JP4151247B2 - Semiconductor device manufacturing method and semiconductor device manufacturing apparatus used therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device in which a semiconductor substrate body on which semiconductor layers are stacked is wet-etched, and a semiconductor device manufacturing apparatus used therefor.
[0002]
[Prior art]
Generally, a semiconductor device such as a large-scale integrated circuit (ULSI) formed of silicon (Si), a laser diode (LD) formed of a compound semiconductor such as gallium arsenide (GaAs), or an electrostatic effect transistor (FET) It has a structure in which p-type and n-type semiconductor films having different conductivity types are stacked, and in the manufacturing process, it is necessary to partially etch these semiconductor films to form a fine structure.
In particular, in the case where a single crystal film is regrown on the surface after etching, such as LD using Si, wet etching is applied in which there is little disorder of crystals at the regrowth interface and high device reliability can be expected. There are many cases.
[0003]
A nitride semiconductor is a wide band gap semiconductor having a wide band gap of 3 eV or more, and is used as a wide short wavelength light emitting element material from orange to ultraviolet region, and operates stably even at a high temperature exceeding 100 ° C. It is expected to be used as a semiconductor for high temperature operation.
Nitride semiconductors are rarely used as a single film, and when fabricating an LD, a nitride semiconductor is laminated and grown, and a groove is formed by etching or an electrode is formed.
Nitride semiconductors are chemically stable materials. However, a method of performing wet etching while irradiating light having energy greater than the band gap has been studied, and etching is performed at the interface between semiconductor films of different conductivity types and compositions. Controlling the stop is important for improving the reliability of the device while suppressing the variations in device quality.
[0004]
Therefore, in order to control the stop of etching at the interface between semiconductor films of different conductivity types and compositions, a method of strictly controlling the etching time, and Japanese Patent Application Laid-Open No. 6-196801, in the case of wet etching, As a method of stopping etching at the semiconductor film interface having a different composition, there is a method of forming an etching stop layer {Eching Stop Layer (ESL)} having a low etching rate.
[0005]
FIG. 12 is a cross-sectional view of a semiconductor laser device having a current stripe structure after providing a conventional etching stop layer and performing wet etching, as disclosed in the above publication.
In the figure, 52 is an n-type GaAs substrate, 53 is an n-type GaAs buffer layer, 54 is an n-type Ga _0.5 Al _0.5 As, 55 is a Ga _0.85 Al _0.15 As active layer, 56 Is a p-type Ga _0.5 Al _0.5 As cladding layer, 57 is an ESL made of p-type Ga _0.8 Al _0.2 As, and 58 is an n-type Ga _0.4 Al _0.6 As current block. 58a is a stripe window, 59 is an I-type Ga _0.5 Al _0.5 As cladding layer, and 60 is a GaAs contact layer.
That is, the n-type Ga _0.65 Al _0.35 As current blocking layer 58 is wet-etched to form the stripe-shaped window 58 a, but the etching is performed on the p-type Ga _0.5 Al _0.5 As cladding layer 56. A p-type Ga _0.8 Al _0.2 As ESL layer 57 is formed so as not to reach. This utilizes the property that the phosphoric acid-hydrofluoric acid mixed solution used as the etching solution is p-type GaAlAs having an Al composition of 0.4 or less, and the etching rate rapidly decreases.
[0006]
[Problems to be solved by the invention]
However, the method of strictly controlling the etching time has a problem in that the etching rate changes due to variations in process conditions such as a subtle temperature change during etching, and the etching does not stop at the target portion.
Further, the etching stop by the conventional insertion of the ESL has a problem that the etching does not stop with good reproducibility in the ESL because it is difficult to control the Al composition ratio and the conductivity type in the ESL.
[0007]
The present invention has been made to solve such a problem, and since the etching state can be monitored, the semiconductor device manufacturing method capable of accurately stopping the etching at the interface between different semiconductor films and improving the wet etching processing accuracy, and It aims at obtaining the manufacturing apparatus used for this.
[0008]
[Means for Solving the Problems]
Manufacturing method of engaging Ru semi conductor arrangement to the invention, on a semiconductor substrate body, while measuring the first layer and the surface electrode potential of the semiconductor substrate provided with a second layer in this order, each with different electrode potentials , I manufacturing method der semiconductor device for wet etching the second layer, the first layer is p-type semiconductor layer, the second layer is an n-type semiconductor layer, the n-type semiconductor layer The n-type semiconductor layer is wet etched while irradiating light having energy larger than the band gap energy and measuring the surface electrode potential of the semiconductor substrate, so that the surface electrode potential of the semiconductor substrate becomes the second layer. A method of manufacturing a semiconductor device, comprising: etching is stopped by applying a negative potential to the surface of the semiconductor substrate in a potential change region where the potential of the first layer changes to the electrode potential of the first layer .
[0015]
Apparatus for producing a locking Ru semi conductor arrangement to the present invention includes an etching solution for immersing the semiconductor substrate, as it is etched in this etching solution, the potential difference measuring device for measuring the surface electrode potential of the semiconductor substrate, in the etching An apparatus for manufacturing a semiconductor device comprising an etching stop means for stopping etching due to a change in surface electrode potential of the semiconductor substrate, wherein the etching stop means applies a negative potential to the surface of the immersed semiconductor substrate. A semiconductor device manufacturing apparatus characterized by being a power supply to be applied .
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a semiconductor device manufacturing apparatus used in the method of manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 2 is a wet-etched semiconductor substrate and measurement of the surface potential of the semiconductor substrate. It is explanatory drawing which is limited and shown and simplified.
1 and 2, 1 is an etching solution, 2 is a semiconductor substrate, 20 is a semiconductor substrate body, 21 is a first layer, 22 is a second layer, and the first layer 21 and the second layer described above. Each 22 has a different electrode potential. 3 is a semiconductor substrate holder, 4 is an etching tank, 7 is a magnetic stirrer, 8 is a reference electrode, 81 is a glass capillary tube of the reference electrode 8, 82 is an etching region, 9 is a potentiometer, and 6 is a potentiometer with the semiconductor substrate 2. Connection electrodes 10 for connecting to 9 are resist films.
In the present embodiment, the semiconductor substrate 2 is formed by laminating I-type AlAs and II-type GaAs as the first layer 21 and the second layer 22 on the semiconductor substrate body 20 made of sapphire. As the etching solution, a mixed solution of hydrogen peroxide and tartaric acid is used.
[0020]
As described above, in order to electrically connect the semiconductor substrate 2 on which the first layer 21 and the second layer 22 are stacked, and the potentiometer 9, the connection electrode 6 is connected to the first layer 21. Connect to the side wall. In this case, the region other than the etching region 82 on the surface of the semiconductor substrate 2 is covered with the resist film 10 to prevent contact with the etching solution 1.
In the present embodiment, since an insulating sapphire substrate is used for the semiconductor substrate main body 20, the first layer 21 is in electrical contact. However, when a conductive substrate is used, a connection electrode is connected to the substrate. It is also possible. However, in that case, it is necessary to cover the entire surface of the semiconductor substrate except for the etching region 82 with a resist film or the like to prevent contact with the etching solution.
[0021]
Next, the semiconductor substrate 2 is immersed in the etching solution 1 and etching of the second layer 22 is started. At the same time, in the vicinity of the etching region 82, a glass capillary connected to a reference electrode 8 made of silver / silver chloride. The electrode 81 is installed, and the potential difference between the surface potential of the semiconductor substrate 2 and the reference electrode 8 is measured by the potential difference measuring device 9.
[0022]
FIG. 3 is a characteristic diagram showing the potential change of the surface potential of the semiconductor substrate with the etching time when wet etching is performed as described above. In the figure, the vertical axis represents the electrode potential, and the horizontal axis represents the etching time.
As shown in the figure, the surface potential of the semiconductor substrate is measured by measuring the electrode potential (second potential in the figure) of the second layer in the state A2 where the bottom surface of the etching region is in the range of the second layer, In the state A1 in which the bottom surface reaches the first layer and is in the range of the first layer, the electrode potential (first potential in the figure) of the first layer is measured, and the first potential is measured from the second potential. There is a change region A1-A2 that changes to a potential.
Even when the bottom surface of the etching region reaches the first layer, the second layer remains on the side surface of the etching region, but the potential of the first layer at the bottom surface of the etching region having the lowest electrical resistance becomes dominant. The measurement potential corresponds to the potential of the first layer.
[0023]
As described above, by measuring the electrode potential on the surface of the semiconductor substrate during wet etching, the etching state can be monitored, and the point where wet etching should be stopped can be determined with high accuracy.
That is, in the present invention, since the wet etching state can be monitored, the stop of the wet etching can be accurately determined, and the processing accuracy can be improved.
[0024]
Embodiment 2. FIG.
In Embodiment 1, the case where the second layer is a typical gallium nitride (GaN) of n-type nitride semiconductors will be described.
The dissolution reaction of an alkaline solution of gallium nitride (GaN) in an etching solution generally involves holes as shown by the following formula (1).
GaN + 6OH ⁻ + 3h ⁺ → GaO ₃ ^{3 −} + ⁰ · 5N ₂ + 3H ₂ O (1)
(In the formula, h ⁺ represents a hole.)
[0025]
FIG. 4 is an explanatory diagram for explaining the dissolution reaction of the nitride semiconductor (n-type semiconductor) in contact with the etching solution at the time of wet etching using a band model of the nitride semiconductor, where Ec is the conduction band edge. , Ef is the Fermi level, and Ev is the valence band edge.
[0026]
As shown in the above equation, in order for the nitride semiconductor to dissolve in the liquid, it is necessary that holes are diffused to the interface between the semiconductor and the solution and consumed in the reaction process.
Considering that the hole concentration at the interface between the semiconductor and the solution determines the dissolution rate of the semiconductor, as shown in FIG. 4, the conduction of electrons in the n-type semiconductor is usually carried by electrons in the conduction band. Since it is usually low, etching does not proceed as it is.
However, by applying a power source for applying a positive potential to the surface of the immersed semiconductor substrate to the manufacturing apparatus used in the first embodiment, and applying a positive potential to the surface of the semiconductor substrate being etched, As shown in FIG. 6, it is possible to increase the etching rate by generating a potential gradient inside the semiconductor, increasing the rate at which valence band holes diffuse into the nitride semiconductor / solution interface. FIG. 6 is an explanatory diagram using a band model of a semiconductor substrate in contact with an etching solution when a positive potential is applied to the surface of the semiconductor substrate during etching.
[0027]
Embodiment 3 FIG.
In Embodiment 2, by applying a positive potential to the surface of the semiconductor substrate being etched, a potential gradient is generated inside the semiconductor, and the rate at which valence band holes diffuse into the nitride semiconductor and solution interface is increased. Instead of adding a light source for irradiating the immersed semiconductor substrate with light having a photon energy larger than the band gap energy of the semiconductor to the manufacturing apparatus used in the first embodiment, the semiconductor substrate being etched is applied to the semiconductor substrate being etched. By irradiating the light, electrons are excited inside the n-type semiconductor to form holes, and the etching proceeds.
FIG. 5 is an explanatory diagram for explaining, using a band model of a semiconductor substrate in contact with an etching solution, when light having an energy larger than the band gap energy is irradiated in the second embodiment of the present invention. In the figure, hν represents the energy of the irradiation light, and the dotted line with arrows represents the direction of movement of electrons or holes.
[0028]
That is, when light is irradiated, charge separation occurs inside the nitride semiconductor and holes are generated in the valence band. During etching, these holes are diffused and consumed at the GaN / solution interface. To advance.
[0029]
Note that, for a p-type semiconductor, even when light having energy greater than or equal to the band gap is not irradiated, holes are present in the valence band, so that the light irradiation hardly affects the etching rate.
[0030]
In the present embodiment, as in the second embodiment, by applying a positive potential to the surface of the semiconductor substrate being etched, a potential gradient is generated inside the semiconductor as shown in FIG. The rate at which the positive holes diffuse into the nitride semiconductor / solution interface can be increased.
[0031]
FIG. 7 is a configuration diagram showing a configuration of a semiconductor substrate etched by the semiconductor device manufacturing method of the present embodiment, in which 61 is a sapphire substrate as a semiconductor substrate body, and 62 is a p-type GaN film (first layer). The film thickness is 200 nm), 63 is an n-type GaN film (film thickness of 600 nm) as a second layer, and 64 is a mask film. All except 64 mask films were laminated by metal organic vapor phase deposition (MO-CVD).
[0032]
At present, the stripe-type LD as shown in FIG. 12 is not realized with a wide band gap semiconductor such as GaN, but in the future, it is essential to develop an LD having a stripe structure with excellent productivity.
In order to realize a stripe-type LD structure similar to that shown in FIG. 12, a technique for forming stripe windows with high controllability by wet etching is required. Therefore, the substrate shown in FIG. 7 was formed as a model structure, and a wet etching experiment was conducted.
[0033]
FIG. 8 is a configuration diagram of the manufacturing apparatus used in this embodiment, 2 is a semiconductor substrate shown in FIG. 7, 5 is a UV irradiation Xe light source, and 5A is a UV light guide made of an optical fiber. In the present embodiment, a potassium hydroxide solution (1 mol / l) is used as the wet etching solution 1, and the capillary tube and the reference electrode 8 formed of silver / silver chloride are connected from the vicinity of the etching region of the semiconductor substrate. did. The UV light is irradiated onto the entire surface of the GaN semiconductor substrate 2 using the UV light guide 5A, and the potential difference between the connection electrode 6 connected to the side surface of the first layer and the reference electrode is measured using the potentiometer 9 while etching. I did it.
[0034]
FIG. 9 is a characteristic diagram showing changes in the surface potential of the semiconductor substrate surface due to the etching time when the semiconductor substrate 2 having the cross-sectional structure shown in FIG. 7 is wet-etched while irradiating UV light as described above.
In the region where the n layer at the initial stage of etching is etched, the potential is −1.33 V (vs Ag / AgCl), but when the P layer is exposed on the surface, the potential changes to −0.83 V (vs Ag / AgCl). To do. From this, the etching state of the sample can be monitored by monitoring the electrode potential on the surface of the semiconductor substrate during etching.
[0035]
In FIG. 9, for example, when the light irradiation is stopped when the electrode potential on the surface of the semiconductor substrate reaches ± 0.1 V of the electrode potential of the P layer (measured in advance), the etching rate is reduced and etching is performed. Stops, and the in-plane variation after etching becomes about ± 0.1 μm.
[0036]
Embodiment 4 FIG.
FIG. 10 is a configuration diagram of the manufacturing apparatus used in the present embodiment. In the manufacturing apparatus of FIG. 8, a power source (potentiostat) 11 having a platinum counter electrode 12 is further used.
In the third embodiment, the semiconductor substrate was wet etched in the same manner as in the third embodiment except that the manufacturing apparatus of FIG. 10 was used.
[0037]
Similar to the third embodiment, a characteristic diagram similar to FIG. 9 was obtained. Although the etching stop time is determined in the same manner as in the third embodiment, in the third embodiment, the etching rate is reduced by stopping the illumination, but when etching is performed under fluorescent lamp illumination, it is generated from the fluorescent lamp. Etching does not stop completely because the light component contains a wavelength component in the ultraviolet region. However, in this embodiment, the etching can be completely stopped by applying a negative potential to the surface of the semiconductor substrate by the potentiostat 11 simultaneously with the stop of the light irradiation.
Actually, it was found that the etching was stopped by stopping the light irradiation and applying the cathode bias to −2 V, and the in-plane variation after etching stopped within ± 0.05 μm with good controllability.
[0038]
FIG. 11 is an explanatory diagram showing a band structure of GaN electrons when a potential of −2 V is applied to a semiconductor substrate to stop etching in this embodiment.
That is, the holes in the valence band generated by the charge separation by light irradiation are bent downward so that the diffusion to the GaN / solution interface is prevented and the etching is completely stopped.
[0039]
Embodiment 5. FIG.
In FIG. 7, a semiconductor substrate in which the semiconductor substrate body 61 is a Si substrate, the second layer 62 is a p-type SiC film (thickness 200 nm), and the first layer 63 is an n-type SiC film (thickness 600 nm) is used. Performs wet etching in the same manner as in the third embodiment.
[0040]
However, in the case of SiC, the potential difference is different from that of GaN. In this case, a 2.5% HF aqueous solution was used as the solution. In this case, when the etching region changes from the n layer to the p layer, it is observed that the difference between the electrode potential of the n layer and the electrode potential of the p layer is +0.8 V, and the wet etching state can be monitored by measuring the potential. I found out. When the electrode potential is changed to the electrode potential of the p layer, UV irradiation is stopped and −2 V cathode bias is applied. As a result, the etching control region may be ± 0.05 μm or less. all right.
[0041]
Embodiment 6 FIG.
In Embodiment Mode 3, sulfuric acid or citric acid may be used as an etchant. In order to accelerate the reaction, hydrogen peroxide may be added to the etching solution.
The same effect can be obtained even if a mixed solution of hydrofluoric acid and an acid that does not etch GaN by itself is used as an etchant. A combination of phosphoric acid and hydrofluoric acid, hydrochloric acid and hydrofluoric acid, sulfuric acid and hydrofluoric acid, tartaric acid and hydrofluoric acid, acetic acid and hydrofluoric acid, or formic acid and hydrofluoric acid may be used.
Hydrogen peroxide may be added to accelerate the reaction in the mixed etching solution of acids. Further, it may be diluted with water, sodium hydroxide or ammonium fluoride in order to reduce the etch rate.
[0042]
Embodiment 7 FIG.
In Embodiment 3, the material to be wet-etched is not limited to GaN, but gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium phosphide (InP), indium gallium phosphide (InGaP), gallium aluminum phosphide (GaAlP), Si or aluminum gallium indium phosphide (AlGaInP) may be used. As a method for manufacturing a semiconductor substrate to be wet-etched, a molecular beam epitaxy method (MBE) or a Czochralski method (CZ) may be used in addition to the manufacturing method by MO-CVD shown in Embodiment Mode 3.
[0043]
【The invention's effect】
Method of manufacturing a semi-conductor device of the present invention, on a semiconductor substrate body, while measuring the first layer and the surface electrode potential of the semiconductor substrate provided with a second layer in this order, each with different electrode potentials, the The method of wet-etching the second layer can monitor the etching state and has an effect of improving the processing accuracy. In the first or second method for manufacturing a semiconductor device, the first layer is a p-type semiconductor layer and the second layer is an n-type semiconductor layer, and the energy is larger than the band gap energy of the n-type semiconductor layer. The method of wet etching the n-type semiconductor layer while measuring the surface electrode potential of the semiconductor substrate by irradiating with light having the effect of improving the etching accuracy of the n-type semiconductor layer. Further, there is an effect that the processing accuracy is improved by a method in which etching is stopped in a potential change region where the surface electrode potential of the semiconductor substrate changes from the electrode potential of the second layer to the electrode potential of the first layer. Moreover, the etching in the potential change region is stopped by applying a negative potential to the surface of the semiconductor substrate, which has the effect of further improving the etching accuracy of the n-type semiconductor layer.
[0045]
The method of manufacturing a semi-conductor device of the present invention, p-type semiconductor layer is a first layer, the second layer is an n-type semiconductor layer, while a positive potential is applied to the surface of the semiconductor substrate, n-type semiconductor layer The wet etching method has an effect of improving the etching accuracy of the n-type semiconductor layer.
[0047]
The method of manufacturing a semi-conductor device of the present invention, while applying a positive potential to the semiconductor substrate surface, a method of wet etching the n-type semiconductor layer has the effect of especially improving the etch rate.
[0048]
The method of manufacturing a semi-conductor device of the present invention, to stop the etching at a potential change region, the method carried out by stopping the light irradiation has the effect of further improving the etching accuracy of the n-type semiconductor layer.
[0050]
Apparatus for manufacturing a semi-conductor device of the present invention, the etching solution immersing the semiconductor substrate, as it is etched in this etching solution, the potential difference measuring device for measuring the surface electrode potential of the semiconductor substrate, the semiconductor being etched An etching stop means for stopping etching according to a change in the surface electrode potential of the substrate is provided, which has an effect of improving the etching processing accuracy. Further, the etching stop means is a power source that applies a negative potential to the surface of the immersed semiconductor substrate, and there is an effect that the processing accuracy of etching of the n-type semiconductor layer is improved.
[0051]
Apparatus for manufacturing semi-conductor devices of the present invention, by Rukoto includes a light source for irradiating light to the immersed surface of the semiconductor substrate, there is an effect that the speed of etching increases.
[0052]
Apparatus for manufacturing semi-conductor devices of the present invention, by Rukoto comprises a power source for applying a positive potential on the surface of the immersed semiconductor substrate, there is an effect that the speed of the etching of the n-type semiconductor layer is increased.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a semiconductor device manufacturing apparatus used in a semiconductor device manufacturing method according to an embodiment of the present invention;
FIG. 2 is an explanatory diagram showing a simplified view of FIG. 1 limited to a wet-etched semiconductor substrate and measurement of the surface potential of the semiconductor substrate.
FIG. 3 is a characteristic diagram showing a potential change of a surface potential of a semiconductor substrate according to an etching time according to the embodiment.
FIG. 4 is an explanatory diagram for explaining a dissolution reaction of a nitride semiconductor (n-type semiconductor) in contact with an etching solution according to the embodiment using a band model of the nitride semiconductor.
FIG. 5 is an explanatory diagram using a band model of a semiconductor substrate in contact with an etching solution when irradiated with light having energy larger than the band gap energy according to the embodiment.
FIG. 6 is an explanatory diagram using a band model of a semiconductor substrate in contact with an etching solution when a positive potential is applied to the surface of the semiconductor substrate being etched according to the embodiment.
7 is a configuration diagram showing a configuration of a semiconductor substrate etched by the semiconductor device manufacturing method of the embodiment. FIG.
FIG. 8 is a configuration diagram of a manufacturing apparatus used in the embodiment.
FIG. 9 is a characteristic diagram showing a change in the surface electrode potential of the semiconductor substrate according to the etching time of the semiconductor substrate according to the embodiment.
FIG. 10 is a configuration diagram of a manufacturing apparatus used in the embodiment.
FIG. 11 is an explanatory diagram showing a band structure of GaN electrons when a negative potential is applied to a semiconductor substrate in the embodiment.
FIG. 12 is a cross-sectional view of a conventional semiconductor laser device having a current stripe structure.
[Explanation of symbols]
Ec conduction band edge, Ef Fermi level, Ev valence band edge, hν irradiation light energy, 1 etching solution, 2 semiconductor substrate, 5 light source, 20 semiconductor substrate body, 21 first layer, 22 second layer, 82 etching region, 9 potentiometer, 6 connection electrodes, 10 resist film, 11 power supply.

Claims (2)

A semiconductor device in which the second layer is wet-etched while measuring the surface electrode potential of the semiconductor substrate in which the first layer and the second layer having different electrode potentials are provided in this order on the semiconductor substrate body. A manufacturing method comprising:
The first layer is a p-type semiconductor layer, the second layer is an n-type semiconductor layer, and the surface electrode potential of the semiconductor substrate is irradiated with light having energy larger than the band gap energy of the n-type semiconductor layer. The n-type semiconductor layer is wet etched while measuring
Etching is stopped by applying a negative potential to the surface of the semiconductor substrate in a potential change region where the surface electrode potential of the semiconductor substrate changes from the electrode potential of the second layer to the electrode potential of the first layer. method of manufacturing a semi-conductor device you wherein a. Etching is performed by an etching solution for immersing the semiconductor substrate, a potential difference measuring device for measuring the surface electrode potential of the semiconductor substrate when etched with the etching solution, and a change in the surface electrode potential of the semiconductor substrate during etching. An apparatus for manufacturing a semiconductor device comprising an etching stop means for stopping,
The etching stop means, apparatus for producing a semi-conductor device you characterized in that the immersed surface of the semiconductor substrate is a power supply for applying a negative potential.

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