JP3402425B2 - Manufacturing method of semiconductor fine structure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor microstructure of nanometer size, shape, and shape on one substrate.
The present invention relates to a method for manufacturing a semiconductor fine structure in which a position on a substrate is accurately controlled and three-dimensionally manufactured.

[0002]

2. Description of the Related Art When the size of a semiconductor fine structure is made smaller than a few tens of nanometers, the energy distribution width 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). By applying a plurality of quantum boxes with uniform dimensions to a semiconductor laser, a semiconductor laser with an extremely low threshold current can be realized. A method called selective growth will be shown below as an example of a method of manufacturing the quantum box having the semiconductor fine structure.

First, as shown in FIG. 7A, the GaAs substrate 71 is heated in vacuum at about 600 ° C. to etch the natural oxide film 72 formed on the surface thereof. By heating in vacuum, the GaAs oxide decomposes and vaporizes. However, at this time, gas As is introduced into the substrate surface. This is performed in order to compensate As at the stage of decomposition by heating. Ga
Compared with the above, since the group V element As is more likely to vaporize,
This is because it is necessary to keep the atmosphere in excess.

However, in this etching, even if vaporized As is introduced to the surface of the GaAs substrate 71, GaA
As defects on the surface of the s substrate 71 cannot be completely compensated, and the surface cannot be made flat. Therefore, following the etching, as shown in FIG. 7B, triethylgallium (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. Flatten the surface. At this time, Si or Zn is introduced as an impurity into the GaAs buffer layer 73 so as to have conductivity.

Then, as shown in FIG. 7C, trimethylgallium is introduced together with dimethylhydrazine onto the surface of the GaAs substrate 71 to deposit a thin film 74 of gallium nitrogen (GaN). Dimethylhydrazine serves as a nitrogen raw material, but instead of this, nitrogen atoms may be supplied by cracking ammonia.

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

[0007]

As described above, in the conventional manufacturing method, electron beam exposure has been used for patterning a fine structure. However, the spread of the focus of the electron beam is about 50 nm even if the focus is minimized. Then, the edges are not sharp, and the energy is distributed so that the central portion has the maximum energy and the energy is gradually attenuated toward the periphery. Therefore, conventionally, by adjusting the irradiation amount of the electron beam, 10 We have tried to form a fine structure with a size of nanometer. But,
The microstructure formed in this way has low reproducibility, and it was very difficult to align the same size when manufacturing a plurality of microstructures. Therefore, conventionally, it has not been possible to form a useful quantum box structure.

Further, the surface cannot be observed in situ during the conventional electron beam irradiation. For this reason, it has not been possible to monitor and control the exposure status and the exposure position on the substrate. Therefore, when multiple microstructures are fabricated on the same substrate, the relative positions between the structures are unknown,
It was very difficult to manufacture it three-dimensionally and also to manufacture it in high density.

The present invention has been made in order to solve the above problems, and it is possible to accurately manufacture a fine structure exhibiting the quantum effect in a uniform size. To aim.

The method for producing a semiconductor fine structure of the present invention is
First, an organic metal gas containing a group V atom is supplied to the surface of the semiconductor substrate to remove and clean the oxide film on the surface of the semiconductor substrate, and secondly, the semiconductor substrate is heated to remove nitrogen on the surface.
By heating the gas, radicalized nitrogen is supplied to form a selective film containing nitrogen. Third, the tip of a probe having a sharpened atomic level tip is always placed on the surface of the selective film for a certain distance. The selective film is selectively etched by causing a tunnel current to flow between the semiconductor substrate and the probe when they are brought close to each other. And fourth, heating the semiconductor substrate and supplying an organometallic gas containing a group III atom and an organometallic gas containing a group V atom onto the semiconductor substrate to etch the group III atom and the group V atom only in the etched region.
A fine semiconductor structure composed of a group atom was grown and, fifth, 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 etching can be observed. As described above, if the size of the semiconductor fine structure is made smaller than several tens of nanometers, the energy distribution width of electrons and holes in the structure can be made extremely narrow according to quantum mechanics. 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 observed with a probe and the tunnel current is detected to observe the surface shape, and at the same time, the selective film for selective growth is finely processed.
A fine structure was grown in that region. For this reason,
According to the present invention, since the formed shape can be observed at the time of forming the pattern, the size, position and composition can be controlled, and a three-dimensionally extremely uniform quantum box structure can be manufactured.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1A to 1D are cross-sectional views showing a method of manufacturing a fine structure according to an embodiment of the present invention. In this embodiment, a case where GaAs and InAs semiconductor fine structures are formed on the same GaAs substrate 1 will be described.

First, as shown in FIG. 1 (a), an oxide film 2 is present on the surface of a GaAs substrate 1 left in the atmosphere. In order to remove this oxide film 2, the GaAs substrate 1
Is heated to 500 ° C. in vacuum to thermally decompose and remove the 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. As a result, the clean surface of the GaAs substrate 1 is exposed.

Conventionally, in the etching of 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, when vaporized As is used, As of the GaAs substrate
In some cases, the Ga defects cannot be completely compensated and Ga droplets are generated on the surface. Therefore, 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 the TBAs are decomposed by heat so that the hydrogen atoms produced together with the As atoms also effectively remove gallium. The surface of the GaAs substrate 1 to which TBAs are supplied is decomposed by heat and mainly As is etched, and gallium is also etched by hydrogen atoms. Since As is also compensated by supplying As atoms, as a whole, gallium and As are uniformly etched.

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 could not be completely compensated, and the GaAs buffer layer had to be grown in order to recover the flat surface after etching. Also, in the past,
Since I was trying to process with electron beam irradiation,
The GaAs buffer layer needs to have conductivity, and Si and Zn must be added as impurities.
The process was complicated. This is because unless it has conductivity, it is charged up when it is irradiated with an electron beam.

However, as shown in this embodiment,
If the introduction of TBAs compensates for As on the surface of the GaAs substrate 1 and the gallium is also etched, the GaAs buffer layer need not be formed. When InP is used as the substrate instead of GaAs, tertiary butylphosphine (TBP) is effective. That is, in etching for removing the oxide film, an organic metal containing a group V atom may be introduced to the surface of the substrate.
In particular, an organic metal having a structure in which a group V atom and hydrogen are directly bonded is effective. However, even if trimethylarsenic is used, the effect is slightly inferior but effective.

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

On the other hand, temperature conditions at the time of GaN deposition and G when GaAs is deposited on GaN deposited at that temperature.
Comparing the film thicknesses of the aAs films, as shown in FIG. 3B, GaAs is scarcely deposited on GaN deposited at 400 ° C. or lower. On the other hand, Ga on GaAs
When the N film is thinly formed, the underlying GaAs surface is partially exposed in the formed GaN film in the polycrystalline state. Therefore, GaAs grows on the GaN film formed on GaAs at a temperature higher than 400 ° C. Ga
Since the N film is used for selective growth of GaAs, from this viewpoint as well, it is necessary to grow GaN at a substrate temperature of 400 ° C. or lower.

Then, as shown in FIG. 1D, the probe 1
1 is used to partially remove the GaN film 4a. Figure 1
In (d), the probe 11 is a part that constitutes 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. The piezos 12a and 12b apply the applied voltages V _x and V _y.
And is displaced in proportion to the value of V _z . The piezo 12a is
It is used to scan the probe 11. With the above configuration,
With the constant voltage V _t applied between the probe 11 and the GaAs substrate 1, the voltage V _z applied to the piezo 12b is controlled so that the current value (tunnel current) flowing through the circuit becomes constant.

In this state, move the probe 11 from the surface to 2 to 3n.
When scanning is performed at a distance of m, the piezo 12b changes the displacement amount in an attempt to keep the distance between the probe 11 and the surface constant, corresponding to the unevenness of the surface being scanned. Then, by measuring this displacement amount, it becomes possible to observe the uneven state of the surface being scanned. This is the principle of observing the surface shape with a scanning tunneling microscope. Note that 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 close 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
Partial etching of the aN film 4a can be performed in units of 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, since the processing state and the observation state can be instantaneously switched by switching the switch 13, it becomes possible to observe the etching processing state on the spot. Further, since the probe 11 can be moved to a place where processing is desired while observing the surface, it becomes possible to form a fine structure with extremely high accuracy.

Hereinafter, this processing method will be described in more detail with reference to the sectional view of FIG. In FIG. 4 (a),
The probe 1 when observing the surface state of the GaAs substrate 1.
1 The locus of the tip is shown by the dotted line. The solid line indicates the locus of the tip of the probe 11 in the case of processing, in which scanning was performed with the tunnel current value increased. When the surface of the observation target is scanned with the scanning tunneling 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, the distance between the tip of the probe 11 and the surface of the observation target is controlled to be constant. Then, the state in which the probe 11 is moved under 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 so as to be kept constant, as shown by the dotted line in FIG.
The tip of the probe 11 operates by 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 to process the surface, as shown by the solid line in FIG. 4A, the probe 11 collides with the surface or is too far from the surface, and the processing is performed under certain conditions. 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 with the tip position being feedback controlled.
If processing is performed in the vicinity of the surface of the substrate 1, processing cannot be performed under certain conditions.

On the other hand, if the surface is processed by repeating the following operation, the surface can be uniformly processed (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 in the direction of the arrow by the distance indicated by the arrow. Then, the current is increased to enter the processing state.
Then, after the working state 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 dot of the arrow. Then, it is moved by a predetermined distance as an 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 during processing can be dramatically processed uniformly as compared with the method shown in FIG.

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

Next, hydrogen atoms are introduced into the heated GaAs substrate 1 to form the GaN film 4 as shown in FIG. 1 (f).
The a is removed by etching. Next, as shown in FIG. 2G, Ga is formed on the GaAs substrate 1 so as to cover the fine structure 5a.
The N film 4b is formed. Then, as described above, the GaN film 4b is selectively removed by the probe 11,
As shown in (h), the GaAs substrate 1 and the fine structure 5
Partly expose the top of a. The state of the switch 13 shown in FIG. 2 (h) indicates the connection in the processed state.

Next, as shown in FIG. 2 (i), trimethylindium (TMIn) and TBA are applied to this exposed region by, for example, a metal organic 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. 2 (j). As a result, the same GaAs substrate 1
A state in which the fine structure 5a and the fine structure 5b are formed on the upper side is realized.

FIG. 5 is a cross-sectional view of a semiconductor device having a fine structure formed as described above. Figure 5 (a)
Indicates a quantum box semiconductor laser, and an n ^{+ type} GaAs substrate 5
1, an AlGaAs layer 52 is formed, and a p ^{+ -type} GaAs cladding layer 54 is formed on the AlGaAs layer 52. Then, 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, unless the GaAs quantum boxes 53 in the active layer are formed uniformly, the emission wavelength width is wide and the emission intensity cannot be increased as shown in FIG. 6 (a).

In comparison with this, in the quantum box semiconductor laser in which the GaAs quantum boxes 53 are formed uniformly according to the above-mentioned embodiment, the half width becomes 1/1000, as shown in FIG. 6B. The emission intensity is 1000 times. And the threshold current was also reduced to 1/10. With conventional technology,
Quantum boxes can be formed, but their sizes cannot be made uniform, and they vary in the range of 3 to 10 nm. However, according to the above-described embodiment, for example, a plurality of quantum boxes each having a size of 5 nm can be formed uniformly and accurately.
As a result, in the quantum box semiconductor laser using this as an active layer, it is possible to oscillate laser light having a uniform emission wavelength and high emission intensity with a low threshold current.

FIG. 5B shows a heterojunction bipolar transistor. This is 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 on the base 63. A collector electrode 61a is also formed on the GaAs substrate 61, a base electrode 63a is formed on the base 63, and an emitter electrode 65a is formed on the emitter 65.

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

FIG. 5C is a sectional view showing another example of the quantum box semiconductor laser shown in FIG. 5A. Figure 5
As shown in (c), a quantum box 53a made of GaAs
And a fine structure including a quantum box 5b made of InAs is formed in the AlGaAs layer 52. As described above, in the quantum box semiconductor laser in which the quantum boxes made of different materials are formed, laser oscillation of two emission wavelengths is possible with a low threshold current.

[0035]

As described above, according to the present invention, the tip of a probe having a sharpened tip at the atomic level is always brought closer to the surface of the selective film by a certain distance, and the tip of the semiconductor substrate and the probe are separated from each other. A selective current is selectively etched by passing a tunnel current between them. Therefore, in the present invention, since the formed shape can be observed at the time of forming the pattern, the size, position and composition can be controlled, and a three-dimensionally extremely uniform quantum box structure can be manufactured. As a result, a semiconductor laser having an extremely low threshold current and a transistor having a higher operating frequency can be realized.

[Brief description of drawings]

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

FIG. 3 is a characteristic diagram showing a change in a concavo-convex 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 the embodiment of the present invention.

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

FIG. 7 is a cross-sectional view showing a conventional method for producing a fine structure.

[Explanation of symbols]

1 ... GaAs substrate, 2 ... Oxide film, 4a, 4b ... GaN thin film, 5a, 5b ... Microstructure, 11 ... Probe, 12a, 12
b ... Piezo, 13 ... Switch.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01L 29/205 H01L 29/66 29/66 29/72 29/73 (56) References JP-A-8-107103 (JP, A ) JP-A-5-175150 (JP, A) JP-A-6-326040 (JP, A) JP-A-7-142404 (JP, A) JP-A-8-32047 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 21/302 H01J 37/30 H01L 21/203 H01L 21/331

Claims (2)

(57) [Claims] 1. A first step of removing and cleaning an oxide film on a surface of a semiconductor substrate; heating the semiconductor substrate; and heating a nitrogen gas on the surface.
Supplying a radicalized nitrogen by a second step of selectively forming film containing nitrogen, the tip of the probe having a sharpened tip atomic level,
A third step of selectively etching the selective film by causing the selective film surface to always approach a predetermined distance and passing a tunnel current between the semiconductor substrate and the probe; It is heated, and an organometallic gas containing a group III atom and an organometallic gas containing a group V atom are supplied on this.
The method includes a fourth step of growing a fine semiconductor structure composed of the group III atoms and group V atoms only in the etched region, and a fifth step of removing the selective film. A method for producing a semiconductor fine structure, characterized in that the surface of the semiconductor substrate is cleaned by supplying an organometallic gas containing a group V atom. 2. The method for manufacturing a semiconductor fine structure according to claim 1, wherein atomic hydrogen is deposited on the semiconductor substrate in the fifth step.
The method for producing a semiconductor fine structure, characterized in that the selective film is removed by supplying to the semiconductor fine structure.