JPH104069A - Method of fabricating fine semiconductor structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of fabricating a fine structure with high accuracy so as to have the same size by allowing the tip of a probe to approach the surface of a selection film only by a predetermined distance on an atom unit basis and selectively etching the selection film by flowing a tunnel current between a semiconductor substrate and the probe. SOLUTION: An oxide film 2 on the surface of a GaAs substrate 1 exposed in the atmosphere is heated and removed in vacuum, thus exposing the surface of the GaAs substrate 1. A GaN film 4a is deposited on the exposed surface of the GaAs substrate 1 and a probe 11 is brought close to the surface of the GaN film 4a at a distance of 1nm. A switch 13 is changed to increase a tunnel current between the probe 11 and the GaAs substrate 1 and partial etching is performed to the GaN film 4a with the energy on an atom unit basis. Consequently, the GaN film 4a is selectively patterned. Thus, the fine structure can be fabricated so as to have the same size with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a nanometer-sized semiconductor microstructure on a single substrate by measuring the size, shape and
The present invention relates to a method for manufacturing a semiconductor microstructure which is three-dimensionally manufactured by accurately controlling a position on a substrate.

[0002]

2. Description of the Related Art If the size of a semiconductor fine structure is made smaller than several tens of nanometers, the width of energy distribution of electrons and holes in the structure can be made extremely narrow according to quantum mechanics. Such a structure is called a quantum dot (quantum box). If a plurality of quantum boxes having uniform dimensions are applied to a semiconductor laser, a semiconductor laser having an extremely low threshold current can be realized. As an example of a method of manufacturing the quantum box having the semiconductor fine structure, a method called selective growth will be described below.

First, as shown in FIG. 7A, a GaAs substrate 71 is heated at about 600 ° C. in a vacuum to etch a natural oxide film 72 formed on the surface thereof. By heating in a vacuum, the GaAs oxide is decomposed and vaporized. However, at this time, gaseous As is introduced into the substrate surface. This is performed to compensate for As at the stage of decomposition by heating. Ga
As, which is a group V element, is easily vaporized as compared with
This is because it is necessary to keep the atmosphere in excess of s.

However, in this etching, even if As vaporized is introduced into the surface of the GaAs substrate 71, the GaAs
As defects on the surface of the s-substrate 71 cannot be completely compensated for, and the surface cannot be made flat. Therefore, following the etching, triethyl gallium (TEGa) and vaporized As are introduced into the surface of the heated GaAs substrate 71, and a GaAs buffer layer 73 is grown on the surface, as shown in FIG. To flatten the surface. At this time, Si or Zn is introduced as an impurity into the GaAs buffer layer 73 to have conductivity.

Then, as shown in FIG. 7C, trimethylgallium is introduced into the surface of the GaAs substrate 71 together with dimethylhydrazine, and a thin film 74 made of gallium nitrogen (GaN) is deposited. Dimethylhydrazine is used as a nitrogen source, but instead, nitrogen atoms may be supplied by cracking ammonia.

[0006] Next, as shown in FIG. 7 (d), the thin film 74 is selectively evaporated by irradiating an electron beam.
The surface of the aAs buffer layer 73 is exposed. Next, FIG.
As shown in (e), trimethylgallium and vaporized A
s is introduced onto the heated GaAs substrate 71 and GaAs
A microstructure 75 made of GaAs is selectively grown in a portion where the buffer layer 73 is exposed. Then, FIG.
As shown in FIG. 7, the thin film 74 made of GaN is removed, and Ga
Ga having microstructure 75 formed on As buffer layer 73
As substrate 71 is obtained.

[0007]

As described above, in the conventional manufacturing method, electron beam exposure has been used in patterning a fine structure. However, the spread of the focal point of the electron beam is about 50 nm even if it is reduced to the minimum. Then, the edge is not sharp, but the energy is distributed so that the central portion has the maximum energy and the energy gradually decreases toward the periphery. Microstructures on the order of nanometers have been formed. But,
The microstructure formed in this way has low reproducibility, and it is very difficult to make the same size when manufacturing a plurality of microstructures. Therefore, conventionally, a useful quantum box structure could not be formed.

Also, during conventional electron beam irradiation, the surface cannot be observed in situ. For this reason, it was not possible to monitor and control the state of exposure and the position of exposure on the substrate. Therefore, when manufacturing a plurality of microstructures on the same substrate, the relative position between the structures is not known,
It has been very difficult to produce a high-density one as well as a three-dimensional one.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to enable a fine structure exhibiting a quantum effect to be accurately manufactured in a uniform size. Aim.

[0010]

According to the method of manufacturing a semiconductor microstructure of the present invention, first, an oxide film on a surface of a semiconductor substrate is removed and cleaned, and second, a semiconductor substrate is heated to form radicals on the surface. Third, a selective film containing nitrogen is formed by supplying the selected nitrogen, and thirdly, the tip of the probe having a tip sharpened to an atomic level is always brought close to the surface of the selective film by a certain distance, and the semiconductor substrate and the probe are contacted. Then, a selective current is selectively etched by passing a tunnel current between them. Fourth, the semiconductor substrate is heated, and an organic metal gas containing group III atoms and an organic metal gas containing group V atoms are supplied thereon. Fifth, a fine semiconductor structure was grown, and fifthly, the selective film was removed.

As described above, since the selective film is etched by the tunnel current between the probe and the semiconductor substrate, the state of the processed surface during the etching can be observed. As described above, when the size of the semiconductor microstructure is made smaller than several tens of nanometers, according to quantum mechanics, the energy distribution width of electrons and holes in the structure can be made extremely narrow. By applying such a plurality of quantum box structures having uniform dimensions to a semiconductor laser, a semiconductor laser having an extremely low threshold current can be realized.

In the present invention, the surface is scanned with a probe, and the surface shape is observed by detecting a tunnel current.
A microstructure was grown in that area. For this reason,
According to the present invention, the shape of the pattern can be observed when the pattern is formed, so that the dimensions, position, and composition can be controlled, and a quantum box structure that is three-dimensionally much more uniform can be produced.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a method for manufacturing a fine structure according to an embodiment of the present invention. In this embodiment, a case will be described in which GaAs and InAs semiconductor fine structures are formed on the same GaAs substrate 1.

First, as shown in FIG. 1A, an oxide film 2 exists on the surface of a GaAs substrate 1 left in the atmosphere. In order to remove the oxide film 2, the GaAs substrate 1
Is heated to 500 ° C. in vacuum to thermally decompose and remove oxide film 2. At this time, as shown in FIG. 1B, tertiary butyl arsine (TBAs), which is an organic metal containing a group V element, is supplied to the surface of the GaAs substrate 1. Thereby, a clean GaAs substrate 1 surface is exposed.

Conventionally, in etching the oxide film 2, vaporized As has been introduced to the substrate surface. This prevents the V-group element having a high vapor pressure from being lost from the GaAs substrate.
However, the use of vaporized As requires the use of As on the GaAs substrate.
May not be compensated for, and Ga droplets may be generated on the surface. For this reason, conventionally, the flatness of the substrate may be lost. However, in this embodiment, TBAs are formed on the substrate 1 where the oxide film 2 is being etched.
Since it is introduced, the surface becomes very flat.

This is because hydrogen atoms generated together with As atoms due to decomposition of TBAs by heat effectively remove gallium by etching. The surface of the GaAs substrate 1 to which TBAs is supplied is decomposed by heat and mainly As is etched, and gallium is also etched by hydrogen atoms. Since As is compensated by the supply of As atoms, both gallium and As are uniformly etched as a whole.

Conventionally, As on the surface of the GaAs substrate 1 has been compensated by introducing vaporized As. However, in this method, the deficiency of As cannot be completely compensated, and a GaAs buffer layer had to be grown in order to recover a flat surface after etching. Conventionally,
Because the processing was done by electron beam irradiation,
The GaAs buffer layer needs to have conductivity, and Si or Zn must be added as an impurity.
The process was complicated. This is because if the film is not made conductive, it will charge up when irradiated with an electron beam.

However, as shown in this embodiment,
By introducing TBAs, the As on the surface of the GaAs substrate 1 is compensated, and if the gallium is also etched, it is not necessary to form a GaAs buffer layer. When InP is used for the substrate instead of GaAs, tertiary butyl phosphine (TBP) is effective. That is, in the etching for removing the oxide film, an organic metal containing a group V atom may be introduced to the substrate surface.
In particular, an organic metal having a structure in which a group V atom and hydrogen are directly bonded is effective. However, even if trimethyl arsenic is used, for example, the effect is slightly inferior but effective.

Next, as shown in FIG. 1 (c), a nitrogen gas is passed through a heated tungsten filament and turned into nitrogen atoms to be supplied to the surface of the GaAs substrate 1 heated to 250 ° C., and is made of amorphous GaN. A GaN film 4a (selective film) is deposited. As shown in FIG. 3A, the state of the surface of the GaN changes depending on the deposition temperature (substrate temperature). When the substrate temperature exceeds 400 ° C., the deposited GaN becomes polycrystalline, and as shown in FIG.
The surface irregularities are large. However, when the substrate temperature is 400 ° C. or lower, the deposited GaN is in an amorphous state, so that the surface irregularities are considerably reduced. Therefore, GaN is preferably grown at 400 ° C. or lower.

On the other hand, the temperature conditions at the time of GaN deposition and the G when GaAs is deposited on the GaN deposited at that temperature.
When comparing the thickness of the aAs film, as shown in FIG. 3B, GaAs hardly deposits on GaN deposited at 400 ° C. or lower. In contrast, Ga on GaAs
When the N film is formed thin, a part of the underlying GaAs surface is exposed in the formed GaN film when the GaN film is in a polycrystalline state. Therefore, GaAs grows on the GaN film formed on GaAs at a temperature exceeding 400 ° C. Ga
Since the N film is used for selective growth of GaAs, from this viewpoint, GaN must be grown at a substrate temperature of 400 ° C. or lower.

Next, as shown in FIG.
1 is used to partially remove the GaN film 4a. FIG.
In (d), the probe 11 is a part constituting a scanning tunneling microscope. The position of the probe 11 is controlled in the xy direction and the z direction by the piezo 12a and the piezo 12b. Piezo 12a, 12b, the voltage V _x to be applied, V _y
And in proportion to the value of V _z . Piezo 12a
Used to scan the probe 11. With the above configuration,
While applying a constant voltage V _t between the probe 11 and the GaAs substrate 1, and controls the voltage V _z to be applied to the piezoelectric 12b as the value of the current flowing through the circuit (tunnel current) is constant.

In this state, the probe 11 is moved 2-3 n from the surface.
If scanning is performed at a distance of m, the piezo 12b changes its displacement amount in an attempt to keep the distance between the probe 11 and the surface constant in accordance with the unevenness of the surface being scanned. Then, by measuring the amount of displacement, it is possible to observe the unevenness of the surface being scanned. This is the principle of observing the surface shape using a scanning tunneling microscope. FIG.
In (d), the switch 13 shows the connection in the observation state. Here, on the surface of the GaN film 4a on the GaAs substrate 1,
The probe 11 is brought closer to a distance of about 1 nm. Then, by switching the switch 13, the current between the probe 11 and the GaAs substrate 1 is increased. Then, with that energy, G
The aN film 4a can be partially etched by one molecule.

As a result, as shown in FIG.
The N film 4a can be selectively patterned. At this time, this processing can be performed on the order of several nm. At the time of this processing, by switching the switch 13, the processing state and the observation state can be instantaneously switched, so that the state of the etching processing can be observed on the spot. Further, since the probe 11 can be moved to a place where processing is desired while observing the surface, it is possible to form a microstructure with extremely high precision.

Hereinafter, this processing method will be described in more detail with reference to the sectional view of FIG. In FIG. 4A,
Probe 1 when observing the surface state of GaAs substrate 1
The trajectory of one tip is indicated by a dotted line. In addition, the trajectory of the tip of the probe 11 in the case of processing when scanning is performed with the value of the tunnel current increased is shown by a solid line. When scanning the surface of the observation object with the scanning tunnel microscope, the probe 11 is moved up and down so that the tunnel current is constant. That is, when the tunnel current decreases, the probe 11 is lowered, and when the tunnel current increases, the probe 11 is raised. As a result, control is performed so that the distance between the tip of the probe 11 and the surface of the observation target is kept constant. Then, the state where the probe 11 is moved by the control indicates the surface state of the observation target. Therefore, the surface state of the GaAs substrate 1 can be observed by moving the probe 11.

However, even if the tunnel current is controlled to be kept constant, as shown by the dotted line in FIG.
The tip of the probe 11 operates while reproducing the surface state of the GaAs substrate 1 with a time delay. Here, when the tip of the probe 11 is brought close to the surface in order to process the surface, as shown by a solid line in FIG. Can not do it. That is,
As in the case of observing the surface condition, the tip of the probe 11 is made of GaAs while the tip position is feedback-controlled.
If processing is performed close to the surface of the substrate 1, processing cannot be performed under certain conditions.

On the other hand, by processing the surface by repeating the following operation, the surface can be processed uniformly (FIG. 4B). That is, first, the observation mode is changed at a certain position from the mode in which the surface state is observed, and the probe 11 is lowered by a certain distance. For example, in FIG. 4B, the distance is lowered by the distance indicated by the arrow in the direction of the arrow. Then, the current increases to be in a processing state.
Next, after the processing state is maintained for a predetermined time, the probe 11 is raised again. In FIG. 4B, the position of the tip of the probe 11 is returned to the position of the original black point of the arrow. Then, it is moved by a predetermined distance as the observation state. For example, in FIG. 4B, the tip of the probe 11 is moved to the position of the adjacent black dot. As described above, by repeating, the tip of the probe 11 at the time of processing can be drastically and uniformly processed as compared with the method shown in FIG.

As described above, G is accurately and uniformly obtained.
After selectively removing the aN film 4a, a fine structure 5a made of GaAs is selectively formed where the surface of the GaAs substrate 1 is exposed, as shown in FIG. This is performed by supplying TMGa and TBAs to the substrate surface in a state where the GaAs substrate 1 is heated to 600 ° C. in a vacuum (organic metal molecular beam epitaxy method). In this molecular beam epitaxy method, selective growth is performed in which GaAs does not grow on the GaN film 4a.

Next, hydrogen atoms are introduced onto the heated GaAs substrate 1 and, as shown in FIG.
a is removed by etching. Next, as shown in FIG. 2 (g), Ga is deposited on the GaAs substrate 1 so as to cover the microstructure 5a.
An N film 4b is formed. Then, as described above, the GaN film 4b is selectively removed by the probe 11, and FIG.
As shown in (h), the GaAs substrate 1 and the fine structure 5
a is partially exposed. Note that the state of the switch 13 shown in FIG. 2H indicates the connection in the processing state.

Next, as shown in FIG. 2 (i), trimethylindium (TMIn) and TBA are formed in the exposed region by, for example, a metalorganic molecular beam epitaxy method.
By supplying s, the fine structure 5b made of InP is formed. Then, hydrogen atoms are introduced onto the heated GaAs substrate 1, and the GaN film 4b is removed by etching as shown in FIG. As a result, the same GaAs substrate 1
A state in which the fine structure 5a and the fine structure 5b are formed thereon is realized.

FIG. 5 is a sectional view of a semiconductor device having a fine structure formed as described above. FIG. 5 (a)
Denotes a quantum box semiconductor laser, and an n ^{+ -type} GaAs substrate 5
1, an AlGaAs layer 52 is formed, and a p ^{+ -type} GaAs clad layer 54 is formed thereon. A GaAs quantum box 53 having a fine quantum box structure is formed in the AlGaAs layer 52, and these constitute an active layer. In such a quantum box semiconductor laser, if the GaAs quantum box 53 in the active layer is not uniformly formed, as shown in FIG. 6A, the emission wavelength is wide and the emission intensity cannot be increased.

In comparison with this, in the quantum box semiconductor laser in which the GaAs quantum box 53 is formed uniformly according to the above-described embodiment, as shown in FIG. The emission intensity is increased by a factor of 1000. Then, the threshold current also decreased to one tenth. With conventional technology,
Although a quantum box can be formed, the size cannot be uniform, and the quantum box varies in a range of 3 to 10 nm. However, according to the above-described embodiment, for example, a plurality of quantum boxes having a size of 5 nm can be uniformly and accurately formed.
As a result, in the quantum box semiconductor laser using the active layer as the active layer, it is possible to oscillate laser light having a high emission intensity with a uniform wavelength at a low threshold current.

FIG. 5B shows a heterojunction bipolar transistor. This is an n ^{+ type} GaAs
A collector 62 made of n-type GaAs on a substrate 61;
A base 63 made of p-type AlyGa1-yAs and an emitter 65 made of n-type AlGaAs are formed thereon. Note that a collector electrode 61 a is also formed on the GaAs substrate 61, a base electrode 63 a is formed on the base 63, and an emitter electrode 65 a is formed on the emitter 65.

In this heterojunction bipolar transistor, a quantum box 64 made of GaAs is formed on a base 63. In such a heterojunction bipolar transistor having a quantum box structure with a uniform size, the base level is quantized, so that the cutoff frequency can be increased from 220 GHz to 450 GHz. became.

FIG. 5C is a sectional view showing another example of the quantum box semiconductor laser shown in FIG. 5A. FIG.
As shown in (c), quantum box 53a made of GaAs
A microstructure composed of a quantum box 5b made of InAs is formed in the AlGaAs layer 52. Thus, in a quantum box semiconductor laser in which quantum boxes made of different materials are formed, laser oscillation of two emission wavelengths can be performed with a low threshold current.

[0035]

As described above, according to the present invention, the tip of the probe having the tip sharpened to the atomic level is always brought close to the surface of the selective film by a fixed distance, and the contact between the semiconductor substrate and the probe is made. The selective film was selectively etched by passing a tunnel current therebetween. Therefore, in the present invention, the formed shape can be observed at the time of pattern formation, so that the size, position, and composition can be controlled, and a three-dimensionally uniform quantum box structure can be manufactured. As a result, a semiconductor laser with an extremely low threshold current and a transistor with a higher operating frequency can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method for manufacturing a fine structure according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view following FIG. 1 showing a method for manufacturing a fine structure in the embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a change in an uneven state of a GaN surface depending on a growth temperature.

FIG. 4 is an explanatory diagram showing a processing method according to the embodiment of the present invention.

FIG. 5 is a sectional view of a semiconductor device having a fine structure formed according to an embodiment of the present invention.

FIG. 6 is a characteristic diagram showing emission characteristics of the quantum box semiconductor laser.

FIG. 7 is a cross-sectional view illustrating a conventional method for manufacturing a fine structure.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... GaAs substrate, 2 ... oxide film, 4a, 4b ... GaN thin film, 5a, 5b ... fine structure, 11 ... probe, 12a, 12
b: piezo, 13: switch.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 29/66 H01S 3/18 21/331 H01L 29/205 29/73 29/72 H01S 3/18

Claims (4)

[Claims] 1. A first step of removing and cleaning an oxide film on a surface of a semiconductor substrate, and heating the semiconductor substrate to supply radicalized nitrogen to the surface to form a selective film containing nitrogen. A second step of: tipping the tip having a tip sharpened to an atomic level,
A third step of selectively etching the select film by always bringing the select film close to the surface of the select film by a certain distance and flowing a tunnel current between the semiconductor substrate and the probe; Heating, and an organic metal gas containing a group III atom and an organic metal gas containing a group V atom are supplied thereon;
A fourth step of growing a fine semiconductor structure comprising the group III atoms and group V atoms only in the etched region; and a fifth step of removing the selective film. Method of manufacturing. 2. The method for manufacturing a semiconductor microstructure according to claim 1, wherein in the first step, cleaning is performed by supplying an organic metal gas containing a group V atom to the surface of the semiconductor substrate. Of manufacturing a semiconductor microstructure. 3. The method for manufacturing a semiconductor microstructure according to claim 1, wherein in the second step, radicalized nitrogen is supplied by heating a nitrogen gas. Production method. 4. The method for manufacturing a semiconductor microstructure according to claim 1, wherein in the fifth step, the selective film is removed by supplying atomic hydrogen onto the semiconductor substrate. A method of manufacturing a semiconductor microstructure.