ni and Ge is stable. It can be seen that an extremely low contact resistance was obtained. In these examples, a contact resistance of about 1 to 1.5 × 10 ⁻⁶ Ω · cm ² was obtained by heat treatment at 430 ° C. to 500 ° C. for 2 minutes.

At this time, the example shown by the solid line G is a case where a thin Ni film having a thickness of 5 nm is deposited between Au and GaAs, and a similarly low contact resistance could be obtained.

Next, the Au concentration is fixed at 59 atomic%,
By changing the concentration X _G of Ge to 7 to 19 atomic%, Ni / G
forming an ohmic metal having an e / Au / GaAs structure,
The contact resistance was measured by performing a heat treatment at 430 ° C to 480 ° C. The result is shown in FIG.

In FIG. 2, the solid line a shows the case where the heat treatment is performed at 400 ° C.
° C and the solid line d show the case where the heat treatment was performed at 480 ° C. The thickness of Au was constant at 140 nm. As a result, when the concentration of Ge is 10 atomic% or more, 1 to 1.5 ×
The contact resistance was as low as about 10 ⁻⁶ Ω · cm ² .

At this time, observation of the surface condition revealed that the surface roughness after the heat treatment was strongly dependent on the Ge concentration. That is, the higher the Ge concentration, the more severe the surface roughness. When the Ge concentration was 19 atomic%, precipitation of Ge was observed.

Next, the laminated film structure was changed to Ni / Ge / Au / N
As i / GaAs, the film thickness X of Au is changed from 50 nm to 18
Ohmic metal is formed by changing the thickness to
Heat treatment was performed at 0 ° C. to 500 ° C. to measure the contact resistance.
The film thickness of each layer is 38 nm for Ni in the upper layer, 5 nm for Ni in the lower layer, the total is 43 nm, and Ge is 3
9 nm, and the composition ratio of Ni and Ge was 2.2 to 1
It was constituted as. The result is shown in FIG.

In FIG. 3, the solid line e indicates that the thickness of Au is 50n.
m (concentration 34 atomic%), and the solid line f is 100 nm (concentration 51
Atom g), the solid line g shows the case of 140 nm (concentration of 59 at%), and the solid line h shows the case of 180 nm (concentration of 65 at%). As can be seen from the result, when the Au film is relatively thin, a good ohmic contact cannot be obtained.
As the film thickness increases, the value of the contact resistance decreases. Au film thickness of about 140 nm or more, particularly 180 nm
In the case of (1), the contact resistance has been made constant at approximately 1 × 10 ⁻⁶ Ω · cm ² . For this reason, in order to obtain a good ohmic contact, 50 to 60 atomic% or more of Au is required.
Turned out to be necessary.

When considering the mechanism of the ohmic contact formation, Au is considered to have a role of forming an excess As region on the GaAs surface by reacting with Ga, and the resulting excess As forms the remaining Ge, Ni and It is believed that they react to form ohmic contacts. That is, when Ge enters the Ga site, an n ⁺ layer is formed to form an ohmic contact, while excess As reacts with Ni to become NiAs or NiAs ₂ . Therefore, when excess As exceeding the limit for reacting with Ni and Ge occurs, the contact resistance seems to be rather deteriorated, and the upper limit at which no excess As occurs is the upper limit of the Au film thickness (concentration). And the concentration that produces a sufficient excess of As is the lower limit.

Therefore, the concentration of Au is expressed as Ni + Ge <Au <2Ni + Ge, that is, the composition ratio is 50 atomic% to 7 atomic%.
It can be seen that a sufficiently low contact resistance can be obtained by setting it to 0 atomic%.

As described above, when the Ge concentration is 10 atomic% or more, a sufficiently low contact resistance can be obtained.
When the content exceeds atomic%, precipitation of Ge is observed on the surface, so that the concentration is desirably 10 to 19 atomic%. Thus, the concentration of Ni becomes a ratio of 22 to 31 atomic%, by configuring the concentration of Ge as a 1/3 to 0.7 atomic percent concentration of Ni, the low contact resistance of the electrode without causing a rough surface Can be formed.

The same effect can be obtained when a Ni thin film having a thickness of several nm, for example, 5 nm is interposed between Au and a GaAs compound semiconductor.

Further, a good ohmic metal can be formed even when an electrode is formed on a lower metal structure by the method of the present invention, and a metal such as Au, W, or Mo is placed on the upper portion and heat-treated. .

Further, in order to suppress the surface roughness after the heat treatment, a good contact resistance can be obtained by forming the insulating layer such as Si ₃ N ₄ or SiO ₂ on the electrode and then performing the heat treatment. Can be.

Incidentally, it goes without saying that the method of the present invention is not limited to the above-described embodiment, but can adopt various other material constitutions and forms.

[0033]

As described above, according to the method of the present invention, the composition ratio of the electrode can be controlled stably, and an electrode having a constant contact resistance with good reproducibility can be formed without causing surface roughness. can do.

Therefore, for example, by applying the present invention to the formation of the FET, the contact resistance of the electrode portion can be made uniform, and variations in characteristics can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in contact resistance of each alloy depending on a processing temperature.

FIG. 2 is a diagram showing a relationship between Ge concentration and contact resistance.

FIG. 3 is a diagram showing a relationship between temperature and contact resistance due to a change in Au concentration.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/28 301

Claims (2)

(57) [Claims] At least Au is coated on a compound semiconductor.
Ni, Ge layers are laminated on Au and deposited.
Then , the composition ratio of each layer of Au, Ni and Ge is set to Au
The concentration of Ge is set to 50 to 70 atomic%, and the concentration of Ge is set to Ni.
An electrode forming method, wherein the concentration is 1/3 to 0.7 atomic%. 2. Ni is deposited on the compound semiconductor .
2. The method according to claim 1, wherein the Au, Ni, and Ge are applied thereafter .