JPH10308358A - Formation of electrode of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate damage to the surface of a semiconductor layer due to a sputtering method by a method wherein after a metal film is formed on the surface of the semiconductor layer by a deposition method, which does not damage the surface of the semiconductor layer, a high-melting point metal film is formed on the surface of the semiconductor layer. SOLUTION: An n-type InGaAs layer 2 is laminated on a sample 1, which is a semi- insulative GaAs substrate, a high-melting point metal film 4 for deposition use is heated by a resistance heating heater 6 and after the vapor pressure in a vacuum chamber 7 reaches a full vapor pressure, a shutter 12 is opened and a prescribed amount of the metal film 4 is deposited on the sample 1 to shut the shutter. Then, the substrate 1 formed with a high- melting point metal film 3 is introduced in the chamber 7 and after the chamber is evacuated into a vacuum state, Ar gas is introduced in the chamber to be subjected to sputtering of a high-melting point metal film 9 and the shutter 12 is opened to form a high-melting point metal film 8 to a thickness requisite for a device process. That is, before the metal film is formed on the surface of the semiconductor layer by a sputtering method, the metal film is previously formed on the surface of the semiconductor layer by a heating deposition method and damage to the surface of the semiconductor layer due to the sputtering method is inhibited by this metal film. Thereby, the sputtering rate of the metal film is increased and the deposition rate of the metal film can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an electrode of a semiconductor device, and more particularly to a method for forming a Schottky electrode and an ohmic electrode.

[0002]

2. Description of the Related Art Conventionally, in such a method of forming an electrode of a compound semiconductor device, for example, Japanese Patent Application Laid-Open No. 01-1181 is disclosed.
As described in JP-A-94-94, in order to enhance the thermal stability of an electrode, a sputtering method is widely used for depositing a high melting point metal.

FIG. 9 is a schematic view showing an example of an apparatus showing a conventional high-melting-point metal deposition method by a sputtering method. In the figure, a vacuum chamber 7 is evacuated by a vacuum pump 5. Ar is introduced into the chamber 7 through the gas inlet 10.
Alternatively, a gas such as N ₂ is introduced, and a source 9 of a high melting point metal such as WSi or W
By applying F power, the source 9 is sputtered,
A high melting point metal is deposited on the sample 1. Shutter 12 is used to control the deposition thickness of sputtered refractory metal from source 9. The greatest feature of the sputtering method is that the deposition rate can be increased even with a metal having a high melting point.

On the other hand, there is an electron beam evaporation method in which a high melting point metal is heated and evaporated using an electron beam. FIG. 8 is a schematic view showing an example of an apparatus showing the method. The source 9 of the refractory metal is irradiated with an electron beam by using the electron gun 13 and heated to deposit the refractory metal on the sample 1. With this method, it is possible to deposit a high melting point metal without damaging the semiconductor substrate.

[0005]

The problems of the prior art are as follows.

When a high melting point metal is deposited by the sputtering method represented by FIG. 9, damage due to sputtering is formed near the surface of the semiconductor sample to be deposited, and the carrier concentration near the metal / semiconductor interface is reduced. It is. For this reason, when a high melting point metal is applied to the non-alloy ohmic electrode, the surface of the semiconductor becomes high in resistance due to damage at the time of sputtering, and the contact resistivity between the semiconductor and the metal increases. In addition, when the conventional sputtering method is used to form a Schottky electrode such as a gate of a field effect transistor, a part of the electron supply layer is inactivated and the carrier concentration decreases, so that the threshold value increases. Would.

On the other hand, a problem with the heating vapor deposition method of a refractory metal using an electron beam as shown in FIG. 8 is that the vapor deposition rate is extremely low. In the heat evaporation method, the carrier concentration does not decrease due to damage as compared with the sputtering method, but the metal has a high melting point, so that the evaporation rate cannot be increased.

An object of the present invention is to provide a method capable of eliminating the influence of damage by a sputtering method in forming a high melting point metal film on a semiconductor substrate.

Another object of the present invention is to provide a method capable of forming a refractory metal film at a sufficient deposition rate.

[0010]

According to the present invention, there is provided a method of forming an electrode of a semiconductor device, comprising: a first step of forming a metal film by a vapor deposition method which does not damage the surface of a semiconductor layer; And a second step of forming a film.

As the first step of the method of the present invention, a method of heating and vaporizing a high melting point metal to deposit it on a semiconductor surface is suitable. As a preferable example, a method of heating the high melting point metal with a resistance heater to be used. And a method in which a refractory metal is heated by an electromagnetic wave such as an electron beam or other particle beam or a laser and deposited on a semiconductor.

As a second step of the method of the present invention, a method of forming a metal film which damages the semiconductor layer when a high melting point metal film is formed directly on the semiconductor layer by the method can be used. A preferred example is a method for forming a high melting point metal film by a sputtering method.

In the method of the present invention, it is more preferable that the metal film thickness formed in the second step is thicker than the metal film thickness formed in the first step. In addition, the method of the present invention is carried out in the following manner.
Preferably, the steps are performed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment of the method of the present invention, before forming a metal film by sputtering, a metal film is formed in advance by a vapor deposition method that does not damage the semiconductor layer surface. In a more specific preferred embodiment, before forming a metal film by sputtering, a metal film serving as a protective film against sputter damage is formed on a semiconductor surface by heating evaporation.

In this preferred embodiment of the present invention, a metal film is formed on the surface of the semiconductor layer by a heating evaporation method before the formation of the high melting point metal film by the sputtering method. In addition, it is possible to prevent damage due to the sputtering method from entering the semiconductor layer. Further, since the film formed by the heat evaporation method is a metal, the film itself is not affected by damage by the sputtering method.

In this preferred embodiment, since sputter damage does not matter, a high-melting-point metal film can be formed at a high deposition rate by a sputtering method.

Next, a preferred embodiment of the method of the present invention will be described in more detail. The electrode forming method of the present invention,
It consists of two steps. In the first step, a thin film is deposited on a semiconductor surface by a heating evaporation method in which a high melting point metal source for evaporation is heated to vaporize and evaporate metal. In the subsequent second step, a thick refractory metal film is formed by sputtering. Here, the metal film formed in the first step and the second step may be exactly the same high melting point metal film,
Different kinds of metal films may be used. Note that the “heating evaporation method” here refers to a method in which a source for evaporation is heated to be vaporized and deposited on a sample.

Examples of the high melting point metal in the first step include W, Mo, Ti, Pt and the like. The first step may be a thin film because it is deposited in order to prevent spatter damage in the subsequent second step from entering the semiconductor layer. W, which has a high melting point, usually has an extremely slow evaporation rate, and it is not practical to form a thick film by using a heating evaporation method, but it is not necessary to form a thick film in the first step of the method of the present invention. Therefore, it is a practically worthy means to heat-deposit such a high melting point metal source.

As the high melting point metal in the second step, a metal material which can provide a sufficient film forming rate by a sputtering method is desirable. Specifically, W and WSi, TiW, WN, and WAl are exemplified. In particular, W and WSi are preferable because they can be easily etched by dry etching and have good consistency with a device process.

FIG. 1 and FIG. 2 are views of a manufacturing apparatus for explaining a first example of a preferred embodiment of the method of the present invention. The manufacturing method in the first step of the present invention will be described in detail with reference to FIG. The semiconductor substrate 1 as a sample is placed in a vacuum chamber 7 and evacuated by a vacuum pump 5. In FIG. 1, since a non-alloy ohmic electrode is assumed as an example, a semi-insulating G
An n-InGaAs layer 2 is laminated on a sample 1 of an aAs substrate. The refractory metal 4 which is a raw material for vapor deposition is heated by a resistance heating type heater 6. The refractory metal 4 may be placed in a crucible with a higher melting point, or the heater 6 may be directly placed in a crucible shape. After the heater 6 is heated and the refractory metal 4 is heated to a sufficient vapor pressure, the shutter 12 is opened and the sample 1 is vapor-deposited. Number 1
When about 00 is deposited, the shutter 12 is closed. Here, the film thickness to be deposited needs to be changed depending on the sputtering conditions in the second step, but the RF output is 300 W and the Ar gas pressure is 5
Under standard conditions of mmTorr, 100 is sufficient. Next, the refractory metal film 3 formed on the semiconductor substrate 1
After being cooled sufficiently, it is taken out of the chamber and moves to the second step.

Next, the manufacturing method in the second step of the present invention will be described in detail with reference to FIG. The semiconductor substrate 1 on which the refractory metal film 3 is formed is introduced into the chamber 7,
Evacuation is performed by the vacuum pump 5. High melting point metal 9 for film forming material
Are connected to the RF power supply 11. After evacuation, Ar gas is introduced from the gas inlet 10 to several mmTorr, and then an RF power source is turned on to sputter the high melting point metal 9.
The shutter 12 is opened to form the high melting point metal film 8. RF
The output and the partial pressure of the Ar gas are determined in consideration of the thickness of the refractory metal film 3 in the first step. If the high melting point metal film 3 is formed in the first step at 100 or more, general sputtering conditions (RF output 300 W, Ar gas 10 mmTorr or less) can be used. In the second step, a metal film is formed by a sputtering method to a thickness of an electrode necessary for a device process. Note that Ar was selected as a gas used for sputtering, but N ₂ may be used.

Next, the operation in each step of the present invention and its effect will be described.

In the first step, a metal film is formed to prevent sputter damage when forming the high melting point metal film by the sputtering method in the second step. The metal film may be thin as long as damage can be suppressed from entering the semiconductor layer, and a low deposition rate which is disadvantageous in the heating vapor deposition method of a high melting point metal does not pose a problem in the first step.

Here, the reason why spatter damage does not enter the metal will be described below. Sputter damage is formed as a deep energy level in the middle of the band gap of the semiconductor. In a semiconductor, since the Fermi level exists in or near the band gap, carriers are trapped in the energy level due to damage, which causes a decrease in carriers. On the other hand, in the case of metal, the Fermi level is located in the middle of the conduction band and is sufficiently away from the band gap, so that the metal is hardly affected by the energy level due to damage formed in the middle of the band gap. For this reason, the carrier does not decrease due to the spatter damage in the metal.

In the second step, since the high melting point metal film is formed by the sputtering method, the deposition rate is high and a thick metal film can be formed. Further, damage caused by the sputtering method can be suppressed from entering the semiconductor layer by the metal film formed in the first step. As described above, by using the electrode forming method of the present invention, the disadvantages of the heat evaporation method and the sputtering method can be well covered, and a thick refractory metal film without spatter damage can be formed. .

Next, the effects of the present invention will be described with reference to Table 1. Table 1 shows the results of evaluating the contact resistivity in the case of forming a non-alloy ohmic electrode by the TLM (transmission line model) method. The semiconductor layer structure of the sample used for this measurement is shown in FIG. 500 2 × 10 ¹⁸ cm on semi-insulating GaAs substrate
^-3 n-GaAs layer ^15, 500 2 × 10 ¹⁹ cm ^-3 n-
An InGaAs graded layer 2 is formed. The graded layer 2 has an In composition changed from 0 to 1. On this layer 2, 2 × 10 ¹⁹ cm ⁻³ n-InA
The s layer 14 is stacked. On this, Ti is formed at a thickness of 100 ° by the heating evaporation method shown in FIG. Next, WSi is deposited by the sputtering method shown in FIG. Ar gas partial pressure is 2mm
Torr, RF output is 300W. The thickness of WSi is 5000. As can be seen from the results in Table 1,
The value of the contact resistivity is obtained by directly forming W on the semiconductor layer by sputtering.
When a Si layer is formed and when Ti is formed thereon
In the case of / WSi, both values are as high as 5 × 10 ⁻⁶ Ωmm, but in the case of WSi / Ti according to the manufacturing method of the present invention, the value can be reduced to 2 × 10 ⁻⁸ Ωmm. . This value is the value of Ti / P formed only by the heat evaporation method.
It is about the same as the case of t / Au, and it can be seen that the damage by the sputtering method can be completely suppressed.

[0027]

[Table 1] Next, a second example of the preferred embodiment of the method of the present invention will be described with reference to FIG.

FIG. 3 is characterized in that the first step and the second step can be performed in the same vacuum-evacuated chamber. Therefore, after the first step, the refractory metal film 3
Since the second step can be performed without exposing the substrate on which is formed to the atmosphere, there is an advantage that the surface of the refractory metal formed in the first step can be prevented from being oxidized.

FIG. 4 is a manufacturing apparatus diagram for explaining a third example of the preferred embodiment of the method of the present invention.
The feature of FIG. 4 is that a heating evaporation method using an electron gun (E-gun heating evaporation method) is used as the heating evaporation method in the first step. In FIG. 4, reference numeral 13 denotes an electron gun (E gun). 1 and 3 by using this method.
The deposition rate can be further improved as compared with the case of the resistance heating deposition method shown in FIG. For example, W cannot be deposited by the resistance heating deposition method shown in FIGS. 1 and 3 because of its high melting point, but can be deposited by using the E gun heating deposition method. As the heating vapor deposition method, a heating method using an electron beam has been described, but a heating method using other particle beams or an electromagnetic wave such as a laser or a microwave may be used.

Using the apparatus shown in FIG. 4, the first step of the method of the present invention is carried out by an E-gun heating evaporation method, and the second step is performed by R
The effect obtained when the sputtering method using F is used will be described with reference to Table 2. Table 2 shows the results of measurement of the Schottky electrode after forming an electrode for a hole measuring element of Ti / Pt / Au, forming each high melting point metal, and removing metal other than the electrode portion by dry etching. It is. The refractory metal was formed by the apparatus shown in FIG. W
Was formed by a heating evaporation method using an electron gun (layer 3), and WSi was formed by a sputtering method using RF (layer 8). The semiconductor layer structure is shown in FIG. 150 i-I on semi-insulating substrate
n _0.15 Ga _0.85 As layer ^17, 400 2 × 10 ¹⁸ cm ⁻³
An n-Al _0.3 Ga _0.7 As layer 16 is formed. Table 2
As can be seen from the results, the sheet carrier concentration is 0.8 × 10 ¹² cm ⁻² in WSi and W / WSi in which W is formed after WSi is formed.
In the case of Si / W, the carrier reduction is suppressed to 1.2 × 10 ¹² cm ⁻² .

[0031]

[Table 2] FIG. 5 is a sectional structural view of an embodiment of the present invention in which the electrode forming method of the present invention is applied to a non-alloy ohmic electrode. Ti was used as the high melting point metal in the first step, and WSi was used as the high melting point metal in the second step. In order to form a non-alloy ohmic, the surface of the semiconductor is 2 × 10 ¹⁹ cm ⁻³ n− on the n-InGaAs graded layer 2.
An epitaxial thin film structure in which 500 InAs layers 14 were stacked was used.

FIG. 6 is a sectional structural view of an embodiment of the present invention in which the electrode forming method of the present invention is applied to a Schottky electrode. 150 i-In _0.15 Ga _0.85 A on GaAs substrate
s layer 17 and 400 2 × 10 ¹⁸ cm ⁻³ n-Al _0.3
Refractory metal layers 3 and 8 are deposited on a semiconductor layer on which a Ga _0.7 As layer 16 is sequentially laminated.

FIG. 7 is a sectional structural view of an embodiment of the present invention in which the electrode forming method of the present invention is applied to a field effect transistor. The source and the drain are formed on the n-InGaAs layer 2 having a high In composition in order to form a non-alloy ohmic electrode. The refractory metal film 3 formed in the first step of the present invention and the refractory metal film formed in the second step of the present invention. 8 and 19 are formed. As the gate, the refractory metal layers 3 and 18 were formed on the n-AlGaAs layer 16 serving as the electron supply layer by the first and second steps of the present invention in order to form a Schottky electrode. Thus, the source and drain,
Since the gate electrode can be made of exactly the same metal film, three electrodes can be simultaneously formed only by performing the electrode forming method of the present invention once by using an appropriate mask pattern. Can be shortened.

In the above-described embodiments and examples, a GaAs substrate is selected as the semiconductor substrate. However, the type of semiconductor may be an InP substrate, Si, GaN, or the like. Further, Ti or W is used as the refractory metal in the first step.
However, other high melting point metals such as WSi, Mo, and Pt may be used. Similarly, the refractory metal in the second step is WS
Although i is mentioned, other high melting point metals such as W, Mo, Ti, and WN may be used.

[0035]

A first effect of the present invention is that it is possible to prevent a semiconductor layer from being damaged by sputtering when a high-melting-point metal film is formed by a sputtering method.

The reason is that a metal film is previously formed on the surface of the semiconductor layer by a heating evaporation method before the metal film is formed by the sputtering method, and this metal film suppresses spatter damage.

The second effect is that a high melting point metal film can be formed at a high deposition rate.

The reason is that, since the metal film is formed on the semiconductor substrate as the damage protection layer, the sputtering rate can be increased and the deposition rate can be increased without worrying about damage.

[Brief description of the drawings]

FIG. 1 is an apparatus diagram for explaining a first step of a first example of an embodiment of the present invention.

FIG. 2 is an apparatus diagram for explaining a second step of the first example of the embodiment of the present invention.

FIG. 3 is a device diagram for explaining a second example of the embodiment of the present invention;

FIG. 4 is a device diagram for explaining a third example of the embodiment of the present invention.

FIG. 5 is a laminated structure diagram for explaining an embodiment in which the present invention is applied to a non-alloy ohmic contact.

FIG. 6 is a diagram showing a laminated structure for explaining an embodiment in which the present invention is applied to a Schottky contact;

FIG. 7 is a sectional structural view for explaining an embodiment in which the present invention is applied to a field effect transistor.

FIG. 8 is a device diagram for explaining a conventional technique.

FIG. 9 is a device diagram for explaining a conventional technique.

[Explanation of symbols]

Reference Signs List 1 GaAs substrate 2 n-InGaAs 3 W, Ti or Mo film 4 W, Ti or Mo source for vapor deposition 5 Vacuum pump 6 Resistance heater 7 Vacuum chamber 8 WSi, WN or W film 9 WSi or W source 10 Ar or N ₂ Gas inlet 11 RF power supply 12 Shutter 13 Electron gun (E gun) 14 n-InAs 15 n-GaAs 16 n-AlGaAs 17 i-InGaAs 18 WSi, WN or W film 19 WSi, WN or W film

Claims (8)

[Claims] 1. A semiconductor device comprising: a first step of forming a metal film by an evaporation method that does not damage the surface of a semiconductor layer; and a second step of forming a high-melting-point metal film after the step. Method for forming a semiconductor device electrode. 2. The method according to claim 1, wherein the first step includes heating and heating the refractory metal.
2. The electrode forming method according to claim 1, wherein the electrode is vaporized and vapor-deposited on the semiconductor surface. 3. The electrode forming method according to claim 2, wherein in the first step, the refractory metal is heated by a resistance heater to deposit the refractory metal on the semiconductor. 4. The method according to claim 1, wherein the first step heats the refractory metal with an electromagnetic wave such as an electron beam or other particle beam or a laser.
3. The method according to claim 2, wherein the electrode is deposited on a semiconductor. 5. The method according to claim 1, wherein the second step is a metal film forming method for forming a damage on the semiconductor layer when the high melting point metal film is formed directly on the semiconductor layer by the method. 5. The electrode forming method according to any one of items 4 to 4. 6. The method according to claim 5, wherein the second step is a method for forming a refractory metal film by a sputtering method.
The electrode forming method according to the above. 7. The metal film formed in the second step is thicker than the metal film formed in the first step. Item 2. The electrode forming method according to Item 1. 8. The electrode forming method according to claim 1, wherein the second step is performed after the first step in a vacuum-evacuated chamber.