JP6572863B2 - Silicon wafer manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a silicon wafer.

  In a silicon wafer manufacturing process, a wafer sliced thinly from a single crystal ingot is generally flattened through chamfering and grinding, and a unique number of the wafer is printed by laser mark processing. At this time, various scratches and distortions due to processing are introduced on the front and back surfaces of the wafer, and if these become obvious in the subsequent process, it may become a serious quality problem.

  Therefore, etching is usually performed after laser mark processing to remove scratches and processing distortion. As an etching method, there are known a batch method in which front and back surfaces of a plurality of wafers are simultaneously processed and a spin etching method in which the front and back surfaces of a wafer are processed in order in a single wafer (see Patent Document 1). Further, there are two methods depending on the purpose: treatment with an acid etching solution and treatment with an alkaline etching solution.

JP 2007-53178 A

  However, when acid etching by spin etching is performed after laser mark processing, a streak-like shape as shown in the laser micrograph of FIG. 9 is formed from the laser mark dot toward the outer periphery of the wafer along the flow of the etching solution. Etching unevenness occurs. This streaky etching unevenness has a height difference of several μm. Therefore, in order to obtain the flatness of the wafer, there arises a problem that the machining allowance in the double-side polishing (DSP) in the subsequent process must be increased more than necessary.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method for manufacturing a silicon wafer that can reduce etching unevenness in the vicinity of laser mark dots.

  In order to achieve the above object, the present invention is configured to rotate the silicon wafer while supplying the acid etching solution to the front or back surface of the silicon wafer through a supply nozzle, thereby reducing the supply range of the acid etching solution. A silicon wafer manufacturing method including a spin etching process in which acid etching is performed by enlarging the entire surface or back surface of the silicon wafer, wherein in the spin etching process, the spin rotation speed of the silicon wafer is 1000 rpm or less, and the viscosity is Provided is a method for producing a silicon wafer, characterized by using the acid etching solution of 6.0 mPa · s or less.

  As in the present invention, by setting the spin rotation number as small as 1000 rpm or less and using an acid etching solution having a viscosity as small as 6.0 mPa · s or less, streaky etching unevenness generated near the laser mark dot is reduced. can do. As a result, it is possible to minimize the machining allowance in the subsequent double-side polishing step.

  At this time, as the acid etching solution, a mixed solution containing hydrofluoric acid, nitric acid, and sulfuric acid, or a mixed solution obtained by adding acetic acid to the mixed solution can be used.

  As the acid etching solution having a viscosity of 6.0 mPa · s or less, the above mixed solution can be used.

  Further, as the acid etching solution, a mixed solution containing 1 to 10% by mass of hydrofluoric acid, 25 to 50% by mass of nitric acid, 0 to 15% by mass of acetic acid, and 5 to 25% by mass of sulfuric acid is used. it can.

  As the acid etching solution having a viscosity of 6.0 mPa · s or less, a mixed solution in which an acid is mixed in the above ratio can be used.

  At this time, the spin etching process can be performed after a laser marking process in which a mark is engraved on the front or back surface of the silicon wafer by a laser.

  The spin etching process according to the present invention is effective in reducing streaky etching unevenness in the vicinity of the laser mark dots engraved in the laser marking process.

  If it is the manufacturing method of the silicon wafer of this invention, an etching nonuniformity can be reduced and the etching nonuniformity of laser mark dot vicinity can be reduced especially.

It is the schematic which shows one Embodiment of the spin etching process in this invention. FIG. 3 is a photograph observing streaky etching unevenness of the wafer after etching in Example 1. FIG. It is the photograph which observed the stripe-shaped etching nonuniformity of the wafer after the etching of the comparative example 2. FIG. It is a graph which shows the depth (height difference) of the etching unevenness of the wafer after the etching of Examples 1 to 3 and Comparative Examples 1 and 2. FIG. 6 is a photograph observing streaky etching unevenness of a wafer after etching in Example 5. FIG. It is the photograph which observed the stripe-shaped etching nonuniformity of the wafer after the etching of the comparative example 5. FIG. It is a graph which shows the depth (height difference) of the etching unevenness of the wafer after the etching of Examples 4 and 5 and Comparative Examples 3 to 5. It is a graph which shows the double-sided polishing allowance required for the wafer after the etching of Examples 4 and 5 and Comparative Examples 3-5. It is a photograph which shows an example of the stripe-shaped etching nonuniformity which generate | occur | produced toward the outer peripheral part of the wafer from the laser mark dot.

  Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.

  As described above, in spin etching using an acid etching solution, streaky etching unevenness occurs from the laser mark dots toward the outer peripheral portion of the wafer along the flow of the etching solution, and double-side polishing in a post process, etc. There was a problem that it became a factor to increase the allowance in the unnecessarily.

  Therefore, as a result of repeated studies by the inventor to solve such problems, the following knowledge was obtained. That is, the present inventor has discovered that the generation of streaky etching unevenness near the laser mark dot is caused by the cavity flow when the acid etching solution as the fluid flows on the laser mark dot. This is considered that when the acid etching solution flows over the laser mark dots, a wake behind the cavity occurs along the direction in which the acid etching solution flows from the laser mark dots, and etching unevenness occurs there.

  Then, the present inventor has found that when the spin rotation speed is large, the average flow rate of the etching solution increases, and the etching unevenness generated in the laser mark dots is emphasized. In addition, although the fluid motion can be considered qualitative behavior by the Reynolds number derived from the Navier-Stokes equation, the present inventors have increased the Reynolds number of the acid etching solution, that is, by reducing the liquid viscosity, the downstream of the cavity It was confirmed that the generation of etching unevenness due to the above was alleviated, and conversely, when the Reynolds number of the acid etching solution was reduced, that is, the viscosity of the solution was increased, etching unevenness was easily generated.

  In view of this, the present inventors diligently studied a suitable range of the spin rotation speed and the viscosity of the acid etching solution. In the spin etching method, the spin rotation speed was set to 1000 rpm or less, and the viscosity of the acid etching solution was set to 6.0 mPa · s. It has been discovered that the following conditions are the conditions that can suppress the occurrence of streaky etching unevenness near the laser mark dots.

  Hereinafter, the manufacturing method of the silicon wafer of this invention is demonstrated. The silicon wafer manufacturing method of the present invention rotates the silicon wafer while supplying the acid etching solution to the front or back surface of the silicon wafer through the supply nozzle, thereby reducing the supply range of the acid etching solution to the front or back surface of the silicon wafer. It includes a spin etching process in which acid etching is performed over the entire surface. Such a spin etching process is performed, for example, after a laser marking process in which a mark is imprinted on the front or back surface of a silicon wafer by a laser. In addition to these processes, processes such as a slicing process in which a silicon single crystal ingot is sliced thinly to produce a silicon wafer, a chamfering process of a silicon wafer, a grinding process, and a polishing process may be included.

  In the present invention, in the above spin etching step, an acid etching solution having a silicon wafer with a spin rotation speed of 1000 rpm or less and a viscosity of 6.0 mPa · s or less is used. Such a spin etching process will be described more specifically with reference to FIG.

  In the spin etching process, for example, an etching apparatus 1 as shown in FIG. 1 can be used. In the etching apparatus 1, a silicon wafer W to be etched is placed horizontally at the center of the vacuum suction stage 2 with the front or back surface facing up, and is held by vacuum suction on the vacuum suction stage 2 connected to the vacuum source 9. . The vacuum suction stage 2 is rotated in the θ direction of FIG. 1 with the center of the vacuum suction stage 2 as a rotation axis by a rotation unit including a θ-axis motor and a θ spindle (not shown) below the stage. At this time, in the present invention, the spin rotation speed of the silicon wafer W is set to 1000 rpm or less as described above. By setting the spin rotation speed to 1000 rpm or less, the average flow rate of the acid etching solution 8 is suppressed, and the generation of etching unevenness due to the cavity wake is alleviated.

  Moreover, it is preferable that a spin rotation speed shall be 1000 rpm or less and 300 rpm or more. If the acid etching solution 8 is supplied at a spin rotation speed of 300 rpm or more, the acid etching solution 8 surely diffuses over the entire surface of the wafer, so that the in-plane distribution of the wafer etching allowance becomes uniform.

  Subsequently, the acid etching solution 8 having a viscosity of 6.0 mPa · s or less is supplied from the liquid supply source 6 to the supply nozzle 3 above the vacuum suction stage 2 and is held and rotated on the vacuum suction stage 2. An acid etching solution 8 is supplied onto the silicon wafer W. If the viscosity of the acid etching solution 8 exceeds 6.0 mPa · s, the level difference of the etching unevenness generated in the laser mark dots becomes extremely large, and the polishing allowance in the subsequent double-side polishing step must be increased more than necessary. However, if the viscosity is 6.0 mPa · s or less, the difference in level of the etching unevenness can be suppressed to a minimum, and the polishing allowance can be minimized. Furthermore, the viscosity of the acid etching solution 8 is 6.0 mPa · s or less and preferably 5.0 mPa · s or more. When the viscosity of the acid etching solution 8 is 5.0 mPa · s or more, the reaction efficiency between the acid etching solution 8 and the silicon wafer 1 is further improved, and a high etching rate can be obtained.

  The acid etching solution 8 having a viscosity of 6.0 mPa · s or less is not particularly limited, but in addition to a mixed solution containing hydrofluoric acid, nitric acid, and sulfuric acid, or hydrofluoric acid, nitric acid, and sulfuric acid, A mixed solution to which acetic acid has also been added can be used. Moreover, although it does not specifically limit, such a liquid mixture is 1-10 mass% for hydrofluoric acid, 25-50 mass% for nitric acid, 0-15 mass% for acetic acid, and 5-25 mass% for sulfuric acid. If included in the range, the viscosity is 6.0 mPa · s or less. In this case, the balance in which the mass% of the acid is less than 100% in total is water.

  While the acid etching solution 8 is being supplied, the supply nozzle 3 generally reciprocates linearly in the radial direction of the silicon wafer W through the center of the silicon wafer W as indicated by an arrow 4 in FIG. Is.

  The acid etching solution 8 supplied onto the silicon wafer W moves on the silicon wafer W toward the outer periphery by the rotation of the silicon wafer W, and is discharged as droplets 5 from the outer periphery of the silicon wafer W.

  When the spin etching with the acid etching solution is completed, the supply of the acid etching solution 8 from the supply source 6 is stopped, the water is supplied from the water supply source 7 to the supply nozzle 3, and is held and rotated on the vacuum suction stage 2. Water is supplied onto the silicon wafer W. The water supplied onto the silicon wafer W moves on the silicon wafer W in the outer peripheral direction by the rotation of the silicon wafer W, and the acid etching solution 8 remaining on the silicon wafer W is replaced with water while the silicon wafer W is replaced. The liquid is discharged as droplets from the outer peripheral portion.

  Thereafter, the supply of water from the water supply source 7 is stopped, and the silicon wafer W is rotated at a high speed to scatter all the water on the silicon wafer W to obtain a dried silicon wafer W.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples.

  First, in Examples 1 to 3 and Comparative Examples 1 and 2, the relationship between the change in spin rotation speed and etching unevenness was investigated by changing the spin rotation speed in the spin etching process.

Example 1
First, a plurality of silicon wafers having laser mark dots on the surface were prepared through a laser marking process. Next, with respect to each of the prepared silicon wafers, the spin etching process according to the present invention was performed in a single wafer type using the etching apparatus 1 as shown in FIG.

  In the spin etching process of Example 1, the spin rotation speed of the silicon wafer was set to 300 rpm, and the viscosity of the acid etching solution was set to 6.0 mPa · s.

(Example 2)
The silicon wafer was spin-etched in a single wafer manner in the same manner as in Example 1 except that the spin rotation number of the silicon wafer was 800 rpm and the spin etching step in the present invention was carried out in a single wafer manner. At this time, the viscosity of the acid etching solution was 6.0 mPa · s as in Example 1.

(Example 3)
The silicon wafer was spin-etched in a single-wafer manner as in Example 1 except that the spin rotation speed of the silicon wafer was 1000 rpm and the spin-etching step in the present invention was carried out in a single-wafer manner. At this time, the viscosity of the acid etching solution was 6.0 mPa · s as in Example 1.

(Comparative Example 1)
The silicon wafer was spin-etched in a single-wafer manner as in Example 1 except that the spin rotation speed of the silicon wafer was 1200 rpm and the spin-etching step was carried out in a single-wafer manner. At this time, the viscosity of the acid etching solution was 6.0 mPa · s as in Example 1.

(Comparative Example 2)
The silicon wafer was spin-etched in a single-wafer manner as in Example 1 except that the spin rotation speed of the silicon wafer was 2000 rpm and the spin-etching step was carried out in a single-wafer manner. At this time, the viscosity of the acid etching solution was 6.0 mPa · s as in Example 1.

  In Example 1 and Comparative Example 2, streaky etching unevenness in the vicinity of the laser mark dots on the etched wafer was observed with a laser microscope. The observation photographs of Example 1 and Comparative Example 2 are shown in FIGS. 2 and 3, respectively. As can be seen from the above, in Example 1 (FIG. 2) in which the spin speed was 1000 rpm or less, streaky etching unevenness was generated compared to Comparative Example 2 (FIG. 3) in which the spin speed was greater than 1000 rpm. It was relaxed.

  FIG. 4 shows the depth (height difference) of etching unevenness in the vicinity of laser mark dots on the wafers after etching in Examples 1 to 3 and Comparative Examples 1 and 2. The height difference was measured by cross section measurement with a laser microscope. As can be seen from FIG. 4, when the spin speed exceeded 1000 rpm, the streak depth increased rapidly. That is, in Comparative Examples 1 and 2, the polishing allowance in the double-side polishing step had to be increased more than in Examples 1 to 3.

  In Examples 4 and 5 and Comparative Examples 3 to 5 below, the relationship between the change in viscosity and etching unevenness was investigated by changing the viscosity of the acid etching solution in the spin etching process.

Example 4
The spin etching process was performed under the same conditions as in Example 1 except that the spin rotation number of the silicon wafer was 300 rpm, the viscosity of the acid etching solution was 5.5 mPa · s, and the other conditions were the same.

(Example 5)
A silicon wafer was spin-etched in the same manner as in Example 4 except that the viscosity of the acid etching solution was 6.0 mPa · s. At this time, the spin rotation number of the silicon wafer was 300 rpm as in Example 4. Thus, Example 5 was made the same conditions as Example 1.

(Comparative Example 3)
A silicon wafer was spin-etched in the same manner as in Example 4 except that the viscosity of the acid etching solution was 6.4 mPa · s. At this time, the spin rotation number of the silicon wafer was 300 rpm as in Example 4.

(Comparative Example 4)
A silicon wafer was spin-etched in the same manner as in Example 4 except that the viscosity of the acid etching solution was 7.0 mPa · s. At this time, the spin rotation number of the silicon wafer was 300 rpm as in Example 4.

(Comparative Example 5)
A silicon wafer was spin-etched in the same manner as in Example 4 except that the viscosity of the acid etching solution was 8.4 mPa · s. At this time, the spin rotation number of the silicon wafer was 300 rpm as in Example 4.

  In Example 5 and Comparative Example 5, streaky etching unevenness in the vicinity of the laser mark dots on the etched wafer was observed with a laser microscope. An observation photograph of Example 5 is shown in FIG. An observation photograph of Comparative Example 5 is shown in FIG. Comparing FIG. 5 (Example 5) and FIG. 6 (Comparative Example 5), in Example 5 in which the viscosity of the acid etching solution was 6.0 mPa · s or less, a comparative example in which the viscosity was greater than 6.0 mPa · s. It can be seen that the occurrence of streaky etching unevenness was alleviated as compared with FIG.

  FIG. 7 shows the depth (height difference) of etching unevenness in the vicinity of the laser mark dots on the wafers after etching in Examples 4 and 5 and Comparative Examples 3 to 5. The height difference was measured by cross section measurement with a laser microscope. As can be seen from FIG. 7, when the viscosity exceeded 6.0 mPa · s, the streak depth increased rapidly.

  FIG. 8 shows a double-sided polishing allowance in a post-process that is necessary for the etched wafers of Examples 4 and 5 and Comparative Examples 3 to 5. As can be seen from FIG. 8, when the viscosity exceeds 6.0 mPa · s, the difference in height of the etching unevenness is large, so that the machining allowance required for double-side polishing has increased.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

DESCRIPTION OF SYMBOLS 1 ... Etching apparatus, 2 ... Vacuum suction stage, 3 ... Supply nozzle, 4 ... Arrow,
5 ... Droplet, 6 ... Supply source, 7 ... Supply source, 8 ... Acid etchant,
9 ... Vacuum source, W ... Silicon wafer.

Claims (3)

While supplying the acid etching solution through the supply nozzle to the front or back surface of the silicon wafer, the silicon wafer is rotated to expand the supply range of the acid etching solution to the entire surface of the silicon wafer or the back surface. A method for manufacturing a silicon wafer including a spin etching process for performing
In the spin etching step, the silicon wafer has a spin rotation speed of 1000 rpm or less, and the viscosity is 6.0 mPa · s or less, and the acid etching solution is used .
The silicon wafer manufacturing method , wherein the spin etching step is performed after a laser marking step in which a mark is engraved on a front surface or a back surface of the silicon wafer by a laser .   2. The method for producing a silicon wafer according to claim 1, wherein a mixed solution containing hydrofluoric acid, nitric acid and sulfuric acid, or a mixed solution obtained by adding acetic acid to the mixed solution is used as the acid etching solution. As the acid etching solution, a mixed solution containing 1 to 10% by mass of hydrofluoric acid, 25 to 50% by mass of nitric acid, 0 to 15% by mass of acetic acid, and 5 to 25% by mass of sulfuric acid is used. The manufacturing method of the silicon wafer of Claim 1 or Claim 2 to do.