JPH03218008A - Growing method of compound semiconductor - Google Patents

Abstract

PURPOSE:To accurately control impurities doping by a method wherein undoped compound is vapor-grown, impurity gas is supplied in the state that growth is interrupted, and doping process is repeated until the surface density of carrier is nearly saturated. CONSTITUTION:Undoped compound is vapor-grown on a substrate 1, and an undoped compound semiconductor layer 12A having a specified thickness is formed. Next, in the state that the growth is interrupted, impurity material gas is supplied to the layer 12A, and doping is performed until the carrier surface density is nearly saturated, thereby forming an impurities doped layer 12B. By repeating this process several times, a compound semiconductor layer 12 is formed. Althorough, in this method, the impurity concentrations of all of the compound semiconductor layers take discrete values, each of the values is uniform, and uniform concentration can be realized all over the region of a wafer independently of wafer position. Hence impurities doping can be accurately controlled, and a device having specified characteristics can be surely obtained with superior reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for growing compound semiconductors such as A 1 1nAs-based compound semiconductors, and in particular to methods for growing compound semiconductors such as high electron mobility transistors HE
A compound semiconductor growth method suitable for use in growing an impurity-doped layer when a compound semiconductor layer doped with impurities and a so-called undoped compound semiconductor layer that is not doped with impurities are layered and grown as in MT etc. related to.

[Summary of the invention]

The present invention relates to a method for growing a compound semiconductor, including a step of growing an undoped compound semiconductor layer in a vapor phase, and supplying an amount of impurity raw material gas with the vapor phase growth stopped so that the areal density of carriers is almost saturated. In order to accurately control impurity doping and selective doping, it is possible to precisely control impurity doping and selective doping.
[Prior Art] Molecular beam epitaxy (
There has been remarkable research and development into methods such as MBE (MBE) and metal organic chemical vapor deposition (MOCVD).

In this case, to obtain n-type A IlInAs, MOC
Taking the VD method as an example, Si is mainly used as the n-type impurity, and Si is used as the raw material gas for doping this Si.
J* is mainly used. This Si is A II
InAs selectively doped n-A I InAs
A laminated structure of this and GalnAs is applied to a heterointerface field effect transistor, so-called HIFET. This selectively doped n-A I InAs is used in the n-A I G of the well-known high electron mobility field effect transistor in the A I GaAs system, so-called HEMT.
Like aAs, it plays a role as an electron supply layer.

A cross-sectional view of an example of application to this type of HEMT is shown in FIG. In this case, a halia layer (2) made of undoped GalnAs is formed on a compound semiconductor substrate (1) made of, for example, InP, and n-A2nAs is formed on this as an electron supply layer (3) in sequence by, for example, MOCVD. ,n-Aj! A two-dimensional electron gas channel (4) with high electron mobility is formed on the side of the GalnAs layer, that is, the barrier layer (2) of the InAs/GalnAs structure.

Reference numeral (5) denotes a gate electrode, which is made of a metal that can form a Schottky junction with the electron supply layer (3). (6) and (7) indicate the source and drain electrodes, respectively. n as such an electron supply layer (3)
- When growing an A I InAs layer by MOCVD, for example, an undoped A is first grown as a spacer layer.
1 After vapor phase growth of 1nAs, Al, In, As
A method is used in which a source gas SiJi containing n-type impurities such as Si is supplied together with the source gas SiJi to grow an n-AI InAs layer. In this case, the supply of Si is limited due to various factors at the time when the undoped AI InAs changes to the n-AI InAs layer.
This substantially increases the thickness of the undoped AlInAs layer, making it impossible to obtain the impurity doping profile as designed. Furthermore, the steepness of the doping distribution is also not good. Furthermore, in order to actually obtain various semiconductor devices, a method is used in which a large number of HEMTs, for example, are simultaneously formed in an array on a single wafer. However, it is difficult to obtain a uniform carrier concentration distribution on this common wafer. This is due to factors such as the shape of the reactor in which the growth process is performed in MOCVD and MBH, the flow rate of carriers, and the positional structure of the wafer support, that is, the susceptor. This is an important problem as it is directly related to fluctuations in threshold voltage vth in devices such as HEMTs. Also, regarding the maximum value of carrier concentration, for example, in MOCVD method, 5
Since the carrier concentration tends to be saturated at about ~6 Provided is a method for growing an InAs compound semiconductor, which allows doping of impurities to a sufficiently large and steeply distributed impurity concentration with good controllability. Means for Solving the Problems] The present invention includes a step of growing an undoped compound semiconductor layer in a vapor phase, and supplying an impurity raw material gas to the undoped compound semiconductor layer itself while the vapor growth is stopped to remove carriers. The target compound semiconductor is grown in vapor phase by doping the layer to an amount that substantially saturates the areal density. [Function] As described above, in the present invention, an undoped compound semiconductor layer is grown in vapor phase. With this vapor phase growth stopped, the impurity raw material gas is supplied in an amount that saturates it, so that the impurity doping amount, that is, the carrier concentration is regulated to a predetermined amount regulated by this saturation amount.

Therefore, when increasing the carrier concentration in a compound semiconductor layer by vapor phase growth, doping is carried out in an amount that saturates the above-mentioned vapor phase growth of the undoped compound semiconductor layer and the impurity doping by supplying the impurity source gas with this stopped. If this step is repeated the required number of times, for example, n times, it is possible to obtain impurity doping that is n times the saturation amount of doping as a total amount, that is, as a total concentration. Compared to the case of doping, the high concentration of an integer multiple of the saturation amount is a so-called limited concentration with discrete values, but it is possible to achieve an accurate concentration at the discrete values and to reach a concentration higher than the saturation concentration, that is, the concentration Impurity doping can be performed at an integral multiple of the concentration, and the concentration at the interface can be formed to have a steep distribution.

〔Example〕

An example of the case where the method for growing a compound semiconductor according to the present invention is applied to the growth of an n-Aj21nAs compound semiconductor by MOCVD will be described with reference to FIG. In this case, first, as shown in FIG. 1A, a single crystal semi-insulating 1nP substrate (1), for example a wafer, is
It is placed at a predetermined position in the reactor where VD is performed, and with the growth temperature, that is, the substrate temperature, set at 640°C, A I InAs growth source gas, such as trimethylaluminum (TMA), trimethylindium (T
M I ), Tn by supplying arsine (AsH2)
Approximately 1,500 undoped compound semiconductors (128) made of AI InAs are grown on a P substrate (1), for example, a wafer. Thereafter, while maintaining the substrate temperature at 640°C, the supply of the group material gases TMA and TMr is stopped, that is, the growth of AI InAs is stopped, and impurity doping, for example, n-type impurity Si
The raw material gas SiJ6 is supplied into the reactor, and the surface of the undoped compound semiconductor layer (12A) is doped with impurities at a concentration that saturates the doping. ) to form.

Furthermore, the impurity source gas is stopped again in the same manner as explained with reference to FIG. 1A, and as shown in FIG. T
MI and arsine are supplied to form an undoped compound semiconductor layer (12A), for example, an A I InAs layer, by vapor phase growth again.

Further, as shown in FIG. 2D, while the supply of the group III source gas is stopped and the vapor phase growth of AI InAs is stopped, the impurity source gas SitHb is supplied and the impurity is added until the doping amount is saturated. Doping is performed to form an impurity doped layer (12B) on the surface. In this way, for example, two so-called planar doping layers (12B) are formed. And on top of this? Similarly, the supply of impurity raw material gas 81■H6 was stopped and Andove's A 1 [n
An As layer (12A) is grown.

For the sample thus obtained, the areal density Ns of carriers in the compound semiconductor layer (12) was obtained by Hall measurement by varying the supply flow rate (supply flow rate ratio SCCMX supply time) of impurity source gas S1H6. Second result
As shown in the figure. As is clear from this, si2}1. It can be seen that if the gas supply amount is set above a certain value, the areal density becomes saturated and becomes constant. Therefore, if the planar impurity doped layer is formed with the SiJ6 gas supply amount at which the areal density is saturated, the same impurity concentration, that is, the carrier concentration will be obtained for each layer (12B). Therefore, the overall carrier concentration of the compound semiconductor layer (12) obtained in this way is
) is a predetermined value corresponding to the sum of the number of layers.

On the other hand, the threshold voltage vth is 2　ε5　・　ε.

It is expressed as Here, ψ9 is the height of Shonotokiharia,
ΔEC is the potential difference at the conduction band discontinuity, and d is the thickness of the current supply layer. In terms of crystal growth, the carrier concentration and the thickness of the Harrier layer are issues, but if the thickness is sufficiently uniform on the wafer (substrate (l)), the distribution of vth is Nd This can be considered to reflect the distribution of The compound semiconductor layer (12
) is the electron supply layer (3) in the HEMT explained in FIG.
). That is, in this case, as shown in FIG. 5, for example, an InP substrate is used as the substrate (1), an undoped GalnAs halia layer (2) is formed on this by MOCVD, and an electron supply layer (3) is formed on this. A two-layer Brenner impurity doped layer (12B) is formed by repeatedly doping the compound semiconductor layer (12), that is, the undoped compound semiconductor layer explained in FIG. Configured HEMT. HE obtained at each position on this common substrate (1), i.e., the wafer, i.e., at different distances from its center.
FIG. 3 shows the results of measuring the threshold voltage vth of each MT with respect to its distance from its center.

According to this, it can be seen that a substantially uniform threshold voltage vth is exhibited at each position on the wafer with a radius of 25 rm from the center of the wafer to the periphery of the wafer in this example.

In other words, it can be seen that the carrier concentration is uniform.

In contrast, in FIG. 4, the electron supply layer (3
) and undoped Ga as the Haria layer (2).
lnAs is formed and undoped A I In is formed on this.
As is formed and nA I In is formed on this as usual.
This figure shows the results of measuring vth of HEMT at each position of a similar wafer in which the electron supply layer (3) was formed by doping As with impurities simultaneously with its vapor phase growth. According to this, v depends on the position on the wafer.
It can be seen that th fluctuates, that is, vth decreases toward the periphery, that is, the carrier concentration increases.

In other words, as is clear from a comparison of FIGS. 3 and 4, the threshold voltage vth of the HEMT with electron supply N(3) obtained by the method of the present invention is uniform with almost no variation depending on each part W of the wafer. In other words, it can be seen that the carrier concentration is uniform within the wafer surface.

In the above-mentioned example, the undoped vapor phase growth step and the impurity doping step are performed continuously while keeping the substrate temperature constant, but the temperature conditions can be adjusted for each.

Furthermore, although the present invention has been mainly described as an example in which it is applied to obtaining n-^I InAs, it can also be applied to a method for growing compound semiconductors in which various other compound semiconductors are doped with impurities.

[Effects of the Invention] As described above, according to the method of the present invention, although the overall impurity concentration of the compound semiconductor layer takes discrete values, each value can be uniformly obtained, regardless of the position of the wafer. Since the concentration can be set uniformly over the area, it is possible to reliably obtain a target semiconductor device having predetermined characteristics with good reproducibility, thereby improving mass productivity and yield. I can do it.

[Brief explanation of drawings]

FIG. 1 is a process diagram for explaining an example of the method for growing a compound semiconductor according to the present invention, FIG. 2 is a diagram showing measurement results of the areal density of carriers with respect to the supply amount of impurity raw material gas, and FIGS. 3 and 4 5 is a diagram showing the measurement results of the relationship between each position on the wafer and the threshold voltage vth by the method of the present invention and the conventional method, and FIG. 5 is a schematic cross-sectional view of a high electron mobility HEMT. (1) is a substrate, (2) is a Haria layer, (3) is an electron supply layer, (12) is a compound semiconductor layer, (12A) is an undoped compound semiconductor layer, and (12B) is an impurity doped layer.

Claims (1)

[Claims] A step of growing an undoped compound semiconductor layer in a vapor phase; A step of doping the layer by supplying an impurity raw material gas while stopping the vapor phase growth until the areal density of carriers is almost saturated; A method for growing a compound semiconductor, characterized by having the following.