JPH057253Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

This invention relates to a molecular beam epitaxy device.
More specifically, the present invention relates to a structure configured to more accurately measure the density of elemental vapor irradiated from an evaporation source.

[Conventional technology]

Molecular beam epitaxy is attracting attention as a method for epitaxially growing - group elements on a single crystal substrate in the process of manufacturing - group compound semiconductors. This is a type of vacuum evaporation method in which group elements such as gallium Ga, aluminum Al, and indium In, as well as group elements such as arsenic As and phosphorus P are grown in an ultra-high vacuum of 10 ^-11 torr. By irradiating these in the form of atomic or molecular beams, Ga
GaAs, InP, etc. single crystal substrate
This is a method of epitaxially growing - group compound semiconductor crystals such as Al Ga As, In P, or In Ga As P. According to this molecular beam epitaxy method, because the deposition is carried out in an ultra-high vacuum, there is very little contamination of impurities from residual gas, and the substrate surface can be kept clean, uniformly and over a large area. A multi-component film that can obtain a flat film at the atomic level, the deposition rate can be extremely slow and precisely controlled, and the film thickness can be controlled with high precision on the order of a single atomic layer of several angstroms. Mixed crystal thin films of systems can be easily obtained by simply increasing the number of evaporation sources.During crystal growth, various information about growth conditions can be obtained from the surface of the growing layer or from molecular beams, and this information can be immediately fed back to growth control. You can enjoy benefits such as: In order to facilitate understanding of the present invention, which will be described later, we will provide an overview of the molecular beam epitaxy apparatus that performs the molecular beam epitaxy method as described above, and the conventional method of monitoring elemental vapor density using an atomic absorption film formation monitor. This will be explained based on FIGS. 2 and 3. The growth chamber 2 connected to the ultra-high vacuum pump 1 has a substantially cylindrical shape, and the axis l of the growth chamber is located at the center of the growth chamber 2.
A substrate holder 3 whose rotation is controlled around the center is arranged horizontally. The reason why the rotation of the substrate holder 3 can be controlled in this way is to make the crystal growth on the substrate uniform. Further, a heater (not shown) is attached to raise the temperature of the substrate held by the substrate holder 3 to a desired temperature.
On one side of the growth chamber 2 facing the substrate holding structure of the substrate holder 3, the axes a, b, c... Evaporation source 5 tilted at
a, 5b, 5c, . . . are arranged in an annular shape centered on the axis l of the growth chamber 2, and at substantially equal distances from the substrate holder 3. Each evaporation source 5
a, 5b, 5c... are constructed by filling a crucible 4... opening toward the center of the substrate holder 3 with each growth material, and are controlled by a heater based on the temperature detected by a temperature sensor (not shown). The temperature is raised to a desired temperature. Further, each of the evaporation sources 5a, 5b, 5c, . . . is surrounded by a liquid nitrogen shroud 6 so that they are not affected by heat or contamination caused by other evaporation sources. Starting and stopping of crystal growth is performed by controlling opening and closing of shutters 7 arranged in front of the opening of each crucible 4. For example, to grow a GaAs layer on a GaAs single crystal substrate, a Ga-filled evaporation source and
The evaporation source filled with As is heated to a predetermined temperature, the temperature of the substrate holder 3 is set to an appropriate temperature, and the shutters 7 of each of the evaporation sources are controlled to be open for a predetermined period of time. Note that at this time, if Al is evaporated together, a Ga _x Al _1-x As layer will grow. At this time, the composition x of Ga and Al can be controlled by controlling the ratio of evaporation amounts. In addition, to make the growth layer n-type, Si, Sn, etc. are evaporated at the same time.
To make the p-type, Be, Mg, etc. are evaporated at the same time. Incidentally, as feedback information for controlling the crystal growth on the substrate as described above, the deposition rate may be detected by an atomic absorption type film formation monitor. This is an application of atomic absorption spectrometry, and as shown in Figures 2 and 3, a hollow cathode lamp with a wavelength specific to a specific element is used as a light source and is emitted from one window of the growth chamber 2. The light that enters the vapor and exits from the other window is passed through a spectroscope or filter, then guided to a photomultiplier tube, and the absorbance, which appears as a monotonic function of the density of the target element in the vapor, is measured.

[Problem that the idea aims to solve]

However, the use of atomic absorption film formation monitors in molecular beam epitaxy equipment is still in its infancy, and there are still various issues to be solved, especially since no consideration has been given to the relationship between the optical path and each evaporation source. be. For example, in many molecular beam epitaxy apparatuses currently using an atomic absorption type film formation monitor, as shown in FIG.
5b, 5c... are arranged in a ring shape around the axis l of the growth chamber, while the optical path P of the atomic absorption film formation monitor
is set in a single pass across the growth chamber 2 in close proximity to the substrate B on the substrate holder, perpendicular to the vapor axis l, which gives rise to the following problem. First, since the optical path P is single, it is necessary to change the light source depending on the target element, and it is not possible to simultaneously monitor the elemental vapor density of each evaporation source with different growth materials. . Second, 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, requiring complicated correction. That's true. As shown in Fig. 2, each evaporation source 5
Since the axes a, b, and c of a, 5b, and 5c are inclined with respect to the axis l of the growth chamber, the cross section of the vapor of each element near the substrate holder is similar to the axes a, b, and c in plan view. This is because although the path P is an ellipse having a long axis, the length of the path P crossing each of the ellipses varies depending on the positional relationship between the ellipse and the path P. By the way, in atomic absorption, the mass of all the atoms traversed by the optical path is measured. Thirdly, the optical path is set to cross the growth chamber 2 in close proximity to the substrate B on the substrate holder, but at this location, the molecular beam flux irradiated from the evaporation sources 5a, 5b, and 5c is greatly expanded. As a result, the accuracy of measuring the vapor density of the target element using the atomic absorption method is inevitably reduced. This invention was devised under the above circumstances, and it solves the above conventional problems with a simple configuration and allows vapor density monitoring for multiple evaporation sources to be performed using an atomic absorption monitor. at the same time,
Moreover, the purpose is to be able to do it accurately.

[Means to solve the problem]

In order to solve the above problems, this invention takes the following technical measures. That is, the present invention includes a growth chamber connected to an ultra-high vacuum pump, a substrate holder placed inside the growth chamber, and a substrate holder arranged on one side of the growth chamber so that each axis faces the substrate holder. In a molecular beam epitaxy apparatus equipped with a plurality of arranged evaporation sources and a shutter provided to shield or release the molecular beam irradiated from each of these evaporation sources, a part or all of each evaporation source is grown. A plurality of atomic absorption type monitors whose target element is the material are provided, and the optical path of each of the atomic absorption type monitors is arranged so as to cross the molecular beam flux from each evaporation source close to the substrate holder side of the shutter. Features.

[Action and effect]

In the present invention, each optical path is arranged in a plurality of atomic absorption type monitors so as to cross the molecular beam flux from each evaporation source close to the substrate holder side of the shutter of each evaporation source. Therefore, there is almost no error caused by the spread of the molecular beam flux in vapor density measurement using an atomic absorption monitor, and the sensitivity is improved accordingly, making it possible to perform accurate measurements. In addition, in the present invention, multiple atomic absorption type monitors whose target elements are the growth materials of each evaporation source are installed for each evaporation source, making it possible to simultaneously monitor the elemental vapor density of each evaporation source with different growth materials. I can do it. Therefore, by feeding back this to the opening/closing of the shutter or temperature control of each evaporation source, it becomes possible to manufacture compound semiconductors with good reproducibility even if they have a complex structure. Furthermore, since the way each molecular beam traverses the optical path is the same in all cases, measurement can be performed easily and accurately without the need for complicated corrections to atomic absorption.

[Explanation of Examples]

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. The molecular beam epitaxy apparatus shown in FIG.
The basic structure is the same as the conventional one shown in the figure.
Similar members are designated by the same reference numerals as in FIG. 2. In this example, the evaporation sources 5a, 5b, etc., whose growth materials are group elements and dopants, are placed in the growth chamber 2.
On one side, the axes a, b... are concentrated toward the center of the substrate holder 3, arranged in a ring shape with the axis l of the growth chamber 2 as the center, and arsenic, which is a group V element, is An evaporation source 5', which serves as a growth material, is placed in the center of the growth chamber to increase its capacity. Each of the above evaporation sources 5a, 5b...
The crucible 4 filled with each growth material is loaded into a bottomed cylindrical housing 8 whose upper end is fixed to the bottom wall of the growth chamber 2. In addition, each evaporation source 5
Shutters 7, which shield and release the molecular beam flux, are provided corresponding to a, 5b, and so on.
In this example, a rotary shutter is disposed in the axially intermediate portion of the cylindrical housing 8 so as to open and close the openings of the crucibles 4. That is, a shutter retraction space 8a is provided on the side surface of the cylindrical housing 8 at an axial position corresponding to the upper end of the crucible 4, a shutter shaft 7a is pivotally supported in an appropriate part of the shutter retraction space 8a, and a shutter plate 7b is mounted at the tip of this shaft. Fixed. When the shaft 7a is rotated, the shutter plate 7b
1, it is possible to select a closed position in which the opening of the crucible 4 is covered, as shown by a solid line in FIG. On the other hand, in the device according to the present invention, the above-mentioned evaporation source 5, which is arranged in an annular manner and uses different elements as growth materials, is used.
Atomic absorption monitors 9 of the number corresponding to a, 5b...
a, 9b, . . . are arranged so that their optical paths Pa, Pb, . In this example, a pair of windows 10, 10 facing each other in the diametrical direction of the evaporation source housing 8 are received at a portion of the evaporation source housing 8 slightly above the shutter 7, and the target element to be detected is placed between these windows 10, 10. Light source 1 consisting of a hollow cathode lamp according to
1 and a light receiver 12 that receives light from this light source 9 are arranged to face each other. As a result, the optical path Pa passes through the evaporation source housing 8 in the diametrical direction close to the shutter. In the photoreceiver 12, the light passes through a spectrometer or a filter, and then is guided to a photomultiplier tube to measure the absorbance, which appears as a monotonous function of the density of the target element in the vapor. And this absorbance is
Information on the vapor density or the vapor deposition rate of the element on the substrate B is fed back to the controller 13 that controls the temperature of each shutter 7 or each part. Note that the other configurations are the same as the basic configuration of the conventional example shown in FIG. In the above configuration, each evaporation source 5a, 5b...
are dedicated atomic absorption monitors 9a and 9b, respectively.
..., it is possible to simultaneously measure the density of molecular beam fluxes from different evaporation sources, and this can be immediately fed back to the control device 13. In addition, the optical path Pa, Pb of each atomic absorption monitor
... is placed so that it passes through a position extremely close to the evaporation source, so accurate measurements can be made with fewer errors due to diffusion of the molecular beam flux. Furthermore, for the same reason, the sensitivity of the monitor is also improved. Furthermore, since the optical paths are equivalent for each evaporation source, it is possible to accurately measure the element density from each evaporation source without making any correction to the absorbance. Of course, the scope of this invention is not limited to the above-described embodiments. For example, in the embodiment, the optical path of each atomic absorption monitor is set to pass through the evaporation source housing in its diametrical direction, but compared to the conventional general evaporation source or shutter shown in FIG. In the device having this configuration, the optical path Pa may be made to pass through a portion close to the shutter.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is an explanatory view of a conventional example, and FIG. 3 is an explanatory view of the operation of the conventional example. 2...Growth chamber, 3...Substrate holder, 5a, 5b
...Evaporation source, 7...Shutter, 9a, 9b...Atomic absorption monitor, Pa, Pb, ...Light path, l...
Axis (of the growth chamber), a, b, c... (of the evaporation source)
Axis line.

Claims (1)

[Scope of Claim for Utility Model Registration] A growth chamber connected to an ultra-high vacuum pump, a substrate holder disposed inside the growth chamber, and each axis on one side of the growth chamber facing the substrate holder. In a molecular beam epitaxy apparatus equipped with a plurality of evaporation sources arranged as shown in FIG. A plurality of atomic absorption type monitors were provided whose target elements were the growth materials of A molecular beam epitaxy device characterized by: