JPH0817693A - Hard material coated wafer and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Purpose] Conventionally, diamond, diamond-like carbon,
There was no large area substrate for materials such as c-BN that were difficult to make bulk crystals. It is an object of the present invention to provide large area wafers of these hard materials. [Structure] A hard material film is vapor-deposited on an existing wafer having a large area so that the film side is convex. The composite material having a convex film side is polished by a polishing device in which the holder surface can be inclined, and the entire surface of the thin film is polished. As a result, it is possible to obtain a large-area mirror wafer of a hard material that is smooth and has a warp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hard material coated wafer which can be used as a SAW (surface acoustic wave device), a thermistor, a semiconductor device substrate or disk protective film, an X-ray window, etc., and a method for manufacturing the same. Here, the hard substance means diamond, c-BN, diamond-like carbon and the like. If it is in bulk state, both are Vickers
The hardness Hv is 3000 or more. The sound velocity of these hard substances is extremely high, which is determined by the ratio of Young's modulus and density. Therefore, the velocity of the surface acoustic wave is also extremely fast. It is expected as a substrate element for SAW. SAW has uses such as a filter, a phase shifter, and a convolver. Diamond, c-
BN can be made into a semiconductor by doping impurities.

These hard materials have excellent physical and chemical properties. However, it is not widely used practically because it is impossible to make an inexpensive material with a large area. It is desired that the technology of Si semiconductor be diverted so that it can be used for various purposes. Therefore, it is necessary to manufacture a large-area wafer.

[0003]

2. Description of the Related Art Diamond, c-BN and diamond carbon can be formed into a thin film by a vapor phase synthesis method. This is a method of vapor-depositing a thin film of a hard material by flowing a raw material gas over an appropriate heated substrate. Hydrogen gas and hydrocarbon gas, or gas containing hydrogen gas and boron, gas containing nitrogen are introduced as raw material gases, given to a heated substrate, and a thin film is synthesized by a chemical reaction, and this is stacked on the substrate. It is something that goes.

There are several known methods for exciting a 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, it is also possible to produce a film of hard material having a large area. However, since the synthesis speed is slow, it is difficult to make a very thick film. If you take the time, you can make a fairly thick film. However, at present, there are no wafers of these hard materials. There is no diamond wafer or c-BN wafer. This is because it cannot be manufactured by the conventional technique.

[0005]

In order to apply diamond, c-BN, and diamond-like carbon to the field of electronics, a large area wafer of hard material is required. Conventionally, a surface acoustic wave device or the like has been made on a substrate having a small size. However, even if such an element is produced on a small substrate of 5 mm square to 10 mm square and it has an excellent effect, it has little industrial significance. Even if a small number of elements are manufactured on a small-area substrate, the productivity is poor and it is not practical.

The success of Si semiconductors lies in the fact that a large area wafer can be subjected to the same processing all at once, and a large number of equivalent elements can be simultaneously manufactured in large quantities. Diamond, c-B
In order for a hard material such as N or diamond-like carbon film to have a practical meaning as a substrate for manufacturing a device thereon, it must have a large area and be manufactured as a circular wafer. Only then, S
It will be possible to apply mature technology to i semiconductors. In the case of a Si wafer, an 8-inch wafer can be manufactured because any large single crystal can be pulled up. However, in the case of diamond or c-BN, a single crystal cannot be manufactured by the pulling method. For Si or GaAs
It is currently difficult to make a uniform material wafer made of the same material as described above.

Therefore, a composite structure in which a thin film is formed on another material is adopted without starting from a bulk single crystal. For example, a thin film of a hard substance is formed on a common and easily available single crystal material such as Si or GaAs.
With such a composite of a substrate and a hard material thin film, there is a possibility that a wafer having a large area can be manufactured. The substrate functions as a base for depositing reaction products during thin film formation. In order to obtain a wafer consisting of pure hard material only, it is necessary to form a thin film and then etch away the substrate material. However, this is not done at present. In order to make it a self-supporting film, you have to make a film that is too thick, but doing so will increase the amount of time and material,
Not realistic.

[0008] Therefore, it is inevitable to use a composite material with the underlying substrate left as a hard material wafer. In other words, it is a composite material wafer with the substrate attached. Since it is often the case that only the properties of the surface are used, there is no problem even if only one surface has a hard substance and the other surface is Si, GaAs or the like. By doing so, it is possible to overcome the problem that it is difficult to manufacture a bulk single crystal. This is because a wafer can be produced by the thin film manufacturing technique. Therefore, even if we say a hard material wafer here, it is quite different from making a wafer by thinly slicing a bulk single crystal such as Si. The composite wafer proposed here is different from a wafer such as Si because of its manufacturing method.

There are further conditions. As described above, there is an example in which a surface acoustic wave element or the like is conventionally formed on a substrate made of a hard material of 3 mm square or 5 mm square. The significance as a technical attempt is recognized. However, such a small substrate is industrially useless. Industrially, it is urgently desired to have a circular shape, a uniform thickness, a flat shape, no warp, and a large diameter. In terms of area, a circular or square wafer having a diameter of at least 1 inch is required for application as an electronic material. Without this size and width, the wafer process cannot be carried out.

Further, a wafer having a diameter of 2 inches rather than a diameter of 1 inch, and a diameter of 3 inches or more is preferable. A large, flat, smooth wafer is desirable. Fortunately, the progress of the vapor phase synthesis method has made it possible to form a considerably wide diamond film and a c-BN film on a suitable substrate. However, simply forming a wide thin film on a substrate does not make a wafer. It is useless if the surface is highly uneven. It also needs to be flat. There should be no warp and it should be a mirror surface. In order to make a device by photolithography on a wafer, the wafer is required to be flat and mirror-finished. This is because the pattern cannot be accurately drawn by optical means unless it is flat.

Since it is a thin film formed by vapor phase growth,
There are irregularities on the surface. A wavy surface is formed or a large number of particle-shaped projections are scattered. As described above, the coating of the hard material formed by vapor phase growth has severe irregularities, and it is very useless as it is. If there is unevenness, it can be polished. By polishing, a smooth and flat wafer should be formed except for protrusions, wavy surfaces, and uneven structures. Even in the case of Si, the ingot is thinly cut, and then etched and mirror-polished. Seems like the same thing as this. But not. There are some problems. Since the surface irregularities are removed by polishing, the initial thin film must be quite thick. It takes a long time to grow thick, and extra material is required.

This is an economic problem and can be overcome if time and materials are fully used. There is even greater difficulty. Hard materials make a very hard film and are difficult to polish. Since both diamond and c-BN are the strongest substances, the difficulty of polishing is incomparable to that of Si and the like. For the polishing, diamond abrasive grains are used, and they are said to be co-sliding, and polishing is performed over time. Since both the abrasive grains and the target thin film are ground, it is called shearing.

However, there is an even greater drawback. Since the thin film and the substrate have different coefficients of thermal expansion and the like, if they are cooled and taken out to the outside after the vapor phase growth, they greatly warp. The thin film side may be convexly curved, and the thin film side may be concavely curved. It may be flat overall. Focusing on the thin film side, what the thin film side warps convexly is called convex warping, and what the thin film side warps concave is called concave warping. When the area is small, the problem of warpage is hidden. As in the conventional case, in the case of a 3 mm square or 5 mm square substrate, no warpage occurs.

The present invention seeks to provide wafers of 1 inch and 2 inch order areas. The difference in the coefficient of thermal expansion between the substrate and the thin film and the warp due to the intrinsic stress of the film itself appear significantly. The large diameter increases the problem of warpage. This is serious. In the case of a Si wafer, a large flatness can be produced, but in the case of a hard substance, since it is a composite system, warpage becomes a serious problem. If there is a warp, there is a drawback in that the pattern cannot be accurately transferred by photolithography. But above all, if there is a warp, polishing cannot be done. If it cannot be polished, it will not become a mirror wafer. An object of the present invention is to provide a smooth hard material wafer having a practical size and width by overcoming many problems existing when a hard material is used as a wafer.

[0015]

A hard material wafer of the present invention comprises a diamond film, a diamond film and a diamond film formed on a substrate by a vapor phase synthesis method.
c-BN film or diamond-like carbon film with a thickness of 5μ
m to 100 μm (preferably 15 μm)
m to 50 μm is preferable), the thin film side is convexly warped, and the warp amount is 2
μm to 150 μm, the thin film of this hard material is polished to obtain Rmax of 500Å (50 nm) or less, Ra
It is set to 200 Å (20 nm) or less.

The vapor phase synthesis method used for forming the 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. In the case of diamond or diamond-like carbon film, the raw material is hydrogen gas, hydrocarbon gas, or the like. In the case of c-BN, hydrogen gas, boron compound gas, nitrogen compound gas or the like is used. In the case of diamond or diamond-like carbon film, hydrogen and hydrocarbon are mainly used as the source gas, but all or part of hydrogen may be replaced with an inert gas. In addition, organic containing carbon
It is also possible to replace the inorganic gas in place of the hydrocarbon. It is also possible to add an organic / inorganic gas containing oxygen.

The sample after vapor phase growth should be convexly warped to the thin film side. A flat one is impossible. It is not possible to have a concave warp on the thin film side. If it is not warped, it cannot be uniformly polished. Rmax 500Å (50 nm), Ra2 by polishing
The surface roughness is set to 00Å (20 nm) or less. With such a surface roughness, a wafer process such as electrode formation, impurity implantation, diffusion, and selective etching can be performed thereon by photolithography.

[0018]

1 is a sectional view of the hard material wafer of the present invention. Since the substrate and the hard material film have different coefficients of thermal expansion and form a thick film, a strong stress is generated when cooled to room temperature.
Therefore, the wafer becomes concavely warped on the film side or becomes convex on the film side. The former is called a concave warp and the latter is called a convex warp. The warp amount in the case of concave warp is positive, and the warp amount in the case of convex warp is negative. In the present invention, the warp of the wafer is from -2 μm to
It should be in the range of −150 μm. That is, the film is warped to the thin film side. Fig. 1 shows the convex warp and the warp Δ
H is negative.

The warp can be controlled by the conditions of vapor phase growth. A flat wafer may be formed depending on the conditions. Flat wafers seem most desirable but not so. This is not good because it is twisted as shown in FIG. 2 and unpolished portions remain after polishing. The present invention does not use a flat wafer. Also, do not adopt a concave warp on the thin film side. This is because a concave warp cannot be polished well.

The hard substance, substrate and warpage will be described below. [A. Hard Material Coating] The diamond film, diamond-like carbon film, and c-BN film should have the following characteristics. 1. Film thickness: 5 μm to 100 μm, especially 15 μm to 50 μm
m is desirable. If the film thickness is large, the cost of film formation increases. Although a film having a thickness of 1000 μm 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, it may even hit the polishing surface and crack. 2. Surface roughness: Rmax is 500 Å (50 nm) or less Ra is 200 Å (20 nm) or less If the surface roughness is higher than this, it cannot be used as a device wafer or a polishing-resistant wafer. This is because if the surface roughness is large, fine wiring cannot be formed on the surface. In addition, the coefficient of friction becomes large and it cannot be used for abrasion resistant tools.

[B. Substrate (Base)] Substrates on which this hard material thin film is formed include Si, GaAs, GaP, and Al.
N, SiC, Si ₃ N ₄ , LiTaO ₃ , LiNbO
₃ 、 Crystal etc. can be used. Of these, a Si wafer is particularly desirable. Furthermore, among Si, (100) Si wafer
Is the best. Depending on the material, the plate thickness t is 0.1 mmt
Approximately 1 mmt is preferable. If it is thinner than this, the warp is large and the probability of breaking increases. On the contrary, if the thickness is thicker than these, the semiconductor process cannot be performed. Device cannot be fabricated on it. Even if it is possible, it cannot be mounted unless it is polished and thinned.

The substrate of the wafer is preferably circular. However, a rectangular substrate may be used. In order to put it on a semiconductor process, a circular wafer like a Si wafer is easy to handle. The diameter is arbitrary, but considering the efficiency of the wafer process, 1 inch or more is necessary. Diameters of 2 inches, 3 inches, 4 inches, 5 inches, or 8 inches are also acceptable.

[C. Warp] It is necessary that the wafer is monotonically warped such that the thin film side is convex from the outer periphery to the center. Further, the absolute value of the warp is between 2 μm and 150 μm. Here, the warp is expressed by the height of the central portion from a plane including the peripheral portion of the base. If the thin film has a convex warp, it is negative, and if the thin film has a concave warp, it is positive. The above condition can be expressed as −150 μm ≦ ΔH ≦ −2 μm. More preferably, -50 μm ≦ ΔH ≦
-5 μm.

In the present invention, a wafer having no warp is denied. It seems best that there is no warp. However, when the warp is 0, it often has undulations as shown in FIG. 2, the structure of the warp is complicated, and polishing cannot be performed well.
Unpolished portions remain at random, or insufficiently polished regions occur. Even if there is some warp, it is better that the warp is simple. Therefore, the minimum value of warpage is set to 2 μm. On the other hand, if the warp is greater than 150 μm, an unpolished region will always remain after polishing. It is necessary to polish the entire surface uniformly, but since this cannot be done, those having a warp of more than 150 μm are excluded.

[0025]

EXAMPLE A diamond wafer, a c-BN, and a diamond-like carbon film of the present invention were formed by the steps as shown in FIG. 3, electrodes were formed, and the disconnection yield was examined. The three materials were made under the conditions and methods shown in the table below. The results are also listed in the table. Here, the diamond film is a representative
The case of a diamond film will be described. As shown in FIG. 3, a flat disk-shaped substrate is prepared. A diamond film was coated on a disk-shaped substrate by a microwave plasma CVD method, a filament CVD method, a plasma jet CVD method, and a flame method. The pressure is 1 to 300 Torr, and the methane / hydrogen ratio (CH ₄ / H ₂ ) is 0.1 vol% to 10
vol%. As shown in FIG. 3, a diamond film having irregularities is formed. Also, the substrate warps due to stress. The irregular diamond film was polished by a mechanical polishing machine.
As shown in FIG. 3, the surface becomes a smooth surface without irregularities.

Further, an aluminum film was vapor-deposited (FIG. 3). A part of aluminum was etched by photolithography to form fine wiring. Line width is 0.6 μm to 2 μm
Varied between. A diamond wafer having a fine parallel line pattern as shown in FIG. 3 is obtained. This is the same size as the comb-shaped electrode in the case of SAW. And the disconnection yield was examined. The results are shown in Tables 1, 2 and 3. The Young's modulus of the diamond film was measured by the vibration lead method. Table 3 shows the results.

[0027]

[Table 1]

Here, sample Nos. 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. As for the substrate, sample 1 is Si (10
0), sample 2 is Si (111), sample 3 is Si (pol)
y), sample 4 is GaAs, sample 5 is AlN, sample 6 is L
iNbO ₃ . Sample 7 is LiTaO ₃ and sample 8 is quartz. Sample 9 of the comparative example is polySi, and sample 10 is Si.
(100), sample 11 is LiNbO ₃ , sample 12 is Ga
It is As.

The thickness of the substrate is 0.1 mm to 1 mm.
The diameter of the substrate is 1 to 8 inches. The unit of the film thickness of the hard material film is μm. The film of hard material is 2 μm to 10 μm
The thing of 00 μm is grown. Sample 5 is a diamond-like carbon film grown. Sample 6 has a c-BN film formed. Sample 12 forms a c-BN film. Other samples grow diamond films as hard materials.

FIG. 4 is a schematic configuration diagram of the filament CVD apparatus. A susceptor 12 is provided inside the vacuum chamber 11. The substrate 13 is placed on this. Chamber 1
1 has a gas discharge port 14 and is connected to a vacuum exhaust device (not shown). Electrodes 15 are provided on the periphery of the susceptor 12. A filament 17 is attached between the electrodes 15. From the gas inlet port 18 of the chamber 11, raw material gas such as hydrogen or hydrocarbon gas is introduced. 19
Is a vacuum gauge. The filament is energized by the power source 21 to heat it. The heat of the filament 17 strongly heats the substrate and the gas. The 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.

FIG. 5 is a schematic configuration diagram of a microwave CVD apparatus. The raw material gas is sent to the vertically long vacuum chamber 22 from top to bottom. A susceptor 24 is provided on the 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 the 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 in the horizontally long vacuum waveguide 30. The plasma advances in a direction orthogonal to the flow of the raw material gas and excites the raw material gas to form plasma 31. The resonance plate 34 is moved by the piston 32, and a standing wave in an appropriate mode can be established.

FIG. 6 shows a plasma jet CVD apparatus. A susceptor 36 is provided below the inside of the chamber 35, and a substrate (substrate) 37 is placed on the susceptor 36. Chamber 35
A plasma torch 38 is installed above. This is to pass the gas 40 between the central cathode and the outer peripheral anode,
A DC voltage is applied by the power source 39 to cause discharge,
Use plasma. The gas is a gas such as argon or hydrogen for maintaining plasma lighting, a carrier gas or the like and a hydrocarbon gas as a raw material.

Diamond film, diamond-like carbon film,
As described above, the c-BN film is synthesized by forming the film on the heated substrate by flowing the raw material gas into the vacuum container and exciting it by heat or microwave. The raw material gas is composed of hydrocarbon gas and hydrogen gas. The hard material film can be formed by any other method, but any one of a microwave plasma CVD method, a filament CVD method, and a plasma jet CVD method is used here.

After synthesizing, the surface roughness Rmax, Ra of the surface
Was measured. Further, since warpage occurs, the warpage was measured as the height of the central portion with respect to the surface including the peripheral portion. The minus sign indicates convex warpage on the thin film side. Table 2 shows the surface roughness and the amount of warpage ΔH of the hard material film after synthesis. Warpage is the difference between the edge of the wafer and the height of the central portion. Even with the same curvature, the larger the diameter, the greater the warp. Assuming that the radius of curvature of the warp is R and the diameter of the wafer is D, and if the warp is along a spherical surface, the warp H is H =
There is a relationship of D ² / 8R.

[0035]

[Table 2]

The Rmax of the hard material film after synthesis is 0.15.
It is widely distributed between 100 μm and 100 μm. Ra is 0.
It is distributed between 05 μm and 40 μm. In sample 1, diamond is grown to a thickness of 30 μm on a 2-inch Si substrate. The surface roughness after synthesis is Rmax 2.5 μm and Ra 0.5 μm. It is quite smooth. The warp is −15 μm. The film is warped to be convex. Sample 2 is 4 inch Si
The substrate is used, but this is also 50μ so that it is convex on the film side.
There is a warp of m.

The Si 8-inch substrate of sample 3 is used. This is warped by 150 μm on the film side convex. Obviously, the warp increases with the size of the substrate. Sample 5 is a diamond-like carbon film formed on a 3-inch AlN substrate. This is also Rmax 0.4μm, Ra 0.18μ
It was m. It turns out that it is extremely smooth. It is a convex warp, and the warp amount is −5 μm. Both unevenness and warpage are small.

Sample 6 is a 30-μm thick c-BN film formed on a 2-inch LiNbO ₃ substrate. Rm
The ax is 1.6 μm, the Ra is 0.5 μm, and the warp is -50 μm (convex to the film side). This is also smooth. Sample 7 is 5
This is a 100 μm thick diamond formed on an inch LiTaO ₃ substrate. Rmax 7 μm, Ra
It is 4.2 μm and has a warp of −5 μm (convex to the film side). There is unevenness, but there is little warpage.

Sample 8 is one in which diamond is grown on a quartz substrate having a thickness of 1 mm and a diameter of 4 inches. This is Rmax of 0.3 μm and Ra of 0.1 μm, and the surface roughness is extremely low. On the other hand, however, the warp is considerably large at -50 μm. Sample 9 is a thin 2-inch Si wafer having a thickness of 50 μm and a thick diamond film (150 μm) formed thereon. This sample with thicker film cracked the substrate. Warpage is not measured. Since this cannot be polished, the subsequent steps are not performed.

Sample 10 has Rmax of 0.15 μm and Ra
It is smooth at 0.05 μm. This is a thin film (2μ
It depends on m). However, the warp is large, and the film side warp is warped by 200 μm. Since the diameter of the Si substrate is as large as 8 inches, the warpage will be large. Sample 1
No. 1 is Rmax 100 μm and Ra 40 μm, and the surface is very rough. The fact that the film thickness is thick (1000 μm) may also have an influence. Moreover, the board is broken. Subsequent polishing cannot be performed.

The sample 12 has zero warpage. This sample is G
Although diamond is formed on aAs, the warpage is likely to be small because the thermal expansion coefficient is similar. The surface roughness of this sample is Rmax 2.1 μm, Ra 0.
Since it is as small as 9 μm, it seems to be a good sample. But it turns out later that this is not the case. Since the vapor-grown hard material film has a large surface roughness, an electronic device cannot be formed on the hard material film by photolithography as it is. I have to polish it. However, it is not possible to polish a warped wafer with an apparatus for polishing Si or GaAs. Even if a warped wafer is attached to a flat polishing head and pressed against a polishing plate to polish, the peripheral portion is unpolished or the central portion,
Alternatively, the middle part becomes unpolished. Special polishing equipment is required.

With a special polishing apparatus, the hard substance film was mechanically polished with the substrate still attached. Then, the surface roughness and the amount of warp after polishing were measured. In addition, some samples cannot be completely polished because they have irregularities. Therefore, the ratio of the area that could be polished was also examined. Polishing reduces the surface roughness. The warp amount may be decreased or increased by polishing. It tends to decrease. Conventional Si and GaAs polishing methods
This is different from the above case, so this will be described first.

An outline of the polishing apparatus is shown in FIG. An enlarged cross-sectional view of the holder portion is shown in FIG. The rotary platen 41 is supported on a rotary spindle 42 and rotates. Abrasive grains of diamond are fixed on this. Since the diamond is polished, the diamond particles are 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 a long time of hundreds of hours. Cushion plate (rubber-like plate) for holder-43
44 is adhered, and a wafer (those obtained by growing a film of diamond, diamond-like carbon, and c-BN on a substrate) is attached onto the wafer. One idea is to use a cushioning material. A holder shaft 46 is attached to the center of the holder 43. It is not fixed but transmits rotational torque, but the holder surface can freely tilt with respect to the shaft. The holder rotates about its axis, and the rotary platen 41 revolves around the sun.

A point on the upper surface of the holder 43 is pressed by the pressure shaft 47. The upper ends of the pressure shaft 47 and the holder shaft 46 are supported by the arm 48. A hydraulic cylinder 49 for applying pressure to the holder shaft 46 is attached to the arm 48. Holder
Polishing is performed by applying a strong force to the shaft 46 so that both the diamond abrasive grains and the diamond film are consumed. Arm 48
Has a motor 50, and the rotational force of the motor 50 is
To rotate. Rotational torque is transmitted from the pulley 54 attached to the output shaft 53 of the motor to the pulley 56 fixed to the holder shaft 46 via the belt 55. This causes the holder to rotate about its axis. A hydraulic cylinder 51 for applying pressure to the pressure shaft 47 is provided on the arm 48. As shown in FIG. 8, there is a circular groove 59 on the upper surface of the holder-43, and the pressure shaft 47 holds the groove.

The holder shaft 46 holds the center of the holder and rotates it, but allows the holder to tilt. Pressure shaft 4
The pressure of 7 causes the surface of the holder-43 to be inclined with respect to the surface of the rotating platen. The wafer-45 has a convex warp, but the holder-
Leans. The tilt angle depends on the pressing force of the pressure shaft. The contact point of the wafer with the rotary platen can be changed by changing the pressure applied to the pressure shaft. By moving the contact point from the center to the periphery, it is possible to evenly polish the periphery. Alternatively, the polishing can be performed from the peripheral portion toward the center.

When the wafer is polished by the usual polishing apparatus in which the holder shaft and the holder are fixed, the entire diamond film cannot be polished. There is always a part that cannot be polished somewhere. If the amount of polishing is increased, it can be scraped, but if so, the diamond is completely removed in other parts, and a part where the substrate is exposed occurs. The results of the polishing using the ordinary shaft fixing holder and the polishing of the present invention using the shaft tilt holder of FIGS. 7 and 8 will be described with reference to FIG. 9 (1)-
(3) is polished by a shaft fixed holder. The state after polishing differs depending on the state of warp of the wafer immediately after synthesis.

(1) In the case of flat wafer: It seems that the flat wafer is polished flat immediately after the synthesis, but it is not so. As shown in (1) of FIG. 9, unpolished portions are randomly generated somewhere. The unpolished part is rough, and the light reflection is weak, so it looks dull. It's easy to see with the naked eye. A flat wafer after synthesis is not good because it becomes uneven and leaves an unpolished portion. This is something else. (2) In case of concave warp ... In case of concave warp (ΔH> 0)
As shown in (2), the ring-shaped unpolished portion remains in the intermediate portion.

(3) In case of convex warp ... In case of convex warp (ΔH
For <0), an unpolished portion remains on the outer peripheral portion as shown in (3) of FIG. However, as in the present invention, when a wafer having a convex warp (ΔH <0) is polished 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 entire surface is polished. can do. Since it is evenly polished,
The polishing results according to the present invention are not shown. 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 after polishing, the polished area, and the amount of warpage were measured.
The results of this are shown in Table 3.

[0049]

[Table 3]

The surface roughness after polishing is Rmax 10Å-100
0Å and Ra3Å to 400Å. It should be noted that the units of surface roughness are different. In Table 2 before polishing, μm is used, and in Table 3 after polishing, Å is used as a unit. Sample 1 has a medium surface roughness immediately after synthesis, but has Rmax80Å after polishing.
Ra10Å has been reduced. The warpage is -14 μm, which is almost unchanged before and after polishing. Sample 2 has a medium surface roughness after synthesis. This is after polishing, Rmax100Å, Ra20
It becomes Å, and also has a medium surface roughness. With this level of surface roughness, a pattern can be drawn sufficiently by photolithography. The warp is −48 μm, which is about the same as that before polishing.

Immediately after the synthesis, the sample 3 having a large surface roughness has Rmax 400Å and Ra 80Å after polishing. If the surface roughness is high before polishing, the surface roughness is high even after polishing. The warp was −150 μm before polishing and −139 μm after polishing.
It becomes m. Warpage is almost unchanged. Sample 4 is a diamond on a GaAs substrate, which has a low surface roughness from the beginning,
After polishing, Rmax50Å and Ra4Å. The warp was -30 μm immediately after the synthesis, but it was −30 μm even after polishing.
It does not change with m.

Sample 5 is a diamond-like carbon film, originally having a small surface roughness, but after polishing, Rmax10.
Å, Ra3 Å. It is extremely smooth. The warp is -5 μm before polishing and -5 μm after polishing, which is unchanged. Sample 6 is an example of growing c-BN. This is also a sample having a small surface roughness, and after polishing, Rmax30
Å, Ra6Å. The warp is also -50 μm and does not change.

Sample 7 is 100 μm on a LiTaO ₃ substrate.
m diamonds are formed. The surface roughness before polishing was poor, but the surface roughness was poor even after polishing. Rmax5
00Å and Ra200Å. Sample 8 is a 4-inch crystal substrate on which diamond is formed. Although the surface roughness was extremely low, the surface roughness was small and smooth even after polishing. Rmax10Å and Ra3Å.

Sample 10 has a small surface roughness after synthesis (before polishing). Rmax is 0.15 μm and Ra is 0.05 μm. The warp at that time is +200 μm. Since the surface roughness is originally low, it seems that the surface roughness becomes smaller by polishing. This is not the case. The surface roughness after polishing is Rmax 700Å and Ra 250Å. Polishing is not effective. Furthermore, 50% of the unpolished portion remains. Why doesn't the originally low surface roughness become smooth by polishing? Since the film is distorted so as to be concave, the film surface does not come into sufficient contact with the polishing plate even when a strong pressure is applied, and polishing is hardly possible. It will be seen from Sample 10 that the positive and negative of the warp affect the polishing.

Sample 12 is obtained by growing c-BN on a GaAs substrate. Surface roughness before polishing is low. Rma
x2.1 μm and Ra 0.9 μm. Moreover, the warp is zero. Looks ideal. If this is polished, an extremely smooth wafer is likely to be produced. But not. By polishing, the surface roughness is Rmax1000Å, Ra400Å
become. Moreover, 10% of the unpolished portion remains. When there is no warp, unpolished parts remain randomly. If there is no overall warpage, there is undulation, and the substrate has irregular distortion. The part that cannot be polished remains because the contact with the polishing plate becomes uneven.

Surface roughness is 1/30 to 1/100 by polishing
Decrease to a degree. However, this is also the case where the warp amount is small, and if the warp amount is large, the polishing cannot be sufficiently performed. The amount of warpage tends to be slightly reduced by polishing. The concave warp remains concave, and the convex warp remains convex, but the warp amount is reduced by about 0 to 20%. Samples 1 to 8 are convexly warped (the hard material film side projects).
The comparative sample 10 has a concave warp (the diamond film is concave).

Next, aluminum was vapor-deposited on the surface of the hard material coating, and a comb-shaped electrode was formed by photolithography. The line width of the electrodes is 0.6 μm to 2 μm. The thickness is 1500Å (150 nm = 0.15 μm).
The electrodes may be broken due to the unevenness. Therefore, the proportion of samples that did not break (breakage yield) was also examined.
The results are shown in Table 4.

[0058]

[Table 4]

The Al electrode patterns formed on the films of Examples (Sample 1 to Sample 8) have a line width of 0.6 μm to 2 μm. Sample 1 is a 2-inch (100) Si substrate coated with 30 μm of diamond. When an aluminum electrode pattern with a line width of 1 μm is formed on this, the yield is 98%.
Is. Sample 2 is 50 on a 4-inch (111) Si wafer
A μm thick diamond film is grown. When an aluminum comb-shaped electrode having a line width of 0.8 μm was formed, the disconnection yield was 96%. This means that submicron electrodes can be formed with a high yield.

Sample 3 is an 8-inch poly-Si wafer,
It is a stack of 100 μm diamond films. Although this has a large warp, the yield of electrodes having a width of 1.2 μm is 97%. The result is satisfactory. Sample 4 is a 1-inch GaAs wafer coated with a 15 μm thick diamond film. If an electrode having a line width of 1.5 μm is formed on this, a yield of 95% is obtained. This is also a good result. Sample 5 is a 3 inch AlN wafer coated with a 5 μm thick diamond-like carbon film. Flatness (warp −5 μm) and smoothness (Rmax10
Å, Ra3Å) is also good. When a comb-shaped electrode having a width of 0.6 μm was produced, the yield was 94%. This is the narrowest electrode, but with such narrowness the yield is amazing.

Sample 6 may be a 2-inch ΦLiNbO ₃ substrate with 30 μm of c-BN. The warp is considerably large (-50 μm). The yield when an electrode having a width of 1 μm is formed is 99%. This means that even if the warp is large, it is possible to make a thin electrode. Also c-BN
But it means that you can make excellent wafers. Sample 7 is 1 on 5 inch LiTaO ₃ substrate
This is an example of forming a diamond film having a thickness of 00 μm.
This has a poor surface roughness (Rmax 50 nm, Ra 20 n
m) The yield of electrodes having a width of 0.8 μm is 94%. This is satisfactory data.

Sample 8 is a 5 inch diamond film formed on a 4-inch Φ quartz crystal. The surface roughness is good, but there is considerable warpage (-50 μm). On top of this,
When a comb-shaped electrode having a line width of 2 μm is formed, the disconnection yield is 9
It became 7%. Hard material wafers according to these examples
Shows a disconnection yield of more than 90% for the formation of comb electrodes. In other words, there is almost no disconnection. This is because the film surface is smooth and there are few irregularities. This means that when used in a surface acoustic wave device, a device with extremely excellent characteristics can be obtained with a high yield. The fact that a thin electrode pattern can be obtained even when used in a semiconductor device means that various structures can be produced by using a lithography technique.

Among the comparative examples, sample 9 was not able to be polished and electrodes could not be formed because the substrate had cracks during synthesis. Sample 11 has a cracked substrate during diamond synthesis,
Cannot polish or form electrodes. Sample 10 was a 8-inch Si substrate on which a diamond having a thickness of 2 μm was formed, but this has a poor surface roughness after polishing (at the polishing portion: Rma:
x70 nm, Ra25 nm). Also the warp is +200 μm
And it is a concave warp. Moreover, there is as much as 50% of the unpolished portion. When a comb-shaped electrode having a width of 1 μm is formed in the polished region, the yield is only 3%. This means that almost no electrodes can be made. This is because the warp is concave,
This may be due to insufficient polishing.

Sample 12 is a 3 inch GaAs wafer with 30
It is coated with c-BN of μm. It is a fairly thick coating. The warp is 0, but as described repeatedly above, in reality, there is undulation and there is twist, so that it cannot be polished smoothly. Surface roughness is poor (Rmax
100 nm, Ra 40 nm). There are 10% of polishing residue. If you try to attach an electrode with a width of 0.6 μm to this,
The yield was 15%. This is not a practical result. It is considered that this is also because polishing cannot be performed and the surface roughness after polishing is poor.

[0065]

EFFECT OF THE INVENTION Diamond, diamond-like carbon, c
Bulk substrates of hard materials such as BN have been made in various ways. However, both of them have a small area,
It may have some meaning for experiments, but it has little practical significance. The present invention provides for the first time a large area wafer of the highest hardness material such as diamond, diamond-like carbon, c-BN and the like. This is a composite structure in which films of these hard materials are formed on a readily available crystal substrate. In this respect, the meaning is different from that of conventional wafers such as Si semiconductors and GaAs semiconductors. Not made entirely of hard material. However, if hard materials are to be used as electronic materials, often only the upper layer of the wafer is needed. The hard material wafer of the present invention is sufficiently effective for such applications.

Since the hard substance is produced by vapor phase growth, it can be made wide without limitation on the area. If a large substrate material is used, an arbitrarily large wafer can be manufactured. However, when a composite material is used, the coefficient of thermal expansion is remarkably different, so that warpage occurs after synthesis. According to the conventional technical idea, a warped object cannot be polished. It was that only flat ones could be polished. However, the inventor believes this is not the case. If the warp is convex toward the film and is −150 μm ≦ ΔH ≦ -2 μm, it can be uniformly polished by a holder that swings and precesses. It is an important point of the present invention that the possibility of polishing a warped plate is noticed. In the case of convex warp, the entire surface can be uniformly polished by the apparatus shown in FIGS.

Since it can be polished, it becomes possible to make a mirror wafer of a hard material. Since it is polishing of a hard substance, it is necessary to grind while consuming diamond abrasive grains over time, but grind while gradually tilting the surface of the holder from the central portion to the peripheral portion. Alternatively, gradually scrape the surface of the holder diagonally and horizontally from the peripheral part to the central part. Rmax 500Å (50 nm), R for the entire warped wafer
A surface roughness of 200 Å (20 nm) or less can be smoothed. If the surface roughness can be lowered to this extent, various devices can be manufactured by photolithography.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a warped hard material wafer having a hard material film formed on a substrate.

FIG. 2 is a cross-sectional view showing an example of a hard material wafer in which the warpage as a whole is 0, but the uneven material warps are mixed and have undulations.

FIG. 3 is a schematic cross-sectional view showing a step of coating a hard material film on a substrate, polishing it, and further forming electrodes.

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

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

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

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

8 is an enlarged cross-sectional view of only a holder portion of the polishing apparatus shown in FIG.

FIG. 9 is a bottom view showing a surface of a wafer after polishing for explaining that an unpolished portion remains when a hard substance-coated wafer is attached to a flat holder and polished. (1) is a polished flat wafer after synthesis, (2) is a concave warped wafer, and (3) is a convex warped wafer.

[Explanation of symbols]

 11 vacuum chamber 12 susceptor 13 substrate 14 gas discharge port 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 Source Gas 41 Rotating 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

Front page continuation (72) Inventor Naoji Fujimori 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (8)

[Claims] 1. A substrate having a slight warp, and a coating made of a hard substance having a Vickers hardness Hv of 3000 or more, which is coated on at least one surface of the substrate by a vapor phase synthesis method, and has a plate thickness of 0. 1 mm to 2.1 mm, the outer diameter is 1 inch or more, and the surface roughness of the hard material coating is Rma.
x500Å (50 nm) or less, Ra is 200Å
There is 50% or more of the portion of (20 nm) or less, the substrate is convexly warped to the hard material coating side, and the height ΔH with respect to the central portion of the peripheral portion is −150 μm ≦ ΔH ≦ −
A wafer coated with a hard material, characterized in that it has a thickness of 2 μm. 2. The hard substance-coated wafer according to claim 1, wherein the wafer has a circular shape, and is monotonically convexly warped from the outer periphery toward the center toward the coating film side. Wherein the thickness of the substrate T _2, the thickness of the hard material coating and T _1, the thickness of the hard material coated T ₁ and the substrate thickness T ₂
Ratio (T ₁ / T ₂ ) is 0.05 to 1, the substrate thickness T ₂ is 0.1 mm to ₂ mm, and the coating thickness T ₁ is 0.002 mm to 0.2 mm. The hard material-coated wafer according to claim 1 or 2, which is characterized in that. 4. The hard material is diamond, c-BN,
The hard substance-coated wafer according to any one of claims 1 to 3, wherein the wafer is a diamond-like carbon film. 5. The substrate, S, which is a single crystal or a polycrystal.
i, GaAs, GaP, AlN, SiC, Si ₃ N ₄ ,
The hard substance-coated wafer according to any one of claims 1 to 4, which is any one of LiTaO ₃ , LiNbO ₃ , and quartz. 6. The hard substance-coated wafer according to claim 5, wherein the substrate is a (100) Si single crystal. 7. A method of vapor phase synthesis on a flat substrate,
The hard material coating is formed so that the coating side is convex and the height ΔH of the central portion with respect to the surface including the peripheral portion of the substrate is 2 μm to 150 μm, and the substrate side is attached to the polishing holder and applied to the rotating surface plate. A hard material characterized by inclining the surface of the polishing holder and gradually polishing the convex surface of the hard material from the center to the outside or from the peripheral portion to the central portion to polish the entire surface. Method for manufacturing coated wafer. 8. The surface roughness after polishing is Rmax500Å
The method for producing a hard substance-coated wafer according to claim 7, wherein the thickness is (50 nm) or less and Ra200Å (20 nm) or less.