GALLIUM OXIDE SUBSTRATE DIVISION METHOD

To divide a β-type gallium oxide substrate having a (001) plane as a main surface satisfactorily. A method of diving a gallium oxide substrate includes: a step of forming a plurality of dividing grooves along the extending direction of the (100) plane of a β-type gallium oxide substrate having the (001) plane as the main surface; a step of processing the β-type gallium oxide substrate into strips by cutting the substrate in a direction perpendicular to the extending direction of the dividing grooves; and a step of cleaving the strip-shaped β-type gallium oxide substrates 10 along the dividing grooves for singulation. Since the plurality of dividing grooves are thus formed along the cleavage planes, the substrate can be divided satisfactorily without causing flaky peeling on the cleavage surfaces by cleaving the substrate along the dividing grooves.

TECHNICAL FIELD

The present invention relates to a method of dividing a gallium oxide substrate and, more particularly, to a method of dividing a β-type gallium oxide substrate.

BACKGROUND ART

The methods described in Patent Documents 1 and 2 are known as methods of dividing a compound semiconductor. The method disclosed in Patent Document 1 includes forming a scratch having a length of 150 μm to 200 μm on the main surface of a substrate using a scriber, then processing the substrate into strips by dicing, and subsequently cleaving the strip-shaped substrates along the scratches for singulation. The method disclosed in Patent Document 2 includes forming cut grooves and scribe lines on both sides of a substrate and cleaving the substrate along the cut grooves and scribe lines for singulation.

CITATION LIST

Patent Document

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

However, since the (100) plane of a β-type gallium oxide substrate is highly cleaved, the method described in Patent Document 1 has the problem that flaky delamination occurs on a cleavage surface in the areas where no scratches are formed. In addition, in the β-type gallium oxide substrate having the (001) plane as the main surface, the (100) plane, which is a cleavage surface, is not perpendicular to the main surface but has a predetermined inclination, so that the method described in Patent Document 2 cannot cleave the β-type gallium oxide substrate correctly.

A method of simply dicing the β-type gallium oxide substrate into a matrix may also be considered; however, as described above, the (100) plane, which is the cleavage surface, is not perpendicular to the main surface, so that when dicing is performed along the extending direction of the cleavage surface, chipping occurs due to partial cleavage.

It is therefore an object of the present invention to provide a method of satisfactorily dividing a β-type gallium oxide substrate having a (001) plane as a main surface.

Means for Solving the Problem

A method of dividing a β-type gallium oxide substrate according to the present invention includes; a step of forming a plurality of first dividing grooves along the extending direction of the (100) plane of a β-type gallium oxide substrate having a (001) plane as a main surface: a step of processing the β-type gallium oxide substrate into strips by cutting the β-type gallium oxide substrate in a direction perpendicular to the extending direction of the first dividing grooves; and a step of cleaving the strip-shaped β-type gallium oxide substrates along the first dividing grooves for singulation.

According to the present invention, since the plurality of first dividing grooves are thus formed along the cleavage planes, the substrate can be divided satisfactorily without causing flaky peeling on the cleavage surfaces by cleaving the substrate along the first dividing grooves.

In the present invention, the first dividing grooves may be formed by etching. This prevents the substrate from being cracked or chipped at the time of forming the first dividing grooves.

In the present invention, the first dividing grooves may be formed on the back surface located on the side opposite to an element forming surface. This eliminates the need to process the element forming surface.

Further, the method for dividing a β-type gallium oxide substrate according to the present invention may further include a step of forming a plurality of second dividing grooves in the element forming surface along the extending direction of the (100) plane, and a straight line connecting the first and second dividing grooves may have an angle of about 76° with respect to the element forming surface. Thus, since the first and second dividing grooves are positioned on the same cleavage surface, singulation by cleavage can be performed more reliably.

Advantageous Effects of the Invention

As described above, according to the present invention, it is possible to satisfactorily divide a β-type gallium oxide substrate having a (001) plane as a main surface.

MODE FOR CARRYING OUT THE INVENTION

FIGS.1to3are schematic views for explaining a method of dividing a β-type gallium oxide substrate according to a first embodiment of the present invention.FIGS.1A,2and3are plan views, andFIG.1Bis a schematic cross-sectional view taken along the line A-A inFIG.1A.

As illustrated inFIG.1, a β-type gallium oxide (Ga2O3) substrate10having a plurality of elements20formed on an element forming surface11, which is the main surface, is prepared. Although not particularly limited, the element20may be a Schottky barrier diode. A Schottky barrier diode using a β-type gallium oxide substrate is an element in which current flows in the substrate thickness direction, and the side on which a drift layer and an anode electrode brought into Schottky-contact with the drift layer are formed is the element forming surface. Gallium oxide has a very large bandgap of 4.8 eV to 4.9 eV and a high dielectric breakdown field of approximately 8 MV/cm, and thus the Schottky barrier diode using gallium oxide is very promising as a switching element for power devices.

The element forming surface11and a back surface12located on the opposite side of the element forming surface11constitute a (001) plane (c-plane). InFIG.1, the (001) plane constitutes the xy plane, and a plurality of elements20are formed in a matrix in the x and y directions. A plurality of dividing grooves13extending in the x-direction are formed in the back surface12of the thus configured β-type gallium oxide substrate10so as to pass between the elements20adjacent in the y-direction. The x-direction is the extending direction of the (100) plane (a plane), which is the cleavage surface. Etching is preferably used as a method of forming the dividing grooves13. When the dividing grooves13are formed by etching, the β-type gallium oxide substrate10is not cracked or chipped at the time of forming the dividing grooves13. The depth of the dividing grooves13may be about 25 μm when the thickness of the β-type gallium oxide substrate10is about 250 μm. The dividing grooves13are not formed partially, but are formed over the entire width of the β-type gallium oxide substrate10in the x-direction.

Then, as illustrated inFIG.2, the β-type gallium oxide substrate10is processed into strips by cutting the β-type gallium oxide substrate10along dicing lines14extending in the y-direction. That is, the cutting direction is a direction perpendicular to the extending direction of the dividing grooves13. The cutting position is between the elements20adjacent in the x direction. As a result, each of the β-type gallium oxide substrates10cut into strips has a plurality of elements20arranged in the y-direction, and the dividing grooves13are formed on the back surface12between the elements20adjacent to each other in the y-direction.

Then, as illustrated inFIG.3, the strip-shaped β-type gallium oxide substrate10is cleaved along the dividing grooves13to singulate the elements20.FIG.4is a yz cross section of the singulated element20, and the cleavage surface15cleaved along the dividing groove13has an angle of about 76° (exactly 76. 3°) and about 104° (precisely 103.7°) with respect to the element forming surface11and the back surface12.

As described above, according to the method of dividing a β-type gallium oxide substrate according to the present embodiment, the plurality of dividing grooves13are formed along the extending direction of the (100) plane, which is the cleavage surface, so that cleavage along the makes a dividing grooves13it possible to obtain substantially flat cleavage surface15without causing flaky peeling or the like. In addition, unlike the simple matrix dicing of the β-type gallium oxide substrate10, chipping does not occur, and the cutting margin associated with dicing can be reduced, so that the number of chips that can be obtained increases. Moreover, the dividing grooves13are formed on the back surface12opposite to the element forming surface11, so that the element forming surface11need not be processed. However, in the present invention, forming the dividing grooves13on the back surface12is not essential, and the dividing grooves13may be formed on the element forming surface11.

FIG.5is a schematic view for explaining a method of dividing a β-type gallium oxide substrate according to a second embodiment of the present invention. Here,FIG.5Ais a plan view, andFIG.5Bis a schematic cross-sectional view taken along line A-A inFIG.5A.

The second embodiment differs from the first embodiment in that dividing grooves16are additionally formed in the element forming surface11. The dividing grooves16extend parallel to the dividing grooves13. However, the dividing grooves13and16do not overlap in the thickness direction (z-direction) and are offset by a distance D in the y-direction. The distance D is found by T×tan θ (θ=13.7°), where T is the thickness of the β-type gallium oxide substrate10. Here, a straight line L connecting the dividing grooves13and16has angles of about 76° and about 104° with respect to the element forming surface11and the back surface12, respectively. That is, the dividing grooves13and16are positioned on the same cleavage surface.

Thus, when the β-type gallium oxide substrate10is cut into strips and then cleaved along the dividing grooves13and16, singulation by cleavage can be performed more reliably.

A drift layer in which an element is formed is a thin film obtained by epitaxially growing gallium oxide on the upper surface of a β-type gallium oxide substrate using reactive sputtering, PLD, MBE, MOCVD, HVPE, or the like. When a thin film is epitaxially grown on the upper surface of a β-type gallium oxide substrate using the HVPE method, it will generally be grown on the (001) plane. However, in the case of a β-type gallium oxide substrate whose surface is the (001) plane, there may be an offset angle of about +1° with respect to the x- and y-axes due to manufacturing variations. Furthermore, in consideration of ease of epitaxial growth and deposition properties, the thin film may be grown on a β-type gallium oxide substrate having an offset angle of several degrees.

In such a case, as illustrated inFIG.6, when the offset angle of the (001) plane with respect to the y-axis is θ2, the distance D is T×tan (θ+θ2).

While the preferred embodiment of the present disclosure has been described, the present disclosure is not limited to the above embodiment, and various modifications may be made within the scope of the present disclosure, and all such modifications are included in the present disclosure.

REFERENCE SIGNS LIST