JP3296148B2 - Wafer and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SAW (surface acoustic wave element), a thermistor, and a semiconductor device (transistor,
The present invention relates to a diamond wafer that can be used as a sensor, a diode) substrate, a pressure-resistant disk, a disk protective film, an X-ray window, and the like, and a method of manufacturing the same. Diamond has a very high sound speed determined by the ratio of Young's modulus to density. Therefore, the speed of the surface acoustic wave is also extremely high. It is expected as a SAW substrate element. The SAW has applications such as a filter, a phase shifter, and a convolver.

[0002] Diamond has excellent physical and chemical properties. However, large-area, inexpensive materials cannot be obtained. Ultra-high pressure synthesis can produce bulk diamond, but only small particles. Small particles of at most a few mm square. At most it is 1 cm square. Only small things can be manufactured. Therefore, there is not yet a thin wafer having a large area like a diamond wafer. It suffices if a thick single crystal ingot such as Si or GaAs can be pulled up by the Bridgman method, but diamond cannot do this. Diamond wafers made of bulk crystals cannot be manufactured.

In order to be usable in the field of electronics, a wafer having a diameter of at least 1 inch is required. It is highly desirable that wafers having a diameter of 2 inches, 3 inches or 5 inches can be manufactured. Further, in order to get on a device production line, the thickness needs to be 1 mm or less. A polycrystalline diamond wafer of 1 inch or more and 1 mm or less is urgently desired. Furthermore, it would be more convenient if a single crystal diamond wafer could be made. The reason why an element having stable characteristics can be manufactured using a Si semiconductor or a GaAs semiconductor is that a high-quality single crystal wafer is present.

[0004]

2. Description of the Related Art Diamond is formed into a thin film by a vapor phase synthesis method. This is a method in which a raw material gas is flowed on a suitable heated substrate to vapor-grow a diamond thin film. At least hydrogen gas and hydrocarbon gas, or a gas containing boron in the gas, a gas containing nitrogen is introduced as a source gas, and given to a heated substrate,
A thin film is synthesized by a chemical reaction, and this is deposited on a substrate. Several methods are known for exciting the gas. There are a hot filament method, a microwave plasma CVD method, a high frequency plasma CVD method, a DC plasma jet CVD method and the like. Depending on the method, a diamond film having a large area can be produced. However, since the synthesis rate is slow, it is difficult to make a very thick film. If you take the time, you can make quite thick films.

However, at present, there is no such thing as a diamond wafer. There is no polycrystalline diamond wafer. Furthermore, there is no single crystal wafer at all. Since large bulk single crystal diamonds cannot be grown, wafers made entirely of diamond cannot, of course, be made. A complex wafer in which a diamond thin film is formed on a suitable substrate wafer.
Could be produced. Even after the film is formed, the film is not removed, and a composite wafer of the substrate and the film is formed. Several techniques have already been proposed for heteroepitaxial growth of diamond. For example, JP-A-63
-224225, JP-A-2-233391, and JP-A-4-132687.

[0006] It is said that they grow a diamond single crystal on a single crystal SiC substrate, a Si substrate, a nickel substrate, and a cobalt substrate. In the case of an electronic material or a wear-resistant disk, it is often the case that only the properties of the surface portion are used. Therefore, there are many cases where such a compound is acceptable. However, even with such a compound wafer, there is no industrially available diamond wafer at present.

[0007]

The reason is that polishing cannot be performed. The diamond film grown by vapor phase has irregularities. Must be smoothed by polishing. Even Si wafers are cut from an ingot and polished to a mirror surface. Diamond wafer
The same is true, however, and the surface must be mirror-like. But cannot be polished. Why can't you grind? One reason is that diamonds are extremely hard. However, it can be polished using diamond abrasives under pressure and over time. Since the abrasive and the object to be polished are made of the same material, they are referred to as scraping.

[0008] There are fatal difficulties. The polishing apparatus attaches a wafer to a flat holder, presses the wafer against a flat polishing plate (polishing platen), rotates the holder around the shaft, revolves the polishing platen, and releases free abrasive grains or The lower surface of the wafer is shaved by the action of the fixed abrasive. The resulting mirror wafer must be flat, so a flat holder is of course used.
In the case of a Si wafer, an 8-inch wafer can be successfully polished. Since it is a composite film composed of a substrate and a diamond thin film, there is a difference in the coefficient of thermal expansion. Cooling after synthesis results in strong thermal stress. There is also an intrinsic stress of the film itself. Depending on the manufacturing conditions, a film having a convex surface (convex warpage), a film having a concave surface (concave warpage), and a flat film can be obtained. In any case, even if pressure is applied and polishing is performed for a long time, a portion that cannot be polished remains.

As shown in FIG. 9, in the case of concave warpage, an unpolished portion remains in the middle of the wafer. It is natural that the periphery is cut off. Since the wafer is pressed with a strong pressure, the center portion contacts the polishing plate. However, the intermediate portion cannot contact the polishing plate and is not polished. In the case of convex warpage, a wide unpolished portion remains on the outer periphery of the wafer. If there is no warp, it seems that it can be polished neatly. But not so. Even if there is no warp, there is actually a twist, and unpolished portions remain randomly. In any case, the conventional polishing apparatus cannot polish the entire diamond composite material uniformly.

[0010]

According to the present invention, a diamond film is formed by vapor phase synthesis on a convexly warped surface of a single crystal substrate made of a material other than diamond, which is originally convexly warped, and the surface is inclined. Affixing the substrate to the holder
Is polished while tilting, and the surface roughness is Rmax500Ｒ (50
nm) or less, and is polished so that Ra 200Å (20 nm) or less. Diamond thickness is 2μm
To 150 μm, preferably 10 μm to 50 μm. For heteroepitaxial growth, it is effective to apply a negative bias to the substrate in the early stage of the growth to increase the ratio of hydrocarbon / hydrogen. Later, the hydrocarbon / hydrogen ratio is reduced.

The vapor phase synthesizing method used for forming a thin film includes a filament CVD method, a plasma CVD method, a microwave plasma CVD method, a flame method and the like. Pressure is 1 Torr
~ 300 Torr. The raw materials for synthesizing diamond are hydrogen gas and hydrocarbon gas. Hydrogen and hydrocarbons are mainly used as raw material gases in the case of diamond gas phase synthesis, but all or part of hydrogen may be replaced with an inert gas. Also, organic and inorganic gases, including carbon, can be substituted for hydrocarbons.
It is also possible to add an organic or inorganic gas containing oxygen.

The present invention uses a warped substrate from the beginning. A thin film is grown on the convex side. The sample after the vapor phase synthesis is convexly warped toward the thin film. A flat thing is not possible. It is not possible to have a concave warpage on the thin film side. Unless it is convex, it cannot be polished uniformly. Polishing uniformly grinds the entire convex surface while tilting the holder surface. This is the eye of the present invention. By polishing, Rmax 500） (50 nm), Ra 200Å
(20 nm) or less. With this level of surface roughness, wafer processes such as electrode formation, impurity implantation, diffusion, and selective etching can be performed thereon by photolithography. Thus, a single crystal diamond wafer can be produced.

[0013]

According to the present invention, a substrate on which a diamond is grown is warped. Then, even after the diamond film is synthesized, a desired warp can be obtained, so that the entire surface can be uniformly polished using the polishing apparatus proposed in the present invention. FIG. 1 shows a sectional view of a diamond wafer of the present invention. Since a warped substrate is used from the beginning and a diamond film is formed thereon, the structure is warped even after synthesis. Since the coefficient of thermal expansion between the substrate and the diamond film is different and a thick film is formed, the degree of warpage may be different between the initial state and the post-synthesis state. However, it is sufficient that the warpage is a convex warpage (to the thin film side) and the warpage amount is 2 μm to 150 μm during polishing. The initial warpage of the substrate is appropriately determined in consideration of the change in the warpage due to the formation of the thin film.

There are various ways to define wafer bow. However, here, the height ΔH of the central portion from a plane including the peripheral portion of the wafer is defined as the amount of warpage. It is assumed that the convexity on the thin film side is negative and the concave on the thin film side is positive. Using this definition, the present invention provides that the wafer bow before polishing is reduced by -1.
It can be expressed as being in the range of 50 μm to −2 μm. In other words, the thin film side is made to be convexly warped. FIG. 1 shows convex warpage, in which the warp ΔH is negative. As the substrate, a single crystal of Si, a single crystal of Ni, a single crystal of Cu, a single crystal of SiC, or the like can be used. When Si is used for the substrate, a thin boundary layer of β-SiC is generated at the boundary with diamond.

Next, the diamond, the substrate, and the warpage will be described. [A. Diamond film] The diamond film should have the following properties. 1. Film thickness: 2 μm to 150 μm, especially 10 μm to 50 μm
m is desirable. When the film thickness is large, the cost of film formation increases. Although a 1000 μm film may be used, it is disadvantageous in terms of film formation time and material. If the film thickness is small, polishing is difficult. During polishing, there is also a case where the wafer is broken against the polished surface.

2. Surface roughness after polishing: Rmax is 500 °
(50 nm) or less Ra is 200 ° (20 nm) or less If the surface roughness is greater than this, it cannot be used as a device wafer or a wear-resistant wafer. This is because if the surface roughness is large, fine wiring cannot be formed on the surface. Also, the coefficient of friction increases, and it cannot be used for abrasive tools. 3. It is a single crystal. Since the epitaxial growth is performed on the single crystal substrate, the single crystal can be obtained.

[B. Substrate (Substrate)] A substrate on which a diamond thin film is formed by heteroepitaxial growth is C
It is a single crystal substrate of u, Ni, SiC, Si, Cu-Ni alloy or the like. It is effective to bias the substrate to promote nucleation. Here, the case of a Si wafer will be described. The Si substrate needs to be a single crystal. (110) diamond can be grown on a (110) Si wafer. (111) diamond can be heteroepitaxially grown on a (111) Si wafer. Also, for (100) Si,
(100) Diamond can be epitaxially grown.

The thickness of the substrate is preferably 0.1 mm to 1 mm. If the substrate is too thin, it cannot be polished. On the other hand, if it is too thick, it cannot be put on a semiconductor process. It is not suitable as a wafer for device fabrication. The shape of the substrate is advantageously circular for facilitating the wafer process. The conventional Si wafer process is designed for a circular wafer, and an apparatus similar to the Si device manufacturing process can be used for a circular wafer. Orientation flat (OF) for indicating direction
Alternatively, an index flat (IF) may be provided. However, it is possible to perform heteroepitaxy in the same manner even with a rectangular shape.

[C. Warp] A substrate having a warp from the beginning is used. Do not use a flat wafer. In this regard, it is not possible to utilize Si single crystal wafers commonly used in the semiconductor industry at present. Initial warpage is -2 m to -150
μm, but warpage after thin film synthesis is -2 μm to-
The thickness is set to 150 μm. The warp ΔH may be such that −150 μm ≦ ΔH ≦ −2 μm immediately before polishing. More preferably, -50 μm ≦ ΔH ≦ −5 μm.

In the previous section, the shape of the wafer before polishing has been described as a condition for performing good polishing. The inside of the wafer had a uniform composition and a uniform structure. Further, in the present invention, a non-uniform film structure can be adopted to further strengthen the film structure. This is an improvement that is effective in performing good polishing.

When the surface of a diamond is polished, a considerable force is applied to its interface. With this powerful force, the diamond film may peel off from the substrate,
And cause chipping. In particular, in the case of a film having a high uniformity, there is a possibility that diamond may be separated from the substrate. Therefore, a device is devised so that the diamond does not separate from the interface. For that purpose, it is necessary to strengthen the bonding force between the diamond and the substrate and disperse the force applied during polishing. The inventor has further studied a method for increasing the bonding force.

In order to increase the bonding force between diamond and the substrate crystal, it is effective to form a different material at the interface.
In many cases, a substrate on which diamond is formed has a larger lattice constant than diamond, such as Si or GaAs. Therefore, a heterogeneous substance having a lattice constant between the diamond and the substrate is formed between the substrate and the diamond. The discontinuity of the lattice constant is relaxed by the intermediate layer of the dissimilar substance, and the bonding strength is enhanced. For example, SiC is desirable. This is optimal when the substrate is Si,
Even for a substrate other than i, SiC can be used for the intermediate layer.

Further experiments were conducted on whether there was any other method for enhancing the bonding strength. Experiments have shown that if the diamond near the interface is nitrogen-containing, the bonding strength between the diamond and the substrate increases and the adhesion increases. The reason for the interface strengthening by nitrogen is considered as follows. The nitrogen atom has five extra-shell electrons. This is one more than the number of out-of-shell electrons of carbon. Extra-shell extra electrons of nitrogen enhance the bonding force with the substrate at the interface. The effect of strengthening the bond by nitrogen was recognized when the nitrogen concentration was 0.1 ppm by weight or more. However, on the other hand, if the content of nitrogen increases, the quality of the diamond film deteriorates. The upper limit of nitrogen concentration is 1
000 ppm by weight. More preferably, 1 ppm or more
Add nitrogen in the range of 100 ppm.

A third means for enhancing the bonding force is to appropriately form a diamond region having a random orientation. To form a partially polycrystalline diamond, since the progression of the crack can be suppressed, it is possible to increase the resistance force against cracking and peeling. Diamond with random crystal orientation,
It can be easily formed by performing a scratching treatment on the substrate surface. Crystals that are oriented in alignment with the substrate grow in portions that are not damaged. Therefore, the surface is partially damaged to form a diamond having a random orientation.

If the content of the polycrystal having a random orientation is 1% or more, the effect of enhancing the bonding strength is obtained. The bonding is strengthened as the polycrystal ratio increases. Chipping and peeling hardly occur.
However, diamonds having a uniform orientation are more excellent in translucency and electrical characteristics. In the first place, an object of the present invention was to produce a single crystal diamond having a uniform orientation. Therefore, it is not desirable to form a polycrystalline diamond having a random orientation on the entire surface. Therefore, a polycrystal having a random orientation is partially formed, and the remaining portion is made of diamond (single-direction diamond) having the same orientation as the substrate.

In order to partially produce a random orientation diamond, a partial damage treatment may be performed. This is because the random orientation diamond grows only in that part. There is a reinforcing effect no matter how the randomly oriented diamonds are arranged. However, there is a preferred arrangement depending on the purpose. One is to make a randomly oriented polycrystalline diamond around the periphery of the wafer. FIG. 16 shows this. The peripheral portion is damaged and polycrystalline diamond is grown thereon.

Another arrangement is to form polycrystalline diamond regions periodically. This is shown in FIGS. When manufacturing an IC or the like on a diamond film, the same IC pattern is periodically formed on a substrate. In this case, it is desirable that diamonds having a uniform orientation (unidirectional diamonds) also exist periodically. Therefore, a polycrystalline diamond is formed at a portion which becomes a boundary between adjacent devices. A portion of the randomly oriented diamond is cut into individual devices. Advantageously, the width of the unidirectional diamond region is matched to the area of the device. Since the device generally has an area of 1 mm ² or more, it is preferable that the width of one unidirectional diamond is 1 mm ² or more. Further, since the wafer is divided after the IC is manufactured, it is desirable that the unidirectional diamond has a plane direction perpendicular to the (111) plane which is the cleavage direction.

[0028]

【Example】

[Thickness of whole film: Examples 1 to 8, Comparative Examples 9-1]
2] The diamond wafer of the present invention was prepared by the process shown in FIG. 3, electrodes were formed, and the disconnection yield was examined. Diamond wafers were made according to the conditions and methods shown in the table below. The results are also listed in the table. Here, the substrate is a single crystal of Si. A warped disk-shaped substrate is prepared as shown in FIG. A diamond film was coated on the convex surface of the disk-shaped substrate by microwave plasma CVD, filament CVD, or plasma jet CVD. The pressure is 1 to 300 Torr.

In the case of a Si substrate, β-SiC is first grown, so a source gas having a high hydrocarbon concentration is used. Further, it is preferable to apply a negative bias (−50 V to −1000 V) to the substrate. When using methane as a hydrocarbon, the volume ratio of methane to hydrogen (CH ₄ / H ₂ ) should be 3% or more.

After the formation of β-SiC, a source gas having a low hydrocarbon concentration is used. In the case of methane, the volume ratio between methane and hydrogen is 0.1 vol% to 3 vol%. However,
The ratio of hydrocarbons in the first step (formation of β-SiC) and the later step is relative. As shown in FIG. 3, a SiC / diamond film whose film side is convex is formed. The warpage of the substrate changes due to the stress between the film and the substrate, which is often slight. The relationship between the initial warpage and the warpage after the synthesis of the diamond film differs depending on the manufacturing method and manufacturing conditions. In any case, the warpage ΔH after diamond synthesis is −1
50 μm ≦ ΔH ≦ −2 μm. The diamond film of the wafer whose thin film side was convex was polished by a mechanical polisher. As shown in FIG. 3, the surface is a smooth surface without irregularities.

Further, an aluminum film was deposited (FIG. 3). Part of aluminum was etched by photolithography to form fine wiring. Line width is 0.5 μm to 2 μm
Varied between. This results in a diamond wafer having a fine parallel line pattern as shown in FIG. This is the same size as the comb-shaped electrode for SAW. Then, the disconnection yield was examined. Tables 1 to 6 show these results.
Twelve samples will be individually described. Table 1 shows the thickness, diameter, and initial warpage (ΔH) of the substrate.

[0032]

[Table 1]

Here, sample numbers 1 to 8 are examples, and 9
-12 are comparative examples. The unit of the thickness of the substrate is mm, and the unit of the diameter is inch. The unit of warpage is μm. The sign of the warpage is not determined at the stage where the thin film has not yet been attached,
Here, negative means that a thin film is grown on a convex surface. The positive is to grow a thin film on the concave surface. The substrate of sample 1 is a 2-inch wafer of Si (100) having a thickness of 1 mm. Warpage is −5 μm. Sample 2 was made of Si (10
0) 1 mm thick, 4 inch diameter and warpage is -15 μm. Sample 3 is a Si (111), 0.35 mm thick, 8-inch wafer, and the warpage is -60 μm.

Sample 4 is made of Si (100) and has a thickness of 0.1 mm.
The diameter is 1 inch and the warpage is -10 μm. Sample 5 is Si
0.8 mm thick at (100), 3 inches, ΔH-2.5μ
m, Sample 6 is made of Si (110) and has a thickness of 0.5 μm, a diameter of 2 inches and a warpage of −10 μm. Sample 7 was Si (11
In 1), the thickness is 0.3 mm, the diameter is 5 inches, and the warpage is -2.5 μm. Sample 8 was made of Si (110), had a thickness of 1 mm, a 4-inch wafer, and had a warp of -15 μm. The above is an Example ((DELTA) H is -150 micrometers --2 micrometers).

The following four are comparative examples. Sample 9 was Si
At (100), the thickness is 0.05 mm, the concave warpage is +200 μm at a diameter of 2 inches. Sample 10 is 1 m in Si (111)
m thickness, 8 inch diameter, warpage +400 μm. Sample 11
Is Si (110), 3 mm thick, 0.5 inch diameter, and without warpage (ΔH = 0). Sample 12 was made of Si (100)
mm thickness, 3 inch diameter, no warpage. The substrate of the comparative example has no warpage or the warpage is positive (ΔH> 0). An SiC film and a diamond film were synthesized thereon by microwave plasma CVD, filament CVD, and plasma jet CVD. In the early and late stages of the reaction,
The volume ratio of hydrogen may be changed. In order to form SiC at an early stage, it is better to increase the ratio of hydrocarbons. Also, a bias may be applied to the substrate side. First, these three manufacturing methods will be described.

FIG. 4 is a schematic configuration diagram of a filament CVD apparatus. A susceptor 12 is provided inside the vacuum chamber 11. The substrate 13 is placed thereon. Chamber 1
1 has a gas outlet 14 which is connected to a vacuum exhaust device (not shown). An electrode 15 is provided around the susceptor 12. A filament 17 is attached between the electrodes 15. A raw material gas such as hydrogen or hydrocarbon gas is introduced from a gas inlet 18 of the chamber 11. 19
Is a vacuum gauge. The filament is energized by the power supply 21 and is heated. The substrate and the gas are strongly heated by the heat of the filament 17. A cooling medium 20 passes through the inner surface of the susceptor, cooling the susceptor 12 and maintaining the substrate at a suitable temperature. The raw material gas is excited by the heat of the filament to cause a gas phase reaction, and a reaction product is deposited on the substrate. The susceptor may be biased. FIG. 17 is a configuration diagram of an apparatus for applying a bias to a substrate. A negative bias is applied by the power supply 62. Grid 6
1 makes the plasma distribution uniform.

FIG. 5 is a schematic configuration diagram of a microwave CVD apparatus. The raw material gas is sent from the top to the bottom in the vertically long vacuum chamber 22. A susceptor 24 is provided at an upper end of the support rod 23, and a substrate 25 is placed on the susceptor 24. The source gas 26 is introduced from above the vacuum chamber 22. This passes through the vicinity of the substrate 25 and is discharged from a lower outlet 27. The part where the plasma is generated is cooled by the cooling device 28. The microwave 33 oscillated by the magnetron 29 propagates through the horizontally long vacuum waveguide 30. Proceeding in a direction orthogonal to the flow of the source gas, the source gas is excited to form plasma 31. The resonance plate 34 is moved by the piston 32, and a standing wave of an appropriate mode can be set up.

FIG. 18 shows an apparatus which has been modified so that the substrate can be biased. This provides a grid 65 above the substrate 25 and averages the plasma distribution. A power source 66 applies a negative bias to the substrate.
FIG. 19 is a schematic configuration diagram of an apparatus capable of applying a microwave in the TM mode. A microwave is generated by the magnetron 70. The light is guided from the coupler 71 to the waveguide 72. Mo
An appropriate microwave mode is selected by the mode selector 73. This bends in chamber 75 and enters reaction chamber 77 through dielectric window 76. The substrate 7 is placed on the susceptor 78.
9 is placed. A negative bias is applied to the susceptor 78 by a power supply 81.

FIG. 6 shows a plasma jet CVD apparatus. A susceptor 36 is provided below the inside of the chamber 35, and a base (substrate) 37 is placed thereon. Chamber 35
A plasma torch 38 is provided above the above. This passes gas 40 between the central cathode and the outer peripheral anode,
A DC voltage is applied by the power supply 39 to cause discharge,
Plasma. The gas includes a gas for maintaining plasma lighting such as argon and hydrogen, a carrier gas, and a hydrocarbon gas as a raw material. FIG. 20 shows an improved device capable of biasing a substrate.

In the synthesis of a diamond film, a raw material gas is caused to flow in a vacuum vessel as described above, and this is excited by heat, microwaves, or the like to form a film on a heated substrate. The source gas is composed of hydrocarbon gas and hydrogen gas. The diamond film can be formed by other methods, but here, any one of microwave plasma CVD, filament CVD, and plasma jet CVD is used. Table 2 shows the manufacturing method and manufacturing conditions for each sample.

[0041]

[Table 2]

Sample 1 was formed by microwave plasma CVD. Methane is used as hydrocarbon gas.
During the first 30 minutes, the volume ratio of methane / hydrogen is 4% and the substrate is biased at -200V. This promotes the generation nucleation of hydrogen radicals. Thereby, SiC can be formed on the Si substrate. Thereafter, the methane / hydrogen volume ratio is lowered, and a source gas having a methane / hydrogen ratio of 1% is supplied. No bias is applied. Sample 2 is formed by a microwave plasma CVD method. For the first 5 minutes, a bias of -300 V was applied and the methane / hydrogen ratio was 15%. The methane / hydrogen after this is 3%. No bias is applied.

Sample 3 was also manufactured by microwave plasma CVD. The initial (30 minutes) methane / hydrogen is 2%,
No bias is applied. The methane / hydrogen ratio in the latter half is 0.5
%. There is no bias in the second half. Sample 4 was formed by the filament CVD method. For the first 30 minutes, the methane / hydrogen ratio is 5%. A bias of −50 V is applied. In the latter half, the methane / hydrogen ratio was reduced to 2%. The bias is zero. Sample 5 is formed by a filament CVD method. For the first 10 minutes, a 4% methane / hydrogen volume ratio is applied and a bias of -150 V is applied to the susceptor. Later, the methane / hydrogen ratio was reduced to 1%. No bias is applied.

Sample 6 was also formed by the filament CVD method. The methane / hydrogen ratio is 30% for the first 60 minutes. Raw materials containing extremely high concentrations of methane are used. The susceptor is not biased. After 60 minutes, the methane / hydrogen ratio has dropped to 3%. No bias is applied. The sample 7 uses a plasma jet CVD method. The first 15 minutes are 1
A feed gas with a methane / hydrogen ratio of 0% is supplied. Apply -400 V to the susceptor. In the latter period, the methane / hydrogen ratio is set to 1% and no bias is applied.

The sample 8 is formed by a microwave plasma CVD method. During the first 90 minutes, feed gas with a methane / hydrogen ratio of 20% is introduced. It is a gas containing a high concentration of methane. No bias is applied. In the second half, the methane / hydrogen ratio is reduced to 0.5%. There is still no bias. Sample 9 which is a comparative example is formed by a microwave plasma CVD method.
The methane / hydrogen ratio is constant at 0.5% from start to finish. First, a positive bias (+150 V) is applied. In the latter half, there is no bias. The sample 10 is formed by a filament CVD method. No bias at first, +
A positive bias of 200 V is applied to the substrate. The methane / hydrogen ratio in the raw material is always 3% by volume.

For sample 11, a diamond film is formed by a filament CVD method. The methane / hydrogen ratio in the source gas is 2%
It is. First, a negative bias of -10 V is applied. Later, 0 bias is applied. The sample 12 is a microwave plasma CVD
The film is formed by the method. The methane / hydrogen ratio in the raw gas is 3% at first
It is. Later reduced to 2%. The bias is not applied all the time.
Although the film was formed under such manufacturing method and conditions, the film thickness of the SiC portion and the diamond portion was measured, and the success or failure of heteroepitaxial growth was evaluated. Table 3 shows the results.

[0047]

[Table 3]

The unit of the thickness of SiC is nm (10 °). The film thickness of diamond is μm (1000 nm = 100
00Å). The success or failure of heteroepitaxial is expressed as pass (〇) when the crystal orientation of the substrate, the crystal orientation of SiC, and the crystal orientation of diamond are the same, and expressed as reject (x) otherwise. . That is, the (111) Si substrate is placed on the (111) Si substrate.
If the C film and the (111) diamond grow, it is judged as acceptable. Naturally, diamond is a single crystal, and the crystal orientation is aligned with the substrate. The conformity of plane orientation is RHEE
It was examined by verifying the diffraction spot by D (high-speed reflection electron beam diffraction).

Sample 1 was placed on a Si substrate at 10 nm (10
0 °) β-SiC film and a 30 μm diamond film are grown epitaxially in alignment. The substrate is Si (10
0), β-SiC and diamond are (10)
0). Sample 2 was a 5 nm β-S
An iC film and a 50 μm diamond film are heteroepitaxially grown. Sample 3 was placed on Si (111)
5 nm (111) β-SiC film, 100 μm (11
1) A diamond film is heteroepitaxially grown. Sample 4 was made of 20 nm β-S on Si (100).
Hetero-epitaxial growth of an iC, 15 μm diamond film was achieved.

In sample 5, 8 nm β-SiC and 5 μm diamond film are heteroepitaxially grown on Si (100). Sample 6 was 25 nm β-Si
C, a 30 μm diamond film is obtained. Sample 7 is
A 15 nm β-SiC, 100 μm diamond film is heteroepitaxially grown. Sample 8 is 8n
He has succeeded in heteroepitaxially growing a β-SiC m m and a 5 μm diamond film. Sample 9, which is a comparative example, obtains an 80 nm β-SiC film and a 150 μm diamond film, but this is not epitaxial growth. Also, the surface roughness is remarkable. Diamond, β-Si
C is not a single crystal.

Sample 10 was a 580 nm β-SiC film, 8
Although a diamond film of 00 μm is obtained, this is not epitaxial growth. The roughness of the surface is even more remarkable than that of Sample 9. This is also not a single crystal. Sample 11 was 1 nm β-
A SiC, 2 μm diamond film is formed. It is heteroepitaxially grown. Sample 12 is 1
A 0 nm β-SiC, 30 μm diamond film is heteroepitaxially grown. Again, the surface is quite rough. After synthesizing β-SiC and diamond film on Si substrate, surface roughness Rmax of diamond surface,
Ra was measured. Table 4 shows the results. Unit is μm
(= 1000 nm = 10000 °).

[0052]

[Table 4]

The Rmax of the diamond film after synthesis is 0.5.
It is widely distributed between 1 μm and 30 μm. Ra is 0.
It is distributed between 04 μm and 9 μm. The surface roughness of sample 1 is
Rmax 0.25 μm (2500 °), Ra 0.08 μ
m (800 °). Sample 2 has an Rmax of 0.32 μm.
m, Ra 0.11 μm. Sample 3 is rough and R
max is 0.95 μm and Ra is 0.38 μm. Sample 1
Surface roughness is larger than that. This is partly because the substrate is wide and the film is thick.

Sample 4 had an Rmax of 0.20 μm, a Ra0.
095 μm. Low surface roughness. Sample 5 is Rma
x0.1 μm and Ra 0.04 μm. This is an example having the lowest surface roughness. This is probably because the film thickness is small. Sample 6 had an Rmax of 0.33 μm and a Ra of 0.1.
3 μm. Sample 7 has an Rmax of 0.98 μm, Ra
0.43 μm. Surface roughness is poor. This may be because the substrate area is large and the film thickness is quite large. Sample 8 is R
max is 0.14 μm and Ra is 0.06 μm. Low surface roughness. This is related to the thin film thickness. Sample 9 of the comparative example has Rmax of 15 μm and Ra of 6 μm.
It is not epitaxially grown. The unevenness is severe, and is significantly different from Samples 1 to 8 of Examples.

Sample 10 had a Rmax of 30 μm and a Ra of 9 μm.
It is. This further reduces the surface roughness. Rough surface instead of epitaxial growth. Sample 11 is Rmax1
μm and Ra 0.3 μm. Although relatively low, it is still significantly higher than in the examples (samples 1 to 8). Sample 1
2 is Rmax 8 μm and Ra 2 μm. Sample 11,
12 has a large surface roughness but is heteroepitaxially grown.

Since the diamond film grown by vapor phase has a large surface roughness, an electronic device cannot be formed on the diamond film by photolithography as it is.
You have to polish it. However, Si and G
An apparatus for polishing aAs cannot, of course, polish a warped wafer. Even if you attach a warped wafer to a flat polishing head and press it against the polishing board to polish it,
The periphery is unpolished, or the center or middle is unpolished. Special polishing equipment is required.

The diamond film was mechanically polished by a special polishing apparatus while the diamond film was still attached to the substrate. Then, the surface roughness and the amount of warpage after polishing were measured. The polishing reduces the surface roughness. Some samples cannot be completely polished due to unevenness. Therefore, the ratio of the polished region was also examined. Since the polishing method is also different from the conventional case of polishing Si, GaAs and other materials, this will be described first.

FIG. 7 schematically shows a polishing apparatus. FIG. 8 shows an enlarged sectional view of the holder. The rotating platen 41 rotates while being supported on a rotating main shaft 42. On this, diamond abrasive grains are fixed. Since the diamond is polished, the diamond particles are also fixed to the surface plate, which is a polishing plate, and the diamond on the wafer is polished while the diamond particles are worn away. It takes hundreds of hours. Buffer plate (plate material like rubber) for holder-43
44, and a wafer (a diamond film grown on a substrate) is attached thereon.

One idea is to use the buffer plate 44.
A holder shaft 46 is attached to the center of the holder 43. Instead of being fixed, it transmits a rotating torque, but the holder surface can be freely tilted with respect to the shaft. The holder rotates by itself, and the rotary platen 41 revolves. One point on the upper surface of the holder 43 is
It is made to hold down. Pressure shaft 4
7. The upper end of the holder shaft 46 is supported by an arm 48. A hydraulic cylinder 49 for applying pressure to the holder shaft 46 is attached to the arm 48. Polishing is performed by applying a strong force to the holder shaft 46 so that the diamond abrasive grains and the diamond film are both consumed. The arm 48 has a motor 50, and the rotational force of the motor 50 rotates the holder shaft 46. Pulley 5 attached to the motor output shaft 53
From 4, the rotation torque is transmitted to the pulley 56 fixed to the holder shaft 46 via the belt 55. This causes the holder to rotate around the axis.

A hydraulic cylinder 51 for applying pressure to the pressure shaft 47 is provided on the arm 48. FIG.
As shown in the figure, there is a circular groove 59 on the upper surface of the holder 43, and the pressing shaft 47 presses the groove. Holder
The shaft 46 holds and rotates the center of the holder, but allows the holder to tilt. Due to the pressure of the pressure shaft 47, the surface of the holder 43 is inclined with respect to the surface of the rotary platen. Wafer-4
5 is convexly curved, but the holder is inclined. The inclination angle depends on the pressure of the pressure shaft. By changing the pressure of the pressure shaft, the point of contact of the wafer with the rotary platen can be changed. By moving the contact point from the center to the periphery, it is possible to uniformly polish the periphery. Alternatively, polishing can be performed from the peripheral portion toward the center.

If the wafer is polished by a usual polishing apparatus in which the holder shaft and the holder are fixed, the entire diamond film cannot be polished. A part that cannot be polished always remains somewhere. If the polishing amount is increased, the diamond can be cut. However, in this case, the diamond is completely removed in other portions, and a portion where the substrate is exposed is generated. The results of polishing using a normal shaft fixing holder and polishing of the present invention using the shaft inclination holders of FIGS. 7 and 8 will be described with reference to FIG. FIGS. 9 to 9 are polished by a shaft fixing holder. The state after polishing differs depending on the state of warpage of the wafer immediately after the synthesis.

In the case of a flat wafer: A flat wafer seems to be polished flat immediately after synthesis, but this is not the case. As shown in FIG. 9, portions that cannot be polished occur randomly somewhere. The unpolished portion is rough and has a weak light reflection, so it looks dull. It can be easily understood with the naked eye. After the synthesis, a flat wafer
On the contrary it is not good. This is a different result. In the case of concave warpage: In the case of concave warpage (ΔH> 0), a ring-shaped unpolished portion remains in the middle as shown in FIG. In the case of convex warpage: In the case of convex warpage (ΔH <0), FIG.
As shown in FIG. 7, an unpolished portion remains on the outer peripheral portion.

However, as in the present invention, when a wafer having a warpage (ΔH <0) is polished by using a holder in which the shaft and the holder surface are not fixed and the holder surface is inclined with respect to the shaft, The whole can be polished. As shown in FIG.
Thus, it is polished uniformly. The whole becomes a mirror surface.
Therefore, the sample wafer was polished by the apparatus shown in FIGS. 7 and 8, and the surface roughness and polished area after polishing were measured. Table 5 shows the results.

[0064]

[Table 5]

The unit of the surface roughness after polishing is Δ. It should be noted that Table 4 is in μm (10000 °). The surface roughness after polishing is Rmax 3Å to 800Å,
Ra1Å to 400Å. Sample 1 had a medium surface roughness immediately after synthesis, but after polishing, Rmax 20 °,
Ra5Å. The entire surface is polished (100
% Polishing). Warpage hardly changes before and after polishing. Sample 2
The surface roughness after synthesis is medium. This is because after polishing, R
max30 °, Ra7 °, and also medium surface roughness. With this level of surface roughness, a pattern can be sufficiently drawn by photolithography. 100% polishing is possible. Warpage is the same as before polishing.

Immediately after the synthesis, the sample 3 having a large surface roughness has a considerably rough surface of Rmax 150 ° and Ra12 after polishing. Those having large surface roughness before polishing seem to have large surface roughness even after polishing. This is also polished all over. Warpage is almost the same as before polishing. In sample 4,
After polishing, they are Rmax 18Å and Ra2Å. 10
0% polishing was achieved. Warpage is almost unchanged. Sample 5 was originally a sample having a small surface roughness, but after polishing, Rmax5
{Ra1}. Surface roughness is the lowest among all samples. Extremely smooth. Warpage does not change before and after polishing. The polishing rate is 100%.

Sample 6 had a medium surface roughness after the synthesis. When polished, Rmax8ｍ and Ra1Å. Excellent smooth surface. 100% polished. Sample 7 had poor surface roughness before polishing, but the surface roughness was poor after polishing. Rmax80 ° and Ra60 °. 100% polishing was possible. Sample 8 was formed by forming diamond on 4-inch Si (110). Although the surface roughness was extremely small, the surface roughness was small and smooth after polishing. Rm
ax3Å and Ra2Å. 100% polishing is possible.

Sample 9 of the comparative example is inferior in surface roughness after synthesis and is not an epitaxial crystal. As a result of polishing, it became Rmax400 ° and Ra300 °. It is a rough surface. Moreover, the entire body cannot be polished. 50
% Of the area remains as an unpolished portion. Polishing, of course, reduces irregularities, but is less pronounced. With such a surface roughness, it is difficult to ride a semiconductor process. Sample 10 has extremely large surface roughness after synthesis (before polishing). Even after polishing, the surface roughness is poor, and Rmax 800Å and Ra400Å
It is. Warpage hardly changes before and after polishing. 80% of unpolished portions remained. Polishing by only 20% was possible.

Sample 11 cannot be polished unevenly. Sample 12 has poor surface roughness after synthesis, but when polished, becomes Rmax 540 ° and Ra280 °. It is still rough and unsuitable for forming semiconductor devices. Samples 11 and 12 are heteroepitaxially formed, but have poor surface roughness, and do not have a sufficiently smooth surface even when polished. Next, aluminum was vapor-deposited on the diamond coating surface, and a comb-shaped electrode was formed by photolithography. The line width of the electrode is 0.5 μm to 2 μm. The thickness of the aluminum film is 1500Å (150nm = 0.15μm)
It is. The electrodes may be disconnected due to the unevenness. Then, the ratio of the sample that did not break (breakage yield) was also examined. Table 6 shows the results.

[0070]

[Table 6]

Sample 1 was 2 inches (1 μm) with -5 μm warpage.
00) A Si substrate coated with 10 nm of β-SiC and 30 μm of diamond. If an aluminum electrode pattern having a line width of 1 μm is formed, the yield is 99%. Sample 2 was 4 inches (10 μm) with a warp of −15 μm.
0) 5 nm β-SiC and a 50 μm thick diamond film are grown on a Si wafer. 0.8 μm line width
When the aluminum comb-shaped electrode is formed, the disconnection yield is 97%
Met. This means that submicron electrodes can be formed with a high yield.

Sample 3 was prepared by placing a 15 nm β-SiC on an 8 inch (111) Si wafer having a warp of −60 μm.
And 100 μm of diamond films are stacked. This is because the warpage is large and the surface roughness after polishing is not good, but the yield of the electrode having a width of 1.2 μm is 94%. It can be said that the result is satisfactory. Sample 4 is -1
On a 1-inch (100) Si wafer having a warp of 0 μm, 20
This is a coating of β-SiC with a thickness of nm and a diamond film with a thickness of 15 μm. If an electrode having a line width of 1.5 μm is formed thereon, the yield will be 96%. This is also a good result.

The sample 5 was formed on a 3-inch (100) Si wafer having a warp of 2.5 μm by using 8 nm β-SiC, 5 μm.
It is covered with a m-thick diamond film. Both flatness and smoothness are good. When a comb-shaped electrode having a width of 0.6 μm was formed, the yield was 95%. This is the narrowest electrode, but with such a narrowness this yield is surprising. Sample 6 is obtained by forming 25 nm β-SiC and 30 μm diamond on a 2-inch (110) Si wafer having a warpage of −10 μm. The yield when forming a 1 μm-wide electrode is 99%. This is a satisfactory value.

The sample 7 was formed on a 5-inch (111) Si wafer having a warp of 2.5 μm and a 15-nm β-Si
C, an example in which a 100 μm diamond film was formed. This is not good in surface roughness (Rmax 8 nm, Ra 6 nm)
However, the yield of electrodes having a width of 0.8 μm is 92%. It is satisfactory data. Specimen 8 was warped-on a 15 inch 4 inch (110) Si wafer, 8 nm of β-Si.
C, 5 μm diamond was formed. Surface roughness is good and warpage is small. When a comb-shaped electrode having a line width of 2 μm was formed thereon, the disconnection yield was 90%.

Each of the diamond wafers according to these examples shows a disconnection yield of more than 90% with respect to the formation of a comb-shaped electrode. That is, there is almost no disconnection. This is because the film surface is smooth and has few irregularities. When used in a surface acoustic wave device, a device having extremely excellent characteristics can be obtained with a high yield. Even when used in a semiconductor device, the fact that a thin electrode pattern can be formed means that various structures can be manufactured using lithography technology. A comparative example will be described. Sample 9 has a warp of +2
80 nm on a 2-inch (100) Si wafer of 00 μm
Of β-SiC, 150 μm diamond. Surface roughness is poor. When a comb-shaped electrode having a line width of 1.5 μm was formed, the disconnection yield was 10%.
This means that a fine electrode structure cannot be formed by photolithography due to large surface irregularities.

The sample 10 was formed by warping +8 μm (111) Si wafer of 400 μm and β-SiC of 580 nm.
A thick diamond film having a thickness of 00 μm was formed.
The surface roughness before polishing is poor, and also after polishing. On the other hand, if an electrode having a line width of 0.5 μm is manufactured, the yield is only 8%. In this case, too, the surface roughness is poor and a fine structure cannot be formed by photolithography. Sample 11 was prepared on a 0.5 inch Si (110) wafer without warpage by a 1 nm β.
-SiC, 2 μm diamond is formed. Since this could not be polished, the test of electrode deposition and etching is not performed.

The sample 12 was a 3-inch Si (1) without warpage.
00) A 10 nm β-SiC and a 30 μm diamond film are formed on a wafer. 1.6μ
When a comb-shaped electrode having a width of m was formed, the disconnection yield was 15%. This also means that fine electrodes cannot be formed on the wafer. Although the warpage is zero, as described above, there is actually undulation and twist, and smooth polishing cannot be performed. There are disadvantages such as poor surface roughness. Therefore, the electrode structure cannot be manufactured with a high yield.

[When the entire film is non-uniform: Sample 13: Example] A single crystal substrate of Si {111} having a diameter of 3 inches was prepared. The substrate was heat-treated at 1000 ° C. for 1 minute in CH ₄ .
As a result, cubic SiC was grown to a thickness of 10 nm. It was confirmed by RHEED that SiC was epitaxially grown. As shown in FIG. 15, a 2 mm outer peripheral area of the substrate was damaged using diamond powder having an average particle size of 50 μm. Diamond was grown on this substrate by hot filament CVD. The filament is tungsten. The growth conditions are

Substrate temperature 930 ° C. Pressure 80 Torr Total flow rate of source gas 800 sccm Filament temperature 2100 ° C. Growth time 100 hours

Composition of Source Gas First 10 minutes H ₂ 97.8% by volume CH ₄ 2.2% by volume H ₂ 99.2% by volume CH ₄ 0.8% by volume Substrate bias First 10 minutes −125V to -150V After that 0V Film thickness 50μm

A diamond film was grown to a thickness of 50 μm on the entire surface of the substrate. The crystal orientation was examined by X-ray diffraction.
At the center of the film, the portion where the normal direction was <111> ± 2 ° was 98% or more. The rotation angle of the crystal grains with respect to the substrate orientation at the center of the plane is at most 4 °. That is, it can be said that the central portion of the film is a crystal having the same orientation as the substrate. FIG. 21 shows this. The orientation was not randomly aligned in the diamond at the periphery where the damage was performed. The warpage of the wafer was -20 μm. The diamond surface was polished. The entire surface was mirror-polished, and no peeling occurred between the film and the substrate.

[When the entire film is non-uniform: Sample 14: Comparative example] A single-crystal substrate of Si {111} having a diameter of 3 inches was prepared. No damage processing is performed. Diamond was grown on this substrate by hot filament CVD. The filament is tungsten. The growth conditions are

Substrate temperature 1050 ° C. Source gas total flow rate 800 sccm Pressure 250 Torr Filament temperature 1900 ° C. Growth time 100 hours

[0084] The composition of the feed gas first 10 minutes H ₂ 97.8 vol% CH ₄ 2.2% by volume subsequent H ₂ 99.2 vol% CH ₄ 0.8 vol% bias the first 10 minutes -125V~ -150V After that 0V Thickness 90μm

A diamond film was grown on the entire surface of the substrate to a thickness of 90 μm. The crystal orientation was examined by X-ray diffraction.
The portion where the normal direction was <111> ± 2 ° was 98% or more in the whole film. The rotation angle of the crystal grains with respect to the substrate orientation in the entire film is at most 4 °. That is, it can be said that the entire film is a crystal having the same orientation as the substrate.
The orientation was not randomly aligned in the diamond at the periphery where the damage was performed. The warpage of the wafer was +52 μm. The diamond surface was polished. 50
%, The peripheral diamond is 30 mm ²
It has been chipped in the size of.

[When the whole film is non-uniform: Sample 15: Example] A single-crystal Si {100} substrate having a diameter of 2 inches was prepared. As shown in FIGS. 10 and 11, a photoresist film was formed at a period of 2 mm × 2 mm in an area of 1.6 mm × 1.6 m. Although only four (2 × 2) are shown in the figure, there are actually many resist patterns vertically and horizontally. Damage treatment was performed with diamond particles having an average particle diameter of 50 μm. Thereafter, the photoresist was removed. The part covered by the resist remains a smooth surface. This means that the portion not covered with the resist has been damaged. Next, two stages of diamond growth are performed.

(First Step) Diamond was grown on this substrate by microwave plasma CVD. The growth conditions are

Substrate temperature 900 ° C. Source gas total flow rate 500 sccm Pressure 120 Torr Growth time 10 hours Composition of source gas H ₂ 97.99% by volume CH ₄ 2% by volume N ₂ 0.01% by volume No substrate bias Film thickness (local) 8 μm

After this growth, the sample was once taken out. As shown in FIG. 12, diamond grew to a height of 8 μm only in the damaged lattice-like portion.
Diamond is not deposited on a 1.6 mm × 1.6 mm square portion. The crystal orientation of the diamond was observed by SEM. It was found that the orientation was completely random polycrystal.

(Second Step) Diamond was grown again by microwave plasma CVD on a substrate on which random orientation diamonds were formed in a lattice. The growth conditions are

Substrate temperature 900 ° C. Source gas total flow rate 500 sccm Pressure 80 Torr Growth time 100 hours Composition of source gas First 5 minutes H ₂ 98% by volume CH ₄ 2% by volume Remaining 99 hours 55 minutes H ₂ 96.2% by volume CH ₄ 3.8% by volume

Substrate bias First 5 minutes -150 V Remaining 99 hours 55 minutes 0 V Film thickness (local) 180 μm Warpage −8 μm

By this growth, a 180 μm diamond film could be obtained. Observation of the growing surface revealed that the entire surface was diamond with a uniform orientation. On the other hand, observation of the cross section revealed that diamonds with random orientation remained in the damaged lattice portion. However, it is not covered by a single-orientation diamond and appears on the surface. FIG. 13 is a sectional view thereof. The film is written thicker than the substrate, to emphasize the structure of the film. In practice, the substrate is thicker. The reason why the random orientation diamond is higher than in FIG. 12 is that the random orientation diamond continues to grow for a while in the second stage of growth.

The diamond surface was polished. The entire surface was mirror-polished. No peeling of the film occurred. FIG.
This is because the randomly oriented diamonds appearing in the matrix reinforce the interface. Excellent diamond film. The effect of the present invention is clearly understood. In this embodiment, the diamonds in the random orientation do not appear on the surface, but may appear on the surface. FIG. 16 shows such a modification.

[When the entire film is non-uniform: Sample 16: Example] A single crystal substrate of Si {100} having a diameter of 2 inches was prepared. 100 μm width and 10 depth by YAG laser
A μm groove was cut on the entire surface of the Si substrate at a cycle of 1 mm × 1 mm. The cross-sectional shape is such that flat portions (projections) and recesses alternate. This is a pattern in which the concave portions are formed in a lattice shape. Diamond was formed on this substrate by microwave plasma CVD for 100 hours. The growth conditions are

Substrate temperature 900 ° C. Source gas total flow rate 500 sccm Pressure 60 Torr Growth time 100 hours Composition of source gas First 5 minutes H ₂ 98% by volume CH ₄ 2% by volume Remaining 99 hours 55 minutes H ₂ 96.2% by volume CH ₄ 3.8% by volume

Substrate bias First 5 minutes -150 V Remaining 99 hours 55 minutes 0 V Film thickness (local) 180 μm Warpage −32 μm

Observation of the growth surface revealed that the diamond was almost uniformly oriented. From observation of the cross section, it was found that the diamond film was as shown in FIG. The portion where the groove was cut first is a hole without diamond growth. However, as the diamond gradually approaches from the periphery, the upper part of the hole is also covered with the diamond. Therefore, the holes are confined. Except for the holes, it is a high-quality diamond with a uniform orientation. When this was polished, the entire surface of the diamond was mirror-polished. No peeling of the film occurred. The presence of the lattice-like holes strengthens the bonding at the interface and prevents peeling.

[When the entire film is non-uniform: Sample 17: Comparative Example] A single-crystal Si {100} substrate having a diameter of 2 inches similar to that of Sample 15 was prepared. Neither scratching nor grooving is performed. Diamond was grown on a smooth substrate by microwave plasma CVD. The growth conditions are

Substrate temperature 700 ° C. Pressure 15 Torr Total flow rate of source gas 500 sccm Growth time 300 hours Composition of source gas First 5 minutes H ₂ 98% by volume CH ₄ 2% by volume Remaining 99 hours 55 minutes H ₂ 96.2% by volume CH ₄ 3.8% by volume

Substrate bias First 5 minutes -180 V Remaining 99 hours 55 minutes 0 V Film thickness (local) 150 μm Warpage −180 μm

By this growth, a diamond film of 150 μm could be obtained. Observation of the growth surface revealed that the entire surface was diamond with a uniform orientation. It is a uniform diamond film. The diamond surface was polished. When almost 20% was mirror-polished, it was split into two almost at the center. In addition, peeling occurred in about 15% of the mirror-polished area. Peeling occurred at the interface between the substrate and the diamond. It can be seen that when the state of the interface is uniform, the bonding force of the interface is weak.

[Embodiment of Fabricating FET: Sample 18] A MESFET was formed on a diamond substrate according to an embodiment of the present invention.
(Metal-semiconductor field effect transistor). A {100} Si single crystal substrate having a diameter of 2 inches (50 mm) was prepared. As shown in FIGS. 24 and 25,
In a cycle of 2.5 mm × 2.5 mm, 2.1 mm × 2.1
A photoresist film was formed in a square shape of mm. FIG.
Indicates only 2 × 2. The entire surface of the Si wafer was damaged by diamond particles having an average particle diameter of 100 μm. This is shown in FIG. Damaged portions are generated in a grid pattern. Thereafter, the resist was removed. The part covered with the resist has a smooth surface. An amorphous carbon was formed on this substrate by microwave plasma CVD under the following conditions.

Generation of aC Substrate temperature 700 ° C. Source gas total flow rate 500 sccm Growth time 5 hours Source gas composition H ₂ 90% by volume CH ₄ 10% by volume Substrate bias 0 V a-C film thickness (local) 10 μm

Amorphous carbon grew only in the damaged portion. Thereafter, a unidirectional diamond film was grown by microwave plasma CVD under the following conditions.

Unidirectional diamond Substrate temperature 900 ° C. Source gas total flow rate 500 sccm Growth time 30 hours Composition of source gas First 5 minutes H ₂ 98% by volume CH ₄ 2% by volume H ₂ 96.2% by volume CH ₄ 3. 8% by volume

Substrate bias -150 V for the first 5 minutes and thereafter 0 V Film thickness 35 μm Warpage -3 μm

The observation of the growth surface revealed that this was a single-oriented diamond with a uniform orientation. At this time, the warpage of the substrate was -3 μm. This wafer was polished by the polishing apparatus of the present invention. The entire surface could be mirror-polished without peeling, chipping or cracking (FIG. 27). Boron-doped diamond was formed on the mirror wafer by microwave plasma CVD under the following conditions.

B-diamond Substrate temperature 950 ° C. Total flow rate of source gas 500 sccm Growth time 2 hours Composition of source gas H ₂ 99% by volume CH ₄ 1% by volume B ₂ H ₆ 1 ppm Substrate bias 0 V Film thickness 1 μm

The thickness of the boron-doped diamond film is 1 μm.
m. Next, a tungsten film was formed on the entire surface of the wafer by electron beam evaporation. This is the state shown in FIG. Further, tungsten was partially removed by photolithography to form an electrode. This is FIG.
This is the state shown in FIG. Then, non-doped diamond was grown thereon by microwave plasma CVD. The conditions are as follows.

Non-doped diamond Substrate temperature 950 ° C. Source gas total flow rate 500 sccm Growth time 3 hours Source gas composition H ₂ 98.8 vol% CH ₄ 1.2 vol% Substrate bias 0 V Film thickness 2 μm

As a result, a non-doped diamond having a thickness of 2 μm was selectively grown. Nothing grows on tungsten. Non-doped diamond grows only on boron-doped diamond. Amorphous car
Amorphous carbon grew on the carbon. As described above, what grows depends on the base. The non-doped diamond grown here has a thickness of 2 μm. FIG.
0 indicates this state.

Further, aluminum was deposited on the entire surface by a resistance heating method. FIG. 31 illustrates this. Photolithography was used to remove aluminum in other portions while leaving only a portion of the aluminum on the non-doped diamond. Thus, as shown in FIGS. 32 and 33, FETs were formed on the entire surface of the diamond wafer. The central tungsten electrode is the drain electrode. The ring-shaped aluminum electrode is the gate electrode. The outermost tungsten is the source electrode. The boron diamond forms a p-type channel. FETs arranged vertically and horizontally are formed on the entire surface of the wafer.

The portion of the amorphous carbon has a width of 200 mm.
Dicing was performed using a μm blade to separate individual FETs. A total of 300 FETs were obtained. Almost everything worked well. This means that the boundary layer did not peel off and was not damaged by the polishing. Thus, the present invention can also provide a diamond FET. The amorphous carbon is provided at the boundary between adjacent elements, and this has the effect of strengthening the boundary layer and facilitating the cutting of the wafer.

[0115]

The substrate of the diamond bulk is manufactured by a high-pressure synthesis method. In this method, high pressure is applied at a high temperature to produce polycrystalline diamond. The area was small, meaningful for experiments, but of little practical significance. The present invention is the first to provide a large area wafer of diamond. This is a composite structure in which these diamond films are formed on an easily available crystal substrate.
If a composite structure is used, warpage occurs and polishing cannot be performed. It could not be made into a mirror wafer. Devices cannot be fabricated by photolithography on wafers that are not specular. The present inventor adopts a warped substrate, forms a diamond film on this substrate so as to be convex,
The convexly-warped wafer is polished by a polishing device capable of tilting the holder surface. With the success of polishing, a practical diamond mirror wafer having a large area can be manufactured for the first time.

Since the diamond wafer of the present invention is heteroepitaxially grown on a single crystal substrate, the diamond itself is a single crystal. By designating the plane orientation of the substrate, a single crystal diamond wafer having an arbitrary crystal orientation can be produced. This is a significant invention that opens a breakthrough in the application of diamond to semiconductor materials.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of a warped diamond wafer in which a diamond film is formed on a convexly warped substrate. Β-SiC is generated in the middle part.

FIG. 2 is a cross-sectional view showing an example of a diamond wafer having an undulation in which the overall warpage is 0 but the uneven warpage is mixed.

FIG. 3 is a schematic cross-sectional view showing a step of coating and polishing a diamond film on a convexly warped substrate and forming an electrode.

FIG. 4 is a schematic configuration diagram of a filament CVD apparatus used for synthesizing a diamond film in the present invention.

FIG. 5 is a schematic configuration diagram of a microwave plasma CVD apparatus used for synthesizing a diamond film in the present invention.

FIG. 6 is a schematic configuration diagram of a plasma jet CVD apparatus used for synthesizing a diamond film in the present invention.

FIG. 7 is a schematic front view of a polishing apparatus used for polishing a diamond film in the present invention.

FIG. 8 is an enlarged sectional view of only a holder part of the polishing apparatus of FIG. 7;

FIG. 9 is a bottom view showing a polished wafer surface for explaining that an unpolished portion remains when a diamond-coated wafer is adhered to a flat holder and polished. Is a polished flat wafer after synthesis, a polished concave warped wafer, and a polished convexly warped wafer.
Indicates the one polished by the polishing method employed in the present invention.

FIG. 10 is a plan view of a part of the substrate showing a state where a large number of square resist films are periodically formed on the substrate except for a lattice-like portion.

FIG. 11 is a side view of the same as FIG.

FIG. 12 is a cross-sectional view of a part of the substrate showing that when the substrate of FIG. 10 is scratched to form diamond, polycrystalline diamond grows only in a portion not covered by the resist.

FIG. 13 is a sectional view of a substrate obtained by further growing diamond on the substrate of FIG. 12;

FIG. 14 is a cross-sectional view of a diamond film formed when diamond is grown on a substrate cut by a YAG laser.

FIG. 15 is a plan view of a wafer in which only an outer peripheral portion of a circular substrate is damaged.

FIG. 16 is a cross-sectional view showing an embodiment in which random-oriented diamond and single-oriented diamond aligned with the substrate are periodically grown on the substrate, and the random-oriented diamond is exposed on the surface.

FIG. 17 is a sectional view showing an improved filament CVD apparatus used for synthesizing a diamond film in the present invention.

FIG. 18 is a schematic configuration diagram of an improved microwave plasma CVD apparatus used for synthesizing a diamond film in the present invention.

FIG. 19 is a schematic configuration diagram of another microwave plasma CVD apparatus used for synthesizing a diamond film in the present invention.

FIG. 20 is a schematic configuration diagram of a plasma jet CVD apparatus used for synthesizing a diamond film in the present invention.

FIG. 21 is a diagram showing a wafer in which the outer peripheral portion of a Si substrate is damaged and a random-oriented diamond is grown on the outer peripheral portion by two-stage growth and a single-oriented diamond aligned with the substrate orientation grows inward. Sectional view

FIG. 22 is a sectional view of an amorphous carbon film having a periodic structure formed on a wafer.

FIG. 23 is a cross-sectional view of a wafer in which an amorphous carbon film is formed on the wafer so as to have a periodic structure, and a unidirectional diamond film is further formed.

FIG. 24 is a plan view showing a square Si resist film formed in a grid pattern on a circular Si wafer in a vertical and horizontal direction. The part with the line is the part without the resist.

FIG. 25 is a plan view and a cross-sectional view of the 2 × 2 element of FIG. 24; The cycle is 2.5 mm × 2.5 mm. The square resist pattern is 2.1 mm × 2.1 mm.

FIG. 26 is a partial plan view of a wafer that has been damaged by blasting diamond particles.

FIG. 27 is a cross-sectional view of a wafer after an amorphous carbon film is periodically formed on a Si wafer, and a unidirectional diamond film is formed thereon and polished.

FIG. 28 is a sectional view of a wafer in which a boron diamond film and a tungsten film are formed on the wafer of FIG. 27;

FIG. 29 is a sectional view showing a state in which tungsten is selectively etched by photolithography on the wafer of FIG. 28 to form electrodes.

FIG. 30 is a sectional view showing a state in which a non-doped diamond film is further selectively grown on the wafer of FIG. 29; Nothing grows on tungsten, amorphous carbon grows on amorphous carbon, and non-doped diamond grows on boron-doped diamond.

FIG. 31 is a cross-sectional view of a case where aluminum is further evaporated on the wafer of FIG. 30;

FIG. 32 is a sectional view showing a state in which aluminum is selectively etched on the wafer shown in FIG. 31 to form a gate electrode, thereby fabricating an FET.

FIG. 33 is a plan view showing a state in which aluminum is selectively etched on the wafer shown in FIG. 31 to form a gate electrode and a FET is manufactured.

[Explanation of symbols]

 Reference Signs List 11 vacuum chamber 12 susceptor 13 substrate 14 gas outlet 15 electrode 16 current introduction terminal 17 filament 18 gas introduction port 19 vacuum gauge 20 cooling medium 21 power supply 22 vacuum chamber 23 support rod 24 susceptor 25 substrate 26 source gas 27 outlet 28 cooling device 29 Magnetron 30 Vacuum waveguide 31 Plasma 32 Piston 33 Microwave 34 Resonance plate 35 Vacuum chamber 36 Susceptor 37 Substrate (substrate) 38 Plasma torch 39 DC power supply 40 Raw material gas 41 Rotating surface plate 42 Rotating spindle 43 Holder 44 Buffer plate 45 Wafer 46 Holder shaft 47 Pressure shaft 48 Arm 49 Hydraulic cylinder 50 Motor 51 Hydraulic cylinder 53 Output shaft 54 Pulley 55 Belt 56 Pulley 59 Groove 61 Grid 62 Power supply 65 Grid 66 Power supply Reference Signs List 70 magnetron 71 coupler 72 waveguide 73 mode selector 75 chamber 76 window 77 reaction chamber 81 power supply

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01L 21/205 H01L 21/205 (72) Inventor Naoji Fujimori 1-1-1, Kunyokita, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Inside the Itami Works (72) Inventor Takashi Tsukino 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Inside the Itami Works, Sumitomo Electric Industries, Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21 / 02 H01L 21/304 C30B 25/00

Claims (15)

(57) [Claims] 1. A substrate made of a material other than diamond having a slight warp, a substrate having a Rmax of 500Å (50 nm) formed by heteroepitaxial growth on the substrate and polishing.
A diamond film having a surface roughness of not more than Ra200 (20 nm), being convexly warped to the film side, and having a height ΔH with respect to a central portion of a peripheral portion of which is −150 μm ≦ ΔH ≦ −2 μm. Wafer. 2. The wafer according to claim 1, wherein the wafer is circular, has a diameter of 1 inch or more, and warps monotonically from the outer periphery toward the center toward the coating side. 3. The substrate is a (100) Si single crystal,
3. The wafer according to claim 2, wherein the (100) diamond film is heteroepitaxially grown. 4. A thin β layer between a diamond and a Si substrate.
4. The wafer of claim 3, wherein -SiC is present. 5. The diamond film has a thickness of 2 μm to 100 μm.
2. The wafer according to claim 1, wherein the thickness is 0 μm. 6. A gas containing at least hydrogen and a hydrocarbon gas is used on a convexly warped surface of a substrate made of a material other than diamond having a warp whose central part height is 2 μm to 150 μm with respect to a plane including a peripheral part. The diamond film is heteroepitaxially grown by a vapor phase synthesis method, and the diamond film is attached to a holder whose surface can be inclined so that the film is on the outside, and the film side is pressed against a polishing plate, and the holder surface is inclined to be convex. The warped thin film surface is polished, and the surface roughness is R
max500Å (50 nm), Ra200Å (20 n
m) A method for manufacturing a wafer, characterized in that: 7. In a cross section parallel to a substrate surface near an interface between diamond and a substrate, diamond or holes having a random orientation relationship with a substrate crystal are present,
Further, the surface is polished by Rmax 50 nm and Ra20n.
A wafer having a surface roughness of not more than m. 8. The diamond film has a thickness of 2 μm to 100 μm.
8. The wafer according to claim 7, wherein the thickness is 0 μm. 9. In the vicinity of a diamond substrate, a diamond material is used.
8. The wafer according to claim 7, wherein the wafer contains 1 ppm or more and 100 ppm or less of nitrogen. 10. A surface of a substrate made of a material other than diamond is partially damaged, and a portion which is initially damaged by a gas phase synthesis method using a gas containing at least hydrogen and a hydrocarbon gas is subjected to random treatment. A diamond film having an azimuth relationship is formed, and a diamond film that is azimuthally aligned with the substrate is formed on a portion not to be damaged thereafter,
This is mechanically polished so that the diamond film surface has a surface roughness of R
A method for manufacturing a wafer, wherein the wafer is smoothed to a maximum of 50 nm and Ra of 20 nm or less. 11. The wafer manufacturing method according to claim 10, wherein only the periodic pattern area on the substrate is damaged, and the other part is not damaged. 12. A concave portion is partially formed on a surface of a substrate made of a material other than diamond, and diamond is formed on a portion other than the concave portion of the substrate by a gas phase synthesis method using a gas containing at least hydrogen and a hydrocarbon gas. Generate a nucleus, form a diamond film oriented in alignment with the substrate, cover the upper part of the recess with diamond oriented in orientation, grow the diamond film so that the whole becomes a continuous film, and mechanically convert the diamond film. A method for producing a wafer, comprising polishing the surface of a diamond film to a surface roughness of Rmax 50 nm and Ra 20 nm or less. 13. The method according to claim 1, wherein the substrate is mounted on a holder whose holder surface is inclined with respect to the axis, the film side is pressed against a polishing plate, and the entire diamond surface is polished by tilting the holder surface. Claim 10 or 12
3. The method for producing a wafer according to 1. 14. An amorphous carbon film is partially formed on the surface of a substrate made of a material other than diamond, and thereafter, a diamond film is formed on the substrate and the amorphous carbon film, the diamond film being oriented with respect to the substrate. The surface of the diamond film is mechanically polished and the surface roughness is Rmax50n.
A method for producing a wafer, wherein the wafer has a smoothness of not more than m and Ra of 20 nm. 15. The method of manufacturing a wafer according to claim 14, wherein an amorphous carbon film is formed on the substrate periodically in a vertical and horizontal direction.