JP2007332012A - Fabrication process of semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fabrication process of a semiconductor wafer, in which a nitride semiconductor film is formed on a substrate of a desired material other than a substrate for the epitaxial growth of a nitride semiconductor film. <P>SOLUTION: A first nitride semiconductor film 2 is formed on a first substrate 1 and a second nitride semiconductor film 3 having a higher melting point than that of the first film 2 is formed on the first nitride semiconductor film 2. Subsequently, a carrier substrate 4 is adhered to the surface of the second nitride film 3. Then, the substrate 1 attached together, the first nitride semiconductor film 2, the second nitride semiconductor film 3 and a wafer containing the carrier substrate 4 are heat treated at a temperature higher than the melting point of the first nitride semiconductor film 2 and lower than that of the second nitride semiconductor film 3, to melt the first nitride semiconductor film 2 and remove the first substrate 1. Further, the second substrate 6 is attached to the surface of the second nitride semiconductor film 3 which is attached on the carrier substrate 4, and the carrier substrate 4 is removed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor wafer manufacturing method, and more particularly to a semiconductor wafer manufacturing method capable of manufacturing a semiconductor wafer in which a nitride semiconductor film is formed on a desired substrate.

  Nitride semiconductors composed of indium, gallium, aluminum, and nitrogen are developed as innovative high-efficiency light-emitting device materials that cover the most area from ultraviolet to visible light by controlling the composition ratio of group III elements. Has been put into practical use. In addition, nitride semiconductors have high saturation electron velocity and high breakdown voltage, so in the future, they are expected to be applied as materials for electronic devices that achieve orders of magnitude higher efficiency and higher output in the high frequency range. .

  When forming a nitride semiconductor thin film, the biggest problem is the selection of the substrate. Conventionally, it has been extremely difficult to manufacture a single crystal nitride semiconductor substrate itself, and it has been almost impossible to obtain it. For this reason, nitride semiconductor devices such as blue LEDs have usually been formed on sapphire substrates. This is because high-quality single crystals of a sapphire substrate can be easily produced industrially, the crystal lattice constant is close to that of a nitride semiconductor, and the crystal system is close to that of a nitride semiconductor. Therefore, the nitride semiconductor is epitaxially grown. This is because it is suitable as a base to be used.

However, the sapphire substrate has the following drawbacks.
The first drawback is that sapphire is an insulator. Since sapphire is an insulator, it is a nitride semiconductor formed on a sapphire substrate, and there is a restriction that all electrodes must be arranged on the surface side in order to produce an LED or a bipolar transistor. Then, since a considerable portion of the surface area of the wafer is covered with the electrodes, for example, in the LED, the light emitting area is substantially reduced, and the efficiency is deteriorated. In addition, since a plurality of etching processes are required, the device manufacturing process becomes complicated and the manufacturing cost increases.

  A second drawback of the sapphire substrate is poor thermal conductivity. The thermal conductivity of sapphire is about 0.4 W / cm · K, which is, for example, less than ¼ compared with 1.5 W / cm · K of silicon. Even if it compares, it is a remarkably low value. When a transistor is made of a nitride semiconductor and operated at a high output, the active layer generates heat violently. However, in such a case, if the thermal conductivity of the substrate is poor, heat dissipation is not performed sufficiently, and the performance of the transistor itself. This causes a problem of deterioration with time.

  In order to overcome the above-mentioned drawbacks, a method of using single crystal silicon carbide or single crystal GaN manufactured by the HVPE method as a substrate for forming a nitride semiconductor thin film instead of a sapphire substrate is known. Yes.

Further, a crack is formed in the first layer made of a nitride semiconductor as an impact relaxation layer for absorbing stress on the growth substrate, and a second layer of the nitride semiconductor is formed on the first layer having the crack. There is a method in which after growing and attaching another substrate over the second layer, the impact when peeling the growth substrate by polishing, etching, or laser irradiation is mitigated by the first layer having cracks. It has been proposed (see, for example, Patent Document 1).
JP 2004-119807 A

  However, in the method using the above-mentioned single crystal silicon carbide or single crystal GaN as a substrate for forming a nitride semiconductor thin film, the cost of these single crystal substrates is several to several tens of times higher than that of a sapphire substrate. The use is limited to the production of high value-added products.

  Further, in the growth substrate peeling method using the first layer having cracks, it is difficult to grow the second layer of nitride semiconductor with good crystallinity on the first layer having cracks. There are problems such as.

  The present invention solves the above problems and provides a method for manufacturing a semiconductor wafer, in which a nitride semiconductor film can be formed on a substrate of a desired material different from a substrate for epitaxial growth of a nitride semiconductor film.

In order to solve the above problems, the present invention is configured as follows.
A first aspect of a method for producing a semiconductor wafer according to the present invention includes a step of forming a first nitride semiconductor film on a first substrate, and the first nitride on the first nitride semiconductor film. A step of forming a second nitride semiconductor film having a higher melting point than the oxide semiconductor film, a step of bonding a carrier substrate to the surface of the second nitride semiconductor film, the bonded first substrate, and The wafer including the first nitride semiconductor film, the second nitride semiconductor film, and the carrier substrate is higher than the melting point of the first nitride semiconductor film and higher than the melting point of the second nitride semiconductor film. A step of melting the first nitride semiconductor film by heat treatment at a low temperature; a step of removing the first substrate; and a surface of the second nitride semiconductor film bonded to the carrier substrate The process of bonding the second substrate to A method of manufacturing a semiconductor wafer, characterized by a step of removing the carrier substrate.

  A second aspect is a method for manufacturing a semiconductor wafer according to the first aspect, wherein the first substrate is made of sapphire, silicon, or zinc oxide.

A third aspect is the semiconductor wafer according to the first or second aspect, wherein the first nitride semiconductor film is made of Ga _x In _(1-x) N (0 ≦ x ≦ 1). It is a manufacturing method.

According to a fourth aspect, in any one of the first to third aspects, the second nitride semiconductor film is made of Al _y Ga _z In _(1-yz) N (0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ y + z ≦ 1). A method of manufacturing a semiconductor wafer, comprising:

  A fifth aspect is the semiconductor wafer according to any one of the first to fourth aspects, wherein the second substrate is made of polycrystalline silicon carbide, silicon, zinc oxide, indium tin oxide, or nickel. It is a manufacturing method.

  A sixth aspect is the semiconductor wafer according to any one of the first to fifth aspects, wherein the heating temperature for melting the first nitride semiconductor film is in the range of 800 ° C. to 1500 ° C. It is a manufacturing method.

  According to a seventh aspect, in any one of the first to sixth aspects, the surface of the second nitride semiconductor film exposed by removing the carrier substrate is a group III surface. A wafer manufacturing method.

  According to the present invention, the second nitride semiconductor film can be formed on the second substrate, which is different from the first substrate which is the growth substrate for the first and second nitride semiconductor films. Therefore, a desired material that is excellent in conductivity, thermal conductivity, cost, and the like can be selected and used as the second substrate.

Hereinafter, an embodiment of a semiconductor wafer manufacturing method according to the present invention will be described.
In the method of manufacturing a semiconductor wafer according to this embodiment, first, a first nitride semiconductor film and a first nitride semiconductor are formed on a first substrate by using a metal organic chemical vapor deposition (MOVPE) apparatus or the like. A second nitride semiconductor film having a higher melting point than the film is sequentially formed. The first substrate is preferably made of sapphire, silicon, zinc oxide, or the like suitable for growing a nitride semiconductor film. In addition, Ga _x In _(1-x) N (0 ≦ x ≦ 1) is used for the first nitride semiconductor film, and Al _y Ga _z In _(1-y— is used for the second nitride semiconductor film. _{z) N (0 ≦ y ≦} 1,0 ≦ z ≦ 1,0 ≦ y + z ≦ 1) is preferred. Note that since the first nitride semiconductor film and the first substrate are removed by melting the first nitride semiconductor film in a later step, the first substrate and Ga _x In _(1-x) N, etc. A low temperature growth AlN film, a low temperature growth GaN film, or the like may be formed between the first nitride semiconductor film and the first nitride semiconductor film.

Next, a carrier substrate is bonded to the surface of the second nitride semiconductor film, and a wafer including the first substrate, the first nitride semiconductor film, the second nitride semiconductor film, and the carrier substrate bonded together, Heat treatment is performed at a temperature higher than the melting point of the first nitride semiconductor film and lower than the melting point of the second nitride semiconductor film to melt the first nitride semiconductor film, and the first nitride semiconductor film and the first nitride semiconductor film One substrate is removed from the wafer.
The heating temperature for melting the first nitride semiconductor film includes a heat treatment atmosphere (normal pressure or reduced pressure, flowing gas type, etc.), a material of the first nitride semiconductor film (Ga _x In _(1-x) N Ga ₎ For example, the composition of the second nitride semiconductor film varies depending on the material of the second nitride semiconductor film (such as Al composition y of Al _y Ga _z In _(1-yz) N). When the second nitride semiconductor film is AlN and heat treatment is performed in a reduced-pressure hydrogen atmosphere, GaN begins to decompose from 800 to 900 ° C., while AlN does not decompose even at 1400 ° C., probably less than 1500 ° C. A thin film form can be maintained sufficiently even at the processing temperature. Therefore, the temperature range for melting the first nitride semiconductor film is preferably in the range of 800 ° C to 1500 ° C.

  Next, after the second substrate is bonded to the surface of the second nitride semiconductor film bonded to the carrier substrate, the carrier substrate is removed. Thereby, a semiconductor wafer in which the second nitride semiconductor film is formed on the second substrate is obtained. The second substrate is preferably a low-cost material excellent in conductivity, thermal conductivity, etc., such as polycrystalline silicon carbide, silicon, zinc oxide, indium tin oxide, or nickel. In order to produce various devices (optical device, electronic device) using the obtained semiconductor wafer, a device active layer of a nitride semiconductor multilayer film is grown on the second nitride semiconductor film.

  By the above manufacturing method, the nitride semiconductor film (second nitride semiconductor film) can be formed on the substrate (second substrate) made of a desired material. As a result, the characteristics of the device active layer of the nitride semiconductor multilayer film and the advantageous physical properties (conductivity, high thermal conductivity, etc.) of the material of the second substrate are adapted to the operation purpose of various devices. It becomes possible to combine freely.

When a nitride semiconductor is formed directly on a substrate by a normal epitaxial growth method, as described above, the substrate is a high-quality single crystal, the lattice constant of the substrate and the nitride semiconductor is close, the substrate and the nitride A necessary condition is that the crystal systems of the physical semiconductors are the same or approximate. For this reason, it was necessary to use a sapphire substrate having poor thermal conductivity.
However, according to the manufacturing method of the present embodiment, the second substrate on which the nitride semiconductor film (second nitride semiconductor film) is attached is not directly used for epitaxial growth. For this reason, the second substrate does not have to satisfy the above-mentioned requirements at all. Therefore, according to this embodiment, it is possible to select a material having advantageous conditions such as excellent conductivity, excellent thermal conductivity, or being available at a low cost, and use this as the second substrate. Thus, an inexpensive device with good performance can be manufactured.

  An embodiment of a semiconductor wafer manufacturing method according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing each manufacturing process of the present embodiment.

  First, as shown in FIG. 1A, a gallium nitride layer as a first nitride semiconductor film is formed on a sapphire substrate 1 as a first substrate by a normal MOVPE method (metal organic vapor phase epitaxy). 2 and an aluminum nitride layer 3 which is a second nitride semiconductor film are grown. The thickness of the gallium nitride layer 2 is desirably so thick that the surface side can be flattened and lowered to some extent. For example, the thickness is in the range of about 0.3 μm to 5.0 μm. The aluminum nitride layer 3 desirably has a thickness that does not cause cracks. For example, a range of about 0.05 μm to 2.0 μm is appropriate.

Next, a quartz substrate 4 is prepared as a carrier substrate processed so as to have high flatness, and the quartz substrate 4 is overlaid on the aluminum nitride layer 3 on the sapphire substrate 1 as shown in FIG. .
Here, the stacked wafers are firmly held from above and below using a jig (not shown), and the held wafers are introduced into an annealing furnace (not shown). Then, the annealing furnace is placed in a hydrogen atmosphere, the annealing temperature is set to 1100 ° C., and the wafer is heat-treated for 30 minutes.

Then, two phenomena occur in this heating process, and the wafer is in a state as shown in FIG. That is, first, in the temperature rising process, quartz and aluminum nitride are strongly bonded by sintering by the action of both pressure bonding and heating. That is, the aluminum nitride layer 3 is bonded to the quartz substrate 4.
Next, when the processing temperature reaches around 1000 ° C., the gallium nitride in the gallium nitride layer 2 melts and starts to decompose. When gallium nitride is decomposed, the nitrogen component is dissipated as a gas, and only gallium 5 becomes a single liquid and remains in a droplet shape. Since the melting point of gallium 5 is about 30 ° C., the gallium 5 remains almost liquid even when the annealing furnace is cooled after the heat treatment.

  When the heat treatment is completed and the wafer is cooled to approximately 40 ° C., the wafer is taken out of the annealing furnace, and the sapphire substrate 1 is peeled off from the aluminum nitride layer 3 attached to the quartz substrate 4. Since the gallium nitride of the gallium nitride layer 2 has already been decomposed and only the liquid gallium 5 droplets remain, the sapphire substrate 1 can be peeled off very easily. This state is shown in FIG.

  The liquid gallium 5 droplets adhering to the surface of the aluminum nitride layer 3 are removed by scrub cleaning or alcohol cleaning to clean the surface of the aluminum nitride layer 3. The state after the cleaning is shown in FIG.

  Next, a polycrystalline silicon carbide substrate 6 processed to have high flatness is prepared as a second substrate, and an aluminum nitride layer attached to the quartz substrate 4 as shown in FIG. 1 (f). 3, the polycrystalline silicon carbide substrate 6 is superimposed. Then, the superposed wafer is pressed down from above and below with a jig, and the wafer is again introduced into the annealing furnace. The annealing furnace is set to a hydrogen atmosphere, the annealing temperature is set to 1100 ° C., and the wafer is heat-treated for 30 minutes. Then, the polycrystalline silicon carbide substrate 6 and the aluminum nitride of the aluminum nitride layer 3 are strongly bonded by sintering by the action of both pressure bonding and heating. That is, the aluminum nitride layer 3 is bonded to the polycrystalline silicon carbide substrate 6 (FIG. 1 (f)).

  Next, the quartz substrate 4, the aluminum nitride layer 3, and the polycrystalline silicon carbide substrate 6 wafer that are bonded to each other are introduced into a hydrofluoric acid-based solution. Then, only the quartz substrate 4 is dissolved, and the polycrystalline silicon carbide substrate 6 and the aluminum nitride layer 3 attached thereto remain (FIG. 1 (g)). The aluminum nitride layer 3 in this state has a group III surface on the surface, similar to that after growth by the MOVPE method.

  Since the group III surface is a thermally and chemically stable surface, a device active layer 7 made of a high-quality nitride semiconductor multilayer film is formed on the aluminum nitride layer 3 attached to the polycrystalline silicon carbide substrate 6. Can be formed by the MOVPE method. A state after the device active layer 7 is formed is shown in FIG.

  The device active layer 7 is processed to produce a field effect transistor. An example of a field effect transistor in which the source electrode 8, the gate electrode 9, and the drain electrode 10 are formed on the device active layer 7 is shown in FIG. In this field effect transistor, unlike a sapphire substrate, it is formed on a polycrystalline silicon carbide substrate (in this case, preferably a high resistance) having a good thermal conductivity. For this reason, sufficient heat dissipation can be achieved through the polycrystalline silicon carbide substrate 6 even during high-power operation.

  Similarly, FIG. 3 shows an example of an LED (light emitting diode) manufactured by processing the device active layer 7 of the semiconductor wafer of FIG. Unlike the sapphire substrate, this LED is formed on a conductive polycrystalline silicon carbide substrate 6. For this reason, while providing the electrode (p-type electrode) 12 on the device active layer 7, it is possible to provide the electrode (n-type electrode) 11 on the back surface of the polycrystalline silicon carbide substrate 6, thereby reducing the LED chip area. In addition, the cost can be reduced because the process can be simplified.

It is process drawing which shows one Example of the manufacturing method of the semiconductor wafer which concerns on this invention. It is sectional drawing which shows the structure of the field effect transistor produced using the semiconductor wafer of FIG. It is sectional drawing which shows the structure of LED produced using the semiconductor wafer of FIG.

Explanation of symbols

1 Sapphire substrate (first substrate)
2 Gallium nitride layer (first nitride semiconductor film)
3 Aluminum nitride layer (second nitride semiconductor film)
4 Quartz substrate (carrier substrate)
5 Liquid gallium droplet 6 Polycrystalline silicon carbide substrate (second substrate)
7 Device active layer made of nitride semiconductor multilayer film 8 Source electrode 9 Gate electrode 10 Drain electrode 11 n-type electrode 12 p-type electrode

Claims (7)

Forming a first nitride semiconductor film on a first substrate;
Forming a second nitride semiconductor film having a melting point higher than that of the first nitride semiconductor film on the first nitride semiconductor film;
Bonding a carrier substrate to the surface of the second nitride semiconductor film;
A wafer including the bonded first substrate, the first nitride semiconductor film, the second nitride semiconductor film, and the carrier substrate is higher than the melting point of the first nitride semiconductor film, and the Melting the first nitride semiconductor film by heat treatment at a temperature lower than the melting point of the second nitride semiconductor film;
Removing the first substrate;
Bonding a second substrate to the surface of the second nitride semiconductor film bonded onto the carrier substrate;
And a step of removing the carrier substrate.   2. The method for manufacturing a semiconductor wafer according to claim 1, wherein the first substrate is made of sapphire, silicon, or zinc oxide. 3. The semiconductor wafer manufacturing method according to claim 1, wherein the first nitride semiconductor film is made of Ga _x In _(1-x) N (0 ≦ x ≦ 1). 4. Manufacturing method. 4. The method of manufacturing a semiconductor wafer according to claim 1, wherein the second nitride semiconductor film is made of Al _y Ga _z In _(1-yz) N (0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ y + z ≦ 1). A method for producing a semiconductor wafer, comprising:   5. The semiconductor wafer manufacturing method according to claim 1, wherein the second substrate is made of polycrystalline silicon carbide, silicon, zinc oxide, indium tin oxide, or nickel. Manufacturing method.   6. The method of manufacturing a semiconductor wafer according to claim 1, wherein a heating temperature for melting the first nitride semiconductor film is in a range of 800 [deg.] C. to 1500 [deg.] C. Production method.   7. The semiconductor wafer manufacturing method according to claim 1, wherein the surface of the second nitride semiconductor film exposed by removing the carrier substrate is a group III surface. Wafer manufacturing method.

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