JPH01294594A - Molecular beam epitaxial growing unit - Google Patents

Abstract

PURPOSE:To provide the title unit so designed that a semiconductor substrate is irradiated with electron beams through a shielding plate intermittently shielding electron beams synchronously with substrate rotation and by detecting the reflectively diffracted electron beams using a detector, thereby observing the growth rate of a crystal during its growth in high accuracy. CONSTITUTION:A semiconductor substrate 110 is supported by a rotatable substrate holder 109 equipped with in a vacuum container 101, and molecular beams are emitted from beam sources 102, 103 while rotating the holder to grow an epitaxial growth layer on the substrate 110. At the same time, electron beams are emitted through an electron gun 111 and irradiated on the substrate 110 via a shielding plate 113 intermittently shielding electron beams synchronously with the rotation of the substrate 110, and the electron beams reflectively diffracted from the substrate 110 are detected using a detector 115; thereby enabling the intensity vibration of RHEED diffraction images to be observed during crystal growth without the need for stopping the rotation of the substrate 110 and the crystal growth rate to be determined on real time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a molecular beam epitaxial apparatus for growing, for example, crystals of a semiconductor multilayer thin film structure.

(Prior Art) Molecular beam epitaxial growth (hereinafter abbreviated as MBE) is a technique for growing a semiconductor single crystal film by irradiating a semiconductor substrate with a molecular beam emitted from a molecular beam source in a vacuum chamber.

A semiconductor element with excellent characteristics can be manufactured using a crystal with a multilayer thin film structure grown by the MBE method (thickness per layer ranges from several to several hundred amps). In order to manufacture such a semiconductor crystal, it is necessary to accurately measure the growth rate of the crystal and achieve a predetermined film thickness.

An example of a conventional molecular beam epitaxial growth apparatus (hereinafter abbreviated as MBE apparatus) will be explained with reference to the cross-sectional view shown in FIG. A plurality of molecular beam sources (12) are installed in the vacuum container (11).
), (13) are installed, and each of them is provided with shutters (14), (15) for opening and closing the molecular beam.

Molecular beam? A semiconductor substrate holder (19) holding a semiconductor substrate (20) is located at a position facing R(12), <13).
) is provided. An electron gun (21) for irradiating semiconductor substrates and grown crystals with electron beams, and a fluorescent screen (24) that projects the diffraction image of the electron beam reflected from the crystal surface.
is located.

By projecting the diffraction image of the electron beam emitted from the electron gun (21) on the fluorescent screen (24), it is possible to examine the surface condition and crystallinity of the semiconductor substrate and the grown crystal.

Conventionally, the following procedure has been used to determine the growth rate of a crystal grown using the above-mentioned MBE apparatus. After the crystal growth is completed, the crystal is cleaved and its cross section is etched to make it easier to see the boundary between the grown layers.The film thickness is measured using a scanning electron microscope (SEM), and the film thickness and growth time are Calculate growth rate. However, with this method, the growth rate cannot be determined until after all layers have been grown. Furthermore, the growth of a multilayer film has the disadvantage that even if the thickness of one of the layers is out of specification, the entire multilayer film becomes defective. Furthermore, in the case of extremely thin films, the measurement accuracy was poor or measurement was impossible.

Recent research on MBE has shown that 10k during crystal growth.
An electron beam accelerated with a high energy of about eV is incident on the crystal surface at an angle almost parallel to the crystal surface, and its reflected electron beam diffraction image (R
Observation of the HEED diffraction image revealed the following. The diffraction intensity of the RHEED diffraction image varies periodically with time, and the variation corresponds to the crystal growth process.

- As an example, Fig. 7 shows GaAs (gallium arsenide) (0
01) shows how the reflected electron diffraction pattern intensity changes over time due to incidence in the <110> direction. It is known that one period of this oscillation corresponds to the growth of one atomic layer of GaAs.

Based on the above knowledge, by observing the period of the diffraction intensity of this RHEED diffraction image, it becomes possible to know the growth rate on an atomic scale in real time and control the growth. However, in order to observe the vibration of this RHEED diffraction image, the direction of incidence of the electron beam on the crystal needs to be in a constant crystal orientation. Therefore, in normal growth, it is not possible to rotate the substrate, which is essential for maintaining the uniformity of the grown layer. Therefore, in the past, it was necessary to precisely control growth by stopping the rotation of the substrate and observing the intensity of the RHEED diffraction image. However, in this method, since the rotation of the substrate is stopped, the in-plane uniformity of the grown layer deteriorates, and the desired precise film thickness control of the semiconductor crystal cannot be performed.

(Problems to be Solved by the Invention) As described above, in the method of observing the crystal layer thickness by cutting the sample and stain-etching the cross section after the completion of crystal growth, the thickness of the grown layer cannot be measured until after the completion of growth. Or you don't know the growth rate. On the other hand, in the method of determining the growth rate by observing vibrations in the diffraction intensity of a RHEED diffraction image, the in-plane uniformity of the grown layer deteriorates because the substrate cannot be rotated. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a growth apparatus that can accurately observe the growth rate of a crystal during crystal growth and control the growth thickness on an atomic layer scale.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, in the present invention, in an MBE apparatus, an electron beam incident on a semiconductor substrate is intermittently blocked in synchronization with the rotation of the semiconductor substrate. A mechanism for observing and signal-processing the reflected and diffracted electron beam in synchronization with the rotation of the substrate is provided, and the crystal surface is irradiated with the electron beam while the crystal is growing on the substrate, resulting in RHEED diffraction from the crystal surface. By observing images, it is possible to simultaneously monitor the growth of crystal layers and the growth rate on an atomic layer scale.

(Function) By providing a mechanism for intermittently blocking the electron beam incident on the semiconductor substrate in synchronization with the rotation of the semiconductor substrate, or a mechanism for observing and signal processing the reflected and diffracted electron beam in synchronization with the rotation of the substrate. Even for a rotating substrate, only RHEED diffraction images from a constant crystal orientation can be viewed.

This allows RHE from a certain crystal orientation during crystal growth.
By observing the intensity oscillation of the ED diffraction image, the growth rate of the crystal can be determined in real time with high precision.

(Embodiment) FIG. 1 shows an embodiment in which the present invention is applied to molecular beam epitaxial growth of a ■-V group compound semiconductor, for example, GaAs.

A Ga and As molecular beam source (1) is placed in a vacuum container (101).
02).

(103) and shutters (104) and (105) are installed, and a semiconductor substrate holder (109) with a GaAs substrate (110) attached is installed at a position facing the molecular beam sources (102) and (103), This semiconductor substrate holder (109) can be rotated at the center of its plane about an axis perpendicular to the plane.

(111) is an electron gun, and the RHEED diffraction image is projected onto a fluorescent screen (114), and a detector (115) consisting of an optical fiber and a photomultiplier tube is attached to the outside of the fluorescent screen (114). , changes in the diffraction image intensity can be observed.

Immediately before the electron gun (lit), there is a rotary plate (113) with slits as shown in Figure 2, for example, and a rotary plate (113) with a width of several hundred μm.
A slit (121) of about 100 mm is opened. Rotating plate (1
13), the electron beam is intermittently blocked by the presence of the slit (121). The timing at which the slit rotates and the electron beam enters the GaAs substrate (110) and the substrate rotation are determined by the R) I of the always fixed crystal orientation of the GaAs substrate.
They are synchronized so that the EED diffraction image can be observed on the fluorescent screen (114).

Next, the operation of the above-described molecular beam epitaxial growth apparatus will be explained.

The surface of the heated GaAs substrate (110) is cleaned while being irradiated with an As molecular beam from an As molecular beam source (103) through a shutter (105). After that, G is applied to the rotating GaAs substrate (110) through the shutter (104) of the Ga molecular beam source (102).
Perform aAs growth. Rotating plate with slits (11
3) while rotating, irradiate an electron beam from the electron gun (1, 11), and project the RHEED diffraction image of the electron beam incident from the <110> direction of the GaAs (001) surface on the fluorescent screen (114), for example. A detector (115) detects intensity oscillations of a bright spot selected in advance for ease of observation, and this is appropriately displayed on a display device. The rotation of the slit is adjusted in advance to be synchronized with the rotation of the substrate so that only the diffraction image of the (001) plane in the <110> direction can be observed.

Normally, the crystal growth rate in MBE method is 0.5 μm
/h to 1 μm/h, and at this time, the period of intensity oscillation of the RHEED rotating image is about 1 second.

When performing growth, the substrate is rotated 6 to 8 times/second, and the rotating plate with slits (113) shown in FIG.
It is possible to observe the vibrations of the electron beam reflected and diffracted from the substrate while rotating the substrate at ~4 times/second.

When the growth of GaAs begins, RIIEED oscillations as shown in FIG. 3, for example, can be observed, and this oscillation period is a reflection of the growth process of the monoatomic layer.

Note that, according to the above, the rotary plate with slits (+13) was provided between the electron gun (111) and the semiconductor substrate holder (109), but this was also installed between the semiconductor substrate holder (109) and the detector (115). There is no problem even if it is provided in between.

Next, FIG. 4 shows the main part of another embodiment. To explain below, a set of two well-known parallel plate electrodes (202) are placed immediately before an electron gun (203) in a vacuum container (201).

(202) is placed. This parallel plate electrode (202),
(202) By changing the applied voltage between the electrodes, the electron beam can be deflected in any direction between the electrodes.

Therefore, by appropriately changing the applied voltage, the electron beam can be made to be incident on the semiconductor substrate or not made to be incident on the semiconductor substrate intermittently. Furthermore, by changing the applied voltage in synchronization with the rotation of the substrate so that the electron beam is incident on the substrate for an extremely short period of time in synchronization with the rotation of the substrate, R)IEED diffraction of the always fixed crystal orientation of the semiconductor substrate can be observed. Only the image can be observed. G under the same conditions as in the above example.
When aAs was grown, RH occurred several dozen times during the growth.
We were able to observe EED vibrations.

Furthermore, instead of intermittent electron beams using the rotary plate with slits or the parallel plate electrodes in each of the above-mentioned embodiments, it is also possible to detect the intensity of the RHEED diffraction image projected on the fluorescent screen and sample the intensity signal. good. According to this method, sampling is performed in synchronization with substrate rotation, and only RIIEED diffraction images of specific crystal orientations can be observed. That is, this method will be explained with reference to FIG.

Note that the same parts as in FIG. 1 are given the same numbers, and detailed explanations are omitted. Outside the fluorescent screen (114) is a detector (l1) consisting of an optical fiber and a photomultiplier tube.
A detection device including 5a) and a signal processing circuit is provided, and is capable of observing changes in diffraction image intensity. That is, unnecessary frequency components are removed from the output signal from the detector (115a) by the bandpass filter (115b). Next, it is sampled and held by a sample and hold device (115c), detected by a DC minute voltmeter (115d), and inputted to a recorder (115e). The sampling pulse input to the sample hold device (l15a) is generated by a sampling pulse generator (115'') from a synchronization signal based on the rotation of the substrate.

In all of the above examples, the surface of the grown GaAs was good, and no abnormality was observed in the grown layer compared to normal growth. The observed oscillations indicate that GaAs during crystal growth
The growth rate can be determined while maintaining the uniformity of the grown layer, making it possible to control growth on a monoatomic layer scale.

In this example, growth of GaAs was described, but AlGa
It can also be applied to the growth of other crystals such as As.

It goes without saying that the present invention is not limited to the above-described embodiments, and that various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described above, according to the present invention, it is possible to observe the intensity oscillation of the RHEED diffraction image while rotating the substrate during growth, and it is possible to observe the intensity fluctuation of the RHEED diffraction image precisely during growth while maintaining the uniformity of the growth layer. Furthermore, it is possible to provide a molecular beam epitaxial growth apparatus that allows the crystal growth rate to be known in real time.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a molecular beam epitaxial apparatus illustrating an embodiment of the present invention, FIG. 2 is a perspective view showing a rotary plate with slits in FIG. 1 of the present invention, and FIG. FIG. 4 is a cross-sectional view of a main part of a molecular beam epitaxial growth apparatus showing another embodiment of the present invention, and FIG. A diagram showing a molecular beam epitaxial growth apparatus according to another embodiment, FIG. 6 is a sectional view of a conventional epitaxial growth apparatus, and FIG. 7 is a conventional RHEE in the example of FIG. 6.
It is a figure which shows an example of the intensity vibration of a D diffraction image. 11.101,201...Vacuum container 10
2.103,12.13...Molecular beam source 104.105
, 14.15... Molecular beam source shutter 109.19.
...... Semiconductor substrate holder 20.
・・・・・・・・・・・・・・・・・・ Semiconductor substrate 110 ・・・・・・・・・・・・・・・・・・CaAs
Substrate 113......Disc plate with slit 121......
・Slit 111.203.21... Electron gun 114.24... Fluorescent screen 202...・・・・・・
・Parallel plate electrodes 115.115a, 25...Detector 116...Detection device 115b...・・・・・・Band pass filter 115C・・・・・・・・・・・・・
...Sample hold device 115d...
・・・・・・・・・DC minute voltmeter 115e...
・・・・・・・・・・・・・・・Recorder 115r...
・・・・・・・・・・・・・・・・Sampling pulse generator applicant's agent Patent attorney Close aide Kensuke Sanno - 101 Okuken Yutsu 115 Detection 6 Figure 2 Figure 3 Figure 4 L -----J

Claims (3)

[Claims] (1) A molecular beam source that emits a molecular beam, a semiconductor substrate holder that is arranged opposite to the molecular beam source and rotates about one axis, and emits an electron beam to the semiconductor substrate held by the semiconductor substrate holder. a shielding plate that intermittently blocks the electron beam emitted from the electron gun in synchronization with the rotation of the semiconductor substrate holder, and housing the molecular beam source, the semiconductor substrate holder, the electron gun, and the shielding plate. A molecular beam epitaxial growth apparatus, comprising: a vacuum vessel for carrying out the electron beam; and a detector for detecting electron beams that are irradiated onto the semiconductor substrate by the electron gun and reflected and diffracted from the semiconductor substrate. (2) A molecular beam source that emits a molecular beam, a semiconductor substrate holder that is arranged opposite to the molecular beam source and rotates about one axis, and emits an electron beam to the semiconductor substrate held by the semiconductor substrate holder. an electron beam intermittent deflection device that intermittently deflects an electron beam emitted from the electron gun by an electric field in synchronization with the rotation of the semiconductor substrate holder, and these molecular beam sources, the semiconductor substrate holder, and the electron gun. and a molecular beam epitaxial growth apparatus comprising: a vacuum container housing an electron beam intermittent deflection device; and a detector configured to detect an electron beam irradiated onto the semiconductor substrate from the electron gun and reflected and diffracted from the semiconductor substrate. (3) A molecular beam source that emits a molecular beam, a semiconductor substrate holder that is arranged opposite to the molecular beam source and rotates about one axis, and that emits an electron beam to the semiconductor substrate held by the semiconductor substrate holder. an electron gun, a molecular beam source, a semiconductor substrate holder, a vacuum container housing the electron gun, and a diffraction intensity signal of an electron beam irradiated from the electron gun to the semiconductor substrate and reflected and diffracted from the semiconductor substrate. A molecular beam epitaxial growth apparatus comprising a detection device having a detector for detecting the diffraction intensity signal and a signal processing circuit for sampling the diffraction intensity signal in synchronization with the rotation of the semiconductor substrate holder.