KR100809211B1 - Method of producing nitride based single-crystal substrate - Google Patents

Abstract

A method for fabricating a nitride single crystalline substrate is provided to minimize a stress on an interface between a substrate and a nitride single crystal by forming grooves on the surface of a substrate for growing a nitride wherein the upper surface of the substrate can be divided into a plurality of regions by the grooves. A substrate(21) for growing a nitride single crystal(23) is prepared. At least one groove is formed on the substrate so that the upper surface of the substrate is divided into a plurality of regions. A nitride single crystal is grown on the substrate. The substrate is removed from the nitride single crystal. In a step for growing the nitride single crystal, the substrate is divided along the groove into a plurality of regions by increased stress caused by an increased thickness of the nitride single crystal. The grooves can have a plurality of straight line types that are arranged widthwise and lengthwise on the upper surface of the substrate.

Description

Nitride single crystal substrate manufacturing method {METHOD OF PRODUCING NITRIDE BASED SINGLE-CRYSTAL SUBSTRATE}

1A and 1B are cross-sectional views showing a nitride single crystal substrate manufacturing process according to the prior art, respectively.

2A to 2E are cross-sectional views of respective processes for explaining a method for manufacturing a nitride single crystal substrate according to one embodiment of the present invention.

FIG. 3A is a SEM photograph of a cross section of a substrate groove employed in the present invention, and FIG. 3B is an optical microscope photograph of an upper surface of a nitride single crystal template layer having grooves arranged in parallelograms.

<Code Description of Main Parts of Drawing>

21 substrate 22 nitride single crystal template layer

23: nitride single crystal layer A: groove

C: Crack L: Laser Beam

F: Stress

The present invention relates to a method for manufacturing a nitride single crystal substrate, and more particularly, to minimize the stress generated at the interface between the substrate and the nitride single crystal in the process of growing the nitride single crystal on a heterogeneous substrate and to reduce the warpage caused by the nitride single crystal substrate It relates to a manufacturing method.

In recent years, in the field of next-generation lighting, research into semiconductor devices emitting light in a short wavelength band has been actively conducted. As a material for forming a semiconductor device capable of emitting light in such a short wavelength band, a nitride semiconductor such as GaN is widely used.

Typically, GaN single crystals have been prepared on heterogeneous substrates by vapor phase growth such as metal organic chemical vapor deposition (MOCVD), hydrolysis vapor phase epitaxy (HVPE), or molecular beam epitaxy (MBE).

Recently, in order to obtain a high quality nitride-based light emitting device, a method of using a homogeneous substrate such as a GaN substrate, rather than a heterogeneous substrate such as a sapphire (? -Al ₂ O ₃ ) substrate or a SiC substrate, has been considered.

Although the nitride single crystal substrate has a somewhat higher defect density than the light emitting device, the nitride single crystal substrate can guarantee excellent crystallinity unlike a conventional heterogeneous substrate. However, these nitride single crystals must be grown to a sufficient thickness (eg several hundred micrometers) required for the substrate.

Therefore, even in growing a nitride single crystal substrate, there is still a stress problem due to the difference in lattice constant and thermal expansion coefficient (e.g., sapphire / GaN, lattice constant: about 13%, thermal expansion coefficient: about 34%) with the hetero substrate. Is present. 1A and 1B show a state in which a warpage phenomenon occurs due to a stress between a sapphire substrate and GaN grown thereon.

As shown in FIG. 1A, when the GaN single crystal is grown due to a difference in thermal expansion coefficient between the sapphire substrate and GaN, the substrate and the GaN single crystal may be seriously bent. In this case, the degree of warpage may have a curvature on the order of tens of centimeters, and this degree of curvature is a serious level considering the size of a typical 2-inch substrate.

In addition, after the laser lift-off process, as shown in Fig. 1B, due to the internal stress, the GaN single crystal is squeezed in the opposite direction. Therefore, in order to obtain a substrate in a flat state, a processing step such as a polishing step must be performed so that the portion indicated by the dotted line remains, so that the final GaN single crystal substrate obtained is inevitably small.

As such, there has been a difficulty in manufacturing a nitride single crystal substrate having a sufficient size and good crystallinity due to the difference in lattice constant and thermal expansion coefficient, such as a dissimilar substrate.

The present invention is to solve the above-mentioned problems of the prior art, the purpose of the nitride single crystal that can minimize the warpage phenomenon and cracks by growing a nitride single crystal in a condition that the influence on the stress between the hetero-substrate and the nitride single crystal is reduced It is to provide a method of manufacturing a substrate.

In order to achieve the above technical problem, the present invention,

Providing a substrate for nitride single crystal growth, forming at least one groove on the substrate such that the upper surface of the substrate is divided into a plurality of regions, growing a nitride single crystal on the substrate and the nitride single crystal Removing the substrate from the nitride single crystal, wherein the substrate is separated into the plurality of regions along the groove by an increase in stress caused by an increase in the thickness of the nitride single crystal in the nitride single crystal growth step. Provided is a substrate manufacturing method.

The grooves employed in the present invention can suppress the warpage due to the increase of stress caused by spontaneous substrate division during the growth process. In consideration of the smoothness of spontaneous division of the substrate and the safety of the growth substrate handling, the groove may be formed to have a depth corresponding to 20% to 70%, more preferably 40% to 70% of the thickness of the substrate. have.

In a preferred embodiment of the present invention, the groove may be formed to form a plurality of straight lines arranged in the longitudinal and transverse directions, respectively, on the upper surface of the substrate. In this case, the groove may be formed to form a plurality of parallelograms of the plurality of linear forms arranged in the longitudinal and transverse directions. This is considered to be easy to separate along the cleaved surface, since the commonly used sapphire substrate is a hexagonal system.

In nitride single crystal growth, nitride single crystals laterally grown around the grooves may be merged on top of the grooves. In this case, since dislocations may be generated at the point of coalescence, it is desirable to properly secure the gap between grooves in order to reduce the potential due to coalescence. In this aspect, it is preferable that the groove is formed to have a distance of 100 μm or more from another adjacent groove.

In a preferred embodiment of the present invention, the groove is narrower from the top to the bottom of the substrate, the bottom of the groove preferably has a tip. At the tip of the groove, the stress that is increased during the nitride growth process is maximized so that cracks can easily propagate down the substrate, thereby facilitating spontaneous division of the substrate.

Further, as described above, since the nitride single crystal grows laterally on the substrate around the groove, it is preferable to limit the width of the groove so that the nitride single crystal can be easily incorporated. In this aspect, the grooves may be formed to have a width of preferably 20 μm or less, more preferably 10 μm or less.

Preferably, the groove may be formed by irradiating a laser beam, and when processing by the laser beam, not only has the advantage that the processing is easy to have a desired groove size, but also the shape of the lowest point can be easily obtained. There is an advantage.

In a particular embodiment of the present invention, prior to forming the groove on the substrate, the method further includes forming a nitride single crystal template layer on the substrate, wherein the groove passes through the nitride single crystal template layer to form the groove. It may be formed on the substrate.

In this case, preferably, the forming of the nitride single crystal template layer may be performed by a MOCVD process, and the growing of the nitride single crystal may be performed by an HVPE process.

Preferably, after the step of forming a groove on the substrate, it may further comprise the step of washing the substrate. Through this process, residues generated in the groove forming process, such as a laser beam, may be removed to provide better growth conditions for nitride single crystal growth.

Meanwhile, the substrate may be removed by a mechanical polishing process or the like, but the removing of the substrate from the nitride single crystal is preferably performed by a laser lift-off process.

Preferably, after removing the substrate from the nitride single crystal, the method may further include processing a surface from which the substrate is removed from the nitride single crystal. Residues of the substrate or the nitride template layer may exist on a surface where the substrate is removed from the nitride single crystal, and thus the nitride single crystal may be manufactured by surface-processing the nitride single crystal.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

2A to 2E are cross-sectional views of respective processes for explaining a manufacturing process of the nitride single crystal substrate according to the embodiment of the present invention.

First, as shown in FIG. 2A, the nitride single crystal template layer 22 is grown on the substrate 21 for nitride single crystal growth.

The substrate 21 for nitride single crystal listing may be a sapphire substrate, but is not limited thereto, and is a heterogeneous substrate made of a material selected from the group consisting of SiC, Si, MgAl ₂ O ₄ , MgO, LiAlO _2, and LiGaO ₂ . Can be. The nitride single crystal template layer 22 may be formed by a MOCVD process as a base layer provided for rapid growth of higher quality nitride single crystal.

Next, as shown in FIG. 2B, a groove A is formed on the substrate 21 so that the upper surface of the substrate 21 is divided into a plurality of regions (see FIGS. 3A and 3B).

The groove A employed in the present invention divides the contact area with the nitride single crystal to be grown into smaller units and completely separates the substrate 21 into the divided regions by the stresses increased during subsequent nitride single crystal growth. Problems caused by stress can be minimized.

The groove (A) forming process according to this step may preferably use a machining process by the laser beam (L), but is not limited thereto, and other suitable methods known in the art, such as a mechanical machining process using a diamond tip, etc. It can be formed using a processing process. Since the residues generated in the groove forming process may exist on the upper surface of the template layer 22 to be provided as the crystal growth surface, it is preferable to additionally perform an appropriate cleaning process.

The spontaneous separation of the substrate 21 during the subsequent growth of the nitride single crystal can be easily realized by appropriately adjusting the depth d of the groove A. In this aspect, the depth d of the groove A may be formed to have a range corresponding to 20% or more, more preferably 40% or more of the thickness t1 of the substrate 21.

However, the depth d of the groove A is the thickness t1 of the substrate 21 so as to prevent unwanted substrate breakage due to the groove A in necessary substrate handling processes such as transfer to the growth chamber and cleaning the substrate. It is preferable to form in the range corresponding to 70% or less of).

In addition, the groove A employed in the present embodiment can be formed to have an appropriate width w and spacing s in consideration of the crystalline side due to lateral growth. Preferably, the width w of the groove A may be 20 μm or less, and more preferably 10 μm or less. This will be described in more detail with reference to FIG. 2C.

2C and 2D, a nitride single crystal 23 having a desired thickness is grown on the nitride single crystal template layer 22.

In the growth stage of the nitride single crystal, as described above, the stress increases due to the growth thickness of the nitride single crystal, and the increased stress is concentrated in a preformed groove to cause spontaneous substrate separation.

Figure 2c shows the spontaneous separation of the substrate where nitride single crystals are generated during the growth process.

As shown in Fig. 2C, in the growth stage of the initial nitride single crystal, the nitride single crystal 23 'is laterally grown around the groove A and coalesced at the top of the groove A. Such a lateral growth mode can be easily realized by appropriately adjusting process conditions such as group V / III ratio, growth pressure and / or growth temperature. Here, it is preferable to form the width w of the groove A in 20 micrometers or less so that coalescence of the nitride single crystal by lateral growth can be made more quickly. In addition, since dislocations may be generated in the portion to be coalesced, the interval s between the grooves A is preferably about 100 μm or less so that the dislocations due thereto are appropriately limited.

The stress between the nitride single crystal 23 'and the substrate 21 gradually increases with the thickness grown and causes a constant warpage, but the stress is concentrated in the groove A, and the nitride single crystal 23' has an arbitrary growth thickness. When it has (t'2), it reaches the critical stress (F) which propagates the crack (C) below the board | substrate 21 along the groove (A).

As described above, the time at which the critical stress F is generated may be adjusted to an appropriate depth d of the groove A. That is, since a large bending phenomenon occurs due to the stress caused by the growth thickness, the depth (d) of the groove (A) so that the point where the possible critical stress (F) is generated in the initial stage of the growth of the nitride single crystal 23 ' It is desirable to define. It is preferable that the groove A is formed so that the lowermost part has the tip portion so that the crack C can be more easily propagated along the groove A.

As such, the substrate 21 may be spontaneously separated into a plurality of regions defined by the grooves as shown in FIG. 2D by the intentional crack C propagating along the grooves A. FIG.

The nitride single crystal 23 may be grown to a desired thickness t2 through an additional growth process. In the state in which the substrate is spontaneously separated, since the portion where the nitride single crystal 23 is in contact with the substrate 21 is completely divided into small units, the stress that may be generated in the thickness of the nitride single crystal that can be used as the substrate is sufficient. The influence on the surface can be reduced, and in particular, the degree of warpage caused can be greatly alleviated.

Subsequently, the substrate 21 is removed from the nitride single crystal 23 to obtain a nitride single crystal 23 from which the substrate 21 has been removed, as shown in FIG. 2E. In this case, as shown in FIG. Likewise, the substrate 21 is preferably removed by a laser lift off process. The nitride single crystal 23 obtained through such a process can minimize the disadvantageous crack generation and warpage which are conventionally problematic through spontaneous division of the substrate generated during the growth process.

Although not shown in the present embodiment, after the substrate 21 is removed from the nitride single crystal 23 in the step shown in FIG. 2D, the surface from which the substrate 21 is removed from the nitride single crystal 23 is shown. Further machining steps can be carried out. This is to obtain a nitride single crystal substrate having a desired mirror surface by processing a rough surface due to a laser lift-off process or the like in the removing step of the substrate 21.

In addition, in this embodiment, as shown in FIG. 2A, in order to grow the nitride single crystal which has more excellent crystallinity, it demonstrates and shows as an example in which the nitride single crystal template layer 22 was formed on the said board | substrate 21. FIG. However, the present invention is not limited thereto.

For example, the nitride single crystal template layer 22 may be embodied in a form of replacing or parallel with a known surface modification process such as another buffer layer or nitriding process. Therefore, in the case where the nitride single crystal is grown directly on the substrate or the nitride single crystal is grown by simply applying nitriding treatment, a step of forming a groove directly on the substrate can be applied.

As described in the foregoing embodiments, the present invention forms grooves for dividing the surface into a plurality of units on the upper surface of the substrate so that the substrate can be spontaneously divided through the increased stress during the nitride single crystal growth process. Since the substrate is spontaneously divided in the nitride single crystal growth process, the influence due to the stress can be reduced, and in particular, the warpage phenomenon of the nitride unity increased according to the growth thickness can be greatly suppressed.

The grooves employed in the present invention are satisfied if the upper surface of the substrate used for nitride growth is formed to be divided into appropriate sizes and shapes, and is not limited to the number, shape and arrangement of the grooves. However, the shape and arrangement of the grooves illustrated in FIGS. 3A and 3B may be preferably employed to facilitate spontaneous division of the substrate during the nitride single crystal growth process.

Referring to Fig. 3A, a groove processed by a laser beam is shown on a sapphire substrate on which a nitride single crystal template layer is formed. The groove is narrower from the top to the bottom of the sapphire substrate, and the lowermost part of the groove A has a tip shape. The shape of such grooves can concentrate stresses necessary for complete division of the sapphire substrate at the tip, thereby facilitating easier substrate division. As described above, the groove formation of the shape can be easily implemented by the laser beam.

As shown in Fig. 3B, the grooves have a plurality of straight lines arranged in the longitudinal and transverse directions so that the upper surface of the substrate (in this example, the actual nitride single crystal template layer) is divided into a plurality of portions using a small number of laser scannings. It may be formed in the form formed.

In particular, as shown in FIG. 3B, the grooves can be easily realized in the nitride single crystal growth process by adopting a shape in which the plurality of linear shapes arranged in the longitudinal and transverse directions form a plurality of parallelograms. have. That is, since a substrate for nitride single crystal growth, which is generally used, such as a sapphire substrate, has a hexagonal structure, expansion of cracks necessary for full division of the substrate can be easily realized according to cleaved surfaces.

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. Accordingly, various forms of substitution, modification, and alteration may be made by those skilled in the art without departing from the technical spirit of the present invention described in the claims, which are also within the scope of the present invention. something to do.

As described above, according to the present invention, grooves are formed on the upper surface of the substrate for nitride growth so as to be divided into a plurality of regions, thereby allowing spontaneous division of the substrate during spontaneous growth of the nitride single crystal. Accordingly, a higher quality nitride single crystal substrate can be obtained by minimizing stress at the interface between the substrate and the nitride single crystal and greatly alleviating the warpage of the nitride single crystal.

Claims (14)

Preparing a substrate for nitride single crystal growth; Forming at least one groove on the substrate such that the upper surface of the substrate is divided into a plurality of regions; Growing a nitride single crystal on the substrate; And Removing the substrate from the nitride single crystal; And the substrate is separated into the plurality of regions along the groove by an increase in stress caused by an increase in thickness of the nitride single crystal in the nitride single crystal growth step. The method of claim 1, The groove has a depth corresponding to 20% to 70% of the substrate thickness of the nitride single crystal substrate manufacturing method. The method of claim 2, And the groove has a depth corresponding to at least 40% of the thickness of the substrate. The method of claim 1, The groove is a nitride single crystal substrate manufacturing method, characterized in that formed on the upper surface of the substrate to form a plurality of straight lines arranged in the longitudinal direction and the transverse direction, respectively. The method of claim 4, wherein The groove is a nitride single crystal substrate manufacturing method, characterized in that the plurality of straight lines arranged in the longitudinal direction and the transverse direction formed to form a plurality of parallelograms. The method of claim 1, The groove is a nitride single crystal substrate manufacturing method, characterized in that the interval between the other groove and 100㎛ or more. The method of claim 1, The groove is narrower from the upper portion to the lower portion of the substrate, the lowermost portion of the groove has a nitride single crystal substrate manufacturing method, characterized in that the shape of the tip. The method of claim 1, The at least one groove is a nitride single crystal substrate manufacturing method, characterized in that each having a width of 20㎛ or less. The method of claim 1, And the groove is formed by irradiating a laser beam. The method of claim 1, Prior to forming the grooves on the substrate, further comprising forming a nitride single crystal template layer on the substrate, wherein the grooves are formed on the substrate through the nitride single crystal template layer. Manufacturing method. The method of claim 10, Forming the nitride single crystal template layer is performed by a MOCVD process, and growing the nitride single crystal is performed by an HVPE process. The method of claim 1, And after forming the grooves on the substrate, cleaning the substrate. The method of claim 1, And removing the substrate from the nitride single crystal is performed by a laser lift off process. The method of claim 1, And after removing the substrate from the nitride single crystal, processing a surface from which the substrate is removed from the nitride single crystal.

Images