JP4415531B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device using a GaN-based compound semiconductor and a manufacturing method thereof.
[0002]
[Prior art]
GaN (gallium nitride) -based compound semiconductors have higher withstand voltage and electron mobility than silicon semiconductors. For this reason, if a GaN-based compound semiconductor is used, it is expected that a semiconductor element having characteristics of high speed, low loss, and high withstand voltage can be realized.
For this reason, application to semiconductor elements such as field effect transistors and Schottky barrier diodes of GaN-based compound semiconductors has been attempted.
[0003]
A field effect transistor using a GaN-based compound semiconductor is disclosed in Patent Document 1, for example.
[0004]
[Patent Document 1]
JP 2001-320054 A (paragraphs 0006-0017, FIG. 1)
[0005]
[Problems to be solved by the invention]
However, when a GaN-based compound semiconductor is actually applied to a field effect transistor, a large leakage current is generated. In addition, a phenomenon in which conductance between the drain and the source changes depending on the frequency of the gate signal, that is, so-called frequency dispersion also occurs.
[0006]
In a field effect transistor using a GaN compound semiconductor, an insulating film (passivation film) is formed on a semiconductor substrate. The trapping effect of electrons generated by the formation of the insulating film and damage to the semiconductor substrate destabilize the surface level of the GaN-based compound semiconductor.
[0007]
The occurrence of the above-described leakage current and frequency dispersion is considered to be caused by the instability of the surface state .
[0008]
When the leakage current and frequency dispersion as described above occur, it is impossible to realize a field effect transistor having properties of high speed, low loss, and high withstand voltage and operating stably.
[0009]
The above problems occur not only in field effect transistors but also in other semiconductor elements such as Schottky barrier diodes using GaN-based compound semiconductors.
[0010]
Accordingly, an object of the present invention is to provide a semiconductor device that uses a GaN-based compound semiconductor, has properties of high speed, low loss, and high withstand voltage and operates stably, and a method for manufacturing the same.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor element according to a first aspect of the present invention includes a semiconductor substrate formed of a gallium nitride (GaN) -based compound semiconductor and a plurality of regions formed in a predetermined region on the semiconductor substrate. An electrode and a surface protective film that is formed of a nickel oxide film and that stabilizes the surface level of the semiconductor substrate by covering at least a portion of the semiconductor substrate between the plurality of electrodes. And
[0012]
According to the present invention, it is possible to provide a semiconductor element using a GaN-based compound semiconductor that has the properties of high speed, low loss, and high withstand voltage and operates stably.
[0013]
The surface protective film may have a thickness of 0.5 to 5.0 nm.
[0014]
The surface protective film may be formed between two electrodes, and may have a sheet resistance of 100 MΩ / □ to 5000 MΩ / □.
[0015]
The surface protective film may be formed so as not to straddle between two electrodes, and may have a sheet resistance of 10 KΩ / □ to 5000 MΩ / □.
[0016]
The semiconductor substrate, the plurality of electrodes, and the surface protective film may be covered, and an insulating film containing activated hydrogen may be further provided.
[0017]
A method for manufacturing a semiconductor device according to a second aspect of the present invention is a method for manufacturing a semiconductor device having a semiconductor substrate formed of a gallium nitride (GaN) -based compound semiconductor. an electrode forming step of forming the electrode, a film forming step of forming a nickel film covering at least a portion of said semiconductor substrate between said plurality of electrodes, by oxidizing the nickel film, the surface state of the semiconductor substrate And an oxidation step for forming a surface protective film for stabilizing the position .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, a semiconductor device using a GaN-based compound semiconductor according to an embodiment of the present invention will be described with reference to the drawings.
Hereinafter, a field effect transistor will be described as an example of a semiconductor device using a GaN-based compound semiconductor.
[0019]
As shown in FIG. 1, the field effect transistor includes a semiconductor substrate 1, a source electrode 2, a drain electrode 3, a gate electrode 4, a surface protective film 5, and an insulating film 6.
[0020]
As shown in FIG. 1, the semiconductor substrate 1 includes a substrate 11 formed of a silicon single crystal, a GaN buffer layer 12, an undoped GaN layer 13, and an n-type GaN layer 14 sequentially stacked on the substrate 11. And a GaN-based compound semiconductor substrate.
[0021]
The source electrode 2 and the drain electrode 3 are respectively formed in predetermined regions on the semiconductor substrate 1 (specifically, the n-type GaN layer 14), and make ohmic contact (low resistance contact) with the n-type GaN layer 14. ing. The source electrode 2 and the drain electrode 3 are composed of a Ti (titanium) film formed on the semiconductor substrate 1 and an Al (aluminum) film formed on the Ti film, and have a thickness of about 300 nm.
[0022]
The gate electrode 4 is formed in a predetermined region between the source electrode 2 and the drain electrode 3 on the semiconductor substrate 1 (specifically, the n-type GaN layer 14). The gate electrode 4 includes a Ni (nickel) film or Pt (platinum) film formed on the semiconductor substrate 1 and an Au (gold) film formed on the Ni film or Pt film, and has a thickness of about 300 nm. Having a thickness of Further, a Schottky barrier having a predetermined height (barrier height) is generated at the contact surface (interface) between the gate electrode 4 and the n-type GaN layer 14.
[0023]
The surface protective film 5 is formed on the surface of the source electrode 2, the drain electrode 3, and the gate electrode 4 and the n-type GaN layer 14 exposed between the source electrode 2, the drain electrode 3, and the gate electrode 4. Formed on the surface. The surface protective film 5 is a nickel oxide film, and has a thickness of 0.5 to 5.0 nm and a sheet resistance of 100 MΩ / □ to 5000 MΩ / □.
[0024]
The insulating film 6 is a silicon oxide film or a silicon nitride film, and is formed on the surface protective film 5. The insulating film 6 is a passivation film that protects the function of the field effect transistor, and electrically insulates the source electrode 2, the drain electrode 3, and the gate electrode 4 from each other.
[0025]
Although omitted in FIG. 1, the formation regions of parts of the wiring portions of the source electrode 2, the drain electrode 3, and the gate electrode 4 overlap each other. However, they are electrically insulated from each other by the insulating film 6.
[0026]
As described above, by coating the surface protective film 5 of the surface of the semiconductor substrate 1 (specifically the n-type GaN layer 14 in), the semiconductor substrate 1 (i.e., GaN-based compound semiconductor) to stabilize the surface state of the be able to. As a result, the leakage current is reduced and the phenomenon that the conductance between the drain electrode 3 and the gate electrode 4 changes depending on the frequency of the gate signal, that is, the so-called frequency dispersion is suppressed.
[0027]
Next, a manufacturing method of the field effect transistor having the above configuration will be described.
First, as shown in FIG. 2A, a GaN buffer layer 12, an undoped GaN layer 13, and an n-type GaN layer 14 are formed in this order on a substrate 11 by MOCVD (metal organic chemical vapor deposition), for example. Are stacked. Thereby, the semiconductor substrate 1 is formed.
[0028]
Next, a Ti film and an Al film are formed in this order on the semiconductor substrate 1 by sputtering or the like, and patterned by dry etching or the like. Thereby, the source electrode 2 and the drain electrode 3 are formed as shown in FIG.
[0029]
Subsequently, a Ni film (or Pt film) and an Au film are formed in this order on the semiconductor substrate 1 on which the source electrode 2 and the drain electrode 3 are formed by sputtering or the like, and patterned by dry etching or the like. As a result, a gate electrode 4 is formed on the semiconductor substrate 1 exposed between the source electrode 2 and the drain electrode 3 as shown in FIG.
[0030]
Then, as shown in FIG. 3A, a nickel film 5 ′ is formed by sputtering or the like on the entire surface of the semiconductor substrate 1 on which the source electrode 2, the drain electrode 3, and the gate electrode 4 are formed.
[0031]
At this time, if the nickel film 5 ′ is too thick, it is difficult to uniformly oxidize the nickel film 5 ′ when the nickel film 5 ′ is oxidized in the next step. On the other hand, if the nickel film 5 ′ is too thin, the entire surface of the semiconductor substrate 1 may not be covered uniformly. Therefore, it is desirable to set the thickness of the nickel film 5 ′ within the range of 0.5 to 5.0 nm.
[0032]
After forming the nickel film 5 ′, the nickel film 5 ′ is oxidized by thermal oxidation or the like to form the surface protective film 5 as shown in FIG.
At this time, since the thickness of the nickel film 5 ′ is as extremely thin as 0.5 to 5.0 nm, the nickel film 5 ′ can be easily oxidized in the entire thickness direction. Further, the resistance value of the nickel film 5 ′ increases due to oxidation. At this time, since the thickness of the nickel film 5 ′ is extremely thin, the sheet resistance of the formed surface protection film 5 is a value (100 MΩ / □ to 5000 MΩ / □) that can be substantially regarded as an insulating film.
[0033]
The surface protective film 5 formed by the above-described oxidation treatment may be an oxygen-poor film having a lower oxygen bonding rate than a complete insulating film (NiO), that is, not a complete insulating film. . However, also in this case, if the sheet resistance of the surface protective film 5 is within the above range, a leak current at a level that causes a problem in use of the device does not flow through the surface protective film 5.
[0034]
After forming the surface protective film 5, as shown in FIG. 3C, an insulating film 6 is formed on the surface protective film 5 by, for example, plasma CVD (chemical vapor deposition), and the field effect shown in FIG. A transistor is completed.
[0035]
Note that the insulating film 6 formed by plasma CVD contains activated hydrogen and the like, and an electron trap effect is likely to occur. However, since the surface level of the semiconductor substrate 1 is stabilized by the surface protective film 5, an increase in leakage current due to the trap effect is effectively prevented.
[0036]
As described above, it is possible to realize a field effect transistor in which leakage current is sufficiently suppressed, high speed, low loss, and high breakdown voltage are achieved at a high level.
Further, as described above, since the increase in leakage current due to the trap effect can be prevented by the surface protective film 5, the material and the formation method of the insulating film 6 are not restricted, and the effect of increasing the degree of freedom is also obtained.
[0037]
When a film other than the nickel oxide film (for example, titanium oxide film) is used as the surface protective film 5, the surface level of the semiconductor substrate 1 cannot be stabilized as much as the case of the nickel oxide film. It has been confirmed. This is presumably because nickel has a catalytic (hydrogen reduction) function as a chemical characteristic, and this causes a hydrogen desorption effect from the surface of the GaN-based compound semiconductor during the heat treatment.
[0038]
The catalytic function as described above is recognized not only by nickel but also by platinum, for example. However, metals such as platinum are less susceptible to oxidation than nickel, and a high-resistance film cannot be easily obtained.
[0039]
When the resistance of the formed surface protective film 5 is low, a leak current flows through the surface protective film 5. If the surface protective film 5 is not uniformly oxidized in the thickness direction, a Schottky barrier is generated between the remaining metal film and the semiconductor substrate 1, and stable electrical characteristics cannot be obtained.
[0040]
For the above reasons, a nickel oxide film is suitable for easily forming the surface protective film 5 that exhibits a good effect of stabilizing the surface level and has a high sheet resistance.
[0041]
Further, the surface protective film 5 may be formed between the semiconductor substrate 1 and the gate electrode 4 as shown in FIG. In this case, an insulated gate field effect transistor having a MIS (metal-insulating film-semiconductor) structure formed by the gate electrode 4, the surface protective film 5, and the semiconductor substrate 1 is obtained.
[0042]
Even in the configuration as shown in FIG. 4, the surface level of the semiconductor substrate 1 is stabilized by the surface protective film 5, so that the leakage current can be suppressed and the field effect transistor can be operated at high speed, low loss, and high breakdown voltage at a high level. can do.
[0043]
For example, as shown in FIG. 5, even when the surface protective film 5 is formed only in the vicinity of the gate electrode 4, the effect of stabilizing the surface level of the semiconductor substrate 1 can be obtained.
[0044]
In the case of FIG. 5, the surface protective film 5 does not extend between the source electrode 2 and the gate electrode 4 and between the drain electrode 3 and the gate electrode 4, in other words, the source electrode 2 and the gate electrode 4 And the drain electrode 3 and the gate electrode 4 are not bridged, so that no leak current flows through the surface protective film 5. For this reason, the resistance value of the surface protective film 5 can be set smaller than the range shown in the said embodiment.
[0045]
However, if the resistance value of the surface protective film 5 is too small, the effect of stabilizing the surface state cannot be sufficiently obtained, and a Schottky barrier having an appropriate height can be obtained at the interface between the semiconductor substrate 1 and the gate electrode 4. Can not.
Therefore, in the configuration shown in FIG. 5, the sheet resistance of the surface protective film 5 must be set within the range of 10 KΩ / □ to 5000 MΩ / □.
[0046]
Further, the substrate 11 constituting the semiconductor substrate 1 may be formed of sapphire or silicon carbide.
[0047]
Further, the layer covered with the surface protective film 5 may not be the n-type GaN layer 14 as long as it is a GaN-based compound semiconductor layer. For example, an AlGaN layer may be used. Also in this case, the surface protective film 5 can provide the same effects as described above.
[0048]
The present invention can also be applied to semiconductor elements other than the above-described field effect transistors (for example, a Schottky barrier diode using a GaN-based compound semiconductor), and the same effects as described above can be obtained.
[0049]
【The invention's effect】
As is clear from the above description, according to the present invention, a semiconductor device having the characteristics of high speed, low loss, and high withstand voltage and using the GaN-based compound semiconductor can be provided. .
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a field effect transistor according to an embodiment of the present invention.
FIGS. 2A and 2B are diagrams showing a part of a manufacturing process of the field effect transistor shown in FIG.
FIGS. 3A to 3C are diagrams showing a part of a manufacturing process of the field effect transistor shown in FIG.
FIG. 4 is another configuration diagram of the field effect transistor according to the exemplary embodiment of the present invention.
FIG. 5 is another configuration diagram of the field effect transistor according to the exemplary embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Source electrode 3 Drain electrode 4 Gate electrode 5 Surface protective film 6 Insulating film 11 Substrate 12 GaN buffer layer 13 Undoped GaN layer 14 n-type GaN layer

Claims (6)

A semiconductor substrate formed from a gallium nitride (GaN) -based compound semiconductor;
A plurality of electrodes formed in a predetermined region on the semiconductor substrate;
A surface protective film that is formed of a nickel oxide film and that stabilizes the surface level of the semiconductor substrate by covering at least a portion of the semiconductor substrate between the plurality of electrodes;
A semiconductor device comprising:   The semiconductor device according to claim 1, wherein the surface protective film has a thickness of 0.5 to 5.0 nm.   3. The semiconductor device according to claim 1, wherein the surface protection film is formed between two electrodes and has a sheet resistance of 100 MΩ / □ to 5000 MΩ / □.   The semiconductor device according to claim 1, wherein the surface protective film is formed so as not to straddle between two electrodes and has a sheet resistance of 10 KΩ / □ to 5000 MΩ / □.   5. The semiconductor device according to claim 1, further comprising an insulating film containing activated hydrogen that covers the semiconductor substrate, the plurality of electrodes, and the entire surface protective film. 6. Semiconductor element. A method for manufacturing a semiconductor device having a semiconductor substrate formed from a gallium nitride (GaN) compound semiconductor,
An electrode forming step of forming a plurality of electrodes in a predetermined region on the semiconductor substrate;
Forming a nickel film covering at least a portion of the semiconductor substrate between the plurality of electrodes; and
An oxidation step of forming a surface protective film that stabilizes the surface state of the semiconductor substrate by oxidizing the nickel film;
The manufacturing method of the semiconductor element characterized by the above-mentioned.

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