DOUBLE-SIDED POLISHING PROCESS FOR A SILICON WAFER

Abstract

Method for double-sided polishing of a silicon wafer (W) using a double-sided polishing device (100) including a carrier plate (10) with one or more holding openings (12) for holding the silicon wafer (W) and an upper plate (14) and a lower plate (16), each having a surface provided with a polishing cloth (18, 20) and arranged such that they face each other with the carrier plate (10) between them, in order to simultaneously polish a front surface and a rear surface of the silicon wafer (W) by rotating the upper plate (14) and the lower plate (16) relative to the carrier plate (10), wherein the polishing cloths (18, 20) of the upper plate (14) and the lower plate (16) are in contact with the front surface and rear surface, respectively, of the silicon wafer (W) loaded into each holding opening (12).which successively comprises: a first polishing step of performing double-sided polishing while a first polishing agent, which is an alkaline aqueous solution containing abrasive grains, is supplied to the polishing cloths (18, 20); following the first polishing step, a polishing agent change step of stopping the supply of the first polishing agent and starting the supply of a second polishing agent, which is an alkaline aqueous solution containing a water-soluble polymer without abrasive grains, wherein the polishing cloths (18, 20) of the upper plate (14) and the lower plate (16) are in contact with the front surface and the rear surface of the silicon wafer (W), respectively, and wherein the upper plate (14) and the lower plate (16) are continuously rotated; and a second polishing step of performing double-sided polishing while the second polishing agent is supplied to the polishing cloths (18, 20) after the polishing agent change step.20) is delivered.,

Description

TECHNICAL AREA

[0001] This disclosure relates to a method for simultaneously polishing a front surface and a rear surface of a silicon wafer. BACKGROUND

[0002] A process for producing a silicon wafer mainly involves a single-crystal pulling step to form a single-crystal ingot and a processing step for the formed single-crystal ingot. This processing step typically includes a slice-cutting step, a lapping step, a chamfering step, an etching step, a polishing step, a cleaning step, etc., and these steps produce a silicon wafer with a highly polished surface.

[0003] In this polishing step, chemical-mechanical polishing (CMP) is typically used, in which a silicon wafer and a polishing cloth are rotated relative to each other and rubbed against each other. As is known, CMP combines the mechanical polishing action of abrasive grains in a polishing compound with the chemical polishing action of the compound (alkaline aqueous solution), resulting in excellent smoothness. In this polishing step, the polishing process is carried out in several stages, for example, a double-sided polishing step (coarse grinding step) involving the simultaneous polishing of the front and back surfaces of a silicon wafer using a double-sided polishing device, as described in [reference to relevant document]. Fig. 5 is illustrated, followed by a final polishing step of high-gloss polishing of at least one side of the silicon wafer.

[0004] In an initial stage, coarse grinding is performed to polish a silicon wafer to a desired thickness. Double-sided polishing is carried out by polishing at a relatively high polishing rate using a hard polishing cloth, for example, made of polyurethane, resulting in a planarized silicon wafer with reduced thickness variation. Final polishing is performed in a final stage to reduce the surface roughness of the silicon wafer. Single-sided polishing is performed using a soft polishing cloth, such as suede, and fine, unbound abrasive grains, reducing the surface roughness of minute irregularities on the silicon wafer surface, such as nanotopography or haze.

[0005] JP 5754659 B (PTL 1 - see claims 1 and 2, example 1, etc.) discloses a method for polishing silicon wafers, comprising: a rough polishing step for simultaneously polishing a front surface and a rear surface of the silicon wafer; and a final polishing step for final polishing of the roughly polished surface after the rough polishing, wherein the rough polishing comprises a first step polishing to remove a native oxide film using a polishing fluid containing unbound abrasive grains, and a second step polishing the front and rear surfaces of the silicon wafer from which the native oxide films have been removed, using a polishing fluid in which a water-soluble polymer has been added to an aqueous amine solution without unbound abrasive grains, such that the polishing removal of the silicon wafer is 5 µm to 10 µm on one side after polishing in the first step.Additionally, in Example 1, the polishing of the second step is carried out using a double-sided polishing device that is used in the polishing of the first step. CITATION LIST Patent literature

[0006] PTL 1: JP 5754659 B SUMMARY (Technical Problem)

[0007] The two-stage coarse polishing described in PTL 1 is performed based on the design concept described below. In the coarse polishing step using a double-sided polishing unit, the polishing material removal in the peripheral part of a wafer is likely to be greater compared to its center, leading to a problem of roll-off in the peripheral part of the wafer. To address this problem, PTL 1 performs the coarse polishing using a polishing fluid containing a water-soluble polymer without abrasive particles. The roll-off amount (ROA) of the wafer's peripheral part is reduced by the action of the water-soluble polymer. Furthermore, in most cases, a native oxide film with a thickness of approximately 5 to 20 angstroms is formed on the silicon wafer prior to the coarse polishing step, and this native oxide film is hardly removed by a polishing fluid without abrasive particles.In this case, the native oxide film is removed by performing a first polishing step using a polishing fluid containing abrasive particles. In Example 1 from PTL 1, the first polishing step, including the removal of the native oxide film, is performed with a polishing removal of 0.5 µm for one side (1 µm for both surfaces), and the second polishing step is performed with a polishing removal of 5 µm for one side (10 µm for both surfaces).

[0008] However, in the double-sided polishing process described in PTL 1, the switching of the polishing fluids between the first step, which uses a polishing fluid containing abrasive particles, and the second step, which uses a polishing fluid without abrasive particles, is not discussed when the first and second steps are performed using a common double-sided polishing device. Investigations carried out by the inventors of this disclosure demonstrated that, depending on how the polishing fluid switch is performed, the substrate was set into oscillation at the beginning of the second step, and this oscillation caused micro-scratches on the front and back surfaces of the silicon wafer during polishing.

[0009] In view of the above problems, it might be helpful to provide a method for double-sided polishing of a silicon wafer that can prevent the formation of micro-scratches on the front and back surfaces of the silicon wafer during polishing. (Solution to the problem)

[0010] The inventors of this disclosure conducted careful studies to solve the above problems and discovered the following. In double-sided polishing, the used polishing compound is typically returned to a polishing compound supply tank and reused for repeated use as a polishing compound.In this regard, if first-stage and second-stage polishing are performed using a common double-sided polishing device, a method can be devised to supply pure water to the polishing cloths simultaneously with the cessation of polishing compound supply to the polishing cloths after the first-stage polishing is complete. This prevents mixing of the polishing compound used in the first stage and the polishing compound used in the second stage, removes abrasive particles adhering to the wafer and the substrate, and cleans the polishing cloths with pressurized water. However, in one such case, it was found that the substrate was set into oscillation, accompanied by noise from the substrate at the beginning of the second-stage polishing.Since the rotation of the upper and lower plates continues in the absence of abrasive grains, the pressure from the polishing cloths is exerted directly on the backing plate. Consequently, the frictional resistance between the wafer, the backing plate, and the polishing cloths increases, leading to the assumption that the oscillation is caused by the increased pressure exerted on the wafer by the upper and lower plates. In light of the above, the inventors investigated techniques for changing the polishing agents without the rotation of the upper and lower plates continuing in the absence of abrasive grains.They considered reducing the oscillation of the support plate by establishing a transition period during which polishing is carried out in the presence of both the polishing agent used in the first stage polishing and the polishing agent used in the second stage polishing, which are intentionally mixed, rather than preventing the polishing agents from mixing, and they have experimentally shown that the idea was correct.

[0011] This revelation is based on the above findings, and we propose the following characteristics. (1) A method for double-sided polishing of a silicon wafer using a double-sided polishing device including a carrier plate with one or more holding openings for holding the silicon wafer and an upper plate and a lower plate, each having a surface provided with a polishing cloth and arranged so that they face each other with the carrier plate between them, to simultaneously polish a front surface and a rear surface of the silicon wafer by rotating the upper plate and the lower plate relative to the carrier plate, wherein the polishing cloths of the upper plate and the lower plate are in contact with the front surface and rear surface, respectively, of the silicon wafer loaded into each holding opening, comprising successively the following: a first polishing step of performing a double-sided polishing, while a first polishing agent, which is an alkaline aqueous solution containing abrasive grains, is supplied to the polishing cloths; Following the first polishing step, a polishing agent change step is performed, in which the supply of the first polishing agent is stopped and the supply of a second polishing agent, which is an alkaline aqueous solution containing a water-soluble polymer without abrasive grains, wherein the polishing cloths of the upper plate and the lower plate are in contact with the front surface and the rear surface of the silicon wafer, respectively, and wherein the upper plate and the lower plate are continuously rotated; and a second polishing step of performing double-sided polishing, while the second polishing agent is supplied to the polishing cloths after the polishing agent change step. (2) The method for double-sided polishing of a silicon wafer according to (1) above, where, with reference to a surface pressure applied by the top plate and the bottom plate to the front surface and the rear surface of the silicon wafer, In the first polishing step, double-sided polishing is carried out with an initial surface pressure, and in a final stage of the first polishing step, the surface pressure is reduced to a second surface pressure that is lower than the initial surface pressure at the end of the first polishing step. The double-sided polishing is carried out with the second surface pressure in the second polishing step. (3) The method for double-sided polishing of a silicon wafer according to (2) above, where the second surface pressure is 5% to 40% lower than the first surface pressure. (4) The method for double-sided polishing of a silicon wafer according to one of (1) to (3) above, wherein in the first polishing step double-sided polishing is carried out to obtain a polishing removal of 80% to 99.5% with respect to a total polishing removal of the first and second polishing steps, and In the second polishing step, double-sided polishing is carried out with a polishing removal of 0.05 µm to 0.5 µm on each surface. (5) The method for double-sided polishing of a silicon wafer according to one of (1) to (4) above, wherein in the first polishing step the first polishing compound that was used is recovered and then delivered again to the polishing cloths, and In the second polishing step, the polishing compound that was used is recovered and then disposed of. (Beneficial effect)

[0012] The process of double-sided polishing of a silicon wafer can prevent the formation of micro-scratches on the front and back surfaces of the silicon wafer during polishing. List of characters

[0013] The following applies to the accompanying drawings: Fig. Figure 1 is a flowchart of a process for double-sided polishing of a silicon wafer according to an embodiment of this disclosure; Fig. Figure 2 is a flowchart of a process for double-sided polishing of a silicon wafer according to comparative example 1; Fig. Figure 3 is a flowchart of a process for double-sided polishing of a silicon wafer according to comparative example 2; Fig.Figure 4 is a diagram illustrating the changing of surface pressures applied to silicon wafers, the changing of slurries supplied, and the changing of methods for processing polishing media used in a method for double-sided polishing of a silicon wafer according to an embodiment of this disclosure; and Fig. Figure 5 is a schematic view of a double-sided polishing device 100 , which is used in a method for double-sided polishing of a silicon wafer according to an embodiment of this disclosure. DETAILED DESCRIPTION

[0014] First, with reference to Fig. 5 the basic structure of the double-sided polishing device 100 described, which is used in the method for double-sided polishing of a silicon wafer according to an embodiment of this disclosure. The double-sided polishing device 100 a carrier plate 10and a top plate 14 and a lower plate 16 on, which are arranged in such a way that they are connected to each other with the support plate 10 are facing each other in between. The support plate 10 is equipped with several holding openings 12 (one of them is in Fig. 5 representative illustrations) for holding silicon wafers W provided and the silicon wafers W are placed in the respective holding openings 12 loaded. Surfaces of the upper and lower plates 14 and 16 are equipped with polishing cloths 18 or 20 equipped with a sun wheel 22 is in the center of the upper and lower plates 14 and 16 provided and an inner wheel 24 is provided around the plates.

[0015] A polishing compound is supplied through a polishing compound supply line. 26 to the space between the upper and lower plates 14 and 16supplied via a channel that runs vertically through the upper plate 14 extends. The details of a supply / recovery system for the polishing compound are described below.

[0016] With the double-sided polishing device 100 are the several into the several openings 12 charged silicon wafer W sandwich-like between the upper plate 14 and the lower plate 16 included, and the sun wheel 22 and the inner wheel 24 are rotated to the top plate 14 and the bottom plate 16 with reference to the carrier plate 10 to rotate relative to the front surface and the back surface of each silicon wafer W in contact with the polishing cloths 18 or 20 are located while a polishing agent is applied to the polishing cloths 18 and 20is delivered. Thus, the front surface and the back surface of the multiple silicon wafers can be examined. W be polished at the same time.

[0017] It should be noted that the structure of a double-sided polishing device that can be used in a method for double-sided polishing of a silicon wafer according to this disclosure is not limited to the structure described above and a sun wheel (planetary wheel) type or a non-sun wheel type in which the carrier plate is moved circularly without rotation can be used.

[0018] In this embodiment, for the coarse grinding of a silicon wafer, a first polishing step is carried out by performing double-sided polishing, while a first polishing agent, which is an alkaline aqueous solution containing abrasive grains, is applied to the polishing cloths. 18 and 20is supplied, and then a second polishing step is carried out by performing double-sided polishing, while a second polishing agent, which is an alkaline aqueous solution containing a water-soluble polymer without abrasive grains, is applied to the polishing cloths. 18 and 20 is supplied using the double-sided polishing device 100 performed, which is used in the first polishing step.

[0019] The first polishing step in this embodiment involves the removal of a natural oxide layer with a thickness of approximately 5 to 20 angstroms, which is present on a surface layer of each silicon wafer. W is formed, and the polishing of the silicon wafer W to a substantial target thickness using a polishing compound containing abrasive grains.

[0020] The total polishing removal of the first and second polishing steps is set for each surface within a range of approximately 2.5 µm to 10 µm. In the first polishing step, double-sided polishing is performed to achieve a polishing removal of 80% to 99.5% relative to the total polishing removal of the first and second polishing steps. If the polishing removal of the first polishing step is less than 80% of the total polishing removal, the second polishing step must be performed at a lower polishing rate for a longer time to achieve the target thickness, resulting in reduced productivity. If the polishing removal of the first polishing step exceeds 99.5% of the total polishing removal, the amount of material removed by polishing in the second polish is too small, so the effect of reducing the amount of wafer periphery debris is insufficient.

[0021] On the other hand, in this embodiment, the second polishing step is carried out to reduce the amount of debris falling off the peripheral part of the wafer by polishing both surfaces of the silicon wafer. W The wafers can be easily polished using a polishing compound containing a water-soluble polymer without abrasive particles. Specifically, the second polishing step involves double-sided polishing to achieve a polishing removal of 0.05 µm to 0.5 µm for each surface. If the polishing removal for each surface is less than 0.05 µm, the reduction in wafer periphery drop is insufficient. Conversely, since the polishing compound, which contains a water-soluble polymer without abrasive particles, has a low polishing rate, a polishing removal exceeding 0.5 µm results in reduced productivity.

[0022] In PTL 1, since the first-step polishing using a polishing fluid containing abrasive particles is primarily aimed at removing a native oxide film, its polishing removal rate is 0.5 µm for each surface. The target thickness is achieved by performing double-sided polishing of 5 µm to 10 µm for each surface in the second step using a polishing fluid containing a water-soluble polymer without abrasive particles. In contrast, in this embodiment, the first-stage polishing is performed at a high polishing rate primarily to achieve the target thickness, thus maintaining high productivity. Furthermore, if a polishing removal rate of 0.05 µm or more for each surface is ensured during the second-stage polishing, the amount of wafer periphery waste can be sufficiently reduced.

[0023] The pH value of the first polishing agent or the second polishing agent is preferably set to a range of 9 until 12 adjusted. If the pH value is below 9 If the pH value is too low, the etching effect is too weak and defects due to processing, such as scratches and errors, easily form on the surfaces of the silicon wafers. 12 If the concentration exceeds the limit, handling the solution itself becomes difficult. Furthermore, the following are preferably used as alkaline agents: an alkaline aqueous solution to which any one basic ammonium salt, basic potassium salt, or basic sodium salt has been added; an aqueous alkali carbonate solution; or an alkaline aqueous solution to which an amine has been added. Alternatively, an aqueous solution of hydrazine or amines may be used, and amine is particularly desirable for increasing the polishing rate.

[0024] In the first polishing compound, the abrasive grains used can be made of silicon dioxide, aluminum oxide, diamond, etc.; and for reasons of low cost, dispersibility in the polishing compound, and ease of controlling the particle diameter of the abrasive grains, etc., the abrasive grains preferably contain SiO2 particles. The mean primary particle diameter of the abrasive grains, when measured according to the BET method, can be adjusted to 30 nm to 100 nm.

[0025] The second polishing agent preferably uses one or more water-soluble polymers selected from nonionic water-soluble polymers. Examples include hydroxyethylcellulose (HEC), polyethylene glycol (PEG), and polypropylene glycol (PPG). To sufficiently reduce the amount of wafer peripheral debris, the concentration of the water-soluble polymer is preferably 1 ppm or more, and particularly preferably 10 ppm or more. Furthermore, to prevent a reduction in productivity due to a significantly reduced polishing rate, the concentration is preferably 200 ppm or less, and particularly preferably 100 ppm or less.

[0026] For the polishing cloths 18 and 20Examples include a non-woven polishing cloth made of polyester and a polyurethane polishing cloth; a foamed polyurethane polishing cloth with excellent high-gloss polishing accuracy on the polished surfaces of silicon wafers is particularly preferred. For the polishing cloths 18 and 20 A Shore D hardness of 70 to 90 according to JIS K 6253-1997 / ISO 7619 and a compressibility of 1% to 5%, particularly 2% to 3%, are preferred.

[0027] The polishing rate in the first polishing step is preferably 0.1 µm / min to 1.0 µm / min and the polishing rate in the second polishing step is preferably 0.03 µm / min to 0.5 µm / min.

[0028] The rotational speed of the upper and lower plates, the rotational speed of the silicon wafers, the surface pressure, and the polishing compound feed rate can be adjusted to achieve the polishing rates mentioned above. The rotational speed of the upper and lower plates can be set within a range of 5 rpm to 40 rpm for the first and second polishing steps. The surface pressure can be adjusted within a range of 50 g / cm². 2 up to 300 g / cm² 2 The frictional resistance is high in the second polishing step because the polishing compound is used without abrasive grains; therefore, the surface pressure in the second polishing step is desirablely set 5% to 40% lower than the surface pressure in the first polishing step.

[0029] Here, this embodiment is achieved through the technique of changing the first polishing medium and the second polishing medium when the first polishing step and the second polishing step are performed using the common double-sided polishing device. 100 to be carried out, marked. To explain the technical significance of this embodiment, double-sided polishing processes according to comparative examples 1 and 2 are first described with reference to the Fig. 2 and Fig. 3 described.

[0030] With reference to Fig. 2 In the double-sided polishing process according to comparative example 1, the first polishing step is carried out by supplying the first polishing medium, whereby the upper and lower plates are in contact with the wafers (resting on them) and are rotated (step 1). S1), and the supply of the first polishing compound is stopped after a defined period. Following the first polishing step, a pure water rinse and polishing cloth cleaning are performed to prevent the first polishing compound from mixing with the second. Specifically, pure water is supplied to the polishing cloths from the upper plate, with the upper and lower plates resting on the wafers and rotated, thereby removing any abrasive particles adhering to the wafers or the backing plate (step ). S2 After the rotation of the upper and lower plates has stopped and the supply of pure water has also stopped, the upper plate is lifted to detach it from the wafers (detached) and the carrier plate and wafers are removed from the lower plate (polishing cloth) (step S3Next, pressurized water is sprayed onto the polishing cloths to remove polishing residues, abrasives, etc., adhering to the cloths (step 1). S4 After cleaning the polishing cloths, the carrier plate and the silicon wafers are placed back into their original positions (step S5 Furthermore, the supply of the second polishing medium is started in a state where the upper and lower plates are resting on the wafers and the rotation of the plates is stopped, and the rotation of the upper and lower plates is then continued to perform the second polishing step (step S6 After the specified time has elapsed, the supply of the second polishing compound is stopped. Then, as after the first polishing step, a pure water rinse and cleaning of the polishing cloth are carried out (steps S7 until S10 ). In this step S10New, unpolished wafers are loaded. The supply of the first polishing compound is then started in a state where the top and bottom plates are resting on the wafers and the rotation of the plates has stopped. Afterward, the double-sided polishing of the new batch is restarted from step 1. S1 carried out.

[0031] Next, with reference to Fig. 3. In the double-sided polishing process according to comparative example 2, in order to shorten the step, only pure water rinsing is carried out after the first polishing step, while preventing the first polishing agent and the second polishing agent from mixing (step 3). S2 ). Then the supply of the second polishing compound is started and the rotation of the upper and lower plates continues to perform the second polishing step (step ). S6 The other steps are the same as those in Fig.2. This process does not include the polishing cloth cleaning step between the first polishing step and the second polishing step; therefore, the top plate does not need to be detached from the wafers and placed back on the wafers.

[0032] However, in the two comparative examples 1 and 2, at the beginning of the second polishing step (step S6 ) the oscillation of the carrier plate. Since the rotation of the upper and lower plates continues in the absence of abrasive grains, the frictional resistance between the wafer, along with the carrier plate and the polishing cloths, increases, so it is assumed that the oscillation is caused by the increased pressure load on the wafer from the upper and lower plates.

[0033] On the other hand, in this embodiment, with reference to Fig.1. After the first polishing step, the second polishing step is started directly, without performing the pure water rinse and polishing cloth cleaning. In other words, after the first polishing step (step 1), the second polishing step is started directly. S1 ) Simultaneously with the termination of the supply of the first polishing compound, the supply of the second polishing compound is started, with the upper and lower plates resting on the wafers and with the plates being continuously rotated (step S20 : Polishing agent change step). The second polishing step (step S6The process is then carried out. In this case, the rotation of the upper and lower plates is not continued in the absence of abrasive grains, and for a certain period (approximately 20 seconds) from the start of the second polishing step, the double-sided polishing continues with a polishing compound that is a mixture of the first polishing compound, which contains abrasive grains, and the second polishing compound without abrasive grains. Accordingly, the pressure exerted on the wafers by the upper and lower plates does not increase, and the oscillation of the carrier plate can be controlled. This can prevent the formation of micro-scratches on the front and back surfaces of the silicon wafers during polishing.

[0034] It is noted that in the second polishing step, the first polishing compound, which contains abrasive grains, and the second polishing compound without abrasive grains are mixed for a certain period of time from the beginning of the second polishing step. Therefore, the recovery, circulation, and reuse of the polishing compound is preferably avoided. In this respect, as in Fig.Figure 4 illustrates that the recovery line is activated in the first polishing step to recover the used first polishing compound, and the recovered compound is then returned to the polishing cloths; in contrast, the recovery line is deactivated at the beginning of the second polishing step, and a disposal line is simultaneously activated to recover the used polishing compound, and the recovered polishing compound is preferably disposed of at any time during the second polishing. As described above, since the second polishing step is very short in this embodiment, the polishing compound costs would not be particularly high, even if the used polishing compound is not reused.

[0035] A feed / recovery system for polishing compound, with which such a method for processing a used polishing compound is implemented, is described with reference to Fig.5 described. The first polishing compound is supplied from a first polishing compound supply tank. 32 to a first polishing compound supply line 30 supplied, whereas the second polishing compound is supplied from a second polishing compound supply tank. 36 to a second polishing compound supply line 34 is delivered. The union of the lines 30 and 34 is equipped with a switching valve 28 The polishing compound is supplied to the polishing compound supply line and the switching valve controls which polishing compound is supplied. 26 to be delivered. On the other hand, the polishing compound used flows from a recovery system (not shown), which is located below the lower plate, into a recovery line. 38 for the polishing compound used. This line 38 is equipped with a switching valve 40 and a disposal fluid line branching off from the changeover valve 46equipped. By controlling the switching valve. 40 It is controlled whether the polishing agent used is deposited into a recovery tank. 42 , with which the management 38 is connected, or into the wastewater disposal line 46 is transferred. The used waste disposal fluid, which goes into the recovery tank. 42 The transfer is carried out via a reuse line. 44 back to the first polishing compound supply tank 32 transferred.

[0036] While the first polishing compound, which contains abrasive grains, is used in the first polishing step by controlling the switching valve 28 through the first polishing compound supply line 30 The first polishing agent used is supplied by controlling the switching valve. 40 into the recovery tank 42recovered and reused. During the second polishing step, the second polishing compound is removed by controlling the switching valve. 28 through the second polishing compound supply line 34 The polishing agent used is supplied by controlling the switching valve. 40 through the wastewater disposal line 46 disposed of.

[0037] Next, the second polishing step is performed using the second polishing compound without abrasive grains, which simply increases the frictional resistance between the wafers, the carrier plate, and the polishing cloths. To counteract this, the second polishing step is preferably performed at a lower surface pressure than that used in the first polishing step, considering the surface pressure exerted on the silicon wafers by the upper and lower plates. This reliably prevents oscillation of the carrier plate. Consequently, the formation of micro-scratches on the front and back surfaces of the silicon wafers during polishing is sufficiently reduced.In this respect, in this embodiment, since the first polishing step and the second polishing step are carried out sequentially, the surface pressure is reduced in the last stage of the first polishing step and is reduced to the surface pressure of the second polishing step at the end of the first polishing step, as shown in . Fig. 4 is illustrated. EXAMPLES (Comparison example 1)

[0038] By using the in Fig. In the double-sided polishing device shown in Figure 5, silicon wafers with a diameter of 300 mm (five wafers / batch × two batches = 10 wafers) were subjected to double-sided polishing according to the process described in Figure 5. Fig.The two polishing agents were subjected to a given flow. For the first polishing agent, an aqueous KOH solution containing 5 wt% colloidal silicon dioxide particles as abrasive grains with a mean primary particle diameter of 70 nm was used. For the second polishing agent, an aqueous piperidine solution containing 10 wt ppm hydroxyethylcellulose (HEC) without abrasive grains was used. In the first polishing step, polishing was carried out with a rotation speed of 15 rpm for the upper and lower plates and a surface pressure of 250 g / cm². 2 The polishing process was carried out and the polishing material removal for each surface was 5 µm. In the second polishing step, polishing was performed with a rotation speed of 15 rpm for the upper and lower plates and a surface pressure of 250 g / cm². 2The polishing process was carried out and the material removal for each surface was 0.5 µm. Between the first and second polishing steps, a pure water rinsing step of 30 seconds and a polishing cloth cleaning step of 60 seconds were performed. (Comparative example 2)

[0039] By using the in Fig. In the double-sided polishing device shown in Figure 5, silicon wafers with a diameter of 300 mm (five wafers / batch × two batches = 10 wafers) were subjected to double-sided polishing according to the process described in Figure 5. Fig. 3. The given flow was applied. In particular, the same conditions and flow were used as in Comparative Example 1, except that the cleaning of the polishing cloths between the first polishing step and the second polishing step was not carried out. (Example 1)

[0040] By using the in Fig.In the double-sided polishing device shown in Figure 5, silicon wafers with a diameter of 300 mm (five wafers / batch × two batches = 10 wafers) were subjected to double-sided polishing according to the process described in Figure 5. Fig. The given flow was applied. The first and second polishing media used were the same as in comparison examples 1 and 2. In the first polishing step, polishing was carried out with a rotational speed of 15 rpm for the upper and lower plates and a surface pressure of 250 g / cm². 2 The polishing process was carried out, and the polishing material removal for each surface was 5 µm. Simultaneously with the cessation of the first polishing compound supply, the supply of the second polishing compound was initiated, with the upper and lower plates resting on the wafers and rotating continuously. In the second polishing step, polishing was performed with a rotation speed of 15 rpm for both the upper and lower plates and a surface pressure of 250 g / cm².2 The procedure was carried out and the polishing removal rate for each surface was 0.5 µm. As described in Fig. As illustrated in Figure 4, the recovery line was activated in the first polishing step, and the recovery line was deactivated at the beginning of the second polishing step, while the disposal fluid line was activated simultaneously. (Example 2)

[0041] As in Fig. Figure 4 illustrates that the surface pressure in the last 10 seconds of the first polishing step was 250 g / cm². 2 per 200 g / cm² 2 reduced and the second polishing step was carried out with a surface pressure of 200 g / cm² 2 carried out. Apart from that, the same conditions and flow as in Example 1 were used to perform the double-sided polishing. < Evaluation of micro-scratches >

[0042] The back surface of each double-sided polished wafer was inspected using a surface defect inspection system manufactured by KLA-Tencor Corporation: Surfscan SP2 in DWO (Darkfield Composite Oblique Mode). The number of light spot defects (LPDs) with a defect size of 160 nm or larger observed on the wafer surfaces was counted as the number of microscratches formed. The results are given in Table 1. Table 1 Wafer No. Comparative example 1 Comparative example 2 Example 1 Example 2 Nr.01 446 90 22 1 Nr.02 482 128 19 1 Nr.03 422 40 20 0 Nr.04 458 79 22 0 Nr.05 424 58 22 4 Nr.06 264 448 27 0 Nr.07 244 210 20 2 Nr.08 142 102 13 1 Nr.09 325 99 17 0 Nr.10 110 109 9 2 Average 331,7 136,3 19,1 1,1 Unit: Number per wafer

[0043] As described above, many micro-scratches were formed in comparison examples 1 and 2, whereas in example 1 micro-scratches were reduced and in example 2 micro-scratches were reduced more than in example 1. < Evaluation of wafer flatness >

[0044] The ESFQR (Edge Site Front Least Squares Range) of each double-polished silicon wafer in Examples 1 and 2 was evaluated using a flatness measurement system (WaferSight, manufactured by KLA-Tencor Corporation). The ESFQR is an evaluation index for the flatness of the edge where the flatness is slightly reduced (site flatness) and indicates the degree of edge drop. The ESFQR is defined as the difference between the maximum and minimum values ​​of the deviation from the reference plane (site with best surface fit), determined by the least squares method from the thickness distribution of each site, which is a unit area obtained by uniformly subdividing an annular region along the wafer edge in the circumferential direction.Here, the ESFQR of the 72 digits obtained by subdividing a ring-shaped peripheral area defined in a range of 2 mm to 32 mm from the outermost periphery of the wafer (sector length: 30 mm) was measured, and the average for all digits: ESFQR average was determined.

[0045] As a result, it was found that silicon wafers exhibiting high flatness with an average ESFQR:ESFQR ratio of 30 nm or less, achieved by reducing edge drop, were obtained in both Example 1 and 2. INDUSTRIAL APPLICABILITY

[0046] The process of double-sided polishing of a silicon wafer prevents the formation of micro-scratches on the front and back surfaces of the silicon wafer during polishing. Reference symbol list 100: Double-sided polishing attachment 10: Carrier plate 12: Holding opening 14: Top plate 16: Bottom plate 18, 20: Polishing cloth 22: Sun wheel 24: Inner wheel 26: Polishing compound supply line 28: Diverter valve 30: First polishing compound supply line 32: First polishing agent supply tank 34: Second polishing compound supply line 36: Second polishing agent supply tank 38: Recovery line for used polishing compound 40: Diverter valve 42: Recovery tank 44: Reuse Management 46: Wastewater disposal line W: Silicon wafer QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 5754659 B [0005, 0006]

Claims

[1] A method for double-sided polishing of a silicon wafer using a double-sided polishing device including a carrier plate with one or more holding openings for holding the silicon wafer and an upper plate and a lower plate, each having a surface provided with a polishing cloth and arranged to face each other with the carrier plate in between, to simultaneously polish a front surface and a rear surface of the silicon wafer by rotating the upper plate and the lower plate relative to the carrier plate, wherein the polishing cloths of the upper plate and the lower plate are in contact with the front surface and rear surface, respectively, of the silicon wafer loaded into each holding opening, comprising successively the following: a first polishing step of performing a double-sided polishing, while a first polishing agent, which is an alkaline aqueous solution containing abrasive grains, is supplied to the polishing cloths; Following the first polishing step, a polishing agent change step is performed, in which the supply of the first polishing agent is stopped and the supply of a second polishing agent, which is an alkaline aqueous solution containing a water-soluble polymer without abrasive grains, wherein the polishing cloths of the upper plate and the lower plate are in contact with the front surface and the rear surface of the silicon wafer, respectively, and wherein the upper plate and the lower plate are continuously rotated; and a second polishing step of performing double-sided polishing, while the second polishing compound is supplied to the polishing cloths after the polishing compound change step. [2] Method for double-sided polishing of a silicon wafer according to claim 1, where, with reference to a surface pressure applied by the top plate and the bottom plate to the front surface and the rear surface of the silicon wafer, In the first polishing step, double-sided polishing is carried out with an initial surface pressure, and in a final stage of the first polishing step, the surface pressure is reduced to a second surface pressure that is lower than the initial surface pressure at the end of the first polishing step. The double-sided polishing is carried out with the second surface pressure in the second polishing step. [3] Method for double-sided polishing of a silicon wafer according to claim 2, wherein the second surface pressure is 5% to 40% lower than the first surface pressure. [4] Method for double-sided polishing of a silicon wafer according to any one of claims 1 to 3, wherein in the first polishing step double-sided polishing is carried out to obtain a polishing removal of 80% to 99.5% with respect to a total polishing removal of the first and second polishing steps, and In the second polishing step, double-sided polishing is carried out with a polishing removal of 0.05 µm to 0.5 µm on each surface. [5] Method for double-sided polishing of a silicon wafer according to any one of claims 1 to 4, wherein in the first polishing step the first polishing compound that was used is recovered and then delivered again to the polishing cloths, and In the second polishing step, the polishing compound that was used is recovered and then disposed of.

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