JP2003221298A - Seed crystal for growing zinc oxide, method and apparatus for growing zinc oxide seed crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine the shape of a seed crystal for growing a zinc oxide single crystal that has good efficiency and quality. <P>SOLUTION: When a single crystal is grown by a hydrothermal synthesis method using the seed crystal that is cut from the single crystal of zinc oxide, the m planes of the seed crystal grow into a crystal having good quality and other planes than the m planes produce crystal defect areas. Therefore, the planes that form the surfaces parallel to the c axis of the seed crystal are formed to have at least two m planes that are parallel to each other along any a axes. Moreover, the planes that form the surfaces parallel to the c axis of the seed crystal form a tetragon that is constituted by two m planes parallel to each other and two m planes along another a axis, or a hexagon that is constituted by six m planes. In particular, when the grown single crystal is cut into a c-cut wafer to form a light emitting device, the single crystal free from any defect area that is grown from the seed crystal having a regular hexagonal cross section is used. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc oxide growing seed crystal used for growing a zinc oxide single crystal that can be used for industrial purposes, and to prevent occurrence of a crystal defect region during single crystal growth. Seed crystals suitable for prevention.

[0002]

2. Description of the Related Art Conventionally, in semiconductor devices,
Semiconductor devices formed using amorphous silicon or polycrystalline silicon as a thin film material have been widely used. In recent years, zinc oxide (ZnO) has attracted attention as a thin film material. , For example, UV LED (LED: Light Emitting)
Diodes, laser diodes (LDs: Laser Diodes), transparent transistors, and other existing semiconductor devices are being applied, and research and development for new applications are underway.

By the way, in manufacturing a semiconductor device, it is known that the quality of a thin film formed on a base substrate has a significant influence on its electrical characteristics, optical characteristics, reliability (lifetime) and the like. Therefore, the better the quality of the thin film, the better the electrical and optical characteristics and the reliability.

Therefore, when forming a semiconductor device using ZnO as a thin film material, it is important to form a high quality ZnO thin film having no crystal defects on the base substrate. The factor that determines the quality of the thin film is the difference in the lattice constant between the thin film material and the base substrate material, and it is known that the smaller the difference in the lattice constant, the better the film can be formed without crystal defects. The lattice constant means the arrangement interval of atoms that are regularly arranged in the crystal.

When forming a semiconductor device having a ZnO thin film, a base substrate made of sapphire or the like having a lattice constant relatively close to that of a ZnO single crystal has been used. However, since the lattice constant of sapphire differs from that of ZnO single crystal by about 18%, it is necessary to form a thin film with a considerably larger thickness than usual in order to form a high-quality ZnO thin film on a base substrate formed of sapphire. However, in terms of profitability, industrial quality had to be compromised to some extent.

Therefore, for example, in order to inexpensively form a ZnO thin film of extremely high quality on a base substrate, the base substrate is formed by Z
It may be formed by using a ZnO single crystal having the same lattice constant as that of the nO thin film, but it has been impossible to grow a ZnO single crystal having a size that can be used as a base material by the conventional techniques. It was In growing a zinc oxide (ZnO) single crystal by a hydrothermal synthesis method, a seed crystal cut out from a zinc oxide single crystal is used, and the single crystal is grown from this seed crystal, but the crystal has an a-axis in a hexagonal structure. The crystal tends to grow selectively in the direction.

Generally, in order to form the above seed crystal from a zinc oxide single crystal, it is often cut out and used as shown in FIG. FIG. 8B is a seed crystal cut out from a zinc oxide single crystal, and FIG. 8C is a schematic diagram showing an example of a method for holding the seed crystal in the growth container. Note that FIG. 8A shows an outline of a zinc oxide single crystal belonging to the hexagonal system and its crystal axis. The crystal axis of the hexagonal system is the c-axis, and three a (1, 2,
3) A total of four axes.

First, a plate-shaped seed crystal is cut out from a zinc oxide single crystal so that the longitudinal direction is along the c-axis (parallel to the c-axis).
Next, the seed crystal plate was divided along the c-axis, and
Cut out the time signature type seed crystal shown in (b). Since almost no growth occurs in the c-axis direction when a single crystal is grown, the c-axis is cut out so as to be the longest. A ZnO seed crystal is mounted on the upper frame 61 in the growth container of the single crystal growth apparatus. For example, a seed crystal is grown by a method of suspending a ZnO seed crystal on a frame 61 using a noble metal wire (platinum wire) 62. The structure of the growing device used in the hydrothermal synthesis method will be described later.

In order to reduce crystal defects in the growth process,
The surface of the seed crystal needs to be a sufficiently clean surface, and the surface is finished by a polishing or lapping process, and a cleaning process is also carefully performed. In order to reduce these man-hours, it is desirable that the surface of the seed crystal is composed of as few faces as possible, and in many cases, it is a timepiece-shaped rectangular parallelepiped long in the c-axis direction as shown in FIG. .

The growth state of the seed crystal in the growth container is as follows. First, in the hydrothermal synthesis method, the growth rate in the c-axis direction is very slow, and growth cannot be expected so much. Next, the manner of growth in the direction perpendicular to the c-axis will be described with reference to FIG. The figure shows a cross section of the seed crystal at right angles to the c-axis, and schematically shows how the crystal is grown along the a-axis in the growing apparatus. As described above, since the hydrothermal synthesis method hardly grows in the c-axis direction, a plurality of seed crystals are bonded in the c-axis direction, or a sapphire substrate is attached with a ZnO thick film to form a seed crystal. Methods have been tried and proposed.

As an example in FIG. 8D, the seed crystal is shown in FIG.
The cross-sectional shape of the seed crystal 21 cut out as shown in (b) is
Two planes (1) parallel to the c-axis and one a-axis (a1 axis in the figure)
10, 110) and one a-axis (a1 in the figure) parallel to the c-axis.
It is a rectangle formed by two surfaces (120, 120) orthogonal to the axis. Here, only the phenomenon of crystal growth will be described, and the explanation will be given later regarding the form of the crystal lattice on each surface, the arrangement state of atoms and molecules, etc. In addition, normally, the plane 110 parallel to the c-axis and one a-axis (a1 axis in FIG. 8D) is
If a single crystal ideally grows, the cross-sectional shape perpendicular to the c-axis will be a regular hexagon surrounded by six m-planes.

A crystal grows around the seed crystal 21 in the growth container, and the surface 11 grows parallel to the surface of the surface 110.
In No. 5, the growth rate is fast, and there is a strong tendency that the size of the surface expands parallel to the surface 110. With respect to the molecular arrangement, a good crystal plane with few defects can be obtained. The arrangement of molecules on the surface 120 is irregular,
It cannot extend parallel to the plane parallel to the plane and parallel to the plane, and is also affected by this plane 120 and two a-axes (a2 and a3 axes in the figure) having a 30 ° inclination. A crystal defect region 44 in which the crystal growth direction is not defined and various transitions are included
It is easy to become.

On the other hand, at the end of the surface 115, crystals are grown along the surface of the crystal defect region 44 as if they were bent by 60 ° from the surface 115 under the influence of the a2 and a3 axes. Therefore, as the crystal growth progresses, a plane 112 parallel to the a2 axis and a plane 113 parallel to the a3 axis, which are equivalent to the relation of the plane 115 to the a1 axis, grow, and the crystal defect region 44 becomes an isosceles triangle and is sealed. It will be stopped. Surface 115, surface 11
2. When the seed crystal is covered by the plane 113 including the crystal defect region 44, the single crystals with few defects are a1, a2, and a after that.
It grows while forming a hexagon parallel to the three axes. That is, planes other than the m-plane of the seed crystal, for example, planes 120 and 120 orthogonal to any a-axis (inclined by 30 ° with respect to the other two a-axes).
In the vicinity of the surface of, the crystal defect regions 44, 44 are included.
Occurrence of crystal defect regions is recognized on the planes other than the m-plane to some extent.

[0014]

As described above, a crystal defect region occurs in the grown single crystal on the surface of the seed crystal other than the m-plane, and a quality defect is generated in the vicinity of the seed crystal in the central portion of the grown single crystal. Often includes bad parts. Since the poor quality part cannot be used, the yield of the cut wafers is a problem, the step of selecting good products is added, and the cost increase cannot be ignored.

Conventionally, a large single crystal for cutting out a seed crystal has not been available, and a plurality of seed crystals have been connected in the c-axis direction, or a ZnO thick film has been formed on a sapphire substrate and cut out. However, there were many drawbacks. It has been earnestly desired to obtain a ZnO seed crystal long enough in the c-axis direction.

It is an object of the present invention to supply a seed crystal in which a crystal defect region does not occur in the vicinity of the seed crystal in the grown single crystal, a method for growing the seed crystal, and a growth container.

[0017]

In order to solve the above problems, the present invention provides a seed crystal for growing zinc oxide, which is cut out from a single crystal of zinc oxide, and has a c-axis of the seed crystal. The planes forming the parallel surfaces provide a seed crystal for growing zinc oxide having at least two m-planes parallel to each other along any a-axis.

The planes forming the surface parallel to the c-axis of the seed crystal are the m-plane two planes parallel to each other along the arbitrary a-axis and the m planes along the other a-axis. A quadrilateral zinc oxide growing seed crystal composed of two faces,
The plane forming the surface parallel to the c-axis of the seed crystal also provides a hexagonal zinc oxide growing seed crystal composed of six m-planes.

Furthermore, the plane forming the surface parallel to the c-axis of the seed crystal is composed of six m-planes, and the cross section of the surface perpendicular to the c-axis is regular. It is a square. Further, the present invention is a seed crystal for growing zinc oxide, which is cut out from a single crystal of zinc oxide, and one surface of the surface shape constituting the seed crystal is a cylindrical surface whose central axis is parallel to the c-axis. A seed crystal for growing zinc oxide is also provided. .

According to the present invention, a zinc oxide single crystal for a nucleus which serves as a nucleus for growing a zinc oxide single crystal by reacting powder zinc oxide as a zinc oxide seed crystal raw material with hydrogen gas in a front container to reduce to zinc. Lead the reduced zinc into the rear container pre-inserted, supply oxygen gas into the rear container, of the zinc oxide seed crystal to grow a zinc oxide seed crystal with the nucleus zinc oxide single crystal as a nucleus Provide a training method.

Further, the present invention is characterized in that a powder zinc oxide as a zinc oxide seed crystal raw material is charged and a front container for supplying hydrogen gas to reduce to zinc and a zinc oxide for a nucleus serving as a nucleus of the zinc oxide seed crystal. A single crystal was charged, the zinc was introduced from the front container, and a rear container was provided to grow a zinc oxide seed crystal using the nucleus zinc oxide single crystal as a nucleus by supplying oxygen gas.
An apparatus for growing a zinc oxide seed crystal is provided.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Before starting the description of a seed crystal, an outline of a hydrothermal synthesis method will be described with reference to FIG. FIG. 2 is a diagram showing an example of a single crystal growth apparatus 51 using the single crystal growth container previously proposed by the applicant.

The single-crystal growing apparatus 51 shown in FIG. 2 includes an autoclave 52 capable of applying the temperature and pressure necessary for growing a ZnO single crystal by hydrothermal synthesis, and an autoclave 52. A growth container 60 is housed and used inside the container 52. The autoclave 52 is configured such that the container body of the autoclave 52 formed of, for example, iron as a main material, such as high-strength steel, is covered with a lid 54 with a packing 57 sandwiched between the container main body and the fixing portion 55 to fix the inside thereof. The structure is hermetically sealed.

The growth container 60, which is used by being housed in the autoclave 52, is made of, for example, platinum (Pt) and has a substantially cylindrical shape. And, a bellows 7 acting as a pressure adjusting portion is provided on the upper portion thereof.
0 is attached in a state where the inside of the growth container 60 is sealed.

In such a single crystal growing apparatus 51, the ZnO seed crystal 3 is hung using the frame 61 and the noble metal wire (platinum wire) 62 on the upper side in the growth container 60, and
The raw material 66 is arranged on the lower side thereof to grow the seed crystal 3. In this case, the ZnO seed crystal 3 and the raw material 66
An internal baffle plate 64 for controlling heat convection is provided between the and, and the inside of the growth container 60 is divided into a melting region and a growth region by the internal baffle plate 64.
A plurality of holes are formed in the inner baffle plate 64,
The opening area of the baffle plate 64, which is determined by the number of the holes, controls the counter flow rate from the melting region to the growth region to obtain a temperature difference between the melting region and the growth region.

Then, for example, sodium hydroxide (NaOH) and calcium carbonate (Na2) are placed in the growth container 60.
CO3), potassium hydroxide (KOH) or other strong alkaline solution is injected, and the autoclave 52 and the growth container 60 are used.
A heat transfer solution 67, such as pure water, is injected for heat transfer between the two and heating the autoclave 52 with the heaters 56, 56, ... A growth solution 71 in which the raw material 66 is dissolved in the solution is generated. Then, the growth solution 71 is supplied to the growth region through the internal baffle plate 64, and Zn
The O seed crystal 3 is grown.

Further, the single crystal growth apparatus 51 shown in FIG.
Then, an external baffle plate 65 is provided outside the growth container 60. With this external baffle plate 65, the growth container 6 is provided.
By limiting the convection outside 0, the temperature difference necessary for growing the ZnO seed crystal 3 is obtained between the regions in the growth container 60.

A bellows 70 is provided on the upper part of the growing container 60 as a pressure adjusting portion, and the expansion and contraction of the bellows 70 balances the internal pressure and the external pressure of the growing container 60.

Such a single crystal growing apparatus 51 can grow a ZnO single crystal from a seed crystal by a hydrothermal synthesis method. Almost no impurities are mixed in the growth container 60, and a ZnO single crystal having a diameter size that can be used for industrial purposes can be grown.

An example of the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram schematically showing an example of the shape of a seed crystal of zinc oxide (ZnO) according to the present embodiment. The ZnO single crystal is a hexagonal crystal, and has a c-axis 42 as a crystal axis and three a (1, 2, 3) axes 43 which form an angle of 120 ° with each other in a plane perpendicular to the c-axis 42. Exists. FIG. 1A shows a perspective view of a ZnO single crystal 40 from which a seed crystal is cut out. First, as shown in FIG. 1A, a ZnO single crystal thin plate 46 is cut out from a ZnO single crystal 40 so as to be parallel to a c-axis 42 and one a-axis 43 (a1 axis in the figure). The seed crystal 21 is formed from the thin plate 46, and the shape of the seed crystal with few crystal defect regions is shown in the same drawing (b to h) as a cross section perpendicular to the c-axis.

A plane parallel to the c-axis and an arbitrary a-axis is called an m-plane, and a plane parallel to the c-axis on the surface of the single crystal is formed by the above-mentioned m-plane. As described above, it is known that the crystal grown based on the m-plane of the seed crystal has few defects and a high growth rate. Therefore, if the plane parallel to the c-axis on the surface of the seed crystal is formed by the above-mentioned m-plane, the crystal grown from the m-plane will have good quality and the growth will be fast. Since the seed crystal is cut out in the longitudinal direction parallel to the c-axis, if a cross section perpendicular to the c-axis of the seed crystal is taken, the outer peripheral line (outline of the cross section) that defines this cross-sectional shape is the c-axis of the seed crystal. It is the line of intersection of the parallel plane and the plane of the cross section. That is, in the outline of the cross section of the seed crystal, a (1
~ 3) A line parallel to any of the axes indicates that the surface is the m-plane.

The most ideal shape of the seed crystal is a seed crystal 21b having a regular hexagonal cross section, which is formed so that all six surfaces are m-planes, as shown in FIG. Two parallel m-planes of 110, 110 parallel to each other along the a1 axis, two parallel m-planes of 112, 112 along the a2 axis, and 113, 113 along the a3 axis. It is composed of two m-planes parallel to each other, a total of 6 m-planes.
Stable growth can be expected for a single crystal grown from a seed crystal having a regular hexagonal cross section. Since the length of the outline of the cross section (width of the m-plane measured at right angles to the c-axis) may be arbitrarily changed,
The shape of the same system need not be a regular hexagon, but may be a thin plate-like seed crystal 21c as shown in FIG. 6C or a hexagon as shown in FIG. Here, these are collectively called a hexagon. These shapes require a large number of man-hours for the grinding / polishing process for forming each m-plane and are costly, but the quality of the single crystal obtained from the regular hexagonal seed crystal 21b is particularly highest.

Next, in the case of the two sets of parallel m-planes shown in FIGS. 3D and 3E, one of the three sets of m-planes has a side length of 0. You can think that it has become. In principle, these seed crystals 21d and 21e have no crystal defect region in the m-plane only, like the hexagons. That is, (d) is the two m-planes of 110 and 110 parallel to each other along the a1 axis,
a, m of two 113, 113 parallel to each other along the 3 axis
It is a quadrilateral (parallelogram) composed of four faces,
(E) is a quadrilateral consisting of four m-planes of 110 and 110 parallel to each other along the a1 axis and two m-planes of 112 and 112 parallel to each other along the a2 axis. is there.

The seed crystals having these parallelogram cross sections are
A large number of seed crystals can be attached to a simple attachment jig, and grinding and polishing processes for seed crystal formation can be performed at the same time, which can reduce the number of polishing steps and the quality and seed of the obtained single crystal. The cost of crystals is balanced and the practicality is high. Also,
The seed crystal 21f shown in FIG. 6F, which is composed of a pair of parallel m-planes and two separate m-planes, is also considered to be a variation of this example.

In the case of the seed crystal 21c shown in FIG.
Two m-planes (1 parallel to each other) along one a1 axis
10 and 110) are close to each other, the m-plane (11
(2, 113, 112, 113) gradually becomes shorter. That is, it is very close to the same figure (h) with the planes 120 orthogonal to the a1 axis at both ends. In the plane 120, FIG.
Although a crystal defect region is generated as shown in FIG. 5D, if the plate thickness of the seed crystal becomes thin to some extent, the isosceles triangle of the crystal defect region 44 shown in FIG. 5D becomes very small. The defect region does not affect the yield of the grown single crystal and can be practically ignored. As described above, when the seed crystal has a thin plate shape with a rectangular cross section, it is practically usable even if at least two wide surfaces are m-planes parallel to each other and the other surfaces are not m-planes. As a thin thin plate, a plane 2 planes (12 planes) orthogonal to a pair of parallel m planes (110 110) like a seed crystal 21h shown in FIG.
0, 120) to reduce the cost of seed crystal processing.

Here, the reason why a crystal plane with few defects grows on the m-plane will be described with a steel ball model. The steel ball model is a steel ball having a diameter equal to the lattice constant (distance of the crystal lattice) arranged at lattice points instead of the molecules or atoms constituting the crystal. First, referring to FIG. 3, a hexagonal single crystal structure in a steel ball model will be described. FIG. 3 (a) shows a hexagonal steel ball arranging method as a perspective view, and FIG. 3 (b) shows a steel ball model projected from the + c-axis direction, showing the degree of overlap between layers A and B. It is a thing. Since the lattice constant is indicated by K in FIG. 3B, the steel balls having a diameter K are regarded as atoms or molecules of crystals and arranged so that there are no gaps (the surfaces are in contact with each other).

The hexagonal single crystal is formed by alternately superposing A layers and B layers. The lowermost diagram of FIG. 3A shows seven steel balls (A1, A2, ...
・ A7) is taken out and drawn. These steel balls are arranged in innumerable numbers on one plane while being in contact with each other to form an A layer. The seven steel balls are centered around A1 and have A2 around their outer circumference.
.. If six steel balls of A7 are in contact with the adjacent steel balls and the centers of the steel balls are connected, a regular hexagon with one side length K is formed.
Usually, a parallelogram connecting the centers of the A-layer steel balls A1 to A4 shown in FIG. The minimum component is an equilateral triangle connecting the centers of the steel balls A1 to A3, and the length of one side of the equilateral triangle is the lattice constant (K). Crystal axes a1, a
2 and a3 are straight lines passing through the centers of three steel balls on one straight line. The axes a1, a2, a3 are perpendicular to the c-axis and are 1
They are separated by 20 ° and are perpendicular to the c-axis. The three a-axes are equivalent to each other, and the crystal is centered on the c-axis.
When rotated by 0 °, each a-axis overlaps (there is no restriction on the axis direction).

When the steel balls are arranged so as to contact the three adjacent steel balls of the A layer, the B layer is formed. For example, the steel balls B1 of the B layer are arranged in a recess formed by the three steel balls of the A layer so as to contact the steel balls (A1, A2, A3) of the A layer. In the same figure (b), the center of the steel ball B1 is the point of reference numeral OB1. Similarly, the steel ball B2 is in contact with the steel balls (A1, A4, A5) of the A layer, and the center of the steel ball B2 is a point indicated by the symbol OB2. Also,
Steel ball B3 is in contact with steel balls (A1, A6, A7), and steel ball B3
The center of is the point OB3. The steel balls forming the B layer are also in contact with each other and arranged innumerably on one plane to form the B layer. A
The centers of the steel balls forming the layers are respectively OB1, OB2, and O.
If you move to B3 ...

A second A layer is disposed on the B layer. When viewed from the + c-axis direction as shown in FIG. 7B, the first steel ball of the A layer and the second steel ball of the A layer appear to overlap each other. That is, steel ball A12 is on steel ball A2, and steel ball A14 is on steel ball A4.
It overlaps with ... Furthermore, a second layer is formed on this second layer A.
B layer is arranged, but the first B layer and the second B layer are also +
When they are viewed from the c-axis direction, they are arranged at positions that completely overlap. In this way, the hexagonal crystals are arranged. In addition,
In the case of a steel ball that is considered to be a rigid body, the lattice constant along the c-axis is 1.633K, but the actual crystal shows a slightly different value.

Here, the plane that is usually found in a hexagonal single crystal will be described. The main plane for growing a crystal is the plane parallel to the c-axis and one a-axis (called the m-plane), and the contrast is parallel to the c-axis and orthogonal to one a-axis. It is the side to do. It has already been described that a single crystal grows smoothly on the m-plane, the growth rate is high, and a crystal defect region is likely to occur on a plane parallel to the c-axis and orthogonal to one a-axis. Steel balls are arranged most densely on a plane orthogonal to the c-axis (parallel to the a-axis). Steel balls that are adjacent to each other with a minimum gap contact each other. The state is shown in FIG. 3B, and the steel ball density (the number of steel balls in the unit plane) is maximized.

The plane parallel to the m-plane and the c-axis and orthogonal to the single a-axis will be described with reference to FIG. The figure is a projection of a steel ball model near the crystal surface. The last 1 in the figure suffix is +
2 is a side view showing a cross section taken along the line AA, and 3 is a front view of the crystal surface as seen from the outside. Although it does not change in the steel ball model, in actual crystals, the lattice constant of the layer close to the surface is different from that of the inside, and the distance between molecules is usually different.

FIG. 4 (a) shows m parallel to the c-axis and one a-axis.
The case where the surface 110 is a surface is shown. Here, in the figure (a1),
As indicated by a chain line in (a2), the surface of the crystal (m-plane 1
Let 10) be the surface that passes through the center of the steel ball arranged at the outermost side. As shown in (a2) of the figure, a total of a steel ball A21 of the A layer located on the surface, a steel ball equivalent to the steel ball A21 of the lower A layer, and a steel ball B21 of the B layer arranged slightly inside is measured. Three pieces are cross-sections, and in the figure, the steel balls of layer A (the equivalent row of steel balls) form the outermost part of the surface of the crystal, and the steel balls of layer B are arranged so as to be pulled inward and arranged in one row. It forms a depression.

When a steel ball B20 corresponding to ZnO molecules is supplied from the outside and is approached and captured by the surface, the steel ball B20 falls into the recess between the two rows of the A layer, and the steel ball of the A layer 2 at the position indicated by the chain line. It occupies a stable position in contact with two steel balls of layer B. A new B layer is formed by attaching the steel ball B20 to the surface, the surface moves outward by about 60% of the diameter of the steel ball, and crystals grow. Steel balls are arranged one after another at the same position as steel ball B20,
When the cavities of the B layer are completely filled, the B layer becomes the crystal surface and the A layer is at the position where it is pulled inward, but the shape of the entire surface is that the A layer and the B layer are simply exchanged. a
It has the same shape as 1 to a3). Even if steel balls (molecules) are attached one after another, the arrangement of steel balls does not change, and the lattice constant K and the lattice constant in the c-axis direction (1.633K for steel balls) always appear as they are. It can be seen that the surface is in a state where defects are less likely to occur. It is also considered that the fast crystal growth is because the shape of the molecular arrangement and the lattice constant do not change and the molecules are stably attached to the surface.

FIG. 6B shows a plane 120 parallel to the c-axis and orthogonal to the a-axis. Similar to (a), the surface that passes through the center of the steel ball disposed on the outermost side of the crystal is the surface 120.
Is indicated by a one-dot chain line. As shown in (b1) of the figure, the distance between the two steel balls of the A layer located on the surface is significantly different from the lattice constant K (1.732K), and the two steel balls of the A layer are in the same plane B. One layer of steel balls is wedge type, and it is in a position where it is drawn in between the two wedge types in a position in contact with the surface.
Two layer steel balls and one layer B steel ball (indicated by a dashed line) form a wedge-shaped mold of the same shape, and are drawn to a position in contact with the surface to face the outside. Since zigzag grooves are repeatedly arranged on this surface 120 and the lattice constant is different from the original lattice constant at a position where molecules are easily trapped, each molecule becomes a self-arranged array and growth of a regular molecular array is difficult to occur. The surface is apt to cause crystal defects.

At the actual molecular level, the surface 1
It is considered that 20 is not formed as a wide surface, and m-planes along each a-axis that is a cleavage plane are irregularly arranged on the surface. Therefore, crystals grow at right angles to the individual m-planes, and as they grow, they interfere with each other to form crystal defect regions.

At the edge of the plane, the crystal growth direction changes as if it was strongly influenced by the other a-axis than the a-axis parallel to the current surface. For example, when the steel ball A20 at the right end in FIG. 4 (a1) is the end of the plane of the seed crystal, the influence of the a3 axis becomes stronger than the a1 axis, and the surface tends to grow in a direction parallel to the a3 axis. Therefore, as shown in FIG. 5D, the surface is bent from the surface 115 to the surface 113 in the direction parallel to the a3 axis, and the m-plane grows. When the m-plane completely covers the crystal defect region of the seed crystal surface layer, the m-plane grows thereafter as a normal m-plane. As described above, as the number of m-planes increases on the surface parallel to the c-axis of the seed crystal from the plane of single crystal growth, the crystal with fewer defects grows faster.

From this point, when the shapes of the seed crystals shown in FIGS. 1 (b to g) are reviewed, all the seed crystals 21b to 21g) are c.
The surface parallel to the axis is composed of only the m-plane. In order to reduce the seed crystal polishing step, if the seed crystal 21 (d, e) is a parallelogram, a large number of isomorphic seed crystals can be simultaneously attached to a simple jig to obtain a large number of seed crystals in one polishing step. You can The seed crystal shown in FIG. 1 (h) includes a plane 120 perpendicular to the a-axis, but by shortening the length of the plane 120 perpendicular to the a-axis with respect to the length of the m-plane 110 parallel to the a1-axis. The size of the crystal defect region can be reduced to such an extent that there is no practical problem. In this way, the seed crystal 21h has a surface 1 other than the m-plane.
If the length of 20 is made as thin as possible, the occurrence of crystal defect regions can be minimized.

By the way, when a ZnO single crystal is actually grown by the hydrothermal synthesis method using the seed crystal described above,
It is recognized that there is a difference in the quality of the grown single crystal depending on the shape of the cross section of the seed crystal perpendicular to the c-axis. In particular, a wafer was cut out from the grown ZnO single crystal at a right angle to the c-axis (c
(It is called “cut”), and when it is further subdivided and used as it is as a light emitting element, it appears remarkably. On the surface of the seed crystal other than the m-plane, a crystal defect region occurs in the grown single crystal,
Although it has already been explained that a poor quality portion is often included in the vicinity of the seed crystal at the center of the grown single crystal, the influence of this crystal defect region is quite wide and, for example, as shown in FIG. Not only the equilateral triangular crystal defect region 44, but also a considerable part of the outer periphery thereof is a region in which the light emitting element is unwell.

Photoluminescence (Photoluminescenc
e) The intensity distribution can be used as a quality evaluation method when a ZnO single crystal is used as a light emitting element. Briefly describing photoluminescence, it is a phenomenon in which a substance is stimulated by radiation such as visible light and ultraviolet light, and emits light having a longer period (the light is called fluorescence or phosphorescence). FIG. 5A schematically shows the intensity distribution of light emission corresponding to the photon energy on the horizontal axis when the c-cut ZnO is selectively irradiated with a laser. The ideal photoluminescence characteristic is shown by a curve drawn by a broken line, and has a peak near 3.3 eV. The wavelength of this peak is about 375 nm in the ultraviolet region.
Which is the wavelength required to realize the ultraviolet light emitting device.

FIG. 5B shows a sample of c-cut ZnO.
Figure 3 shows a schematic view of a surface that has been cut and polished perpendicular to the c-axis. A substantially square seed crystal 21 is provided at the center, and isosceles crystal defect regions 44 are formed on the left and right non-m-planes. Furthermore,
It was recognized that the seed crystal peripheral portion 92 inside the outer peripheral surface 91, which was divided into hexagons by the broken line, was a portion with many crystal defects that was unsatisfactory as a light emitting element, and the outside thereof was a substantially good crystal portion. In FIG. 5A, A indicates the characteristics of the peripheral portion considered to be a good quality crystal portion, and B indicates the characteristics of the peripheral portion of the seed crystal. In the measured ZnO crystal, the cause of the contamination of impurities and the oxygen defect was not completely removed, and both A and B had low peak values near 3.3 eV, but the decrease of B was particularly large.

In the growth of a single crystal of ZnO belonging to the hexagonal system, a seed crystal peripheral portion having many crystal defects exists in a fairly wide area centered on the seed crystal 21 and the crystal defect region 44, and ZnO in this portion is present. Single crystals cannot be used as light emitting devices. This indicates that the yield of wafers for manufacturing light emitting devices is significantly deteriorated. Further, it is considered that a good quality crystal part 93 is not formed unless the outer peripheral surface 91 of the part having many crystal defects is formed into a substantially regular hexagon.

Taking all of these into consideration, the cross-sectional shape of the seed crystal in consideration of the yield when a ZnO single crystal is used as a light-emitting element is shown in FIG.
(B) has the same shape) is optimal. However, as described above, polishing the outer shape of the seed crystal of ZnO having a regular hexagonal cross section has many disadvantages in terms of cost, such as an increase in the number of steps. As one expedient, as shown in FIG. 6 (b), which is a schematic drawing of a cross section perpendicular to the c-axis of the seed crystal, the central axis is parallel to the c-axis as a surface constituting the surface shape of the seed crystal. If a columnar shape is adopted, polishing and other processes can be performed mostly by machining. Since machining similar to cylindrical polishing can be done until finishing, compared to all the seed crystals other than the cylindrical shape requiring a processing method similar to plane lapping, complete automation is easy and processing cost can be expected to be reduced. . The surface shape of the seed crystal is not particularly limited except for the above-mentioned cylindrical surface portion. The planes corresponding to the upper and lower bottom surfaces of a normal cylinder may be the crystal planes of the single crystal as they are, but it is preferable in terms of machining that the planes are machined into planes perpendicular to the c-axis in advance.

At one point on the cylindrical surface, the angle between the tangent to the cylindrical surface passing through the point and the m-plane is the error angle between the cylindrical surface and the m-plane.
The maximum error angle is 30 ° at the intersections 94 (6 places) of the m-planes passing through the a1 to a3 axes on the cylindrical surface, and is 0 ° at the minimum at each midpoint separated from the three a axes by 30 °. Becomes At least the shaded portion in the figure becomes the crystal defect region 95, but since the change in the error angle is gentle near the point of error 0, the m-plane is likely to be formed over a wide range early. Therefore, the regular hexagonal outer peripheral surface 91 which covers the crystal defect region 95 relatively quickly is obtained, and a good quality crystal portion is formed on the outside thereof. Compared with a seed crystal having a regular hexagonal cross section, the existence of some crystal defect regions may be covered by the low cost of machining the seed crystal.

Conventionally, it has been very difficult to obtain a large single crystal as a seed crystal, and a plurality of single crystals cut out from a small single crystal are joined together in the c-axis direction, or Z is formed on the surface of a different substrate.
Efforts were made to obtain even larger seed crystals by growing thick nO films. As described above, the ideal seed crystal is a ZnO single crystal that is long in the c-axis direction and has a hexagonal column-shaped cross section perpendicular to the c-axis. Next, a method for growing a ZnO single crystal that can be used as a seed crystal by the vapor phase growth method will be described.

The chemical vapor deposition method (Chemical Vap
As a method for growing a ZnO single crystal by (or Deposition), a method which should be called a chemical vapor transport method is adopted, which will be described with reference to FIG. FIG. 7 shows Zn by the chemical vapor transport method.
An example of a growth container 80 for growing an O seed crystal is shown as a schematic cross-sectional view.

The growth container 80 has a shape in which the front container 80a and the rear container 80b are combined, and the internal gas can communicate with each other through the communication hole 85. In the figure, as an example, these containers have a cylindrical shape, and the rear container 80b is provided with a communication hole 86 to the outside. A pipe 83 penetrates the front container 80a and a pipe 84 penetrates the rear container 80b so that gas can be supplied from the outside.
In advance, a sintered ZnO powder 87, which is a raw material of a ZnO seed crystal, is charged in the front container 80a, and a ZnO single crystal 88 for a nucleus, which is a seed crystal nucleus, is charged in the rear container 80b. There is.

About 1 part of ZnO powder 87 in the front container 80a is added.
It is placed in a high temperature atmosphere near 300 ° C., hydrogen gas (H ₂ ) as a reducing gas is flown through the pipe 83, and sprayed onto the ZnO powder. At high temperature ZnO is deprived of oxygen and reduced,
n and H ₂ O.

The released Zn is introduced into the rear container 80b through the communication hole 85. Pipe 8 in the rear container 80b
Oxygen gas (O ₂ ) is supplied via 4. Free Z
n and oxygen are deposited as a single crystal with the single crystal 88 as a nucleus,
A ZnO single crystal 89 is grown. According to this chemical vapor transport method, the growth direction of the c-axis of the single crystal 89 is induced in the flow direction of the air flow, and a high-purity ZnO single crystal (product seed crystal) long in the c-axis direction is obtained. Further, according to this chemical vapor transport method, there is a high probability that an ideal seed crystal whose c-cut plane is close to a regular hexagon is obtained. In this way, the reduction and single crystal growth are separated into a dedicated growth container, so that the seed crystal can be efficiently grown. Since these reactions can be performed near atmospheric pressure, the pressure in the container 80 can be atmospheric pressure. Further, there is no danger if the excess hydrogen gas is discharged after being burned by an igniter connected to the communication hole 86 with the outside.

By slicing a single crystal grown using such a seed crystal, a ZnO wafer having a good yield is obtained, and a substrate having a size sufficient for industrial use is obtained as a final product. Also, a single crystal may be mass-produced by using a seed crystal cut out from this single crystal.

Therefore, if such a ZnO wafer is used as a base material and a ZnO thin film is formed on this base material, a ZnO thin film of extremely high quality can be formed. Therefore, if such a ZnO single crystal is used as a base material and a ZnO thin film is formed on this base material to form a semiconductor device such as an ultraviolet LED, a laser diode, or a transparent transistor, electrical and optical It is possible to realize a semiconductor device having excellent characteristics and reliability.

[0061]

As described above, the seed crystal for growing zinc oxide, which is cut out from the zinc oxide single crystal of the present invention, has a thin plate shape in which at least two wide surfaces are m-planes parallel to each other. , The size of the crystal defect region is such that the yield phenomenon can be practically ignored even if the others are composed of other than the m-plane,
It has the effect of minimizing the cost of seed crystal processing.

Also, the cross section of the seed crystal was defined as two m-planes and another a
A seed crystal having a parallelogram cross section composed of two m-planes along the axis can provide a seed crystal with relatively low processing cost. Furthermore, if a hexagonal seed crystal composed of six m-planes is used, all of them can be composed of m-planes, so that a zinc oxide single crystal of even more stable quality can be obtained.

As a cross-sectional shape of a seed crystal when a ZnO single crystal is used as a light-emitting element, a seed crystal having a cross section close to a regular hexagon whose m-plane lengths are almost equal to each other is theoretically It does not occur, and a high quality crystal part is formed in the immediate vicinity of the seed crystal surface, which is optimal. In order to reduce the cost of machining a seed crystal with a regular hexagonal cross section, a cylindrical seed crystal whose axis is parallel to the c-axis is very easy to form by polishing or other means. It is excellent in that the processing cost of the seed crystal is low. The thickness of the crystal defect region is also small, and a regular hexagonal outer peripheral surface is obtained relatively quickly to form a good quality crystal portion. Compared with a seed crystal having a regular hexagonal cross section, some poor yield has an advantage that it is canceled due to low machining cost.

Furthermore, since a high-quality ZnO single crystal can be obtained, it can be expected to improve the electrical / optical characteristics and reliability of semiconductor devices such as ultraviolet LEDs, laser diodes and transparent transistors. Is.

By adopting the chemical vapor transport method to self-produce the seed crystal, a ZnO single crystal long in the c-axis direction and having high purity can be easily obtained from the sintered ZnO powder, and the seed crystal is easily produced. The advantages of making it available to Further, it is also a great effect that the growth container can be divided into a front part container for zinc oxide reduction and a rear part container for single crystal growth to grow a good quality zinc oxide single crystal for seed crystals.

[Brief description of drawings]

FIG. 1 is a schematic view showing various cross sections of a seed crystal cut out from a ZnO single crystal.

FIG. 2 is a cross-sectional view of a single crystal growth apparatus used in a hydrothermal synthesis method.

FIG. 3 is a schematic view by perspective view and orthographic projection for explaining a hexagonal crystal state, a crystal lattice, and a crystal axis by a steel ball model.

FIG. 4 is a schematic diagram showing the molecular arrangement of the seed crystal surface in two directions parallel and at right angles to the a-axis as a projection view of a steel ball model.

FIG. 5 is a schematic diagram showing a measurement result of photoluminescence intensity of a ZnO single crystal and a measurement position of a cross section of the single crystal.

FIG. 6 is a diagram schematically showing regular hexagonal and circular cross-sectional shapes of a ZnO seed crystal.

FIG. 7 is a cross-sectional view showing one form of a growth container for growing a ZnO seed crystal using a chemical vapor transport method.

FIG. 8 is a schematic diagram illustrating a conventional method of cutting a seed crystal from a zinc oxide single crystal and a crystal defect region generated in the vicinity of the seed crystal.

[Explanation of symbols]

3, 21 seed crystal, 10, 20, 40 ZnO single crystal, 42 c-axis, 43, a-axis (a1 to a3), 44, 9
5 crystal defect region, 45 crystal lattice (unit cell), 51
Single crystal growing device, 52 autoclave, 54 lid, 55 fixing part, 56 heater, 57 packing,
60 growth container, 61 frame, 62 platinum wire, 64
Inner baffle plate, 65 Outer baffle plate, 66 raw material, 67 heat transfer solution, 70 bellows, 71 growing solution, A1, A2, ... Steel balls forming layer A, B1,
B2, ... Steel balls constituting layer B, 110 m-plane of seed crystal, 112, 113, 115 single crystal surface (m-plane),
Planes perpendicular to the a-axis of 120 seed crystals, OB1, OB2, O
B3 Projected position of center of steel ball constituting B layer, K lattice constant, 80 growth container, 80a front container, 80b rear container, 83 pipe, 84 pipe, 85, 86 connecting hole, 87 ZnO powder, 88 for nuclear ZnO single crystal, 89
ZnO single crystal (seed crystal ... product), 91 outer peripheral surface,
92 seed crystal peripheral part, 93 good quality crystal part 94 m
Intersections of faces (6 places),

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Yoshioka             5-6-11 Chuo, Ota-ku, Tokyo TEPCO             Nami Co., Ltd. (72) Inventor Hiroshi Yoneyama             5-6-11 Chuo, Ota-ku, Tokyo TEPCO             Nami Co., Ltd. (72) Inventor Yutaka Shimizu             5-6-11 Chuo, Ota-ku, Tokyo TEPCO             Nami Co., Ltd. (72) Inventor Koji Horikawa             5-6-11 Chuo, Ota-ku, Tokyo TEPCO             Nami Co., Ltd. F term (reference) 4G077 AA02 BB07 CB03 ED02 HA02                       HA12 KA01 KA03 KA07 KA11

Claims (7)

[Claims] 1. A zinc oxide growing seed crystal cut out from a zinc oxide single crystal, wherein planes forming a surface parallel to the c-axis of the seed crystal are parallel to each other along arbitrary a-axes. A seed crystal for growing zinc oxide, which has at least two faces. 2. The planes forming the surface parallel to the c-axis of the seed crystal are the two m-planes parallel to each other along the arbitrary a-axis and the m planes along the other a-axis. The seed crystal for growing zinc oxide according to claim 1, wherein the seed crystal is a quadrangle composed of two faces. 3. The oxidation according to claim 1, wherein the plane forming the surface parallel to the c-axis of the seed crystal is a hexagon composed of six m-planes. Seed crystals for growing zinc. 4. The plane forming the surface parallel to the c-axis of the seed crystal is composed of 6 m-planes, and a cross section of the surface perpendicular to the c-axis is a regular hexagon. The seed crystal for growing zinc oxide according to claim 1, wherein 5. A seed crystal for growing zinc oxide, which is cut out from a single crystal of zinc oxide, wherein one surface of the surface shape constituting the seed crystal is a cylindrical surface whose central axis is parallel to the c-axis. A seed crystal for growing zinc oxide, characterized in that 6. A zinc oxide single crystal for nuclei, which is a nucleus for growing a zinc oxide single crystal, by reacting powdered zinc oxide, which is a zinc oxide seed crystal raw material, with hydrogen gas in a front container to reduce to zinc. In a pre-inserted rear container, the reduced zinc is introduced, oxygen gas is supplied into the rear container, and a zinc oxide seed crystal is grown with the zinc oxide single crystal for nuclei as nuclei. Method for growing zinc oxide seed crystal. 7. A front container for charging powdered zinc oxide, which is a raw material for zinc oxide seed crystals, and supplying hydrogen gas to reduce to zinc, and a zinc oxide single crystal for nuclei which serves as nuclei of the zinc oxide seed crystals. Introducing the zinc from the front container, and supplying an oxygen gas, the rear container for growing a zinc oxide seed crystal with the zinc oxide single crystal for nuclei as a nucleus, the oxidation characterized by the following: Zinc seed crystal growth device.