JP2005228836A - Manufacturing method of nitride compound semiconductor, semiconductor device, and heat treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a nitride compound semiconductor having higher hole concentration with low electric resistance by improving activation of doped p-type impurities. <P>SOLUTION: In a manufacturing method of the nitride compound semiconductor for growing a GaN layer with the p-type impurities doped on a substrate by the MOCVD method and thereafter activating the impurities by heat treatment, the heat treatment is performed in an inert gas atmosphere or in a vacuum. To do so, a grown wafer 1 with the GaN layer is doped with the p-type impurities and is sandwiched between electrode plates 2 and 3. A direct-current voltage is applied from a power source 5 having the GaN layer side as a cathode between the electrode plates 2 and 3 to generate an electric field in the GaN layer. Hydrogen deviating during the heat treatment due to the electric field is extracted from the GaN layer to improve the activation of the doped impurities. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a nitride compound semiconductor having a high hole concentration, a semiconductor device obtained thereby, and a heat treatment apparatus suitable for the production.

  Nitride-based compound semiconductors such as GaN, AlGaN, and GaInN are attracting attention as light-emitting element materials capable of emitting red to ultraviolet light.

  When a device is configured using a nitride-based compound semiconductor, control of the conductivity type and the hole or electron density is very important.

  For example, when manufacturing a light emitting diode (LED), a semiconductor laser (LD), etc., AlGaN, GaInN, GaN, etc. are laminated in multiple layers, and the light emitting layer (active layer) is formed by an n-type cladding layer and a p-type cladding layer. It is necessary to form a sandwich structure.

  Also in a heterojunction bipolar transistor (HBT), it is necessary to stack AlGaN, GaInN, GaN, etc. in multiple layers to form an npn or pnp junction.

Conventionally, in order to grow, for example, a p-type GaN layer by a vapor deposition method such as a metal organic chemical vapor deposition (MOCVD) method, in a mixed gas of hydrogen (H ₂ ) or H ₂ and nitrogen (N ₂ ). , Trimethylgallium (TMG, Ga (CH ₃ ) ₃ ) as a Ga raw material, ammonia (NH ₃ ) as an N raw material, cyclopentadienyl magnesium (CP ₂ Mg) as a p-type dopant, and the like were heated. An Mg-doped GaN layer is grown on a sapphire substrate, SiC substrate, GaAs substrate, etc. by thermal decomposition reaction.

  This Mg-doped GaN layer is a high-resistance layer as it is, and exhibits low-resistance p-type conductivity only after heat treatment in a vacuum or an inert gas after growth. In this heat treatment, for example, annealing is performed at 400 ° C. or higher in a nitrogen atmosphere pressurized to a pressure higher than the decomposition pressure of the gallium nitride compound semiconductor, thereby obtaining a low-resistance p-type gallium nitride compound semiconductor. It is. In this case, hydrogen bonded to Mg in GaN by this heat treatment is dissociated by heat treatment (annealing) and is discharged from the surface of the GaN crystal, so that Mg acts as an acceptor and becomes p-type. It has been.

  However, it is known that crystals immediately after growth have high resistance due to hydrogen passivation in which hydrogen contained in a gas in a vapor phase growth process binds to magnesium and electrically inactivates magnesium.

Therefore, as a p-type method, a vapor phase growth method using ammonia as a nitrogen raw material is used to deposit a gallium nitride based semiconductor doped with p-type impurity Mg, and then at a temperature range of 600 ° C. or higher during cooling. There is a method of switching the cooling atmosphere from ammonia to a mixed atmosphere of hydrogen or nitrogen (for example, see Patent Document 1). According to this method, since the supply of atomic hydrogen supplied from ammonia can be avoided by switching the cooling atmosphere in a temperature range of 600 ° C. or higher, a p-type gallium nitride compound semiconductor with low resistance without hydrogen passivation is obtained. It is done.
JP-A-8-115880

However, as already mentioned, in the case of the p-type method by performing the heat treatment after the growth, the carrier concentration of the p-type GaN layer obtained by the heat treatment after the growth is currently about 4 × 10 ¹⁷ cm ⁻³ . There is a problem that the resistivity is high.

  According to the findings of the present inventors, this is because the hydrogen atom bonded to Mg once dissociates from Mg in ordinary heat treatment, but remains in the crystal layer. This is because it cannot be fully implemented. For this reason, for example, in a light emitting device using a nitride III-V compound semiconductor, problems such as voltage loss in the p contact layer and deterioration due to heat generation are unavoidable. Moreover, HBT has a high resistance of the base layer, and a high frequency characteristic cannot be obtained.

  Although Patent Document 1 can also be an effective method for solving this problem, it merely switches the gas phase atmosphere during cooling, and does not more positively increase the hole concentration in the p-type GaN layer.

  Accordingly, an object of the present invention is to solve the above-mentioned problems, increase the activation of doped p-type impurities, and produce a nitride-based compound semiconductor having a higher hole concentration and a lower electrical resistance, and thereby An object of the present invention is to provide a semiconductor device to be obtained and a heat treatment apparatus suitable for its manufacture.

  In order to achieve the above object, the present invention is configured as follows.

  In the method of manufacturing a nitride-based compound semiconductor according to the first aspect of the present invention, after a GaN layer doped with a p-type impurity is grown on a substrate by MOCVD, heat treatment is performed to activate the doped impurity. In the method for producing a nitride-based compound semiconductor, the heat treatment is performed in an inert gas atmosphere or in a vacuum, and a wafer on which a GaN layer doped with the p-type impurity is grown is sandwiched between electrode plates. A voltage is applied between the GaN layer side as a negative electrode to generate an electric field in the GaN layer, and hydrogen separated by the electric field during heat treatment is extracted from the crystal to increase the activation of the doped impurities. To do.

  As the inert gas, mainly nitrogen, helium and argon are preferably used.

  As the substrate, a sapphire substrate is mainly preferably used. However, the substrate is not necessarily limited to the sapphire substrate, and basically any substrate can be used as long as a GaN layer can be formed thereon. . For example, the substrate may be a SiC substrate, a GaN substrate, or the like.

  The invention of claim 2 is the method for producing a nitride-based compound semiconductor according to claim 1, wherein the electric field strength generated between the electrode plates is 3 kV / cm or more, preferably 10 kV / cm or more. .

  According to a third aspect of the present invention, in the nitride compound semiconductor manufacturing method according to the first or second aspect, Mg is used as a p-type impurity doped into the GaN layer.

A semiconductor device according to a fourth aspect of the present invention is a semiconductor device in which a p-type GaN layer is formed on a substrate by the manufacturing method according to any one of the first to third aspects, wherein the p-type GaN layer after the heat treatment is The carrier concentration is higher than 4 × 10 ¹⁷ cm ⁻³ .

  According to a fifth aspect of the present invention, there is provided a heat treatment apparatus comprising: an electrode plate disposed opposite to each other so as to sandwich a wafer on which a GaN layer doped with a p-type impurity (p-type impurity doped GaN layer) is sandwiched; A heat treatment furnace in which a wafer is placed inside and heated in an inert gas atmosphere or in a vacuum state, and a voltage for applying a voltage with the GaN layer side as a negative electrode between the electrode plates during heating in the heat treatment furnace And a circuit.

  According to a sixth aspect of the present invention, in the heat treatment apparatus according to the fifth aspect, the peripheral portions of the electrode plates facing each other are warped in a direction away from each other.

  According to the present invention, the following excellent effects can be obtained.

  According to the manufacturing method described in claims 1 to 3, during the p-type heat treatment, a wafer on which a p-type impurity-doped GaN layer, for example, an Mg-doped GaN layer is grown, is sandwiched between the electrode plates, and p By applying a voltage so that the negative impurity-doped GaN layer side becomes a negative electrode and extracting the hydrogen dissociated during the heat treatment from the crystal by the electric field generated in the GaN layer, the activation rate of the doped impurity is increased. Can do.

In particular, according to the invention of claim 2, since the electric field strength generated between the electrode plates is 3 kV / cm or more, preferably 10 kV / cm or more, as can be seen from FIG. 2, 4 × 10 ¹⁷ cm ^−3. A nitride-based compound semiconductor device having a higher carrier concentration, for example, a wafer on which a semiconductor element structure such as an LED, LD, or HBT is formed, and a semiconductor element such as an LED, LD, or HBT manufactured using the same can be obtained ( Claim 4).

  Further, according to the heat treatment apparatus of claim 5, the electrode plates disposed opposite to each other to sandwich the wafer on which the p-type impurity doped GaN layer is grown, and the wafer sandwiched between the electrode plates are installed inside, A heat treatment furnace that can be heated in an inert gas atmosphere or in a vacuum state, and a voltage circuit that applies a voltage with the GaN layer side as a negative electrode between the electrode plates during heating in the heat treatment furnace. Therefore, an electric field is generated in the GaN layer, and the hydrogen activated during the heat treatment can be extracted from the GaN layer by this electric field, thereby increasing the activation of impurities.

  In particular, according to the invention of claim 6, since the periphery of the electrode plates facing each other is warped away from each other, electric field concentration in the peripheral portion is avoided and electric field strength uniformity in the wafer surface is improved. be able to.

  Hereinafter, the present invention will be described based on the illustrated embodiments.

  The main point of the present invention is that hydrogen ions dissociated by heat treatment in a crystal are forcibly extracted from the surface by an electric field. That is, by interposing a wafer between electrode plates and applying a high electric field during heat treatment, atoms that cause inactivation are extracted.

  FIG. 1 shows the configuration of a heat treatment apparatus for this purpose. In this heat treatment apparatus, electrode plates 2 and 3 disposed opposite to each other to sandwich a wafer 1 on which a p-type impurity-doped GaN layer is grown, and a wafer 1 sandwiched between the electrode plates 2 and 3 are installed inside, A heat treatment furnace 4 capable of heating the inside in an inert gas atmosphere or a vacuum state, and a voltage having a negative electrode on the GaN layer side between the electrode plates 2 and 3 is applied from the power supply 5 during the heating in the heat treatment furnace 4. A voltage circuit for generating an electric field in the GaN layer and for extracting hydrogen dissociated during the heat treatment from the crystal by the electric field.

In the above heat treatment apparatus, for example, a wafer 1 having a p-type GaN layer grown by MOCVD is sandwiched between electrode plates 2 and 3 which are parallel plate electrodes, and 650 ° C. in an inert gas atmosphere or vacuum while applying voltage. Heat treatment for 30 minutes. At this time, when a DC voltage of about 500 V is applied between the electrode plates 2 and 3, a high electric field of 10 kV / cm is generated in the crystal having a thickness of about 500 μm including the substrate, and the surface side is a negative electrode. By doing so, dissociated hydrogen can be extracted from the crystal. This makes it possible to significantly increase the hole concentration in the p-type GaN layer, although it depends on the Mg doping concentration as shown in FIG. FIG. 2 shows a case where the Mg doping concentration is 2 × 10 ²⁰ cm ^{−3 and} a case where the Mg doping concentration is 2 × 10 ¹⁹ cm ⁻³ , and the former has a larger effect of improving the hole concentration. .

  A first embodiment of the present invention will be described with reference to FIG.

  A wafer 1 is prepared by sequentially growing an undoped GaN layer (thickness 500 nm) and an Mg-doped p-type GaN layer (thickness 1000 nm) on a (0001) plane sapphire substrate by a known MOCVD method. As a raw material gas, trimethylgallium was used as a Ga raw material, ammonia was used as a N raw material, and cyclopentadienyl magnesium was used as a p-type dopant.

  The wafer 1 is sandwiched between the electrode plate 2 and the electrode plate 3 and placed in the heat treatment furnace 4. In this embodiment, tantalum was used as the material for the electrode plates 2 and 3. In addition to tantalum, there is no change in the effect as long as it is a conductive material with little degassing even at high temperatures such as titanium, tungsten, molybdenum and graphite.

  The reason for deforming the periphery of the electrode plate is to avoid the concentration of the electric field in the peripheral portion and to increase the uniformity of the electric field strength in the wafer surface. A DC voltage is applied from the power source 5 so that the electrode plate on the p-type GaN layer side becomes a negative electrode and the electrode plate on the sapphire substrate side becomes a positive electrode while flowing high-purity nitrogen gas as an inert gas into the heat treatment furnace 4. In this state, the temperature is raised to 650 ° C. and heat treatment is performed for 30 minutes.

FIG. 2 shows the relationship between the electric field intensity and the hole concentration during heat treatment at two Mg doping concentrations (sample A of 2 × 10 ²⁰ cm ⁻³ and sample B of 2 × 10 ¹⁹ cm ⁻³ ). It is. A sample doped with Mg at a high concentration has a greater effect of improving the hole concentration by applying an electric field. This is a phenomenon that can be explained by the high concentration of hydrogen in the sample A having a high Mg concentration.

  As can be seen from FIG. 2, according to the present embodiment, the hole concentration starts to increase compared with the case where the electrolysis strength is 3 kV / cm or more and there is no normal electrolysis, and it is 2 to 10 times at 10 kV / cm or more. The improvement effect is obtained.

  A second embodiment in which the present invention is applied to the manufacture of a light emitting diode (LED) will be described with reference to FIG.

  FIG. 3 shows the structure of an LED using a wafer according to the present invention. In the manufacturing process, an n-type GaN layer 8 doped with silicon is grown at 1100 ° C. on an undoped GaN layer 7 formed on the sapphire substrate 6 by MOCVD, and an n-type InGaN layer 9 doped with silicon is formed thereon. After growing at a low temperature of 800 ° C., the growth temperature was raised again to 1100 ° C. to grow the p-type GaN layer 10.

  After this crystal growth, as in Example 1, heat treatment was performed in the heat treatment furnace 4 with an electric field strength of 10 kV / cm. That is, the wafer 1 is placed in the heat treatment furnace 4 with the electrode plate 2 and the electrode plate 3 being sandwiched, and the high purity nitrogen gas, which is an inert gas, is allowed to flow into the heat treatment furnace 4 while the electrode plate on the p-type GaN layer 10 side. A direct current voltage was applied from the power source 5 so that the electrode plate on the sapphire substrate 6 side was a negative electrode, and heat treatment was performed at 650 ° C. for 30 minutes in this state.

  While the surface of the semiconductor wafer is partially removed by RIE (Reactive Ion Etching), a part of the n-type GaN layer 8 is exposed, and a Ti / Al electrode 11 is formed on the exposed part. A Ni / Au electrode 12 was formed on the surface of the p-type GaN layer 10.

  When the light emission output and the light emission start voltage were measured for an LED having the structure of this example and an LED having a similar structure using a conventional wafer that was heat-treated without applying an electric field, the light emission output at 20 mA energization was measured. However, the LED of this example was 51 mW, whereas the LED using a conventional wafer was 1 mW. The light emission starting voltage was 2.8 V in the LED of the example, whereas it was 4.0 V in the LED using the conventional semiconductor wafer. As described above, the effect of the present invention is remarkably exhibited also in the LED.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, Various deformation | transformation based on the technical idea of this invention is possible. For example, the numerical values given in the above embodiment are merely examples, and different numerical values may be used as necessary.

It is the schematic which showed the structure of the heat processing apparatus which concerns on Example 1, 2 of this invention. It is the figure which showed the relationship between the hole density | concentration of Mg dope GaN, and the electric field strength during heat processing. It is sectional drawing which showed the structure of LED which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wafer 2, 3 Electrode plate 4 Heat processing furnace 5 Power supply 6 Sapphire substrate 7 Undoped GaN layer 8 n-type GaN layer 9 n-type InGaN layer 10 p-type GaN layer 11 Ti / Al electrode 12 Ni / Au electrode 50 Voltage circuit

Claims (6)

In a method for manufacturing a nitride-based compound semiconductor in which a GaN layer doped with a p-type impurity is grown on a substrate by MOCVD, followed by heat treatment to activate the doped impurity.
The above heat treatment is performed in an inert gas atmosphere or in a vacuum. At this time, a wafer on which the GaN layer doped with the p-type impurity is grown is sandwiched between electrode plates, and a voltage with the GaN layer side as a negative electrode between the electrode plates. Is added to generate an electric field in the GaN layer, and hydrogen dissociated during the heat treatment by this electric field is extracted from the crystal to increase the activation of the doped impurity, thereby producing a nitride compound semiconductor. In the manufacturing method of the nitride type compound semiconductor of Claim 1,
A method for producing a nitride-based compound semiconductor, wherein an electric field strength generated between the electrode plates is 3 kV / cm or more, preferably 10 kV / cm or more. In the manufacturing method of the nitride type compound semiconductor of Claim 1 or 2,
A method for producing a nitride-based compound semiconductor, wherein Mg is used as a p-type impurity doped into the GaN layer. A semiconductor device in which a p-type GaN layer is formed on a substrate by the manufacturing method according to claim 1, wherein the carrier concentration of the p-type GaN layer after the heat treatment is from 4 × 10 ¹⁷ cm ⁻³ . A semiconductor device characterized by being expensive. an electrode plate disposed opposite to each other to sandwich a wafer on which a GaN layer doped with a p-type impurity is grown;
A heat treatment furnace in which a wafer is installed inside this electrode plate, and the inside can be heated in an inert gas atmosphere or in a vacuum state;
A heat treatment apparatus comprising: a voltage circuit that applies a voltage having a GaN layer side as a negative electrode between electrode plates during heating in the heat treatment furnace. The heat treatment apparatus according to claim 5, wherein
A heat treatment apparatus characterized in that peripheral portions of the electrode plates facing each other are warped in a direction away from each other.

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