WO2010016388A1 - ショットキーバリアダイオードおよびショットキーバリアダイオードの製造方法 - Google Patents
ショットキーバリアダイオードおよびショットキーバリアダイオードの製造方法 Download PDFInfo
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- WO2010016388A1 WO2010016388A1 PCT/JP2009/063149 JP2009063149W WO2010016388A1 WO 2010016388 A1 WO2010016388 A1 WO 2010016388A1 JP 2009063149 W JP2009063149 W JP 2009063149W WO 2010016388 A1 WO2010016388 A1 WO 2010016388A1
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- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 claims abstract description 252
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
- H01L29/861—Diodes
- H01L29/872—Schottky diodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/0603—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by particular constructional design considerations, e.g. for preventing surface leakage, for controlling electric field concentration or for internal isolations regions
- H01L29/0607—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by particular constructional design considerations, e.g. for preventing surface leakage, for controlling electric field concentration or for internal isolations regions for preventing surface leakage or controlling electric field concentration
- H01L29/0611—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by particular constructional design considerations, e.g. for preventing surface leakage, for controlling electric field concentration or for internal isolations regions for preventing surface leakage or controlling electric field concentration for increasing or controlling the breakdown voltage of reverse biased devices
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/08—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/20—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds
- H01L29/2003—Nitride compounds
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/47—Schottky barrier electrodes
- H01L29/475—Schottky barrier electrodes on AIII-BV compounds
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/66007—Multistep manufacturing processes
- H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
- H01L29/66083—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by variation of the electric current supplied or the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched, e.g. two-terminal devices
- H01L29/6609—Diodes
- H01L29/66143—Schottky diodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/402—Field plates
Definitions
- the present invention relates to a Schottky barrier diode and a manufacturing method of the Schottky barrier diode, for example, a Schottky barrier diode with improved breakdown voltage and a manufacturing method of the Schottky barrier diode.
- Gallium nitride has various excellent characteristics such as a band gap about three times that of silicon (Si), a breakdown electric field strength about 10 times higher, and a larger saturation electron velocity. Since GaN can be expected to achieve both high breakdown voltage, which is difficult with conventional Si power devices, and low loss, that is, low on-resistance, power devices (power semiconductor elements) such as Schottky barrier diodes (SBD) Application to is expected.
- Si silicon
- SBD Schottky barrier diodes
- Non-Patent Document 1 discloses that the barrier height is increased by heat-treating the Schottky electrode.
- Non-Patent Document 1 the n-type GaN layer is formed on the sapphire substrate. Since the lattice constant and dislocation density of sapphire and GaN are different, the crystallinity of the GaN layer formed on the sapphire substrate is generally poor. In Non-Patent Document 1, a method for improving the crystallinity of the n-type GaN layer is not disclosed. For this reason, the n-type GaN layer disclosed in Non-Patent Document 1 has a problem that the breakdown voltage of the Schottky barrier diode cannot be sufficiently improved because of its poor crystallinity.
- the present invention has been made in view of the above problems, and is to provide a Schottky barrier diode and a method for manufacturing the Schottky barrier diode capable of improving the breakdown voltage.
- the present inventor has found that the reason why the breakdown voltage of the Schottky barrier diode of Non-Patent Document 1 cannot be improved is that the dislocation density of the GaN layer in contact with the Schottky electrode is high. That is, if the dislocation density of the GaN layer is high, the reverse leakage current increases even if the barrier height of the Schottky electrode increases. Further, as a result of intensive studies, the present inventors have found that an increase in reverse leakage current due to the dislocation density of the GaN layer in contact with the Schottky electrode is a factor that greatly affects the breakdown voltage of the Schottky barrier diode. As a result, even if the barrier height of the Schottky electrode is increased as in Non-Patent Document 1, the reverse leakage current cannot sufficiently improve the breakdown voltage of the Schottky barrier diode.
- the Schottky barrier diode in one aspect of the present invention includes a GaN substrate, a GaN layer formed on the GaN substrate, and a Schottky electrode formed on the GaN layer.
- the Schottky electrode is formed at a position in contact with the GaN layer and includes a first layer made of Ni or Ni alloy.
- the Schottky barrier diode manufacturing method includes the following steps. First, a GaN substrate is prepared. A GaN layer is formed on the GaN substrate. A Schottky electrode including a first layer made of Ni or Ni alloy in contact with the GaN layer is formed. The step of forming the Schottky electrode includes a step of forming a metal layer to be the Schottky electrode, and a step of heat-treating the metal layer to form the metal layer on the Schottky electrode including the first layer. It is out.
- the GaN layer is formed on the GaN substrate. Since the underlying substrate and the grown layer have the same composition, the dislocation density of the GaN layer can be reduced. For this reason, the reverse leakage current can be reduced when a reverse bias is applied to the Schottky barrier diode.
- the Schottky electrode capable of effectively increasing the barrier height by heat treatment is Ni or Ni alloy.
- the barrier height of the Schottky electrode can be effectively increased by forming Ni or a Ni alloy at a position in contact with the GaN layer.
- the reverse leakage current due to dislocation is small, so that the breakdown voltage of the Schottky barrier diode can be improved by increasing the barrier height of the Schottky electrode.
- the dislocation density in the region in contact with the Schottky electrode in the GaN layer is preferably 1 ⁇ 10 8 cm ⁇ 2 or less.
- a GaN substrate having a dislocation density of 1 ⁇ 10 8 cm ⁇ 2 or less is prepared.
- the present inventor has found that the reverse leakage current can be reduced by reducing the dislocation density in the region in contact with the Schottky electrode. Further, as a result of earnest research, the inventor is more effective in reducing the reverse leakage current.
- the dislocation density in the region in contact with the Schottky electrode is 1 ⁇ 10 8 cm ⁇ 2 or less. I found out. For this reason, the breakdown voltage of the Schottky barrier diode can be further improved.
- the GaN layer takes over the dislocation density of the GaN substrate that is the base substrate. For this reason, by setting the dislocation density of the GaN substrate to 1 ⁇ 10 8 cm ⁇ 2 or less, the dislocation density of the GaN layer formed thereon can be set to 1 ⁇ 10 8 cm ⁇ 2 or less.
- a Schottky barrier diode includes a GaN layer and a Schottky electrode formed on the GaN layer.
- the dislocation density in the region in contact with the Schottky electrode in the GaN layer is 1 ⁇ 10 8 cm ⁇ 2 or less, and the Schottky electrode is formed at a position in contact with the GaN layer and is made of Ni or Ni alloy. Contains layers of.
- a method for manufacturing a Schottky barrier diode includes the following steps. First, a GaN layer is prepared. A Schottky electrode including a first layer made of Ni or Ni alloy in contact with the GaN layer is formed. The step of preparing the GaN layer includes the step of preparing a GaN layer in which the dislocation density in the region in contact with the Schottky electrode is 1 ⁇ 10 8 cm ⁇ 2 or less. The step of forming the Schottky electrode includes a step of forming a metal layer to be the Schottky electrode, and a step of heat-treating the metal layer to form the metal layer on the Schottky electrode including the first layer. It is out.
- the present inventors have found that the reverse leakage current can be greatly reduced when the dislocation density in the region in contact with the Schottky electrode is 1 ⁇ 10 8 cm ⁇ 2 or less. Further, Ni or Ni alloy that can increase the barrier height by heat treatment as a Schottky electrode is used. Therefore, when a reverse bias is applied to the Schottky barrier diode, the reverse leakage current due to dislocation is small, so that the breakdown voltage of the Schottky barrier diode can be improved by increasing the barrier height of the Schottky electrode.
- the Schottky barrier diode in the above other aspect further includes a GaN substrate in contact with the surface opposite to the surface in contact with the Schottky electrode in the GaN layer.
- the method for manufacturing a Schottky barrier diode in the other aspect further includes a step of preparing a GaN substrate, and in the step of preparing the GaN layer, the GaN layer is epitaxially grown on the GaN substrate.
- the dislocation density of the GaN layer can be reduced. Therefore, the reverse leakage current can be further reduced when a reverse bias is applied to the Schottky barrier diode. Therefore, the breakdown voltage of the Schottky barrier diode can be further improved.
- the Schottky electrode further includes a second layer formed on the first layer and containing gold (Au).
- the step of forming the Schottky electrode further includes a step of forming a second layer containing Au on the first layer.
- Au has a small electrical resistance and is therefore preferably used for connection to wiring. For this reason, it can be suitably used for a device including a Schottky barrier diode.
- the Schottky barrier diode in the one and other aspects described above, preferably, the Schottky barrier diode is formed on the GaN layer, and the Schottky electrode formed therein is formed with an insulating layer, and connected to the Schottky electrode, And a field plate electrode formed so as to overlap the insulating layer.
- a step of forming an insulating layer having an opening on the GaN layer, and a field plate connected to the Schottky electrode and overlapping the insulating layer A step of forming an (FP) electrode, and in the step of forming the metal layer, the metal layer is formed in contact with the GaN layer inside the opening of the insulating layer.
- the reverse leakage current can be reduced. Under this condition, electric field relaxation occurs due to the field plate structure. As a result, the reverse leakage current is further reduced and the reverse withstand voltage can be increased.
- the field plate structure is a structure constituted by an insulating layer and a field plate electrode formed on the insulating layer.
- the field plate electrode is electrically connected to the Schottky electrode, and the Schottky electrode and the field plate electrode have the same potential.
- the field plate structure alleviates the electric field concentration at the end of the Schottky electrode during operation, which causes device destruction, and makes it possible to increase the breakdown voltage and output of the Schottky barrier diode.
- the material of the insulating layer can be SiN x , for example.
- the metal layer in the step of heat-treating the metal layer, is heat-treated at a temperature of 300 ° C. or higher and 600 ° C. or lower. More preferably, in the step of heat treating the metal layer, the metal layer is heat treated at a temperature of 400 ° C. or higher and 550 ° C. or lower.
- the barrier height of the Schottky electrode can be effectively increased by performing heat treatment in a temperature range of 300 ° C. or higher and 600 ° C. or lower. By performing the heat treatment in a temperature range of 400 ° C. or higher and 550 ° C. or lower, the Schottky barrier height can be increased more effectively. For this reason, the breakdown voltage of the Schottky barrier diode can be further improved.
- the step of forming the metal layer and the step of heat treatment are preferably performed in parallel.
- the metal layer can be heat-treated by using heat applied when the metal layer is formed. For this reason, the energy required for forming the Schottky electrode can be reduced. Further, the Schottky barrier diode can be manufactured by simplifying the process.
- the metal layer is heat-treated at a temperature of 200 ° C. or higher and 600 ° C. or lower.
- the heat applied when forming the metal layer can be used, so that the Schottky barrier height can be increased even at a low temperature. Can do. That is, by performing heat treatment in a temperature range of 200 ° C. or more and 600 ° C. or less, the Schottky barrier height can be effectively increased. For this reason, the breakdown voltage of the Schottky barrier diode can be further improved.
- the metal layer is heat-treated in an atmosphere containing nitrogen.
- the GaN layer is formed by a step of heat-treating the GaN layer prior to the step of forming the metal layer, and a plasma CVD (Chemical Vapor Deposition) method. It further includes at least one of a step of forming an insulating layer thereon.
- the inventor has improved the barrier height of the metal layer formed thereafter by heat-treating the GaN layer before forming the metal layer and forming an insulating layer on the GaN layer by plasma CVD. I found what I could do. For this reason, the breakdown voltage of the Schottky barrier diode can be further improved.
- the Schottky barrier diode and the Schottky barrier diode manufacturing method of the present invention when a reverse bias is applied to the Schottky barrier diode, the reverse leakage current due to the dislocation is small, so that the barrier height of the Schottky electrode is increased. As a result, the breakdown voltage of the Schottky barrier diode can be improved.
- FIG. 1 is a perspective view schematically showing a Schottky barrier diode in a first embodiment of the present invention. It is sectional drawing which shows schematically another Schottky barrier diode in Embodiment 1 of this invention. It is a flowchart which shows the manufacturing method of the Schottky barrier diode in Embodiment 1 of this invention in process order. It is sectional drawing which shows schematically the Schottky barrier diode in Embodiment 2 of this invention. It is a perspective view which shows roughly the Schottky barrier diode in Embodiment 2 of this invention.
- FIG. 10 is a cross-sectional view schematically showing a Schottky barrier diode of Comparative Example 2.
- FIG. It is a figure which shows the relationship between the heat processing temperature and the height of barrier height in Example 2.
- FIG. It is a figure which shows the relationship between a reverse voltage and current density in Example 1.
- FIG. 1 is a cross-sectional view schematically showing a Schottky barrier diode in the present embodiment.
- FIG. 2 is a perspective view schematically showing the Schottky barrier diode in the present embodiment.
- FIG. 1 is a cross-sectional view taken along line II in FIG.
- the Schottky barrier diode (SBD) 1 is formed on the GaN substrate 2, the GaN layer 3 formed on the surface 2 a of the GaN substrate 2, and the GaN layer 3.
- a Schottky electrode 4 and an ohmic electrode 6 formed under the back surface 2b of the GaN substrate 2 are provided.
- the GaN substrate 2 has a front surface 2a and a back surface 2b.
- the dislocation density in the GaN substrate 2 is preferably as low as possible, for example, preferably 1 ⁇ 10 8 cm ⁇ 2 or less, more preferably 1 ⁇ 10 7 cm ⁇ 2 or less, and 1 ⁇ 10 6 cm ⁇ 2. More preferably, it is the following. Since the dislocation density of the GaN layer 3 formed on the GaN substrate 2 can be similarly reduced, when the dislocation density of the GaN substrate 2 is 1 ⁇ 10 8 cm ⁇ 2 or less, the dislocation density of the GaN layer 3 is 1 ⁇ 10 6.
- GaN substrate 2 dislocation density can be reduced dislocation density of GaN layer 3 to 1 ⁇ 10 7 cm -2 or less in the case of 1 ⁇ 10 7 cm -2 or less, GaN substrate 2 dislocation density can be reduced dislocation density of GaN layer 3 to 1 ⁇ 10 6 cm -2 or less in the case of 1 ⁇ 10 6 cm -2.
- the lower limit of the dislocation density of the GaN substrate 2 is, for example, about 1 ⁇ 10 3 cm ⁇ 2 .
- the dislocation density in the present embodiment can be measured, for example, by counting the number of pits formed by etching in molten KOH (potassium hydroxide) and dividing by the unit area.
- the GaN substrate 2 is, for example, a self-supporting substrate, and has a thickness of, for example, 100 ⁇ m or more.
- the carrier concentration of the GaN substrate 2 is, for example, about 1 ⁇ 10 16 cm ⁇ 3 .
- the dislocation density of the region 3c in contact with the Schottky electrode 4 in the GaN layer 3 is preferably as low as possible. For example, it is preferably 1 ⁇ 10 8 cm ⁇ 2 or less, and more preferably 1 ⁇ 10 7 cm ⁇ 2 or less. Preferably, it is 1 ⁇ 10 6 cm ⁇ 2 or less.
- the dislocation density in the region 3c is 1 ⁇ 10 8 cm ⁇ 2 or less, the reverse leakage current when a reverse bias is applied to the Schottky barrier diode 1 can be reduced.
- the dislocation density in the region 3c is 1 ⁇ 10 7 cm ⁇ 2 or less, the reverse leakage current can be further reduced.
- the dislocation density in the region 3c is 1 ⁇ 10 6 cm ⁇ 2 or less, the reverse leakage current can be further reduced.
- the lower limit of the dislocation density of the GaN layer 3 is, for example, about 1 ⁇ 10 3 cm ⁇ 2 .
- the GaN layer 3 has a thickness of about 5 ⁇ m, for example.
- the conductivity type of the GaN layer 3 is not particularly limited, but is preferably n-type from the viewpoint that it can be easily formed.
- Schottky electrode 4 is formed at a position in contact with GaN layer 3 and includes a first layer made of Ni or Ni alloy (for example, Schottky electrode 4 as a whole in FIG. 1, first layer 4a in FIG. 3). It is out.
- the Schottky electrode 4 forms a Schottky junction with the GaN layer 3.
- the barrier height of the first layer of the Schottky electrode 4 is preferably as high as possible, for example, 0.83 eV or more and 1.20 eV or less, and 0.83 eV or more and 0.98 eV or less from the viewpoint of easy realization.
- FIG. 3 is a cross-sectional view schematically showing another Schottky barrier diode in the present embodiment.
- the Schottky electrode 4 includes a first layer 4a formed at a position in contact with the GaN layer 3, and a second layer 4b formed on the first layer 4a. May be.
- the first layer 4a is made of Ni or a Ni alloy
- the second layer 4b is made of an arbitrary metal.
- the second layer 4b is preferably made of Au.
- the Schottky electrode 4 may be formed with one or more other layers on the second layer 4b.
- the planar shape of the Schottky electrode 4 is, for example, a circular shape having a diameter of about 220 ⁇ m.
- the first layer 4a has a thickness of 25 nm to 50 nm, for example, and the second layer 4b has a thickness of about 300 nm, for example.
- the ohmic electrode 6 is formed so as to cover the entire back surface 2 b of the GaN substrate 2.
- the ohmic electrode 6 is made of, for example, any one of Ti (titanium), Al (aluminum), Au, or two or more kinds of these materials.
- the ohmic electrode 6 has a thickness of about 100 nm to 340 nm, for example.
- the Schottky barrier diode 1 has a vertical structure in which a current flows from one of the Schottky electrode 4 and the ohmic electrode 6 to the other.
- the vertical structure can pass a larger current than the horizontal structure, and therefore the vertical structure is a structure more suitable for the power device.
- the GaN substrate 2 and the GaN layer 3 are conductive, a vertical structure in which the ohmic electrode 6 is formed on the back side is possible.
- the ohmic electrode 6 is formed as an electrode on the back surface 2b side of the GaN substrate 2, but the present invention is not particularly limited thereto, and may be a Schottky electrode or the like.
- FIG. 4 is a flowchart showing the manufacturing method of the Schottky barrier diode in the present embodiment in the order of steps.
- a substrate preparation step (S10) is performed.
- the GaN substrate 2 is prepared.
- a substrate formed by an arbitrary manufacturing method can be used.
- the main surface of the (0001) plane manufactured by HVPE (Hydride Vapor Phase Epitaxy) method is used.
- a GaN substrate 2 is prepared.
- the dislocation density in the GaN substrate 2 is preferably as low as possible. For example, it is preferably 1 ⁇ 10 8 cm ⁇ 2 or less, more preferably 1 ⁇ 10 7 cm ⁇ 2 or less, and 1 ⁇ 10 6 cm ⁇ 2 or less. Is more preferable.
- a GaN layer forming step (S20) is performed.
- the GaN layer 3 is formed on the GaN substrate 2.
- the GaN layer 3 is grown on the GaN substrate 2 by OMVPE (Organo-Metallic Vapor Phase Epitaxy) method.
- the dislocation density of the GaN layer 3 grown in this manner is preferably as low as possible. For example, it is preferably 1 ⁇ 10 8 cm ⁇ 2 or less, more preferably 1 ⁇ 10 7 cm ⁇ 2 or less, and 1 ⁇ 10 6 cm 2 or less. More preferably, it is not more than cm ⁇ 2 .
- an ohmic electrode forming step (S30) is performed.
- the ohmic electrode 6 is formed on the back surface 2b of the GaN substrate 2.
- the following steps are performed.
- the back surface 2b of the GaN substrate 2 is cleaned with organic cleaning and hydrochloric acid.
- a metal material such as Ti, Al, Au or the like is formed on the entire back surface 2b by, for example, EB (Electron Beam) vapor deposition or resistance heating vapor deposition.
- heat treatment is performed at 600 ° C. for about 2 minutes in a nitrogen atmosphere to alloy the metal material, and the ohmic electrode 6 is formed.
- the GaN layer 3 is heat-treated as a result.
- the heat treatment temperature is not limited to the above temperature, and is, for example, 400 ° C. or higher and 800 ° C. or lower, preferably 600 ° C. or higher and 700 ° C. or lower. Can do.
- the barrier height of the metal layer formed in the metal layer forming step (S41) described later can be improved, the barrier height of the Schottky electrode 4 can be improved.
- a Schottky electrode forming step (S40) is performed.
- the Schottky electrode 4 including the first layer 4a (see FIG. 3) made of Ni or Ni alloy on the GaN layer 3 and at a position in contact with the GaN layer 3 is used. Form.
- a resist having a circular opening (pattern) is formed on the surface 3a of the GaN layer 3 by photolithography. Thereafter, the surface treatment of the GaN layer 3 by hydrochloric acid cleaning is performed at room temperature for 3 minutes.
- a metal layer to be the Schottky electrode 4 is formed (metal layer forming step (S41)).
- metal layer forming step (S41) a first metal layer made of Ni or Ni alloy to be the first layer of the Schottky electrode 4 is formed, and a second metal made of Au is formed on the first metal layer. It is preferable to form a metal layer.
- This metal layer can be formed by an arbitrary method.
- the first metal layer can be formed by an EB method or the like, and the second metal layer can be formed by a resistance heating vapor deposition method. Thereafter, when the resist is removed, the metal layer formed on the resist is simultaneously removed (lifted off), and a metal layer to be the Schottky electrode 4 is formed.
- the shape of the metal layer can be formed, for example, so that the planar shape is circular.
- this metal layer is heat-treated (heat treatment step (S42)).
- the Schottky electrode 4 including the first layer is formed from the metal layer.
- the barrier height of the first layer 4a made of Ni or Ni alloy can be increased, the barrier height of the Schottky electrode 4 is increased.
- the metal layer is preferably heat-treated at 300 ° C. or more and 600 ° C. or less, more preferably 400 ° C. or more and 550 ° C. or less.
- the barrier height of the first layer 4a made of Ni and Ni alloy can be increased.
- the barrier height of the first layer 4a can be greatly increased.
- the barrier height of the first layer 4a of the Schottky electrode 4 can be increased by a short heat treatment.
- the barrier height of the Schottky electrode 4 including the layers 4a and 4b increases further.
- a material such as gold can be used as the metal layer (second layer 4b) that can increase the barrier height of the Schottky electrode 4 as described above.
- the heat treatment step (S42) it is preferable to heat treat the metal layer in an atmosphere containing nitrogen. Since N atoms are likely to transition at low energy, when heat is applied to the GaN layer 3, N tends to escape from the region exposed to the heat treatment atmosphere on the surface 3a of the GaN layer 3. However, if nitrogen is contained in the atmosphere to be heat-treated, it is difficult for N to escape from the GaN layer 3, and N that has escaped from the GaN layer 3 can be compensated. For this reason, N which escapes from the GaN layer 3 can be suppressed. For this reason, even if the heat treatment step (S42) is performed, it is possible to suppress the formation of defects such as dislocations due to the loss of N in the GaN layer 3. Therefore, an increase in reverse leakage current can be suppressed.
- the heat treatment step (S42) it is preferable to heat treat the metal layer in an atmospheric pressure.
- the metal layer may be heat-treated in a pressurized atmosphere.
- the metal layer forming step (S41) and the heat treatment step (S42) can be performed in parallel.
- the metal layer is preferably heat treated at a temperature of 200 ° C. or higher and 600 ° C. or lower.
- a metal layer is formed on the front surface 3 a of the GaN layer 3 and heated from the back surface 2 b of the GaN substrate 2.
- the metal layer formed on the surface 3a of the GaN layer 3 from the back surface 2b of the GaN substrate 2 can be heat-treated.
- the method of heating from the back surface 2b of the GaN substrate 2 is not particularly limited. For example, a method of heating with a laser beam or the like, or a heating member such as a thermocouple mounted on the susceptor with the GaN substrate 2 back surface 2b mounted on the susceptor. The method of doing is mentioned.
- metal layer forming step (S41) and the heat treatment step (S42) only need to be performed at least partially.
- the Schottky barrier diode 1 shown in FIGS. 1 to 3 can be manufactured.
- the GaN layer 3 is formed on the GaN substrate 2, the dislocation density of the GaN layer 3 can be reduced. For this reason, when a reverse voltage is applied to the Schottky barrier diode 1, the occurrence of reverse leakage current can be suppressed.
- the first layer made of Ni or Ni alloy is formed so as to be in contact with the GaN layer 3. For this reason, the barrier height of the Schottky electrode can be increased. Therefore, the leakage current due to dislocation can be suppressed, and the breakdown voltage of the Schottky barrier diode 1 can be effectively improved by increasing the barrier height of the Schottky electrode.
- FIG. 5 is a cross-sectional view schematically showing the Schottky barrier diode in the present embodiment.
- FIG. 6 is a partially cutaway view schematically showing the Schottky barrier diode in the present embodiment.
- FIG. 5 is a cross-sectional view taken along line VV in FIG.
- the Schottky barrier diode 11 in the present embodiment is different in that it further includes a field plate (FP) electrode 16 and an insulating layer 17.
- FP field plate
- the insulating layer 17 is formed on the surface 3a of the GaN layer 3, and an opening in which the Schottky electrode 4 is formed is formed.
- the insulating layer 17 is made of, for example, a silicon nitride film (SiN x ).
- the field plate electrode 16 is connected to the Schottky electrode 4 located in the opening of the insulating layer 17 and is formed so as to overlap the insulating layer 17.
- the field plate electrode 16 is, for example, a ring shape having a diameter of about 220 ⁇ m in plan view.
- the field plate electrode 16 and the Schottky electrode 4 constitute an electrode 15. That is, the electrode 15 includes the Schottky electrode 4 that is a portion in contact with the surface 3 a of the GaN layer 3 inside the opening of the insulating layer 17 and the field plate electrode 16 that is a portion overlapping the insulating layer 17.
- the field plate electrode 16 and the insulating layer 17 form a field plate structure.
- the breakdown voltage of the Schottky barrier diode 11 can be further improved.
- the field plate structure will be described.
- the thickness t of the insulating layer 17 is preferably 10 nm or more and 5 ⁇ m or less.
- the thickness t of the insulating layer 17 is 10 nm or more, it is possible to suppress the resistance of the insulating layer 17 from being lowered, and the effect of the field plate structure is exhibited without the insulating layer 17 being destroyed first.
- the thickness of the insulating layer 17 is 5 ⁇ m or less, electric field relaxation by the field plate structure can be obtained.
- the field plate length L is preferably 1 ⁇ m or more and 1 mm or less.
- the field plate structure can be easily manufactured, and the effect of the field plate structure can be stably obtained.
- the field plate length L is 1 mm or less, electric field relaxation by the field plate structure is obtained.
- the field plate length L is a length in which the field plate electrode 16 overlaps the insulating layer 17.
- the field plate length L is a length in which the field plate electrode 16 overlaps the insulating layer 17 in a cross section of the Schottky barrier diode 11 passing through the center of the circular electrode 15. is there. That is, when the planar shape of the opening of the insulating layer 17 is circular and the planar shape of the Schottky electrode 4 which is a part of the electrode 15 is circular, the field plate length L is the radial direction of the electrode 15. The length of the field plate electrode 16 overlaps the insulating layer 17 in FIG.
- the field plate length L means that the field plate electrode 16 has the insulating layer 17 in a linear direction connecting the center of gravity with respect to the planar shape of the Schottky electrode 4 and a certain point on the outer periphery of the planar shape. It is the length that overlaps.
- the insulating layer 17 has an end face 17 a that faces an opening that is a part where the electrode 15 contacts the GaN layer 3.
- the end face 17a is inclined with respect to the surface 3a of the GaN layer 3 so as to form an angle ⁇ .
- the field plate electrode 16, which is a portion overlapping the insulating layer 17 in the electrode 15, is overlaid on the insulating layer 17 so as to adhere to the end face 17 a.
- the end face 17a is inclined with respect to the surface 3a, the effect of electric field relaxation by the field plate structure can be increased. As a result, the breakdown voltage of the Schottky barrier diode 11 can be further improved.
- Such an inclination of the end surface 17a of the insulating layer 17 can be formed by wet etching, dry etching, or the like. End face 17a is formed such that angle ⁇ is in the range of, for example, not less than 0.1 ° and not more than 60 °. When the angle of inclination is 0.1 ° or more, the angle reproducibility is easily obtained. On the other hand, when the inclination angle is 60 ° or less, the effect of electric field relaxation is increased.
- FIG. 7 is a flowchart which shows the manufacturing method of the Schottky barrier diode in this Embodiment in process order.
- the manufacturing method of the Schottky barrier diode in the present embodiment basically has the same configuration as that of the first embodiment, but the insulating layer forming step (S50), the insulating layer etching step (S60), and the field plate The difference is that an electrode forming step (S70) is further provided.
- the substrate preparation step (S10) and the GaN layer formation step (S20) are performed as in the first embodiment.
- an insulating layer forming step (S50) is performed.
- the insulating layer 17 having an opening is formed on the GaN layer 3.
- the insulating layer 17 made of SiN x is formed on the GaN layer 3 by, for example, plasma CVD (Chemical Vapor Deposition).
- plasma CVD Chemical Vapor Deposition
- the insulating layer 17 is formed on the GaN layer 3 by the plasma CVD method prior to the step of forming the metal layer.
- the insulating layer 17 is formed at a temperature of 300 ° C. or higher and 400 ° C. or lower, for example.
- the GaN layer 3 is heat-treated at 300 ° C. or higher and 400 ° C. or lower.
- the barrier height of the Schottky electrode 4 can be improved.
- the film thickness t of the insulating layer 17 is, for example, about 1 ⁇ m.
- SiN x is deposited using, for example, NH 3 , SiH 4 (monosilane), NH 3 (ammonia), H 2 (hydrogen), N 2 or the like as a source gas. Note that it is preferable to form a SiN x film from SiH 4 and N 2 without using NH 3 because the hydrogen concentration in the insulating layer 17 can be lowered.
- an ohmic electrode forming step (S30) is performed as in the first embodiment.
- an insulating layer etching step (S60) is performed. In the insulating layer etching step (S60), the region where the Schottky electrode 4 is formed and the region where the field plate electrode 16 is formed in the insulating layer 17 are removed by etching.
- a resist having an opening is formed on the insulating layer 17 by photolithography. Thereafter, the insulating layer 17 exposed from the opening of the resist is wet-etched with BHF (Buffered Hydrogen Fluoride). Thereafter, the resist is removed by organic cleaning and ashing in an atmosphere containing oxygen and nitrogen. In this way, the insulating layer 17 is etched to form an opening in the insulating layer 17. At this point, the GaN layer 3 is exposed in the opening.
- the side surface of the opening can be formed to have a truncated cone shape having a maximum diameter of 200 ⁇ m, for example.
- a Schottky electrode forming step (S40) including a metal layer forming step (S41) and a heat treatment step (S42) is performed.
- a metal layer is formed in contact with the GaN layer 3 inside the opening of the insulating layer 17 formed in the insulating layer etching step (S60).
- a field plate electrode forming step (S70) is performed.
- the field plate electrode 16 is formed so as to be connected to the Schottky electrode 4 and to overlap the insulating layer 17.
- a resist having an opening is formed on the region excluding the vicinity of the opening of the insulating layer 17 and the Schottky electrode 4.
- an electrode material to be the field plate electrode 16 is formed so as to be connected to the Schottky electrode 4 and overlap the insulating layer 17. Thereafter, when the resist is removed, the electrode material formed on the resist is simultaneously removed (lifted off), and the field plate electrode 16 can be formed.
- the field plate electrode 16 may be formed of the same material as the Schottky electrode 4. Alternatively, the field plate electrode 16 may be formed using a material different from the material of the Schottky electrode 4, such as a material having good adhesion to the insulating layer 17.
- the Schottky barrier diode 11 shown in FIGS. 5 and 6 can be manufactured.
- the field plate electrode 16 is formed after the Schottky electrode 4 is formed.
- the Schottky electrode 4 and the field plate electrode 16 may be formed simultaneously.
- a resist having an opening is formed, and a metal layer to be the Schottky electrode 4 and an electrode material to be the field plate electrode are formed in the opening by an evaporation method. Thereafter, when removing the resist, the metal layer and the electrode material on the resist are simultaneously removed (lift-off).
- the Schottky electrode 4 that is in contact with the surface 3 a of the GaN layer 3 inside the opening of the insulating layer 17 and the field plate electrode 16 that is connected to the Schottky electrode 4 and overlaps the insulating layer 17. are formed. That is, since the diameter of the field plate electrode 16 is larger than the diameter of the opening formed in the insulating layer 17, a part of the electrode 15 overlaps with the insulating layer 17 to form the field plate electrode 16.
- the Schottky barrier diode 11 and the manufacturing method thereof are formed on the GaN layer 3 and the insulating layer 17 in which the opening having the Schottky electrode 4 formed therein is formed. It further includes a field plate electrode 16 connected to the Schottky electrode 4 and formed to overlap the insulating layer 17. Since the GaN layer 3 is formed on the GaN substrate 2, the GaN layer 3 having a low dislocation density can be formed by preparing the GaN substrate 2 having a low dislocation density. For this reason, reverse leakage current can be reduced.
- the Schottky barrier diode 11 having the field plate structure under the condition that the reverse leakage current is reduced and under the condition that a heat-treated Ni or Ni alloy Schottky electrode capable of realizing a high barrier height is used. Electric field relaxation due to the field plate structure occurs remarkably. As a result, the reverse leakage current can be further reduced and the breakdown voltage can be increased. This effect is remarkable when the dislocation density in the region in contact with the Schottky electrode 4 in the GaN layer 3 is 1 ⁇ 10 8 cm ⁇ 2 or less.
- the GaN layer 3 is heat-treated (in this embodiment, the ohmic electrode forming step (S41)), and the GaN layer 3 is formed by plasma CVD. At least one of the steps of forming the insulating layer 17.
- the inventor conducted heat treatment on the GaN layer 3 before forming the metal layer to be the Schottky electrode 4, and formed the insulating layer 17 on the GaN layer 3 by plasma CVD. It has been found that the barrier height of the metal layer formed thereafter can be improved. For this reason, the breakdown voltage of the Schottky barrier diode 11 can be further improved. The reason for this will be described below.
- the GaN layer 3 is heat-treated (for example, 600 ° C. or lower) before the metal layer forming step (S41), the surface state of the GaN layer 3 is changed by the heat treatment.
- the state of the Schottky interface changes in the heat treatment after the metal layer forming step (S41), and it is considered that the barrier height can be increased.
- the state of the Schottky interface changes in the heat treatment after the metal layer forming step (S41), and an increase in barrier height can be obtained.
- the surface state of the GaN layer 3 is changed by exposing the surface 3a of the GaN layer 3 to plasma by plasma CVD film formation.
- the state of the Schottky interface changes in the heat treatment after the metal layer forming step (S41), and it is considered that the barrier height can be increased.
- the insulating layer 17 is formed on the GaN layer 3 during the heat treatment, N omission on the surface 3a of the GaN layer 3 is less likely to occur. Thereby, it is considered that the state of the Schottky interface changes in the heat treatment after the metal layer forming step (S41), and an increase in barrier height can be obtained.
- the barrier height of the metal layer is provided by including at least one of a step of heat-treating the GaN layer 3 and a step of forming the insulating layer 17 on the GaN layer 3 by plasma CVD.
- the barrier height of the Schottky electrode 4 can be greatly improved.
- FIG. 8 is a cross-sectional view schematically showing a Schottky barrier diode in the present embodiment.
- Schottky barrier diode 21 in the present embodiment has basically the same configuration as Schottky barrier diode 11 in Embodiment 2, but does not have a GaN substrate. Different in.
- the Schottky barrier diode 21 includes a support substrate 23, a GaN foundation layer 22, a GaN layer 3, an electrode 15, an insulating layer 17, and an ohmic electrode 6.
- the dislocation density of the region 3c in contact with the Schottky electrode 4 in the GaN layer 3 is 1 ⁇ 10 8 cm ⁇ 2 or less, preferably 1 ⁇ 10 7 cm ⁇ 2 or less, and more preferably 1 ⁇ 10 6 cm ⁇ 2 or less.
- the support substrate 23 is a conductive substrate.
- a GaN foundation layer 22 is formed on the support substrate 23.
- a GaN layer 3 is formed on the GaN foundation layer 22.
- the support substrate 23 and the GaN foundation layer 22 are in ohmic contact. Moreover, when the support substrate 23 is a metal, the ohmic electrode 6 may be omitted. Since other configurations are the same as those in the second embodiment, description thereof will not be repeated.
- FIG. 9 is a flowchart showing the manufacturing method of the Schottky barrier diode in the present embodiment in the order of steps.
- the manufacturing method of the Schottky barrier diode according to the present embodiment basically has the same configuration as that of the second embodiment, but instead of the substrate preparation step (S10), a bonded substrate preparation step (S80). It differs in that it has.
- the GaN substrate 2 is prepared (substrate preparation step (S81)) in the same manner as the substrate preparation step (S10) of the second embodiment.
- the ion implantation step (S82) impurities are ion implanted from the front surface 2a or the back surface 2b of the GaN substrate 2.
- a layer containing a large amount of impurities is formed in the vicinity of the front surface 2a or the back surface 2b of the GaN substrate 2.
- the support substrate forming step (S83) the ion-implanted surface and the support substrate 23 are bonded together.
- the heat treatment step (S84) heat treatment is performed in a state where the GaN substrate 2 and the support substrate 23 are bonded together.
- the GaN substrate 2 is divided with a region containing a large amount of impurities as a boundary.
- the bonded substrate in which the GaN base layer 22 thinner than the GaN substrate 2 is formed on the support substrate 23 and the support substrate 23 can be formed (bonded substrate preparation step (S80)).
- the manufacturing cost can be reduced.
- the GaN layer 3 is formed on the GaN foundation layer 22.
- the dislocation density in a region in contact with a Schottky electrode described later is 1 ⁇ 10 8 cm ⁇ 2 or less.
- the insulating layer forming step (S50), the ohmic electrode forming step (S30), the insulating layer etching step (S60), the Schottky electrode forming step (S40), and the field plate electrode forming step ( S70) is performed.
- the Schottky barrier diode 21 shown in FIG. 8 can be manufactured.
- the GaN base layer 22 is formed using the GaN substrate 2, and the GaN layer 3 is formed using the GaN base layer 22, but the present invention is not limited to this.
- the Schottky barrier diode 21 having the field plate structure has been described as an example.
- the Schottky barrier diode of the present invention may not have the field plate structure.
- the dislocation density of the region 3c in contact with the Schottky electrode 4 in the GaN layer 3 is 1 ⁇ 10 8 cm ⁇ 2 or less.
- the present inventor has found that the lower the dislocation density in the Schottky junction region 3c in the GaN layer 3, the lower the reverse leakage current, and the more effective the reduction of the reverse leakage current in the region 3c is 1 ⁇ 10. It was found to be 8 cm -2 or less. For this reason, reverse leakage current can be reduced. Further, the present inventor has found that when the material of the Schottky electrode 4 to be Schottky bonded is Ni or Ni alloy, the barrier height can be effectively increased by heat treatment.
- the barrier height of the Schottky electrode 4 can be improved. Therefore, when a reverse bias is applied to the Schottky barrier diode 21, since the reverse leakage current due to dislocation is small, the breakdown voltage of the Schottky barrier diode 21 can be improved by increasing the barrier height of the Schottky electrode 4.
- an n-type GaN free-standing substrate prepared by the HVPE method and having a main surface of (0001) plane was prepared.
- This GaN substrate had a dislocation density of 1 ⁇ 10 6 cm ⁇ 2 or less, a carrier concentration of 3 ⁇ 10 18 cm ⁇ 3 , and a thickness of 400 ⁇ m.
- the n-type GaN layer 3 was epitaxially grown on the GaN substrate by OMVPE.
- the GaN layer 3 had a dislocation density of 1 ⁇ 10 6 cm ⁇ 2 , a carrier concentration of 1 ⁇ 10 16 cm ⁇ 3 , and a thickness of 5 ⁇ m.
- the dislocation density was a value measured by a method of counting the number of pits formed by etching in molten KOH and dividing by the unit area.
- the insulating layer 17 made of SiN x was formed by plasma CVD.
- This insulating layer 17 had a thickness of 0.5 ⁇ m.
- the back surface 2b of the GaN substrate 2 was subjected to organic cleaning and hydrochloric acid cleaning. Thereafter, 20 nm thick Ti, 100 nm thick Al, 20 nm thick Ti, and 200 nm thick Au are formed on the back surface 2b of the GaN substrate 2 by EB vapor deposition and resistance heating vapor deposition. The layers were laminated in this order. After forming this metal layer, this metal layer was heat-treated at 600 ° C. for 2 minutes in an atmosphere containing nitrogen to form an alloy. Thereby, the ohmic electrode 6 was formed.
- the following steps were performed. First, patterning was performed on the insulating layer 17 using photolithography. Thereafter, wet etching of the insulating layer 17 was performed by BHF. Next, the resist was removed by organic cleaning treatment. As a result, the insulating layer 17 was etched, and an opening was formed in the insulating layer 17. The side surface of the opening was formed to have a truncated cone shape having a maximum diameter of 200 ⁇ m.
- the Schottky electrode formation step (S40) and the field plate electrode formation step (S70) were performed simultaneously as follows.
- a resist having an opening was formed on the insulating layer 17 using photolithography.
- the surfaces of the GaN layer 3 and the insulating layer 17 were washed by washing with hydrochloric acid.
- Ni having a thickness of 50 nm was formed on the insulating layer 17 and the position in contact with the GaN layer 3 (that is, the opening of the insulating layer 17) by EB vapor deposition.
- Au having a thickness of 300 nm was formed on Ni by resistance heating vapor deposition.
- a metal layer in which Ni and Au were laminated on the insulating layer 17 and the position in contact with the GaN layer 3 was formed (S41).
- the metal layer was heat-treated in a nitrogen atmosphere at 450 ° C. for 2 minutes (S42).
- the electrode 15 including the field plate electrode 16 that is connected to the Schottky electrode 4 and overlaps the insulating layer 17 was formed. Since the diameter of the electrode 15 is larger than the diameter of the opening formed in the insulating layer 17, the field plate electrode 16 in which the electrode 15 partially overlaps the insulating layer 17 is formed. From the above, the Schottky barrier diode of Example 1 of the present invention shown in FIG. 5 was manufactured.
- Comparative Example 1 The manufacturing method of the Schottky barrier diode of Comparative Example 1 was different from the Schottky barrier diode of Inventive Example 1 only in that the metal layer was not heat-treated.
- FIG. 10 is a cross-sectional view schematically showing a Schottky barrier diode of Comparative Example 2.
- the Schottky barrier diode 101 of Comparative Example 2 was different in that a sapphire substrate 102 was used instead of the GaN substrate.
- a vertical structure Schottky barrier diode cannot be manufactured because the sapphire substrate 102 is an insulator. Therefore, as shown in FIG. 10, a Schottky barrier diode 101 having a field plate structure having a horizontal structure was manufactured.
- a specific method for manufacturing the Schottky barrier diode 101 shown in FIG. 10 is as follows.
- a sapphire substrate 102 was prepared as a substrate preparation step.
- an n-type GaN layer 3 having a carrier density of 1 ⁇ 10 16 cm ⁇ 3 and a thickness of 5 ⁇ m was grown on the sapphire substrate 102 by the HVPE method.
- the dislocation density of the GaN layer 3 shown in FIG. 10 was 1 ⁇ 10 9 cm ⁇ 2 .
- an insulating layer 117 for forming a field plate structure was formed on a region other than the outer peripheral region on the surface 3a of the GaN layer 3.
- the conditions for forming the insulating layer 117 were the same as in Example 1 of the present invention.
- the following steps were performed.
- a resist having an opening was formed over the insulating layer 117 by photolithography.
- organic cleaning and hydrochloric acid cleaning were performed, and a metal layer similar to that in Invention Example 1 was formed on the surface 3 a of the GaN layer 3.
- lift-off was performed to simultaneously remove the electrode material formed on the resist.
- alloying was performed to form an ohmic electrode 106.
- a Schottky electrode formation step and a field plate electrode formation step were performed in the same manner as Example 1 of the present invention.
- the Schottky electrode 104 that is in contact with the surface 3 a of the GaN layer 3 inside the opening of the insulating layer 117 and the field plate electrode 116 that is connected to the Schottky electrode 104 and overlaps the insulating layer 117.
- the electrode 115 containing these was formed.
- Comparative Example 4 The manufacturing method of the Schottky barrier diode of Comparative Example 4 was different only in that a GaN substrate having a dislocation density of 1 ⁇ 10 7 cm ⁇ 2 was used in the manufacturing method of the Schottky barrier diode of Comparative Example 1. For this reason, the dislocation density of the GaN layer of Comparative Example 4 was 1 ⁇ 10 7 cm ⁇ 2 .
- FIG. 12 is a diagram showing the relationship between the voltage (reverse voltage) and current (current density) in Comparative Examples 1, 3, and 4 in which heat treatment was not performed after the metal layer was formed.
- the horizontal axis represents the reverse voltage (unit: V)
- the vertical axis represents the current density (unit: A / cm 2 ).
- the breakdown voltage of the Schottky barrier diode of Example 1 of the present invention in which the GaN layer was formed on the GaN substrate and the metal layer was heat-treated was as high as 605V.
- inventive example 1 provided with the GaN layer 3 having a low dislocation density was able to improve the withstand voltage of 475 V as compared with the comparative example 2 provided with the GaN layer having a high dislocation density. From this, it was found that the breakdown voltage can be improved by reducing the dislocation density and causing reverse leakage current.
- Comparative Example 1 that was not heat-treated and had a GaN layer with a low dislocation density improved the breakdown voltage of 156 V over Comparative Example 3 that was not heat-treated and had a GaN layer with a high dislocation density. I was able to. From this, it can be seen that the breakdown voltage can be improved by heat treatment and the dislocation density is reduced, and that the increase in reverse leakage current due to the dislocation density of the GaN layer 3 is the dominant factor in the breakdown voltage. It was.
- the comparative example 2 in which the heat treatment process was performed and the comparative example 3 in which the heat treatment process was not performed were compared, and the withstand voltage that could be improved by performing the heat treatment was 30V.
- the withstand voltage which can be improved by carrying out the heat treatment step (S42) was 349 V, comparing the inventive example 1 in which the heat treatment step (S42) was performed with the comparative example 1 in which the heat treatment step was not carried out. From this, it was found that the breakdown voltage can be significantly improved by increasing the barrier height of the Schottky electrode by the heat treatment step (S42) and reducing the dislocation density of the GaN layer 3.
- the dislocation density of the GaN substrate 2 and the GaN layer 3 is 1 ⁇ 10 6 cm ⁇ 2
- the dislocation density of the GaN substrate 2 and the GaN layer 3 is 1 ⁇ .
- Comparative Example 4 having a dislocation density of 10 7 cm ⁇ 2 the relationship between the current density and the reverse voltage was almost the same, and the breakdown voltage was also about the same.
- the dislocation density of the GaN substrate 2 and the GaN layer 3 is 1 ⁇ 10 9 cm ⁇ 2 .
- inventive example 1 in which the metal layer of the comparative example 1 was heat-treated was able to significantly improve the withstand voltage compared to the comparative example 1, and the withstand voltage of the comparative example 1 and the comparative example 4 was comparable. From the results, it is considered that the inventive example in which the metal layer of Comparative Example 4 is heat-treated can achieve a high breakdown voltage comparable to that of Inventive Example 1.
- the Schottky electrode material that includes the GaN layer formed on the GaN substrate and is in contact with the GaN layer is Ni, thereby reducing the reverse leakage current, and It was confirmed that the breakdown voltage can be improved because the barrier height of the Schottky electrode can be increased.
- the material of a Schottky electrode is Ni alloy, it can be estimated that it has the same effect as the case where it is Ni.
- Examples 1 to 4 The Schottky barrier diodes of Samples 1 to 4 were manufactured in the same manner as Example 1 of the present invention, but differed only in the metal layer formation step (S41) and the heat treatment step (S42). Specifically, in the metal layer forming step (S41), Ni was formed to 25 nm and then Au was formed to 300 nm on Ni. In the heat treatment step (S42) of Samples 1 to 4, the heat treatment temperatures were 300 ° C., 400 ° C., 500 ° C., and 550 ° C., respectively. The heat treatment time was 1 minute.
- FIG. 11 is a figure which shows the relationship between the heat processing temperature and the height of barrier height in a present Example.
- the horizontal axis indicates the temperature (unit: ° C) at which the metal layer is heat-treated in the heat treatment step (S41), and the vertical axis indicates the height of the barrier height (unit: eV).
- the samples 1 to 4 having the Schottky electrode whose first layer is Ni are heat-treated compared to the samples 5 to 8 having the Schottky electrode whose first layer is Pt.
- the barrier height could be increased.
- the barrier height could be greatly increased by performing the heat treatment at 400 ° C. or more and 550 ° C. or less.
- the present inventor since the heat treatment time in the heat treatment step (S41) is 1 minute, the effect is not sufficiently obtained at 300 ° C.
- the present inventor has obtained the knowledge that the barrier height can be improved by making the heat treatment time longer than 1 minute. Therefore, the barrier height of the Schottky electrode 4 can be increased by performing heat treatment at 300 ° C. or more and 600 ° C. or less.
- the heat treatment is performed at 400 ° C. or more and 550 ° C. or less
- the Schottky barrier height of the Schottky electrode 4 can be stably increased in a short time, and thus the production efficiency is good.
- heat treatment is performed at 400 ° C. or more and 550 ° C. or less, it is possible to spend more time for heat treatment than when heat treatment is performed at a temperature exceeding 550 ° C. and not more than 600 ° C. Therefore, the characteristics of the Schottky electrode 4 can be stabilized.
- the barrier height of the Schottky electrode can be increased by heat treatment when the Schottky electrode is Ni.
Abstract
Description
図1は、本実施の形態におけるショットキーバリアダイオードを概略的に示す断面図である。図2は、本実施の形態におけるショットキーバリアダイオードを概略的に示す斜視図である。なお、図1は、図2における線分I-I線に沿った断面図である。図1および図2に示すように、ショットキーバリアダイオード(SBD)1は、GaN基板2と、GaN基板2の表面2a上に形成されたGaN層3と、このGaN層3上に形成されたショットキー電極4と、GaN基板2の裏面2b下に形成されたオーミック電極6とを備えている。
図5は、本実施の形態におけるショットキーバリアダイオードを概略的に示す断面図である。図6は、本実施の形態におけるショットキーバリアダイオードを概略的に示す一部破断図である。なお、図5は、図6における線分V-V線に沿った断面図である。図5および図6に示すように、本実施の形態におけるショットキーバリアダイオード11は、フィールドプレート(FP)電極16と、絶縁層17とをさらに備えている点において異なる。
次に、絶縁層エッチング工程(S60)を実施する。絶縁層エッチング工程(S60)では、絶縁層17においてショットキー電極4を形成する領域およびフィールドプレート電極16を形成する領域をエッチングにより除去する。
図8は、本実施の形態におけるショットキーバリアダイオードを概略的に示す断面図である。図8を参照して、本実施の形態におけるショットキーバリアダイオード21は、実施の形態2のショットキーバリアダイオード11と基本的には同様の構成を備えているが、GaN基板を備えていない点において異なる。
本発明例1のショットキーバリアダイオードは、図5および図6に示す実施の形態2のショットキーバリアダイオード11の製造方法にしたがって、製造した。
比較例1のショットキーバリアダイオードの製造方法は、本発明例1のショットキーバリアダイオードにおいて、金属層を熱処理しなかった点においてのみ異なっていた。
図10は、比較例2のショットキーバリアダイオードを概略的に示す断面図である。図10に示すように、比較例2のショットキーバリアダイオード101は、GaN基板の代わりにサファイア基板102を用いた点において異なっていた。サファイア基板を用いた場合、サファイア基板102が絶縁体のため、縦型構造のショットキーバリアダイオードは作製できない。よって図10に示すように、横型構造によるフィールドプレート構造を有するショットキーバリアダイオード101を作製した。
次に、GaN層形成工程として、サファイア基板102上に、1×1016cm-3のキャリア密度を有し、5μmの厚みを有するn型GaN層3を、HVPE法により成長した。このとき図10に示すGaN層3の転位密度は、1×109cm-2であった。
比較例3のショットキーバリアダイオードの製造方法は、比較例2のショットキーバリアダイオードの製造方法において金属層を熱処理しなかった点においてのみ異なっていた。
比較例4のショットキーバリアダイオードの製造方法は、比較例1のショットキーバリアダイオードの製造方法において1×107cm-2の転位密度を有するGaN基板を用いた点においてのみ異なっていた。このため、比較例4のGaN層の転位密度は1×107cm-2であった。
本発明例1および比較例1~4のショットキーバリアダイオードについて、逆バイアスを印加したときの耐圧をそれぞれ測定した。逆方向耐電圧の測定方法としては、高耐圧プローバーを用いてフッ素系不活性液体中に浸漬させた状態で電流と電圧とを測定するという方法を用いた。本発明例1および比較例1~4のショットキーバリアダイオード耐圧は、電流密度が1mA/cm2の電圧とした。その結果を下記の表1および図12に示す。なお、図12は、金属層形成後に熱処理を行なわなかった比較例1、3および4の電圧(逆方向電圧)と電流(電流密度)との関係を示す図である。図12中、横軸は、逆方向電圧(単位:V)を示し、縦軸は、電流密度(単位:A/cm2)を示す。
表1に示すように、GaN基板上にGaN層を形成し、かつ金属層の熱処理を行なった本発明例1のショットキーバリアダイオードの耐圧は、605Vと非常に高かった。
試料1~4のショットキーバリアダイオードは、本発明例1と同様に製造したが、金属層形成工程(S41)および熱処理工程(S42)のみ異なっていた。具体的には、金属層形成工程(S41)では、Niを25nm形成した後に、Ni上にAuを300nm形成した。また、試料1~4の熱処理工程(S42)では、熱処理温度を、それぞれ300℃、400℃、500℃および550℃とした。また、熱処理時間は1分とした。
試料5~8のショットキーバリアダイオードは、第1の金属層としてPt(白金)を形成し、この第1の金属層上に第2の金属層としてAuを形成した点、および熱処理工程(S42)での熱処理温度を、300℃、400℃、500℃および600℃とした点においてのみ試料1~4と異なっていた。
試料9のショットキーバリアダイオードは、比較例2において第1の金属層としてのNiの厚みを25nmとした点のみ異なっていた。つまり、試料1~4の製造方法において熱処理工程(S42)を実施しなかった。
試料10のショットキーバリアダイオードは、試料5~8の製造方法において熱処理工程(S42)を実施しなかった。
試料1~10のショットキーバリアダイオードのショットキー電極について、バリアハイトを測定した。バリアハイトの測定方法は、順方向のI-V特性から導出した。その結果を図11に示す。なお、図11は、本実施例において熱処理温度とバリアハイトの高さとの関係を示す図である。図11中、横軸は、熱処理工程(S41)において金属層を熱処理した温度(単位:℃)を示し、縦軸は、バリアハイトの高さ(単位:eV)を示す。
図11に示すように、第1の層がNiであるショットキー電極を形成した試料1~4は、第1の層がPtであるショットキー電極を形成した試料5~8に比べて、熱処理工程(S42)を実施することにより、バリアハイトを増加することができた。
Claims (28)
- GaN基板(2)と、
前記GaN基板(2)上に形成されたGaN層(3)と、
前記GaN層(3)上に形成されたショットキー電極(4)とを備え、
前記ショットキー電極(4)は、前記GaN層(3)と接触する位置に形成され、かつNiまたはNi合金よりなる第1の層(4a)を含む、ショットキーバリアダイオード。 - 前記GaN層(3)において前記ショットキー電極(4)と接触する領域(3c)の転位密度は、1×108cm-2以下である、請求の範囲第1項に記載のショットキーバリアダイオード(1、11、21)。
- 前記ショットキー電極(4)は、前記第1の層(4a)上に形成され、かつAuを含む第2の層(4b)をさらに含む、請求の範囲第1項に記載のショットキーバリアダイオード(1、11、21)。
- 前記GaN層(3)上に形成され、内部に前記ショットキー電極(4)が形成された開口部が形成されている絶縁層(17)と、
前記ショットキー電極(4)に接続するとともに、前記絶縁層(17)に重なるように形成されたフィールドプレート電極(16)とをさらに備えた、請求の範囲第1項に記載のショットキーバリアダイオード(11、21)。 - GaN層(3)と、
前記GaN層(3)上に形成されたショットキー電極(4)とを備え、
前記GaN層(3)において前記ショットキー電極(4)と接触する領域(3c)の転位密度は、1×108cm-2以下であり、
前記ショットキー電極(4)は、前記GaN層(3)と接触する位置に形成され、かつNiまたはNi合金よりなる第1の層(4a)を含む、ショットキーバリアダイオード(1、11、21)。 - 前記GaN層(3)において前記ショットキー電極(4)と接する面と反対側の面に接触するGaN基板(2)をさらに備えた、請求の範囲第5項に記載のショットキーバリアダイオード(1、11、21)。
- 前記ショットキー電極(4)は、前記第1の層(4a)上に形成され、かつAuを含む第2の層(4b)をさらに含む、請求の範囲第5項に記載のショットキーバリアダイオード(1、11、21)。
- 前記GaN層(3)上に形成され、内部に前記ショットキー電極(4)が形成された開口部が形成されている絶縁層(17)と、
前記ショットキー電極(4)に接続するとともに、前記絶縁層(17)に重なるように形成されたフィールドプレート電極(16)とをさらに備えた、請求の範囲第5項に記載のショットキーバリアダイオード(11、21)。 - GaN基板(2)を準備する工程と、
前記GaN基板(2)上にGaN層(3)を形成する工程と、
前記GaN層(3)上に接触するNiまたはNi合金よりなる第1の層(4a)を含むショットキー電極(4)を形成する工程とを備え、
前記ショットキー電極(4)を形成する工程は、前記ショットキー電極(4)となるべき金属層を形成する工程と、前記金属層を熱処理して、前記金属層を前記第1の層(4a)を含む前記ショットキー電極(4)に形成する工程とを含む、ショットキーバリアダイオード(1、11、21)の製造方法。 - 前記GaN基板(2)を準備する工程では、転位密度が1×108cm-2以下である前記GaN基板(2)を準備する、請求の範囲第9項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を熱処理する工程では、300℃以上600℃以下の温度で前記金属層を熱処理する、請求の範囲第9項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を熱処理する工程では、400℃以上550℃以下の温度で前記金属層を熱処理する、請求の範囲第11項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を形成する工程と、前記熱処理する工程とを並行して行なう、請求の範囲第9項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を熱処理する工程では、200℃以上600℃以下の温度で前記金属層を熱処理する、請求の範囲第13項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を熱処理する工程では、窒素を含む雰囲気で前記金属層を熱処理する、請求の範囲第9項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記ショットキー電極(4)を形成する工程は、前記第1の層(4a)上に、Auを含む第2の層(4b)を形成する工程をさらに含む、請求の範囲第9項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記GaN層(3)上に開口部を有する絶縁層(17)を形成する工程と、
前記ショットキー電極(4)に接続するとともに、前記絶縁層(17)に重なるようにフィールドプレート電極(16)を形成する工程とをさらに備え、
前記金属層を形成する工程では、前記絶縁層(17)の前記開口部の内部に前記GaN層(3)と接するように前記金属層を形成する、請求の範囲第9項に記載のショットキーバリアダイオード(11、21)の製造方法。 - 前記金属層を形成する工程に先立って、前記GaN層(3)を熱処理する工程、およびプラズマCVD法により前記GaN層(3)上に絶縁層(17)を形成する工程の少なくとも一方をさらに備えた、請求の範囲第9項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- GaN層(3)を準備する工程と、
前記GaN層(3)上に接触するNiまたはNi合金よりなる第1の層(4a)を含むショットキー電極(4)を形成する工程とを備え、
前記GaN層(3)を準備する工程は、前記ショットキー電極(4)と接触する領域(3c)の転位密度が1×108cm-2以下である前記GaN層(3)を準備する工程を含み、
前記ショットキー電極(4)を形成する工程は、前記ショットキー電極(4)となるべき金属層を形成する工程と、前記金属層を熱処理して、前記金属層を前記第1の層(4a)を含む前記ショットキー電極(4)に形成する工程とを含む、ショットキーバリアダイオード(1、11、21)の製造方法。 - GaN基板(2)を準備する工程をさらに備え、
前記GaN層(3)を準備する工程では、前記GaN基板(2)上に前記GaN層(3)をエピタキシャル成長する、請求の範囲第19項に記載のショットキーバリアダイオード(1、11、21)の製造方法。 - 前記金属層を熱処理する工程では、300℃以上600℃以下の温度で前記金属層を熱処理する、請求の範囲第19項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を熱処理する工程では、400℃以上550℃以下の温度で前記金属層を熱処理する、請求の範囲第21項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を形成する工程と、前記熱処理する工程とを並行して行なう、請求の範囲第19項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を熱処理する工程では、200℃以上600℃以下の温度で前記金属層を熱処理する、請求の範囲第23項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記金属層を熱処理する工程では、窒素を含む雰囲気で前記金属層を熱処理する、請求の範囲第19項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記ショットキー電極(4)を形成する工程は、前記第1の層(4a)上に、Auを含む第2の層(4b)を形成する工程をさらに含む、請求の範囲第19項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
- 前記GaN層(3)上に開口部を有する絶縁層(17)を形成する工程と、
前記ショットキー電極(4)に接続するとともに、前記絶縁層(17)に重なるようにフィールドプレート電極(16)を形成する工程とをさらに備え、
前記金属層を形成する工程では、前記絶縁層(17)の前記開口部の内部に前記GaN層(3)と接するように前記金属層を形成する、請求の範囲第19項に記載のショットキーバリアダイオード(11、21)の製造方法。 - 前記金属層を形成する工程に先立って、前記GaN層(3)を熱処理する工程、およびプラズマCVD法により前記GaN層(3)上に絶縁層(17)を形成する工程の少なくとも一方をさらに備えた、請求の範囲第19項に記載のショットキーバリアダイオード(1、11、21)の製造方法。
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US13/935,344 Continuation US8901698B2 (en) | 2008-08-05 | 2013-07-03 | Schottky barrier diode and method for manufacturing schottky barrier diode |
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JP (2) | JP5531959B2 (ja) |
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JP2014017285A (ja) * | 2012-07-05 | 2014-01-30 | Advanced Power Device Research Association | 窒化物系化合物半導体素子 |
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JP2016004899A (ja) * | 2014-06-17 | 2016-01-12 | 住友電気工業株式会社 | ショットキーバリアダイオードおよびその製造方法 |
JP2016039210A (ja) * | 2014-08-06 | 2016-03-22 | 住友電気工業株式会社 | Iii族窒化物半導体デバイスおよびその製造方法 |
JP2016162785A (ja) * | 2015-02-27 | 2016-09-05 | 豊田合成株式会社 | 半導体装置およびその製造方法 |
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WO2020235691A1 (ja) * | 2019-05-23 | 2020-11-26 | 株式会社Flosfia | 半導体装置 |
Also Published As
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US20130292695A1 (en) | 2013-11-07 |
EP2320465A1 (en) | 2011-05-11 |
CN103441140A (zh) | 2013-12-11 |
JPWO2010016388A1 (ja) | 2012-01-19 |
CN102119443B (zh) | 2013-08-14 |
US8901698B2 (en) | 2014-12-02 |
TW201013935A (en) | 2010-04-01 |
JP2014158044A (ja) | 2014-08-28 |
US8502337B2 (en) | 2013-08-06 |
US20110133210A1 (en) | 2011-06-09 |
JP5531959B2 (ja) | 2014-06-25 |
EP2320465A4 (en) | 2014-01-22 |
CN102119443A (zh) | 2011-07-06 |
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