JP2011101930A - Surface smoothing method for silicon wafer before final polishing, and surface smoothing device for silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface smoothing method for a silicon wafer before final polishing capable of previously improving the flatness of a wafer surface after rough polishing before final polishing when the final polishing is applied to the surface of the silicon wafer after the rough polishing is applied and stably securing the surface characteristic of the wafer after the final polishing in a manufacturing step of the silicon wafer, and a surface smoothing device for the method. <P>SOLUTION: The flatness of the wafer surface is measured at a flatness measurement step (step #42) before the final polishing is applied, and after projection areas concentrically distributed on the surface are specified, a cup member for covering the projection areas in a radial direction of the wafer is arranged at a projection area removal step (step #44). A mixture gas of an ozone gas and the vapor of hydrogen fluoride is introduced into the cup member while rotating the wafer around at center of the wafer, and the projection areas are etching-removed by a chemical reaction with the mixture gas. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides a surface flattening method of a silicon wafer before finish polishing, in which the surface of the silicon wafer is preliminarily flattened before performing the final polishing to finish the surface of the wafer to a mirror surface after rough polishing the surface of the silicon wafer, and The present invention relates to a surface flattening apparatus suitable for carrying out the method.

  A silicon wafer used for a semiconductor device is manufactured from a silicon single crystal ingot grown by the Czochralski method or the like.

  FIG. 1 is a flowchart schematically showing a conventional silicon wafer manufacturing process. As shown in the figure, the single crystal ingot is processed into a cylindrical shape in the outer periphery grinding process in Step # 10, and is sliced into a disk shape in the slicing process in Step # 20. The sliced wafer is chamfered at the outer periphery in the chamfering process in step # 30 to be finished to a product diameter, and double-side polished in the rough polishing process in step # 40 (Double Side Polishing, hereinafter referred to as “DSP”). Then, in the finish polishing step of Step # 50, single side polishing (single side polishing, hereinafter referred to as “SSP”) using mechanochemical polishing using an abrasive such as colloidal silica liquid is used. Each side can be mirror finished.

  Immediately after the rough polishing in step # 40 and immediately after the finish polishing in step # 50, a cleaning process is performed on the entire surface of the wafer in order to remove foreign matters such as particles and metal remaining on the wafer surface. Further, if necessary, an etching process for chemically removing processing strain is added, or a grinding process by double-sided simultaneous grinding or single-sided grinding is added before the rough polishing of step # 40.

  When used as a so-called polished wafer (hereinafter referred to as “PW”), the mirror-finished wafer is shipped after undergoing various inspection processes such as magic mirror inspection, surface defect inspection, and appearance inspection. When used as an epitaxial wafer (hereinafter referred to as “EW”), an epitaxial process for vapor-phase growth of an epitaxial layer is performed on the surface of PW, and then a cleaning process and various inspection processes are performed again. When used as an annealed wafer, the PW is subjected to heat treatment at 1200 ° C., for example, in a hydrogen atmosphere, and then undergoes a cleaning process and various inspection processes again.

  In the above-described silicon wafer manufacturing process, the main purpose of rough polishing by DSP is to adjust the flatness of the wafer surface by adjusting the parallelism of the wafer, and the main purpose of finish polishing by the next SSP is micro-polishing. The purpose is to adjust minute surface characteristics such as roughness and LPD (Light Point Defect). For this reason, the shape of the wafer surface after rough polishing by DSP greatly affects the shape of the wafer surface after finish polishing by SSP.

  Actually, in rough polishing by a DSP, depending on polishing conditions, the action of polishing on the wafer surface may be greater at the outer peripheral portion than at the central portion of the wafer, or conversely, may be greater at the central portion than at the outer peripheral portion of the wafer. When the polishing action is biased, the wafer surface after the rough polishing by the DSP is formed with a convex region having a wafer thickness thicker than the outer peripheral portion at the central portion, or conversely, the wafer thickness is larger than the central portion at the outer peripheral portion. A thick convex region is formed. In other words, a convex region distributed concentrically may be formed on the wafer surface after rough polishing by the DSP. This concentric convex region deteriorates the flatness of the wafer surface after rough polishing, and does not substantially disappear even by finish polishing by SSP, which causes deterioration of the surface characteristics of the wafer after finish polishing.

  For this reason, in the manufacturing process of a silicon wafer, a technique that can improve the flatness of the wafer surface after rough polishing and stably ensure the surface characteristics of the wafer after finish polishing is strongly desired.

On the other hand, in Patent Document 1, in order to accurately etch only a portion where etching of a silicon wafer is desired, a gas ejection nozzle that ejects an etching gas to the desired portion, a gas etching apparatus including the nozzle, And a gas etching method using the nozzle has been proposed. In the technique proposed in this document, ClF ₃ gas is used as an etching gas, and the gas ejection nozzle has a double tube structure composed of a gas ejection pipe and an exhaust pipe, so that the wafer portion where the nozzle is disposed is locally disposed. It can be etched.

  However, the technique proposed in Patent Document 1 is merely for etching only a desired portion on the wafer, and without considering the shape of the wafer surface after the rough polishing, after the rough polishing, There is no intention to improve the flatness of the wafer surface.

Japanese Patent Laid-Open No. 10-242129

  The present invention has been made in view of the above-described problems. In the silicon wafer manufacturing process, when performing the final polishing after the rough polishing, the flatness of the wafer surface after the rough polishing is determined in advance before the final polishing. An object of the present invention is to provide a surface flattening method and a surface flattening apparatus for a silicon wafer before finish polishing, which can improve the surface properties of the wafer after finish polishing stably.

  In order to achieve the above object, the present inventor has studied the manufacturing process of the silicon wafer in detail. As a result, in order to stably secure the surface characteristics of the silicon wafer after the finish polishing, the surface of the wafer before the finish polishing is previously determined. It has been found that it is effective to newly add a step of flattening.

  Then, when flattening the wafer surface before finish polishing, a cup member that covers the convex region in the radial direction of the wafer is arranged with respect to the concentric convex region formed on the wafer surface by rough polishing, and the wafer is placed on the wafer. By introducing a mixed gas of ozone gas and hydrogen fluoride vapor into the cup member while rotating around the center, the convex region can be etched away by a chemical reaction with the mixed gas over the entire circumferential direction. It was found that the wafer surface can be planarized.

  The present invention has been completed on the basis of the above findings, and the gist of the present invention is the following (1) surface flattening method for a pre-polishing silicon wafer and (2) a surface flattening apparatus for a silicon wafer.

  (1) A method of flattening the surface of the silicon wafer after rough polishing of the silicon wafer and before finishing polishing, measuring the flatness of the surface of the silicon wafer, and concentrically distributing on the surface. A flatness measurement step for identifying the convex region to be performed, and a cup member that covers the convex region in the radial direction of the silicon wafer, and ozone gas and fluorination in the cup member while rotating the silicon wafer around the center of the wafer. And a convex region removing step of introducing a mixed gas of hydrogen vapor and etching away the convex region by a chemical reaction with the mixed gas.

In the surface planarization method (1), in the convex region removing step, 100 to 300 g / m ³ ozone concentration of the ozone gas, and the hydrogen fluoride concentration of the hydrogen fluoride vapor and 500 to 2000 g / m ³ The molar fraction of hydrogen fluoride in the mixed gas is preferably in the range of 0.90 to 0.98.

  Further, in the surface flattening method of (1) above, the protrusion amount of the convex region is calculated from the measurement result in the flatness measurement step, and the etching region and the etching rate corresponding to the protrusion amount are calculated in the convex region removal step. It is preferable that the processing time is set.

  (2) A silicon wafer surface flattening apparatus that blows an etching gas onto the surface of a rotating silicon wafer to flatten the surface of the silicon wafer, and a table that supports the silicon wafer and rotates it around the wafer center; A cup member covering a part of the surface of the silicon wafer; a gas introducing means for introducing an etching gas into the cup member; a cup moving means for moving the cup member in the radial direction of the silicon wafer; And a cup movement amount control means for controlling the movement amount of the cup member from flatness information.

  According to the method for planarizing a surface of a silicon wafer before finish polishing according to the present invention, a mixture of ozone gas and hydrogen fluoride vapor is mixed in the cup member while rotating the wafer in a state where the cup member is arranged on the convex region of the wafer surface. By introducing the gas, the convex region existing in the cup member is forcibly oxidized by a chemical reaction with ozone gas, and the oxidized convex region is dissolved by a chemical reaction with hydrogen fluoride vapor. It is possible to etch and remove the convex region over the entire circumferential direction, and as a result, the surface of the wafer before finish polishing can be efficiently planarized.

  Further, according to the surface flattening apparatus of the present invention, such a wafer surface flattening process can be effectively performed. And since the flatness of the surface of the wafer obtained by such flattening treatment is improved, the surface characteristics are stably secured by performing finish polishing.

It is a flowchart which shows the manufacturing process of the conventional silicon wafer schematically. It is a schematic diagram which shows the structural example of the surface planarization apparatus of the silicon wafer of this invention, The figure (a) shows a top view, The figure (b) shows a side view, respectively. It is a flowchart which shows roughly the manufacturing process of the silicon wafer to which the surface planarization method of the silicon wafer before the finish polishing of this invention is applied. It is a figure which shows the specific example of the processing condition which planarizes the surface of the wafer before final polishing, The figure (a) shows the case where the convex area | region is formed in the center part of the wafer surface, The figure (b) shows the wafer. The case where the convex area | region is formed in the outer peripheral part of the surface is each shown. It is a figure which shows the correlation with the mole fraction of HF in mixed gas, and an etching rate.

  Below, the embodiment is explained in full detail about the surface planarization method and surface planarization apparatus of the silicon wafer before final polishing of this invention.

1. FIG. 2 is a schematic diagram showing a configuration example of a surface flattening apparatus for a silicon wafer according to the present invention. FIG. 2 (a) shows a plan view and FIG. 2 (b) shows a side view. As shown in the figure, the surface flattening device 1 is a device for flattening the surface of a silicon wafer 20 that has been subjected to rough polishing by a DSP before finishing polishing by an SSP, and a table that supports the wafer 20 before finishing polishing. 2 and a cup member 4 disposed above the table 2. The overall operation of the surface flattening device 1 is performed by a command from a control unit (not shown).

  The table 2 has a top surface formed in a horizontal horizontal plane, and an electric motor 3 is connected to the center thereof. On the upper surface of the table 2, the wafer 20 before final polishing is placed so that the center thereof coincides with the center of the table 2, and the wafer 20 is sucked from the back surface side by a suction mechanism built in the table 2. 2 is held on. The table 2 is rotationally driven by the power from the electric motor 3, whereby the wafer 20 supported on the table 2 can be rotated around the center of the wafer.

  The cup member 4 is a cylindrical container whose bottom end is opposed to the upper surface of the table 2. At the center of the upper end of the cup member 4, a base tube portion 5 communicating with the inside of the cup member 4 is integrally projected with the cup member 4, and the base tube portion 5 has a block-like support member 6 having an internal space. It is detachably connected to. A first pipe 7 connected to the ozone gas tank and a second pipe 8 connected to the hydrogen fluoride vapor generator are connected to the support member 6. The first pipe 7 and the second pipe 8 are supplied with ozone gas and hydrogen fluoride vapor, respectively, and these ozone gas and hydrogen fluoride vapor are mixed in the internal space of the support member 6, and this mixed gas is used as an etching gas. It is introduced into the cup member 4 through the base tube portion 5.

  Further, a support column 9 is erected on the outside of the table 2, and an arm member 10 projects from the support column 9 in the horizontal direction. A support member 6 connected to the cup member 4 is fixed to the tip of the arm member 10. The support column 9 is configured to be rotated and moved up and down by power from an electric motor or a cylinder (not shown). The arm member 10 swivels or moves up and down in accordance with the rotation driving and lifting driving of the support column 9, thereby supporting the cup member 4 connected to the tip of the arm member 10 via the support member 6 on the table 2. The wafer 20 can be moved in the radial direction, and can be moved up and down.

2. FIG. 3 is a flowchart schematically showing a silicon wafer manufacturing process to which the surface polishing method for a pre-polishing silicon wafer according to the present invention is applied. In the figure, the same steps as those shown in FIG. 1 are denoted by the same step numbers, and repeated description is omitted as appropriate.

  In the surface flattening method of the present invention, after the rough polishing by the DSP is performed on the silicon wafer in Step # 40 and before the final polishing by SSP is performed in Step # 50, the flatness measurement process in Step # 42 and the subsequent steps are performed. Then, the convex region removing process of step # 44 is performed. Usually, in the rough polishing by the DSP, a convex region is generated concentrically with the center of the wafer as the central axis with respect to the thickness distribution in the radial direction of the wafer surface.

  In step # 42, the flatness of the surface of the wafer before finish polishing is measured using a conventional wafer flatness measuring device, and the rough polishing by the DSP is performed from the flatness information of the wafer surface based on the measurement result. A concentric convex region formed on the wafer surface is identified. As a flatness measuring apparatus for measuring the flatness of the wafer surface with high accuracy, for example, a product manufactured by KLA-Tencor: WaferSight can be cited.

  In step # 44, using the surface flattening apparatus shown in FIG. 2, the convex region is removed from the surface of the pre-polishing wafer whose convex region has been specified, and the wafer surface is flattened. A specific procedure of the flattening process will be described with reference to FIG.

  As shown in FIG. 2, the unpolished wafer 20 in which the convex region is specified is supported on the table 2. Next, the support column 9 is rotated to turn the arm member 10, and the cup member 4 is moved to a position covering the convex region in the radial direction of the wafer 20, that is, a position covering a part of the convex region in the circumferential direction. At this time, the wafer surface flatness information obtained in the previous flatness measurement step is transmitted in advance to the memory of the control unit that controls the entire surface flattening apparatus, and the cup member 4 accompanying the turning of the arm member 10. The movement in the wafer radial direction is performed by a command from the control unit based on the flatness information.

  Subsequently, the arm member 10 is lowered together with the support column 9, and the cup member 4 is disposed in a state where a slight gap is provided between the lower end thereof and the surface of the wafer 20. From this state, the table 2 is rotationally driven to rotate the wafer 20, and at the same time, ozone gas and hydrogen fluoride vapor are supplied to the first pipe 7 and the second pipe 8, respectively. And mixed gas of hydrogen fluoride vapor.

Thus, by introducing the mixed gas of ozone gas and hydrogen fluoride vapor into the cup member 4 while rotating the wafer 20 in a state where the cup member 4 is arranged in the convex region of the wafer surface, the cup member 4 is introduced. convex region present within the mixed gas is blown, the convex region forcibly oxidized by the composition by chemical reaction becomes SiO _2, which further a SiO ₂ with ozone gas in the gas mixture, the gas mixture As the chemical reaction with the hydrogen fluoride vapor therein dissolves and these chemical reactions are continuously repeated, the etching of the wafer surface proceeds in an annular shape with the center of the wafer 20 as the central axis. The convex region can be etched away over the entire circumferential direction. As a result, it is possible to efficiently flatten the surface of the wafer before finish polishing.

  Since this wafer has improved surface flatness, the surface characteristics are stably secured by finishing polishing with SSP. This finished polished wafer can be used as PW, and can also be used as an EW or annealed wafer.

  FIG. 4 is a diagram showing a specific example of a processing state of flattening the surface of the wafer before finish polishing. FIG. 4A shows a case where a convex region is formed at the center of the wafer surface. b) shows a case where a convex region is formed on the outer peripheral portion of the wafer surface. In the figure, the convex region is exaggerated.

  As shown in FIG. 4A, when the convex region 21 is formed at the center of the surface of the wafer 20 after rough polishing, the cup member 4 is arranged at the center of the wafer surface, The mixed gas is introduced into the cup member 4 while being rotated. On the other hand, as shown in FIG. 4B, when the convex region 21 is formed on the outer peripheral portion of the surface of the wafer 20, the cup member 4 is disposed on the outer peripheral portion of the wafer surface, and while rotating the wafer 20, A mixed gas is introduced into the cup member 4.

  In either case shown in FIGS. 4A and 4B, the convex region 21 on the wafer surface can be etched away over the entire circumferential direction by a chemical reaction with the mixed gas, and the wafer surface is flattened before finish grinding. Can be made.

In the surface flattening method of the present invention, the ozone (O ₃ ) concentration of ozone gas supplied through the first pipe 7 shown in FIG. 2 is in the range of 100 to 300 g / m ³ , and is supplied through the second pipe 8. The hydrogen fluoride (HF) concentration of the hydrogen fluoride vapor is set within a range of 500 to 2000 g / m ³ , and further, the ozone gas and the hydrogen fluoride vapor are mixed and introduced into the cup member 4 in the mixed gas. The molar fraction is preferably in the range of 0.90 to 0.98. The O ₃ concentration can be adjusted by controlling the supply flow rate of ozone gas. Similarly, the HF concentration can be adjusted by controlling the supply flow rate of hydrogen fluoride vapor. These ranges are preferred for the following reasons.

When the O ₃ concentration of the supplied ozone gas is less than 100 g / m ³ , the ability to forcibly oxidize the convex region is low before the convex region can be dissolved and removed by hydrogen fluoride vapor only after the convex region is converted to SiO ₂ . As a result, the convex region cannot be made into SiO ₂ sufficiently. On the other hand, an O ₃ concentration exceeding 300 g / m ³ is not practical due to the limitation of equipment capacity.

When the HF concentration of the hydrogen fluoride vapor to be supplied is less than 500 g / m ³ , the etching removal of the convex region cannot be sufficiently performed due to the low ability to dissolve SiO ₂ . On the other hand, under the condition where the HF concentration exceeds 2000 g / m ³ , the hydrogen fluoride vapor is liquefied and becomes a mist, covering the convex region. For this reason, the oxidation of the convex region by ozone gas is prevented, and not only the etching removal of the convex region does not proceed, but also adhesion of foreign matters is induced.

FIG. 5 is a diagram showing the correlation between the mole fraction of HF in the mixed gas and the etching rate. The correlation shown in the figure shows the HF mole fraction in a mixed gas of ozone gas and hydrogen fluoride vapor using a pre-polished wafer used for p / p ⁺⁺ type EW with a crystal orientation of (100) as a specimen. Is a result of performing a test for etching the surface of the specimen in each mixed gas atmosphere. As shown in the figure, when the molar fraction of HF is about 0.96, the etching rate becomes a maximum of about 1000 L / min.

  The etching rate is preferably higher because it corresponds to the removal efficiency of the convex region by the mixed gas. For example, if the etching rate is 500 Å / min or more, it can be said that the convex region can be efficiently removed by the mixed gas without requiring a long-time treatment. Therefore, in order to sufficiently satisfy the etching rate of 500 Å / min or more, it is preferable that the molar fraction of HF is in the range of 0.90 to 0.98 from the correlation shown in FIG.

The mole fraction of HF in the mixed gas can be adjusted in accordance with the adjustment of the O ₃ concentration of ozone gas and the HF concentration of hydrogen fluoride vapor. By adjusting the HF mole fraction, the etching rate for the convex region is adjusted. Can also be adjusted.

  Further, in the surface flattening method of the present invention, a configuration for calculating the protrusion amount of the convex region on the basis of the region other than the convex region based on the measurement result in the flatness measuring step of Step # 42 shown in FIG. Can be adopted. Then, in the convex area removing step of Step # 44, the convex area can be accurately removed by etching by appropriately setting the etching rate and the processing time for the convex area corresponding to the protrusion amount. In setting the processing time, the number of rotations of the table supporting the wafer is also taken into consideration.

  Furthermore, in the step of removing the convex region in step # 44, a plurality of cup members having different opening diameters are prepared in advance, and a cup member having an opening diameter that matches the width of the convex region in the wafer radial direction is selected to make the surface flat. Attach to the converter. Thereby, the etching removal process can be performed on all the convex regions regardless of the width of the convex region in the wafer radial direction.

  In addition, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the surface flattening apparatus shown in FIG. 2, a swiveling mechanism is employed as a mechanism for moving the cup member 4 in the radial direction of the wafer 20, but a mechanism that moves back and forth on a straight line can also be employed.

  According to the method for planarizing a surface of a silicon wafer before finish polishing according to the present invention, a convex region existing in a cup member is forcibly oxidized by a chemical reaction with ozone gas in a mixed gas, and the oxidized convex region is mixed. Because it dissolves by a chemical reaction with the hydrogen fluoride vapor in the gas, the concentric convex regions can be removed by etching over the entire circumferential direction, and as a result, the surface of the wafer before finish polishing can be efficiently flattened. Is possible.

  Further, according to the surface flattening apparatus of the present invention, such a wafer surface flattening process can be effectively performed. And since the wafer obtained by such a planarization process has improved the flatness of the surface, by performing finish polishing, the surface characteristics are stably secured, and as PW, It can also be used as an EW or annealed wafer.

1: surface flattening device, 2: table, 3: electric motor,
4: cup member, 5: base tube part, 6: support member, 7: first pipe,
8: 2nd piping, 9: support, 10: arm member,
20: Silicon wafer, 21: Convex area

Claims (4)

A method of flattening the surface of a silicon wafer after performing rough polishing on the silicon wafer and before finishing polishing,
A flatness measurement step of measuring the flatness of the surface of the silicon wafer and identifying a convex region distributed concentrically on the surface;
A cup member that covers the convex region in the radial direction of the silicon wafer is disposed, and a mixed gas of ozone gas and hydrogen fluoride vapor is introduced into the cup member while rotating the silicon wafer around the center of the wafer. And a step of removing the convex region by a chemical reaction with the mixed gas, and a method of planarizing the surface of the silicon wafer before finish polishing. In the convex region removing step, the ozone concentration of the ozone gas and 100 to 300 g / m ^3, and 500 to 2000 g / m ³ of hydrogen fluoride concentration of the hydrogen fluoride vapor, moles of hydrogen fluoride in the mixed gas The method for flattening the surface of a silicon wafer before finish polishing according to claim 1, wherein the fraction is in the range of 0.90 to 0.98. Calculate the protrusion amount of the convex region from the measurement result in the flatness measurement step,
3. The method for planarizing a surface of a silicon wafer before finish polishing according to claim 1, wherein an etching rate and a processing time are set in accordance with the protruding amount in the protruding region removing step. A silicon wafer surface flattening apparatus for flattening the surface of a silicon wafer by blowing an etching gas onto the surface of the rotating silicon wafer,
A table that supports the silicon wafer and rotates around the wafer center;
A cup member covering a part of the surface of the silicon wafer;
Gas introduction means for introducing an etching gas into the cup member;
Cup moving means for moving the cup member in the radial direction of the silicon wafer;
A silicon wafer surface flattening device comprising: a cup movement amount control means for controlling a movement amount of the cup member from flatness information of the surface of the silicon wafer.

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