JP2717786B2 - Semiconductor crystal epitaxial growth method and molecular layer epitaxy apparatus used in the method - Google Patents

Description

The present invention relates to a method for epitaxially growing a semiconductor crystal and an apparatus used for the method, and more particularly to a method and an apparatus for epitaxially growing a semiconductor crystal in a evacuated growth chamber. The present invention relates to a molecular layer epitaxy apparatus used. [Prior art] Conventionally, as an epitaxial growth method of a semiconductor crystal,
A vapor phase method of growing under an atmosphere reduced to normal pressure or reduced pressure is widely known. Although the gas phase method has a simple apparatus and is excellent in mass productivity, there is a limit in controlling the film thickness, so that the film thickness controllability on the order of a single molecule is not provided. For this reason, for example, an ultra-high frequency device such as an electrostatic induction transistor (SIT) operable in the terahertz band, or a super lattice (S
L) Since the device needs to control the film thickness on the order of single molecules, it has been difficult to manufacture the device by the conventional gas phase method. On the other hand, an epitaxial growth method in which growth is performed in a high vacuum, for example, molecular beam epitaxy (MBE) is capable of controlling the film thickness on the order of angstroms, and is suitable for manufacturing the device requiring a high degree of film thickness control. There are various studies for practical use. In the MBE, by heating and evaporating the raw material, a raw material gas and molecules of the raw material gas are deposited on a substrate in the form of a beam,
Epitaxial growth is performed. In this case, the motion of the incident molecular beam in a high vacuum has a strong directivity, and the growth on a large-area substrate tends to be non-uniform. Although a method for improving the performance is adopted, the entire device becomes complicated and expensive. Also, if a molecular beam incident on the substrate is blocked by a shield, crystal growth cannot be performed in the shielded portion of the substrate. On the other hand, crystal growth is not performed at all on the substrate portion, particularly the side wall portion, which is shielded by the unevenness, or the crystal growth becomes extremely uneven. This is the same in MO-MBE using an alkyl metal compound that is a gaseous molecule at room temperature. In addition, molecular layer epitaxy (MLE), which is one of the epitaxial growth methods for growing in a high vacuum, is based on III-V
In the method of growing a group III compound crystal, a group III compound gas and a group V compound gas are alternately introduced onto a crystal substrate to grow the crystal in a monomolecular layer (for example, a paper by Junichi Nishizawa et al. [J. Nishizawa, H. .Abe and T.Kurabayashi; J.Electroche
m. Soc. 132 (1985) p. 1197-1200]). According to this method, a monomolecular film growth layer can be obtained by introducing a group III compound gas and a group V compound gas once, for example, in the case of a group III-V crystal, utilizing the adsorption and surface reaction of a compound gas. . This is due to the fact that monomolecular layer growth always occurs within a certain pressure range even when the pressure of the introduced gas changes, because monolayer adsorption of the compound gas is used. in this way,
Conventionally, trimethylgallium (TMG), which is an alkyl gallium, and arsine (AsH ₃ ), which is a hydride of arsenic, have been used for crystal growth of GaAs. Instead of TMG,
By using triethylgallium (TEG), which is an alkyl gallium, a high-purity GaAs growth layer can be obtained by growth at a lower temperature (for example, see the paper by Junichi Nishizawa et al. [J. Ni.
shizawa, H.Abe, T.Kurabayashi and N.Sakurai; J.Vac.Sc
i.Technol.A Vol. 4 (3), (1986) pp. 706-710]. According to this method, a high-purity single-crystal thin film having a flat surface can be obtained at a growth temperature of about 300 ° C. [Problems to be Solved by the Invention] By the way, in order to obtain good quality crystals by MBE described above, it is necessary to set the growth temperature to a high temperature of 500 to 600 ° C., but to realize a steep impurity profile. In this case, 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 generation of crystal defects such as oval defects also occur. On the other hand, it is clear that MLE can be grown at a lower temperature than MBE and is superior in film thickness controllability, but it has some problems as described below. That is, in MLE, since the growth of a monomolecular layer is fundamental, the uniformity of crystal growth is good. For example, in the growth of Al _x Ga _{1 -x} As, which is one of the ternary compound semiconductors, trimethyl is used as a group III alkyl metal compound. Gallium (TMG) and trimethylaluminum (TMA) form arsine (AsH
₃ ) is used. When a methyl-based alkyl metal compound is used, the dependence of the growth thickness on the plane orientation of the crystal substrate increases. For example, even if a single molecular layer is grown on the (100) plane, (11) of the side wall of the groove provided on the (100) plane
1) It may not grow on other plane orientations such as a plane, or the growth rate may be very low. Furthermore, when an ethyl-based alkyl metal compound such as triethylaluminum (TEA) or triethylgallium (TEG) is used, the plane orientation dependence is small and almost disappears under certain conditions. In this case, the directivity depending on the incident direction of the introduced gas molecules is reduced. Will be expressed. Further, when the directivity of the incident direction of the gas molecules is lost, the gas molecules collide with the inner wall of the vacuum vessel and release impurities, so that the purity of the formed film is reduced. [Purpose of the Invention] In view of the above, the present invention makes it possible to grow a thin film with good uniformity and step coverage even on a large-area substrate or a substrate having irregularities in the above-described MLE. It is an object of the present invention to provide an epitaxial growth method of a semiconductor crystal and a molecular layer epitaxy apparatus used for the method, which is effective for growing a thin film on a side wall portion formed by a concave portion or a convex portion. [Means and Actions for Solving the Problems] According to the first aspect of the present invention, the above object is achieved by introducing gas from each of a plurality of source gas sources provided outside the growth chamber. Nozzles are introduced to the vicinity of the crystal substrate installed in the evacuated growth chamber, and each source gas is alternately pulsated from each gas outlet of the nozzle to form a semiconductor crystal on the crystal substrate. In the method of epitaxially growing layers by layer, the nozzle is formed so that conductance from a gas inlet to a plurality of pipe-shaped gas outlets is equal, and each end of the pipe-shaped gas outlet is formed into a flat shape. Thus, the source gas is introduced into the crystal growth chamber in a direction from the pipe-shaped gas ejection port toward the crystal substrate. Achieved by the Long Law. According to the method of the present invention, the source gas is ejected from a plurality of directions toward the crystal substrate while having directivity through a plurality of flat gas ejection ports, and directly reaches the crystal substrate, thereby achieving the conventional method. Therefore, uniform step coverage can be easily obtained even on a large-sized crystal substrate, and impurities can be mixed from the inner wall of the vacuum vessel. There is no.
Thus, this method makes it possible to control the thickness of the semiconductor crystal thin film on the order of single molecules and does not exhibit directivity, so that even on a large-area crystal substrate having irregularities, even on these irregularities. High-purity crystal growth is possible. Further, the invention described in Item 6 is a crystal growth chamber capable of maintaining a high vacuum inside, a susceptor holding a crystal substrate in the crystal chamber, a vacuum exhaust system for evacuating the crystal growth chamber, and a growth chamber. A plurality of gas introduction nozzles each of which is introduced from a source gas source of a plurality of types of source gases provided outside to a vicinity of a crystal substrate installed in a growth chamber evacuated, and a plurality of gas introduction nozzles. In a molecular layer epitaxy apparatus in which a semiconductor crystal is epitaxially grown on a monocrystalline layer by monolayer on the crystal substrate by alternately pulsating the gas jets from the gas jets of the nozzles, the gas jets of the plurality of nozzles have the same length. And a pipe having an appropriate thickness so that the conductance from the gas inlet becomes equal, and each end is formed in a flat structure. And which is characterized in that the raw material gas was set to be introduced into the crystal growth chamber in a direction towards the crystalline substrate from the pipe-shaped gas ejection ports. According to the present invention, it is possible to provide a molecular layer epitaxy apparatus capable of epitaxially growing a high-quality semiconductor crystal. EXAMPLES Hereinafter, the present invention will be described with reference to a group III-V compound semiconductor such as Al _x
The case where the present invention is applied to the Ga _1-x As MLE will be described in more detail based on an embodiment shown in the accompanying drawings. FIG. 1 shows an embodiment of a molecular layer epitaxy (MLE) apparatus for carrying out the present invention. The MLE apparatus 1 is basically provided for holding a crystal growth chamber 2 capable of maintaining the inside in an ultra-high vacuum and a crystal substrate 3 for growing a semiconductor crystal in the crystal growth chamber 2. And the raw material gas, that is, the elements necessary for the crystal to be grown, in this case, gallium (Ga), aluminum (Al), arsenic (A
gas or gaseous compound each containing s).
Gas introduction part 5 for introducing into the inside, and the above-mentioned crystal growth chamber 2
A vacuum exhaust system 7 composed of, for example, a cooling trap, a cryopump, a turbo molecular pump, etc., for evacuating the inside to an ultra-high vacuum via a gate valve 6, and a substrate heating provided in the upper part of the crystal growth chamber 2. And a lamp chamber 9 in which an infrared lamp 8 is incorporated. The gas introduction unit 5 includes three nozzles 11, 12, and 13 made of, for example, quartz, Pyrex glass, stainless steel, and the like, which are disposed toward the crystal substrate 3 in the crystal growth chamber 2, respectively. , 12, and 13 are cylinders of a compound gas containing gallium (Ga), aluminum (Al), and arsenic (As) via flow control mechanisms (CTL) 11a, 12a, and 13a and valves 11b, 12b, and 13b, respectively. (Not shown). The flow rate adjusting mechanisms 11a, 12a and 13a are controlled by the gas introduction mode control system 14 as shown in a time chart of FIG. 2, for example, whereby the flow rate and the introduction rate of the source gas introduced into the crystal growth chamber 2 are increased. Time can be controlled accordingly. Each of the nozzles 11, 12, and 13 has the same shape, and a gas ejection port shown in FIG. 6 is connected to each tip. In the conventional MLE apparatus, the gas ejection port is provided with one gas ejection port 11c as shown in FIG. 3, but according to the present invention, the nozzle 11 is, for example, as shown in FIG. Pipe-shaped gas outlets 11d, 11e, 11
f, and the tip of the spout forms a flat structure as shown in FIG. Each gas outlet 11d, 11e, 11f has the same length, but is formed to an appropriate thickness so that the conductance from the gas inlet 11g is equal,
Thus, the same amount of source gas is introduced from each of the pipe-shaped gas outlets 11d, 11e, 11f having a flat structure at the tip. Further, as shown in FIG. 5, for example, the nozzle 11 forms a pipe-shaped gas ejection port for ejecting a plurality of gases, that is, pipe portions 11i inside the annular passage 11h, and the thickness of each pipe portion 11i is the same. An amount of feed gas is selected to be introduced through these. The shape of the gas outlet has a flat structure as shown in FIG. As a result, the distribution of the source gas on the crystal substrate 3 becomes more uniform, and even when a large-area crystal substrate is used, uniform step coverage can be obtained over the entire substrate. In addition, as shown in FIG. 6, the tip of the pipe-shaped gas outlet is formed to be flat like a laterally crushed shape or an elliptical shape, and is ejected from the pipe-shaped gas outlet by this flat shape. Since the gas molecules spread in the horizontal direction, the in-plane distribution of the gas supplied onto the crystal substrate 3 becomes more uniform, and it becomes possible to grow crystals on the crystal substrate having a larger area. The embodiment according to the present invention is configured as described above,
When crystal growth of Al _x Ga _{1 -x} As is performed using this MLE apparatus 1, the following procedure is performed. First, the crystal substrate 3 is set on the quartz susceptor 4 in the crystal growth chamber 2 of the MLE apparatus 1, and the inside of the crystal growth chamber 2 is evacuated to about 10 ^-8 to 10 ^-10 Torr by a vacuum evacuation system 7 through a gate valve 6. Evacuate until the pressure reaches. Next, the infrared lamp 8 is turned on to heat the crystal substrate 3 to a predetermined temperature, and a certain temperature, for example, 250 to 500
Keep in the range of ° C. Subsequently, each source gas, that is, a compound gas containing gallium (Ga), aluminum (Al), and arsenic (As) is supplied to a predetermined amount by the action of the flow rate adjusting mechanisms 11a, 12a, and 13a controlled by the gas introduction mode control system 14. Flow through each nozzle 11, 12, 13 at a flow rate. In the case of the embodiment shown in FIG. 4, the gas is ejected onto the crystal substrate 3 from a gas ejection port (flat structure shown in FIG. 6) provided at the tip of the nozzle. that time,
For example, triethyl gallium (TEG) is used as a compound gas containing gallium (Ga), triisobutyl aluminum (TIBA) is used as a compound gas containing aluminum (Al), and arsine (AsH ₃ ) is used as a compound gas containing arsenic (As). Here, the gas control mode controlled by the gas introduction mode control system 14 is, as shown in FIG. 2, the introduction waiting time t ₀ and the introduction time t _{1 of} the compound gas containing Al, and the introduction of the compound gas containing Ga. The waiting time t ₂ and the introduction time t ₃ , and the introduction waiting time t ₄ and the introduction time t ₅ of the compound gas containing As, the time required for one cycle for introducing a series of source gases t ₆
In this gas introduction mode, a single angstrom Al _x Ga _1-x As single crystal thin film is grown. In the above gas introduction mode, the gas introduction pressure of the compound gas containing Al is 10 ^-6 to 10 ^-4 Torr, and the gas introduction pressure of the compound gas containing Ga contains 10 ^-6 to 10 ^-4 Torr, As. The gas introduction pressure of the compound gas is 10 ^-5 to 10 ^-3 Torr, and t ₀ = 0
5 seconds, t ₁ = 0 to 6 seconds, t ₂ = 0 to 5 seconds, t ₃ = 1 to 6 seconds, t ₄ = 0
5 seconds, t ₅ = 5 to 20 seconds, is set to t ₆ = six to forty-seven seconds.
Thus, the thickness of the Al _x Ga _1-x As crystal grown by one cycle of the gas introduction mode is in the range of 1 to 10 °. Therefore, the value of one molecular layer is about 2.8Å on the (100) plane.
Since it is about 3.3Å on the (111) plane, the gas introduction pressure and introduction time of each source gas can be appropriately selected to
Crystal growth of one molecular layer can be easily achieved by gas introduction in the cycle. Similarly, the Al composition x of Al _x Ga _{1 -x} As can be arbitrarily selected in the range of 0 <x <1 by appropriately selecting the gas introduction pressure and the introduction time of each source gas. . FIG. 7 shows an example of the structure of the crystal substrate 3 used for evaluating the in-plane distribution of the film thickness of the crystal growth in the MLE method according to the present invention. The crystal substrate 3 has a size of 15 mm × 15 mm. A Si ₃ N ₄ film 32 is formed on the surface of a GaAs crystal substrate 31 by plasma CVD using SiH ₄ and NH _3, and has a width of 200 μm and a thickness of 10 μm.
A square G defined by the Si ₃ N ₄ film 32 is formed by patterning a mesh of
aAs crystal substrate surface 33 in the vertical direction from A to L, horizontal direction from 1 to 1
Number 1 and sign. Using this crystal substrate 3, the substrate temperature 3
80 ° C, TEG, AsH ₃ introduction pressure 3 × 10 ^-6 Torr, 2 × 10 ^-4 Torr
And the gas introduction mode is (10 ″, 2 ″, 2 ″, 2 ″), that is, AsH ₃
With the introduction time at 10 seconds, the AsH ₃ exhaust time at 2 seconds, the TEG introduction time at 2 seconds, and the TEG exhaust time at 2 seconds, the nozzle shown in FIG.
When the film thickness of the crystal growth was measured by a contact step meter,
A film thickness distribution for crystal growth as shown in FIG. 8 was obtained. As a result, on a substrate of 15 mm x 15 mm, ± 2%
It has been found that a film thickness distribution of crystal growth within can be achieved. FIGS. 9 (A) to 9 (C) show the above-described MLE apparatus 1 using a crystal substrate 3 on which uneven portions 3a, 3b, 3c having different shapes are formed by, for example, wet etching or dry etching. This shows an example in which a molecular layer epitaxy of Al _x Ga _{1-x As} 3 ′ was performed on a substrate, and in each case, almost the same crystal growth film thickness was obtained in the plane portion and the side portion, and the side portion, particularly the As shown in FIG. 9 (A), it was found that a uniform molecular layer could be formed even on the side portion facing downward. Note that, in the following description, Al _x Ga
_The case where the crystal growth of _1-x As is performed has been described. However, the present invention is not limited to this. For example, TMIn (trimethylindium), TEI
n (triethylindium), PH ₃ (phosphine), etc., can be used together to obtain GaP, InP, InAs, In _x Ga _1-x A
s, In _x Ga _1-x P, InAs _x P _1-x , GaAs _X P _1-x , In _x Ga _1-x As _y P _1-y , Al
_For the molecular layer epitaxy of III-V compounds such as _x Ga _1-x P, DEZn (diethyl zinc), DETe (diethyl tellurium), DESe (diethyl selenium), H ₂ Se (hydrogen selenium), ZnS, ZnTe, ZnSe _x Te _1-x using H ₂ S (hydrogen sulfide)
It is obvious that the present invention can also be applied to molecular layer epitaxy of II-VI group compounds, and the same effects can be obtained. In the molecular layer epitaxy described above, for example,
In the case of doping in III-V compound semiconductors, Si, II and VI elements are used as dopants, and these are used as Si ₂ H ₆ , DEZn, DETe, DESe, H ₂ Se, H ₂ S, etc. If the compound gas is obtained by introducing the compound gas into the crystal growth chamber through the nozzle of the present invention, the uniformity of the in-plane distribution of the dopant is remarkably improved. Furthermore, SiCl ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , SiH ₃ Cl, SiH ₄ etc.
Si compound gas and gases such as H ₂ and HCl are introduced alternately to form a single crystal
Also in the Si molecular layer epitaxy in which Si is crystal-grown one molecular layer at a time, the uniformity of the in-plane distribution of the film thickness of each molecular layer grown film is significantly improved by the crystal growth method according to the present invention. [Effects of the Invention] As described above, according to the present invention, a source gas is ejected toward a crystal substrate from a plurality of directions via a plurality of pipe-shaped gas ejection ports, and directly reaches the crystal substrate. Thereby, a more uniform supply of the source gas can be performed than when the source gas is introduced from one direction in the related art. Therefore, uniform step coverage can be easily obtained even on a large-area crystal substrate. Further, since the gas outlet is formed in a flat shape, the raw material gas does not collide with the inner wall of the vacuum vessel, so that a high-purity crystal containing no impurities can be obtained. Also, in the case of growing a ternary mixed crystal semiconductor by molecular layer epitaxy, for example, in the case of crystal growth of Al _x Ga _{1 -x} As, the uniformity of the in-plane distribution of the value of the composition x of Al is significantly improved. Becomes Thus, according to the present invention, it is possible to control the thickness of the semiconductor crystal thin film on the order of single molecules, and the directivity does not appear. , Uniform crystal growth is possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of one embodiment of an MLE device for carrying out the present invention, FIG. 2 is a time chart showing an example of an introduction mode of the MLE device of FIG. FIG. 4 is a perspective view showing an example of a nozzle used in a conventional MLE apparatus, FIGS. 4 and 5 are perspective views showing examples of forming a nozzle used in the MLE apparatus of FIG. 1, and FIG. 4 and 5 are perspective views showing the tip of a pipe-shaped gas outlet of the nozzle of FIG. 4. FIG. 7 shows an example of the structure of a crystal substrate used for evaluating the in-plane distribution of the film thickness of crystal growth. 8A shows a plan view, FIG. 8B shows a partial sectional view, and FIG. 8 shows a film thickness distribution of a crystal growth film when crystal growth is performed using the crystal substrate of FIG. 9A is a three-dimensional graph, FIG. 9B is a horizontal graph, and FIG. 9C is a vertical graph. FIGS. 9A to 9C have uneven portions. Although was crystal grown by MLE apparatus of FIG. 1 using the crystal substrate is a sectional view. 1,41 …… MLE device; 2… Crystal growth chamber; 3 …… Crystal substrate; 3 ′
…… Crystal growth film; 3a, 3b, 3c …… Unevenness part; 4 …… Quartz susceptor; 5 …… Gas introduction part; 6… Gate valve; 7… Vacuum exhaust system; 8 …… Infrared lamp; 9… … Lamp room; 11, 12, 13, 42, 43,
44 …… Nozzle; 11a, 12a, 13a …… Flow control mechanism; 11b, 12b, 1
3b …… Valve; 11c, 11d, 11e, 11f …… Pipe-shaped gas outlet; 11g …… Gas inlet port; 11h …… Circular path; 11i, 42a …… Tube section; 14 …… Gas introduction mode control system; 31: GaAs crystal substrate; 32: Si ₃ N ₄ film; 33: GaAs crystal substrate surface.

   ────────────────────────────────────────────────── ─── Continuation of front page    (56) References JP-A-61-160927 (JP, A)                 JP-A-63-129610 (JP, A)

Claims (1)

(57) [Claims] From each source gas source of a plurality of types of source gases provided outside the growth chamber, a nozzle for introducing each gas is introduced and introduced to the vicinity of the crystal substrate installed in the evacuated growth chamber. In the method in which a semiconductor crystal is epitaxially grown on a monocrystalline layer on the crystal substrate alternately in a pulsed manner from each gas ejection port of the nozzle, the nozzle is connected to a plurality of pipe-shaped gas ejection ports from a gas introduction port. The source gas is formed into the crystal growth chamber in a direction from the pipe-shaped gas jet toward the crystal substrate by forming the conductance so as to be equal and making each end of the pipe-shaped gas jet flat. An epitaxial growth method of a semiconductor crystal, characterized by being introduced. 2. 2. The method according to claim 1, wherein a portion of the nozzle including a plurality of gas outlets is heated to a predetermined temperature. 3. The at least one source gas is a gas containing a group III element, a gas containing a group V element,
An epitaxial growth method of a semiconductor crystal according to claim 1. 4. The at least one source gas is a gas containing a group II element, a gas containing a group VI element,
An epitaxial growth method of a semiconductor crystal according to claim 1. 5. 2. The method according to claim 1, wherein the at least one kind of source gas is a gas containing a group IV element. 6. A crystal growth chamber capable of maintaining a high vacuum inside, a susceptor for holding a crystal substrate in the crystal chamber, a vacuum exhaust system for evacuating the crystal growth chamber, and a plurality of types of source gases provided outside the growth chamber A plurality of gas introduction nozzles each introduced and piped to the vicinity of a crystal substrate installed in a growth chamber evacuated from each of the source gas sources, and the source gases are pulsed from each gas outlet of the nozzle. In a molecular layer epitaxy apparatus in which semiconductor crystals are epitaxially grown one by one on the crystal substrate by alternately ejecting the same, each gas ejection port of the plurality of nozzles is formed to have the same length, and from the gas introduction port. Are formed in a pipe shape having an appropriate thickness so that the conductances thereof are equal, and further, each end thereof is formed in a flat structure. A molecular layer epitaxy apparatus for use in an epitaxial growth method of a semiconductor crystal, which is introduced into a crystal growth chamber in a direction from an ip-shaped gas ejection port toward a crystal substrate. 7. 7. The molecular layer epitaxy apparatus according to claim 6, wherein a portion including the plurality of pipe-shaped gas ejection ports of the nozzle is heated to a predetermined temperature. 8. The at least one source gas is a gas containing a group III element, a gas containing a group V element,
7. A molecular layer epitaxy apparatus for use in a method for epitaxially growing a semiconductor crystal according to claim 6. 9. The at least one source gas is a gas containing a group II element, a gas containing a group VI element,
A molecular layer epitaxy apparatus for use in a method for epitaxially growing a semiconductor crystal according to claim 6. 10. 7. The method according to claim 6, wherein the at least one kind of source gas is a gas containing a group IV element.
Molecular layer epitaxy apparatus used for the epitaxial growth method of a semiconductor crystal according to the above item.