JP3347175B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a III-V compound semiconductor device in which a field effect transistor is integrated and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a field effect transistor (FET) of a III-V compound semiconductor, a high electron mobility transistor (HEMT), a MESFET and the like are known.
When a plurality of these FETs are integrated on the same semiconductor substrate, the side gate effect becomes a problem.

In order to operate a transistor at high speed,
It is preferable that portions other than the transistor, such as the substrate, have a high resistivity to reduce the accompanying capacitance of the transistor. In such a situation, when a voltage is applied to the gate (side gate) of one transistor, the channel of the adjacent transistor is affected. That is, it is affected by the side gate.

[0004] This phenomenon can be understood as a phenomenon in which lines of electric force generated from one gate reach another gate. According to recent studies, it is reported that such lines of electric force pass through the substrate and the buffer layer near the substrate.

In order to prevent the side gate effect, it is necessary to stop the lines of electric force halfway. If electric charges are distributed on the substrate, the buffer layer or in the vicinity thereof, the passage of electric lines of force could be prevented.

In the case of a HEMT on a GaAs substrate, it is known that a high-resistivity buffer layer of oxygen-doped AlGaAs is effective for suppressing the side gate effect. AlGaAs
It is known that the concentration of doped oxygen increases as s grows at lower temperatures.

[0007]

SUMMARY OF THE INVENTION However, AlG
A clear relationship between the oxygen concentration in the aAs layer and the side gate effect was not clear. Furthermore, if AlGaAs is doped with enough oxygen to sufficiently suppress the side gate effect, a hysteresis loop easily occurs in the DC characteristics of the transistor.

An object of the present invention is to provide a semiconductor device capable of efficiently suppressing the side gate effect and a method of manufacturing the same. Another object of the present invention is to provide a semiconductor device capable of suppressing a side gate effect and also suppressing a hysteresis loop of DC characteristics, and a method of manufacturing the same.

[0009]

According to the present invention, there is provided a semiconductor device comprising:
A semiconductor device comprising an active layer (4) serving as an element region on a semiconductor substrate (1), wherein the semiconductor device is disposed between the semiconductor substrate (1) and the active layer (4) and has a size of 1 × 10 ¹⁸ cm ^{− It} has an oxygen concentration of ³ or more and a carbon concentration of 5 × 10 ¹⁷ cm ⁻³ or less, and has an oxygen concentration of 1 × 10 ¹⁸ cm ⁻³ with the same composition as its lattice constant.
The mismatch with the lattice constant of the following AlGaAs layer is 2 × 10
A semiconductor device including a high resistivity AlGaAs layer (2) of not more than ^-5 .

[0010]

[0011]

The side gate effect can be efficiently suppressed by controlling not only the oxygen concentration of the high resistivity AlGaAs layer but also the carbon concentration.

The hysteresis loop of the DC characteristics can be suppressed by making the lattice constant of the AlGaAs layer close to the lattice constant when oxygen is not substantially doped.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a case where an oxygen-doped Al _x Ga _{1 -x} As buffer layer is grown by metal organic chemical vapor deposition (MOCVD) will be described as an example. The case where x = 0.28 is mainly taken as an example. To dope the AlGaAs layer with oxygen,
It is preferable to use a substance containing at least one of an alkoxy group, a hydroxyl group, and an acyloxy group as a dopant.

For example, as the oxygen dopant, tertiary butyl arsine, ethyl arsine, which are group V raw materials,
Based on at least one of phenylarsine, tetraethyldiarsine, and tridimethylaminoarsine, a substance of each system containing the above-described dopant can be used.

Other source materials include, for example, trimethyl aluminum (TMA) as an Al source, triethyl gallium (TEG) or trimethyl gallium (TMG) as a Ga source, and arsine (A) as an As source.
sH ₃ ) can be used. However, it is not limited to these source materials.

Incidentally, when oxygen is doped into the AlGaAs layer, carbon is also incidentally added. It has been found that the side gate effect depends on both the oxygen concentration and the carbon concentration, and depends on the supply amount of the oxygen dopant and the growth temperature of the AlGaAs layer.

Therefore, the dependence of the carbon concentration and oxygen concentration on the growth temperature and the dopant supply rate were measured. In this specification, the dopant supply rate indicates the ratio of the supply amount of the carrier gas containing the oxygen dopant to the supply amount of the carrier gas of all the group V elements. More specifically,
In the case of the present embodiment, [tBA-based carrier gas flow rate] /
{[TBA carrier gas flow rate] + [arsine carrier gas flow rate]}.

The dopant supply rate and the growth temperature were changed, and the dependence of the oxygen concentration and the carbon concentration on the dopant supply rate and the growth temperature were examined by SIMS analysis. Tables 1 and 2 show the measurement results.

[0019]

[Table 1]

[0020]

[Table 2] As is clear from Table 1, when the oxygen dopant is not supplied, the oxygen concentration depends on the growth temperature and increases as the temperature decreases. For example, when the growth temperature is reduced from 660 ° C. to 580 ° C., the growth temperature is reduced from 8 × 10 ¹⁷ cm ⁻³ to 3 × 10 ¹⁸ cm.
^-3 and an improvement in oxygen concentration of approximately 2 × 10 ¹⁸ cm ⁻³ are observed. This oxygen concentration can be called an intrinsic oxygen concentration, and is considered to appear depending on the growth temperature regardless of the presence or absence of the oxygen dopant.

[0021] Incidentally, as it will be apparent to the oxygen concentration of 6 × 10 ¹⁹ cm ^-3 in the case of the dopant feed rate = 0.25, the addition of oxygen dopants actively, oxygen concentration increases, to some extent more oxygen In the increased state,
The oxygen concentration hardly depends on the growth temperature. It is considered that even if the intrinsic oxygen concentration shows the growth temperature dependency, the difference becomes negligible with respect to the whole oxygen concentration.

When doping oxygen to a certain degree or more, it is necessary to positively add an oxygen dopant, and the oxygen concentration obtained at that time does not substantially depend on the growth temperature. When the dopant supply rate is 1, the maximum oxygen concentration obtained is about 2 × when the growth temperature is 580 ° C.
It was 10 ²⁰ cm ^-3 .

Along with the doping of oxygen, doping of carbon occurs. Referring to Table 2, the carbon concentration due to oxygen doping depends on the growth temperature, and decreases as the growth temperature increases.

Further, the dopant supply rate = 0.25, 1.
As can be seen from the value of 0, when the oxygen dopant is increased to some extent, the concomitant carbon concentration reaches saturation. In Table 2, when the growth temperature is 580 ° C., the carbon concentration is saturated at 7 × 10 ¹⁷ cm ⁻³ . This saturation already appears near the dopant supply rate = 0.25.

From these results, it can be seen that the oxygen concentration in the AlGaAs layer can be determined by the dopant supply rate, and the accompanying carbon concentration can be controlled by the growth temperature. Therefore, if the supply rate of the dopant is first determined so as to satisfy the required oxygen concentration, and then the growth temperature is determined so as to satisfy the desired carbon concentration, the oxygen concentration and the carbon concentration can be controlled almost independently. Is possible.

FIG. 1 schematically shows a configuration of a HEMT according to an embodiment of the present invention. On a semi-insulating GaAs substrate 1,
An oxygen-doped AlGaAs layer 2 and an i-type GaAs layer 3 are formed as buffer layers. The AlGaAs layer 2 has a thickness of, for example, 300 nm, and the GaAs layer 3 has a thickness of, for example, 200 nm.

On these buffer layers 2 and 3, electron transport
I-type In functioning as a layer_0.2Ga _0.8As layer 4 is thick
I-type I having a thickness of about 1 nm and having a thickness of about 1 nm
nGaP spacer layer 5, impurity concentration n = 2 × 10¹⁸cm
^-3N-type InGaP electron supply layer 6 is grown to a thickness of about 30 nm.
Have been.

A contact layer 7 made of a pair of n-type GaAs is formed on the electron supply layer 6 so as to sandwich a part of the region. The thicknesses of the electron supply layer 6 and the contact layer 7 are, for example, about 30 nm and about 50 nm, respectively. The impurity concentration of the contact layer 7 is about n = 2 × 10 ¹⁸ cm ⁻³ .

A gate electrode 9 is formed on a partial region of the electron supply layer 6, and a source electrode 8 a and a drain electrode 8 b are formed on the contact layer 7 so as to sandwich the gate electrode 9. Source electrode 8a and drain electrode 8b are formed of, for example, AuGe / Au, and gate electrode 9 is formed of, for example, Al or WSi.

In this structure, how to form the AlGaAs buffer layer 2 becomes a problem for suppressing the side gate effect. Samples in which the buffer layer 2 was formed under various conditions were formed.

Table 3 shows conditions for preparing representative samples and their measurement results.

[0032]

[Table 3] Sample S113 is a HEMT including an AlGaAs layer formed at a growth temperature of 660 ° C. without supplying an oxygen dopant. In the sample S111, the HEM prepared with the dopant supply rate being 0.25 and the other conditions being the same.
This is a sample of T.

Sample S116 has a dopant supply rate of 0.25, which is equivalent to that of sample S111, and has a growth temperature of 5%.
This is a sample when lowered to 80 ° C. The oxygen and carbon concentrations in each sample are the same as those in Tables 1 and 2.

FIGS. 2 and 3 show the side gate effect measurement results and the hysteresis loop measurement results of three representative samples shown in Table 3. FIG. FIG. 2 shows the measurement results of the side gate effect. The abscissa indicates the voltage applied to the side gate in V, and the ordinate indicates the change in threshold voltage ΔV of the target HEMT.
It is indicated by th (V).

In the sample S113 in which oxygen is not positively doped, a change in the threshold voltage due to the side gate effect is remarkably exhibited. On the other hand, oxygen
In sample S111 doped with 10 ¹⁹ cm ^-3 and having a carbon concentration of 2 × 10 ¹⁷ , almost no side gate effect was observed, and the threshold voltage was kept constant.

In the sample S116 in which the growth temperature is lowered, the threshold voltage is set to about 0.5 due to the side gate voltage although the oxygen concentration is equal to that of the sample S111.
It shows a change of 05V. However, the change in the threshold voltage indicates a saturation tendency.

It is considered that carbon doped into AlGaAs acts almost completely as a p-type impurity. The fact that the side gate effect did not appear in sample S111 and the side gate effect occurred in sample S116 means that the carbon concentration was 2 × 10 ¹⁷ cm ⁻³ to 7 × 10 ¹⁷ cm ^−3.
It is considered that a phenomenon that could not be compensated for by oxygen doping occurred when the value changed to.

It is considered that a very small portion of the oxygen doped into the AlGaAs layer is electrically activated to form an electron trap. On the other hand, it is considered that almost all of the carbon doped into the AlGaAs layer is activated and becomes a hole donor.

When the amount of electron traps is larger than the amount of holes, the lines of electric force generated from the holes extend toward the electron traps and terminate. Thus, the holes need not move. Then, even if the electric lines of force come from the side gate, they can be terminated by the remaining electron traps. Therefore, the threshold does not change.

On the other hand, when the amount of holes is larger than the amount of electron traps, holes not connected to the electron trap by lines of electric force can move around. In addition, the lines of electric force from the side gate cannot be stopped, the band is tilted, and the threshold voltage fluctuates.

If the electrically activated oxygen forms a deep carrier trap level, the sample S11
1. The oxygen concentration of 6 × 10 ¹⁹ cm ⁻³ in S116 is considered to correspond to a value between 2 × 10 ¹⁷ cm ⁻³ and 9 × 10 ¹⁷ cm ⁻³ of sample S116 in terms of hole concentration.

FIG. 3 shows samples S113, S111 and S111.
116 shows IV characteristics. In these IV characteristics,
In sample S116, a non-negligible hysteresis loop is observed. The growth temperature of sample S116 is set to be about 80 ° C. lower than that of sample S113 and sample S111.

FIG. 4 shows the change of the lattice constant depending on the dopant supply rate and the growth temperature. The horizontal axis represents the dopant supply rate, and the vertical axis represents the lattice constant. The vertical axis is G
A scale indicating the lattice mismatch with the aAs substrate in units of 10 ^-4 is given.

When the growth temperature Tg is 580 ° C., as the oxygen dopant supply rate is increased, the lattice constant is gradually reduced. Oxygen is a Group VI element, and is considered to be disposed substitutively at the Group V element As site of AlGaAs.

The atomic radius of As and the atomic radius of O are different, and the atomic radius of O is much smaller. Therefore, it is considered that the lattice constant decreases when O is substituted for As. It is considered that the characteristic at Tg = 580 ° C. indicates a decrease in lattice constant due to O substitution.

As the growth temperature is gradually increased, the change in the lattice constant becomes gentle. In oxygen doping, it is considered that the site occupied by oxygen is not limited to the group V element site, but is also doped at interstitial positions (interstitial).

When oxygen is doped into interstitial sites, the distance between adjacent constituent elements is extended. It is considered that the phenomenon in which the lattice constant changes slowly at a high temperature is such that the oxygen occupying the interstitial site increases as the temperature increases, and the effect of decreasing the lattice constant and the phenomenon of increasing the lattice constant cancel each other.

By the way, it has been found that when the hysteresis loop of the DC characteristic does not exist or is small, the lattice constant of the AlGaAs layer has a smaller degree of lattice mismatch than the lattice constant in the case of non-doping with oxygen. D
For a sample having an extremely small hysteresis loop of the C characteristic, the degree of lattice mismatch is approximately 2 × 10 ⁻⁵ or less for a sample having an oxygen concentration of 1 × 10 ¹⁸ cm ⁻³ .

Therefore, it is preferable that the oxygen dopant supply rate is determined based on the above-mentioned criterion, and that the growth temperature is selected so as not to cause lattice irregularity of 2 × 10 ⁻⁵ or more when determining the growth temperature.

Combining the above results, in order to suppress the side gate effect, the oxygen concentration in the AlGaAs layer is preferably about 1 × 10 ¹⁸ cm ⁻³ or more, and the carbon concentration is about 5 × 10 ¹⁷ cm ^−3. cm ^-3 or less.

The side gate effect of the sample S116 is as follows.
This is considered to be caused by holes caused by shallow impurity levels in the valence band. It is thought that this phenomenon occurs due to the effect of the remaining holes and the lines of electric force from the side gates, because all the deep carrier trap levels caused by oxygen are connected by holes caused by carbon. .

That is, when the carbon concentration is equal to or higher than the carrier trap level caused by oxygen, a side gate effect occurs, which is considered to be undesirable. Therefore, it is desired that the carrier trap level due to the oxygen concentration is higher than the carbon concentration.

The Al composition x of the Al _x Ga _{1 -x} As layer, which is effective for suppressing the side gate effect, is preferably set to 0.1.
1 ≦ x ≦ 0.5. If it is less than 0.1, oxygen is difficult to enter, and if it exceeds 0.5, carbon enters too much. Empirically x
Is preferably 0.2 or more.

In recent years, a GaAs layer has been formed on a Si substrate,
Attempts to produce GaAs integrated circuits have been actively made. In this case, Si is easily taken into the GaAs layer,
It is difficult to increase the resistance of the GaAs layer. Therefore, G on the Si substrate
On the aAs layer, the above-described oxygen-doped high-resistance AlGaAs
If a layer is grown once and a GaAs layer or the like is further grown thereon, an integrated circuit on a high-resistance substrate can be easily realized.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example,
GaAs or the like can be used as the electron transit layer instead of InGaAs. Also, instead of HEMT, M
The ESFET may be integrated. M as a crystal growth method
Instead of OCVD, gas source MBE (molecular beam epitaxy) can be used.

It will be obvious to those skilled in the art that various changes, improvements, combinations, and the like can be made.

[0057]

As described above, according to the present invention,
A III-V compound semiconductor device in which a side gate effect is effectively suppressed is provided.

Further, it is possible to provide a semiconductor device in which a hysteresis loop of DC characteristics is suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a HEMT according to an embodiment of the present invention.

FIG. 2 is a graph showing measurement results of a side gate effect of a sample.

FIG. 3 is a graph showing measurement results of IV characteristics of a sample.

FIG. 4 is a graph showing the dependence of the lattice constant of a sample on the dopant supply rate and the growth temperature.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 GaAs substrate 2 oxygen-doped AlGaAs layer 3 i-type GaAs layer 4 i-type InGaAs layer 5 i-type InGaP layer 6 n-type InGaP layer 7 n-type GaAs layer 8 a source electrode 8 b drain electrode 9 gate electrode

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-280897 (JP, A) JP-A-4-328822 (JP, A) WO 92/15113 (WO, A1) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/20-21/205 H01L 21/338 H01L 29/778 H01L 29/812

Claims (6)

(57) [Claims] 1. A semiconductor device comprising an active layer (4) serving as an element region on a semiconductor substrate (1), wherein the semiconductor device is disposed between the semiconductor substrate (1) and the active layer (4). Oxygen concentration of × 10 ¹⁸ cm ^-3 or more and 5 × 10 ¹⁷ c
a mismatch between the lattice constant of the AlGaAs layer having a carbon concentration of not more than m ^-3 and the lattice constant of the AlGaAs layer having the same composition and the oxygen concentration of not more than 1 × 10 ¹⁸ cm ^{-3 is not} more than 2 × 10 ^-5. Resistivity A
A semiconductor device including an lGaAs layer (2). 2. The semiconductor device according to claim 1, wherein a concentration of a carrier trap level caused by the oxygen concentration is equal to or higher than the carbon concentration. 3. A high-resistivity AlGaAs layer (2)
3. The semiconductor device according to claim 1, wherein the l composition is 0.2 or more. 4. The semiconductor device according to claim 1, wherein said semiconductor substrate is a Si substrate. 5. An at least one of an alkoxy group, a hydroxyl group, and an acyloxy group is supplied as an oxygen dopant contained in a group V raw material, and is supplied onto the semiconductor substrate (1) by metal organic chemical vapor deposition at a substrate temperature of 660 ° C. 1 × 10 ¹⁸ cm ^-3
It has the above oxygen concentration and a carbon concentration of 5 × 10 ¹⁷ cm ⁻³ or less, and has the same composition as the lattice constant and the oxygen concentration of 1 × 10 ¹⁸ cm ^−3.
The mismatch with the lattice constant of the AlGaAs layer of cm ⁻³ or less is 2
A method for manufacturing a semiconductor device, comprising a step of growing an AlGaAs layer having a size of ^10-5 or less. 6. The method of manufacturing a semiconductor device according to claim 5, wherein the group V material is tertiary butylarsine, and a supply rate of the group V material containing an oxygen dopant to all the group V materials is 0.04 or more.