JPH07263512A - Measuring method for dimer density of outer surface of semiconductor and its organic metal vapor phase growth method - Google Patents

Abstract

PURPOSE:To provide a measuring method for the dimer density of the outer surface of a semiconductor for measuring the dimer density of the outer growing surface of a compound semiconductor during crystal growth and an organic metal vapor phase growing method using said measuring method. CONSTITUTION:P-polarized incident light 12 is radiated near the angle of polarization to the surface of a semiconductor substrate 11 being crystal-growing on the surface, reflected light 13 obtained by reflection from the surface of the semiconductor substrate 11 is detected, and the situation of the surface of the semiconductor substrate is observed from the difference in reflectance of the reflected light 13. At this time, while crystal-growing on a plurality of sloped substrates having difference angles of slope, the relation between the decrease in dimer density of the surface of a sloped substrate in response to the increase of the sloped angle and the change in the difference of reflectance is measured in advance and, in this way, the information of the change in reflectance difference signal due to the surface dimer density obtained is compared to the reflectance difference signal obtained from the reflected light detected, and the dimer density of the top surface layer of the semiconductor substrate is measured at that place.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the measurement of the bonding state of atoms or molecules on the outermost growth surface in the crystal growth of III-V group compound semiconductors and a crystal growth method using the same.

[0002]

2. Description of the Related Art In order to realize an optical functional device or an electronic functional device, it is indispensable to improve the crystal growth technique for a high quality III-V compound semiconductor. Recently, in order to realize an advanced optical / electronic functional device having a semiconductor quantum well structure, a plurality of semiconductor thin films grown under control in atomic order on a III-V compound semiconductor substrate are stacked to form atomic order crystal growth. Technology is evolving. In order to establish atomic-order crystal growth technology on semiconductor substrates,
It is essential to understand the crystal growth mechanism and improve the observation and analysis technology for the outermost surface of crystal growth.

A scanning tunneling microscope (STM) is well known as a technique for observing and analyzing the outermost surface of crystal growth of a III-V group compound semiconductor in atomic order. It is known by STM observation of the outermost surface that the atoms and molecules of the semiconductor constituent material form a surface structure in various bonding states on the outermost surface of the semiconductor. As a typical example, M. D. Pa
shley, K .; W. Hab erern, W.M. Fri
day, J.M. M. Woodall and P.W. D. K
irchner's paper "Structure o
f GaAs (001) (2 × 4) -c (2 × 8) De
terminated by Scanning Tun
nelling Microscopy ”, Phys.R
ev. Lett. No. 60, (1988), 2176, and observation of the outermost surface of a (001) substrate of GaAs can be mentioned. M. D. Pashley et al. Observed from observation of the GaAs (2 × 4) surface that the (4 ×) periodicity of the (2 × 4) structure is due to the As dimer row defect structure, that is, the regular disappearance of the As dimer row. It revealed that. Here, the dimer is a dimer, which is a substance formed by the polymerization of two molecules, and Ga
On the surface of As, As binds to each other to form a dimer.

In order to improve the quality of compound semiconductors such as GaAs and InP and the quality of hetero interfaces such as InGaAs / InP, it is necessary to quantitatively observe the dimer density in-situ. The reason is that an excessive dimer exists on the outermost surface of the crystal of the compound semiconductor depending on the crystal growth conditions of the constituent raw materials, and when a molecular layer of the compound semiconductor is formed thereon, the excessive dimer causes a sharp dip in atomic order. The hetero interface cannot be formed, or excessive dimer moves to the outermost surface of the molecular layer of the new compound semiconductor, so that the stoichiometry of the compound semiconductor growth thin film layer is deviated and the quality of the crystal growth layer is deteriorated. Will lead to a decline. Therefore, the observation of the dimer density on the outermost surface of the semiconductor is
This is an extremely important issue for crystal growth of III-V group compound semiconductors, and establishment of an observation method with high analytical sensitivity is required.

In the conventional method of observing the dimer density by STM, the surface of the crystal growth substrate is directly scanned with a deep needle to measure the tunnel current, so that it is necessary to separate the compound semiconductor crystal growth chamber and the analysis / observation chamber of the growth surface. However, there are problems such as the necessity of moving the semiconductor substrate, the long growth time of the semiconductor multilayer film, and the possibility of impurities being mixed into the crystal. Further, in order to measure the tunnel current, doping with Si element or the like may be necessary depending on the observation sample.

On the other hand, the metal organic chemical vapor deposition method (MOCVD
Method for observing the growth surface during crystal growth,
The surface light absorption method (Surf) is used to utilize the reflection of light.
ace Photo Absorption: Abbreviation SP
A method). This corresponds to the electronic transition of the chemical bond contained in the adsorbed atom or molecule on the growth surface by p-polarizing visible light and ultraviolet light, entering the semiconductor substrate surface at Brewster's angle, and measuring the reflected light. The change in reflectance is observed.

FIG. 7 is a schematic diagram for explaining this SPA method. A semiconductor substrate 6 is mounted on the susceptor 5 of the MOCVD reaction tube 4. On one side around the reaction tube 4,
The light source 1, the chopper 2, and the polarizer 3 are arranged on the other side, and the photodetector 7 is arranged on the other side, and the light emitted from the light source 1 and p-polarized by the polarizer 3 is emitted to the semiconductor substrate 6, The reflected light is detected by the light detector 7. Specifically, the light emitted from the light source 1 is converted into p-polarized light by the polarizer 3 and is incident on the surface of the semiconductor substrate 6 at Brewster's angle. Of the incident light, the light corresponding to the electronic transition of the chemical bond contained in the adsorbed molecule or atom on the crystal surface is absorbed, so that the reflected light detected by the photodetection unit 7 has the reflectance corresponding to the transition. Show changes. Based on this change in reflectance, information such as decomposition and desorption of the raw material gas and surface structure can be detected with high sensitivity regardless of the presence or absence of anisotropy in the growth surface.

As described above, in the SPA method, the electronic transition of the chemical bond contained in the adsorbed atom or molecule on the semiconductor growth surface is detected as the change in reflectance, so that regardless of whether the growth surface is anisotropic or not. The crystal growth surface can be analyzed in atomic order and in real time (JP-A-3-17).
4739 publication). In fact, according to the SPA method, GaAs
When observing the state of crystal growth, the observation signal detects a periodic signal for each growth of one molecular layer, and the uppermost surface of the growth is detected in atomic order like the reflected high energy electron analysis (RHEED) signal. I know that

However, even with this SPA method, the dimer density on the surface cannot be measured. The reason is that the relationship between the reflected signal and the surface dimer density is not clear.

[0010]

As described above, in the conventional method for observing the dimer density, it is necessary to separate the compound semiconductor crystal growth chamber and the analysis / observation chamber for the growth surface, and further, each time the observation is carried out. Since it is necessary to move the semiconductor crystal growth substrate, there are problems such as a longer growth time of the semiconductor multilayer film and the possibility of impurities being mixed into the crystal. Further, depending on the observation sample, it may be necessary to dope the Si element or the like. On the other hand, even in the SPA observation method, the chemical bond signal on the outermost surface can be observed during the growth of the growth layer, but there is a problem that the relationship between the observed signal and the dimer density on the outermost surface does not correspond clearly.

The present invention provides a method for measuring the outermost surface dimer density of a semiconductor for measuring the dimer density on the outermost growth surface of a compound semiconductor during crystal growth, which is the above-mentioned problem, and a metal organic chemical vapor deposition method using the same. The purpose is to do.

[0012]

A first aspect of the present invention for achieving the above object is to irradiate a surface of a semiconductor substrate having a crystal grown on the surface thereof with p-polarized incident light in the vicinity of Brewster's angle. In the method of detecting the reflected light obtained by reflecting from the surface, and observing the situation of the semiconductor substrate surface from the reflectance difference obtained from the detected reflected light, while growing crystals on a plurality of inclined substrates with different inclination angles, Information on the change of the reflectance difference signal due to the surface dimer density obtained by measuring the relationship between the decrease of the dimer density of the inclined substrate surface with the increase of the angle and the change of the reflectance difference in advance, and the detected reflection A reflectance difference signal obtained from light, and a method for measuring the outermost surface dimer density of the semiconductor, characterized by performing in-situ measurement of the dimer density of the outermost surface layer of the semiconductor substrate. Located in.

According to a second aspect of the present invention, in the first aspect, the plurality of tilted substrates having different tilt angles are in the [-110] direction or the [110] direction from the (001) plane of the III-V group compound semiconductor. A method for measuring the outermost semiconductor surface dimer density is characterized in that a plurality of substrates are inclined in the direction.

A third aspect of the present invention is a metal-organic chemical vapor deposition method in which a semiconductor substrate is mounted in a reaction container for crystal growth, and an organic metal raw material is supplied to crystal-grow a semiconductor multilayer film on the semiconductor substrate. During the crystal growth of the semiconductor multilayer film, the semiconductor substrate is irradiated with p-polarized incident light in the vicinity of Brewster's angle, and reflected light obtained by being reflected from the surface of the semiconductor substrate is detected to detect a plurality of different tilt angles. The difference in reflectance due to the surface dimer density obtained by measuring the relationship between the decrease in the dimer density on the surface of the inclined substrate and the change in the difference in reflectance with the increase in the inclination angle while growing crystals on the inclined substrate Information on the change in the signal and the reflectance difference signal obtained from the detected reflected light are compared to measure the dimer density of the outermost surface layer of the semiconductor substrate in-situ, and based on this measurement, In metal-organic chemical vapor deposition method characterized by controlling the crystal growth conditions of the conductive multilayer film.

According to a fourth aspect of the present invention, in the third aspect, the plurality of tilted substrates having different tilt angles are in the [-110] direction or the [110] direction from the (001) plane of the III-V group compound semiconductor. The metal-organic vapor phase epitaxy method is characterized in that a plurality of substrates are inclined in the direction.

Here, the direction with respect to the crystal plane, for example, [-
"-1" in the [110] direction is usually represented by "bar 1", but is represented by "-1" in the present specification (the same applies hereinafter).

[0017]

The operation of the present invention will be described with reference to FIG. 1 using GaAs which is a III-V group compound semiconductor as an example. GaAs (001) surface 10 under As irradiation at a substrate temperature of 600 ° C.
A GaAs (2 × 4) plane is formed on the top. And
As shown in FIG. 1, in the GaAs (2 × 4) plane,
As dimer 11 has a bond along the [-110] direction. Light 12 in the visible or ultraviolet region is p-polarized and incident on the surface in the vicinity of the Brewster's angle from the [-110] direction, and the reflected light 13 is supplied to the surface (Ga surface) where the supply of As is stopped and As. The reflectance is obtained by measuring the reflectance with respect to the surface being supplied to obtain the SPA spectrum. Wavelength 470
Light near nm is absorbed by As dimer 11 having a bond in the [-110] direction, an electric dipole is induced in As dimer 11, and the same light is emitted. As a result, an increase in reflectance according to the As dimer density is observed.

When a substrate tilted from the (001) plane in the [-110] direction is used, the terrace width changes depending on the tilt angle. As the tilt angle increases, the terrace width decreases and the As dimer density on the surface decreases. That is, the dimer density on the surface can be changed by using the inclined substrate. When the SPA spectrum is measured for the substrate, the increase in reflectance due to the light absorption of As dimer (the increase in reflectance near the wavelength of 470 nm) is (0
01) surface is reduced. Since this decrease in reflectance is proportional to the surface As-dimer density, it is possible to relate a specific As-dimer density to the SPA spectrum, and the change in As-dimer density and reflectance at the wavelength of 470 nm indicates that the As-dimer light It is possible to obtain the absorption coefficient.

From the relationship between the SPA spectrum and As dimer density obtained for this tilted substrate and the optical absorption coefficient of As dimer, the As dimer density which varies depending on the growth conditions can be observed in situ during growth. For example, for a GaAs (001) substrate, if the As pressure under As irradiation at a substrate temperature of 600 ° C. is reduced, the As dimer density on the surface decreases. By measuring the SPA spectrum under the growth conditions and referring to the relationship between the As dimer density and the SPA spectrum measured for the tilted substrate and the optical absorption coefficient of As dimer, the As dimer density can be measured in situ during growth. .

[0020]

EXAMPLES Examples of the present invention will be described in detail below.

(Embodiment 1) Description will be made taking GaAs as an example. First, a substrate tilted in the [-110] direction from the (001) plane will be described.

2A and 2B are views for explaining the relationship between the substrate tilt direction and the surface structure. In FIG. 2, (a) is a non-tilted GaAs (001) plane 20, and (b) is from the (010) plane to [010] plane. Tilted 11.4 degrees in the -110] direction (117)
Regarding the B surface 21 and (c), the (113) B surface 22 inclined by 25.2 degrees from the (010) surface in the [-110] direction is
As in the As irradiation state at a substrate temperature of 600 ° C.
The surface structure is shown. The structure of the As plane is a (2 × 4) structure, and the step (step of atomic order) is a single step.

On the (001) plane 20 of (a),
As dimers with dimer bonds along the [-110] direction are formed. In the (117) B plane 21 of (b), since it is tilted by 11.4 degrees in the [-110] direction, the terrace width becomes small, and only one As dimer can exist on one terrace. As a result (00
1) Compared to the surface 20, the As-dimer density having bonds in the [-110] direction is reduced to about half. (1) of (c)
13) Since the B plane 22 is inclined at [-110] by 25.2 degrees, the terrace width is (001) plane and (11) plane.
7) It becomes smaller than the B side 21, and no As dimer can exist on one terrace, and [11
The As dimer density having bonds in the [0] direction becomes 0.

From the GaAs (001) plane 20 [-11
This corresponds to the tilt angle when tilted in the [0] direction (11
The corresponding relationship between the (n) plane (n is a positive integer) and the As dimer density is shown in FIG. GaAs surface is (2 x 4)
A dimer array missing (missing dimer) structure is used, and a monolayer (monolayer) and a bilayer (2
It shows about two cases of the (molecular layer) step. In FIG. 2, as described with reference to the schematic diagram of FIG. 1, as the tilt angle is increased, the As dimer density is reduced, and the As dimer density is significantly reduced on the (117) plane. It can be seen that no dimer is formed on the (113) plane. In the bilayer structure, (11
The As dimer density on the 4) plane is greatly reduced, and (113)
At a large inclination angle above the plane, As dimer is not formed. As described above, by using the substrate tilted from the (001) plane in the [-110] direction, the dimer density on the surface can be changed. Then, as shown below, from the observation of the SPA spectrum using this tilted substrate, the relationship between the SPA spectrum and the As dimer density, As,
It is possible to obtain the light absorption coefficient of the dimer, and based on this information, measure the As dimer density, which changes depending on the growth conditions, in-situ using the SPA spectrum.

FIG. 4 shows an embodiment of a crystal growth method using the present invention. As shown in the figure, the reaction furnace 31 is equipped with a supply pipe 34 for supplying the group V hydride (AsH ₃ ) gas 32 and the hydrogen gas 33, and for starting and stopping the supply of the AsH ₃ gas 32. Valve 35 is provided. A semiconductor substrate 37 is provided on the susceptor 36 in the reaction furnace 31.
Is placed. A radio frequency (RF) coil 38 for heating the inclined substrate 37 is provided around the reaction furnace 31. Further, a light source 39 for irradiating the semiconductor substrate 37 with visible light or ultraviolet light in the vicinity of Brewster's angle is arranged on one side of the reaction furnace 31, and a surface of the semiconductor substrate 37 is arranged on the other side. An optical multi-channel analyzer 42 for observing the reflected light from is arranged. The optical multi-channel analyzer 42 measures the reflected light from the semiconductor surface by 300-8.
The spectrum is measured over a wavelength band near 00 nm.

Using such a device, first, a GaAs (001) substrate is placed on the susceptor 36 in the reaction furnace 1 as a substrate 3.
7, the AsH ₃ gas 32 is introduced together with the hydrogen gas 33 while opening the valve 35, and the RF coil 38
The substrate 37 is heated to 600 ° C. In this state,
The substrate 37 is irradiated with p-polarized light from the light source 39 through the polarizer 40 in the [-110] direction, and the reflection spectrum is measured by the optical multichannel analyzer 42. Next, with the valve 32 closed and the supply of the AsH ₃ gas 32 stopped (in this state, As vaporizes from the substrate surface to become a Ga-only surface), the polarizer 40 is passed from the light source 39 again. The polarized light is irradiated on the substrate 37, and the reflection spectrum is measured by the optical multi-channel analyzer 42. Then, the SPA spectrum is obtained from the difference between the two reflection spectra.

Then, the substrate 37 is described with reference to FIG.
(119) B, (118) B, (117) B planes, which are inclined substrates inclined in the [-110] direction from the (01) plane.
(116) B, (115) B, (114) B, (11
3) Similar to the (001) plane, instead of the B plane, the reflection spectra of the state in which the raw material is supplied and the state in which the raw material is stopped are measured, and the SPA spectrum is obtained from the difference between the two.

FIG. 5 shows As standardized on the basis of the Ga plane.
The SPA spectrum of the surface is shown. Incident azimuth is [-110]
Direction. On the GaAs (2 × 4) surface, As dimers are bound in the [−110] direction as shown in FIG. 1, and light absorption occurs due to As dimer binding, resulting in (001)
In the plane, the level of the As plane increases near the wavelength of 470 nm. On the other hand, in the (117) B plane, as described with reference to FIGS. 2 and 3, as compared with the (001) plane, since it is inclined to [−110], the terrace width becomes smaller, and Since the As dimer density in the −110] direction decreases, the level of the As plane near the wavelength of 470 nm decreases as shown in FIG. 5, as compared with the (001) plane.
Further, in the (113) B plane, as described with reference to FIGS. 2 and 3, the terrace width is smaller than that in the (001) plane and the (117) B plane, and the [-110] direction is obtained. A
Since s-dimer is not formed, as shown in FIG.
Compared to the (001) plane and (117) B, the wavelength is 470n.
The level of As plane near m decreases. This (113) B
The level of the As plane of the plane corresponds to the As dimer density of 0.

FIG. 6 shows the As-dimer density dependence of the SPA reflection intensity difference between the Ga plane and the As-plane at the wavelength of 470 nm where the As-dimer has optical absorption from the SPA spectrum obtained in FIG. The As dimer density is (001)
It is calculated from the tilt angle of the substrate tilted from the substrate to [-110]. The obtained SPA reflection intensity difference and the As dimer density are in a substantially proportional relationship, and by using this graph, the light absorption coefficient per As dimer per unit area can be obtained.

Based on the obtained SPA spectrum, As dimer density, and optical absorption coefficient of As dimer, Ga
Different substrate temperature, different A in As (001) substrate
By measuring the SPA spectrum under s pressure, the As dimer density can be measured in situ during growth.

That is, a substrate 37 (which may be a (001) substrate or a tilted substrate) is placed on the susceptor 36 of the reaction furnace 31 described above, and the AsH ₃ gas 32 is heated while heating the substrate 37 as in the above-described example. Then, hydrogen gas 33 is supplied to vapor-deposit GaAs on the substrate 37. Here, the reflection spectrum is similarly measured while performing the vapor phase growth, and at the time of measuring the dimer density, the raw material supply is temporarily stopped and the reflection spectrum is measured. Then, the SPA spectrum is obtained from the difference between these reflection spectra, and by comparing this SPA spectrum with the relationship between the above-mentioned dimer density and the SPA spectrum, the dimer density during growth can be measured in-situ. Based on this, the growth conditions (substrate temperature, supply amount of raw material, etc.) are controlled at any time.

Although the present invention has been described in detail above using GaAs as an example, the present invention is also effective for InP and other III-V group compound semiconductors and mixed crystals.

[0033]

As described above, according to the present invention,
In-situ measurement of the outermost surface dimer density during crystal growth of III-V group compound semiconductors enables realization of high-quality and steep heterojunctions, and various devices including semiconductor quantum well structures, optical functions, and electronic functions. The device can be realized.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an operating principle of the present invention.

FIG. 2 is a diagram illustrating a substrate plane orientation and a surface structure.

FIG. 3 is a diagram showing a relationship between a substrate tilt angle and an As dimer density.

FIG. 4 is a schematic diagram for explaining an outline of an embodiment of the present invention.

FIG. 5 is a diagram showing a SPA spectrum of a GaAs (2 × 4) As plane.

FIG. 6 is a diagram showing a relationship between a reflection intensity difference at a wavelength of 470 nm and an As dimer density.

FIG. 7 is a diagram for explaining a surface light absorption method.

[Explanation of symbols]

 10 Semiconductor Substrate 11 As Dimer 12 Incident Light 13 Reflected Light 31 Reaction Tube 32 V Group Hydride 33 Hydrogen Gas 34 Supply Tube 35 Valve 36 Susceptor 37 Semiconductor Substrate 38 RF Coil 39 Light Source 40 Polarizer 42 Optical Multichannel Analyzer

Claims (4)

[Claims] 1. Reflected light obtained by irradiating p-polarized incident light on the surface of a semiconductor substrate having crystals grown on the surface in the vicinity of Brewster's angle, and detecting reflected light obtained from the semiconductor surface, and determining from the reflected light. In the method of observing the condition of the surface of the semiconductor substrate from the difference in reflectance, while growing crystals on a plurality of tilted substrates having different tilt angles,
Information on the change of the reflectance difference signal due to the surface dimer density obtained by measuring the relationship between the decrease of the dimer density of the inclined substrate surface and the change of the reflectance difference with the increase of the inclination angle, and the detected. A method for measuring the outermost surface dimer density of a semiconductor, which comprises in-situ measuring the dimer density of the outermost surface layer of the semiconductor substrate by comparing with a reflectance difference signal obtained from reflected light. 2. The plurality of tilted substrates having different tilt angles according to claim 1, wherein the tilted substrates are made of III-V group compound semiconductor (001).
A method for measuring a semiconductor outermost surface dimer density, which comprises a plurality of substrates tilted in a [-110] direction or a [110] direction from a plane. 3. A metal-organic chemical vapor deposition method in which a semiconductor substrate is mounted in a reaction container for crystal growth, and an organic metal raw material is supplied to crystal-grow a semiconductor multilayer film on the semiconductor substrate. During growth, the semiconductor substrate is irradiated with p-polarized incident light in the vicinity of Brewster's angle, reflected light obtained by reflecting from the surface of the semiconductor substrate is detected, and crystals are grown on a plurality of tilted substrates with different tilt angles. While
Information on the change in the reflectance difference signal due to the surface dimer density obtained by measuring the relationship between the decrease in the dimer density on the surface of the inclined substrate and the change in the reflectance difference with the increase in the tilt angle, and the detection By contrasting the reflectance difference signal obtained from the reflected light, in-situ measurement of the dimer density of the outermost surface layer of the semiconductor substrate, based on this measurement to control the crystal growth conditions of the semiconductor multilayer film. Characteristic metal-organic vapor phase growth method. 4. The plurality of tilted substrates having different tilt angles according to claim 3, wherein the tilted substrates are (001) III-V compound semiconductors.
2. A metal-organic vapor phase epitaxy method comprising a plurality of substrates tilted in the [-110] direction or the [110] direction from the surface.