Method for double-sided polishing of wafers made of semiconductor material

Abstract

The invention relates to a method for double-sided polishing of at least one wafer made of semiconductor material, comprising the following steps: placing the at least one wafer made of semiconductor material in at least one carrier plate between an upper polishing plate and a lower polishing plate of a double-sided polishing machine, the lower side of the upper polishing disk and the upper side of the lower polishing disk are respectively covered with polishing cloth; rotating the at least one carrier disk, the upper polishing disk, and the lower polishing disk; circulating a polishing agent between a collection container and the at least one wafer made of semiconductor material disposed between the upper polishing disk and the lower polishing disk of the double-sided polishing machine; measuring the pH value of the polishing agent; controlling the pH value of the polishing agent; the method is characterized in that the target value of the pH value is not less than 11.4 and not more than 12.4, and the pH value is controlled by temporarily adding an alkaline component to the polishing agent according to the measured pH value, the pH value is measured such that during circulation of the polishing agent between the collection container and the at least one wafer made of semiconductor material disposed between the upper and lower polishing disks of the double-sided polishing machine, the deviation of the measured pH value from the target value of the pH value is from no more than + / -0.2.

Description

Technical Field

[0001] The invention provides a method for double-side polishing of at least one wafer made of semiconductor material. Background Art

[0002] Wafers made of semiconductor material (ie, semiconductor material wafers) are produced in a number of process steps including pulling a single crystal ingot from a melt, sawing the crystal into wafers, and surface treatment of the wafers.

[0003] The goal of surface treatment is to achieve a defect-free, highly flat (planar) wafer surface. Polishing is one of the surface treatment methods. Various methods for polishing wafers made of semiconductor materials are known in the prior art. These include single-sided and double-sided polishing methods, with double-sided polishing being particularly important.

[0004] Double-sided polishing (DSP) is a double-sided polishing method in which the front side (or front side) and the back side (or back side) of the wafer are polished simultaneously. To this end, the wafer is carried in a carrier plate (or carrier disc) which is located in the working gap formed by the upper polishing platen (or upper polishing disc) and the lower polishing platen (or lower polishing disc) of the double-sided polishing machine. Each polishing platen is lined with a polishing pad. The wafer made of semiconductor material is arranged in the carrier plate between the polishing platens so that the front and back sides of the wafer are in sliding contact with the polishing pads. While providing polishing, the polishing platens are set to rotate in opposite directions so that the front and back sides are polished simultaneously. In the case of double-sided polishing, multiple wafers are usually polished simultaneously.

[0005] In double-sided polishing, surface flatness is influenced by the composition of the polishing agent. For example, EP 4 039 767 A1 describes how to improve wafer edge flatness by using a polishing agent composition comprising abrasive particles, an alkaline compound, and a phosphorus compound. WO 2022 / 130800 A1 describes the influence of polishing agent composition, particularly the concentration of base and abrasive particles, on the removal rate during polishing and the geometry of semiconductor wafers.

[0006] DE 11 2015 005 277 T5 describes the recovery and reprocessing of polishing slurry, wherein the recovered polishing slurry is recycled without adding unused abrasive particles for polishing. Summary of the Invention

[0007] The object of the present invention is to provide a method for double-side polishing of semiconductor wafers which allows reducing edge roll-off of wafers made of semiconductor material and also reducing the consumption of polishing agent.

[0008] This object is achieved by a method according to the invention for double-side polishing of at least one wafer made of semiconductor material, comprising the following steps:

[0009] placing the at least one wafer made of semiconductor material in at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-side polishing machine, the lower side of the upper polishing platen and the upper side of the lower polishing platen each being covered with a polishing pad;

[0010] rotating the at least one carrier plate, the upper polishing platen, and the lower polishing platen;

[0011] circulating a polishing agent between a collecting container and the at least one wafer made of semiconductor material disposed between an upper polishing platen and a lower polishing platen of the double-side polishing machine;

[0012] measuring the pH of the polishing agent; and

[0013] regulating the pH of the polishing agent;

[0014] It is characterized in that the target pH (or target value) is not less than 11.4 and not more than 12.4, and the pH is controlled by temporarily supplying an alkaline component to the polishing agent as a function of the measured pH (or according to the measured pH), so that during the circulation of the polishing agent between the collection container and the at least one wafer made of semiconductor material arranged between the upper polishing platen and the lower polishing platen of the double-side polishing machine, the deviation of the measured pH from the target pH does not exceed ±0.2 at any instant (i.e., never exceeds ±0.2).

[0015] Surprisingly, it has been found that the method of the present invention allows the production of wafers made of semiconductor material that exhibit improved edge roll-off. Furthermore, it has been found that, by means of the method of the present invention, it is possible to increase the removal rate during polishing and prevent the polishing pad from grinding (or calendering) for a longer period of time, thereby achieving an overall improvement in the efficiency and economy of the polishing operation.

[0016] Preferred embodiments of the method according to the invention are the subject matter of the dependent claims. Furthermore, the method according to the invention makes it possible to reduce the consumption of polishing agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A device suitable for carrying out the method of the present invention is schematically shown. The device comprises a double-sided polishing machine (1), a collection container (2) for the polishing agent, a meter (3) for determining the pH, and a storage container for the alkaline solution with a metering pump (4) for regulating the pH.

[0018] Figure 2The radial thickness variation of a single crystal silicon wafer polished according to the method described in Comparative Example 1 is shown.

[0019] Figure 3 The radial thickness variation of a single crystal silicon wafer polished according to the method of the present invention as described in Working Example 1 is shown.

[0020] Figure 4 A pH curve over time is shown, wherein a first polishing pass is performed during time period (or time interval) a and a second polishing pass is performed during time period b. Each of the first and second polishing passes is performed according to the method of the present invention at a pH of 11.8, and the pH measured during polishing does not deviate from the target by more than ±0.05. Subsequently, during the polishing pass, under otherwise identical process conditions, the metering pump is shut off for 10 minutes during a third time period c to control the pH, and a decrease in pH is observed. The peaks in the pH curve that occur between the time periods are attributed to the renewal of the polishing agent. DETAILED DESCRIPTION

[0021] The method of the invention for double-side polishing of at least one wafer made of semiconductor material comprises the following steps:

[0022] placing the at least one wafer in at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-side polisher, the lower side of the upper polishing platen and the upper side of the lower polishing platen each being covered with a polishing pad;

[0023] rotating the at least one carrier plate, the upper polishing platen, and the lower polishing platen;

[0024] circulate a polishing agent between a collection container and the at least one wafer disposed between an upper polishing platen and a lower polishing platen of the double-side polisher;

[0025] measuring the pH of the polishing agent; and

[0026] regulating the pH of the polishing agent;

[0027] It is characterized in that the target pH is not less than 11.4 and not more than 12.4, and the pH is controlled by temporarily supplying an alkaline component to the polishing agent as a function of the measured pH, so that during the circulation of the polishing agent between the collection container and the at least one wafer made of semiconductor material arranged between the upper polishing platen and the lower polishing platen of the double-side polishing machine, the deviation of the measured pH from the target pH does not exceed ±0.2 at any instant.

[0028] In the method of the present invention, a defined target pH of the polishing agent is specified, and the pH of the polishing agent is strictly regulated within the defined limits (or limit values). In particular, a target pH of the polishing agent is specified in the range of not less than 11.4 and not more than 12.4, with a deviation from the target of not more than ±0.2, preferably ±0.1, and most preferably not more than ±0.05. The maximum deviation from the specified target is also referred to below as the control range. Surprisingly, strict regulation of the pH within this range makes it possible to improve the edge roll-off of the polished wafer. In addition, strict regulation of the pH within this range stabilizes the polishing agent. In particular, coagulation of colloidal components, especially abrasive particles contained in the polishing agent, is prevented. Coagulation leads to a deterioration of the flatness and edge roll-off of the polished wafer, and therefore requires replacement of the polishing agent.

[0029] Therefore, the method of the present invention firstly improves the flatness and edge roll-off of the polished wafer, and secondly increases the service life of the polishing agent, thereby reducing the consumption of the polishing agent over time.

[0030] The method of the present invention is preferably applied to double-side polishing of at least one wafer made of semiconductor material 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-crystalline silicon. The semiconductor material may optionally be p-doped or n-doped. The crystal orientation of the main surface of the single-crystalline silicon wafer is preferably {100}, {110}, or {111}.

[0031] The method for double-sided polishing of at least one wafer made of semiconductor material of the present invention can be performed using a commercial double-sided polishing machine with appropriate size. Such a polishing machine is described, for example, in US 4,974,370, EP 787 562B1 or DE 100 60697B4. The polishing pressure (applied pressure) applied to the wafer made 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, most preferably 15 to 45 minutes. The polishing time generally depends on the pre-treatment of the wafer. Therefore, the polishing time can be reduced, for example, by implementing a fine grinding step before the method of the present invention.

[0032] The double-sided polishing machine includes a lower polishing platen that can rotate freely horizontally and an upper polishing platen that can rotate freely horizontally, 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. A wafer made of semiconductor material can be arranged horizontally in a polishing gap between the polishing platens and can contact or slide in contact with the polishing platen covered with the polishing pad during polishing. The double-sided polishing machine includes a polishing platen drive for rotating the platens. The drive can be aligned so that the two polishing platens can be set to rotate in the same direction or in opposite directions, preferably in opposite directions. The double-sided polishing machine also includes a device for continuously supplying polishing agent to the wafer made of semiconductor material arranged between the polishing platens and continuously discharging polishing agent from the wafer made of semiconductor material arranged between the polishing platens, wherein the supply preferably occurs in the polishing gap.

[0033] The at least one wafer made of semiconductor material can be located in at least one carrier plate arranged horizontally between the polishing platens. One carrier plate can typically accommodate 1 to 5 wafers. 3 to 5 carrier plates are preferably arranged between the polishing platens. The at least one carrier plate has a cutout sized to accommodate the at least one wafer made of semiconductor material and has a thickness smaller than the wafer. During polishing, the wafer made of semiconductor material can be guided accordingly by the carrier plate, i.e., kept on a geometric path determined by the machine parameters and operating parameters. The at least one carrier plate can be in contact with the polishing machine via a rotating internal drive pin or gear ring and a generally counter-rotating external drive pin or gear ring using a rack-and-pinion gear mechanism or an involute gear mechanism (which causes the carrier plate to perform a rotational movement between the two polishing platens).

[0034] In the method of the present invention, in a first step, at least one wafer made of semiconductor material is placed in at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-side polishing machine, 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.

[0035] A polishing pressure (applied pressure) is then applied to the at least one semiconductor material wafer via a polishing platen with 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 can be varied during the polishing process, preferably stepwise or continuously.

[0036] In the next step, the carrier plate, the upper polishing platen, and the lower polishing platen are then rotated. The upper polishing platen and the lower polishing platen can rotate in the same direction or in opposite directions, preferably in opposite directions. The carrier plate preferably has a peripheral transmission (or gearing) and is rotated by complementary external and internal transmissions of the polishing machine.

[0037] In a further step, which preferably occurs while the carrier plate, the upper polishing platen, and the lower polishing platen are rotating about a common vertical axis, a polishing slurry circulates between a collecting container and at least one wafer made of semiconductor material disposed between the upper polishing platen and the lower polishing platen of the double-side polishing machine. The polishing slurry can be directed to the at least one wafer made of semiconductor material via a polishing gap. Within the meaning of the present invention, the polishing gap is the space between the underside 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 delimited on one side by the surface of the underside of the polishing pad on the upper polishing platen and on the other side by the surface of the upper side of the polishing pad on the lower polishing platen.

[0038] During circulation, the polishing agent is directed from the collecting container (2) to at least one wafer made of semiconductor material arranged between an upper polishing platen and a lower polishing platen of the double-side polishing machine (1), and from the wafer back to the collecting container (2). This circulation of the polishing agent between the collecting container (2) and the double-side polishing machine (1) is as follows: Figure 1 As shown. The polishing agent can reach the wafer made of semiconductor material, for example, by a combination of gravity and centrifugal force caused by rotation, or by applying pressure in multiple supply lines. For example, the polishing agent can be supplied via multiple openings with or without nozzles in the upper polishing platen. The upper polishing platen preferably includes multiple openings to achieve a uniform distribution of the polishing agent between the polishing pads, wherein the number of openings depends essentially on the size of the polishing machine. The return of the polishing agent to the collection container can be achieved by an interception device with a discharge pipe arranged below the lower polishing platen. The configuration of this interception device with a discharge pipe can be such that the polishing agent traveling over the edge of the lower polishing platen is intercepted by the interception device and returned to the collection container via the discharge pipe. The collection container can be connected to the openings in the upper polishing platen and to the discharge pipe via a hose. The circulation can be driven by a pump. The circulation rate, which is the flow rate of the polishing agent in the polishing circuit, is preferably in the range of 0.5 to 50 liters / minute, more preferably 2 to 20 liters / minute, and very preferably 3 to 10 liters / minute. The polishing agent can also be temporarily conveyed through the double-side polisher via a bypass, so that the circulation of the polishing agent does not need to be interrupted during wafer changes or during an additional step of final polishing with a different polishing agent.

[0039] The steps described above are preferably performed in the following order: (i) placing at least one semiconductor material wafer in 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 a polishing agent between a collecting container and the at least one wafer disposed between the upper polishing platen and the lower polishing platen of the double-side polisher. In this case, the rotational movement produces a uniform distribution of the polishing agent on the polishing pad and on the front and back sides of the semiconductor material wafer. The more uniform distribution of the polishing agent achieves a more uniform material application and, therefore, an improved flatness and reduced edge roll-off of the semiconductor material wafer. Polishing pressure is applied to the at least one semiconductor material wafer by the polishing platen covered with the polishing pad.

[0040] The polishing agent used in the method of the present invention may contain abrasive particles, preferably colloidal silica particles. The polishing agent preferably comprises abrasive particles and one or more compounds selected from the group consisting of a surfactant additive, a preservative, a biocide, an ethanol, and a complexing agent. The polishing agent used in the method of the present invention is preferably a dispersion or slurry having a solid 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 polishing agent is a dispersion comprising silica particles as colloidal solids. The specific density of the polishing agent is preferably 1.0 to 1.2, more preferably 1.02 to 1.10. The average particle size (or particle size) of the colloidal silica particles is preferably 10 to 200 nm, more preferably 20 to 100 nm, and very preferably 40 to 80 nm.

[0041] The method according to the 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. A further improvement in edge roll-off can be achieved when using a polishing pad having a hardness of 80 to 95. The Shore hardness can be determined according to DIN ISO 7619-1. The polishing pad used in the method according to the invention is preferably a so-called "foam pad." However, the invention is not limited to such pads, and other polishing pads can also be used to achieve the objects on which the invention is based.

[0042] If the target pH of the polishing agent is not less than 11.4 and not more than 12.4, and if the control range of ±0.2 is not exceeded, the edge roll-off of wafers made of semiconductor material (especially, single crystal silicon wafers) can be improved. In addition, in this way, polishing of the polishing pad after multiple polishing steps can be prevented. A particularly significant improvement in edge roll-off can be achieved if the pH of the polishing agent is not less than 11.5 and not more than 12.3, preferably not less than 11.5 and not more than 12.0, more preferably not less than 11.7 and not more than 11.9, and if the deviation of the pH measured during the circulation of the polishing agent between the collection container and at least one wafer made of semiconductor material arranged between the upper polishing platen and the lower polishing platen of the double-side polishing machine from the target pH does not exceed ±0.2 at any instant. In a particularly preferred embodiment, the target pH is not less than 11.7 and not more than 11.9, and the control range (i.e., the deviation from the target) is within the range of ±0.1. A particularly significant improvement in edge roll-off is observed if the target is within this range and if only a deviation of ±0.1 from the target is permitted.The edge roll-off can be further reduced if the method of the invention only allows a deviation of ±0.05 from the target pH.

[0043] The target pH of the polishing agent and the maximum deviation from the target (control range) are based on the pH at a defined point in the polishing circuit. The target pH of the polishing agent and the maximum deviation from the target are preferably based on the pH in the collecting container. Therefore, in the method according to the invention, the pH of the polishing agent is preferably measured in the collecting container. In the sense of the present invention, the collecting container is a container in the polishing circuit, from which container the polishing agent is directed to at least one wafer made of semiconductor material, preferably via the polishing gap, during the polishing operation, and from which container the polishing agent is returned to the at least one wafer made of semiconductor material. The collecting container is preferably equipped with or connected to a measuring instrument for pH measurement, more preferably a pH electrode.

[0044] If the pH is not regulated during double-side polishing, a continuous drop in pH is observed during the polishing process (polishing pass). Interrupting pH regulation for only 10 minutes during polishing results in a pH drop of 0.3. Figure 4 It is shown that interrupting the pH regulation for 10 minutes during the polishing pass in period c results in a pH drop from 11.8 to approximately 11.5.

[0045] The pH is regulated by temporarily supplying an alkaline component to the polishing agent. Here, the alkaline component is supplied so that the deviation of the measured pH from the target pH does not exceed ±0.2 at any instant, preferably does not exceed ±0.1 at any instant, and most preferably does not exceed ±0.05 at any instant, during the circulation of the polishing agent between the collection container and the at least one wafer made of semiconductor material arranged between the upper and lower polishing platens of the double-sided polishing machine. More frequent measurements of pH make it possible to reduce the deviation from the target because the shift of pH, in particular the continuous decrease of pH, can be offset more quickly and efficiently by supplying the alkaline component. In addition, by regularly (periodically) calibrating the pH measuring instrument, preferably the pH electrode, the accuracy of the pH measurement can be improved and thus the control range (deviation from the target pH) can also be reduced.

[0046] The alkaline component is preferably an alkaline solution. More preferably, the alkaline component is an alkaline solution comprising at least one compound selected from the group consisting of sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, ammonium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide.

[0047] The pH can be regulated by temporarily supplying an alkaline component, preferably an alkaline solution, to the collecting container. In one embodiment of the method of the present invention, the collecting container is connected to a storage container containing the alkaline component. In this embodiment, the pH is regulated by temporarily supplying the alkaline component (preferably an alkaline solution) from the storage container to the collecting container by means of a pump or a valve. The pH electrode can be connected to a control unit that drives a valve or a metering pump to supply the alkaline component. Therefore, the collecting container can be temporarily supplied with an alkaline component (as a function of pH) to regulate the pH. The more frequent the pH measurement and the pH regulation associated with the measurement, the narrower the control range, and therefore the smaller the deviation from the target.

[0048] The pH is preferably measured continuously or at intervals of 0.01 to 60 seconds, more preferably at intervals of 0.1 to 10 seconds. It is also preferred to control the pH at regular intervals (intermittent), preferably at the same intervals as the pH measurement. The measurement can be performed using a Knick SE554X / 2-NMSN pH electrode. The electrode is preferably calibrated regularly, more preferably at least monthly, using a variety of calibration solutions with defined pH values ​​in the range of 7 to 12.

[0049] In each case, the pH is regulated as a function of the measured pH. In a particularly preferred embodiment of the method of the present invention, regulating the pH in the collecting container comprises the following steps: (i) supplying an alkaline solution as soon as the pH in the collecting container drops below a specified lower limit, and (ii) pausing or ending the supply of alkaline solution as soon as the pH in the collecting container exceeds a specified upper limit, the lower limit and the upper limit deviating from the target by no more than ±0.2. The specified lower limit and the specified upper limit preferably deviate from the target by no more than ±0.1, more preferably no more than ±0.05. The supply of alkaline solution and the suspension or termination of the supply of alkaline solution can be achieved, for example, by turning a pump on and off, by driving a metering pump accordingly, or by opening and closing a valve preferably driven by a control unit, which in turn is connected to the pH electrode. The alkaline solution is preferably supplied from a storage container using a metering pump, which is connected to the collecting container via a pipeline.

[0050] In another embodiment of the method of the present invention, the pH can be regulated by adding a specified amount of alkaline solution from the storage container to the collection container at variable time intervals. The lower the measured pH, the shorter the time interval between adding the specified amount of alkaline solution.

[0051] After polishing of at least one semiconductor material wafer is completed, one or more additional polishing steps can be performed on at least one replacement, unpolished wafer. Wafers are replaced by removing a polished wafer and inserting an unpolished wafer into at least one carrier plate disposed between an upper polishing platen and a lower polishing platen of a double-side polisher. After inserting the at least one new, unpolished wafer, a new polishing step begins. Wafers are thus replaced between polishing steps (also known as polishing passes). After polishing (polishing step) of the at least one wafer is completed and before a new polishing step is initiated for the at least one replacement, unpolished wafer, polishing agent can be circulated via a bypass, temporarily removing the polishing agent from the double-side polisher. Thus, during the replacement of the at least one wafer, the polishing agent is not circulated through the double-side polisher. During the replacement of the at least one wafer, the polishing agent can be refreshed by replacing 1% to 30% of the polishing agent by volume with new polishing agent (or fresh polishing agent) and subsequently adjusting the pH to a target value by adding an alkaline component. Between the individual polishing passes, preferably 2 to 20% by volume, more preferably 4 to 10% by volume, very preferably 4 to 5% by volume of the polishing agent is replaced with new polishing agent, and the pH is subsequently adjusted to the target by adding alkaline solution.

[0052] Surprisingly, it has been observed that the improved edge geometry achieved in the method according to the invention is achieved over a plurality of consecutive polishing steps (polishing passes), for example more than 10 polishing passes, even when only 1% to 30% (by volume) of the polishing agent in the collecting container is replaced with new polishing agent between the polishing passes and the pH is subsequently adjusted to the target by adding an alkaline component.

[0053] Therefore, the method of the present invention can improve the edge geometry of wafers made of semiconductor materials (especially, wafers made of single crystal silicon), i.e., edge roll-off, on the one hand, and can improve the economy and efficiency of polishing operations by reducing polishing agent consumption on the other hand.

[0054] Alternatively, in the method of the present invention, a final polishing step can be performed in a double-side polisher by: (i) switching the circulation of a polishing agent (a first polishing agent) to a bypass, thereby interrupting the supply of the circulating polishing agent to the polisher, and (ii) subsequently delivering a polishing agent (a second polishing agent) for final polishing to at least one wafer made of semiconductor material disposed between an upper polishing platen and a lower polishing platen of the double-side polisher, wherein the second polishing agent is not circulated during the final polishing step. During the final polishing step, the rotation of the polishing platen and the carrier plate is continued. The final polishing step is shorter than the previous polishing step that occurs with the circulation of the first polishing agent.

[0055] After removing the at least one wafer made of semiconductor material from the double-side polisher, it may optionally be followed by final polishing, such as chemical mechanical polishing (CMP), and / or by final cleaning. Final cleaning is typically a wet chemical cleaning operation carried out in multiple baths at a temperature of 30 to 90° C. In this case, 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 another bath, hydrochloric acid, hydrogen peroxide and deionized water are used, for example, in a ratio of 1:1:6 to 1:2:8. In addition, after the final cleaning, the at least one wafer made of semiconductor material may also undergo epitaxial coating.

[0056] In the sense of the present invention, edge roll-off is the 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 semiconductor wafers and are also the focus of SEMI standards. For example, standard SEMI M68-1015 refers to ZDD, while standard SEMI M67-1015 refers to ESFQR.

[0057] The front-side ZDD describes the average near-edge curvature of the surface of the front side of a semiconductor wafer. Specifically, the ZDD represents the second derivative of the vertical height from the midplane to the surface of the front side of the wafer. The ZDD is preferably determined by dividing the wafer surface into 16 sectors with a 1 mm edge exclusion.

[0058] ESFQRmax specifies the ESFQR of the sector where the ESFQR is maximum.ESFQRmax is preferably determined by dividing the surface of the wafer edge into 72 sectors (each sector having a length of 35 mm) with an edge exclusion of 1 mm.

[0059] Detailed description of working examples and comparative examples of the present invention

[0060] In working example 1, a plurality of wafers made of single-crystal silicon having a diameter of 300 mm and a {100} orientation were polished according to the method of the invention in a commercial double-side polisher model AC2000 from the manufacturer Lapmaster Wolters using a foamed polishing pad of the Exterion SM-11D type from the manufacturer Nitta DuPont.

[0061] Glanzox 7100 polishing slurry from the manufacturer Fujimi is used and circulates between the collection container and the wafer positioned between the upper and lower polishing platens of the double-side polisher (the polishing gap) during the polishing operation. The polishing slurry contains colloidal silica. The target pH of the polishing slurry in the collection container is specified to be 11.8. The pH in the collection container is regulated by adding potassium hydroxide solution from a storage container to the collection container via a metering pump, so that the deviation from the target pH does not exceed ±0.05. The pH is continuously measured by a pH electrode in the collection container. The pH electrode is connected to a control unit for driving the pump, so that potassium hydroxide solution is temporarily supplied as a function of pH through the operation of the pump. This is followed by the final polishing step. For this step, the supply of Glanzox 7100 polishing slurry to the polisher is first suspended and circulated via a bypass, thereby directing the polishing slurry past the polisher. A second polishing slurry for the final polish is then delivered to the wafer positioned between the upper and lower polishing platens of the double-side polisher, and polishing is performed in a time period of less than 5 minutes.

[0062] After the polishing process is complete, the polished wafers are removed. Subsequently, on a random basis, one of the polished wafers is inspected and found to have -5 nm / mm 2 The front ZDD was 0.000 nm and the ESFQRmax was 25 nm. In addition, no pad polishing was observed.

[0063] In Comparative Example 1, a wafer made of single crystal silicon having a diameter of 300 mm, a {100} orientation, and the same specifications as in Working Example 1 was polished in a commercial double-side polisher, and the operating conditions employed were the same as in Working Example 1, except that a target pH of 11.0 was specified. For a randomly selected wafer after polishing, it was found that -12 nm / mm 2 Front ZDD and ESFQRmax of 45nm.

[0064] In Working Example 1 and Comparative Example 1, ZDD was determined by dividing the wafer surface into 16 sectors with an edge exclusion of 1 mm. In Working Example 1 and Comparative Example 1, ZDD was determined by dividing the wafer edge surface into 72 sectors (each sector having a length of 35 mm) with an edge exclusion of 1 mm. Figure 2 and Figure 3 The thickness variation of the polished wafer in the radial direction is shown. Figure 2 Thickness variation of the wafer after polishing according to Comparative Example 1 is shown. Figure 3 Thickness variation of the wafer after polishing according to Working Example 1 is shown. Figure 2 and Figure 3 The comparison reveals the relatively low edge roll-off of the wafers polished according to the method of the present invention (see Figure 2 and Figure 3 the circled area at the center right edge).

[0065] Comparison of Working Example 1 with Comparative Example 1 shows that a target pH in the range of 11.4 to 12.4 (with a low fluctuation span, ie, a small deviation from the target) results in a reduction in edge roll-off.

[0066] Furthermore, several methods for double-side polishing according to Working Example 1 were performed one after another, wherein the polished wafer was replaced with a new unpolished wafer between each polishing method. During the replacement of the polished wafer with the unpolished wafer, the polishing agent circulated via a bypass and was refreshed. Refreshing was performed by draining 5% (by volume) of the polishing agent in the circulation loop, adding 5% by volume of new polishing agent, and then adjusting the required pH by supplying potassium hydroxide solution. It was possible to show that, in the subsequent polishing operation (polishing pass), replacing only 5% by volume of the polishing agent was sufficient to achieve improved edge geometry (measured in terms of ZDD and ESFQRmax) and to fully refresh the polishing agent overall.

[0067] Furthermore, in another comparative example, the pH control was suspended during polishing by shutting off the metering pump for 10 minutes during the polishing pass (which means that no potassium hydroxide solution was supplied). Suspending the pH control for 10 minutes during the polishing pass resulted in the pH of the polishing agent dropping from an initial 11.8 to 11.5 (see Figure 4 Period c).

Claims

1. A method for double-side polishing of at least one wafer made of semiconductor material, comprising the following steps: Placing the at least one wafer made of semiconductor material in at least one carrier plate between an upper polishing platen and a lower polishing platen of a double-sided polishing machine (1), the lower side of the upper polishing platen and the upper side of the lower polishing platen each being covered with a polishing pad; rotating the at least one carrier plate, the upper polishing platen, and the lower polishing platen; circulate polishing agent between a collecting container (2) and at least one wafer made of semiconductor material arranged between an upper polishing platen and a lower polishing platen of the double-side polishing machine (1); measuring the pH of the polishing agent, the pH being measured continuously or at regular time intervals having a duration of 0.01 to 10 seconds; as well as regulating the pH of the polishing agent; It is characterized in that the target pH is not less than 11.4 and not more than 12.4, and the pH is controlled by temporarily supplying an alkaline component to the polishing agent as a function of the measured pH, so that during the circulation of the polishing agent between the collection container and the at least one wafer made of semiconductor material arranged between the upper polishing platen and the lower polishing platen of the double-side polishing machine, the deviation of the measured pH from the target pH does not exceed ±0.2 at any instant.

2. Method for double-side polishing of at least one wafer made of semiconductor material according to claim 1, characterized in that The target pH is not less than 11.5 and not more than 12.

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3. Method for double-side polishing of at least one wafer made of semiconductor material according to claim 1 or 2, characterized in that The target pH is not less than 11.7 and not more than 11.

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4. Method for double-side polishing of at least one wafer made of semiconductor material according to any one of claims 1 to 3, characterized in that measuring the pH of the polishing agent in the collecting container (2), and The pH is regulated by temporarily supplying an alkaline component into the collection container (2).

5. Method for double-side polishing of at least one wafer made of semiconductor material according to any one of claims 1 to 4, characterized in that The alkaline component is an alkaline 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.

6. Method for double-side polishing of at least one wafer made of semiconductor material according to any one of claims 1 to 5, characterized in that The collecting container (2) is connected to a storage container (4) containing the alkaline component, and The pH is regulated by temporarily supplying the alkaline component from the storage container (4) to the collection container (2) by means of a pump or a valve.

7. Method for double-side polishing of at least one wafer made of semiconductor material according to any one of claims 1 to 6, characterized in that During the circulation of the polishing agent between the collection container and the at least one wafer made of semiconductor material arranged between the upper polishing platen and the lower polishing platen of the double-side polishing machine, the deviation of the measured pH from the target pH does not exceed ±0.1 at any instant, preferably does not exceed ±0.

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8. Method for double-side polishing of at least one wafer made of semiconductor material according to any one of claims 1 to 7, characterized in that Regulating the pH in the collection container (2) comprises the following steps: supplying the alkaline component as soon as the pH measured in the collection container (2) drops below a specified lower limit, and Once the pH measured in the collection container (2) exceeds a specified upper limit, the supply of the alkaline component is interrupted, wherein the specified lower limit and the specified upper limit deviate from the target pH by no more than ±0.2, and the alkaline component is a solution.

9. Method for double-side polishing of at least one wafer made of semiconductor material according to claim 8, characterized in that The specified lower limit and the specified upper limit do not deviate from the target pH by more than ±0.1, preferably by more than ±0.

05.

10. Method for double-side polishing of at least one wafer made of semiconductor material according to any one of claims 1 to 9, characterized in that The pH is regulated by adding a specified amount of alkaline solution from the storage container (4) to the collection container (2) at variable time intervals, the length of each of the time intervals depending on the measured pH.

11. Method for double-side polishing of at least one wafer made of semiconductor material according to any one of claims 1 to 10, characterized in that The polishing agent is a dispersion comprising abrasive particles and one or more compounds selected from the group consisting of a surfactant additive, a preservative, a biocide, an alcohol, and a complexing agent, and the solid content of the dispersion is 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.

12. Method for double-side polishing of at least one wafer made of semiconductor material according to any one of claims 1 to 11, characterized in that After polishing of the at least one semiconductor material wafer is finished and before polishing of at least one replaced, unpolished semiconductor material wafer is started, the polishing agent is no longer circulated through the double-sided polisher and, while no longer circulated through the double-sided polisher, the polishing agent is renewed by replacing 1% to 30% by volume of the polishing agent in the collecting container (2) with new polishing agent and subsequently adjusting the pH to the target pH by adding the alkaline component.

13. Method for double-side polishing of at least one wafer made of semiconductor material according to claim 12, characterized in that The polishing agent is renewed by replacing 2% to 8% by volume of the polishing agent in the collecting container (2) with new polishing agent and then adjusting the pH to the target pH by adding the alkaline solution.

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

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