JPH0364073A - Compound semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To make composition of an insulating film homogeneous and to obtain a MOSFET having excellent characteristics by vacuum-sealing other element of the same group as an element of a compound semiconductor substrate in an ampule, heating it, and forming a mixed crystal layer between the substrate and the insulating film. CONSTITUTION:An Fe-doped semi-insulating InP single crystal is grown by an LEC method, cut in a direction perpendicular to a pulling-up axis, and Si<+> ions are implanted to a cut wafer. An SiNx film is deposited on the surface of an ion implanted substrate by a sputtering method. Thereafter, it is annealed to be activated, the film is removed by etching with a fluoric acid. The thus treated wafer 2 is introduced together with rod phosphorus in a quartz ampule 1, evacuated in vacuum, oxygen gas is then introduced, heat treated to form a uniform insulating oxide film on the wafer. Thus, electrons can be moved in a mixed crystal layer formed between the insulating film and the substrate at a high speed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an MO3 type field effect transistor (hereinafter referred to as MOSFET) based on a compound semiconductor, and in particular to a method for manufacturing an InP single crystal and its ternary and quaternary The present invention relates to the most effective technique when forming a MOSFET on a mixed crystal substrate.

[Conventional technology] Compound semiconductors such as GaAs and InP have higher electron mobility than Si, and also have excellent radiation resistance and heat resistance, and are expected to have future potential as high-frequency, high-speed electronic devices that can replace Si. However, a stable oxide film with a small interface state density could not be obtained, so MO
SFETs have not yet been put into practical use, so
In GaAs, MES using Schottky electrodes
FETs have been put into practical use, as have discrete high-frequency FETs and small-scale digital ICs. However, since the Schottky barrier potential of GaAs MESFET is small, the logic amplitude cannot be large, and it has the disadvantage that large-scale digital ICs cannot be manufactured with high yield. .

On the other hand, MESF has a smaller logic amplitude than GaAs.
Efforts have been made to make MOSFETs using InP, which can only be produced by ETu, using thermal oxidation, anodic oxidation, plasma oxidation, etc., but all of these methods result in non-uniform oxide film composition, poor insulation, and the ability to produce good MOSFETs. This type of MOSFET has not yet been realized and put into practical use.
As an alternative to S I Oz t S I N
X p A Q 20 s.

Many studies have been conducted on MISFETs in which insulating films such as PN are deposited at low temperatures by CVD, plasma CVD, photo-excited CVD, sputtering, vapor deposition, spin-on methods, and the like.

[Problem to be solved by the invention] However, the MISFET manufactured by the above method
All of these have a fatal drawback as an electronic device in that the drain current drifts, and so they have not been put into practical use.

By the way, as mentioned earlier, MOSFETs have not been put to practical use in compound semiconductors, and the reason for this is that the composition of the oxide film becomes non-uniform. For example, in the case of InP, when thermally oxidized in oxygen, InPO4 initially becomes 20λ
After that, InPO grows, and InPO grows on the outside of the film.
It is known that P precipitates at the interface between InP and TnPO4. This phenomenon is caused by anodic oxidation.

This occurs regardless of the method used, such as plasma oxidation, and is the cause of not being able to obtain a uniform, high-quality oxide film.

As described above, it is difficult to form a high-quality insulating film by thermal oxidation, so various low-temperature deposition methods as mentioned above are being researched. In addition to the lattice mismatch that occurs at the interface between the insulating film and the compound semiconductor substrate due to the deposition of a system of There is a problem that current drift occurs.

Therefore, the present inventors first created a high-quality thermal oxide film, and
We have developed and proposed a method for forming a MOSFET without drain current drift (Japanese Patent Application Nos. 1-61603, 1-61604, and 1-61605).

However, in these MOSFETs, the substrate is, for example, InP.
In this case, the high-speed operability of the MOSFET was physically determined by the saturation speed of electrons in InP. Of course, it is possible to operate much faster than Si MOSFET, but AQ G a A s / G a
HEMT using two-dimensional electron channels such as As system
You cannot expect high-speed operation like that.

However, A Q Ga As / Ga As
The HEMT system uses an Al2GaAs/GaAs layer with Ga
When forming on As substrate, MBE method or MOCV method is used.
It must be formed using a vapor phase epitaxial method such as the D method, and since it basically uses a MESFET structure, when making a logic IC, it is difficult to obtain a large logic amplitude and requires expensive equipment. However, since the epitaxial layer is grown over a period of time, the cost is high.

An object of the present invention is to provide a new electronic device and a method for manufacturing the same in a compound semiconductor MOSFET structure that can operate at higher speed than conventional electronic devices.

[Means for solving the problem] In a MOSFET, a carrier inversion layer is formed at the interface between the compound semiconductor substrate and the MID film on the compound semiconductor substrate side by applying a potential to the gate electrode, thereby inverting the minority carriers. It operates by moving near the interface. Therefore, in MOSFETs, the properties of the compound semiconductor material near the interface are extremely important.

For example, when forming an insulating film, if some constituent elements with high vapor pressure are reduced in the compound semiconductor substrate near the interface and defects occur, this will significantly affect the characteristics of the MOSFET. In fact, the main reason why the various MOSFETs and MISFETs that have been conventionally devised could not be put into practical use was due to the occurrence of defects as described in 2 and the accompanying drift of drain current.

In order to solve this essential problem, the present inventors have attempted to prevent elements with high vapor pressure among the constituent elements from leaving the substrate during thermal oxidation in a quartz ampoule as described above, and to always We have already developed and proposed a very important technology to form an insulating film in a thermal equilibrium state.

The present invention is a further development of the invention of the prior application. That is, when forming an insulating film as described above, the homologous atoms of the elements constituting the compound semiconductor are present in a vapor phase in the quartz ampoule when forming the insulating film, and are These elements are mixed to form a two-dimensionally extremely thin mixed crystal layer or a layer similar thereto between the compound semiconductor substrate and the insulating film (at the boundary).

Two primary methods can be considered for making the homologous element exist in the ampoule during the formation of the insulating film.

(1) In the ■-■ group compound semiconductor of elements with high vapor pressure, P, As,
In II-Vl group compound semiconductors such as Sb, S,
Se.

Regarding elements such as Cd, as shown in FIG.
As shown in Figure (b), the ampoule 1 is equipped with a vapor pressure control section 1a, and the temperature is controlled using a multi-stage furnace (heater) 3. Either method or a combination of both methods can be used.

(2) Elements with low vapor pressure ■-Aα, In for group V compound semiconductors.

For elements such as Ga, sufficient vapor pressure cannot be obtained just by placing them in a quartz ampoule.

Furthermore, even if the quartz ampoule 1 is provided with a vapor pressure control section 1a for these elements, these elements will precipitate on the substrate side, which is inconvenient. For these elements with low vapor pressure, these oxides may be mixed with the element and heated to form lower oxides.For example, in the case of Ga, it is sufficient to mix these oxides with the element and heat it to form a lower oxide.

3Ga20. By the reaction of +40a450a, O+20°, Ga and O with high vapor pressure can be generated, so as shown in Fig. 1 (Q), a boat 4 containing a mixture of an appropriate oxide and the relevant elements is placed in a quartz ampoule. 1 to control the pressure of the lower oxide in the gas phase. Or Figure 1 (d
), the pressure of the lower oxide may be adjusted by controlling the temperature of the boat section 4 containing the mixture of the oxide and the element in the multistage furnace 3.

The composition of the mixed crystal or similar layer formed between the compound semiconductor substrate and the insulating film is controlled by optimizing the heating temperature of the ampoule, its profile, the vapor pressure of the component elements, etc. for each system. be able to. In addition, since an insulating film containing the constituent elements of these mixed crystal layers is formed in the insulating film, the conditions for optimizing the mixed crystal layer composition and #@edge film composition can be found through experiments for each system. good.

[Function] According to the above means, the composition of the insulating film becomes uniform, and the insulating film is formed under pressure by evaporating the high vapor pressure component among the constituent elements in the ampoule. A MOSFET with excellent characteristics that prevents decomposition and volatilization of constituent elements from a compound semiconductor substrate during the formation of an insulating film.
In addition, a mixed crystal or a layer similar to it is formed between the insulating film and the compound semiconductor substrate (at the boundary), and electrons move at high speed in this layer or at its interface, making it possible to It is possible to create a compound semiconductor device that can operate much faster than MISFETs and MOSFETs.

[Example 1] The characteristics of the MOSFET according to the present invention were evaluated using a Kolpino-Dix type FET.

Fe-doped semi-insulating ZnP single crystal with a diameter of 2 inches was LE
The wafer was grown using the C method, cut in the direction perpendicular to the pulling axis, and the cut wafer was organically cleaned and etched with brome methanol.
Ion implantation was performed at room temperature with a dose of 2×10”ol.

After the ion implantation, the substrate was washed with organic water and washed with water, and a SiNx film was deposited on the surface by sputtering, followed by activation annealing at 620° C. for 15 minutes in an infrared heating furnace. In order to prevent P from being removed during annealing, both surfaces of the sample were sandwiched between other InP substrates and annealed. After activation annealing, the SiNx film was removed by etching with hydrofluoric acid. The active layer in the gate region was removed by mesa etching using a sulfuric acid-based etchant.

The wafer treated as described above was placed in a quartz ampoule of an apparatus as shown in FIG. 1(a) together with red phosphorus, and after evacuating the ampoule, oxygen gas was introduced and sealed. At this time, metallic arsenic was simultaneously placed in the quartz ampoule. As for the amount, the pressure during heating is 0°2~1. The quartz ampoule containing the wafer was placed in the 4th order determined to be Oat@.
Heat treatment was performed at 50 to 600° C. for 5 to 20 hours to form a uniform N-edge oxide film on the wafer.

In the insulating oxide film produced as described above, contact holes were opened by selective etching in the parts activated by ion implantation, and an Au-Ge alloy was deposited and patterned to form source and drain electrodes. Note that annealing to obtain ohmic contact was performed at 350°C in a N2 atmosphere for 7
I did it for a minute.

Finally, after the AQ layer was deposited on the entire surface, the AQ layer was patterned using a phosphoric acid etching solution to form source, drain, and gate electrodes. The inner diameter of the gate electrode is 150μ.
m, and the outer diameter of the gate electrode was 250 μm.

The effective electron mobility μof of the FET made as above
f is the channel conductance (gd), where Ci
is gate capacitance, Vg is gate applied voltage, Vth is FET
is the threshold voltage of The gate capacitance value Ci is n-type In
It was determined from the measured values of an MIS diode made using a P substrate using a similar oxide film formation process.

FIG. 2 shows the measurement results of the mobility μssf.

In the figure, the actual MA indicates the case where As was put into the quartz ampoule, and the solid line B shows the case where As was not put in the quartz ampoule. From this, it can be seen that when As is added, the mobility is significantly higher than when it is not added.

[Example 2] A Kolpino disk type FET was formed using the same procedure as in Example 1. As the substrate, the same i, rre doped semi-insulating InP single crystal as in Example 1 was used. When forming an insulating oxide film, zero
2 gas and red phosphorus, and place a quartz boat 4 in the vapor pressure control part 1a of the quartz ampoule 1, and put Ga, Ga,
03 mixture was added.

The temperature of the substrate part is 450 to 600°C, and the temperature of Ga and G
The temperature of the boat portion of a, 03 was set at 600 to 1000° C., and heat treatment was performed for 5 to 20 hours to form a uniform insulating oxide film.

The effective electron mobility μoff of a Kolpino disk FET manufactured in the same manner as in Example 1 except for the above oxidation process was measured. The measurement results are shown in Figure 3, where the solid line C is G
When a, O, is included, the solid line indicates the case where it is not included.

When Ga and Ga2O were added, an FET with a higher effective electron mobility was created than when Ga, Ga, and O were not added.

Note that in the above example, a MOSFE is mounted on an InP single crystal substrate.
The case where T was also formed was also explained, but In and P
When forming a MOSFET on a ternary or quaternary mixed crystal substrate containing
It can be applied when forming an OSFET, and similar effects can be obtained.

[Effects of the Invention] As explained above, the present invention places a compound semiconductor substrate in a quartz ampoule, and simultaneously vacuum-seals an element with a high vapor pressure among the constituent elements of the compound semiconductor substrate together with oxygen gas and heats it. At this time, among the constituent elements of the compound semiconductor substrate, an oxide of an element with a low vapor pressure is mixed with that element and simultaneously vacuum-sealed into an ampoule, and the ampoule is heated to form a lower oxide with a high vapor pressure. When forming an insulating film by controlling the composition of the insulating film, at least one of the constituent elements of the substrate and one or more other elements in the same group are simultaneously vacuum sealed in an ampoule and heated. By forming a layer with a mixed crystal or a similar composition between the compound semiconductor substrate and the insulating film, the composition of the insulating film becomes uniform, and elements with high vapor pressure among the constituent elements are contained in the ampoule. Since the insulating film is formed under pressure by evaporation, decomposition and volatilization of the constituent elements from the compound semiconductor substrate during the insulating film formation are prevented.
In addition to being able to obtain MOSFETs with excellent characteristics, electrons move at high speed through the newly formed layer or interface between the insulating film and the compound semiconductor substrate (boundary), making it more efficient than conventional MISFETs and MOSFETs. This has the effect that a compound semiconductor device capable of high-speed operation can be obtained.

[Brief explanation of drawings]

FIGS. 1(a) to (d) are cross-sectional views showing a configuration example of an insulating film forming apparatus used in the method of the present invention, and FIG. 2 is an effective electron transfer measured for an FET formed according to the first embodiment. FIG. 3 is a graph showing the relationship between the effective electron mobility measured for the FET formed according to the second example and the Fc concentration in the crystal. 1...Quartz ampoule, 2...Wafer, 3...
...Heater, 4...Boat. (1st rlA 2nd figure Fc density, 1 (cm-3)

Claims (2)

[Claims] (1) A compound semiconductor device in which an electrode metal layer is formed on a compound semiconductor substrate with an insulating film interposed therebetween, in which constituent elements of the semiconductor substrate and their homologous elements are disposed between the compound semiconductor substrate and the insulating film. A compound semiconductor device characterized by having a layer having a composition similar to a mixed crystal consisting of. (2) A compound semiconductor substrate is placed in a quartz ampoule, and at the same time, an element with a high vapor pressure among the constituent elements of the compound semiconductor substrate is sealed in vacuum with oxygen gas and heated, or at this time, the constituent elements of the compound semiconductor substrate are The composition of the insulating film is controlled by mixing an oxide of an element with a low vapor pressure with the other element, vacuum-sealing the mixture into an ampoule, and heating the ampoule to form a lower oxide with a high vapor pressure. When forming the compound semiconductor substrate, one or more other elements in the same group as at least one of the constituent elements of the substrate are vacuum-sealed and heated at the same time in an ampoule to create a bond between the compound semiconductor substrate and the insulating film. A method for manufacturing a compound semiconductor device, comprising forming a layer having a composition of mixed crystal or similar thereto.