JP2007173744A - Method of manufacturing n-type aluminum-nitride and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain n-type aluminum-nitride through ion implantation. <P>SOLUTION: Silicon ions (Si<SP>+</SP>) are implanted on a front surface of an aluminum-nitride layer with acceleration energy of 90keV and dosage of 5×10<SP>15</SP>cm<SP>-2</SP>. Thermal treatment is performed for 10 min at 1400°C under N<SB>2</SB>atmosphere of 10 Torr. The silicon is approximately uniformly implanted from the front surface of an AlN layer to the depth of 0.2μm. At a measured temperature 50°C, an electron density is calculated as 2.0×10<SP>15</SP>, at a measured temperature 300°C, the electron density is calculated as 3.0×10<SP>16</SP>cm<SP>-3</SP>and at a measured temperature 300°C, the electron density is calculated as 2.8×10<SP>17</SP>cm<SP>-3</SP>. Furthermore, it is concluded that the donor level of silicon in the aluminum-nitride (AlN) is 311meV. Thus, the present invention enables n-type aluminum-nitride (AlN) to be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing n-type aluminum nitride, which is a group III nitride compound semiconductor.

  For group III nitride compound semiconductors, various field effect transistors such as HEMTs and other functional elements have been developed, including light emitting elements such as LEDs and LDs. Here, in order to form a p-type layer and an n-type layer, when a semiconductor layer is formed by metal organic chemical vapor deposition (hereinafter referred to as MOCVD), an acceptor and a donor are supplied together with a base material compound. The method is used.

  An LED or LD can be formed with a structure in which semiconductor layers are simply stacked by MOCVD, and supply of donors and acceptors is relatively easy. However, elements such as transistors cannot be formed by simple lamination of semiconductor layers, and it is necessary to form p-type regions and n-type regions at different depths depending on the location. At this time, if MOCVD is performed for each region using, for example, a mask, the epitaxial layer formed in the vicinity of the boundary with the mask becomes thick, which becomes an obstacle in the subsequent element formation process.

As techniques for forming an n-type layer, the following Non-Patent Documents 1 and 2 report Si ion implantation into GaN, and Non-Patent Document 3 reports Si ion implantation into Al _0.13 Ga _0.87 N. A technique for forming a HEMT or other elements by forming a low resistance n-type layer by ion implantation in a part of the i layer or the high resistance layer is also known.
JC Zolper, HH Tan, JS Williams, J. Zou, DJH Cockayne, SJ Pearton, M. Hagerott Crawford, and RF Karlicek, Jr., "Electrical and structual analysis of high-dose Si implantation in GaN," Appl. Phys. Lett., 70 (1997) pp. 2729-2731 XACao, CR Abernathy, RK Singh, SJ Pearton, M. Fu, V. Sarvepalli, JA Sekhar, JC Zolper, DJ Rieger, J. Han, TJ Drummond, RJ Shul, and RG Wilson, "Ultrahigh Si + implant activation efficiency inGaN using a high-temperature rapid thermal process system, "Appl. Phys. Lett., 73 (1998) pp. 229-231 Y. Irokawa, O. Fujishima, T. Kachi. SJ Pearton, and F. Ren, "Activation characteristics of ion-implanted Si + in AlGaN," Appl. Phys. Lett., 86 (2005) 192102 (downloaded document)

  Aluminum nitride (AlN) has a high band gap of 6.1 eV and is expected to have a breakdown electric field larger than that of other semiconductors. In comparison, 4H-SiC has a band gap of 3.26 eV and GaN has 3.39 eV. However, it has not been reported yet that n-type aluminum nitride (AlN) can be obtained by Si ion implantation into aluminum nitride (AlN) containing no Ga, and it is considered that it is impossible with the current technology.

  In order to overcome the above-described present situation, the present inventors have studied and found that n-type aluminum nitride can be produced under the following conditions.

The invention according to claim 1 is an ion implantation step of implanting silicon (Si) into aluminum nitride (AlN) at a dose of 10 ¹⁵ / cm ⁻² or more and 10 ¹⁷ / cm ⁻² or less, and after the ion implantation step. And an annealing step of annealing at a temperature exceeding 1300 ° C. and less than 1500 ° C. for 5 minutes to 2 hours, and a method for producing n-type aluminum nitride.

Further, the invention according to claim 2 has an n-type region formed on a part of the surface of aluminum nitride and having a measurement temperature at which the electron concentration is 3 × 10 ¹⁶ / cm ⁻³ or more is 150 ° C. or less. It is a semiconductor element characterized by this.

Si ion implantation into aluminum nitride (AlN) is carried out with a large dose, and subsequent high-temperature and long-time annealing can result in an electron concentration of 3 × 10 ¹⁶ / cm ⁻³ or more at a measurement temperature of 150 ° C. or less. It was found. The implanted Si is considered to be activated by high-temperature annealing to replace Al. At this time, it was also found that the donor level was 311 meV. According to the present invention, Si ions can be implanted into aluminum nitride (AlN) by selecting a region, and can be applied to various element configurations. In addition, when annealing gallium nitride (GaN) or aluminum gallium nitride (AlGaN) at 1000 ° C. or higher, it is necessary to cover it with an insulating film or the like to protect it from decomposition. Activation is possible without forming a film. Note that activation after coating with an insulating film is not excluded.

  The manufacturing method of aluminum nitride to which the present invention is applied is arbitrary as long as it is a single crystal. In order to obtain a single crystal with extremely good crystallinity, MOCVD is preferably used on a different substrate such as sapphire via a buffer layer. In addition, single crystal aluminum nitride can be formed by any method. In addition, the aluminum nitride which should apply this invention assumes what does not contain other elements substantially. Here, “substantially not containing other elements” means that other elemental compounds are not intentionally supplied in the manufacturing process, and dope that cannot be avoided due to contamination in the manufacturing process. It is not excluded. For example, it does not exclude those containing trace amounts of other elements.

  As an ion implantation apparatus for silicon ions, a public apparatus capable of achieving the dose of the present invention can be used. In addition, it is desirable that the annealing be performed in an inert gas such as nitrogen under reduced pressure.

A single crystal aluminum nitride (AlN) layer having a thickness of 1 μm was formed on the sapphire substrate by MOCVD through a buffer layer. Next, silicon ions (Si ⁺ ) were implanted into the surface of the single crystal aluminum nitride (AlN) layer at an acceleration energy of 90 keV and a dose of 5 × 10 ¹⁵ cm ⁻² . This was decompressed and heat-treated at 1400 ° C. for 10 minutes in an N ₂ atmosphere of 10 Torr. It was confirmed by SIMS measurement that silicon was implanted over a depth of 0.2 μm from the surface of the single crystal aluminum nitride (AlN) layer.

The thus formed aluminum injection layer of aluminum nitride (AlN) is subjected to hole measurement, and the resulting sheet carrier concentration (unit cm ⁻² ) and the injection layer thickness of 0.2 μm give the electron concentration (unit cm). ^-3 ) was calculated. In addition, since it was less than the measurement limit at room temperature (˜25 ° C.), the sample was kept warm at intervals of 25 ° C. in the range of 50 ° C. to 300 ° C., and hall measurement was performed. The result is shown in FIG. In FIG. 1, the horizontal axis is an inverse of absolute temperature T (unit K), and an Arrhenius plot is used. The electron concentration is 2.0 × 10 ¹⁵ cm ^{−3 at} a measurement temperature of 50 ° C., the electron concentration is 3.0 × 10 ¹⁶ cm ^{−3 at} a measurement temperature of 150 ° C., and the electron concentration is 2.8 × 10 ^{17 at} a measurement temperature of 300 ° C. Calculated as cm ^-3 . It was also concluded that the silicon donor level in aluminum nitride (AlN) was 311 meV. Thus, n-type aluminum nitride (AlN) could be obtained according to the present invention.

Next, the dose of silicon ions (Si ⁺ ) implanted into the surface of the single crystal aluminum nitride (AlN) layer is changed in the range of 1 × 10 ¹⁴ to 1 × 10 ¹⁶ cm ⁻² , and the same as in Example 1. The electron concentration at the measurement temperature of 150 ° C. of n-type aluminum nitride (AlN) obtained by annealing was calculated. The result is shown in FIG. When the dose was 1 × 10 ¹⁵ cm ⁻² or less, the electron concentration was 0, that is, below the detection limit of hole measurement. Hole measurement was possible when the dose was 5 × 10 ¹⁵ cm ⁻² or more.

Next, the electron concentration of n-type aluminum nitride (AlN) at a measurement temperature of 150 ° C. when the annealing temperature was changed was calculated. The conditions were the same as in Example 1 except for the annealing temperature. The result is shown in FIG. When the annealing temperature was 1300 ° C. or lower and 1500 ° C. or higher, it was below the detection limit of hole measurement. When the annealing temperature is 1400 ° C., the electron concentration at 150 ° C. is 3.0 × 10 ¹⁶ cm ⁻³ , and when the annealing temperature is 1450 ° C., the electron concentration at 150 ° C. is 8.8 × 10 ¹⁵ cm ⁻³ . there were.

  The n-type aluminum nitride (AlN) of the present invention can be used for a source such as a MOSFET, a drain region, or a Schottky diode. In either case, since n-type aluminum nitride (AlN) is used, it is possible to increase the breakdown voltage with a smaller size than when using gallium nitride (GaN), which is higher than conventional silicon power devices. Low loss can be expected.

FIG. A is a cross-sectional view showing the structure of the MOSFET 100. FIG. In the MOSFET 100, two portions of the surface of the intrinsic aluminum nitride substrate 10 are formed as an n-type aluminum nitride region (n-AlN) by silicon ion implantation of the present invention, one as a source region S and the other as a drain region D. Further, a region sandwiched between them is referred to as a channel region C. A gate insulating film I made of SiO ₂ is formed so as to partially cover the upper part of the channel region C and the source region S and drain region D, and a gate electrode G made of metal is formed thereon.

  FIG. B is a cross-sectional view showing the structure of the Schottky diode 200. FIG. In the Schottky diode 200, an n-type aluminum nitride region (n-AlN) 25 is formed on one surface of the intrinsic aluminum nitride substrate 20 by silicon ion implantation of the present invention. In this region, the ohmic electrode 31 and the Schottky electrode 32 are formed.

FIG. 3 is a graph showing the relationship between the hole measurement temperature T (absolute temperature, the horizontal axis is 1 / T) and the electron concentration in the aluminum injection layer of AlN obtained in Example 1. The graph which shows the relationship between the dose of silicon ion (Si ^<+> ) inject | pouring, and electron concentration. The graph which shows the relationship between annealing temperature and electron concentration. 4). 3A is a cross-sectional view showing the structure of a MOSFET 100 according to the present invention. B is a sectional view showing the structure of a Schottky diode 200 according to the present invention.

Explanation of symbols

10, 20: Intrinsic aluminum nitride substrate (i-AlN)
25: n-type aluminum nitride region (n-AlN)
31: Ohmic electrode 32: Schottky electrode

Claims (2)

An ion implantation step of implanting silicon (Si) into aluminum nitride (AlN) at a dose of 10 ¹⁵ / cm ^{−2 to} 10 ¹⁷ / cm ⁻² ;
A method for producing n-type aluminum nitride, comprising: an annealing step after the ion implantation step and annealing at a temperature exceeding 1300 ° C. and less than 1500 ° C. for 5 minutes to 2 hours. A semiconductor element having an n-type region formed at a part of the surface of aluminum nitride and having a measurement temperature of 150 ° C. or less at which an electron concentration is 3 × 10 ¹⁶ / cm ⁻³ or more.

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