Patent Application
20140217470
The invention relates to a Ga2O3-based semiconductor element.
A β-Ga2O3-based semiconductor element using a β-Ga2O3 crystal film formed on an α-Al2O3 (sapphire) substrate is known (see, e.g., NPL 1).
[NPL 1]
K. Matsuzaki et al. Appl. Phys. Lett. 88, 092106, 2006.
However, it is difficult to grow a monoclinic β-Ga2O3 crystal film on an α-Al2O3 substrate having a corundum structure and it is not possible to obtain a high-quality β-Ga2O3 crystal film. Thus, it is difficult to form a high-quality Ga2O3-based semiconductor element by using a β-Ga2O3 crystal film grown on an α-Al2O3 substrate.
It is an object of the invention to provide a high-quality Ga2O3-based semiconductor element.
According to one embodiment of the invention, a Ga2O3-based semiconductor element as defined in [1] to [4] below is provided so as to achieve the above object.
[1] A Ga2O3-based semiconductor element, comprising:
[2] The Ga2O3-based semiconductor element according to [1], wherein the α-(AlxGa1-x)2O3 single crystal film, the first contact region and the second contact region are of an n-type, and
[3] The Ga2O3-based semiconductor element according to [1], wherein the α-(AlxGa1-x)2O3 single crystal film comprises a high resistance region including no dopants, and
[4] The Ga2O3-based semiconductor element according to [1], wherein the α-(AlxGa1-x)2O3 single crystal film is of a p-type, and
According to an embodiment of the invention, a high-quality Ga2O3-based semiconductor element can be provided.
[
[
[
[
According to the present embodiment, it is possible to form a high-quality α-(AlxGa1-x)2O3 single crystal film on an α-Al2O3 substrate by homoepitaxial growth and use of such a high-quality α-(AlxGa1-x)2O3 single crystal film allows a high-quality Ga2O3-based semiconductor element to be formed. Examples of embodiments thereof will be described in detail below.
A Ga2O3-based MISFET (Metal Insulator Semiconductor Field Effect Transistor) having a planar gate structure will be described as the Ga2O3-based semiconductor element in the first embodiment.
The gate electrode 11 is located above the body region 17 in a region between the source electrode 12 and the drain electrode 13.
The Ga2O3-based MISFET 10 functions as a normally-off transistor. When voltage of more than the threshold is applied to the gate electrode 11, a channel is formed in a region of the body region 17 under the gate electrode 11 and a current thus flows from the source electrode 12 to the drain electrode 13.
The n-type α-(AlxGa1-x)2O3 single crystal film 3 is an α-(AlxGa1-x)2O3 (0≦x<1) single crystal film formed on the α-Al2O3 substrate 2. The n-type α-(AlxGa1-x)2O3 single crystal film 3 includes an n-type dopant such as Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, C, Si, Ge, Pb, Mn, As, Sb, Bi, F, Cl, Br and I. The n-type α-(AlxGa1-x)2O3 single crystal film 3 includes an n-type dopant at a concentration of, e.g, not less than 1×1015/cm3 and not more than 1×1019cm3. In addition, the thickness of the n-type α-(AlxGa1-x)2O3 single crystal film 3 is, e.g., 0.01 to 10 μm.
Here, another film such as an undoped β-Ga2O3 single crystal film may be formed between the α-Al2O3 substrate 2 and the n-type α-(AlxGa1-x)2O3 single crystal film 3. In this case, the undoped P-Ga2O3 single crystal film is formed on the α-Al2O3 substrate 2 by epitaxial growth and the n-type (AlxGa1-x)2O3 single crystal film 3 is formed on the undoped β-Ga2O3 single crystal film by epitaxial growth.
The gate electrode 11, the source electrode 12 and the drain electrode 13 are formed of, e.g., a metal such as Au, Al, Ti, Sn, Ge, In, Ni, Co, Pt, W, Mo, Cr, Cu and Pb, an alloy containing two or more of such metals, or a conductive compound such as ITO. In addition, the structure thereof may be a two-layer structure composed of two different metals, e.g., Al/Ti, Au/Ni or Au/Co.
The gate insulating film 16 is formed of a material such as SiO2, AlN, SiN or α-(AlyGa1-y)2O3 (0<y<1). Of those, α-(AlyGa1-y)2O3 has the same crystal structure as the α-Al2O3 crystal and thus allows a good semiconductor/insulating film interface with less interface states to be formed, resulting in better gate characteristics than when using other insulating films.
The contact regions 14 and 15 are regions having a high n-type dopant concentration formed in the n-type α-(AlxGa1-x)2O3 single crystal film 3 and are respectively connected to the source electrode 12 and the drain electrode 13. The n-type dopant included in the contact regions 14 and 15 and that included in the n-type α-(AlxGa1-x)2O3 single crystal film 3 may be either the same or different. The contact regions 14 and 15 include the n-type dopant at a concentration of, e.g., not less than 1×1018/cm3 and not more than 5×1019cm3.
In addition, the n-type dopant concentration in the contact region 15 may be the same as that in the n-type α-(AlxGa1-x)2O3 single crystal film 3. In other words, a region of the n-type α-(AlxGa1-x)2O3 single crystal film 3 into which the n-type dopant is not additionally implanted can be used as the contact region 15.
The body region 17 includes a p-type dopant such as Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N or P. The body region 17 is a p-type region or a high resistance region which behaves like i-type due to charge compensation.
A process using the Molecular Beam Epitaxy (MBE) will be described below as an example of the method of manufacturing the α-(AlxGa1-x)2O3 single crystal film. The MBE is a crystal growth method in which a single or compound solid is heated in an evaporation source called cell and vapor generated by heat is supplied as a molecular beam onto the surface of the substrate.
A Ga raw material of the α-(AlxGa1-x)2O3 single crystal film, such as Ga powder, is loaded in the first cell 103a. The Ga powder desirably has a purity of not less than 6N. Powder of an n-type dopant raw material to be doped as a donor is loaded in the second cell 103b. An Al raw material of the α-(AlxGa1-x)2O3 single crystal film, such as Al powder, is loaded in the third cell 103c. A shutter is provided at an opening of each of the first cell 103a, the second cell 103b and the third cell 103c.
Firstly, the α-Al2O3 substrate 2 is attached to the substrate holder 101 of the MBE system 100. Next, the vacuum pump 106 is activated to reduce atmospheric pressure in the vacuum chamber 107 to about 10−10 Torr. Then, the α-Al2O3 substrate 2 is heated by the heating devices 102. Here, radiation heat of heat source such as graphite heater of the heating device 102 is thermally transferred to the α-Al2O3 substrate 2 via the substrate holder 101 and the α-Al2O3 substrate 2 is thereby heated.
After the α-Al2O3 substrate 2 is heated to a predetermined temperature, oxygen-based gas is supplied into the vacuum chamber 107 through the gas supply pipe 105.
After a period of time required for stabilization of gas pressure in the vacuum chamber 107 (e.g., after 5 minutes) since the oxygen-based gas was supplied into the vacuum chamber 107, the first cell 103a, the second cell 103b and the second cell 103c are respectively heated by the first heater 104a, the second heater 104b and the third heater 104c while rotating the substrate holder 101 so that Ga, Al and n-type dopant are evaporated and are radiated as molecular beam onto the surface of the α-Al2O3 substrate 2.
As such, the α-(AlxGa1-x)2O3 single crystal is epitaxially grown on the main surface of the α-Al2O3 substrate 2 while being doped with the n-type dopant such as Sn and the n-type α-(AlxGa1-x)2O3 single crystal film 3 is thereby formed. It should be noted that as the n-type dopant other than Sn, it is possible to use Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, C, Si, Ge, Pb, Mn, As, Sb and Bi, etc., for substituting Ga or Al site and it is possible to use F, Cl, Br and I, etc., for substituting oxygen site. The addition concentration of the n-type dopant can be controlled by temperature of the second cell 103b during film formation.
Alternatively, the n-type ct-(AlxGa1-x)2O3 single crystal film 3 may be formed by the PLD (Pulsed Laser Deposition) or the CVD (Chemical Vapor Deposition) etc.
After forming the n-type α-(AlxGa1-x)2O3 single crystal film 3, the body region 17 is formed by ion-implanting a p-type dopant such as Mg into the n-type α-(AlxGa1-x)2O3 single crystal film 3. It should be noted that the ion to be implanted is not limited to Mg and, when substituting, e.g., Ga or Al site, it is possible to use H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl or Pb. In addition, it is possible to use N or P when substituting oxygen site. After implanting the p-type dopant, damage caused by implantation is repaired by performing annealing treatment.
It should be noted that the method of forming the body region 17 is not limited to ion implantation and thermal diffusion process may be used. In this case, after metal such as Mg is brought into contact with the n-type α-(AlxGa1-x)2O3 single crystal film 3 in a region for the body region 17 to be formed, heat treatment is performed to diffuse a dopant such as Mg into the n-type α-(AlxGa1-x)2O3 single crystal film 3.
Next, the contact regions 14 and 15 are formed by ion-planting the n-type dopant into the body region 17 of the n-type α-(AlxGa1-x)2O3 single crystal film 3. It should be noted that the ion to be implanted is not limited to Sn and, when substituting, e.g., Ga or Al site, it is possible to use Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, C, Si, Ge, Pb, Mn, As, Sb or Bi. In addition, it is possible to use F, Cl, Br or I when substituting oxygen site.
The implantation concentration is, e.g., not less than 1×1018/cm3 and not more than 5×1019cm3. The implantation depth is not less than 30 nm. After implantation, the surface of the implanted region is etched about 10 nm by hydrofluoric acid. Sulfuric acid, nitric acid or hydrochloric acid may be used for the etching. After that, implantation damage is repaired by performing annealing treatment in a nitrogen atmosphere at not less than 800° C. for not less than 30 minutes. In case of performing the annealing treatment in an oxygen atmosphere, treatment temperature is not less than 800° C. and not more than 950° C. and treatment time is not less than 30 minutes.
It should be noted that the method of forming the contact regions 14 and 15 is not limited to ion implantation and thermal diffusion process may be used. In this case, after metal such as Sn is brought into contact with the n-type α-(AlxGa1-x)2O3 single crystal film 3 in a region for the contact regions 14 and 15 to be formed, heat treatment is performed to diffuse a dopant such as Sn into the n-type α-(AlxGa1-x)2O3 single crystal film 3.
After that, the gate insulating film 16, the gate electrode 11, the source electrode 12 and the drain electrode 13 are formed.
The Ga2O3-based MISFET 20 functions as a normally-off transistor. When voltage of more than the threshold is applied to the gate electrode 21, a channel is formed in a region of the undoped α-(AlxGa1-x)2O3 single crystal film 4 under the gate electrode 21 and a current thus flows from the source electrode 22 to the drain electrode 23.
The gate electrode 21, the source electrode 22, the drain electrode 23 and the gate insulating film 26 are respectively formed of the same materials as the gate electrode 11, the source electrode 12, the drain electrode 13 and the gate insulating film 16 in the first embodiment.
The undoped α-(AlxGa1-x)2O3 single crystal film 4 is a high-resistance α-(AlxGa1-x)2O3 (0≦x<1) single crystal film which does not include a dopant. Although there may be a case where conductivity thereof is low due to crystal defects, etc., electric resistance thereof is sufficiently high and a current never flows from the source electrode 22 to the drain electrode 23 unless voltage is applied to the gate electrode 21. The thickness of the undoped α-(AlxGa1-x)2O3 single crystal film 4 is, e.g., 0.01 to 10 μm.
The method of forming the undoped α-(AlxGa1-x)2O3 single crystal film 4 is, e.g., based on the method of forming the n-type α-(AlxGa1-x)2O3 single crystal film 3 in the first embodiment where the process of implanting the n-type dopant is eliminated.
The contact regions 24 and 25 are regions having a high n-type dopant concentration formed in the undoped α-(AlxGa1-x)2O3 single crystal film 4 and are respectively connected to the source electrode 22 and the drain electrode 23. The contact regions 24 and 25 include the n-type dopant at a concentration of, e.g., not less than 1×1018/cm3 and not more than 5×1019cm3.
The third embodiment is different from the second embodiment in that a p-type α-(AlxGa1-x)2O3 single crystal film is formed instead of the undoped α-(AlxGa1-x)2O3 single crystal film 4. The explanations for the same features as the first embodiment will be omitted or simplified.
The Ga2O3-based MISFET 30 functions as a normally-off transistor. When voltage of more than the threshold is applied to the gate electrode 21, a channel is formed in a region of the p-type α-(AlxGa1-x)2O3 single crystal film 5 under the gate electrode 21 and a current thus flows from the source electrode 22 to the drain electrode 23.
The p-type α-(AlxGa1-x)2O3 single crystal film 5 is an α-(AlxGa1-x)2O3 (0≦x<1) single crystal film which includes a p-type dopant such as Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N or P. The p-type α-(AlxGa1-x)2O3 single crystal film 5 includes the p-type dopant at a concentration of, e.g., not less than 1×1015/cm3 and not more than 1×1019cm3. In addition, the thickness of the p-type α-(AlxGa1-x)2O3 single crystal film 5 is, e.g., 0.01 to 10 μm.
The method of forming the p-type α-(AlxGa1-x)2O3 single crystal film 5 is, e.g., based on the method of forming the n-type α-(AlxGa1-x)2O3 single crystal film 3 in the first embodiment where the process of implanting the n-type dopant is replaced with a process of implanting the p-type dopant.
The contact regions 34 and 35 are regions having a high n-type dopant concentration formed in the p-type α-(AlxGa1-x)2O3 single crystal film 5 and are respectively connected to the source electrode 22 and the drain electrode 23. The contact regions 34 and 35 include the n-type dopant at a concentration of, e.g., not less than 1×1018/cm3 and not more than 5×1019cm3.
According to the present embodiment, it is possible to form high-quality α-(AlxGa1-x)2O3 single crystal films by homoepitaxial growth and use of such α-(AlxGa1-x)2O3 single crystal films allows high-quality Ga2O3-based semiconductor elements to be formed. In addition, these Ga2O3-based semiconductor elements have excellent performance since a high-quality α-(AlxGa1-x)2O3 single crystal film is used as a channel layer.
It should be noted that the invention is not intended to be limited to the above-mentioned embodiments, and the various kinds of modifications can be implemented without departing from the gist of the invention. For example, the Ga2O3-based semiconductor element has been described as the n-type semiconductor element in the embodiments but may be a p-type semiconductor element. In this case, the conductivity type (n-type or p-type) of each member is all inverted. In addition, constituent elements of the above-mentioned embodiments can be arbitrarily combined without departing from the gist of the invention.
Although the embodiments of the invention have been described above, the invention according to claims is not to be limited to the above-mentioned embodiments. Further, it should be noted that all combinations of the features described in the embodiments are not necessary to solve the problem of the invention.
A high-quality Ga2O3-based semiconductor element is provided.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-196437 | Sep 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/072899 | 9/7/2012 | WO | 00 | 3/7/2014 |
