JP2587624B2 - Epitaxial crystal growth method for compound semiconductor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for growing a compound semiconductor epitaxial crystal from a monolayer to a high-purity single crystal thin film of a compound semiconductor having a thickness controllability of several angstroms. About.

(Prior Art) For example, there have been many proposals for a semiconductor device using a heterojunction of a thin film of GaAs and AlxGa1 _- xAs, or a heterojunction such as a HEMT structure or a superlattice structure using a two-dimensional electron gas. Along with the proposal of these semiconductor devices, development of an excellent technique for growing a thin film crystal of a compound semiconductor is urgent. Semiconductor and thin film forming technologies such as GaAs and AlxGa _-1 As include molecular beam epitaxy (MBE), metal-organic vapor phase epitaxy (MO-CVD), and molecular layer epitaxy (ML).
E) has been proposed.

Although MO-CVD is widely used because of its simplicity and good mass productivity, it does not have the controllability of a thin film on the order of a monolayer. Therefore, it is not necessarily suitable for the fabrication of a HEMT structure or a superlattice structure.

MBE uses a method of heating a raw material and vapor-depositing the vapor on a substrate crystal. Since the growth rate can be extremely reduced, the growth film thickness controllability is superior to that of MO-CVD. However, it is not easy to control the film thickness with a precision of the order of a monolayer. This problem is finally being solved using a monitor with RHEED. Also, in order to obtain good quality crystals by MBE, the growth temperature must be set to a high temperature of 500 to 600 ° C. Usually, the temperature is set to 550 to 600 ° C. for GaAs and to 600 ° C. or higher for AlxGa ₁ -xAs to improve the crystallinity. Al has a serious drawback such that Al is more easily oxidized at high temperature and AlxGa ₁ -xAs crystals have poor flatness. When trying to realize a steep impurity profile, redistribution of the impurity profile due to a high growth temperature becomes a problem. In addition, since it is based on the vapor deposition method, problems such as deviation from the stoichiometric composition of the grown film and insertion of crystal defects such as oval defects occur.

Molecular weight epitaxy is a method for growing a group III-V compound crystal by introducing a group III compound gas and a group V compound gas alternately onto a substrate crystal and growing the crystal in monomolecular layers (for example, Junichi Nishizawa et al.). Paper [J. Nishizawa,
H. Abe and T. Kurabayashi; J. Electrochem. Soc. 132 (198
5) 1197-1200]). This method utilizes the adsorption and surface reaction of a compound gas. For example, in the case of a group III-V crystal, a monomolecular film growth layer is obtained by introducing a group III compound gas and a group V compound gas once each. Since this method utilizes the monolayer adsorption of the compound gas, the monolayers always grow in a certain pressure range even when the pressure of the introduced gas changes. This method used trimethylgallium (TMG), an alkyl gallium, and arsine (AsH ₃ ), a hydrogen compound of arsenic, in growing GaAs crystals.
Instead of using gallium triethylgallium (TEG), a high-purity GaAs growth layer can be obtained at a lower temperature (for example, see J. Nishizawa, H. Abe, T. et al. Kurabayashi and N. Sakurai; T.
Vac. Sci. Technol. A4 (3), (1986) 706-710]).

(Problems to be Solved by the Invention) However, in the above-mentioned conventional molecular layer epitaxy, when crystal growth is performed using an alkyl metal,
There was a problem that carbon was mixed in the grown film and a high-purity thin film could not be obtained.

Accordingly, an object of the present invention is to improve this point and to suppress the amount of carbon mixed into the grown film, and to provide a method of epitaxially growing a compound semiconductor capable of obtaining a crystal growth thin film with higher purity. .

(Means for Solving the Problems) For this reason, the present invention is to alternately introduce a gas containing each elemental component of a compound semiconductor and hydrogen onto a substrate crystal alternately. More specifically, instead of TMG and TEG, triisopropylgallium (TI
PG) and triisobutyl gallium (TIBG), and triisopropyl aluminum (TI
PA) and triisobutylaluminum (TIBA), which combine to provide higher purity GaAs and AlxGa1 _- xAs compared to conventional molecular layer epitaxy.
This is a method for obtaining an epitaxial layer.

(Action) When alkylaluminum and alkylgallium are introduced onto a substrate heated in a vacuum, aluminum compounds and gallium compounds are adsorbed while being partially decomposed in a certain temperature range, and are completely decomposed in a high temperature region. And
Aluminum and gallium precipitate on the substrate surface. After the introduction of alkyl aluminum and alkyl gallium, AsH ₃
When GaAs and AlxGa are introduced on the substrate surface by surface reaction
_{A 1-} xAs epitaxial growth layer is formed. Gas used as material is trimethylaluminum (TMA), triethylaluminum (TEA), trimethylgallium (TMG)
In the case of triethylgallium (TEG), a large proportion of carbon is taken into the grown film, and the grown film becomes a p-type crystal having a high carrier density. However, by introducing a hydrogen molecule, a hydrogen atom, or a hydrogen ion only for a certain time during the growth, for example, in synchronization with the introduction of AsH ₃ , carbon contamination can be significantly reduced. Further, by selecting a raw material having an isopropyl group or an isobutyl group such as triisopropylaluminum (TIPA), triisobutylaluminum (TIBA), triisopropylgallium (TIPG) or triisobutylgallium (TIBG) as a raw material gas, carbon contamination is prevented. It is possible to reduce it more significantly.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an epitaxial crystal growth apparatus according to one embodiment of the present invention that incorporates hydrogen. In this figure, 1 is an alkyl aluminum inlet, 2 is an alkyl gallium inlet, 3 is an AsH ₃ inlet, 4 is an alkyl aluminum introduction control system, 5 is an alkyl gallium introduction control system, and 6 is an alkyl gallium introduction control system.
AsH ₃ introduction amount control system, 7 GaAs substrate crystal, 8 quartz susceptor, 9 lamp chamber, the 10 infrared lamp, 11 the crystal growth chamber, 12 is a gate valve, 13 a vacuum evacuation system,
14 is a gas introduction mode control system, 15 is a hydrogen (hydrogen molecule, hydrogen atom or hydrogen ion) inlet, and 16 is a hydrogen introduction control system.

Using this crystal growth apparatus, a GaAs or AlxGa1 _- xAs single crystal thin film is grown in the following procedure. First, the GaAs substrate crystal 7 is set in the crystal growth chamber 11 and evacuated by the vacuum evacuation system 13 until the degree of vacuum becomes about 10 ^-9 to 10 ^-19 Torr. The evacuation system 13 is constituted by a vacuum pump such as a cryopump or a turbo molecular pump. The evacuation system 13 is constituted by a vacuum pump such as a cryopump or a turbo molecular pump.

The GaAs substrate crystal 7 is heated to a crystal growth temperature (300 to 500 ° C.) by an infrared lamp 10 and set at a constant temperature. next,
Alkylaluminum, alkyl gallium, introducing a gas separate AsH ₃ and hydrogen in predetermined gas introduction pressure controlled by the respective introduction amount control system 4, 5, 6 and 16, a GaAs or Al x Ga _1-xAs grown layer obtain. The hydrogen used is a hydrogen molecule, a hydrogen atom and a hydrogen ion. Hydrogen atoms or ions are generated by applying light irradiation or plasma discharge to hydrogen molecules.

FIG. 2 shows an example of a gas introduction mode when GaAs is grown. This gas introduction mode is controlled by the gas introduction mode control system 14. In the figure, the gas containing Ga is alkyl gallium, and the gas containing As is AsH ₃ . Mode I is a mode in which hydrogen is introduced in synchronization with the evacuation time of ASH ₃ and alkyl gallium. Mode II is a mode in which hydrogen is introduced in synchronization with alkyl gallium. Mode III
Is a mode in which hydrogen is introduced in synchronization with the evacuation time of alkyl gallium and AsH ₃ . Mode IV is a mode of introducing hydrogen in synchronism with the introduction time of AsH _3.

When growing AlxGa _1- xAs, in addition to modes I to IV shown in FIG. 2, a mode in which hydrogen is introduced in synchronization with the introduction of alkyl aluminum or a mode in which hydrogen is introduced in synchronization with the evacuation time of alkyl aluminum Will be added.

As described above, by introducing hydrogen into the crystal growth chamber 11 at a predetermined timing together with various gases containing an alkyl metal, the alkyl group remaining on the substrate surface is surface-reacted with the hydrogen after the introduction of the alkyl metal, thereby stably. Hydrocarbons can be separated from the substrate surface as a stable hydrocarbon, the amount of carbon mixed into the grown film can be suppressed, and a single crystal thin film with high purity can be grown.

In this case, hydrogen is introduced into the crystal growth chamber 11 at a predetermined timing, and alkyl indium, alkyl gallium, AsH ₃ and PH ₃ are used as a gas containing a crystal growth component element.
By selecting a combination of gases such as GaP, InP, InGaP and InGaAsP, a high-resistance II
A single crystal thin film of an I-group compound semiconductor can be grown.

In addition, DMZn (dimethyl zinc), H ₂ Se (hydrogenated selenium)
And DMTe (dimethyl tellurium), DMHg
(Dimethylmercury), DMCd (dimethylcadmium) and D
By selecting a combination of MTe and performing growth with the introduction of hydrogen, a high-purity single crystal thin film of a II-VI group compound semiconductor such as ZnSe _1- xTex or HgxCd _1- xTe can be obtained.

In addition, instead of TMG and TEG used in the conventional method,
By using BG, a high-resistance GaAs epitaxial layer can be formed. For III-V binary, ternary and quaternary mixed crystals, the use of an organometallic material having an isopropyl group or an isobutyl group enables high resistance AlxGa1 _- xAs, GaP, InP, InxGa1 _- x.
It becomes possible to form a high-resistance single-crystal thin film of P, InGaAsP, AlGaAsP or the like. In addition, the use of an organic metal and a hydride containing a group II and group VI element enables formation of a high-resistance single crystal thin film of a group II-VI compound semiconductor.

FIG. 3 shows p-type and n-type GaAs and Al
FIG. _{1 is} a schematic configuration diagram of an xGa ₁ -xAs epitaxial crystal growth apparatus. In the figure, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts, and further, reference numeral 20 denotes an inlet for a compound gas of an n-type dopant, and reference numeral 21 denotes an inlet for a compound gas of a p-type dopant. 22 and 23 are respective gas introduction amount control systems. Reference numerals 24 and 25 are light irradiation windows. 26 and
27 is irradiation light.

Using this crystal growth apparatus, n-type GaAs or AlxGa1 _- x
When As is obtained, Si ₂ H ₆ , SiH ₄ , H ₂ Se, H ₂ S
Alternatively, a compound gas such as DMTe is introduced. In addition, p-type Ga
To obtain As or AlxGa1 _- xAs, DMCd, DMZ from inlet 21
Compound gas such as n and DEZn is introduced. Further, the irradiation light 26 and 27 from the light irradiation windows 24 and 25 for a certain time during the growth.
Is periodically applied to the substrate surface. As an irradiation light source, an excimer laser beam, a mercury lamp beam, a xenon lamp beam, an argon ion laser beam or the like is used. By this light irradiation, a high-purity single crystal thin film can be formed even at a low growth temperature.

As described above, even when impurities are added, by introducing hydrogen into the crystal growth chamber 11 at a predetermined timing, a region having a desired conductivity can be accurately formed,
High quality semiconductors can be formed.

(Effects of the Invention) As described above, according to the present invention, since hydrogen is introduced in synchronization with a certain time in the mode of the source gas, the incorporation of carbon into the grown film is reduced, and Purification can be realized. In addition, by selecting a raw material having an isopropyl group or an isobutyl group as the organometallic material, carbon contamination can be reduced, and GaAs, GaP, InP, I
A high-purity single crystal thin film of a compound semiconductor such as nGaP or InGaAsP can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an apparatus for epitaxially growing GaAs and AlxGa1 _- xAs according to the present invention, and FIG. 2 is a timing chart showing an example of a gas introduction mode during crystal growth.
FIG. 3 is a schematic configuration diagram of an epitaxial growth apparatus for GaAs and AlxGa1 _- xAs when adding impurities and irradiating light. 1 ...... alkylaluminum inlet, 2 ...... inlet alkyl gallium, 3 ...... inlet AsH _3, 4 ...... alkylaluminum introduction amount control system, 5 ...... alkyl gallium introduction amount control system, 6 ... AsH ₃ introduction amount control system, 7 ... GaAs substrate crystal, 8 ... Quartz susceptor, 9 ... Lamp chamber, 10 ... Infrared lamp, 11 ... Crystal growth chamber, 12 ... Gate valve 13 is vacuum Exhaust system, 14
... gas introduction mode control system, 15 ... hydrogen (hydrogen molecule, hydrogen atom or hydrogen ion) inlet, 16 ... hydrogen introduction control system, 20 ... compound gas inlet for n-type dopant, 21 ... ... p-type dopant compound gas inlet, 22, 23 ... gas introduction amount control system, 24, 25 ... light irradiation window, 26, 27 ... irradiation light.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toru Kurabayashi 7-25 Kasumi-cho, Yagiyama, Sendai City 2nd-Apartment Apartment 2A (56) References JP-A-61-34928 (JP, A) JP-A-59-3099 (JP, A)

Claims (3)

(57) [Claims] A vacuum chamber is evacuated to a crystal growth chamber in which a crystal substrate is installed, and a predetermined gas is introduced without simultaneously introducing two kinds of gases, a group III alkylated gas and a group V metal hydride gas. By repeating the operation of alternately introducing and evacuating with pressure and time, a monolayer is formed on the crystal substrate.
A method for epitaxially growing a group III-V compound semiconductor, wherein hydrogen is introduced for a predetermined time in synchronization with one of timings of introducing and exhausting the two gases into the crystal growth chamber. A method of epitaxially growing a compound semiconductor. 2. A method according to claim 1, wherein at least one of a hydrogen molecule, a hydrogen atom and a hydrogen ion is used as said hydrogen. 3. The method according to claim 1, wherein
A method for epitaxially growing a compound semiconductor, comprising using an isopropylated compound and an isobutylated compound as a group alkylating gas.