Method for handling a substrate with an electrostatic holding device

Abstract

Method for handling a substrate when a substrate to be processed is held by an electrostatic holding device (C), wherein the electrostatic holding device (C) comprises: - a holding device main body (1) with a plurality of electrodes (3a, 3b); - a holding plate (2) made of a dielectric material, wherein the holding plate (2) has a ribbed part (2a) with which an outer edge part of the substrate to be processed can come into surface contact, and a plurality of holding parts arranged vertically at a predetermined distance from one another in an interior space (2b) surrounded by the ribbed part (2a); and - a gas introduction device for introducing a predetermined gas into the interior (2b); - wherein the electrostatic holding device (C) is arranged to attract the substrate by applying a predetermined DC voltage between the electrodes (3a, 3b) when the substrate is held by the electrostatic holding device (C), - wherein the electrostatic holding device (C) is arranged to form a gas atmosphere by supplying a predetermined gas into the interior (2b), - creating a substrate state that is free from damage occurring on the substrate, - the procedure includes: - Monitoring a current value by causing an alternating current to flow through a capacitor of the holding plate (2) using an alternating power supply; - Monitoring a quantity of flowing gas by causing gas to flow from the gas inlet device; and - Controlling the substrate state by changing at least one of the current value and gas flow quantity, - the procedure further includes: if the change in at least one of the current value and gas flow quantity has exceeded a predetermined threshold: Assessing the substrate condition that leads to substrate damage; and Control at least one of the DC voltage applied to both electrodes (3a, 3b) and the amount of gas flow from the gas inlet device, thereby eliminating the substrate condition.

Description

[Technical field]

[0001] The present invention relates to a method for handling a substrate and, in particular, a method for handling a substrate state when essentially a silicon wafer is handled as the substrate to be processed (hereinafter referred to as "substrate to be processed"), wherein the handling is carried out when a predetermined processing treatment is performed on the substrate while the substrate is held against a so-called bipolar electrostatic holding device in order not to damage the substrate during, before and after the silicon wafer is held. [Technical background]

[0002] Various processing steps are performed in semiconductor manufacturing to obtain desired component structures, such as layer-forming processing using PVD, CVD, or similar methods, as well as ion implantation, heat treatment, etching, or similar processes. In a vacuum processing unit, an electrostatic holding device is arranged to perform these processing operations and to hold a silicon wafer (hereinafter simply referred to as "wafer") in position within the processing chamber. A conventional electrostatic holding device, known from JP H01-321 136 A, is a so-called bipolar electrostatic holding device in which a holding plate made of dielectric material is mounted on an upper surface of the main body of the holding device, into which positive and negative electrodes are embedded.

[0003] Depending on the processing to be performed in the vacuum processing device, there are cases in which the wafer is heated to a predetermined temperature. In such a case, it is known that, for example, a heating device of the resistance heater type is integrated into the main body of the holding device, and that a finned section is formed which comes into surface contact with an outer edge section on a rear face of the wafer (i.e., the side opposite the surface on which the predetermined processing is performed). Within an interior enclosed by this finned section, a plurality of holding elements are arranged vertically, for example, coaxially, to form a holding plate. During the heating and cooling of the wafer, a protective gas, such as argon gas or the like, is supplied to the interior through a gas passage formed in the main body of the holding device.By creating such a protective gas atmosphere in the interior, which is delimited by the ribbed part and the rear surface of the wafer, heat transfer to the wafer is supported in order to heat or cool the wafer efficiently.

[0004] Incidentally, in the electrostatic holding device with the aforementioned design, the ribbed portion and the holding portion of the holder plate are abrasionally worn by the wafer during heating and cooling, gradually deteriorating due to the difference in thermal expansion between the wafer and the electrostatic holding device. One solution, as described in the aforementioned document JP H01-321 136 A, is as follows: Alternating current is applied through the capacitance of the holding plate from an AC voltage source to monitor the current value. By assessing the operating limit as quickly as possible, damage to the wafer in the processing chamber due to poor wafer adhesion or similar issues can be prevented, thereby improving productivity.

[0005] JP 2008-159 875 A discloses a substrate suction system comprising a heating plate for suctioning a substrate, a gas filling chamber formed on the surface of the heating plate, a gas passage for supplying inert gas to the gas filling chamber, a control unit for adjusting the opening of a flow control valve based on a measurement result from a pressure gauge in order to regulate the gas pressure in the gas filling chamber to a prescribed pressure, a flow sensor arranged on the upstream side of the flow control valve to measure a gas flow of the gas passage, and a shut-off valve arranged on the upstream side of the flow sensor to open / close the gas passage.

[0006] On the other hand, there has recently been a trend to use wafers with a larger diameter and thinner slices (less than 700 µm) in order to further improve productivity. This type of wafer results in warping in various directions due to the specified machining operations. Furthermore, the wafer's warping state changes with each machining operation due to heating and cooling. Therefore, there are instances of wafer damage, not only during machining operations but also while the warped wafer is held by the electrostatic holding device or during transport when the holding force is released.One consequence is that simply evaluating the operating limits of the electrostatic holding device cannot improve productivity while simultaneously increasing product yield. Therefore, determining the best way to manage the wafer's condition becomes crucial. [Summary of the invention][Problems to be solved by the invention]

[0007] In view of the points mentioned above, this invention has the objective of providing a method for handling a substrate condition that leads to damage to the substrate being processed, in which the substrate condition that leads to damage to the substrate being processed (handled) by the electrostatic holding device can be precisely controlled. [Means of solving the tasks]

[0008] To solve the aforementioned problems, this invention is a method for handling a substrate when the substrate to be processed is held by an electrostatic holding device. The electrostatic holding device comprises: a holding device main body with a plurality of electrodes; a holding plate made of a dielectric material, the holding plate having a ribbed portion with which an outer edge portion of the substrate to be processed can come into surface contact, and a plurality of holding elements arranged vertically at a predetermined distance from one another in an interior space surrounded by the ribbed portion; and a gas introduction device for introducing a predetermined gas into the interior space.When the substrate is held by the electrostatic holding device, which is configured to attract the substrate by applying a predetermined voltage between the electrodes and to create a gas atmosphere by supplying a predetermined gas into the interior, a substrate state is maintained that is free from damage occurring to the substrate. The method comprises: monitoring a current value by causing an alternating current to flow through a capacitor of the holding plate by means of an alternating power supply; monitoring a quantity of gas flow by causing gas to flow from the gas introduction device; and maintaining the substrate state based on a change in at least one of the current value and gas flow quantity.The procedure for handling the substrate further comprises, if the change in at least one of the current value and gas flow quantity has exceeded a predetermined threshold: assessing the substrate condition as leading to damage to the substrate; and controlling at least one of the DC voltage applied to both electrodes and the quantity of gas flow from the gas introduction device, thereby eliminating the said substrate condition.

[0009] According to this invention, predetermined processing operations, such as heating, layering, or the like, are carried out in a state where the substrate remains attracted by the electrostatic holding device, which has the aforementioned arrangement. As a result, if the substrate's curvature increases in the direction where the distance between the ribbed portion and the substrate's edge surface (direction of tensile force) changes, the change in the amount of gas flowing out of the interior through the opening will cause the amount of gas supplied by the gas inlet device to change. Conversely, if the substrate's curvature increases in the direction where the central portion of the substrate moves away from the interior (direction of compression), the impedance will increase due to the change in capacitance, and as a result, the current will change.

[0010] According to this invention, while the substrate is attracted by the electrostatic holding device, if the substrate warps in any direction or the warping increases, the change in the amount of gas flow or in impedance, and consequently in the alternating current value, will increase accordingly. As a result, the substrate condition that leads to damage can be precisely controlled. Consequently, damage to the substrate inside the processing chamber can be reliably prevented, thereby improving productivity and increasing the product yield (available percentage).

[0011] Furthermore, it can prevent excessive stress from being placed on the substrate, thus reliably preventing damage to the substrate.

[0012] Preferably, the method for handling the substrate further comprises, after the substrate has been mounted on the holding plate: monitoring the current value by causing an alternating current to flow before a direct voltage is applied to the electrodes; and judging the substrate as unacceptable if the current value exceeds a predetermined threshold. This prevents damage to the substrate by forcibly attracting an excessively warped substrate to the electrostatic holding device.

[0013] Furthermore, the method for handling the substrate preferably comprises, after the application of DC voltage has ceased, assessing the substrate's attraction state based on the current value.

[0014] The condition in which the substrate can be removed from the holding plate. In a state where the substrate remains attracted under the influence of the residual charge immediately after the attraction is released, damage to the substrate inside the processing chamber can be safely and advantageously prevented, e.g., by lifting it to attempt to transfer the substrate, or by ensuring that the transfer robot has access to the substrate. [Brief description of the drawing] Fig. Figure 1 schematically shows the structure of an electrostatic holding device. The Fig. 2(a) and Fig. Figure 2(b) schematically shows the curvature of a wafer as a substrate. Fig. Figure 3 is a graphical representation that illustrates the change in impedance and gas flow rate as a function of the wafer's curvature. [Embodiments of the invention]

[0015] With reference to the figures, a method for handling a substrate according to an embodiment of this invention is now described, in which, by defining a substrate to be processed as a wafer W, the wafer W is not damaged by an electrostatic holding device C which is arranged in the vacuum processing device in which processing operations are carried out, such as layer-forming processing with the PVD process, CVD process or the like, ion implantation processing, heating processing, etching processing or the like.

[0016] As in Fig. As shown in Figure 1, the electrostatic holding device C is formed from: a holding device main body 1, which is arranged on a bottom part of the processing chamber (not shown); and a holding plate 2, which is formed from a dielectric material and is arranged on an upper surface of the holding device main body 1. For example, the holding device main body 1, made of aluminum nitride, has positive and negative electrodes 3a, 3b with an insulating layer (not shown) embedded therein, so that a DC voltage can be applied from a DC power supply E1 to a known holding device power supply E.

[0017] Furthermore, a gas passage 4 is formed in the main body 1 of the holding device, penetrating in a vertical direction. The lower end of this gas passage 4 extends over a gas tube 6, into which a flow regulator 5 is inserted, in connection with a gas supply 7 containing a protective gas, such as argon gas or the like. These components constitute the gas inlet device according to this embodiment. The main body 1 of the holding device also includes a built-in heater 8 of the resistance heater type, which has a known design, enabling the wafer W to be heated to a predetermined temperature and maintained at that temperature. This embodiment describes an example in which only the heater 8 is arranged. However, it can also be constructed by incorporating a known cooling device.

[0018] The holding plate 2 is made, for example, of aluminum nitride and comprises: a ring-shaped ribbed section 2a, which allows an outer edge section on the back of the wafer W to be brought into surface contact; and a plurality of rod-shaped holding sections 2c, which are arranged coaxially and vertically in the interior 2b, surrounded by the ribbed section 2a. In this case, the height of the holding sections 2c is set so that it is slightly less than the height of the ribbed section 2a. In this way, when the wafer W is attracted to the surface of the holding plate 2, it can be supported by each of the holding sections 2c.

[0019] Then, due to the electrostatic force generated by applying a DC voltage to both electrodes 3a and 3b after the wafer W has been placed on the holding plate 2, the wafer W is attracted to the surface of the holding plate 2. In this process, the outer edge portion on the back of the wafer W comes into surface contact with the finned portion 2a over its entire circumference, thus essentially hermetically sealing the interior 2b. In this state, an argon gas atmosphere can be created in the aforementioned interior 2b by introducing argon gas through the gas introduction device. According to this arrangement, when the heater 8 is operated to heat the wafer W, an argon gas atmosphere is formed in the interior 2b, which is bounded by the finned portion 2a and the back of the wafer W, thereby facilitating heat transfer to the wafer W and heating it efficiently.

[0020] Since no sealing element is provided between the outer edge part on the back of the wafer W and the rib part 2a, a small amount (e.g. 0.01 to 0.03 sccm) of protective gas will escape through leakage, even if the outer edge part 2a on the back of the wafer W and the rib part 2a are in surface contact with each other over the entire circumference.

[0021] As in the Fig. 2(a) and Fig. As shown in Figure 2(b), the wafer W has formed bulges in the direction of compression or in the direction of tension, for example, due to stresses from the wafer itself or from stresses from the thin layer formed on the surface of the wafer W. When this type of wafer W is attracted to the electrostatic holding device C, it is necessary to ensure that the substrate is not damaged (cracks, breakage, or the like) while the heating or layering process is carried out in a state where the wafer remains attracted to the electrostatic holding device C, or while the substrate is being transported after the attraction by the electrostatic holding device C has been released when the processing operations have been completed.

[0022] In this embodiment, to control the wafer's state, an AC power supply E2 is connected in series with the DC power supply E1 in the holding device power supply E (not shown). This causes AC current from the AC power supply E2 to flow through the capacitor of the electrostatic holding device 1. The impedance is monitored via the current value measured by a known ammeter A, and the flow rate of Ar gas is monitored by inserting a known flow meter 9 into a gas tube 6 on the downstream side of the flow regulator 5.

[0023] With reference to Fig. 3. A description of the effect that the wafer states can be handled is given, with reference to a case in which the wafer W, which has a bulge, is attracted by the electrostatic holding device C, in particular in an example where a bulge has occurred in the direction of compression in the wafer W. In this embodiment, as in Fig. Figure 1, shown by an imaginary line, shows a known laser displacement measuring device positioned above the central position of the wafer W, so that the displacement at the central position can be measured. Here, in Fig. 3. The change in impedance is shown by the double-dashed line “a”. The solid line b shows the change in gas flow rate, the dotted line c shows a change, the dashed line d shows a current value, and the solid line e shows the change in DC voltage across the electrodes.

[0024] First, after the wafer W has been mounted on the surface of the mounting plate 2, alternating current is supplied by the AC power supply E2. Based on the current value measured at that time in the ammeter A, the impedance of the capacitance is measured, and a displacement of the central position of the wafer is also measured using a laser displacement measuring device.

[0025] Then, a predetermined DC voltage (e.g., 400 V) is applied between both electrodes 3a, 3b by the DC power supply E1 of the holding device power supply E, in order to attract the wafer W to the surface of the holding plate 2. The outer edge of the back side of the wafer W then comes into surface contact with the ribbed part 2a over its entire circumference, and as a result, the wafer will attain a substantially horizontal state (see Fig. 1) The impedance measured at this time and the central position showed that the impedance had decreased (by approximately 10 kΩ), and it was found that the central position of wafer W had shifted towards the holding plate 2. When argon gas was introduced into the chamber 2b through the gas inlet device at a constant flow rate, and the gas flow rate was measured by the flow meter 9, the gas flow rate initially increased and then remained constant over time. Simultaneously with the introduction of the argon gas, the heater 8 was then activated to heat wafer W to a predetermined temperature (e.g., 400 °C) and maintained it for a predetermined time.

[0026] While wafer W was being heated, the current measured by the ammeter remained essentially constant, and consequently, the impedance also remained essentially constant. Furthermore, the gas flow rate and displacement showed little or no change. When the operation of heater 8 and the introduction of Ar gas were stopped, and the application of voltage between both electrodes 3a and 3b was discontinued after a predetermined time interval, the current and, again, the impedance measured at that time showed an increase of approximately 20% compared to the values ​​before the heating. When the measurement was performed with the laser displacement meter, the displacement became larger than before the heating, and the bulging of wafer W in the direction of compression increased.

[0027] As stated above, it is found that the warping of wafer W can be precisely controlled based on its impedance. Furthermore, in the case where the laser displacement measurement showed that wafer W warped in the direction of compression, a correlation exists between impedance and the displacement of wafer W, and this correlation is essentially proportional. From the above, it can therefore be seen that by measuring the impedance and, in turn, the current value, the degree of warping of wafer W can be assessed. And by acting accordingly, the condition leading to damage of wafer W can be appropriately managed.As described above, according to the embodiment of this invention, the condition leading to damage of the wafer W can be suitably controlled by changing the impedance and, in turn, by changing the current value. Therefore, productivity can be improved while simultaneously increasing product yield by reliably preventing damage to the wafer W, particularly in the processing chamber.

[0028] In the event that the impedance and, consequently, the current value change above the predefined thresholds during processing, it can be assessed that this condition could lead to wafer damage. In such a case, by appropriately interrupting the predefined processing, at least one of the DC voltages applied between the two electrodes 3a, 3b and the amount of gas flow from the gas inlet device are controlled in such a way as to eliminate the condition in which excessive stress is applied to the wafer W. According to this arrangement, damage to the wafer W in the processing chamber can be prevented. The thresholds can be appropriately adjusted, taking into account the size and thickness of the wafer W.

[0029] Given that the impedance and the displacement of wafer W are correlated, the current and, consequently, the impedance are monitored after wafer W is mounted on the holding plate 2. This is achieved by ensuring that the alternating current flows before the direct current is applied between electrodes 3a and 3b. If it is determined that the predefined thresholds have been exceeded, it can be concluded that excessive warping of wafer W must have occurred and that damage may therefore occur if wafer W is forcibly held by the electrostatic holding device C. Thus, damage to wafer W in the processing chamber can be prevented.

[0030] On the other hand, an arrangement can be created in which, based on the impedance, an assessment is made of the state in which the wafer W can be removed from the holding plate 2 after the application of DC voltage has ceased while the wafer W is attracted. Then, in a state where the wafer W remains attracted under the influence of the residual charge immediately after the attraction is released, it can advantageously be prevented that the wafer W is damaged inside the processing chamber, e.g., by being lifted to attempt to transfer the substrate, or by allowing the transfer robot access to the substrate.

[0031] Furthermore, this embodiment mainly describes an example in which a warping of the wafer W occurred in the direction of compression. In the case that the warping occurred during processing or before or after processing in the direction of tensile force, as in Fig.As shown in Figure 2(b), the ribbed portion 2a and the outer edge portion of the wafer W do not come into surface contact with each other, even when the wafer W is pulled by the holding plate 2. As a result, the distance between the two increases, and the amount of gas escaping as leakage increases. Consequently, the gas flow rate measured by the flow meter 9 will also change. In this way, since there is a correlation between the gas flow rate and the curvature of the wafer W in the direction of the pulling force, the degree of curvature of the wafer W can be assessed by monitoring the gas flow rate, and the condition leading to damage to the wafer W can be appropriately managed by controlling it. In a manner similar to the above, damage to the wafer W in the processing chamber can be prevented. [Description of reference numbers and symbols] C electrostatic holding device 1 Holding device main body 2 Mounting plate 2a Rib section 2b Interior 2c Holding part 3a, 3b Electrode 5 Flow regulators (gas inlet device) 7 Gas source (gas inlet device) 9 Flow meter A Ammeter E Holding device power supply W Wafer

Claims

[1] A method for handling a substrate when a substrate to be processed is held by an electrostatic chuck (C), the electrostatic chuck (C) comprising: - a holding device main body (1) having a plurality of electrodes (3a, 3b); - a holding plate (2) made of a dielectric material, the holding plate (2) having a rib part (2a) with which an outer edge part of the substrate to be processed can come into surface contact, and a plurality of holding parts arranged vertically at a predetermined distance from one another in an inner space (2b) surrounded by the rib part (2a); and - a gas introduction device for introducing a predetermined gas into the interior space (2b); - wherein the electrostatic chuck (C) is arranged to attract the substrate by applying a predetermined DC voltage between the electrodes (3a, 3b) when the substrate is held by the electrostatic chuck (C), - wherein the electrostatic holding device (C) is arranged to form a gas atmosphere by supplying a predetermined gas into the interior space (2b), - whereby a substrate condition is created which is free from damage to the substrate, - the method comprising: - monitoring a current value by causing an alternating current to flow through a capacitance of the holding plate (2) by means of an alternating power supply; - monitoring an amount of flowing gas by causing gas to flow from the gas introduction device; and - Controlling the substrate state by changing at least one of the current value and the gas flow rate, - the method further comprising: if the change in at least one of the current value and the gas flow rate has exceeded a specified threshold: Assessing the substrate condition leading to the substrate damage; and Controlling at least one of a DC voltage to be applied to both electrodes (3a, 3b) and the amount of gas flow from the gas introduction device, thereby eliminating the substrate state. [2] A method of handling the substrate according to claim 1, further comprising, after the substrate has been mounted on the holding plate (2): monitoring the current value by causing an alternating current to flow before a direct voltage is applied to the electrodes (3a, 3b); and Assessing the substrate condition leading to substrate damage as unacceptable if the current value exceeds a predetermined threshold. [3] A method for handling a substrate when a substrate to be processed is held by an electrostatic chuck (C), the electrostatic chuck (C) comprising: - a holding device main body (1) having a plurality of electrodes (3a, 3b); - a holding plate (2) made of a dielectric material, the holding plate (2) having a rib part (2a) with which an outer edge part of the substrate to be processed can come into surface contact, and a plurality of holding parts arranged vertically at a predetermined distance from one another in an inner space (2b) surrounded by the rib part (2a); and - a gas introduction device for introducing a predetermined gas into the interior space (2b); - wherein the electrostatic chuck (C) is arranged to attract the substrate by applying a predetermined DC voltage between the electrodes (3a, 3b) when the substrate is held by the electrostatic chuck (C), - wherein the electrostatic holding device (C) is arranged to form a gas atmosphere by supplying a predetermined gas into the interior space (2b), - whereby a substrate condition is created which is free from damage to the substrate, - the method comprising: - monitoring a current value by causing an alternating current to flow through a capacitance of the holding plate (2) by means of an alternating power supply; - monitoring an amount of flowing gas by causing gas to flow from the gas introduction device; and - controlling the substrate state by a change in at least one of the current value and the gas flow amount, further comprising, after the substrate has been mounted on the holding plate (2): monitoring the current value by causing an alternating current to flow before a direct voltage is applied to the electrodes (3a, 3b); and Assessing the substrate condition leading to substrate damage as unacceptable if the current value exceeds a predetermined threshold. [4] A method of handling the substrate according to any one of claims 1 to 3, further comprising, after the application of the DC voltage has been terminated from the state of attracting the substrate: Assessing the condition based on the current value in which the substrate can be removed from the holding plate (2).

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