JP2010219130A - Semiconductor device and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device that can suppress deterioration of characteristics, and to provide a method of manufacturing the same. <P>SOLUTION: A Schottky barrier diode 100 includes a semiconductor layer 1 containing GaN, and a Schottky electrode 2. The Schottky electrode 2 includes: an electrode body 6; a connection electrode 8, which is formed in a position apart from the electrode body 6 when viewed from the semiconductor layer 1, and contains Al; and a barrier layer 7 formed between the electrode body 6 and connection electrode 8, and containing at least one selected from a group consisting of W, TiW, WN, TiN, and Ta. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device including a semiconductor layer containing GaN (gallium nitride) and a manufacturing method thereof.

  Since GaN has a band gap in the ultraviolet region, it has been applied as a material for optical devices such as laser devices that oscillate light with a short wavelength such as blue or ultraviolet light. In an optical device using GaN, Au having a low resistance is employed as a pad electrode for connecting an external wiring (wire or the like).

  In view of the property of having a wide band gap and the property of having high carrier mobility and breakdown electric field strength, in recent years, not only is GaN used as an optical device, but also a Schottky barrier diode (SBD), There are active attempts to apply it to power semiconductor devices such as transistors. In a power semiconductor device using GaN, a large-diameter wiring (wire) of 200 μm or more made of Al is usually used for connection between the power semiconductor device and an external device because of the necessity of flowing a large current.

Here, the structure of a conventional power semiconductor device using GaN is disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-196964 (Patent Document 1), F. Ren et al., “Wide Energy Bandgap Electronic Devices”, World Scientific, 2003. , p.152-155 (Non-patent Document 1) and H. Otake et al., "Vertical GaN-Based Trench Gate Metal Oxide Semiconductor Field-Effect Transistors on GaN Bulk Substrates", Appl. Phys. Express., 1 ( 2008) 011105 (Non-Patent Document 2) and the like. In Patent Document 1, a diffusion preventing layer made of Ti _x W _1-x N (0 <x <1) is provided between a compound semiconductor layer made of GaN, a Ni layer that is in Schottky junction, and a low-resistance metal layer. It is disclosed. Non-Patent Document 1 discloses a GaN Schottky rectifier formed on a GaN substrate. In this rectifier, the Schottky electrode is made of Pt / Ti / Au. Non-Patent Document 2 discloses a GaN-based vertical MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) formed on a GaN substrate. In this MOSFET, the gate electrode is made of Ni / Au.

JP 2006-196664 A

F.Ren et al., "Wide Energy Bandgap Electronic Devices", World Scientific, 2003, p.152-155 H.Otake et al., "Vertical GaN-Based Trench Gate Metal Oxide Semiconductor Field-Effect Transistors on GaN Bulk Substrates", Appl. Phys. Express., 1 (2008) 011105

  When Au is used as a pad electrode in a power semiconductor device made of a GaN-based material, it is included in the Au and wire of the pad electrode due to heat generated when the wire is bonded to the pad electrode and heat generated when the device is driven. An alloy is formed with Al, and the quality of the pad electrode may be deteriorated. Further, in a power semiconductor device, the pad electrode needs to have a thickness that can withstand damage when a thick Al wire is mounted. If Au is used as the pad electrode, the cost increases. For this reason, in a GaN-based power device, Al, which is the same material as the wire, is used as the pad electrode.

  However, for example, in power devices made of GaN-based materials such as SBDs and vertical MOSFETs, when a pad electrode containing Al (connection electrode) is adopted, the characteristics of the device are generated by heat generated during device mounting or device operation. There was a problem of deterioration.

  Accordingly, an object of the present invention is to provide a semiconductor device capable of suppressing deterioration of characteristics and a manufacturing method thereof.

  The semiconductor device of the present invention includes a semiconductor layer containing GaN and an electrode. The electrode is formed at a position distant from the electrode main body and the electrode main body as viewed from the semiconductor layer, and is formed between the connection electrode containing Al and the electrode main body and the connection electrode, W, TiW, WN And a barrier layer containing at least one selected from the group consisting of TiN and Ta.

  The method for manufacturing a semiconductor device of the present invention includes the following steps. A semiconductor layer containing GaN is formed. An electrode is formed. The step of forming the electrode includes the following steps. An electrode body is formed. A connection electrode containing Al is formed at a position distant from the electrode body as viewed from the semiconductor layer. A barrier layer containing at least one selected from the group consisting of W, TiW, WN, TiN, and Ta is formed between the electrode body and the connection electrode.

  The inventors of the present application have found that the reason why the characteristics of a semiconductor device including a connection electrode containing Al is deteriorated is that Al contained in the connection electrode diffuses into the semiconductor layer due to heat. Therefore, in the present invention, a barrier layer containing at least one selected from the group consisting of W, TiW, WN, TiN, and Ta is formed between the semiconductor layer and the connection electrode, thereby forming the connection electrode. It is possible to suppress the diffusion of Al contained and suppress the deterioration of characteristics.

  In the semiconductor device of the present invention, preferably, the electrode body is in Schottky contact with the semiconductor layer. Thereby, a function as an SBD can be added to the semiconductor device, and a high-performance SBD can be realized.

  According to the semiconductor device and the manufacturing method thereof of the present invention, it is possible to suppress deterioration of characteristics.

It is sectional drawing which shows typically the structure of the semiconductor device in Embodiment 1 of this invention. It is sectional drawing which shows typically the structure of the semiconductor device in Embodiment 2 of this invention. It is a figure which shows the current density change with respect to a reverse voltage in the sample A of Example 1 of this invention. It is a figure which shows the current density change with respect to a reverse voltage in the samples B and C of Example 1 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a cross-sectional view schematically showing the configuration of the semiconductor device according to the first embodiment of the present invention. Referring to FIG. 1, SBD 100 as a semiconductor device in the present embodiment includes semiconductor layer 1, Schottky electrode 2 as an electrode, and ohmic electrode 3. A Schottky electrode 2 is formed on the upper surface side of the semiconductor layer 1, and an ohmic electrode 3 is formed on the lower surface side of the semiconductor layer 1.

  The semiconductor layer 1 includes a substrate 4 and a drift layer 5 formed on the substrate 4. The substrate 4 and the drift layer 5 contain GaN, and are made of, for example, n-type GaN. The n-type impurity concentration of the drift layer 5 is lower than the n-type impurity concentration of the substrate 4.

  The Schottky electrode 2 includes an electrode body 6, a barrier layer 7, and a connection electrode (pad electrode) 8. The electrode body 6 is in contact with the drift layer 5 and forms a Schottky barrier with the drift layer 5. The electrode body 6 is composed of, for example, a Ni / Au laminated film, that is, a Ni layer that is in Schottky contact with the drift layer 5 and an Au layer formed on the Ni layer. A barrier layer 7 is formed on the electrode body 6, and a connection electrode 8 is formed on the barrier layer 7. The connection electrode 8 is a portion to which a wiring (for example, a wire made of Al) for electrically connecting the Schottky electrode of the SBD 100 and an external device is directly connected. The connection electrode 8 contains Al, and is made of, for example, Al. The barrier layer 7 suppresses diffusion of Al contained in the connection electrode 8 into the semiconductor layer 1 due to heat. The barrier layer 7 contains at least one selected from the group consisting of W, TiW, WN, TiN, and Ta. The barrier layer 7 is made of, for example, W, TiW, WN, TiN, or Ta.

  The ohmic electrode 3 is made of a material that makes ohmic contact with the substrate 4, and is made of, for example, a laminated film of Ti / Al / Ti / Au.

  In the SBD 100, when a voltage exceeding the Schottky barrier between the electrode body 6 and the drift layer 5 is applied between the Schottky electrode 2 and the ohmic electrode 3, the semiconductor layer 1 A current flows through the ohmic electrode 3 in a direction perpendicular to the main surface of the substrate 4 (longitudinal direction in the figure).

  For example, the SBD 100 is manufactured by the following method. First, the drift layer 5 is formed on the substrate 4. Next, the Schottky electrode 2 is formed on the upper surface of the drift layer 5, and the ohmic electrode 3 is formed on the lower surface of the substrate 4. When forming the Schottky electrode 2, the electrode body 6 is formed on the upper surface of the drift layer 5, then the barrier layer 7 is formed on the electrode body 6, and then the connection electrode 8 is formed on the barrier layer 7. To do.

  The SBD 100 in the present embodiment includes a semiconductor layer 1 containing GaN and a Schottky electrode 2. The Schottky electrode 2 is formed at a position distant from the electrode body 6 and the electrode body 6 when viewed from the semiconductor layer 1, and between the electrode body 6 and the connection electrode 8. And a barrier layer 7 formed on the substrate.

  The manufacturing method of SBD 100 in the present embodiment includes the following steps. A semiconductor layer 1 containing GaN is formed. A Schottky electrode 2 is formed. The step of forming the Schottky electrode 2 includes the following steps. The electrode body 6 is formed. A connection electrode 8 containing Al is formed at a position distant from the electrode body 6 when viewed from the semiconductor layer 1. A barrier layer 7 is formed between the electrode body 6 and the connection electrode 8.

  According to the SBD 100 and the manufacturing method thereof in the present embodiment, even if the connection electrode 8 is heated by heat generated at the time of mounting (for example, at the time of die bonding) or heat generated at the time of driving the SBD 100, the connection electrode 8 The diffusion of Al contained therein is blocked by the barrier layer 7, and Al can be prevented from entering the Schottky junction interface. As a result, deterioration of the characteristics of the SBD 100 due to heat can be suppressed.

(Embodiment 2)
FIG. 2 is a cross-sectional view schematically showing the configuration of the semiconductor device according to the second embodiment of the present invention. Referring to FIG. 1, a vertical n-channel MOSFET 101 as a semiconductor device in the present embodiment includes a semiconductor layer 11, a gate electrode 12 as an electrode, a source electrode 13, and a drain electrode 14. A trench 11 a is formed on the upper surface of the semiconductor layer 11, and a gate electrode 12 is formed on the inner wall surface of the trench 11 a and the upper surface of the semiconductor layer 11 near the trench 11 a with a gate insulating film 19 interposed therebetween. A source electrode 13 is formed on the upper surface of the semiconductor layer 11 where the trench 11a and the gate insulating film 19 are not formed. A drain electrode 14 is formed on the lower surface of the semiconductor layer 11.

  The semiconductor layer 11 includes a substrate 15, an n-type drift layer 16, a p-type body layer 17, and an n-type layer 18. An n-type drift layer 16 is formed on the substrate 15, a p-type body layer 17 is formed on the n-type drift layer 16, and an n-type layer 18 is formed on the p-type body layer 17. ing. The trench 11 a penetrates the n-type layer 18 and the p-type body layer 17 and reaches the n-type drift layer 16. The substrate 15, the n-type drift layer 16, the p-type body layer 17, and the n-type layer 18 all contain GaN, and are made of, for example, GaN. The n-type impurity concentration of the n-type drift layer 16 is lower than the n-type impurity concentration of the substrate 15 and the n-type layer 18.

  The gate electrode 12 includes an electrode body 6, a barrier layer 7, and a connection electrode (pad electrode) 8. The electrode body 6 is formed on the gate insulating film 19, a barrier layer 7 is formed on the electrode body 6, and a connection electrode 8 is formed on the barrier layer 7. The connection electrode 8 is a portion to which a wiring for electrically connecting the gate electrode 12 of the MOSFET 101 and an external device is directly connected. Since the configuration of electrode body 6, barrier layer 7, and connection electrode 8 is the same as the configuration of the electrode body, barrier layer, and connection electrode in the first embodiment, description thereof will not be repeated.

  The source electrode 13 has an ohmic electrode 13a and an ohmic electrode 13b. The ohmic electrode 13a is formed so as to surround the periphery of the trench 11a, and is made of, for example, a Ti / Al laminated film. The ohmic electrode 13b is formed so as to surround the ohmic electrode 13a, and is electrically connected to the p-type body layer 17 and the ohmic electrode 13a. The ohmic electrode 13b is made of, for example, a Ni / Au laminated film. The drain electrode 14 is formed on the entire lower surface of the substrate 15 and is made of, for example, Ti / Al.

  In the MOSFET 101, when the gate electrode 12 and the drain electrode 14 are at a higher potential than the source electrode 13, a channel is formed in the p-type body layer 17 facing the gate electrode 12 with the gate insulating film 19 interposed therebetween. Current flows through this channel. As a result, a current flows from the drain electrode 14 through the semiconductor layer 11 to the source electrode 13 in a direction perpendicular to the main surface of the substrate 15 (vertical direction in the drawing).

  MOSFET 101 is manufactured, for example, by the following method. First, the n-type drift layer 16, the p-type body layer 17, and the n-type layer 18 are formed on the substrate 15 in this order, so that the semiconductor layer 1 is manufactured. Next, a trench 11 a reaching the n-type drift layer 16 is formed on the upper surface of the semiconductor layer 1. Next, the gate insulating film 19 is formed on the inner wall surface of the trench 11 a, and the gate electrode 12 is formed on the gate insulating film 19. Next, the ohmic electrode 13a is formed on the n-type layer 18, and the n-type layer 18 on the outer periphery of the ohmic electrode 13a is etched to expose the P-type body layer 17. Then, ohmic electrode 13 b is formed so as to be electrically connected to ohmic electrode 13 a and p-type body layer 17. The ohmic electrode 13a and the ohmic electrode 13b constitute a source electrode 13. Thereafter, the drain electrode 14 is formed on the lower surface of the substrate 15. When forming the gate electrode 12, the electrode body 6 is formed on the gate insulating film 19, then the barrier layer 7 is formed on the electrode body 6, and then the connection electrode 8 is formed on the barrier layer 7. .

  MOSFET 101 in the present embodiment includes a semiconductor layer 11 containing GaN and a gate electrode 12. The gate electrode 12 is formed at a position distant from the electrode body 6 and the electrode body 6 when viewed from the semiconductor layer 11, and between the electrode body 6 including Al and the electrode body 6 and the connection electrode 8. The formed barrier layer 7 is included.

  The manufacturing method of MOSFET 101 in the present embodiment includes the following steps. A semiconductor layer 11 containing GaN is formed. A gate electrode 12 is formed. The step of forming the gate electrode 12 includes the following steps. The electrode body 6 is formed. A connection electrode 8 containing Al is formed at a position distant from the electrode body 6 when viewed from the semiconductor layer 11. A barrier layer 7 is formed between the electrode body 6 and the connection electrode 8.

  According to MOSFET 101 and the method of manufacturing the same in the present embodiment, even if connection electrode 8 is heated by heat generated during mounting (for example, during die bonding) or heat generated when MOSFET 101 is driven, The diffusion of the contained Al is blocked by the barrier layer 7 and the entry of Al into the MOS interface can be suppressed. As a result, the deterioration of the characteristics of the MOSFET 101 due to heat can be suppressed.

  In the present embodiment, the case where the electrode constituted by the electrode body, the barrier layer, and the connection electrode is applied as the gate electrode of the MOSFET has been described. However, the electrode in the present invention may be applied as a source electrode of a MOSFET.

  Further, in the first and second embodiments, the case where the semiconductor device of the present invention is an SBD and a vertical MOSFET has been described. However, the semiconductor device of the present invention may be a capacitor, a lateral MOSFET, a high electron mobility transistor, a bipolar transistor, or the like in addition to these devices. The semiconductor device of the present invention is particularly preferably a vertical device, that is, a device having a current path substantially perpendicular to the main surface of the substrate.

In this example, first, SBDs of samples A to C were manufactured under the following conditions.
Sample A (Invention Example): An SBD having the structure shown in FIG. 1 was produced. Specifically, a GaN free-standing substrate prepared by HVPE (Hydride Vapor Phase Epitaxy) was prepared. This substrate had an n-type impurity concentration of 3 × 10 ¹⁸ cm ⁻³ , a thickness of 400 μm, and an average dislocation density of 1 × 10 ⁶ / cm ² . Next, a drift layer made of GaN having an n-type impurity concentration of 5 × 10 ¹⁵ cm ⁻³ and a thickness of 5 μm is epitaxially grown on the (0001) surface of the substrate using an OMVPE (Organometallic Vapor Phase Epitaxy) method. It was. Next, after the substrate was washed with an organic solvent, an ohmic electrode was formed on the lower surface of the substrate. As the ohmic electrode, a laminated film of Ti (thickness 20 nm) / Al (thickness 100 nm) / Ti (thickness 20 nm) / Au (thickness 300 nm) was formed by using an EB (Electron Beam) vapor deposition method. Thereafter, the ohmic electrode was heat-treated in a nitrogen atmosphere at 600 ° C. for 1 minute. Next, a Schottky electrode was formed on the upper surface of the drift layer. As a Schottky electrode, an electrode body made of Ni (thickness 50 nm) / Au (thickness 300 nm) is formed by EB vapor deposition, and Ti and W are sputtered simultaneously to form TiW on the electrode body. A barrier layer having a thickness of 0.15 μm was formed, and subsequently, Al was sputtered to form a connection electrode having a thickness of 3 μm. Next, the Schottky electrode was patterned into a square shape with one side of 1 mm. Specifically, a resist is patterned on the connection electrode by photolithography, and using this resist as a mask, Al is etched using a mixed acid etchant (phosphoric acid + nitric acid + acetic acid + pure water) at 40 ° C., Subsequently, the barrier layer was etched with an ammonia-based etchant (ammonia water + hydrogen peroxide water + pure water) at room temperature. When the composition of Ti in the barrier layer after etching was examined by ICP (Inductively Coupled Plasma) analysis, it was 8% by weight. Immediately before vapor deposition of the ohmic electrode and the Schottky electrode, the vapor deposition surface was treated for 1 minute using a room temperature HCl aqueous solution (hydrochloric acid for semiconductor 1: pure water 1). As sample A, two SBDs (chip A and chip B) were produced.

  Sample B (comparative example): After forming an electrode body made of Ni (thickness 50 nm) / Au (thickness 300 nm) as a Schottky electrode using EB vapor deposition, sputtering is performed without forming a barrier layer. As a result, a connection electrode having a thickness of 3 μm was formed on the electrode body. Further, when patterning the Schottky electrode, Al was etched using a mixed acid etchant (phosphoric acid + nitric acid + acetic acid + pure water) at 40 ° C. The manufacturing method other than the above is the same as that of the sample A.

  Sample C (Comparative Example): After forming an electrode body made of Ni (thickness 50 nm) / Au (thickness 300 nm) as a Schottky electrode by using the EB vapor deposition method, a thickness of 0. A 15 μm Ti layer was formed, and then a 3 μm thick connection electrode was formed on the Ti layer by sputtering Al. When patterning the Schottky electrode, Al is etched using a mixed acid etchant (phosphoric acid + nitric acid + acetic acid + pure water) at 40 ° C., followed by an ammonia etchant (ammonia water + hydrogen peroxide solution) at room temperature. The Ti layer was etched with (+ pure water). The manufacturing method other than the above is the same as that of the sample A.

  Next, the thermal stability of samples A to C was evaluated. Specifically, each of the samples A to C is heat-treated at 350 ° C., which is a temperature assumed as a temperature at the time of mounting (die bonding) of the SBD, and the current against the reverse voltage before and after the heat treatment. Density was measured.

  FIG. 3 is a diagram showing a change in current density with respect to the reverse voltage in the sample A of Example 1 of the present invention. FIG. 4 is a diagram showing a change in current density with respect to a reverse voltage in samples B and C of Example 1 of the present invention. 3 and 4, sample A, which is an example of the present invention, shows no significant change in current density change with respect to the reverse voltage in either case of chip A or chip B. Deterioration was suppressed. On the other hand, in Samples B and C, the current density with respect to the reverse voltage after the heat treatment was extremely increased, and the characteristics were deteriorated by heating.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is suitable as a power semiconductor device made of a GaN-based material.

  DESCRIPTION OF SYMBOLS 1,11 Semiconductor layer, 2 Schottky electrode, 3 Ohmic electrode, 4,15 Substrate, 5 Drift layer, 6 Electrode body, 7 Barrier layer, 8 Connection electrode, 11a Trench, 12 Gate electrode, 13 Source electrode, 13a, 13b Ohmic electrode, 14 drain electrode, 16 n-type drift layer, 17 p-type body layer, 18 n-type layer, 19 gate insulating film, 100 SBD, 101 MOSFET.

Claims (3)

A semiconductor layer comprising gallium nitride;
With electrodes,
The electrode is formed at a position farther from the electrode body as viewed from the semiconductor body and the electrode body, and is formed between the connection electrode containing aluminum and the electrode body and the connection electrode. And a barrier layer containing at least one selected from the group consisting of W, TiW, WN, TiN, and Ta.   The semiconductor device according to claim 1, wherein the electrode body is in Schottky contact with the semiconductor layer. Forming a semiconductor layer containing gallium nitride;
Forming an electrode,
The step of forming the electrode includes the step of forming an electrode body, the step of forming a connection electrode containing aluminum at a position farther from the electrode body as viewed from the semiconductor layer, and the electrode body and the connection Forming a barrier layer containing at least one selected from the group consisting of W, TiW, WN, TiN, and Ta between the electrode and the electrode.

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