KR20030084476A - Method for lifting off Nitride chemical material group - Google Patents

Abstract

PURPOSE: A lift-off method of nitride chemical material group is provided to be capable of improving stability and productivity of lift-off processing by using a line laser instead of a spot laser. CONSTITUTION: A wafer is formed by growing a nitride thin film on a substrate. The wafer is loaded in a heat apparatus. The wafer is heated at a desired setting temperature. By irradiating a light into the heated wafer using a line laser, the nitride thin film is isolated to the substrate. At this time, the line width(W) of the line laser light is at least 100 micrometer over, and the length(L) of the line laser light is larger than the diameter of the wafer.

Description

Method for lifting off Nitride chemical material group

The present invention relates to a lift-off method of a nitride using a laser, and more particularly, to lift a nitride-based material to improve the stabilization and mass production of the lift-off process by irradiating a line laser light to a wafer located on the plate. It's about how to turn off.

Recently, as the demand for high-efficiency short-wavelength optical devices increases, many studies on compound semiconductors of nitride-based materials known to be suitable for such applications have been conducted.

In particular, gallium nitride (GaN), a nitride-based material, is a wide bandgap semiconductor having a band gap energy of 3.39 eV, a direct transition type, and is a useful material for manufacturing a light emitting device having a short wavelength region.

These gallium nitrides require high temperatures of 1500 ° C or higher and nitrogen pressures of about 1500 atm or higher for normal liquid crystal growth due to the high nitrogen vapor pressure at the melting point, which is difficult to mass produce, and the size of crystals currently available is 80 mm2. Because of its thin plate shape, it is difficult to use this for device fabrication.

Therefore, a light emitting device using gallium nitride has vapor phase growth such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride or halide vapor phase epitaxy (HVPE), and sublimition vapor phase epitaxy (SVPE). The thin film was grown by the method.

At this time, silicon carbide (SiC) or sapphire single crystal has been used as a heterogeneous substrate. Silicon carbide is stable at high temperature, has a hexagonal structure such as gallium nitride, and has a lattice constant and thermal expansion coefficient with gallium nitride. Cars are smaller than sapphire, have excellent thermal and electrical conductivity, but are more expensive than sapphire, and defects in silicon carbide propagate directly to gallium nitride, thereby degrading optical characteristics of the device.

Meanwhile, in the case of other materials except sapphire, for example, silicon carbide (SiC) and GaAs, a gallium nitride layer may be grown, and then the base material may be removed using an etching solution.

However, in the case of sapphire, lapping or laser lift-off method is used because there is no suitable etching solution, and in particular, "removing sapphire by lapping" is shown in FIG. 1 because the gallium nitride layer is easily broken by a small stress or impact. As shown in the drawing, a laser lift-off method of irradiating laser light to separate the gallium nitride layer 11 attached to the hot plate upper portion 10 from the transparent sapphire substrate 12 is mainly used.

Looking at such a conventional laser lift off process in more detail as follows.

First, the gallium nitride layer 11 is grown on the sapphire substrate 12 in the chamber 13 having a high temperature of 1000 ° C. or higher, and then transferred to the outside.

Then, gallium nitride is bonded to the top of the hot plate using an epoxy bond, and a square or circular spot laser, for example, Q-switched Nd: YAG or 248 nm wavelength excitation laser, is applied to the sapphire substrate. Focus and irradiate the light of the (Excimer laser).

Then, the thermal energy of the laser light is concentrated on the interface between the gallium nitride layer and the sapphire substrate, and the temperature is about 800 ⁰ C, which is high enough to separate the gallium metal and the nitrogen molecules. Separation of gallium and sapphire substrates occurs.

However, since the conventional laser lift-off method uses the spot laser light as described above, the laser light or the substrate must be moved to irradiate the laser light evenly on the entire surface of the wafer.

Accordingly, a large amount of irradiation time for separating the sapphire substrate and the gallium nitride layer takes a long time, resulting in a decrease in mass productivity. In particular, since the laser light must be repeatedly moved from left to right several times, the output uniformity of the laser light is deteriorated.

In order to solve the above problems, the present invention replaces a square or circular spot laser light conventionally used for separating a nitride layer from a sapphire substrate with a line laser light, and sequentially replaces the spot laser light with a plurality of wafers located above the hot plate. An object of the present invention is to provide a lift-off method of a nitride-based material using line laser light to improve stabilization and mass productivity of a laser lift-off process by irradiation.

To this end, in the present invention, a nitride layer is grown on the sapphire substrate through vapor phase growth, etc., the grown nitride layer is bonded to the top of the hot plate using an epoxy bond, and then a line is irradiated through the sapphire substrate in a predetermined direction. Laser light is used to separate the nitride layer from the sapphire substrate.

1A to 1B are conceptual views illustrating a general lift off method,

2 is a view conceptually illustrating a lift off method applied to the present invention;

3A to 3D are diagrams showing an embodiment applied to the present invention.

<Explanation of symbols for the main parts of the drawings>

30: first chamber 31: heating furnace

32: sapphire substrate 33: gallium nitride layer

34: gallium boat 35: injection tube

36: gallium powder 37: discharge pipe

40 gate valve 50 second chamber

51: heating RF coil 52: transfer arm

53: bellows

Hereinafter, the present invention will be described with reference to the accompanying drawings.

First, the lift-off method of the present invention includes metal organic chemical vapor deposition (MOCVD), beam epitaxy (MBE), hydride or halide vapor phase epitaxy (HVPE), and A wafer in which a nitride-based material is grown is formed on the dissimilar substrate through the same vapor growth method.

Subsequently, the formed wafer is transferred to a heater, and the nitride-based material is attached to and fixed on the heating apparatus.

At this time, the fixing method is fixed by attaching an epoxy bond on top of the heating device or by forming a separate vacuum chuck, in particular, by placing SUS or Al plate on the top of the heating device. It is preferable to form and attach and fix a nitride-based material on the formed plate by using a high temperature adhesive.

In addition, the heating device is preferably using a hot plate (Hot plate) should be able to control the temperature to 600 ℃ ~ 900 ℃.

This is because the difference between the lattice constants of nitride-based materials such as gallium nitride (GaN) and sapphire mainly used as a substrate is about 16%, and the difference in thermal expansion coefficient is about 25%. If the wafer is lowered to room temperature (approximately 25 ℃), the wafer is bent in a convex shape, and thus the focusing and pattern may be changed when irradiating the laser light, which may lower the efficiency and reproducibility of the process. It is preferable to reduce the amount of warpage by heating.

Next, after the wafer is fixed so that the nitride-based material is directed downward on the heating device, and the temperature of the heating device is adjusted within a set temperature range, high power line laser light is irradiated vertically on the dissimilar substrate.

At this time, it is preferable to irradiate in an atmosphere of a chamber or outside air, and as shown in FIG. 2, a line laser light having a length L and a line width W is irradiated from a predetermined direction, for example, from left to right or top to bottom. do.

The irradiation direction can be modified as much as possible, and as described above, the hot plate to which the wafer is attached may be fixed and the irradiation position of the laser light may be moved. Alternatively, the hot plate may be moved after fixing the irradiation position of the laser light. You can also investigate.

In addition, the length L of the line laser light is slightly larger than the diameter 2 of the general substrate, and the line width W is within the range of the light output density where separation of nitride may occur at the interface between the heterogeneous substrate and the nitride layer. It is desirable to make it as large as possible.

In addition, the unit wafers may be irradiated by placing one unit wafer on top of the heating apparatus, but as illustrated in FIG. 2, the plurality of unit wafers are placed on the heating apparatus to perform a lift-off process of the plurality of wafers with one light output. It is preferable.

The lift-off process using the line laser light has the following great advantages over the lift-off process using the conventional spot laser light.

1) Since the lift-off process of the present invention uses line laser light, the scanning time is relatively shorter during the lift-off process of the unit wafer than the conventional spot laser light.

2) In the conventional lift-off process of a nitride-based material, the laser light must move the laser light up and down several times, but the present invention improves the output uniformity of the light irradiated onto the unit wafer because the number of movements is relatively small. There is a number.

3) In addition, since the present invention uses the line laser light, it is possible to place several unit wafers on the heating device and to perform lift-off process of several unit wafers with one light output, thereby greatly improving mass productivity. There are such advantages.

Next, when the line laser light is irradiated as shown in FIG. 2, thermal energy by laser light is concentrated at the interface between the nitride layer and the dissimilar substrate, and a nitride-based material made of nitride, for example, a group III-V element. In Group V element is vaporized by the thermal energy of the line laser light to escape to the outside and the Group III element is left on the interface between the dissimilar substrate and the nitride material in the form of metal.

The gallium metal thus left is heated and liquefied at a temperature above 30 ° C., or removed with an etching solution such as hydrogen chloride (HCL) to terminate the lift-off process.

Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 3A to 3D. In addition, the heterogeneous substrate applied to the embodiment to be described later is referred to as a "sapphire substrate", and the nitride-based material is referred to as "gallium nitride (GaN)".

According to an embodiment of the present invention, as shown in FIG. 3A, the transfer arm 52 is inserted into the second chamber 50 through the bellows 53 corrugated pipe, and then the sapphire substrate on which the gallium nitride layer is to be grown ( When 32 is placed on the transfer arm 52, the transfer arm 52 sucks the sapphire substrate 32 in a vacuum.

Then, the gate valve 40 is opened, the sapphire substrate 32 is placed on the inner surface of the first chamber 30 by the transfer arm 52, and the transfer arm 52 is placed on the second chamber 50. ) And then close the gate valve 40 (FIG. 3b).

Subsequently, when the heating furnace 31 of the outer circumferential surface of the first chamber 30 is heated, N molecules generated from a gas such as nitrogen or ammonia injected from the injection tube 35 of the first chamber 30, and the first The gallium molecules sublimed in the gallium boat 34 in the first chamber 30 are bonded to form a wafer on which the gallium nitride layer 33 is grown on the sapphire substrate 32.

When the formation is completed, the gate valve 40 is opened to transfer the transfer arm 52 staying in the second chamber 50 to the first chamber to adsorb the gallium nitride layer 33 (FIG. 3C). ) The wafer is transferred to the second chamber 50 (FIG. 3D).

Subsequently, the wafer is removed from the second chamber 50 and fixed using a high temperature adhesive such as an epoxy bond on top of a hot plate (not shown) provided in a separate chamber (not shown).

Then, a high power line laser light is irradiated from the left end side to the right end side of the transparent sapphire substrate.

At this time, the length (L) of the line laser light is preferably made slightly larger than the diameter of the general substrate, the line width (W) is the light output that can be separated from the gallium nitride layer on the interface between the sapphire substrate and gallium nitride layer It is desirable to make it as large as possible within the range of density. Specifically, it is preferable that the light output density at the interface is at least 400 mJ / cm 2 or more and its line width is 100 μm or more.

On the other hand, when the line laser light is irradiated on the wafer, the thermal energy of the laser is concentrated on the interface between the gallium nitride layer and the sapphire substrate to instantly separate the gallium metal and nitrogen molecules, the separated nitrogen molecules are vaporized and eventually the gallium nitride Only gallium metal remains at the interface between the and sapphire substrates.

Then, the gallium metal is heated and liquefied at a temperature of 30 ° C. or higher to separate the gallium nitride layer from the sapphire substrate, thereby completing the process of the embodiment to which the present invention is applied.

As described in detail above, in the lift-off method of the nitride-based material according to the present invention, when the line laser light is irradiated onto the wafer located above the hot plate, the irradiation time can be relatively shortened than when the conventional lift-off method is performed. In addition, since the lift-off process of several wafers can be performed with one laser light output, the stability and mass productivity of the process can be remarkably improved.

Although the invention has been described in detail only with respect to the specific examples described, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims.

Claims (5)

Forming a wafer on which a nitride thin film is grown on a substrate; A second step of transferring and fixing the formed wafer to a heating apparatus; A third step of heating the fixed wafer within a set temperature range; A laser beam is irradiated to the heated wafer to separate the substrate and the nitride thin film, wherein the laser light is a lift of a nitride-based material comprising a fourth step using a line laser light having a line width (W) and a length (L). Off way. The method of claim 1, wherein the second step; The formed wafer is adhered to the upper portion of the heating apparatus with a high temperature adhesive to fix the wafer, or a vacuum chuck is formed between the wafer and the heating apparatus to fix the wafer. The method according to claim 1 or 2, The substrate is a sapphire substrate, The heating device is a hot plate (Hot plate) characterized in that the lift-off method of the nitride-based material. The method of claim 1, wherein the set temperature range is: Lift-off method of the nitride-based material, characterized in that 600 ℃ ~ 900 ℃. The method of claim 1, The line width (W) is to be at least 100㎛ within the power density range of the light, And the length L is larger than the diameter of the wafer.