JP3394512B2 - Manufacturing method of magnetic semiconductor thin film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electronic device, and more particularly to a method for manufacturing a magnetic semiconductor thin film.

[0002]

2. Description of the Related Art By introducing a magnetic atom into a compound semiconductor, an electronic device having a combination of magnetism and electric conduction can be manufactured. In compound semiconductor thin films applied to electronic devices,
A function is provided by changing the composition or intentionally mixing impurities. Magnetic semiconductors containing magnetic atoms such as manganese have attracted attention as materials for devices having a new function of combining magnetism and electrical conduction.

In order to grow such a thin film, epitaxial growth in which a crystal substrate is irradiated with an atomic beam in an ultra-high vacuum and laminated is widely used. In general, magnetic atoms are more stable when they are bonded to atoms forming a semiconductor in a crystal arrangement different from the original semiconductor crystal structure, so that when crystals are grown at a high temperature close to thermal equilibrium, clusters are formed, Magnetic semiconductors cannot be constructed. Therefore, the conventional technique has been to lower the substrate temperature during growth by several hundred degrees from the normal temperature and grow the substrate under conditions of high nonequilibrium.

[0004]

If the compound composition can be optimized when or after the introduction of the magnetic atom into the compound semiconductor, the crystal quality is improved and the physical properties are stabilized.

In view of the above situation, it is an object of the present invention to overcome the problems of the prior art, to show the means for such optimization, and to provide a method of manufacturing a magnetic semiconductor thin film of high quality and stability. .

[0006]

In order to achieve the above object, the present invention provides, on a crystal substrate, [1] a magnetic semiconductor in which magnetic atoms are introduced into a compound semiconductor containing a component element having a high vapor pressure. In a method of manufacturing a magnetic semiconductor thin film using a molecular beam epitaxial growth method in which an atomic (molecular) beam of component atoms is irradiated in an ultra-high vacuum, the component element having a high vapor pressure exceeds the stoichiometric composition. the compound magnetic semiconductor thin film is grown at a growth temperature region is mixed into the semiconductor
And the magnetic semiconductor thin film has a high vapor pressure.
It is possible to evaporate and desorb an excess of component elements, higher than the growth temperature, and high in the magnetic atom and the vapor pressure.
The constituent elements combine to form lattice defects in the magnetic semiconductor.
By performing heat treatment in a temperature range lower than the temperature, the semiconductor characteristics and magnetic characteristics of the magnetic semiconductor thin film , and
And a step of improving thermal stability of conductor characteristics and magnetic characteristics .

[2] In the method for producing a magnetic semiconductor thin film according to the above [1], the compound semiconductor is a III-V group compound,
This compound semiconductor is a magnetic semiconductor thin film in which magnetic atoms are introduced.

[3] In the method for producing a magnetic semiconductor thin film as described in [1] or [2] above, the heat treatment is performed in any one of nitrogen gas, hydrogen gas, other inert gas or a mixed gas thereof. It is characterized by being performed.

[4] In the method for producing a magnetic semiconductor thin film according to the above [1], [2] or [3], when the magnetic semiconductor thin film is grown by a molecular beam epitaxial growth method, crystal lattice points of the compound semiconductor The compound semiconductor thin film growth method of alternately opening and closing the shutter of the raw material cell of each component is adopted so that each component of each raw material is laminated by one atomic layer, and the magnetic atom is replaced in the shutter of the raw material cell of magnetic atoms. It is characterized by opening and closing in synchronization with a shutter of a raw material cell of a component of a compound semiconductor at a crystal lattice point position.

[5] In the method for producing a magnetic semiconductor thin film according to the above [1], [2], [3] or [4], since each component is laminated by one atomic layer, reflection caused by the progress of growth It is characterized by measuring high-speed electron beam diffraction and synchronizing the opening and closing of the shutter during growth with changes in this diffraction pattern.

The molecular beam epitaxial growth method (MBE) for a compound semiconductor thin film is generally performed in an excess atmosphere of an element having a high vapor pressure. During growth, it is necessary to keep the substrate temperature low because it takes in magnetic atoms, but after the magnetic atoms are placed in metastable positions after growth, the substrate is heat-treated at a temperature higher than the evaporation temperature of excess elements. Selectively evaporate excess elements.

The amount of the excess element during the thin film growth is monitored by the change in the reflected high energy electron beam diffraction pattern and is fed back to the opening and closing of the shutter to stack one atomic layer for each component occupying a predetermined crystal lattice point of the compound semiconductor. By doing so, after suppressing the introduction amount of the excess element during the growth of the thin film as much as possible, the heat treatment at a high temperature is performed to enhance the effect of improving the film quality.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described.

Epitaxial growth of compound semiconductors is generally performed in an atmosphere in which a beam of an element having a high vapor pressure is excessively irradiated. As an example, A with element A and element B
Consider the compound B. It is assumed that A has a high vapor pressure. In the growth at high temperature, the A atom that could not be bonded to B spontaneously evaporates, so that the composition of the compound grows at 1: 1. However, during low temperature growth, the rate at which A atoms evaporate from the growth surface is slow, and the crystals take in excess A atoms. This excess A atom bonds with the introduced magnetic atom or becomes an interstitial atom by itself to deteriorate the crystal quality. Poor reproducibility of magnetic semiconductor manufacturing and thermal instability after growth are caused by these excess atoms.

The present invention takes advantage of the property that magnetic atoms once incorporated into a crystal in the same form as a semiconductor crystal do not form clusters even if kept at a slightly high temperature.

FIG. 1 is a flow chart for manufacturing a magnetic semiconductor thin film showing a first embodiment of the present invention.

(1) First, a semiconductor substrate is introduced into the load lock chamber (step S1).

(2) Next, ordinary low temperature epitaxial growth is performed (step S2).

(3) Next, the low temperature epitaxially grown magnetic semiconductor substrate is once taken out into the atmosphere for surface oxidation (step S3).

(4) Next, the substrate is heat-treated. Here, the heat treatment is performed for a short time in nitrogen (step S4), but it can be performed in an inert gas such as nitrogen or argon or a gas such as hydrogen. Care must be taken that this kind of heat treatment gas does not contain excess atoms that are desired to be expelled. In the past reported examples of heat treatment, for example, heat treatment of a magnetic semiconductor (Ga, Mn) As is performed in an arsenic atmosphere in order to suppress arsenic loss, and the effect of the present invention is not obtained.

As an example, the case of (Ga, Mn) As is shown. The heat treatment is performed for about 10 minutes at a temperature slightly higher than the growth temperature (usually within 100 ° C.). The growth is performed at about 230 ° C., but the heat treatment is performed in nitrogen gas.

FIG. 2 is a diagram showing the experimental results of the magnetic semiconductor thin film of the first embodiment of the present invention, showing that the crystalline film quality is dramatically improved by the heat treatment after growth.
a, Mn) As is shown. Horizontal axis shows heat treatment temperature Tan
The neal (° C.) and the vertical axis represent the hole concentration p (10 ¹⁹ cm ⁻³ ) and the ferromagnetic transition temperature Tc (K).

In both cases, the higher the quality, the better the crystalline quality. As the crystal quality is improved, the hole concentration p and the ferromagnetic transition temperature Tc increase. From this figure, it can be seen that the heat treatment temperature up to about 300 ° C. has the effect of improving the film quality, but 260 ° C. is the optimum heat treatment temperature.

In FIG. 3, heat treatment was performed at 260 ° C. for 10 minutes (G
(a, Mn) As is a diagram showing changes in the ferromagnetic transition temperature Tc in an air atmosphere at 350 ° C., which is not heat treated, where the horizontal axis represents time (minutes) and the vertical axis represents the ferromagnetic transition temperature T.
c (K) is shown.

As shown in FIG. 3, when the thin film heat-treated at 260 ° C. is kept at a higher temperature thereafter, the deterioration of the quality is extremely smaller than that of the thin film not heat-treated. That is, those that have not been heat-treated are significantly deteriorated in the initial stage, and those that have been heat-treated are dramatically stable.

Next, a second embodiment of the present invention will be described.

In the first embodiment, the heat treatment is performed after the ordinary low temperature epitaxial growth, but in the second embodiment, the pattern change of the reflection high energy electron diffraction (RHEED) is monitored to open / close the shutter during the growth. It is intended to give feedback.

FIG. 4 is a flow chart of manufacturing a magnetic semiconductor thin film showing a second embodiment of the present invention.

(1) First, similarly to the first embodiment, the semiconductor substrate is introduced into the load lock chamber (step S11).

(2) Next, low temperature epitaxial growth is performed in which the composition is controlled by opening and closing the shutter (step S1).
2).

(3) Next, as in the first embodiment, the low temperature epitaxially grown magnetic semiconductor substrate is once taken out into the atmosphere for surface oxidation (step S13).

(4) Next, similar to the first embodiment, a short time heat treatment is performed in nitrogen (step S14).

Hereinafter, the point that an optimization process is applied to MBE, which is a feature of the second embodiment, will be described.

FIG. 5 is a diagram showing data obtained by detecting the luminance change of the RHEED pattern during the low temperature epitaxial growth of (Ga, Mn) As, in which the horizontal axis represents time (sec) and the vertical axis represents luminance (arbitrary unit). In the figure, one cycle of vibration corresponds to the growth of one atomic layer. Therefore, for example, in the case of growing a compound semiconductor AB, if the elements A and B are laminated by one atomic layer while opening and closing the shutter, the ratio of AB is 1 :.
Can be maintained at 1. Furthermore, if the element that the magnetic atom replaces is, for example, B, the anti-site defect that enters the A site can be prevented by opening the shutter of the magnetic atom only when B is stacked.

A block diagram of this growth method is shown in FIG.

In this figure, 1 is a RHEED electron gun,
2 is a growth substrate holder, 3 is an A element molecular beam cell, 4 is a B element molecular beam cell, 5 is a magnetic element molecular beam cell, and 6 is RHEE.
D screen, 7 a CCD camera, 8 a personal computer (PC), and 9 a shutter controller.

The RHEED pattern is taken into the PC 8 by using the CCD camera 7 and the information on the crystal growth is obtained by integrating the reflection spot where vibration is easily picked up. RH
The peak of vibration is detected by differentiating the EED data with respect to time. The detection signal is transmitted to the shutter controller 9 through the software of the PC 8 to open / close the shutter.

FIG. 7 is a diagram showing the experimental results of the magnetic semiconductor thin film showing the second embodiment of the present invention, in which the horizontal axis represents the heat treatment temperature T.
Anneal (° C.), the vertical axis shows the hole concentration p (10 ¹⁹ cm ⁻³ ) and the ferromagnetic transition temperature Tc (K).

This figure shows the result of heat treatment performed on the sample for which the shutter was opened and closed while the RHEED pattern was monitored during MBE growth and the composition was optimally controlled, as in FIG. The hole concentration p and the ferromagnetic transition temperature Tc show high values before the heat treatment, and the heat treatment at 260 ° C. shows the highest value so far.

As can be seen from this figure, a higher quality crystalline thin film can be obtained by the method of the present invention.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention, and these modifications are not excluded from the scope of the present invention.

[0042]

As described above in detail, according to the present invention, the epitaxial growth conditions can be optimized, and a magnetic semiconductor crystal thin film of higher quality and thermal stability can be easily manufactured. can do.

[Brief description of drawings]

FIG. 1 is a manufacturing flowchart of a magnetic semiconductor thin film showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an experimental result of the magnetic semiconductor thin film of the first embodiment of the present invention.

FIG. 3: Heat treatment at 260 ° C. for 10 minutes (Ga, Mn)
It is a figure which shows the change of the ferromagnetic transition temperature Tc in 350 degreeC air atmosphere which is not heat-processed with As.

FIG. 4 is a manufacturing flowchart of a magnetic semiconductor thin film showing a second embodiment of the present invention.

FIG. 5 is a diagram in which the luminance of the direct reflection spot of RHEED is integrated during the low temperature epitaxial growth of (Ga, Mn) As and plotted against time, and one cycle of vibration corresponds to the growth of one atomic layer. Equivalent to.

FIG. 6 is a block diagram of an apparatus for performing low temperature epitaxial growth while monitoring a RHEED pattern and opening and closing a shutter.

FIG. 7 is a diagram showing an experimental result of a magnetic semiconductor thin film showing a second embodiment of the present invention.

[Explanation of symbols]

1 RHEED electron gun 2 Growth substrate holder 3 A element molecular beam cell 4 B element molecular beam cell 5 Magnetic element molecular beam cell 6 RHEED screen 7 CCD camera 8 Personal computer (PC) 9 Shutter controller

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 2000-21671 (JP, A) JP 5-55144 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/203, 21/363 H01F 41/30

Claims (5)

(57) [Claims] 1. A magnetic semiconductor in which magnetic atoms are introduced into a compound semiconductor containing a component element having a high vapor pressure is grown on a crystal substrate by irradiating an atomic (molecular) beam of the component atom in an ultrahigh vacuum. In the method for producing a magnetic semiconductor thin film using the molecular beam epitaxial growth method, the following steps are performed: (a) Magnetization is performed in a growth temperature range in which the component element having a high vapor pressure is mixed into the compound semiconductor in excess of stoichiometric composition. A step of growing a magnetic semiconductor thin film, and
An element that has a higher vapor temperature than the growth temperature and that has a high vapor pressure and is capable of evaporating and desorbing an excess of the element.
The temperature above which the elements combine to form lattice defects in the magnetic semiconductor
The semiconductor characteristics and magnetic characteristics of the magnetic semiconductor thin film, and the semiconductor characteristics by heat treatment in a lower temperature range.
And a step of improving the thermal stability of magnetic properties, the method for producing a magnetic semiconductor thin film. 2. The method for producing a magnetic semiconductor thin film according to claim 1, wherein the compound semiconductor is a III-V group compound and a magnetic atom is introduced into the compound semiconductor. Thin film manufacturing method. 3. The method for manufacturing a magnetic semiconductor thin film according to claim 1, wherein the heat treatment is performed in any one of nitrogen gas, hydrogen gas, other inert gas or a mixed gas thereof. A method of manufacturing a magnetic semiconductor thin film, which is characterized. 4. The method for manufacturing a magnetic semiconductor thin film according to claim 1, 2 or 3, wherein when the magnetic semiconductor thin film is grown by a molecular beam epitaxial growth method, each component at each crystal lattice point of the compound semiconductor is The compound semiconductor thin film growth method is used in which the shutters of the raw material cells of each component are alternately opened and closed so that atomic layers are stacked, and the shutter of the raw material cell of magnetic atoms is a compound semiconductor at the crystal lattice point position where the magnetic atoms are replaced. A method of manufacturing a magnetic semiconductor thin film, which comprises opening and closing in synchronization with a shutter of a raw material cell of the component. 5. The method for producing a magnetic semiconductor thin film according to claim 1, 2, 3 or 4, wherein, in order to stack each component by one atomic layer, a reflection high-energy electron diffraction along with the progress of growth is measured, A method of manufacturing a magnetic semiconductor thin film, characterized in that opening and closing of a shutter at the time of growth is synchronized with changes in the diffraction pattern.