JPS63132475A - Thin film and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce resistance while restraining the diffusion of volatile component, by stacking, in the direction of film thickness, a first layer wherein content of nitrogen is high and the film thickness is small, and a second layer wherein content of nitrogen is low and the film thickness is large. CONSTITUTION:A thin film constituted by stacking a first layer 8 and a second layer 9 in the direction of film thickness is formed on a compound semiconductor substrate 1. As to the first layer, the content of nitrogen is high and the film thickness is small. As to the second layer, the content of nitrogen is low and the film thickness is large. Material of a sputter target in this forming method is tungsten silicide or a mixture of tungusten and silicon. An input power supplied to this target is set in a first condition wherein the degree of sticking to the semiconductor substrate is low, and the first layer 8, whose content of nitrogen is high, is formed thin so as to have high accuracy. Next, the input power is set in a second condition wherein the degree of sticking is high, and the second layer 9 is formed thick at a fast speed. In each process, nitrogen gas and inactive gas are introduced with a constant partial pressure ratio into reactive sputtering equipment.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the structure of thin films such as electrodes and wiring layers on a compound semiconductor substrate such as GaAs, and a method for manufacturing the same.
The present invention relates to a structure of a thin film containing tungsten, silicon, and nitrogen, and having a function of suppressing volatile components in a semiconductor substrate from being mixed into the electrodes, etc., and a method for manufacturing the same.

[Conventional technology]

The inventors of the present application have discovered that when a material containing tungsten (W), silicon (Si), and nitrogen (N) is first formed on a compound semiconductor substrate such as GaAs, even if high-temperature treatment is performed, for example, mainly Volatile components such as As do not migrate to the thin film of the above material, and therefore there is no change in composition, so we propose that it is suitable as an electrode or wiring material that requires precise control of parameters such as abrasiveness. did. For example, if the above thin film is used as an electrode, the electrical characteristics of the junction between the semiconductor substrate and the electrode will not change. Furthermore, when another low resistance metal layer is provided on top of these materials,
It was also proposed that this region is excellent as a so-called diffusion barrier, a region that inhibits mutual movement of components of the metal layer and semiconductor substrate. Regarding the contents of these proposals, please refer to the patent application No. 61-4418.
It is stated in No. 4.

That is, as shown in FIG. 7, if a film 2 containing tungsten, silicon, and nitrogen is formed as an electrode and wiring layer on a GaAs substrate 1 by reactive sputtering, the nitrogen compound acts as a barrier and is mainly used in the heat treatment process. It has the effect of inhibiting As in the substrate 1 from invading into the coating 2 by diffusion, and although Ga also diffuses to some extent, this diffusion can also be inhibited), and does not change the composition of the electrodes, the wiring layer, or the composition of the substrate 1. Therefore, an extremely stable and highly reliable semiconductor device can be realized.

Furthermore, as shown in FIG. 8, even when using other metal wiring layers with low resistivity, such as gold (Au) 3, gold
By interposing extremely thin Wi2 containing tungsten, silicon, and nitrogen between the As substrate 1 and the As substrate 1, mutual diffusion of gold into GaAs and As into GaAs can be suppressed.

However, it has been found that when the above thin film is used as a single layer film with a constant nitrogen content, the following drawbacks occur.

That is, a film with a high nitrogen content has a high function as a diffusion barrier, but has a high resistance, and a film with a low nitrogen content has a low function as a diffusion barrier, but has a low resistance.

FIG. 9 is a graph showing an example of the relationship between the nitrogen content in the deposited film (single layer) and the resistance value of the film.

In the same figure, when the nitrogen content is 10%, 3 x 10-
'Ω・cm, and when the nitrogen content is 40%, L
10-''Ω·cm, and as shown in the same figure, it was found that the semi-logarithmic graph was almost a straight line.

It was also found that nitrogen atoms cannot be mixed in the film at a concentration of 50% or more.

Furthermore, films of the above materials are usually formed on substrates by reactive sputtering, but various experimental conditions that define the reactive sputtering conditions, such as the partial pressure ratio of nitrogen gas and inert gas, input power, etc. Until now, there have been no guidelines as to how to control this to most efficiently obtain a multilayer film with the desired composition.

[Problem that the invention seeks to solve]

Therefore, if the film of the above material is composed of a single layer film, GaA
If the nitrogen content is increased primarily to suppress the diffusion of As from the s-substrate 1, the resistance increases, which has the drawback of restricting high-speed operation of the semiconductor device and increasing power consumption. Furthermore, if a low resistance metal layer is separately provided as shown in FIG. 8, separate vapor deposition and etching processes are required.
The disadvantage is that the complication of the process leads to a decrease in yield.

The present invention has been made in view of these points, and its purpose is to obtain a thin film that has both a barrier effect of suppressing diffusion from a semiconductor substrate and an effect of lowering resistance, and a method for manufacturing the same. It is in.

Means for Solving Problem c] To achieve such an object, the present invention provides a thin film formed on a compound semiconductor substrate containing tungsten, silicon, and nitrogen as constituent elements, which has a high nitrogen content. A thin first layer and a thick second layer with a low nitrogen content are laminated in the thickness direction.

In addition, the constituent elements are tungsten, silicon, and nitrogen, and a thin first layer with a high nitrogen content and a thick second layer with a low nitrogen content are laminated in the thickness direction. In a method of forming a thin film formed by a method on a compound semiconductor substrate, a first setting condition is such that the input power supplied to a sputter target whose material is tungsten silicide or a mixture of tungsten and silicon has a low deposition rate on the semiconductor substrate. A process of forming a first layer with a high nitrogen content thinly and with high precision by setting the input power to a second setting condition with a high deposition rate, and forming a second layer with a low nitrogen content by setting the input power to a second setting condition with a high deposition rate. The method includes a step of forming a thick layer at a high speed, and in each step, nitrogen gas and inert gas are introduced into a reactive sputtering apparatus at a constant partial pressure ratio.

[Effect]

In the thin film of the present invention, the invasion of volatile components from the semiconductor substrate is prevented, and the resistance value is also sufficiently low.

〔Example〕

First, a reactive sputtering apparatus applied to the implementation of the present invention,
Also, the relationship between various experimental parameters and deposition rate characteristics to explain the physical phenomena that form the basis of the present invention will be explained.

FIG. 2 shows a reactive sputtering apparatus applied to the practice of the present invention. In FIG. 2, a represents a sputtering gas and b represents a reactive gas. Ar, Xe as sputtering gas a
, Kr, Ne, and the like are used, and N2 is used as the reactive gas b. Each of the gases a and b is mixed after being controlled to a constant flow rate by a mask flow meter 4 and introduced into a vacuum chamber 5 for sputtering. In the sputtering vacuum chamber 5, a sputtering target 5 is connected to a direct current or high frequency power source, and a substrate 52 to which a sputtered film is attached faces the target 51. The sputtering vacuum chamber 5 is connected via a conductance pulp 6 to an exhaust device 7 such as a diffusion pump or a talion bomb.

In the reactive sputtering apparatus having the above configuration, the pressure inside the sputtering vacuum chamber is usually set at 3 to 30 x 10-'To-rr.
Perform sputtering while maintaining a certain level. Sputter target 5
FIG. 3 shows the results of actually measuring the relationship between the input power to the substrate 1 and the adhesion rate to the substrate 52. In FIG. 3, the horizontal axis shows the input power (unit: W), and the vertical axis shows the deposition rate (devosification rate, D, R,). The deposition rate, R, is the thickness of the deposited film formed on the substrate 52 per unit time, that is, the rate of increase in the thickness. As shown in FIG. 3, the deposition rate, R, increases in proportion to the amount of human power supplied to the sputter target 51, indicating that the film can be formed at high speed by increasing the input power. . The reason why the deposition rate increases when the input power is increased is because the energy of sputtering Ar increases in proportion to the input power, and the sputtering rate increases.
Using tungsten silicide as a sputter target,
This is data when Ar is used as an inert gas.

In this case, similar data will be obtained even if a mixture of tungsten and silicon is used instead of tungsten silicide.

Figure 4 shows the composition ratio of nitrogen, which is a reactive gas, and Ar, which is an inert gas (sputtering gas), that is, the partial pressure ratio of the supplied mixed gas (horizontal axis) in the deposited film at a constant input power. It is a graph showing the relationship between nitrogen content (left vertical axis) and deposition rate, R, (right vertical axis) using characteristics vAL1 and L2. It can be seen from the characteristic lines L1 and L2 that as the nitrogen partial pressure ratio increases, the deposition rate, R, decreases and the nitrogen content increases. This can be explained as follows. First, the reason why the deposition rate, R, decreases when the nitrogen partial pressure ratio is increased is as follows. The partial pressure ratio of the reactive gas nitrogen is equal to: reactive gas partial pressure/(sputter gas partial pressure+reactive gas partial pressure)X100%-N2M/(Nz amount+Ar amount)X100%. Here, there is a large difference in sputtering efficiency for sputtering targets between nitrogen and Ar, and it is known that the sputtering efficiency of reactive gas nitrogen for sputtering targets is extremely low compared to inert gases A and R. ing. Therefore, increasing the nitrogen partial pressure ratio means that Ar in the total gas
This is equivalent to reducing the absolute amount of the sputtering target and reducing the sputtering ability of the sputter target, so that the formation rate of the deposited film, which is mainly composed of sputtered components, is reduced. Furthermore, although increasing the nitrogen partial pressure ratio lowers the sputtering efficiency, the composition ratio of nitrogen in the total gas increases, so the nitrogen content in the deposited film that is formed increases.

Next, using the data in FIGS. 3 and 4, we will calculate the deposition rate, R, when the input power is changed to change the deposition rate, R,
When the nitrogen content in the deposited film is rearranged with respect to the nitrogen partial pressure ratio using as a parameter, the relationship shown in FIG. 5 is obtained. In FIG. 5, characteristic line L3. L4 and L5 each have a deposition rate, R, of 100 persons/min (input power 80
W).

It corresponds to 400 people/min (input power 260W) and 650 people/min (input power 500W).

From FIG. 5, it can be seen that there are two methods possible to obtain the multilayer film shown in FIG. That is, in FIG. 1, the first layer 8 has no effect of inhibiting diffusion from the substrate 1 unless the nitrogen content is high, so in order to form this portion, for example, point A or C in FIG. As such, it is necessary to increase the nitrogen content. Further, the second layer 9 in FIG. 1 needs to have a low nitrogen content to achieve a low resistance, so it is necessary to form the point B. Here, the first method is a method that takes a step from point C to point B. In other words, the adhesion rate.

This is a method in which the nitrogen partial pressure ratio is changed from about 14% to 2.5% while keeping the input power (500 W) constant, which gives R, = 650 people/min. When manufactured by this method, since the volume of the vacuum chamber is generally large, the responsiveness to changes in the gas partial pressure ratio is extremely poor, and there is a drawback that the partial pressure ratio does not converge until about 5 minutes have elapsed. For this reason, if the first method is used to manufacture the deposited film 10, as shown in FIG. As a result, the first
Compared to the structure shown in the figure, the overall resistance is higher and the A
A thin film was formed which also had an insufficient effect of suppressing the diffusion of s and the like.

An embodiment of the thin film manufacturing method according to the present invention is a second method made in consideration of the above points, and in FIG. setting conditions).

In other words, in order to form a multilayer film with a different nitrogen composition ratio, instead of taking the common-sense measure of changing the nitrogen partial pressure ratio, which can be easily estimated, do not change the input power while keeping the nitrogen partial pressure ratio constant. The adhesion rate DR9 is changed by changing the .

By this means, input power has an extremely fast response speed, so a steep nitrogen content can be easily achieved, and the first layer 8 and the second layer 9 can be divided as shown in FIG. becomes possible.

Furthermore, as an additional advantage of this method (second method), the first layer 8 having a thin film thickness has a high deposition rate and R as shown at point A.
, that is, the film is formed slowly, so the film thickness can be easily controlled. Also, thick second
Since the layer 9 is formed under the conditions of high deposition rate and high Ro as shown by point B, it can be formed at high speed and the required film thickness can be achieved in a short time. Therefore, overall, it can be said that this is an excellent manufacturing method that realizes each layer with desired properties most efficiently and with high precision.

Next, an experiment to confirm the effects of the above-described structure and manufacturing method will be described. In the experiment, reactive sputtering was performed on a GaAs substrate under the condition that the input power to the sputter target was 80 W. Note that tungsten silicide was used as the sputtering target, a mixed gas of Ar and nitrogen was used, and the nitrogen partial pressure ratio was 2.5%. Then, the first layer was formed by about 500 people with a nitrogen content of 20%, and then the input power was changed to 500 W with the nitrogen partial pressure ratio unchanged, and the second layer was formed by about 3,500 people with a nitrogen content of 2%. . As a result, the resistance of the entire layer was good at approximately 2 x 10-' Ωcm, and even if the heating process was changed, no deterioration of characteristics due to diffusion of As, etc. from the substrate was observed. The structure and the validity of this method were verified.

In the above embodiment, Ar is used as the inert gas.
was used, but similar effects can be expected with Xe, Kr, and Ne. Further, effects can be expected even if 02 is used as the reactive gas other than nitrogen.

〔Effect of the invention〕

As explained above, the present invention is achieved by forming a thin first layer with a high nitrogen content and a thick second layer with a low nitrogen content by laminating them in the thickness direction. Since it is possible to suppress the diffusion of volatile components (mainly As) from the semiconductor substrate and to lower the resistance, it is possible to prevent the high-speed operation of the semiconductor device from being restricted and to prevent the power consumption from increasing. It has the effect of preventing this.

In addition, by changing the input power and forming a first layer with a high nitrogen content and a second layer with a low nitrogen content, the first
The first layer is formed slowly, the second layer is formed quickly, and the response from the formation of the first layer to the formation of the second layer is fast, so thin films can be formed with high precision and efficiency. It has the effect of being

Furthermore, since thin films such as electrodes and wiring layers can be formed by changing the input power, there is also the advantage that they can be formed only by a reactive sputtering process without involving the process of forming and processing other metal films such as Au.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a thin film according to the present invention;
Fig. 2 is a system diagram showing a reactive sputtering apparatus applied to the implementation of the present invention, and Fig. 3 shows the deposition rate versus input power, R
, Figure 4 is a graph showing the nitrogen content rate and deposition rate, R, with respect to the nitrogen partial pressure ratio. Fig. 5 is a graph showing the nitrogen content against the nitrogen partial pressure ratio using the adhesion rate, R, as a parameter.
The figure is a block diagram showing a thin film formed by changing the nitrogen partial pressure ratio, Figures 7 and 8 are block diagrams showing a conventional thin film, and Figure 9 is a block diagram showing a thin film formed by changing the nitrogen partial pressure ratio.
The figure is a graph showing the resistance value versus the nitrogen content in the deposited film. DESCRIPTION OF SYMBOLS 1... Qa, As substrate, 8... 1st layer, 9...
Second layer.

Claims (2)

[Claims] (1) In a thin film made of tungsten, silicon, and nitrogen as constituent elements and formed on a compound semiconductor substrate, a first layer with a high nitrogen content and a thin film thickness, and a second layer with a low nitrogen content and a thick film thickness. A thin film characterized by being formed by laminating the layers in the film thickness direction. (2) The constituent elements are tungsten, silicon, and nitrogen, and a thin first layer with a high nitrogen content and a thick second layer with a low nitrogen content are laminated in the thickness direction. In the method of forming a thin film on a compound semiconductor substrate on a compound semiconductor substrate, input power supplied to a sputter target whose material is tungsten silicide or a mixture of tungsten and silicon is set such that the deposition rate on the semiconductor substrate is low. a step of forming a first layer with a high nitrogen content thinly and with high precision by setting the input power to a second setting condition with a high deposition rate; forming a thick layer at high speed, and in each of the steps, nitrogen gas and inert gas are introduced into a reactive sputtering apparatus at a constant partial pressure ratio.