JPH0796474B2 - Molecular beam epitaxy system - Google Patents

Description

Detailed Description of the Invention

[Industrial applications]

The present invention relates to a molecular beam epitaxy apparatus, and more particularly to an apparatus configured to more accurately monitor film formation on a substrate.

[Prior art]

A molecular beam epitaxy method is drawing attention as a method for epitaxially growing a III-V group element on a single crystal substrate in the process of manufacturing a III-V group compound semiconductor. This is a type of vacuum deposition method, and includes group III elements such as gallium Ga, aluminum Al, and indium In, and arsenic As,
Irradiation of these elements in the form of atomic or molecular beams in an ultrahigh vacuum of 10 ^-11 torr using a Group V element such as phosphorus P as a growth material.
Ga As, Al Ga A on a single crystal substrate such as As or In P
It is a method of epitaxially growing a III-V group compound semiconductor crystal such as s, InP or InGaAsP. According to such a molecular beam epitaxy method, since vapor deposition is performed in an ultra-high vacuum, impurities from residual gas are very little mixed, the surface of the substrate can be kept clean, and it is uniform over a large area. It is possible to obtain a flat film at the atomic level. The deposition rate can be extremely slowed down and the control can be performed accurately. Therefore, the film thickness can be controlled with high accuracy on the order of a few atomic layers, which is a multi-component. The mixed crystal thin film of the system can be easily obtained only by increasing the evaporation source. Various information about the growth condition can be obtained from the growth layer surface or the molecular beam during the crystal growth, and it is immediately fed back to the growth control. You can enjoy the advantages such as being able to. In order to facilitate understanding of the present invention to be described later, an outline of a molecular beam epitaxy apparatus for performing the molecular beam epitaxy method as described above, and a method for substrate deposition monitoring by a conventional atomic absorption type film deposition monitor A description will be given based on FIGS. 3 and 4. A growth chamber 2 connected to the ultra-high vacuum pump 1 has a substantially cylindrical shape, and a substrate holder 3 whose rotation is controlled around an axis l of the growth chamber is horizontally arranged in the center thereof.
The rotation of the substrate holder 3 is controlled in this manner in order to make the crystal growth on the substrate uniform.
Further, a heater (not shown) for raising the temperature of the substrate held by the substrate holder 3 to a desired temperature is attached.
On one side of the growth chamber 2 facing the substrate holding surface of the substrate holder 3, the axes a, b, c ... Are concentrated toward the center of the substrate holder 3 with respect to the axis l of the growth chamber. The inclined evaporation sources 5a, 5b, 5c ... Are arranged annularly around the axis l of the growth chamber 2 and at substantially equal distances from the substrate holder 3. Each evaporation source 5a, 5b, 5c
Is constituted by filling each growth material in a crucible 4 opening toward the center of the substrate holder 3, and is heated to a desired temperature by a heater controlled based on the temperature detected by a temperature sensor (not shown). It is supposed to be done. Also,
Each evaporation source 5a, 5b, 5c ... Is surrounded by a liquid nitrogen shroud so as not to be affected by heat and pollution by other evaporation sources. The start and stop of crystal growth are performed by opening and closing a shutter 7 arranged in front of the opening of each crucible 4. For example, in order to grow a Ga As layer on a Ga As single crystal substrate, the evaporation source filled with Ga and the evaporation source filled with As are heated to a predetermined temperature, and the temperature of the substrate holder 3 is adjusted to an appropriate value. While setting the temperature, the shutter 7 of each evaporation source is controlled to be opened for a predetermined time. At this time, when Al is evaporated together, a Ga _X Al _1-X As layer grows. The composition x can be controlled by controlling the ratio of the evaporation amounts of Ga and Al at this time. In order to make the growth layer n-type, Si,
In order to evaporate Sn and the like at the same time to form p type, Be and Mg are evaporated at the same time. By the way, as the feedback information for controlling the crystal growth on the substrate as described above, the vapor deposition rate may be detected by the atomic absorption type film formation monitor. This is an application of atomic absorption spectrometry, and as shown in FIGS. 3 and 4, a hollow cathode lamp having a wavelength peculiar to a specific element is used as a light source, and this is used from one window of the growth chamber 2. The incident light and the light emitted from the other window are guided to a photomultiplier tube after passing through a spectroscope or a filter, and the absorbance which appears as a monotone function of the density of the target element in the vapor is measured.

[Problems to be Solved by the Invention]

However, the use of the atomic absorption type film formation monitor in the molecular beam epitaxy apparatus is still in its infancy, and since the arrangement relationship between the optical path and each evaporation source is not taken into consideration, there are various problems to be solved. There is. For example, at present, in many of the molecular beam epitaxy apparatuses using the atomic absorption type film formation monitor, as shown in FIG. 3, a plurality of evaporation sources 5a, 5b, 5c ...
On the other hand, the optical path P of the atomic absorption type film formation monitor is arranged in a ring shape around the circumference, and the optical path P is set to a single path that crosses the growth chamber 2 so as to be orthogonal to the vapor axis line l. The problem arises. First, since the light path P is single, it is necessary to change the light source according to the target element, and it is not possible to simultaneously monitor the elemental vapor densities of the evaporation sources having different growth materials. . Secondly, since the optical path is constant, the planar positional relationship between this path and each evaporation source is different, and the absorbance does not directly correspond to the elemental vapor density, so it is necessary to make a complicated correction. That is. This is because, as shown in FIG. 4, the axes a, b, and c of the evaporation sources 5a, 5b, and 5c are inclined with respect to the axis l of the growth chamber. This is because the cross section is an ellipse having the axes a, b, and c as long axes in a plan view, and the positional relationship between the ellipse and the path P causes the path P to have different lengths across the respective ellipses. . Incidentally, in atomic absorption, all the atomic weights that the optical path crosses are measured. The present invention has been devised under the above circumstances, and solves the above-mentioned conventional problems with a simple configuration.
It is an object of the present invention to enable film formation monitoring for a plurality of evaporation sources to be simultaneously and accurately performed by an atomic absorption film formation monitor.

[Means for Solving the Problems]

In order to solve the above problems, the present invention takes the following technical means. That is, the present invention is a growth chamber connected to an ultra-high vacuum pump, a substrate holder arranged on the axis of the growth chamber inside the growth chamber, and on one side of the growth chamber, each axis faces the substrate holder, In addition, in a molecular beam epitaxy apparatus comprising a plurality of evaporation sources annularly arranged around the axis of the growth chamber, a plurality of atomic absorption type film formation monitors in which a growth material of a part or all of each evaporation source is a target element. And the optical path of each of the atomic absorption type film formation monitors intersects with the axis line of the evaporation source in which each target element is a growth material at a substantially constant angle in the axial direction of the growth chamber, and in the vicinity of the substrate holder. In (1), it is arranged so as to pass through a plane orthogonal to the laying line of the growth chamber. Note that the concept of “intersecting at a certain angle” includes “match”.

[Action]

In the present invention, each optical path of the plurality of atomic absorption type film formation monitors is made to intersect at a constant angle with respect to the axis of evaporation of each target element as a growth material when viewed in the axial direction of the growth chamber. Therefore, for example, when the above optical paths are made to coincide with each other in the axial direction of the evaporation chamber and the growth chamber in which the target element is a growth material, all the optical paths are
Corresponding to this, the elemental vapor from the evaporation source passes through the long axis of the elliptical cross section. Since the elliptical shapes of the cross-sections of the elemental vapors from each evaporation source near the substrate holder are similar, the way of passing through the corresponding elemental vapors of all optical paths is equivalent, and each atomic absorption type film formation monitor The atomic absorption by means of will correspond to the density of each elemental vapor without any correction.

【The invention's effect】

As described above, according to the present invention, since a plurality of atomic absorption type film formation monitors using the growth material of each evaporation source as the target element are provided, the vapor density generated from each evaporation source, that is,
The vapor deposition rate on the substrate can be simultaneously monitored, and this can be fed back to a controlled object such as opening and closing of the shutter or the temperature of the evaporation source to manufacture a compound semiconductor having a complicated structure with good reproducibility. It will be possible. Moreover, since the optical path of each monitor is equivalently passed through the vapor of each target element, the measurement can be easily and accurately performed without complicated correction for atomic absorption.

[Explanation of Examples]

An embodiment of the present invention will be specifically described below with reference to FIGS. 1 and 2. The molecular beam epitaxy apparatus shown in FIG. 1 has the same basic structure as the conventional one shown in FIG. The same members are designated by the same reference numerals as in FIG. Each of the evaporation sources, especially the evaporation sources 5a, 5b, 5c ... Using Group III elements and dopants as growth materials, has their axes a, b, c facing the center of the substrate holder 3 on one side of the growth chamber 2. They are arranged so as to be concentrated and annularly around the axis l of the growth chamber 2. The evaporation source 5'using arsenic, which is a group V element, as a growth material is arranged in the center of the growth chamber 2 because it evaporates in a molecular state and its concentration cannot be measured by atomic absorption. On the other hand, the apparatus of the present invention is equipped with a number of atomic absorption type film formation monitors 8a, 8b, 8c ... Which correspond to the above-mentioned annularly arranged evaporation sources 5a, 5b, 5c. .
Each of the atomic absorption type film formation monitors 8a, 8b, 8c ... Is equipped with a light source 9 composed of a hollow cathode lamp according to the target element to be detected, and a light receiver 10 for receiving light from the light source 9, respectively. After passing the above-mentioned light through a spectroscope or a filter, it is guided to a photomultiplier tube, and the absorbance that appears as a monotone function of the density of the target element in the vapor is measured. Then, the absorbance is fed back to the control device 11 for controlling the temperature of each shutter 7 or each part as vapor deposition rate or vapor deposition rate information of the element on the substrate B. Further, in the present invention, the above atomic absorption type film formation monitors 8a, 8
The optical paths Pa, Pb, Pc ... of b, 8c ... Are viewed in the direction of the axis (l) of the growth chamber 2 (FIG. 2), and the axes a, 5b, 5c of the evaporation sources 5a, 5b, 5c using the respective target elements as growth materials, Although they intersect with b and c at a substantially constant angle, in this example, as shown in FIG.
Pa, Pb, Pc ... Align with the above-mentioned respective axes a, b, c. Further, the positions of the paths Pa, Pb, Pc ... In the direction of the axis (1) of the growth chamber are orthogonal to the axis l in the vicinity of the substrate B on the substrate holder 3 as shown in FIG. It is set to pass through a plane. The other structure is the same as the basic structure of the conventional example shown in FIG. In the above configuration, the axes a, b, c of the evaporation sources 5a, 5b, 5c ...
... are inclined at a substantially constant angle with respect to the axis l of the growth chamber 2 so that they are concentrated in the center of the substrate holder 3,
The cross section of the elemental vapor radiated toward the substrate B from each evaporation source 5a, 5b, 5c, ... Is elliptical as shown in FIG. Optical path Pa, P
Since b, Pc ... Are set as described above, all the optical paths Pa, Pb, Pc ... Will pass through the major axis of each ellipse. As is clear from the comparison of this situation with the conventional example of FIG. 4, in the present invention, the density of elemental vapor irradiated from each evaporation source is determined by an optical path that is passed through in an equivalent form. Therefore, the measurement can be performed as it is without correcting the absorbance. Of course, the scope of the present invention is not limited to the above embodiments. For example, in the embodiment, each optical path is aligned with the axis of each corresponding evaporation source when viewed in the axial direction of the growth chamber, but even if these intersect at a certain angle, each optical path is equivalent. When passing through each elemental vapor in the state of.

[Brief description of drawings]

FIG. 1 is an explanatory view of the basic configuration of an embodiment of the present invention, and FIG.
FIG. 4 is a diagram showing the configuration of the main part, FIG. 3 is an explanatory diagram of a conventional example, and FIG. 2 ... Growth chamber, 3 ... Substrate holder, 5a, 5b, 5c ... Evaporation source, 8a, 8b, 8c ... Atomic absorption type film formation monitor, Pa, Pb, Pc ...
Light path, l ... (growth chamber) axis, a, b, c ... (evaporation source) axis.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-72590 (JP, A) JP 62-78186 (JP, A) JP 58-52475 (JP, A)

Claims (1)

[Claims] 1. A growth chamber connected to an ultra-high vacuum pump, a substrate holder arranged inside the growth chamber on the axis of the growth chamber, and on one side of the growth chamber, each axis faces the substrate holder, and In a molecular beam epitaxy apparatus equipped with a plurality of evaporation sources arranged in a ring around the axis of the growth chamber, a plurality of atomic absorption type film formation monitors in which a part or all of the growth material of each evaporation source is the target element are used. Along with the provision, the optical path of each of the above-mentioned atomic absorption type film formation monitors intersects with the axis of the evaporation source where each target element is a growth material at a substantially constant angle in the axial direction of the growth chamber, and in the vicinity of the substrate holder. A molecular beam epitaxy device, which is arranged so as to pass through a plane orthogonal to the axis of the growth chamber.