Patent Application
20070254445
The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
According to an exemplary embodiment of the present invention, a group III metal source may be an alloy added with a small amount of desired impurities. A metal source for forming an n type nitride film may be an alloy of a group III metal and one of a group IV element and group VI element as impurities. For example, to form an n type GaN doped with Te, a Ga source added with a small amount of Te is used for a metal source. In this case, an amount of one of the group IV element and the group VI element may be controlled according to doping concentration.
Though sapphire is mainly used for the substrate, the substrate may be formed of a material of one of SiC, Si, MgAl2O4, MgO, LiAlO2, and LiGaO2.
In operation S22, the reaction chamber in which the at least one group III metal source including the impurities and the substrate are disposed is heated at a temperature required for reaction. Generally, the group III metal source is heated at a temperature of approximately 700 to 900° C. for a reaction of generating a chloride and the substrate is heated at a temperature of approximately 900 to 1090° C. for a reaction for nitride growth.
In operation S23, hydrogen chloride gas and a carrier gas are supplied to the group III metal source. The hydrogen chloride gas reacts with the group III metal source and a group III metal chloride is formed. In this case, the impurities included in the metal source forms a certain chloride via a reaction according to the kind of the impurities.
For example, in the case of group IV impurities such as Si, Si may be substituted for a portion of Ga, namely, a metal chloride may be formed as (Ga, Si)Cl. However, in the case of group VI impurities, a process of a reaction has been not clearly defined. Only, the present inventor may estimate the process of the reaction as two types. For example, Ga source added with Te may be provided in the form of (Ga, Te)Cl, similar to the case of Si, and may form a chloride of TeCln in addition to GaCl.
Also, the carrier gas transferring the chloride generated together with the hydrogen chloride gas to the substrate is supplied. An inactive gas such as nitrogen gas and argon gas may be used for the carrier gas.
In operation S24, a nitride film doped with the impurities is formed on the substrate by reacting a nitrogen source gas with the transferred metal chloride. NH3 gas may be used for the nitrogen source gas. A desired nitride film is grown on the substrate by reacting NH3 gas with the transferred metal chloride at a high temperature. In the process of growth of the nitride film, the chloride including impurities may be uniformly added into the nitride film by reacting with NH3 gas.
The embodiment of the present invention may be used as an alloy made by adding desired impurities into a metal source used in an HVPE process. Impurities capable of being used are not limited to a certain conductive type. Particularly, the embodiment of the present invention may be very effect when growing a nitride doped with group VI element impurities such as Te. Namely, according to an exemplary embodiment of the present invention, different from a conventional ion implantation process, the nitride film may be formed without deterioration of crystal and high temperature heat treatment for activation and uniform doping concentration may be distributed in an entire thickness. In addition, a problem of residue due to a DETe source, caused in a conventional process of forming a nitride film by using a MOCVD method, may be solved.
The embodiment of the present invention may be very effectively applied when using a group VI element metal as impurities for forming an n type nitride film. For example, at least one of Se and Te may be used for the group VI element metal impurities. However, the present invention is not limited to the group VI element metal impurities and other n type impurities such as a group IV element metal may be used. For example, the group IV element metal impurities may be at least one of Si, Ge, Sn, and Pb.
As described above, a metal chloride for growing a nitride film 37 may be generated and the metal chloride may be transferred to the substrate 34 by supplying hydrogen chloride gas and an inactive carrier gas such as N2 and Ar to the group III metal source 33 in the external reaction chamber 31a via a first pipeline 35a. In this case, the metal chloride includes chlorides including various forms of impurities in addition to the group III metal chloride. On the other hand, the nitride film 37 doped with impurities is formed on the substrate 35 by reacting the metal chloride transferred to the substrate 35 in the internal reaction chamber 31b with a nitride source gas such as NH3.
In this case, though the HVPE apparatus has a form including a horizontal path of a reaction chamber and gas, as obvious to those skilled in the art, a HVPE apparatus having a form including a vertical path may be used.
The metal source 33 including impurities may be embodied in various forms. According to an embodiment of the present invention, a group III single metal source including impurities may be used. For example, the group III metal source may be a Ga source including Te. Also, in this case, an n type GaN doped with Te may be grown on the substrate 34. When forming one of a group III compound semiconductor and a group IV compound semiconductor such as AlGaN and AlGaInP, another group III metal source such as In may be further disposed in addition to the group III single metal source doped with impurities.
On the other hand, the group III metal source may be an alloy source formed of a plurality of types of group III metals including the impurity metal. For example, the group III metal source may be an Al—Ga alloy source including Te. In this case, an n type AlGaN doped with Te may be grown on the substrate 34. In the present embodiment, a nitride satisfying a desired composition formula may be acquired by controlling a atomic fraction of Al and Ga in the alloy, without flow control with respect to two or more metal sources.
In the method of forming a nitride film according to an exemplary embodiment of the present invention, impurities difficult to be doped may be easily doped to the nitride film, without deterioration of crystal and additional heat treatment. Particularly, doping concentration of the nitride film may be controlled to be relatively accurate by controlling an amount of impurities included in a metal source.
Hereinafter, effects of the present invention will be described in detail referring to an exemplary embodiment of the present invention.
An alloy source of the present example was formed of Al and Ga, including a small amount of desired Te by fusing Al and Te into Ga metal and saturated at a temperature of 900° C. In the present example, seven alloy sources whose atomic fractions were 0.003, 0.008, 0.012, 0.016, 0.018, 0.035, and 0.043, respectively, under a condition of maintaining a ratio of an amount of Al to a total amount of Al and Ga as 16% were used.
A sapphire substrate on which an undoped GaN had been formed was cleaned by using an ultrasonic cleaner using solutions of acetone and methanol and etched in a solution of hafnium for one minute to remove an oxide film. The sapphire substrate and the alloy source were disposed in a reaction chamber, respectively.
The reaction chamber was heated to a 1090° C. that was a crystal growth temperature, 20 sccm of HCl and 500 sccm of ammonia were supplied to the reaction chamber, and Al0.16Ga0.84N doped with Te was grown for approximately 40 minutes. Under the same condition, additional six Al0.16Ga0.84N doped with Te were formed by using six alloy sources having other atomic fractions of Te.
As described above, a nitride film having excellent conductivity may be grown by using the metal source doped with impurities according to the example of the present invention. Also, a nitride film having excellent n type characteristics may be acquired when atomic fraction of Te was 0.01 or more.
In addition, in a similar experiment with respect to Si, doping concentration was 2×1016 to 3×1017/cm3 when atomic fraction of Si was changed from 0.102 to 0.218 g/mol.
Since the method of forming a nitride film according to the example of the present invention employs the HVPE process, the nitride doped with impurities whose thickness is difficult to be acquired from one of MOCVD and MBE processes may be formed. Particularly, an n type nitride substrate available for a free standing substrate may be formed by using the method. Also, though a thick nitride film is formed by using the HVPE process, different from conventional methods of doping impurities via ion implantation and heat treatment, a nitride film in which impurities of a certain conductive type are uniformly distributed in the direction of thickness may be formed.
Accordingly, according to another aspect of the present invention, there is provided a group III nitride structure having a thickness of more than 5 μm, in which concentration of certain conductive type impurities is uniform lengthwise and 1016 to 1020/cm3. The group III nitride structure may be a nitride film having a thickness more than 50 μm to be used for a substrate.
As described above, according to an exemplary embodiment of the present invention, an n type nitride substrate doped with Te, whose doping process is difficult, may be formed and may have high conductivity. The nitride structure according to an exemplary embodiment of the present invention may have electrical conductivity of at least 4×102 (Ω cm)−1. The electrical conductivity may be acquired by doping Te to have concentration of 2×102 to 1020/cm3.
As described above, according to an exemplary embodiment of the present invention, there is provided a method of forming a nitride film not limited to characteristics of elements of impurities and acquiring improved carrier density and electrical conductivity by adding a small amount of elements of impurities required to give a conductive type to one of a group III metal source or an alloy source used in an HVPE process.
According to an exemplary embodiment of the present invention, additional heat treatment is not required, a residue is not generated, and a growth process is performed together with the method, thereby largely improving process efficiency. Particularly, since the HVPE process advantageous for a thick film process is employed, a thick film such as an n type conductive nitride substrate having doping concentration uniform in the direction of a thickness and excellent conductivity may be formed.
While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-38260 | Apr 2006 | KR | national |
