JPH03116723A - Formation of ohmic electrode - Google Patents

Abstract

PURPOSE:To enable the formation of an excellent ohmic junction without influences of a natural oxide film on the substrate surface by a method wherein a silicon crystal substrate whose surface is patterned with an insulating film mask having openings is heat-treated in an organic aluminum gas atmosphere containing one or two atoms of aluminum and a halogen to form an aluminum thin film and deposit a wiring metal. CONSTITUTION:A p<+> layer 103 of 2000Angstrom thickness is formed on an n-Si (100) substrate 102 having an ohmic junction window 101 of 2mum diameter and an Au-Sb electrode 104 is deposited on the rear to make an ohmic junction. As the first step, this workpiece is heat-treated in a DEAlCl atmosphere to form an aluminum layer 105 of 1500Angstrom thickness. The condition of heat treatment should be a hydrogen atmosphere of 90Torr, a substrate temperature of 340 deg., a DEAlCl partial pressure of 0.05Torr, and a time of 3 minutes. As the second step, an aluminum layer of 1mum thickness is deposited to form an electrode 106. A substrate-aluminum interface is formed inside the substrate; therefore, an excellent ohmic junction is formed without influences of a natural oxide film on the substrate surface even if the substrate undergoes no heat treatment after deposition.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method of forming an ohmic electrode.

[Conventional technology]

In order to realize large-capacity communications such as optical communications and high-speed computers, it is desired to realize semiconductor integrated circuits that can operate at higher speeds. The miniaturization of devices not only contributes to increasing the degree of integration, but also shortens the electron transit time, which is essential for realizing high-speed, highly integrated devices. For this reason, for example, in bipolar transistors, the base layer thickness is set to 1000 Å or less in order to shorten the base transit time, and even in MOS-FETs, the source and drain regions tend to become thinner. On the other hand, the formation of electrode wiring is becoming more difficult year by year due to miniaturization. Taking the base contact of a bipolar transistor as an example, if the base layer is sufficiently thick, after depositing aluminum,
An ohmic junction was formed by heat treatment at 0°C. By this heat treatment, the natural oxide film layer at the silicon-aluminum interface disappeared, and good contact was obtained. However, when the base layer thickness is less than 1000 Å, the conventional method has a problem in that aluminum penetrates into the collector layer and the pn junction is destroyed. A similar phenomenon occurs in MOS-F
In ET, this has become a major problem as the source and train layers become thinner.

In order to prevent this penetration, conventionally, aluminum containing more than the solid solubility limit of silicon has been used as a wiring material to suppress the penetration of the silicon substrate into the aluminum. Another method is to form a polysilicon underlay and deposit aluminum on it. In this case, the polysilicon melts into the aluminum, so the silicon of the substrate is not affected.Another method is to deposit a thin layer of aluminum, heat treat it to form a contact in advance, and then deposit the wiring metal. methods may also be used. In this method, since the first aluminum layer is thin, penetration can be minimized.

[Problem to be solved by the invention]

The first conventional method using an aluminum-silicon alloy as a wiring material has a problem in that silicon in the film re-grows at the aluminum-silicon interface after heat treatment. Therefore, when the contact window becomes smaller, the effective contact area decreases.
There was a drawback that contact resistance increased.

The second method, the method of depositing a polysilicon underlay, has the advantage that polysilicon undergoes a non-directional, isotropic reaction with aluminum. However, it is necessary to select the optimum polysilicon film thickness. For example, when heat-treating an aluminum film with a thickness of 1 μm at 500° C., the polysilicon film thickness must be precisely controlled within 80 to 110 degrees.

Further, the third method of forming a contact in advance with a thin aluminum film requires a photolithography process for the first layer of aluminum film. This made the process complicated and the yield decreased. Furthermore, there was a drawback that the aluminum in the negative layer was oxidized by the heat treatment, resulting in an increase in contact resistance.

An object of the present invention is to provide a method for forming an ohmic t@ that solves the above problems.

[Means to solve the problem]

In order to achieve the above object, in the method for forming an ohmic electrode according to the present invention, a silicon single crystal substrate or a silicon polycrystalline substrate, on which an insulating film mask pattern having an opening for ohmic contact is formed on the substrate surface, is combined with aluminum. The method includes at least a first step of forming an aluminum thin film by heat treatment in an organic aluminum gas atmosphere containing one or two halogen atom bonds, and a second step of depositing a wiring metal.

[Effect]

Hereinafter, diethylaluminum chloride (Cx Hs ) jA QCQ:DEA is used as an organic aluminum containing one or two bonds between aluminum and halogen atoms.
This will be explained using QCQ) as an example.

The decomposition process of DEAQCQ occurs on semiconductor and metal surfaces.
102, and it has been reported that the former decomposes at a lower temperature (Haka Sasaoka, 36th Applied Physics Conference Proceedings 3p-P-1, page 507)
Therefore, the SL substrate on which the 5i02 pattern was formed was kept at 300 to 400°C, and DEA (1CQ
By supplying DEAQCQ to AQCH, DEAQCQ decomposes into AQCH only in the exposed portion of the St substrate.

The generated AQCIl reacts with the silicon of the substrate, and 4AQ
CQ+Si→4AQ+5iCQ.

Aluminum is deposited by this reaction. This makes it possible to deposit aluminum only on the contact window portion.

Since the aluminum film according to the present invention is deposited by a reduction reaction of Si in the substrate, the substrate-aluminum interface is formed inside the substrate. Therefore, after the aluminum film volume 4
Even without heat treatment at 00 to 500° C., a good ohmic junction can be formed without being affected by the natural oxide film on the surface of the silicon substrate. Furthermore, since the film contains SL with a solid solubility limit, penetration does not occur even if heat treatment is performed.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

FIG. 1 is a diagram showing a manufacturing process of a diode having an ohmic junction according to the present invention.

In the figure, a P+ layer 103 with a thickness of 2,000 layers was formed by ion implantation on an n-S i (100) substrate 102 on which an ohmic bonding window 101 with a diameter of 2 μm was formed. An Au-3b electrode 104 was deposited on the back surface of the substrate to form an ohmic connection. As a first step, this substrate 10
2 was heat treated in a DEAQCQ atmosphere to form an aluminum layer 105 with a thickness of 1500 mm.The heat treatment conditions were 9.
In a hydrogen atmosphere of 0 Torr, substrate temperature 340°C, DEA
The QCQ partial pressure was 0.05 Torr, and the heat treatment time was 3 minutes.

After the above heat treatment, as a second step, a thickness of 1
.mu.m aluminum was deposited and photolithographically formed $1106.

FIG. 2 is a diagram showing the current-voltage characteristics of the manufactured diode. This shows that a good ohmic junction can be obtained according to the present invention without heat treatment. When contact resistance was measured using the Kelvin method, i, s
xio-'Ω-, which was sufficiently low. This current-voltage characteristic did not change even after the diode was heat-treated at 450° C. for 1 hour in a nitrogen atmosphere.

For comparison, similar measurements were performed on a diode manufactured without heat treatment in a DEAQCQ atmosphere.

When the diode was not heat-treated after fabrication, a low-resistance ohmic junction could not be obtained. 400℃ in nitrogen atmosphere,
Diode characteristics were obtained by heat treatment for 30 minutes, but D
The reverse current was larger than that in the case where heat treatment was performed in an EAQCQ atmosphere. When heat treatment was performed at 450° C. for 1 hour, the pn junction was destroyed due to aluminum penetration, resulting in the current-voltage characteristics shown in FIG.

In this example, the bond between aluminum and halogen atoms is
Although diethylaluminium chloride was used as the organoaluminium containing one or two, the present invention is not limited thereto, and the organic group is either a methyl group, an ethyl group, or a butyl group, and the halogen atom is a fluorine, chlorine,
A similar effect can be obtained by using organoaluminium, which is either bromine or iodine.

In this example, heat treatment under reduced pressure was performed as the first step, but selective aluminum formation in the present invention utilizes the fact that decomposition of organic aluminum occurs selectively due to the catalytic action of the substrate surface. Therefore, similar effects can be obtained by heat treatment under normal pressure.

〔Effect of the invention〕

According to the present invention, a good ohmic contact was formed without being affected by the natural oxide film on the surface of the silicon substrate even without heat treatment. Further, since the aluminum film contains St in the solid solubility limit, penetration does not occur even if heat treatment is performed, and a shallow pn junction can be formed.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the manufacturing process of a diode with ohmic junction according to the present invention, Fig. 2 is a diagram showing the current-voltage characteristics of the diode according to the present invention, and Fig. 3 is a diagram showing the current-voltage characteristic of the diode according to the conventional technology. FIG. 3 is a diagram showing characteristics. 101...Ohmic junction window 102--- n-S i (100) substrate t03-p
+ layer 104-A u -S b electrode 105.
...Aluminum layer 106...Electrode Fig. 1 0 / Voltage < V) Fig. 2 / Voltage (V) Fig. 3

Claims (1)

[Claims] (1) A silicon single-crystal substrate or a silicon polycrystalline substrate, on which an insulating film mask pattern with openings for ohmic bonding is formed on the substrate surface, is placed in an organic aluminum gas atmosphere containing one or two bonds of aluminum and halogen atoms. 1. A method for forming an ohmic electrode, comprising at least a first step of forming an aluminum thin film by heat treatment, and a second step of depositing a wiring metal.