Method for double-sided polishing of wafers of semiconductor material - Patent Application 20070122997

Abstract

A method for double-sided polishing of at least one wafer of semiconductor material includes the steps of placing the at least one wafer of semiconductor material on at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-sided polisher, wherein the lower side of the upper polishing platen and the upper side of the lower polishing platen are each covered with a polishing pad, and the method further includes the steps of rotating the at least one carrier plate, the upper polishing platen, and the lower polishing platen; circulating a polishing agent between a collection container and the at least one wafer of semiconductor material disposed between the upper polishing platen and the lower polishing platen of the double-sided polisher; measuring a pH of the polishing agent; and adjusting the pH of the polishing agent, wherein the target value of the pH is 11.4 or more and 12.4 or less, and the pH is adjusted by temporarily supplying a basic composition to the polishing agent in accordance with the measured pH so that the deviation of the measured pH from the target value measured during the circulation of the polishing agent between the collection container and the at least one wafer of semiconductor material disposed between the upper polishing platen and the lower polishing platen of the double-sided polisher is ±0.2 or less at any time.

Description

[Technical Field]

[0001] Technical Field The present invention provides a method for double-sided polishing of at least one wafer of semiconductor material. [Background technology]

[0002] Background technology Wafers of semiconductor material are produced in a variety of manufacturing steps, including pulling a single crystal ingot from a melt, slicing the crystal into wafers, and surface processing of the wafers.

[0003] The goal of surface preparation is a highly flat (planar) wafer surface that is free of defects. Polishing is one of the surface preparation methods. Various methods for polishing wafers of semiconductor materials are known in the prior art. These methods include single-side polishing and double-side polishing, and double-side polishing is particularly important.

[0004] Double-side polishing (DSP) is a double-side polishing method in which the front and back surfaces of a wafer are polished simultaneously. To this end, wafers are transported on a carrier plate located within a working gap formed by the upper and lower polishing platens of a double-side polisher. Each of the polishing platens is lined with a polishing pad. A wafer of semiconductor material is disposed on the carrier plate between the polishing platens so that the front and back surfaces of the wafer are in sliding contact with the polishing pad. The polishing platens are rotated in opposite directions while an abrasive is supplied to simultaneously polish the front and back surfaces. In double-side polishing, multiple wafers are typically polished simultaneously.

[0005] In double-side polishing methods, the surface flatness is affected by the composition of the abrasive.For example, EP4039767A1 describes a method for improving the flatness at the wafer edge by using a polishing composition containing abrasive particles, a basic compound, and a phosphorus compound.WO2022 / 130800A1 describes the influence of the composition of the abrasive, particularly the concentration of the base and the concentration of the abrasive particles, on the removal rate during polishing and the geometric shape of the semiconductor wafer.

[0006] DE 112015005277 T5 describes the recovery and reprocessing of abrasive slurries, in which the recovered abrasive slurries are recycled for polishing without adding virgin abrasive particles. Summary of the Invention [Problem to be solved by the invention]

[0007] Technical Objectives of the Invention and Achievement of These Objectives It is an object of the present invention to provide a method for double-side polishing of semiconductor wafers that allows for reduced edge roll-off of wafers of semiconductor material and reduces consumption of abrasives. [Means for solving the problem]

[0008] This object is achieved by a method for double-side polishing of at least one wafer of semiconductor material, the method comprising: The method includes placing at least one wafer of semiconductor material on at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-sided polisher, wherein a lower side of the upper polishing platen and an upper side of the lower polishing platen are each covered with a polishing pad, and the method further includes: rotating at least one of the carrier plate, the upper polishing platen, and the lower polishing platen; circulating a polishing agent between a collection container and at least one wafer of semiconductor material disposed between an upper polishing platen and a lower polishing platen of a double sided polisher; Measuring the pH of the polishing agent; and adjusting the pH of the polishing agent. The target pH value is 11.4 or more and 12.4 or less, and the pH is adjusted by temporarily supplying a basic composition to the polishing agent in accordance with the measured pH so that the deviation of the measured pH from the target value measured while the polishing agent is circulating between the collection container and at least one wafer of semiconductor material disposed between the upper polishing platen and the lower polishing platen of the double-sided polishing machine is ±0.2 or less at any point in time.

[0009] It has been surprisingly found that the method of the present invention enables the production of wafers of semiconductor material that exhibit improved edge roll-off. Furthermore, it has been found that the method of the present invention can increase the removal rate during polishing and prevent pad glazing for a longer period of time, thereby increasing the overall efficiency and economics of the polishing operation.

[0010] Preferred embodiments of the method according to the invention are the subject of the dependent claims.Furthermore, the method according to the invention allows a reduction in consumption of abrasives. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagrammatic representation of an apparatus suitable for carrying out the method of the present invention; [Figure 2] FIG. 1 is a diagram showing the change in radial thickness of a single crystal silicon wafer polished according to the method described in Comparative Example 1. [Figure 3] FIG. 2 shows the radial thickness variation of a single crystal silicon wafer polished according to the method of the present invention as described in specific example 1. [Figure 4] FIG. 1 shows the pH profile over time. DETAILED DESCRIPTION OF THE INVENTION

[0012] Detailed Description of the Invention The apparatus of Figure 1 includes a double-sided polisher (1), a collection container (2) for the polishing agent, a meter (3) for determining pH, and a reservoir container (4) for a basic solution with a metering pump for adjusting the pH. In Figure 4, a first polishing run is performed during time interval a, and a second polishing run is performed during time interval b, each polishing run being performed according to the method of the present invention at a pH of 11.8, with the measured pH during polishing varying less than ±0.05 from the target value. The metering pump is then turned off for 10 minutes during the polishing run under otherwise identical process conditions during a third time interval c to adjust the pH, and a drop in pH is observed, with the spike in the pH profile occurring during the time interval being attributed to refreshing the polishing agent.

[0013] The method of the present invention for double-side polishing of at least one wafer of semiconductor material comprises: placing at least one wafer on at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-sided polisher, wherein a lower side of the upper polishing platen and an upper side of the lower polishing platen are each covered with a polishing pad; and the method further comprises: rotating at least one of the carrier plate, the upper polishing platen, and the lower polishing platen; circulating a polishing agent between a collection container and at least one wafer disposed between an upper polishing platen and a lower polishing platen of a double-sided polisher; Measuring the pH of the polishing agent; and adjusting the pH of the polishing agent. The target pH value is 11.4 or more and 12.4 or less, and the pH is adjusted by temporarily supplying a basic composition to the polishing agent in accordance with the measured pH so that the deviation of the measured pH from the target value measured while the polishing agent is circulating between the collection container and at least one wafer of semiconductor material disposed between the upper polishing platen and the lower polishing platen of the double-sided polishing machine is ±0.2 or less at any point in time.

[0014] In the method of the present invention, a specific target pH value for the polishing agent is specified, and the pH of the polishing agent is precisely adjusted within specified limits. Specifically, a target pH value for the polishing agent is specified within the range of 11.4 or more and 12.4 or less, with a deviation from the target value of no more than ±0.2, preferably no more than ±0.1, and most preferably no more than ±0.05. The maximum deviation from the specified target value is hereinafter referred to as the control range. By precisely adjusting the pH within this range, it is surprisingly possible to improve the edge roll-off of the polished wafer. Furthermore, by precisely adjusting the pH within this range, the polishing agent is stabilized. In particular, coagulation of the colloidal components, particularly the abrasive particles contained in the polishing agent, is prevented. Coagulation deteriorates the flatness and edge roll-off of the polished wafer, necessitating replacement of the polishing agent.

[0015] Thus, the method of the present invention firstly improves the flatness and edge roll-off of the polished wafer, and secondly extends the useful life of the abrasive, reducing abrasive consumption over time.

[0016] The method of the present invention is used for double-side polishing of at least one wafer of semiconductor material, preferably having a diameter of 150 to 450 mm, more preferably 200 to 300 mm, and most preferably 300 mm. The semiconductor material is preferably single-crystal silicon. The semiconductor material may also be optionally p-doped or n-doped. The crystal orientation of the front major surface of the single-crystal silicon wafer is preferably {100}, {110}, or {111}.

[0017] The method of the present invention for double-sided polishing of at least one wafer of semiconductor material can be carried out using a commercially available double-sided polishing machine of appropriate size. Such polishing machines are described, for example, in US Pat. No. 4,974,370, EP 787562 B1, or DE 10060697 B4. The polishing pressure (applied pressure) applied to the wafer of semiconductor material during polishing is preferably in the range of 0.05 to 0.5 bar. The polishing time is preferably 5 to 90 minutes, more preferably 10 to 60 minutes, and most preferably 15 to 45 minutes. The polishing time is usually determined by the pretreatment of the wafer. Therefore, for example, the polishing time can be shortened by performing a fine grinding step before the method of the present invention.

[0018] The double-sided polisher includes a horizontally rotatable lower polishing platen and a horizontally rotatable upper polishing platen, with the lower side of the upper polishing platen and the upper side of the lower polishing platen each covered with a polishing pad. A semiconductor wafer may be horizontally disposed in a polishing gap between the polishing platens and may contact or be in sliding contact with the polishing pad-covered polishing platen during polishing. The double-sided polisher includes a polishing platen drive device for rotating the platens. The drive device may be positioned so that the two polishing platens can rotate in the same direction or in opposite directions, preferably in opposite directions. The double-sided polisher further includes a device for continuously supplying and recovering a polishing agent to and from the semiconductor wafer disposed between the polishing platens, with the supply preferably occurring within the polishing gap.

[0019] At least one wafer of semiconductor material may be placed in at least one carrier plate horizontally disposed between the polishing platens. One carrier plate can typically accommodate one to five wafers. Preferably, three to five carrier plates are disposed between the polishing platens. The at least one carrier plate has a notch of sufficient size to accommodate at least one wafer of semiconductor material and is thinner than the wafer. During polishing, the wafer of semiconductor material can be appropriately guided by the carrier plate, i.e., held on a geometric path determined by machine and operating parameters. The at least one carrier plate can contact the polishing machine via a rack-and-pinion gearing or involute gearing via a rotating inner drive pin or gearing and a generally counter-rotating outer drive pin or gearing, thereby rotating the carrier plate between the two polishing platens.

[0020] In the method of the present invention, in a first step, at least one wafer of semiconductor material is placed on at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-sided polisher, and the lower side of the upper polishing platen and the upper side of the lower polishing platen are each covered with a polishing pad.

[0021] Thereafter, a polishing pressure (applied pressure) is applied to at least one wafer of semiconductor material by a polishing platen having a polishing pad. The polishing pressure (applied pressure) is preferably in the range of 0.05 to 0.5 bar, and the magnitude of the polishing pressure may be varied, preferably stepwise or continuously, during the polishing method.

[0022] Thereafter, in a next step, the carrier plate, upper polishing platen, and lower polishing platen are rotated, where the upper and lower polishing platens may rotate in the same or opposite directions, preferably in opposite directions. The carrier plate preferably has circumferential gearing and is rotated by complementary external and internal gearing of the polishing machine.

[0023] In yet another step, preferably performed while the carrier plate, upper polishing platen, and lower polishing platen rotate about a common vertical axis, the polishing agent is circulated between a collection container and at least one wafer of semiconductor material disposed between the upper and lower polishing platens of the double-sided polisher. Here, the polishing agent may be guided to the at least one wafer of semiconductor material through a polishing gap. The polishing gap in the sense of the present invention is the space between the lower side of the upper polishing platen and the upper side of the lower polishing platen, each of which is covered with a polishing pad. Thus, the polishing gap is bounded on one side by the lower surface of the polishing pad on the upper polishing platen, and on the other side by the upper surface of the polishing pad on the lower polishing platen.

[0024] During circulation, the abrasive is guided from the collection container (2) to at least one wafer of semiconductor material disposed between the upper and lower polishing platens of the double-sided polisher (1) and then returned from the wafer to the collection container (2). Such circulation of the abrasive between the collection container (2) and the double-sided polisher (1) is shown in FIG. 1. The abrasive can access the wafer of semiconductor material, for example, by a combination of gravity and centrifugal force induced by rotation, or by applying pressure to multiple supply lines. The abrasive can be supplied, for example, through multiple bores, with or without nozzles in the upper polishing platen. The upper polishing platen preferably includes multiple bores to ensure uniform distribution of the abrasive between the polishing pads; the number of bores essentially depends on the size of the polisher. A shutoff device with a drainage duct disposed below the lower polishing platen allows the abrasive to return to the collection container. The configuration of this blocking device with a drain duct may be such that the abrasive flowing over the edge of the lower polishing platen is blocked by the blocking device and then conveyed back into the collection container via the drain duct. The collection container may be connected to the bore in the upper polishing platen and the drain duct via a hose. Circulation may be driven by a pump. The circulation rate, which is the flow rate of the abrasive in the polishing circuit, is preferably in the range of 0.5 to 50 liters per minute, more preferably 2 to 20 liters per minute, and most preferably 3 to 10 liters per minute. The abrasive may also be temporarily conveyed through the double-sided polisher via a bypass to avoid the need to interrupt the abrasive circulation during wafer exchange or an additional final polishing step with a different abrasive.

[0025] The above-mentioned steps of (i) placing at least one semiconductor wafer on at least one carrier plate between an upper polishing platen and a lower polishing platen covered with a polishing pad, (ii) rotating the at least one carrier plate, the upper polishing platen, and the lower polishing platen, and (iii) circulating an abrasive between a collection container and at least one wafer disposed between the upper polishing platen and the lower polishing platen of a double-sided polisher are preferably performed in this order. In this case, the rotational movement generates a uniform distribution of the abrasive on the polishing pad and on the front and back sides of the semiconductor wafer. The more uniform distribution of the abrasive results in a more uniform application of material, improving the flatness of the semiconductor wafer and reducing edge roll-off. A polishing pressure is applied to the at least one semiconductor wafer by the polishing platen covered with a polishing pad.

[0026] The abrasive used in the method of the present invention may contain abrasive particles, preferably colloidal silicon dioxide particles. The abrasive preferably comprises abrasive particles and one or more compounds selected from the group consisting of surface-active additives, preservatives, biocides, alcohols, and complexing agents. The abrasive used in the method of the present invention is preferably a dispersion or slurry having a solids content of 0.1% to 10.0% by weight, preferably 0.3% to 5.0% by weight, and more preferably 0.5% to 2.0% by weight. In a particularly preferred embodiment, the abrasive is a dispersion containing silicon dioxide particles as a colloidal solid. The specific gravity of the abrasive is preferably 1.0 to 1.2, more preferably 1.02 to 1.10. The average particle size of the colloidal silicon dioxide particles is preferably 10 to 200 nm, more preferably 20 to 100 nm, and most preferably 40 to 80 nm.

[0027] The method of the present invention preferably uses a polishing pad having a hardness (Shore A hardness) of 40 to 100, more preferably 70 to 95, and most preferably 80 to 95. Using a polishing pad with a hardness of 80 to 95 can further improve edge roll-off. Shore hardness can be determined according to the standard DIN ISO 7619-1. The polishing pad used in the method of the present invention is preferably a so-called "foam pad." However, the present invention is not limited to such pads, and other polishing pads can also be used to achieve the objectives of the present invention.

[0028] Edge roll-off of semiconductor wafers, more particularly single-crystal silicon wafers, can be improved when the target pH value of the polishing agent is 11.4 or higher and 12.4 or lower, without exceeding a control range of ±0.2. In this way, pad glazing over multiple polishing procedures can be further prevented. Edge roll-off can be particularly significantly improved when the pH of the polishing agent is 11.5 or higher and 12.3 or lower, preferably 11.5 or higher and 12.0 or lower, more preferably 11.7 or higher and 11.9 or lower, and the deviation of the pH measured during circulation of the polishing agent between the collection container and at least one wafer of semiconductor material disposed between the upper and lower polishing platens of a double-sided polisher is ±0.2 or lower at any time. In a particularly preferred embodiment, the target pH value is 11.7 or higher and 11.9 or lower, and the control range, i.e., the deviation from the target value, is within ±0.1. When the target value is within this range and only a deviation of ±0.1 from the target value is allowed, a particularly significant improvement in edge roll-off is observed. Edge roll-off can be further reduced if the method of the present invention allows for a deviation from the target pH of only ±0.05.

[0029] The target value of the pH of the polishing agent and the maximum deviation from the target value (control range) are based on the pH at a specified point in the polishing circuit. The target value of the pH of the polishing agent and the maximum deviation from the target value are preferably based on the pH in the collection container. Therefore, in the method of the present invention, the pH of the polishing agent is preferably measured in the collection container. The collection container in the sense of the present invention is a container in the polishing circuit, through which the polishing agent is guided to at least one wafer of semiconductor material from the polishing circuit, preferably through the polishing gap, during the polishing operation, and through which the polishing agent is returned from the at least one wafer of semiconductor material to the polishing circuit. The collection container preferably comprises or is connected to a measuring device for pH measurement, more preferably a pH electrode.

[0030] If the pH is not adjusted during double-sided polishing, a continuous decrease in pH is observed during the polishing procedure (polishing run). Even interrupting pH adjustment for just 10 minutes during polishing results in a pH decrease of 0.3. Thus, Figure 4 shows that interrupting pH adjustment for 10 minutes during a polishing run at time interval c causes the pH to decrease from 11.8 to approximately 11.5.

[0031] The pH is adjusted by temporarily supplying a basic composition to the polishing agent. The basic composition is supplied so that the deviation of the pH measured during the circulation of the polishing agent between the collection container and at least one wafer of semiconductor material disposed between the upper and lower polishing platens of the double-sided polishing machine from the target value is ±0.2 at any time, preferably ±0.1 at any time, and most preferably ±0.05 at any time. By measuring the pH more frequently, changes in pH, especially continuous decreases in pH, can be counteracted more quickly and efficiently by supplying the basic composition, thereby reducing deviation from the target value. Furthermore, by regularly calibrating the pH meter, preferably the pH electrode, the accuracy of the pH measurement can be improved, thereby reducing the control range (deviation from the target pH value).

[0032] The basic composition is preferably a basic solution, and more preferably a basic solution containing at least one compound selected from sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, ammonium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide.

[0033] The pH can be adjusted by temporarily supplying a basic composition, preferably a basic solution, to the collection container. In one embodiment of the method of the present invention, the collection container is connected to a reservoir container containing the basic composition. In this embodiment, the pH is adjusted by temporarily supplying the basic composition, preferably a basic solution, from the reservoir container to the collection container via a pump or valve. The pH electrode may be connected to a control unit that drives the valve or metering pump to supply the basic composition. Thus, depending on the pH, the basic composition can be temporarily supplied to the collection container to adjust the pH. The more frequently the pH measurement and the pH adjustment associated with this measurement are performed, the narrower the control range and therefore the smaller the deviation from the target value.

[0034] The pH is preferably measured continuously or at regular time intervals of 0.01 to 60 seconds, more preferably at regular time intervals of 0.1 to 10 seconds. The pH is also preferably adjusted at regular time intervals, preferably at the same time intervals as the pH is measured. Measurements can be performed using a Knick SE554X / 2-NMSN pH electrode. The electrode is preferably calibrated periodically, more preferably at least monthly, using multiple calibration solutions with defined pHs ranging from 7 to 12.

[0035] The pH is adjusted in each case depending on the measured pH. In a particularly preferred embodiment of the method of the present invention, adjusting the pH in the collection container comprises the steps of (i) supplying a basic solution as soon as the pH in the collection container falls below a specified lower limit, and (ii) interrupting or terminating the supply of the basic solution as soon as the pH in the collection container exceeds a specified upper limit, the deviation of the lower and upper limits from the target values ​​being no more than ±0.2. The deviation of the specified lower and upper limits from the target values ​​is preferably no more than ±0.1, more preferably no more than ±0.05. The supply and interruption or termination of the supply of the basic solution can be achieved, for example, by switching the pump on and off, correspondingly driving a metering pump, or by opening or closing a valve, preferably driven by a control unit connected to a pH electrode. The basic solution is preferably supplied from a reservoir container with a metering pump, which reservoir container is connected to the collection container via a conduit.

[0036] In another embodiment of the method of the present invention, the pH can be adjusted by adding a specified amount of basic solution from the reservoir container to the collection container at varying time intervals, the lower the measured pH, the shorter the time interval between adding the specified amount of basic solution.

[0037] After polishing of at least one wafer of semiconductor material is completed, one or more additional polishing procedures can be performed on at least one replaced, unpolished wafer. Wafers are exchanged by removing the previously polished wafer and inserting the corresponding unpolished wafer into at least one carrier plate disposed between the upper and lower polishing platens of the double-sided polisher. Following the insertion of the at least one new unpolished wafer, a new polishing procedure begins. Thus, wafers are exchanged during a polishing procedure, also referred to as a polishing run. After polishing of at least one wafer (polishing procedure) is completed but before the start of a new polishing procedure on the at least one replaced, unpolished wafer, the polishing agent may be circulated through a bypass, so that the polishing agent is temporarily not circulated through the double-sided polisher. Therefore, during the exchange of at least one wafer, the polishing agent is not circulated through the double-sided polisher. During the exchange of at least one wafer, the polishing agent can be refreshed by replacing 1% to 30% by volume of the polishing agent with new polishing agent, followed by adjusting the pH to a target value by adding a basic composition. Between different polishing runs, preferably 2% to 20% by volume, more preferably 4% to 10% by volume, and very preferably 4% to 5% by volume of the polishing agent is replaced with new polishing agent, followed by adjusting the pH to the target value by adding a basic solution.

[0038] Surprisingly, it has been observed that the improved edge geometry obtained by the method of the present invention is achieved over multiple successive polishing procedures (polishing runs), e.g., more than 10 polishing runs, even when only 1% to 30% by volume of the polishing agent in the collection container is replaced with new polishing agent between polishing runs, and the pH is then adjusted to a target value by the addition of a basic composition.

[0039] The method of the invention therefore makes it possible, on the one hand, to improve the edge geometry, i.e. the edge roll-off, of wafers of semiconductor material, more particularly wafers of monocrystalline silicon, and, on the other hand, to increase the economy and efficiency of the polishing operation by reducing the consumption of abrasives.

[0040] Optionally, in the method of the present invention, a final polishing step may be performed in the double-sided polisher by (i) switching the circulation of the polishing agent (first polishing agent) to a bypass and interrupting the supply of the circulated polishing agent to the polisher, and (ii) subsequently flowing a final polishing agent (second polishing agent) that is not circulated during the final polishing step onto at least one wafer of semiconductor material disposed between the upper and lower polishing platens of the double-sided polisher. During the final polishing step, the rotation of the polishing platen and the carrier plate continues. The final polishing step is shorter than the preceding polishing step performed with the circulation of the first polishing agent.

[0041] After the at least one wafer of semiconductor material is removed from the double-sided polisher, it may optionally undergo final polishing, such as chemical-mechanical polishing (CMP), and / or final cleaning. The final cleaning is typically a wet chemical cleaning operation in multiple baths at temperatures between 30°C and 90°C. In one bath, ammonium hydroxide, hydrogen peroxide, and deionized water are used, for example, in a ratio of 1:1:5 to 1:2:7. In yet another bath, hydrochloric acid, hydrogen peroxide, and deionized water are used, for example, in a ratio of 1:1:6 to 1:2:8. Furthermore, after the final cleaning, the at least one wafer of semiconductor material may be subjected to an epitaxial coating.

[0042] In the sense of the present invention, edge roll-off is edge roll-off measured as ROA, ESFQR or ZDD. Edge roll-off preferably refers to ESFQRmax or ZDD. ZDD and ESFQR are parameters that characterize the edge geometry of a semiconductor wafer and are related to SEMI standards. For example, standard SEMI M68-1015 relates to ZDD, and standard SEMI M67-1015 relates to ESFQR.

[0043] The front-side-based ZDD describes the mean near-edge curvature of the front-side surface of a wafer of semiconductor material. More specifically, the ZDD represents the second derivative of the perpendicular height from the wafer midplane to the front-side surface. The ZDD is preferably determined with the wafer surface divided into 16 sectors and an edge exclusion of 1 mm.

[0044] ESFQRmax denotes the ESFQR of the sector where ESFQR is maximum. ESFQRmax is preferably determined by dividing the surface of the wafer edge into 72 sectors, each 35 mm long with an edge exclusion of 1 mm.

[0045] Detailed Description of Specific Examples and Comparative Examples of the Present Invention In specific Example 1, 300 mm diameter wafers of {100} oriented single crystal silicon were polished according to the method of the present invention on a commercial double sided polisher, Lapmaster Wolters Model AC2000, using Nitta DuPont Type Exterion SM-11D foam polishing pads.

[0046] During the polishing operation, Fujimi's Glanzox 7100 abrasive was used and circulated between a collection container and a wafer placed between the upper and lower polishing platens (polishing gap) of a double-sided polisher. The abrasive contained colloidal silicon dioxide. A target pH value of 11.8 was specified for the abrasive in the collection container. The pH in the collection container was adjusted by adding potassium hydroxide solution from a reservoir container to the collection container using a metering pump so that the deviation from the target pH was less than ±0.05. The pH was continuously measured using a pH electrode in the collection container. The pH electrode was connected to a control unit used to drive the pump, so that the potassium hydroxide solution was temporarily supplied by the pump's operation according to the pH. This was followed by a final polishing step. For this step, the supply of Glanzox 7100 abrasive to the polisher was first interrupted, and the abrasive was circulated through a bypass, guiding the abrasive through the polisher. Next, a second polishing agent for final polishing was flowed onto the wafer, which was placed between the upper and lower polishing platens of the double-sided polisher, and polishing was carried out for less than 5 minutes.

[0047] After the polishing process was completed, the polished wafer was taken out. After that, one polished wafer was randomly inspected and the front side ZDD was -5nm / mm. 2 and the ESFQRmax was found to be 25 nm. Furthermore, no pad glazing was observed.

[0048] In Comparative Example 1, single crystal silicon wafers with a diameter of 300 mm, {100} orientation, and specifications identical to those of Specific Example 1 were polished on a commercial double-sided polisher under the same process conditions as those used in Specific Example 1, except that the designated pH target value was a pH of 11.0. Randomly selected polished wafers had a front-side ZDD of -12 nm / mm. 2 and the ESFQRmax was found to be 45 nm.

[0049] In Specific Example 1 and Comparative Example 1, ZDD was determined by dividing the wafer surface into 16 sectors with a 1 mm edge exclusion. In Specific Example 1 and Comparative Example 1, ESFQRmax was determined by dividing the wafer edge into 72 sectors, each 35 mm long and with a 1 mm edge exclusion. Figures 2 and 3 show the thickness variation of polished wafers in the radial direction. Figure 2 shows the thickness variation of a wafer polished according to Comparative Example 1. Figure 3 shows the thickness variation of a wafer polished according to Specific Example 1. A comparison of Figures 2 and 3 shows that the edge roll-off of wafers polished according to the method of the present invention is relatively low (see the circled areas on the right edge of Figures 2 and 3).

[0050] Comparing specific Example 1 with Comparative Example 1, it can be seen that when the target pH value is in the range of 11.4 to 12.4 and the fluctuation range is small, that is, when the deviation from the target value is small, the edge roll-off is reduced.

[0051] Furthermore, multiple double-side polishing methods according to specific Example 1 were carried out in succession, with the polished wafer being replaced with a new unpolished wafer between each polishing method. During the replacement of the polished wafer with an unpolished wafer, the polishing agent was circulated through a bypass to refresh the polishing agent. Refreshment was achieved by draining 5% by volume of the polishing agent in the circulation circuit, adding 5% by volume of new polishing agent, and then adjusting the desired pH by supplying potassium hydroxide solution. It was shown that replacing only 5% by volume of the polishing agent was sufficient to improve the edge geometry measured as ZDD and ESFQRmax in subsequent polishing runs, and generally sufficient to refresh the polishing agent.

[0052] Furthermore, in another comparative example, the pH adjustment was interrupted during polishing by switching off the metering pump for 10 minutes during the polishing run, meaning that no potassium hydroxide solution was supplied. When the pH adjustment during the polishing run was interrupted for 10 minutes, the polishing pH dropped from the initial 11.8 to 11.5 (see time interval c in Figure 4).

Claims

1. 1. A method for double-sided polishing of at least one wafer of semiconductor material, comprising: The method comprises the step of placing at least one wafer of the semiconductor material on at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-sided polisher (1), wherein the lower side of the upper polishing platen and the upper side of the lower polishing platen are each covered with a polishing pad, and the method further comprises: rotating the at least one carrier plate, the upper polishing platen, and the lower polishing platen; circulating a polishing agent between a collection container (2) and at least one wafer of the semiconductor material disposed between the upper polishing platen and the lower polishing platen of the double-sided polisher (1); measuring the pH of the polishing agent continuously or at regular time intervals having a duration of 0.01 to 10 seconds; adjusting the pH of the polishing agent; The method is characterized in that the target value of the pH is 11.4 or more and 12.4 or less, and the pH is adjusted by temporarily supplying a basic composition to the polishing agent in accordance with the measured pH so that the deviation of the measured pH from the target value measured while the polishing agent is circulating between the collection container and at least one wafer of the semiconductor material disposed between the upper polishing platen and the lower polishing platen of the double-sided polishing machine does not exceed ±0.2 at any point in time.

2. 2. A method for double-side polishing of at least one wafer of semiconductor material according to claim 1, characterized in that the target value of pH is greater than or equal to 11.5 and less than or equal to 12.

3.

3. 3. A method for double-side polishing of at least one wafer of semiconductor material according to claim 1 or 2, characterized in that the target value of pH is ≧11.7 and ≦11.

9.

4. The pH of the polishing agent is measured in the collection vessel (2); 4. The method for double-sided polishing of at least one wafer of semiconductor material according to claim 1, wherein the pH is adjusted by temporary supply of a basic composition to the collection vessel (2).

5. 5. The method for double-side polishing of at least one wafer of semiconductor material according to claim 1, wherein the basic composition is a basic solution comprising at least one compound selected from sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, ammonium hydroxide, tetramethylammonium hydroxide and tetraethylammonium hydroxide.

6. The collection vessel (2) is connected to a reservoir vessel (4) containing the basic composition; 6. The method for double-side polishing of at least one wafer of semiconductor material according to claim 1, wherein the pH is adjusted by temporarily supplying the basic composition from the reservoir vessel (4) to the collection vessel (2) by means of a pump or a valve.

7. 7. The method for double-sided polishing of at least one wafer of semiconductor material according to claim 1, wherein the pH measured during circulation of the polishing agent between the collection container and the at least one wafer of semiconductor material disposed between the upper polishing platen and the lower polishing platen of the double-sided polishing machine deviates from the target value by no more than ±0.1 at any one time, preferably no more than ±0.

05.

8. The adjustment of the pH in the collection vessel (2) is dispensing said basic composition as soon as said pH measured in said collection vessel (2) falls below a specified lower limit; and interrupting the supply of the basic composition as soon as the pH measured in the collection vessel (2) exceeds a specified upper limit value, 8. The method for double-side polishing of at least one wafer of semiconductor material according to claim 1, wherein the specified lower limit and the specified upper limit deviate from the target value of pH by no more than ±0.2, and the basic composition is a solution.

9. 9. The method for double-sided polishing of at least one wafer of semiconductor material according to claim 8, characterized in that the specified lower limit value and the specified upper limit value deviate from the target value of pH by no more than ±0.1, preferably no more than ±0.

05.

10. 10. The method for double-sided polishing of at least one wafer of semiconductor material according to any one of claims 1 to 9, characterized in that the pH is adjusted by adding a specified amount of basic solution from the reservoir vessel (4) to the collection vessel (2) at variable time intervals, the length of each of the variable time intervals being determined by the measured pH.

11. 11. The method for double-side polishing of at least one wafer of semiconductor material according to claim 1, wherein the abrasive is a dispersion comprising abrasive particles and one or more compounds selected from the group consisting of surface-active additives, preservatives, biocides, alcohols and complexing agents, the dispersion having a solids content of 0.1% to 10.0% by weight, preferably 0.3% to 5.0% by weight, more preferably 0.5% to 2.0% by weight.

12. 12. The method for double-sided polishing of at least one wafer of semiconductor material according to claim 1, wherein after the polishing of the at least one wafer of semiconductor material is completed and before the start of polishing of the at least one replaced unpolished wafer of semiconductor material, the abrasive is no longer circulated by the double-sided polisher, and the abrasive is refreshed by replacing 1% to 30% by volume of the abrasive in the collection container (2) with new abrasive, without being circulated by the double-sided polisher, and subsequently adjusting the pH to the target value by adding the basic composition.

13. 13. The method for double-side polishing of at least one wafer of semiconductor material according to claim 12, characterized in that the abrasive is refreshed by replacing 2% to 8% by volume of the abrasive in the collection container (2) with fresh abrasive, followed by adjusting the pH to the target value by adding the basic solution.

14. 14. Method for double-sided polishing of at least one wafer of semiconductor material according to any one of claims 1 to 13, characterized in that it further comprises a final polishing step and / or a final cleaning step of the at least one wafer of semiconductor material.

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