JPS5850409B2 - Method for manufacturing gallium arsenide epitaxial thin layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing thin gallium arsenide layers for varactor diodes.

As shown in FIG. 1, a barrack diode is produced by growing a thin epitaxial thin layer 2 on a low resistivity substrate 1 by, for example, vapor phase growth, and then depositing a metal layer 3 on this epitaxial thin layer 2. A Schottky junction 4 is formed, and changes in the thickness of the depletion layer, that is, the junction capacitance, due to a reverse voltage applied to this junction are utilized.

The electron concentration of the epitaxial thin layer that becomes the active layer of the device is
The larger the value, the lower the resistance value in series with the Schottky junction, which is advantageous because it reduces the source of thermal noise in the device. This is rather an inconvenient direction and cannot be increased unnecessarily.

Currently, the electron concentration of the thin film is constant and 0.6X IX 1
The epitaxial thin layer thickness is within the range of 0'' crc3, and the epitaxial thin layer thickness is 0.4 to 0.3 μm.

Since barac diodes utilize changes in junction capacitance due to reverse bias, the wider the change in this capacitance, the greater the dynamic figure of merit, which is well known as a parameter expressing the performance of the device. The characteristics of the Paran I-IJ rack width device made using the device are improved.

In order to increase the range of change in capacitance, the electron concentration in the epitaxial thin layer should not be constant in the depth direction, but should decrease as it approaches the interface with the substrate from the surface.

It is necessary that the electron concentration has a gentle slope because if it is too large, the electron concentration at the interface between the epitaxial thin layer and the substrate decreases, resulting in an increase in series resistance.

In order to create a slope in the electron concentration distribution in this way, it is possible to grow an epitaxial thin layer in the vapor phase while gradually increasing the flow rate of the doping gas, but this control is quite difficult and has poor reproducibility. It has been problematic and difficult to implement on an industrial scale even though it is known to yield good results.

Therefore, the current situation is that methods that are easy to control and have good reproducibility are still being sought.

In view of this point, the present invention provides a method for manufacturing a gallium arsenide thin layer for a varactor diode having a sloped electron concentration distribution with good reproducibility using simple control.

That is, the method of the present invention implants sulfur ions, which are donor impurities, into an epitaxial thin layer grown on a low resistivity gallium arsenide substrate using an ion implantation method, and then anneals the epitaxial thin layer grown on a low resistivity gallium arsenide substrate. The epitaxial thin layer is characterized in that the electron concentration in the epitaxial thin layer is gradually decreased from the epitaxial thin layer toward the interface with the substrate by actively utilizing the enhanced diffusion effect. This is the manufacturing method.

Hereinafter, details of the present invention will be explained with reference to an example of implementation.

An undoped gallium arsenide substrate with an electron concentration of 2x 1016/- is prepared, and sulfur ions are added to it at 150 k.
Implantation at 1013/deg at eV, Si on both sides of the sample after implantation
o 2 membrane covered, 700.800.900.

Annealing was carried out for 10 minutes at each temperature of 1000° C., and the electron concentration distribution was measured by the Cv measurement method, and the results shown by curves 6, 7, and 8.9 in FIG. 2 were obtained.

6, 7.8 and 9 are 700.800.900 respectively
and annealing results at 1000°C.

Each distribution shows a distribution specific to each annealing temperature, and is significantly different from the theoretically predicted distribution 5 of sulfur impurities immediately after implantation.

This indicates the enhanced diffusion effect of sulfur impurities during annealing, and it is difficult to obtain a similar distribution by implanting other donor impurities such as silicon, selenium, tellurium, etc.

Next, as an example of the implementation of the present invention, an epitaxial thin layer with a layer thickness of 0.35 μm and an electron concentration of I x 1016/- is formed on a low resistivity substrate with an electron concentration of 2 x 1018/-. Then, implantation and annealing were performed under the same conditions as when obtaining the results shown in FIG. 2, and the electron concentration distribution was measured by the C2 measurement method.

FIG. 3 illustrates this result, and it is clear that an epitaxial thin layer with a gradient distribution of electron concentration, which is optimal for use in a varactor diode, has been obtained.

In the figure, curves 10, 11, 12 and 13 have annealing temperatures of 700, 800, 900 and 1000°C, respectively.
This is the result.

First, the effects of the epitaxial thin layer having a gradient distribution of electron concentration according to the present invention will be described.

1×1017/c on a low resistivity substrate as shown in Figure 4a.
Prepare a sample 14 having a constant electron concentration of riL, and a sample 15 in which the electron concentration at the surface is approximately 1 x 1017/- and decreases as the depth increases by carrying out this method,
The reverse bias dependence of the junction capacitance of a Schottky junction obtained by depositing palladium with a diameter of 500 μm was measured.

The results are shown in Figure 4.

In sample 15 obtained by implementing the present invention, as shown in Figure 4, 17, the amount of change in capacitance is clearly increased compared to result 16 of sample 14, showing excellent performance. It can be seen that the figure of merit can be achieved.

According to the method of the present invention, as will be described below, the yield of manufacturing an epitaxial thin layer for a bevel varactor diode is improved compared to the conventional method.

In other words, as mentioned above, in order to improve the performance of varactor diodes, it is necessary to reduce the value of the series resistance in series with the junction capacitance as much as possible. It is necessary to adjust the thickness of the thin film so that the area falls within the operating region of the device.

In the conventional method, for example, an epitaxial thin layer having an electron concentration of ~1017/- is grown to a thickness of about 0.5 μm, which is slightly thicker than the designed value of ~0.3 μm, and a part of this sample is used to increase the electron concentration of this epitaxial thin layer. By measuring the concentration distribution using CV measurement and knowing the depth at which the electron concentration changes to that of the substrate, we can determine the layer thickness of this epitaxial thin layer and chemically etch the remaining sample to the designed layer thickness. Adjustments are made to make it thinner.

At this time, the depth that can be measured by C measurement is limited by the reverse breakdown voltage of the Schottky junction, and ~io
With an electron concentration of '/i, it is possible to measure only a thickness of about 0.3 μm in height.

However, since conventional methods grow thicker than this, it is not possible to measure the electron concentration distribution over the entire thickness of the epitaxial thin layer using only the Schottky junction formed on the as-grown surface of the epitaxial thin layer to be measured. do not have.

Therefore, a sample is formed by etching the surface and reducing the layer thickness on a part of the original sample so that the edge of the depletion layer reaches the substrate with a reverse bias below the reverse breakdown voltage. The original thickness of the epitaxial thin layer is measured from the etched electron concentration distribution and the etched depth.

However, according to the method of the present invention, the electron concentration in the epitaxial thin layer before sulfur ion implantation is I
Since it can be carried out satisfactorily using a material of about 0.016/-,
The reverse breakdown voltage is large, and therefore it is possible to determine the electron concentration distribution over the entire thickness of the epitaxial thin layer in one step, using only a Schottky junction formed on the surface of the epitaxial thin layer as it is grown. be.

Therefore, based on the layer thickness measured in this way, the layer thickness is adjusted by chemical etching to the designed layer thickness, and then ion implantation is performed, but the steps up to this point are largely omitted. .

In this method as well, although an etching step is necessary to adjust the layer thickness, the etching step for determining the layer thickness of the epitaxial thin layer, which is required in the conventional method, can be omitted, and the variation caused by this etching step can be reduced accordingly. The influence can be avoided, and as a result, the yield rate can be improved when looking at the entire process of manufacturing epitaxial thin layers for varactor diodes.

In the method of the present invention, the final electron concentration is the sum of the electron concentration in the epitaxial thin layer before sulfur ion implantation and the concentration of electrons released from the donor level created by the implanted sulfur.

Therefore, it is desirable that the electron concentration in the epitaxial thin layer before sulfur ion implantation is sufficiently lower than the electron concentration created by the implanted sulfur, but on the other hand, as mentioned above, it is necessary to reduce the layer thickness before sulfur ion implantation. The need for measurement and adjustment led to epitaxial growth.

The Schottky junction formed on the surface as it is requires an electron concentration of such a degree that the electron concentration distribution over the entire thickness can be measured, and from both of these constraints, it is appropriate to set it to about 1 to 2X 1016/-.

The amount of sulfur impurity ions implanted is such that the resulting electron concentration at the surface of the epitaxial thin layer is 6X.
It is best selected to be in the range of 1016 to 3 x 1017/cyyt, typically 0.5 to 1.5 x 10
13/c11t is appropriate.

As for the ion energy, if it is too high, the desired electron concentration distribution slope will be difficult to achieve. Conversely, if it is too small, the electron concentration distribution slope will become too steep, and the influence of series resistance cannot be ignored.

For these reasons, the ion energy is lOO~
150 keV is optimal.

The slope of the electron concentration distribution is 1.5≦N/, where Ns and N are the electron concentrations at the surface of the epitaxial thin layer and at a depth of ~0.3 μm from this surface, respectively.
It is optimal that N8≦4, and this gradient in electron concentration can be easily achieved by selecting an annealing temperature in the range of 700°C to 1000°C.

The effects of the present invention will become clear when a varactor diode is prototyped using an epitaxial thin layer manufactured by the conventional method and an epitaxial thin layer manufactured by the method of the present invention, and their characteristics are compared.

Prototype a varactor diode using each epitaxial thin layer whose electron concentration distribution is shown in FIG. 4a, 18.
When the dynamic figure of merit of these varactor diodes was measured at 6 GHz, the average value was 5.5 for those fabricated using the epitaxial thin layer 9 according to the conventional method, whereas the average value was 5.5 for the varactor diodes fabricated using the epitaxial thin layer 9 according to the present invention. The average value of the thin epitaxial layer produced using the method of the present invention was as high as 6.5, confirming the effectiveness of the epitaxial thin layer obtained by the method of the present invention.

Above, the method of the present invention has been explained in the order of steps of implanting sulfur ions and then annealing again, but it is clear that the same effect can be obtained by applying the so-called hot implantation technique, in which ions are implanted while annealing. be.

Another effect of the present invention is that when sulfur ions are implanted, by partially covering the epitaxial thin layer with a suitable mask, such as a metal mask or a dielectric mask, it is easy to selectively implant the desired varactor in any position. It is possible to form diodes and the like.

When considering the gallium arsenide integrated circuits that will be developed in the future, this is considered to be a great advantage, considering that selective vapor phase growth is difficult using conventional methods.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a Schottky single-junction varactor diode, where 1 is a low resistivity substrate, 2 is an epitaxial thin layer,
3 indicates a deposited metal layer, and 4 indicates a Schottky junction. FIG. 2 is an electron concentration distribution diagram for explaining the accelerated diffusion effect caused by sulfur ion implantation.
The results of annealing at 000℃ for 10 minutes are 6 and 7, respectively.
, 8°9 shows. FIG. 3 shows an example of the electron concentration distribution of an epitaxial thin layer manufactured by implementing the present invention. lL12
, 13 are respectively 700°800.900.1000℃
It was annealed for 10 minutes. Figure 4 shows the electron concentration distribution of epitaxial thin layers produced by the conventional method and the method of the present invention (Figure 4a), and the bias dependence of the junction capacitance of the varactor diode manufactured using the same (Figure 4B). ), curves 14 and 16 show the results obtained by the conventional method, and curves 15 and 17 show the results obtained according to the present invention, respectively.

Claims (1)

[Claims] 1. An epitaxial thin layer having an electron concentration of 1 to 2 x 1016 crIL-3 is formed on a gallium arsenide low resistivity substrate using a vapor phase growth method, and sulfur ions are applied to this epitaxial thin layer at 100 to 150 keV. 0.5~
After implantation with an implantation amount of 1.5 x 1013CrrL-2 and further covering both surfaces of this substrate with a protective film, the
By performing high-temperature annealing in the range of 00°C, sulfur ions are electrically activated, and at the same time, the implanted sulfur ion distribution is changed into an epitaxial thin layer by the accelerated diffusion effect peculiar to sulfur impurities, which is determined by the annealing temperature. The electron concentration decreases monotonically from the surface to the interface with the substrate, and the electron concentration at the surface of the epitaxial thin layer decreases by 0.3 from the surface.
A method for producing a gallium arsenide epitaxial thin layer having a gradient electron concentration distribution, such that the ratio of the electron concentration at a depth of μm varies between 1.5 and 4.