JP6188152B2 - Method and apparatus for planarizing Si substrate - Google Patents

Description

  The present invention relates to a method and apparatus for planarizing a Si substrate, and more particularly to a method and apparatus for planarizing a Si substrate with less environmental impact.

  2. Description of the Related Art Conventionally, in the field of manufacturing semiconductor devices, various methods for flattening or polishing the surface of a Si substrate including a Si wafer or polishing (polishing) have been provided. Typically, there is CMP (Chemical Mechanical Polishing). Recently, CARE (Catalyst-Referred Etching) has been proposed as a new technique for processing difficult-to-work products such as SiC and solid oxides such as optical glass.

CMP increases the mechanical polishing (surface removal) effect due to the relative movement of the polishing agent and the object to be polished by the surface chemical action of the polishing agent (abrasive grains) itself or the action of chemical components contained in the polishing liquid. This is a technique for obtaining a smooth polished surface. Generally, an object to be polished is held by a member called a carrier, pressed against a flat plate (lap) with a polishing cloth or polishing pad, and a slurry containing various chemical components and hard fine abrasive grains is allowed to flow together. Polishing is performed by making the relative movement. By changing the surface of the object to be polished by the chemical component, the processing speed can be improved as compared with the case of polishing with a single abrasive. In addition, the fine scratches on the surface remaining when polishing with a single abrasive and the work-affected layer remaining in the vicinity of the surface are extremely reduced, and an ideal smooth surface can be obtained. Here, fine particles of cerium oxide mainly containing colloidal silica (SiO ₂ ), cerium oxide (CeO ₂ ), or lanthanum are used as polishing agents for CMP depending on the material of the workpiece. For example, the processing speed of the general final finishing by CMP of the Si substrate is supposed to be about 0.12 μm / min (7.2 μm / hr).

  However, cerium, a rare earth, is unevenly distributed, and its stable supply is accompanied by geopolitical risks, and it has recently been remembered that the price has fluctuated in recent years and has caused major problems in the industry. In the future, it will be unavoidable to be exposed to the problem of depletion of rare earth resources. Further, since CMP uses fine particles such as colloidal silica, there are problems such as high cost for the treatment of the polishing liquid and poor compatibility with the clean room.

  According to Patent Document 1, the present inventor arranges a workpiece in a treatment solution in which a molecule containing a halogen that is not normally soluble in the workpiece is dissolved, and forms a platinum, gold or ceramic solid catalyst. A catalyst composed of the material is placed in contact with or in close proximity to the processing surface of the workpiece, and the halogen compound generated by the chemical reaction between the halogen radicals generated on the surface of the catalyst and the surface atoms of the workpiece is eluted. Has proposed a catalyst-assisted chemical processing method characterized by processing a workpiece. Specifically, an example is shown in which Si, SiC, sapphire, or the like is processed using a hydrogen fluoride solution or a hydrogen chloride solution as a treatment solution in which molecules containing halogen are dissolved.

  This processing method based on the catalyst reference surface is an ultra-precision flattening technique named CARE by the present inventor. CARE is a processing technique that does not use abrasives or abrasive grains at all, and is an ideal processing method that does not introduce scratches or work-affected layers at all on the surface to be processed, but a processing solution in which molecules containing halogen are dissolved. In particular, since a hydrogen fluoride solution is used, airtightness of the processing space and processing equipment for exhaust gas and waste liquid are required, so that there are problems that handling and apparatus costs are higher than CMP. CARE was originally developed for the purpose of processing difficult-to-work materials such as SiC with high efficiency and high accuracy without introducing a work-affected layer. It has not been researched and developed as an object to be processed until a polishing method has already been established. Of course, even CARE (HF-CARE) using a hydrogen fluoride solution can process Si at a high speed, but since elution by hydrogen fluoride proceeds even in the concave portion of the surface, there is a problem that the Si surface becomes porous. It was not considered as a means for industrially processing the Si substrate.

  On the other hand, Patent Document 2 uses only ultrapure water except for a small amount of inevitable impurities, and uses an ion reaction function or a catalytic function on a solid surface having a catalytic function disposed in the ultrapure water. The workpiece is immersed in ultrapure water having an increased concentration of hydroxyl groups or hydroxyl ions, the workpiece is used as an anode, or the workpiece is maintained at a high potential. A processing method is disclosed in which hydroxyl ions are attracted to the surface of the substrate and the workpiece is removed or oxidized by a chemical elution reaction or oxidation reaction with hydroxyl groups or hydroxyl ions.

  The processing method described in Patent Document 2 is basically electrolytic processing in which a high voltage is applied, and a hydroxyl group increasing treatment for increasing the concentration of hydroxyl groups or hydroxyl ions in water is an important requirement. As this hydroxyl group increasing treatment, a solid surface having an ion exchange function or a catalytic function is used, but there is a problem that the solid surface is damaged by contact with the workpiece and adheres to the workpiece surface. Therefore, basically, the solid surface having an ion exchange function or a catalytic function and the workpiece are in a non-contact state, and the processing proceeds by supplying the hydroxyl group or hydroxyl ions generated on the solid surface to the workpiece surface. However, this processing method has not been put into practical use because there is no processing reference surface, a highly accurate surface cannot be obtained, and the processing speed is low.

In Patent Document 3, a solid oxide in which one or two or more elements are bonded via oxygen, or a multi-component solid oxide composed of a plurality of oxides is used as a workpiece, and A processing method for flattening the surface or processing it into an arbitrary curved surface, in which water molecules dissociate and adsorb by cutting off the back bonds of the oxygen element and other elements that constitute the solid oxide, resulting from hydrolysis Using a catalytic substance that helps the generation of as a processing reference surface, in the presence of water, the workpiece and the processing reference surface are placed in close contact or in close proximity, and the potential of the processing reference surface includes the natural potential. A solid oxide processing method characterized in that H ₂ and O ₂ are not generated, and the decomposition product is removed from the workpiece surface by relatively moving the workpiece and a processing reference surface. It is disclosed.

  The processing method described in Patent Document 3 does not use any rare earth, abrasives or abrasive grains, and it is difficult to handle hydrogen fluoride or the like, does not use any solution with a large environmental load, and uses only water. CARE (Water-CARE), which was an epoch-making material capable of processing a solid oxide such as an optical material without introducing a work-affected layer.

JP 2006-114632 A JP-A-10-58236 International Publication No. 2013/084934

  In order to meet the demand for de-rare earth, the present inventors removed the oxide film by using Water-CARE described in Patent Document 3 when the surface of the Si substrate is oxidized, thereby industrializing the Si substrate. Based on the idea that flattening (polishing) can be performed at a processing speed that can be used in general, a processing method capable of obtaining a surface with a higher quality than the CMP finished surface has been studied, and the present invention has been achieved.

  In other words, in view of the above-mentioned situation, the present invention intends to solve a solution that does not use rare earths, does not use any abrasive or abrasive grains, is difficult to handle hydrogen fluoride, and has a large environmental load. Provide a Si substrate planarization method and apparatus that can planarize Si substrates at various processing speeds without using them, and that can provide a surface with a higher quality than the CMP finished surface, and that are compatible with clean rooms. There is in point to do.

  In the present invention, in order to solve the above-mentioned problems, the processing speed is 10 nm / h to 10 μm / h and the surface roughness is RMS 0.2 nm or less without using abrasive grains or abrasives on the surface of the Si substrate. A processing method for flattening, wherein a catalytic substance that promotes both oxidation of Si and hydrolysis of a Si oxide film is used as a processing reference surface, and the Si substrate and the processing reference surface are set in a predetermined manner in the presence of water. While making contact with pressure, the Si substrate and the processing reference surface are moved relative to each other, and the catalytic function provided on the processing reference surface oxidizes the Si surface and decomposes it by preferential hydrolysis from the convex portions of the oxide film. A flattening method for the Si substrate, which is characterized by advancing the removal of objects, was constructed.

  Further, the present invention provides a processing apparatus for flattening the surface of a Si substrate with an accuracy of 10 nm / h to 10 μm / h and a surface roughness of RMS 0.2 nm or less without using abrasive grains or an abrasive. A container for holding water and a processing reference surface formed on the surface with a catalytic substance that promotes both oxidation of Si and hydrolysis of the Si oxide film, and is immersed in water and disposed in the container. Relative motion while holding the Si substrate and holding the Si substrate in contact with the processing reference surface and contacting the processing reference surface with the processing pad and the holder at a predetermined pressure. The Si substrate and the processing reference surface are brought into contact with each other at a predetermined pressure in the presence of water, and the Si substrate and the processing reference surface are moved relative to each other to provide the processing reference surface. The catalytic function of the Si surface To constitute a flattening device of the Si substrate, characterized in that advancing the removal of the decomposition product by preferential hydrolysis of the convex portion of the reduction and the oxide film.

Further, the present invention provides a processing apparatus for flattening the surface of a Si substrate with an accuracy of 10 nm / h to 10 μm / h and a surface roughness of RMS 0.2 nm or less without using abrasive grains or an abrasive. a is processed, comprising a container provided so that water does not splash, the machining reference surface to form a catalyst material on a surface that promotes both hydrolysis of oxide and Si oxide films of Si, which is arranged in said container and Pat, while holding the Si substrate, the in contact with the processing reference surface and the holder being disposed in said container, and a drive mechanism for relative movement while contacting the processing pad and the holder at a predetermined pressure, the A water supply means for supplying water between the processing reference surface of the processing pad and the Si substrate held by the holder, and in the presence of water, the Si substrate and the processing reference surface are brought into contact with each other at a predetermined pressure. The Si substrate and Relative movement of the process reference plane, and the catalytic function provided on the process reference plane advances the oxidation of the Si surface and the removal of decomposition products by preferential hydrolysis from the convex portions of the oxide film. An Si substrate planarization processing apparatus was configured.

  In these inventions, the catalyst material is preferably one or more selected from Pt, Pd, Ru, Ni, Co, Cr, and Mo. In addition, the water is more preferably pure water or ultrapure water to which an oxidation accelerator and / or a complex that helps dissolution of decomposition products is added. Furthermore, the oxidation accelerator is particularly preferably hydrogen peroxide.

  Here, in the present invention, the processing reference surface is formed by forming the entire surface or part of the hard surface with the catalyst material, or forming the catalyst material on the entire surface or portion, or the entire surface or portion of the soft surface. It is a concept that includes a catalyst material formed on the entire surface or a part of the catalyst material, or a catalyst material that is kneaded or supported on the base material and the catalyst material appears on at least a part of the surface. . Further, the processing reference surface may be provided with grooves in a radial pattern, a concentric pattern, a spiral pattern, or other patterns.

  The Si substrate planarization processing method and apparatus according to the present invention as described above use a catalytic substance that promotes both Si oxidation and Si oxide film hydrolysis as a processing reference plane, and in the presence of water, The Si substrate and the processing reference surface are brought into contact with each other at a predetermined pressure, and the Si substrate and the processing reference surface are moved relative to each other so that the catalytic function provided on the processing reference surface causes the oxidation of the Si surface and the convex portion of the oxide film. The removal of decomposition products by preferential hydrolysis of the substrate proceeds, the surface of the Si substrate is processed at a processing speed of 10 nm / h to 10 μm / h without using abrasive grains or a polishing agent, and the surface roughness is RMS 0.2 nm. Since the flattening process is performed with the following accuracy, compatibility with a clean room is good, and application to a semiconductor device manufacturing process is easy. In addition, since the present invention is a chemical processing, the surface of the Si substrate can be processed without introducing a work-affected layer, and the processing surface does not use any abrasive or abrasive grains, so the surface roughness Can be made extremely small, and a surface having a higher quality than that of the CMP finished surface can be obtained. Further, the present invention can be processed regardless of the plane orientation of the Si single crystal. Furthermore, since the present invention does not use hydrogen fluoride or other difficult-to-handle chemicals or fine particles, the waste liquid treatment is extremely simple and it can be said to be a processing method with less environmental load, and the working environment is greatly improved. There are advantages such as. Furthermore, since no rare earth is used, the running cost can be greatly reduced without being affected by the raw material market. In addition, the present invention can easily control the processing speed, and does not need to change the processing liquid in order to change from rough polishing to precision polishing as in CMP.

  The surface of the Si substrate is oxidized by the catalytic function provided on the processing reference surface. Then, water molecules dissociate on the oxide film formed on the Si substrate surface by the catalytic function provided on the processing reference surface, and the back bonds between the oxygen element and Si element are cut and adsorbed to remove decomposition products due to hydrolysis. As a result, processing proceeds. Here, since the etching is preferentially performed from the convex portion of the oxide film of the Si substrate, the function of transferring the pad surface on average is realized in the same manner as in CMP, and it is purely chemical without using abrasive grains or abrasives. Therefore, a surface having a higher quality than that of the CMP finished surface can be obtained.

  When the catalyst material is one or more selected from Pt, Pd, Ru, Ni, Co, Cr, and Mo, there is an action of promoting the oxidation of the Si surface, and electrons from the water molecules. It has a large shared effect, which causes water molecules to dissociate and adsorb by cutting back bonds between the oxygen element and the Si element constituting the oxide film on the Si substrate surface, and helping to generate decomposition products by hydrolysis. It becomes large and processing speed can be increased. Furthermore, the processing speed is further increased when the water is a mixture of pure water or ultrapure water to which an oxidation accelerator and / or a complex that aids the decomposition product is added. In particular, when the oxidation accelerator is hydrogen peroxide, the processing speed can be increased, and processing can be performed at a processing speed comparable to CMP.

1 is a simplified perspective view showing a first embodiment (planarization processing apparatus) of a processing apparatus of the present invention. It is a simplified perspective view which shows 2nd Embodiment (planarization processing apparatus) of the processing apparatus of this invention. The AFM image of the surface before and behind planarization of a 6 inch Si (100) substrate is shown. It is explanatory drawing which shows the observation position of a 6 inch Si (100) board | substrate. 5 shows AFM images of the surface before and after planarization at the observation position in FIG. The phase shift interference microscope image and the AFM image of the surface before and after flattening processing of quartz glass (SiO ₂ ) are shown. It is a graph which shows the contact pressure dependence of processing speed. It is a graph which shows the processing speed of quartz glass with respect to various catalyst substances (catalyst metal). It is the graph which showed the processing speed in each solution pH. pH1 is a graph showing the catalytic potential dependence of the processing rate under (HNO ₃ aqueous solution). pH3 is a graph showing the catalytic potential dependence of the processing rate under (HNO ₃ aqueous solution). It is a graph which shows the catalyst potential dependence of the processing speed in pH7 (phosphate buffer solution). It is a graph which shows the catalyst potential dependence of the processing speed in pH11 (KOH aqueous solution). It is the graph which showed the relationship between the natural potential in each pH, and the peak position of processing speed. pH3 is a graph showing the (HNO ₃ aqueous solution) As a result of examining in detail the catalytic potential dependence of the processing rate under.

  In the Si substrate planarization processing method of the present invention, the processing speed is 10 nm / h to 10 μm / h and the surface roughness is RMS 0.2 nm or less without using abrasive grains or abrasives on the surface of the Si substrate. A processing method for flattening, wherein a catalytic substance that promotes both oxidation of Si and hydrolysis of a Si oxide film is used as a processing reference surface, and the Si substrate and the processing reference surface are set in a predetermined manner in the presence of water. While making contact with pressure, the Si substrate and the processing reference surface are moved relative to each other, and the catalytic function provided on the processing reference surface oxidizes the Si surface and decomposes it by preferential hydrolysis from the convex portions of the oxide film. Advances the removal of objects. Here, RMS is a root mean square roughness (RMS), and RMS is represented by Rq in JIS. In the present invention, the flattening process is equivalent to a process generally called mirror polishing. The Si substrate may be a Si wafer or a Si epitaxial surface.

  The processing reference surface is made of a catalyst material that promotes both the oxidation of Si and the hydrolysis of the Si oxide film. Since the processing reference surface is literally a processing reference surface, the shape should not change during processing. In addition, since the surface state of the processing reference surface is transferred to the surface of the workpiece, it is preferable that the processing reference surface be formed with as low a surface roughness as possible and high flatness. In addition, since the surface roughness and flatness of the processing reference surface are averaged by moving the processing reference surface and the workpiece relative to each other, the surface of the workpiece becomes a surface with higher accuracy than the processing reference surface. .

  It is preferable to use a catalyst material surface containing a transition metal element as the catalyst material for forming the processing reference surface and having an electron d orbit of the transition metal element near the Fermi level. In the present invention, since a solution reactive with a metal element is not used, various transition metal elements can be used. Among them, it is particularly preferable to use a transition metal element that is hard and has a stable shape, and has a work function of In addition to large Pt, Pd, Ru, Ni, Co, Cr, Mo, or the like can be used. Further, the catalyst material serving as the processing reference surface may be a metal element alone or an alloy composed of a plurality of metal elements. Here, it is known that the use of a metal having a vacant d-electron trajectory is highly effective in processing speed. Practically, it is preferable to use Pt, Ru, Ni, Cr for the processing reference surface. Here, the catalyst material does not need to be a bulk, and may be a thin film formed by vapor deposition, sputtering, electroplating or the like of a metal or a transition metal on the surface of a base material that is inexpensive and has good shape stability. The base material on which the catalyst material is deposited may be a hard elastic material, and for example, a fluorine rubber material can be used. When the catalyst material is conductive, the processing speed can be controlled by controlling the potential of the processing reference surface from the outside. Further, even a compound containing a transition metal element and an insulating catalyst material can be used satisfactorily if the d-orbit of electrons of the transition metal element is a catalyst material in the vicinity of the Fermi level. In this case, the potential of the processing reference plane is a natural potential. Leave as it is.

In addition, it is necessary to use pure water or ultrapure water, which has few impurities and constant characteristics, in order to realize a pure processing environment and to accurately control processing conditions. Generally, pure water has an electrical resistivity of about 1 to 10 MΩ · cm, and ultrapure water has an electrical resistivity of 15 MΩ · cm or more, but there is no boundary between them. In addition, it is more preferable that the water is mixed with pure water or ultrapure water mixed with an oxidation accelerator and / or a complex that helps the decomposition product to increase the processing speed. Here, the oxidation accelerator promotes oxidation of the Si substrate surface, and hydrogen peroxide water, ozone water, or the like can be used. In addition, the complex promotes dissolution of the decomposition product and also functions to form a complex ion and maintain it stably in water. The pH of water (processing fluid) can be adjusted, for example, by adding HNO _{3 in} the acidic region and KOH in the alkaline region. In the processing of the Si substrate in the present invention, it is preferable to use a processing solution in an acidic region in order to promote oxidation of the Si surface. The hydrogen peroxide solution is slightly acidic although the pH changes depending on the concentration. HNO ₃ also acts as an oxidizing agent.

The processing mechanism of the present invention is considered as follows from a phenomenological viewpoint. First, when a catalytic material made of a transition metal element having a work function larger than that of Si comes into contact with the surface of the Si substrate, electrons are extracted from the surface of the Si substrate, holes are generated, and surface oxidation (anodic oxidation) occurs. On the other hand, when at least the surface of the oxide film (SiO ₂ ) of the Si substrate comes into contact with a processing reference surface having a catalytic material having a d-electron orbit near the Fermi level, the d-electron orbit approaches the surface of the oxide film. become. The d electrons act to lower the barrier of reaction against both the dissociation of water molecules and the phenomenon when the oxide backbond becomes loose. Phenomenologically, when the catalyst material approaches the oxide, the bonding force of the back bond between the oxygen element and the Si element constituting the oxide becomes weak, the water molecules dissociate, and the oxygen element of the oxide and the Si element. It breaks the element's back bond and adsorbs, producing a decomposition product by hydrolysis. And it is a principle that a decomposition product elutes in a processing liquid. Here, the processing reference surface having the catalyst substance is brought into contact with the surface of the oxide film of the Si substrate and rubbed to give a mechanical force to the decomposition product, thereby promoting elution into water. At this time, it is possible to significantly increase the processing speed by adding an oxidation accelerator that promotes the oxidation of Si and a complex that assists the dissolution of decomposition products by hydrolysis to the processing liquid.

Further, if the catalyst substance forming the processing reference surface is a conductive material, the processing speed can be controlled by adjusting the potential of the catalyst substance. The oxidation-reduction potential changes the property that the surface of a conductive substance (eg, Pt) “extracts” and “gives” electrons from the oxide side. The electric potential of the conductive material is a parameter for changing to an optimum processing speed in accordance with the accuracy to be finally aimed. However, if the potential of the conductive substance is increased positively, O ₂ is generated, and if it is negatively increased, H ₂ is generated, and bubbles interfere with processing. Therefore, adjustment is made within a range in which H ₂ and O ₂ are not generated. The potential control range is about 2V at most.

For example, a silicon dioxide (SiO ₂ ) crystal has a structure in which Si is located at the center of a regular tetrahedron and O is bonded to four vertices, and Si is three-dimensionally bonded through O, In the processing, Si—O—Si bonds are broken, and H ₂ O is hydrolyzed to become Si—OH and OH—Si. Thus, silicic acid {[SiO _x (OH) _4-2x ] _n } is generated by hydrolysis. Here, 0 <x <2. Typically, there are orthosilicic acid (H ₄ SiO ₄ ), metasilicic acid (H ₂ SiO ₃ ), metadisilicic acid (H ₂ Si ₂ O ₅ ) and the like. These decomposition products are eluted in water. The same applies to the oxide film of the Si substrate.

Next, the present invention will be described in more detail based on the embodiments shown in the accompanying drawings. The processing apparatus A according to the first embodiment shown in FIG. 1 has a structure in which processing is performed in a state where a workpiece and a processing reference surface are immersed in water. The processing apparatus A includes a container 2 for holding water 1, a processing reference surface 3 having at least a catalytic substance on the surface, a processing pad 4 that is immersed in water 1 and disposed in the container 2, and the workpiece Holding the object 5 and immersing it in the water 1, making contact with the processing reference plane 3 or bringing it in close contact with the holder 6 disposed in the container 2, the processing pad 4 and the holder 6 in contact with each other. And a voltage applying means 8 for adjusting the potential of the catalyst material forming the processing reference surface 3 in a range where H ₂ and O ₂ are not generated. Further, a water circulation system 9 is provided to purify the water 1 in the container 2 and keep the water level constant. The water circulation system 9 includes a supply pipe 9A, a drain pipe 9B, a treatment liquid purifier (not shown), a buffer tank, a pump, and the like. The voltage application means 8 sets the potential of the catalytic material forming the processing reference surface 3 in the range of about −0.4 to +1.4 V (including zero). Furthermore, it is also preferable to irradiate the surface of the workpiece with excitation light having a specific wavelength and to process the surface while activating it.

  In the illustrated processing apparatus A, the processing pad 4 is a disk-shaped rotating surface plate, and the holder 6 and the processing pad 4 holding the workpiece 5 having a smaller area than the surface plate are parallel and eccentric to each other. The rotating shaft is rotated at a predetermined speed. In the present embodiment, the rotational speed of the surface plate on which the processing pad 4 is formed is controlled as a processing condition. The holder 6 can adjust the contact pressure (processing pressure) of the workpiece 5 with respect to the processing reference surface 3 by adjusting the load. This processing pressure is also controlled as a processing condition. Further, it is desirable to incorporate a temperature control function in the processing pad 4 or the holder 6 because the processing temperature can be kept constant at a predetermined temperature. If the processing reference plane 3 is made narrower than the surface of the workpiece 5, the position and stay time of the small processing pad 4 with respect to the surface of the workpiece 5 are controlled, and the local processing amount of the surface of the workpiece 5 is controlled. In other words, local processing by numerical control can be performed.

Moreover, the processing apparatus B of 2nd Embodiment shown in FIG. 2 is a structure which processes while supplying the water dripped between the to-be-processed object and the process reference plane. The processing apparatus B includes a processing pad 11 having a processing reference surface 10 having at least a catalytic substance on the surface, a holder 13 that holds the workpiece 12 facing the processing reference surface 10, and processing of the processing pad 11. A drive mechanism 14 that moves the reference surface 10 and the workpiece 12 held on the holder 13 relative to each other while making contact or close proximity, and the workpiece 12 held on the processing reference surface 10 of the processing pad 11 and the holder 13. Water supply means 16 for supplying water 15 between them, and voltage application means 17 for adjusting the potential of the catalytic material forming the processing reference surface 10 in a range where H ₂ and O ₂ are not generated. . Here, a container 18 is provided around the processing pad 11 so that water does not scatter. Also in this case, it is also preferable to irradiate the surface of the workpiece with excitation light having a specific wavelength and to process the surface while activating it.

  First, as a preliminary experiment, a 6-inch Si (100) substrate having a surface roughness (RMS) of 0.156 nm was planarized by a processing apparatus A using Pt as a catalyst material for forming a processing reference surface. The processing conditions are: processing fluid: pure water, potential: natural potential, processing pressure: 200 hPa, rotation speed: 10 rpm, processing time: 4 minutes. FIG. 3 is an AFM image showing the surface state before and after planarization of the Si substrate by the processing apparatus A. It was found that the surface roughness (RMS) of the Si substrate before processing was 0.156 nm, but it was greatly improved to 0.068 nm after processing for only 4 minutes. Here, AFM is an atomic force microscope. As a result, a surface having a high quality equivalent to or higher than that of CMP can be obtained according to the present invention, and since no abrasive grains or abrasives are used, it can be used in a clean room where CMP could not be installed so far. Device manufacturing man-hours can be shortened.

  Next, a 6-inch Si (100) substrate was flattened by a processing apparatus A using Pt as a catalyst material for forming a processing reference surface, and a plurality of locations on the surface were observed and compared before and after processing. The processing conditions are: processing fluid: pure water, potential: natural potential, processing pressure: 200 hPa, rotation speed: 10 rpm, processing time: 10 minutes. Here, the 6-inch Si (100) substrate before processing is a finished surface by CMP. FIG. 4 shows observation positions 1 to 5 on the surface of the Si substrate. Specifically, the observation positions are five positions (observation positions) extending from one peripheral portion to the other peripheral portion along the diameter of the Si wafer. 3 is set to the center). At observation positions 1 to 3, the surface state before and after processing is observed with an AFM image, and at observation positions 4 and 5, the surface state after processing is observed with an AFM image, and the results are shown in FIG.

  As shown in FIG. 5, at the observation position 1, the surface roughness (RMS) of the Si substrate before processing was 0.054 nm, but after processing for 10 minutes, it became 0.050 nm. The surface roughness (RMS) before processing was 0.057 nm, but it was 0.037 nm after processing. In the observation plate 3, the surface roughness (RMS) before processing was 0.054 nm. After processing, the thickness was 0.054 nm, and at observation positions 4 and 5, 0.041 nm and 0.036 nm were obtained after processing, respectively. As a result, it was found that no processing spots were observed in the Si substrate, and the processing progressed uniformly over the entire surface. In this case, the average processing speed was 74.3 nm / h. Here, no improvement was observed in the surface roughness at the center of the Si substrate, but the processing pressure at the center of the Si substrate was lower than that at the periphery, or due to rotation of the holder of the Si substrate. The reason is that the action at the center is smaller than that at the periphery, and these can be solved by devising and optimizing the structure of the holder.

  Further, a 6-inch Si (100) substrate was planarized by adding hydrogen peroxide water to the processing liquid. Processing conditions are: processing solution: pure water + hydrogen peroxide solution (concentration 5%), potential: natural potential, processing pressure: 200 hPa, rotation speed: 10 rpm, processing time: 10 minutes. The average processing speed in this case was 480 nm / h. It was found that by using a 5% aqueous hydrogen peroxide solution, oxidation was accelerated and the processing speed was increased by about 6.5 times. Depending on the convenience of the apparatus, a processing pressure of 1000 hPa and a rotation speed of 30 rpm are normally possible, so it is theoretically possible to further increase the processing speed by about 15 times, in which case the processing speed is 7.2 μm / h. Furthermore, in the present invention, if the processing conditions are optimized, it is possible to sufficiently increase the processing speed up to about 10 μm / h while maintaining a higher quality than the CMP surface. Further, the processing speed can be reduced to about 10 nm / h because the processing speed and the number of rotations are reduced. Here, although the pH of the hydrogen peroxide solution varies depending on the concentration, it is weakly acidic. Furthermore, the processing speed can be controlled by the pH of the processing liquid and the contact potential.

Next, FIG. 6 shows an example in which quartz glass (pure SiO ₂ ) is planarized by a processing apparatus A using Pt as a catalyst material for forming a processing reference surface. The processing of quartz glass can simulate the processing of the Si oxide film (SiO ₂ ) formed on the surface of the Si substrate, and since the surface state is stable, it is optimal for experiments for examining processing characteristics. Quartz glass used a CMP surface as a pre-processed surface, and the processing characteristics were evaluated by observing the surface before and after processing with a phase shift interference microscope (Zygo, NewView) and an atomic force microscope (AFM).

FIG. 6 shows the result of flattening processing of quartz glass (SiO ₂ ). Processing conditions are: processing pressure: 200 hPa, rotation speed: 10 rpm, processing liquid: ultrapure water, processing time: 1 hour. The processing speed was 831 nm / h. In the phase shift interference microscope image by processing, rms: 0.338 nm before processing becomes rms: 0.147 nm after processing, and the surface roughness is greatly improved. In the AFM image, rms: 1.455 nm before processing was greatly improved to rms: 0.103 nm after processing, and scratches were confirmed on the surface before processing, but such scratches were removed, It was found to have a smooth surface at the atomic level.

  Next, the controllability of the processing speed was examined by using a basic experimental device that rotates the catalyst material sphere without bringing it into contact with the surface to be processed at a predetermined pressure. First, quartz glass was processed using Pt as a catalyst metal. The contact pressure is about 500 to 2000 hPa, the rotation speed is 24 rpm, the working fluid is pure water, and the potential of Pt is a natural potential. FIG. 7 shows the result of examining the contact pressure dependence of the machining speed, with only the elliptical region in contact with Pt being machined, with the maximum depth at the machining trace as the machining amount. It can be seen that the machining amount increases as the pressure increases. That is, it can be seen that the processing speed is proportional to the contact pressure, and when the pressure is increased five times from 200 hPa to 1000 hPa, the processing speed is also increased five times. Further, the processing speed is proportional to the rotational speed, and when the rotational speed is tripled from 10 rpm to 30 rpm, the processing speed is also tripled.

  Next, quartz glass was processed under the same processing conditions using a catalyst material sphere on which various catalytic metals were formed, with a contact pressure of about 1000 hPa, a rotation speed of 24 rpm, and a processing liquid of pure water. The potential of the catalytic metal is a natural potential. It is known that the ease of dissociative adsorption to the catalytic metal can be qualitatively arranged by the degree of electron non-occupancy of d orbitals and can be grouped as follows. Group A is a group 4, 5, 6, or 8 element such as Cr, Fe, or Mo having many d orbital vacancies. Group B1 is a group 9 or 10 element made of Ni or Co having 1 to 3 vacancy d orbitals. Group B2 is a group 9 or 10 element such as Pt or Pd. Group C is a group 7 or 11 element made of Cu or Mn. Group D is a group 11 element made of Au in which d orbitals are occupied. Group E is a group 11 or 12 element such as Ag or Zn. It is known that the chemisorption characteristics become smaller in the order of groups A, B1, B2, C, D, and E.

Therefore, quartz glass was processed by selecting one element from each group as the catalyst metal. The result of the dependence of the processing speed on the catalytic metal is shown in FIG. As a result, there is a clear correlation between the chemisorption characteristics and the processing speed, and the processing speed when Cr (group A) or Ni (group B1) is used is higher than when Pt (group B2) is used. It turned out to be up to an order of magnitude larger. Further, when Au or Ag belonging to the group D or E is used, since the d orbit is occupied by electrons, the processing hardly proceeds. From the above results, it became clear that the catalytic metal promotes dissociation of H ₂ O molecules in the present invention. Here, even when stainless steel (SUS316) was used as the catalyst metal, a large processing speed was obtained. SUS316 contains 10 to 14% by weight of Ni, 16 to 18% by weight of Cr, 2 to 3% by weight of Mo, and other elements, but mainly Cr and Ni contribute to the processing. I believe that. Moreover, although it can process also when graphite is used as a catalyst substance, the processing speed was as slow as Au and Ag.

  As a result, it is preferable to use metals of group A, B1, and B2 as the catalyst metal composed of a single element from the viewpoint of processing speed, and more practically relatively inexpensive and easy to handle. To use. In this case, it is also preferable to use an alloy composed of a plurality of metal elements in addition to the metal element alone. Further, since the d orbital of Cu is occupied by electrons, Cu itself has a low processing speed, but CuO has a catalytic function even if it is insulative. Thus, even if a metal having a poor catalytic function is formed into a compound, if the d orbit of the electron of the metal element becomes near the Fermi level and appears on the surface, the water molecule dissociates and the oxide film is formed. It functions as a catalytic substance that cuts and adsorbs back-bonds of the oxygen element and other elements to assist in the generation of decomposition products by hydrolysis.

Next, the pH dependence of the processing speed in the quartz glass substrate was examined. The result of changing the pH of the solution and evaluating the processing speed is shown in FIG. Processing conditions are catalyst: Pt, processing pressure: 400 hPa, rotation speed: 24 rpm, processing liquid: pH adjustment, processing time: 30 minutes. It is the solution pH dependence of the processing speed, excluding the influence of the adsorption state on the Pt surface. It was found that the processing speed was maximized when an acidic solution having a pH in the range of 2 to 4 was used, and increased by about 4 times compared to when pure water was used, followed by a basic solution and a neutral solution. Considering this result, H atoms are first dissociated from the H ₂ O molecules by the action of the catalyst in the etching process, and the generated hydroxyl groups are adsorbed on the Si atoms. Subsequently, H atoms are adsorbed on the O atoms, but it is considered that not only the H atoms on the catalyst dissociated from the H ₂ O molecules but also the hydrogen ions in the solution move. Therefore, the processing speed is large in an acidic solution. On the other hand, the reason why the processing rate in the basic solution is larger than that in the neutral solution is considered to be that the dissolution rate of the processed product Si (OH) x is basic and maximum. In order to make the processing speed the fastest, practically, the pH of the processing liquid may be adjusted to a range of 3 ± 0.5.

Since not only the ion concentration in the solution but also the surface potential of the catalyst changes by changing the solution, the results of evaluating the processing speed by controlling only the potential in a solution with a fixed pH are shown below. In other words, the dependence of the processing speed on the quartz glass substrate on the catalytic potential was investigated using solutions of pH 1, 3, 7, and 11. The solution was adjusted to each pH by using an HNO ₃ aqueous solution, a phosphate buffer, and a KOH aqueous solution. As processing conditions, the catalyst metal is Pt, the contact pressure is about 1000 hPa, the rotation speed is 24 rpm, the processing liquid is pure water, and the processing time is 15 minutes. The measured values of the natural potential (open circuit potential) were 0.68, 0.57, 0.32, 0.17 V vs. Ag / AgCl at pH 1, 3, 7, and 11, respectively. The processing results in each solution are shown in FIGS. It became clear that the processing speed varied depending on the catalyst potential in all solutions. The processing result when using a pH 11 KOH solution shown in FIG. 12 will be considered as an example. The peak of the processing speed exists in the vicinity of about −0.7 V vs. Ag / AgCl, and the processing speed was almost zero at a potential of 0.5 V or more or −1.5 V vs. Ag / AgCl or less. This is because when the potential is scanned in the positive and negative directions, the generated oxygen and hydrogen are adsorbed, and the processing does not proceed at all when the adsorption amount is excessive. On the other hand, in the vicinity of the peak value, the amount of adsorption on the Pt surface is considered to be the minimum amount, and the processing speed was about three times that when no voltage was applied. As a result, it is shown that the processing speed can be controlled by controlling the potential of the catalytic material constituting the processing reference surface.

FIG. 14 shows a comparison between the peak potential of the processing speed at each pH and the position of the natural potential. As the pH moves to the alkali side, the peak potential becomes negative. This can be understood that at higher pH, the adsorption of hydroxyl groups or oxygen to the catalytic metal becomes significant, and a more negative potential is required to desorb them. Conversely, at pH 1, hydrogen is excessively adsorbed, and the maximum processing speed can be obtained by setting the potential to the positive side of the natural potential. The lower straight line in FIG. 14 indicates the H ₂ generation limit, and the upper straight line indicates the O ₂ generation limit, and the potential is controlled between the upper and lower straight lines.

  FIG. 15 shows that a flattening apparatus is used to fix an aqueous solution of pH 3 that maximizes the processing speed to quartz glass, the catalyst is Pt, the processing pressure is 400 hPa, the rotation speed is 24 rpm, and the processing time is 30 minutes. , The result of processing by further changing the potential of Pt. Here, the potential of Pt was measured based on a standard hydrogen electrode (SHE). As described above, the use of a pH 3 solution provides the highest processing speed, but it can be seen that a wide processing speed can be realized by accurately controlling the potential. For example, when the potential of Pt is changed from 1 V vs. SHE to 0 V vs. SHE, the processing speed becomes about ½.

In the present invention, it is obvious that the machining speed can be controlled by changing the potential of the machining reference plane. In addition, the processing speed can be controlled by changing the pH of the processing liquid. In the present invention, the processing speed can be controlled by adjusting the potential of the catalyst material forming the processing reference surface in a range that includes natural potential and does not generate H ₂ and O _2. Machining conditions can be easily changed up to low-speed precision machining. That is, according to the present invention, since a series of processing from rough processing to precision processing can be performed only by changing the electric potential of the conductive catalyst substance while the workpiece is set in the processing apparatus, the work efficiency is high. On the other hand, conventionally, when using the same processing device, it is necessary to interrupt the processing operation and replace the polishing pad, abrasive and abrasive grains, or when using a dedicated device for roughing and precision processing In other words, it was necessary to transfer the work piece between these devices. In the present invention, since SiO ₂ is hydrolyzed by water, the Si oxide film is eluted only from the convex portion, and an extremely high-quality Si surface can be obtained.

A processing equipment, B processing equipment,
1 water, 2 containers,
3 machining reference plane, 4 machining pad,
5 Workpiece, 6 Holder,
7 drive mechanism, 8 voltage application means,
9 Water circulation system, 9A supply pipe,
9B Drain pipe, 10 processing reference plane,
11 processing pads, 12 workpieces,
13 holder, 14 drive mechanism,
15 water, 16 water supply means,
17 Voltage application means, 18 container.

Claims (9)

A processing method of flattening the surface of a Si substrate with an accuracy of 10 nm / h to 10 μm / h and a surface roughness of RMS 0.2 nm or less without using abrasive grains or an abrasive,
A catalytic substance that promotes both the oxidation of Si and the hydrolysis of the Si oxide film is used as a processing reference surface. In the presence of water, the Si substrate and the processing reference surface are brought into contact with each other at a predetermined pressure. Relative movement with the processing reference plane, and the catalytic function provided on the processing reference plane advances the oxidation of the Si surface and the removal of decomposition products by preferential hydrolysis from the convex portions of the oxide film. A method for planarizing a Si substrate.   The method for planarizing a Si substrate according to claim 1, wherein the catalyst material is one or more selected from Pt, Pd, Ru, Ni, Co, Cr, and Mo.   3. The method for planarizing a Si substrate according to claim 1, wherein the water is obtained by adding an oxidation accelerator and / or a complex that aids dissolution of decomposition products to pure water or ultrapure water. 4.   The method for planarizing a Si substrate according to claim 3, wherein the oxidation accelerator is hydrogen peroxide. A processing apparatus for flattening the surface of an Si substrate with an accuracy of 10 nm / h to 10 μm / h and a surface roughness of RMS 0.2 nm or less without using abrasive grains or an abrasive,
A container for holding water;
A processing pad having a processing reference surface formed on the surface with a catalytic substance that promotes both oxidation of Si and hydrolysis of the Si oxide film, and a processing pad that is immersed in water and disposed in the container;
Holding the Si substrate and immersing it in water, contacting the processing reference surface and placing the holder in the container;
A drive mechanism for relatively moving the processing pad and the holder in contact with each other at a predetermined pressure;
In the presence of water, the Si substrate and the processing reference surface are brought into contact with each other at a predetermined pressure, and the Si substrate and the processing reference surface are moved relative to each other, and the Si surface is provided by a catalytic function provided on the processing reference surface. An apparatus for planarizing a Si substrate, wherein oxidation of the substrate and removal of decomposition products by preferential hydrolysis from the convex portions of the oxide film are advanced. A processing apparatus for flattening the surface of an Si substrate with an accuracy of 10 nm / h to 10 μm / h and a surface roughness of RMS 0.2 nm or less without using abrasive grains or an abrasive,
A container provided to prevent water from splashing;
A processing pad provided on the surface with a catalyst material that promotes both oxidation of Si and hydrolysis of the Si oxide film, and a processing pad disposed in the container;
While holding the Si substrate, and a holder disposed in said container in contact with the working reference face,
A drive mechanism for relatively moving the processing pad and the holder in contact with each other at a predetermined pressure;
Water supply means for supplying water between the processing reference surface of the processing pad and the Si substrate held by the holder;
In the presence of water, the Si substrate and the processing reference surface are brought into contact with each other at a predetermined pressure, and the Si substrate and the processing reference surface are moved relative to each other, and the Si surface is provided by a catalytic function provided on the processing reference surface. An apparatus for planarizing a Si substrate, wherein oxidation of the substrate and removal of decomposition products by preferential hydrolysis from the convex portions of the oxide film are advanced.   The Si substrate planarization apparatus according to claim 5 or 6, wherein the catalyst material is one or more selected from Pt, Pd, Ru, Ni, Co, Cr, and Mo.   8. The Si substrate flattening apparatus according to any one of claims 5 to 7, wherein the water is obtained by adding an oxidation accelerator and / or a complex that aids dissolution of decomposition products to pure water or ultrapure water. .   9. The Si substrate planarization apparatus according to claim 8, wherein the oxidation accelerator is hydrogen peroxide.