JP2006131969A - Anodic chemical conversion method and apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anodic chemical conversion method and an apparatus therefor in which a substrate to be treated is almost horizontally held. <P>SOLUTION: A silicon wafer is almost horizontally placed, and utilizing its buoyancy, the silicon wafer is floated on an electrolytic solution. An edge is formed of an expansive and corrosion resistant material on the outer circumference of the silicon wafer, and the edge is floated on the electrolytic solution. Further, a liquid reservoir is made also inside the edge, and an electrode is floated thereon, and is used as an anode side. In this state, anodic reaction is performed, thus the face in contact with the liquid is chemically converted, and the upper side functions as a current feed face. Both anode and cathode are arranged utilizing the buoyancy of the electrode material via the liquid and play roles as current feed and electrode holding. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an anodizing method and apparatus, and more particularly to an anodizing method and apparatus for holding a substrate to be processed substantially horizontally.

  At present, various anodizing treatment methods for silicon wafers have been proposed with a focus on the manufacturing process of SOI (Silicon On Insulator) wafers. The basic principle of the anodizing treatment method is that when a silicon wafer is placed in the HF solution with the anode side as the anode side, and a cathode electrode is formed with platinum or the like, the silicon reacts with the HF solution and dissolves on the surface of the silicon wafer. The surface of the silicon substrate has a porous shape with a single crystal structure.

  Anodized substrates are used in fields such as the formation of intermediate layers in the production of light emitters and SOI wafers. Further, in the future, it is expected that the porous shape will be applied to a manufacturing process of a diffusion wafer used as a substrate for a power transistor or a switching element.

The diffusion wafer diffuses phosphorus or boron at a high concentration into a silicon lightly doped wafer (its impurity concentration is about 10 ¹⁴ atoms / cc) (its impurity concentration is about 10 ²⁰ atoms / cc) and uses that portion as an electrode. However, by making the Si surface porous when diffusing impurities, the surface area can be increased 100 to 1000 times, and the diffusion rate can be greatly improved. In other words, in the current manufacturing process, it is possible to reduce the time required for diffusion from one hundred to three hundred hours to less than half of this, which greatly reduces the manufacturing process time and the manufacturing cost, especially the furnace used for diffusion. Therefore, there is a great prospect as a low-cost technology in the diffusion wafer manufacturing process.

  There are various methods that can be applied to the manufacturing process of diffusion wafers, but a method has been proposed in which the HF solution is divided into two parts on the wafer and the anodization treatment is performed using one side as the anode and the other side as the cathode (for example, , See Patent Document 1). In manufacturing a diffusion wafer, it can be said that a method using this method is suitable for practical use.

That is, since the wafer is not directly used as an electrode, there is an advantage that it is not necessary to perform conductive processing on the wafer, the wafer is not damaged, the time and labor for processing each wafer can be omitted, and it is suitable for mass batch processing.
Japanese Patent Laid-Open No. 5-198556

  In the conventional method described above, the wafer is placed vertically as a method for dividing the solution into two by the wafer. This is advantageous in terms of mass batch processing, but dividing the liquid requires prevention of liquid leakage, and various methods such as crimping of Teflon (registered trademark) material and setting of ring-shaped jig Has been proposed. However, since it is fundamentally placed vertically, it is difficult to completely eliminate the possibility of leakage to the opposite side of the liquid due to the influence of water pressure and energization even if the jig is designed with high accuracy. In addition, wafer formation is not performed in the process where the liquid is directly energized without passing through the wafer due to liquid leakage. However, it is also difficult to detect the direct energization of the liquid in advance, and a detection device is displayed. If you try to install it in there, it will cost too much. The product check after the completion of the process reveals it for the first time, but in the case of a diffusion wafer, whether or not it is formed to a predetermined thickness in the depth direction is an important guarantee item in terms of product characteristics, and this involves destructive inspection, Cannot judge immediately.

  In general, the wafer jig has a complicated structure and requires high precision. However, it is inevitable to increase the cost in terms of design and manufacturing under the constraints that the material is not eroded by HF and does not damage the wafer.

  Therefore, if a solution splitting method using a wafer can be proposed with an anodization method that can be manufactured at a lower cost than existing known technologies by performing the solution splitting method more easily and reliably, stable mass production is possible. Can be expected to be possible.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an anodizing method and apparatus for holding a substrate to be processed substantially horizontally.

  According to one aspect of the present invention, there is provided an anodizing method characterized in that only one surface of a substrate to be processed held substantially horizontally is brought into contact with an electrolyte solution and the substrate to be processed is subjected to chemical conversion treatment.

  According to another aspect of the present invention, an electrolyte bath containing an electrolyte solution, a negative electrode plate disposed in the electrolyte solution, and disposed in the electrolyte solution facing the negative electrode plate. And a substrate supporting means for supporting the substrate so that one surface of the substrate is immersed in the electrolyte solution, and a means for applying a voltage to the electrode. The substrate supporting means is a side surface of the substrate to be processed. Sealing and supporting the entire circumference of the outer peripheral portion, supporting the positive electrode plate spaced from the substrate to be processed, and filling the conductive liquid between the substrate to be processed and the positive electrode plate. A featured anodizing device is provided.

  It is preferable that a stopper member for preventing sedimentation of the substrate to be processed into the electrolyte solution is further provided below the substrate to be processed supporting means.

  Further, the electrolyte solution is preferably a hydrofluoric acid mixed solution composed of hydrofluoric acid or alcohol diluted with pure water.

  According to the anodizing method and apparatus therefor according to the present invention, since only one side of the substrate to be processed is in contact with the electrolyte solution, both surfaces of the substrate to be processed are completely separated, and the liquid between both surfaces of the substrate to be processed is visually observed. The presence or absence of energization can be determined, and no special detection device is required.

Further, the substrate support jig to be processed only needs to secure the airtightness only on the outer periphery of the substrate to be processed, and can be produced relatively easily and at low cost.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an apparatus used in an anodizing method according to an embodiment of the present invention. An anodizing apparatus 10 shown in FIG. 1 is arranged in an electrolyte solution 2 containing an electrolyte solution 1, a negative electrode plate 3 arranged in the electrolyte solution, and opposed to the negative electrode plate 3 in the electrolyte solution. A substrate support means 5 for supporting the surface of the silicon wafer 4 as a treatment substrate so as to be immersed in the electrolyte solution, and a voltage application means 6 to the electrodes are provided.

  The target substrate support means seals and supports the entire outer periphery of the side surface of the target substrate, supports the anode plate 7 at a distance from the target substrate, and conducts electricity between the target substrate 4 and the anode plate 7. The working liquid 8 is filled.

  The silicon wafer 4 is floated on the electrolyte solution 1 by placing the silicon wafer 4 substantially horizontally and using its buoyancy. First, the edge 5 a is formed on the outer periphery of the silicon wafer with a material excellent in stretchability and corrosion resistance, and this is floated on the electrolyte solution 1. Further, a liquid reservoir is also formed inside the edge, and the anode plate 7 is floated on the inside to make the anode side. By performing anodization in this state, the surface in contact with the liquid is formed, and the upper surface side functions as a current supply surface. That is, both the anode and the cathode are arranged by utilizing the buoyancy of the electrode material through the liquid, and play a role of supplying current and holding the electrode. As a result, the area of the cathode can be gained with almost the same area as the chemical conversion surface of the silicon wafer, so that the current density necessary for the anodization can be secured and the anode side liquid and the cathode side liquid are completely removed by the silicon wafer 4. A separate state can be created. The electrolyte solution is a silicon-soluble solution, and for example, a hydrofluoric acid mixed solution composed of hydrofluoric acid and alcohol diluted with pure water can be used. The electrode is preferably made of a metal material having corrosion resistance against a silicon-soluble solution, and for example, platinum or a platinum alloy can be used.

  The material of the substrate support means 5 to be processed, that is, the silicon wafer support means, is preferably, for example, fluororesin, rubber, or tetrafluoroethylene resin. It is because it is preferable that electrical insulation, acid resistance, and alkali resistance are favorable. Of course, the selection is made in consideration of flexibility, elasticity, airtightness or machinability.

  In the anodizing method according to the present invention, it is important that the outer peripheral edge 5a formed on the outer periphery of the silicon wafer 4 has sufficient leakage resistance. With respect to leakage resistance, it can be sufficiently handled by existing well-known and commonly used techniques, and since ensuring leakage resistance is not the gist of the present invention, detailed description thereof is omitted.

  Since buoyancy is used, if there is a liquid leak, the silicon wafer 4 will be submerged, and at that time, an error can be confirmed visually. Needless to say, a silicon wafer immersion sensing system may be constructed in combination with a liquid level sensor, a current sensor, and the like.

  As shown in FIG. 1, a stopper 9 may be provided that receives the silicon wafer 4 when it is submerged and submerged. It is possible to incorporate safety measures such as installing a sensor here to activate an interlock for emergency stop when a silicon wafer is inundated.

FIG. 2 shows a schematic structure of the outer peripheral edge 5a. As shown in FIG. 2 (a), the material is in close contact with the edge of the silicon wafer to prevent the ingress of liquid and is excellent in HF corrosion resistance. At present, Teflon (registered trademark) -based materials are used. It is valid. Alternatively, a plastic material coated with Teflon (registered trademark) may be used. As shown in FIG. 2B, the belt-like material 5b slightly longer than the outer periphery of the silicon wafer is wound tightly so as to bite into the outer periphery of the wafer. As shown in FIG. Secure with. Because it looks like a box shape, if you pay close attention to balance, weight distribution, and weight limit, even if you put more liquid in this and float the electrode, you can hold it with this box-shaped buoyancy and it is airtight It is only necessary to hold this outer peripheral part.
A conductive liquid 8 is further spread on the upper surface of the silicon wafer provided with the outer peripheral edge 5a, and an electrode 7 having the same area as that of the silicon wafer 4 made of the same conductive material is floated on the water surface. The electrode 7 has a lead wire shape so that the floating electrode does not cover the surface, and the electrode 7 has a function of maintaining a height that does not sink into the liquid. The liquid 8 used here may be any conductive liquid that does not corrode the silicon wafer 4, the outer peripheral edge 5 a, and the electrode 7 and does not adversely affect the electrical characteristics of the silicon wafer 4. There is no need. Since there is no need to use an HF solution, the electrode material must also be a material that copes with corrosiveness and metal contamination of silicon, and can be a light material that floats in a liquid. (Material coating etc.) In addition, since silicon and the electrode are in electrical contact with each other through a liquid, it is not necessary to directly process the silicon wafer 4 itself, and the electrical contact performance is as high as that of a known technique.

  In the actual anodizing treatment, the liquid level at the edge of the silicon wafer 4 may be disturbed due to vibration of the liquid or other changes in the liquid level due to external factors, so that the silicon wafer 4 may settle down. The design which we did becomes necessary. Furthermore, in order to realize this method, the liquid injection method, the installation method on the liquid surface, the method for dealing with abnormalities, the silicon wafer recovery method, the inspection method, etc. are not necessarily limited to a single method, Depending on the shape of the aquarium, the scale of the processing equipment, etc., the shape and material can be used to some extent, and can basically be dealt with by applying existing technology. For example, it is preferable that the silicon wafer 4 is once positioned with pins or the like, and the liquid is slowly poured into the water tank, and the liquid injection is stopped after confirming that the silicon wafer 4 has floated.

  Next, another anodizing apparatus for performing anodizing treatment by bringing only one side of a silicon wafer held substantially horizontally into contact with an electrolyte solution will be described. FIG. 3 shows an anodizing apparatus 30 using a spin coater. In this anodizing apparatus 30, for example, an HF solution is supplied from a primary supply tank 31 and a secondary supply tank 32 to a liquid tank 33, and a chuck unit 34 for mounting a silicon wafer 4 and a chuck unit 34 are placed in the liquid tank 33. And a vacuum line 36 for evacuating the silicon wafer 4. A discharge nozzle 37 that discharges the solution is provided below the secondary supply tank 32, and an open portion of the liquid tank 33 is covered with a scattering prevention cover 38.

  In FIG. 3, the anode side has a structure in which the silicon wafer 4 is vacuum adsorbed to the spin coater. The chuck surface of the chuck portion 34 has a conductive portion 34a having substantially the same shape and area as that of the silicon wafer, but is not protruded from the silicon wafer. This is to prevent the HF solution from being applied to the conductive portion 34a of the chuck.

  The shape of the chuck portion 34 can be arbitrarily set depending on the balance between the vacuum suction hole and the suction area. In this state, the silicon wafer 4 is rotated relatively slowly, and the HF solution is continuously discharged onto the silicon wafer 4. The HF solution has conditions (concentration, presence / absence of additives) according to the anodizing treatment. The discharge nozzle 37 is made of platinum, and a negative potential is applied using the nozzle 37 as a cathode. The potential is set according to the chemical conversion conditions. The anodizing device 30 includes an applied current circuit 39.

  The chuck unit 34, the surface of the silicon wafer 4, the discharge HF, and the nozzle 37 are energized, and a current is applied continuously. All HF solutions can be recovered and recycled. Further, it is desirable to attach a cover or the like so that the HF solution scattered on the nozzle 37 and the chuck portion 34 is not applied. In this anodizing apparatus 30, the electric charge is moved through the discharge liquid in which the anode and the cathode are flowing, and the anodizing proceeds here. As the chuck surface, the entire surface of the silicon wafer can be used as the contact portion of the anode and the HF solution can be prevented from contacting, so that only one surface can be selectively anodized. Next, by rotating the silicon wafer 4, the HF solution spreads uniformly on the surface of the silicon wafer, and also has a function of constantly removing hydrogen bubbles adhering to the surface of the silicon wafer during anodization. For this reason, there is no fear of the progress of the anodization due to the immobilization of bubbles on the surface, and the anodization reaction proceeds faster.

  If the rotational speed is too high, the liquid scatters, which is not preferable. In addition, the contact time between the HF solution and the silicon wafer 4 is shortened and the formation is slowed down. On the other hand, if it is too slow, there is a concern that the in-plane uniformity of the solution deteriorates and the HF liquid wraps around the back surface of the silicon wafer. Therefore, for example, the rotation speed is preferably about 100 to 300 rpm.

  The height of the discharge nozzle 37 from the surface of the silicon wafer is preferably lowered within a range where there is no danger of splashing or contact with the silicon wafer 4 since the flow of the liquid also serves as the conductive portion. Set to about 25mm.

  The discharge nozzle 37 is made of platinum and has a structure that also functions as an electrode, and the discharge diameter is about 2 to 10 mm depending on the spin rotation and the liquid amount. This is because the current density cannot be obtained if the diameter is too thin. In addition, since the liquid contact surface of the discharge nozzle is made large and elongated, it will be designed according to the applied current and the required current density, but the nozzle shape will be a tank shape upstream of the discharge part to increase the contact area It may be. The parts with which the HF solution comes into contact, such as pipes, pumps, tanks, containers, etc., are made of Teflon (registered trademark). Liquid breakage and disturbance of the HF discharge liquid during the anodizing treatment cause deterioration of the chemical conversion characteristics, so it is desirable to manage the line with, for example, a sensor. Since the HF solution conducts electricity in the HF line, take measures to prevent leakage from the site in contact with the liquid to the inside and outside of the device.

  In this embodiment, the HF solution is circulated, but when the HF solution recovered in the primary supply tank is supplied to the secondary supply tank, the energization is temporarily interrupted, and when the supply is completed, the energization is resumed. It has a structure that locally suppresses the range where the liquid is energized. As a result, electrical safety can be ensured and power saving can be achieved with a minimum required amount of applied current.

  Thus, the silicon wafer in which only one surface is anodized is a silicon wafer having a surface (porous shape) formed on the entire one surface in a sufficient depth direction. When impurities are deposited on the chemical conversion surface, they can be diffused deeply and uniformly in the silicon wafer in a short time.

  Silicon wafer anodized with the above-mentioned spin coater, using an anodized wafer prepared by a method in which one side of the silicon wafer is protected with a non-conductor (WAX) and an electrode is attached and immersed in an HF solution as a reference (reference 1) The formation time was 1 to 1.1, the formation depth was 1, the uniformity within the formation surface was excellent, the amount of HF solution used per wafer was 0.2 to 0.3, and the back surface property was excellent.

As is clear from this result,
(1) Since the contact area between the silicon wafer and the electrode can be increased, the current density can be increased, and the chemical reaction can be advanced in a short time.

(2) Only one surface of the silicon wafer can be selected and formed, and the material wafer can be used as a back surface diffusion layer of the diffusion wafer at low cost without special pretreatment.

(3) Since the HF solution is constantly flowing, the chemical reaction on the silicon wafer surface proceeds without stagnation. Further, since the bubbles generated on the surface layer of the wafer can be removed by rotating, the progress of chemical conversion is rapid.

(4) Since the HF solution can be circulated and used, the amount of HF solution used per silicon wafer is smaller than that of the batch-type method.

An excellent effect was obtained.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a schematic cross section showing a schematic configuration of an apparatus used in an anodizing method according to an embodiment of the present invention. It is explanatory drawing which shows schematic structure of the outer periphery of a to-be-processed substrate support means. 1 is a schematic cross section showing a schematic configuration of an anodizing apparatus using a spin coater.

Explanation of symbols

  10 ... anodizing device, 1 ... electrolyte solution, 2 ... electrolyte bath, 3 ... negative electrode plate, 4 ... silicon wafer, 5 ... substrate support means, 6. ..Voltage application means, 7 ... anode plate, 8 ... conductive liquid, 9 ... stopper.

Claims (8)

  An anodizing method characterized in that only one surface of a substrate to be processed held substantially horizontally is brought into contact with an electrolyte solution, and the substrate to be processed is subjected to chemical conversion treatment.   2. The anodizing method according to claim 1, wherein the anode side electrolyte solution and the cathode side electrolyte solution are separated by the substrate to be treated.   3. The anodizing method according to claim 1, wherein the substrate to be processed is a silicon wafer, and the electrolyte solution is a hydrogen fluoride solution. An electrolyte bath containing an electrolyte solution;
A negative electrode plate disposed in the electrolyte solution;
A substrate support means disposed in the electrolyte solution facing the negative electrode plate, and supporting the substrate so that one surface of the substrate to be processed is immersed in the electrolyte solution;
Voltage application means to the electrodes;
Have
The target substrate support means seals and supports the entire outer periphery of the side surface of the target substrate, supports the positive electrode plate spaced from the target substrate, and the target substrate and the positive electrode plate. In between is filled with conductive liquid,
An anodizing apparatus characterized by that.   5. The anodizing apparatus according to claim 4, further comprising a stopper member for preventing the substrate to be processed from settling into the electrolyte solution below the substrate to be processed supporting means.   The anodizing apparatus according to claim 4, wherein the substrate support means is made of any one of fluororesin, rubber, and ethylene tetrafluoride resin.   5. The anodizing apparatus according to claim 4, wherein the electrolyte solution is a hydrofluoric acid mixed solution composed of hydrofluoric acid or alcohol diluted with pure water.    The anodizing apparatus according to claim 4, wherein the electrode is made of platinum or an alloy with platinum.

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