Apparatus and method for forming single crystalline nitride substrate using hydride vapor phase epitaxy and laser beam

The present invention relates to an apparatus and a method for forming a single crystalline nitride substrate, and more particularly, to an apparatus and a method for preventing cracks from being generated in a single crystalline nitride substrate. A method for forming a compound semiconductor substrate includes the steps of: a) preparing a parent substrate; b) forming a single crystalline film on the parent substrate in a reacting chamber; c) maintaining the single crystalline film in a predetermined temperature which is higher than a room temperature; and d) illuminating laser beam on a backside of the parent substrate and separating the single crystalline film from the parent substrate. Accordingly, the present invention provides a large single crystalline nitride substrate, by preventing cracks caused by the lattice mismatch with the parent substrate.

TECHNICAL FIELD

The present invention relates to an apparatus and a method for making a single crystalline nitride substrate; and, more particularly, to an apparatus and a method for preventing cracks from being generated in a single crystalline nitride substrate.

BACKGROUND ART

A GaN single crystalline substrate, as an example of a single crystalline nitride substrate, will be described. Generally, the GaN materials has a melting point more than of 2400 and the dissociation pressure of nitride in the GaN materials is about ten thousand atmospheres. Accordingly, this high melting point and high dissociation pressure make it impossible to create a large single crystalline GaN bulk using typical growing methods of the semiconductor crystals. A needle-shaped crystal growing method, in which a gallium gas directly reacts on an ammonia gas at a high temperature of about 1000 C. to 1150 C., and a plate-shaped crystal growing method, in which nitrogen is dissolved in liquid gallium at a high temperature of about 1500 C. to 1600 C. and at a high nitrogen pressure corresponding to about 20000 atmospheres has been used to create a single crystalline GaN bulk (hereinafter, referred to as a GaN bulk).

However, these crystal growth methods have made a small-sized GaN bulk which has only a few millimeters in size and about 100 m in thickness. Accordingly, it is impossible to achieve a commercial success in using the GaN bulk.

To solve the above problem, a hydride vapor phase epitaxy has been used to create the GaN bulk at a growing rate of 100 m/hour. That is, after forming a thick GaN film on a parent substrate, such as sapphire or SiC substrate, the parent substrate is removed and then the GaN bulk is finally formed.

The removal of the parent substrate is carried out by the mechanical polishing method or laser beam. In particular to laser, as shown in FIG. 1 , after forming the thick GaN film on the parent substrate at a high temperature of about 1000 C. to 1100 C., the thick GaN film on the parent substrate is cooled down to a room temperature. After increasing the temperature of the parent substrate up to about 600 C., the thick GaN film is separated from the parent substrate using laser beam in an additional apparatus different from the hydride vapor phase epitaxy ( Large free-standing GaN substrate by hydride vapor phase epitaxy and laser induced lift-off, by K. Kelly et al, Jpn. J. Appl. Phys. Vol. 38, No. 3A (pt 2), 1999).

In the above-mentioned hydride vapor phase epitaxy, since the thick GaN film is formed on the sapphire substrate at a high temperature and it is cooled down to the room temperature, cracks are generated by the lattice mismatch and thermal expansion coefficients between the GaN film and the sapphire substrate. Because of these cracks, the GaN bulk is restricted within a small-sized substrate and electric characteristics therein are also deteriorated.

DISCLOSURE OF INVENTION

It is, therefore, an object of the present invention to provide an apparatus and a method for preventing cracks from being generated in a single crystalline nitride substrate which is made by a hydride vapor phase epitaxy method.

Another object of the present invention is to provide an apparatus and a method for forming a large single crystalline nitride substrate on a commercial basis.

In accordance with an aspect of the present invention, there is provided an apparatus for forming a compound semiconductor substrate, the apparatus comprising: a reacting chamber for forming a single crystalline film on a parent substrate; a heating chamber connected to the reacting chamber within a processing channel, wherein the single crystalline film is separated from the parent substrate at a higher temperature than a room temperature; and a supporter for supporting the single crystalline film and the parent substrate and maintaining the single crystalline film in a predetermined temperature.

In accordance with another aspect of the present invention, there is provided a method for forming a compound semiconductor substrate, the method comprising the steps of: a) preparing a parent substrate; b) forming a single crystalline film on the parent substrate in a reacting chamber; c) maintaining the single crystalline film in a predetermined temperature which is higher than a room temperature; and d) illuminating laser beam on a backside of the parent substrate and separating the single crystalline film from the parent substrate.

According to the present invention, a thick GaN film is formed on a parent substrate, such as sapphire (Al 2 0 3 ), spinel (MgAl 2 O 4 ) or silicon carbide (SiC), which has the lattice mismatch with the single crystalline GaN film and a different thermal expansion coefficient, and the parent substrate is heated up to a range of 600 C. to 1000 C. In this temperature range, the single crystalline GaN film is separated from the parent substrate by laser beam.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 3 , a horizontal type hydride vapor phase epitaxy apparatus of an atmospheric pressure is shown in order to form a single crystalline nitride substrate. The hydride vapor phase epitaxy apparatus includes a reacting chamber 11 A in which a quartz boat (not shown), is placed, a heating chamber 11 C having a supporter 40 to maintain a specimen, and an exhausting chamber 11 B positioned between the reacting chamber 11 A and the heating chamber 11 C and coupled to an exhausting system 16 . The temperature of the supporter 40 in the heating chamber 11 C is maintained in a specific temperature range and laser beam illumination to separate a single crystalline nitride film from a parent substrate 30 is carried out in the heating chamber 11 C. Further, each of the chambers 11 A to 11 C adjacent to the exhausting chamber 11 B is sealed up with shutters 12 and flanges 12 A are mounted on both ends of the chambers 11 A and 11 C. Conventional mechanisms may be used to position and move specimens and quartz boats in the chambers.

The reacting chamber 11 A is surrounded by a multi-step electric furnace 13 and is connected to a first inlet 14 to supply an ammonia gas and a second inlet 15 to supply hydrochloric acid and nitrogen gases. These gases react on Ga materials 20 within the reacting chamber 11 A and then a thick GaN film is deposited on the parent substrate 30 adjacent to the Ga materials 20 . While the thick GaN film is grown in the reacting chamber 11 A, the reacting gases are purged away through the exhausting system 16 in the exhausting chamber 11 B and when the growth of the single crystalline nitride substrate (the think GaN film) has been finished, the reacting chamber 11 A is isolated from the exhausting chamber 11 B by the shatter 12 . The parent substrate 30 on which the thick GaN film is formed is removed onto the supporter 40 in the heating chamber 11 C without being exposing to air and laser beam is illuminated on the backside of the parent substrate 30 at a temperature of about 600 C. to 1000 C. to separate a single crystalline GaN film (think GaN film) from the parent substrate 30 . It should be noted that the thick GaN film and the parent substrate 30 are not cooled down to a room temperature.

Although the exhausting chamber 11 B, as shown in FIG. 3 , is positioned between the reacting chamber 11 A and the heating chamber 11 C, the reacting chamber 11 A may be adjacent to the heating chamber 11 C and the exhausting system 16 may be directly connected to the reacting chamber 11 A.

The hydride vapor phase epitaxy apparatus shown in FIG. 3 may be used to form group III-N (nitrogen) compounds of single crystalline substrates, such as AlN, InN, GaInN, AlInN and AlGaInN, as well as the GaN single crystalline substrate, containers having Ga and In materials may be provided in the reacting chamber 11 A and the hydrochloric acid and nitrogen gases flow into the reacting chamber 11 A. FIGS. 4A to 4 D illustrate a method for forming the GaN single crystalline substrate.

First, referring to FIG. 4A , the parent substrate 30 selected from one of an oxide substrate, such as sapphire (Al 2 0 3 ) or spinel (MgAl 2 O 4 ), and a silicon carbide substrate, such as SiC, is prepared and generally these parent substrates may have the lattice mismatch with the GaN materials and a different thermal expansion coefficient.

Next, referring to FIG. 4B , the thick GaN film 31 is formed on the parent substrate 30 in the hydride vapor phase epitaxy apparatus, as shown in FIG. 3 , having the quartz boat in its reacting chamber 11 A and the supporter 40 in its heating chamber 11 C. The group III elements such as Ga are positioned at a region which is maintained at a temperature of about 600 C. to 900 C. by the multi-step electric furnace 13 . At this time, the parent substrate is maintained at a temperature of about 1000 C. to 1100 C. The reacting chamber 11 A in which the quartz boat is placed is pumped out up to about 10-3 torr, the reacting chamber 11 A is gradually heated, and then the nitrogen gas injection into the reacting chamber 11 A starts from about 600 C. When the reacting chamber 11 A reaches to a temperature at which the thick GaN film is to be grown, the hydrochloric acid gas flows onto the Ga materials in the quartz boat and the ammonia gas is provided to the parent substrate 30 to form the thick GaN film 31 on the parent substrate 30 at a thickness of about 100 m to 550 m.

After forming the thick GaN film 31 on the parent substrate 30 , the supply of the hydrochloric acid gas is broken off and the parent substrate 30 on which the thick GaN film 31 is formed is cooled with the supply of nitrogen and the ammonia gases until the temperature of the thick GaN film 31 reaches to a predetermined temperature range, e.g., about 600 C. to 1000 C.

Referring to FIG. 4C , when the temperature of the reacting chamber 11 A reaches to 600 C. to 1000 C., the parent substrate 30 on which the thick GaN film 31 is formed is moved into the supporter 40 in the heating chamber 11 C. At this time, the temperature of supporter 40 is maintained at about 600 C. to 1000 C. and the bottom of the parent substrate 30 is turned over top so that the thick GaN film 31 is directly on the supporter 40 . The turned upside of the parent substrate 30 is illuminated by laser beam ( 50 ). It should be noted that the thick GaN film 331 and the parent substrate 30 are not cooled down to a room temperature.

Referring to FIG. 4D , the parent substrate 30 is separated from the thick GaN film 31 by the high power laser beam. Nd:YAG laser beam, which has wavelength of 355 nm, power of about 500 mJ, pulse period of 10 to 20 Hz and pulse width of 5 to 6 ns, may be used. When this high power laser beam is illuminated on the parent substrate 30 , the beam passes through the parent substrate 30 and is absorbed into the thick GaN film 31 . If the thick GaN film 31 absorbs the high power laser beam, the GaN material, which is in a range of a few micrometers in thickness (dissolution area 32 ), are dissolved into gallium and nitrogen and the thick GaN film 31 is separated from the parent substrate 30 by this dissolution of the thick GaN film 31 .

Since the single crystalline GaN substrate (the separated thick GaN film 31 A has an uneven surface, the mechanical and chemical polishing using a diamond slurry is applied to the single crystalline GaN substrate 31 A.

As apparent from the above, the present invention provides a high growing rate of the single crystalline nitride substrate without cracks caused by the lattice mismatch between other materials, by using the hydride vapor phase epitaxy method. Furthermore, the present invention provides stability and reliability of processing by effectively separating the single crystalline nitride substrate from the parent substrate by laser beam.