DEVICE AND METHOD FOR ELECTROSTATIC CLAMPING OF A SUPPORT PLATE CONTAINING A DIELECTRIC MATERIAL

Abstract

TITLE OF THE INVENTION: DEVICE AND METHOD FOR ELECTROSTATIC CLAMPING OF A SUPPORT PLATE CONTAINING A DIELECTRIC MATERIAL. The device (400) for electrostatic clamping of a support plate comprising a dielectric material includes: - at least two electrodes (405, 410) configured to generate an electrostatic attractive force on the support plate and - a dynamic polarity control element (415) for each electrode, configured to control, for each electrode, the establishment of a stable state among: - a positive polarity state, - a negative polarity state and - a neutral polarity state, said control element being configured so that at least one electrode among all the electrodes is in a neutral polarity state while at least one other electrode is in a positive or negative polarity state. Figure for the abstract: Figure 4

Description

Title of the invention: DEVICE AND METHOD FOR ELECTROSTATIC CLAMPING OF A SUPPORT PLATE CONTAINING A DIELECTRIC MATERIAL Technical field of the invention

[0001] The present invention relates to a device and a method for electrostatic clamping of a support plate comprising a dielectric material. It is applicable, in particular, to the field of semiconductor circuit manufacturing. State of the art

[0002] The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section constitutes prior art simply because of its inclusion in this section.

[0003] In the semiconductor industry, support wafers are used on which microelectronic circuits are assembled. Considering the very small size of these circuits, the stability of the support wafers during the assembly process is critical.

[0004] Beyond this stability constraint, considering that the assembly process is carried out under vacuum, the wafers also function as thermal conductors, either dissipating the heat generated by, or conversely supplying heat to, the assembly of the semiconductor circuit, and transferring it to a heat transfer gas. Since this heat transfer gas must not break the vacuum, and the wafer is by definition removable, it is essential that the wafer does not allow the gas to leak.

[0005] For this reason, several approaches have been implemented to clamp these support plates. Such clamping is achieved using a chuck.

[0006] Such a chuck has several advantages: - to allow the introduction of a thermal coupling gas between the mandrel and the wafer, - to orient the wafer (for example to tilt the wafer in the case of an ion beam implantation process), - flatten the wafer (when the wafer is convex or twisted) to obtain better thermal coupling, better deposition or better accuracy for high aspect ratio profiles and - to support the initial force applied to the wafer due to acceleration and deceleration during wafer transfer, during wafer scanning or any other movement performed on the wafer.

[0007] A certain category of chucks is called electrostatic chucks, as opposed to mechanical chucks (of the collet type, for example). Such electrostatic chucks have the following advantages:

[0008] - no mechanical contact is made on the treated face of the insert, thus avoiding to generate scratching, particles or contamination,

[0009] - no masking or edge effect is induced by the presence of mechanical clamps near the treated side of the plate and

[0010] - the implemented plate is flatter than in the case of plates for mechanical chucks that require the insert to be curved in order to function.

[0011] An electrostatic mandrel comprises an electrically insulating body (typically made of ceramic such as Al₂O₃, A₂N, or BN) and at least one electrode made of an electrically conductive material (for example, W, Mo, Pt, Pd, Ag, or graphite) covered by a dielectric material. The upper surface of this dielectric material can be arranged to correspond to a particular topography (called "dimple," "mesa," "embossing," etc.) in order to limit the contact areas between the mandrel and the insert and to improve the pressure distribution of the thermal coupling gas. Such an electrostatic mandrel is shown in [Fig. 1]. Such a mandrel 100 comprises: - an electrically insulating layer 105, - at least one electrode 110, and - a dielectric material 115.

[0012] When a wafer is placed on the mandrel, the corresponding electrical system can be understood as an electrical circuit consisting of capacitors. When a voltage is applied to the electrodes, an electrostatic field appears between the electrodes and the wafer, leading to a displacement of charges in the wafer and the appearance of an electrostatic force according to Coulomb's law. Such a correspondence is represented in [Fig. 2].

[0013] This electrostatic force presses the insert against the mandrel. Such an assembly is shown in [Fig. 3]. Such an assembly thus comprises: - a vacuum chamber 301, - an insert 305, - a thermal coupling gas layer 310, - at least one electrode, 110 and 111, - a dielectric material 115, - an electrically insulating layer 105 and - a pedestal 310.

[0014] Such electrostatic chucks have a number of weaknesses which the present invention remedies.

[0015] Firstly, the clamping force “F” generated by the electrostatic field is relatively weak.

[0016] The clamping pressure can generally be modeled by the following equation:

[0017] p * tightening c ^2

[0018] Where £ corresponds to the relative permissiveness of the dielectric, V to the clamping voltage (electrical potential difference between the plate and the electrode) and d to the distance between the plate and the electrode.

[0019] To increase the clamping pressure, it is possible to increase the clamping tension or reduce the thickness of the dielectric material. However, increasing the clamping tension leads to a risk of sticking, dielectric collapse, damage to the back face of the insert and a reduction in the mean time before failure (MBTF), which is a measure of industrial performance.

[0020] In the remainder of this document, it is assumed that the clamping pressure is already optimized for the use case considered according to the type of electric chuck (dimensions, material, dimensions) with the exception of the electrode design.

[0021] We therefore consider that P tightening is a constant and that V = V tightening = Vmax.

[0022] Thus, firstly, in current systems, one of the challenges is to maximize the clamping force for a given clamping pressure (and, therefore, for a given clamping tension).

[0023] Secondly, because dielectric materials are not perfect and, more generally, as electrical resistance (or local resistivity) is not infinite, sticking phenomena occur. Such phenomena indicate that residual clamping pressure remains even though the clamping system has returned to a physical state in which the clamping pressure is theoretically zero.

[0024] One consequence of this bonding phenomenon can be the shifting of the insert, which can lead to insert loss during transfer operations. These bonding phenomena can also lead to insert breakage when the bond is too strong to lift the insert during the unloading operation, or because the insert shifting causes the insert to fall.

[0025] The sticking phenomenon is a major problem that can lead to a decrease in productivity, loss of wafers and the shutdown of production tools.

[0026] Thus, secondly, in current systems, one of the challenges is to reduce the phenomenon of sticking without losing clamping force.

[0027] Thirdly, a constraint related to electrostatic clamping is the electrical charge of a plate resulting from the clamping.

[0028] Consider a wafer that is not connected to ground or to a reference voltage, regardless of the reference and the connection (grounding pin, conductive layer surrounding the wafer, plasma resulting from the assembly process). In such a case, the wafer's potential is said to be floating.

[0029] As the wafer is coupled with the electrodes of the mandrel, the wafer potential floats at a value Vpiaquette with:

[0030] _ 'Lcivi ^palette — £

[0031] Where Vi is the voltage of electrode i and Ci is the capacitance formed by electrode i and the portion of the plate that faces electrode i.

[0032] For reasons of simplification, we consider the case in which all the capacitances Ci are identical (for example, if all the electrodes have the same surface area and if the dielectric layers between the electrodes and the plate are identical), but the principle remains the same if the capacitances are not equal.

[0033] In such a case, if for any i, Ci is a constant, then:

[0034] _ brochure — “

[0035] Where n is the number of electrodes.

[0036] If Y is not constant, then the potential of the platelet is not constant. i >

[0037] If the wafer is truly floating, then it floats at this voltage, which can have an impact on the repeatability of the assembly process (an accumulation of charges in the wafer is undesirable).

[0038] If the wafer is connected to an external reference voltage, this induces a transfer of charges from the wafer and this reference, but such a transfer of charge is likely to damage the patterns already assembled on the wafer.

[0039] Thus, thirdly, in current systems, one of the challenges is to reduce the voltage of the wafer resulting from electrostatic coupling.

[0040] In current systems, to solve the problem of the occurrence of the sticking phenomenon, different approaches have been proposed to promote the removal of residual charges after the insert has been loosened and before the removal of the insert.

[0041] Some of these methods involve electrically connecting the pad to the ground by means of mechanical contact with an electrically conductive object or via a plasma gun. Such approaches are illustrated, in particular, in US patent application US2011036990.

[0042] Some consist of applying a specific loosening sequence in which the current, voltage amplitude, frequency and / or the activation cycle The work varies over time. Such approaches are illustrated in particular in US patent US6236555.

[0043] All these approaches are based on the fact that there is a sufficient accumulation of charges in the wafer, the dielectric and / or the interface between the wafer and the mandrel to generate bonding.

[0044] To prevent, reduce or delay the occurrence of the sticking phenomenon, a solution that is mostly implemented today consists of reversing the polarity of the electrodes.

[0045] Typically, as soon as the clamping method is monopolar or multipolar, the most common practice is to reverse the polarity of the clamping tension for each new pad. Such an approach is described, for example, in European patent application EP0294556.

[0046] This practice is not an ideal solution: while it is beneficial to limit the slow, long-term shift in the electrical state of the mandrel-dielectric, insert by insert, from the perspective of a single insert, the electrical state during clamping is static. Therefore, there is no reduction in accumulated charges for an individual insert. This can be a problem, particularly for long processes or for low-resistivity dielectrics, such as those used in high-temperature applications, for example.

[0047] Another approach, rather than aiming at the removal of residual charges, consists in preventing this accumulation of charge.

[0048] Since this charge accumulation is related to the V / d ratio (as seen previously) and to time, and given that the value of V / d is imposed to obtain the greatest clamping force, the concept behind these solutions is to reduce the clamping time for a given electrical state. This is achieved by replacing the constant clamping voltage Vi with an alternating signal. This approach is described, in particular, in U.S. patent application US2005052817 and in international patent application WO9411944.

[0049] The benefits of this approach are to stress the dielectric layer as well as the interface between the dielectric, the wafer and the dielectric for a short period of time by a voltage difference of a given polarity and then, for a similar period of time, by a voltage difference of the reversed polarity.

[0050] Nevertheless, using a "direct" polarity reversal sequence has a major weakness with regard to the minimum average clamping force during the entire clamping sequence and / or with regard to the circulation of charges towards the insert.

[0051] The benefits of this approach are exemplified below for five different cases, corresponding to electrostatic chucks comprising one, two, three, four and six electrodes. These examples are considered for an alternating profile of the square type (i.e., whose polarity reverses abruptly, in the most instantaneous way possible), as represented in [Fig.3], as described in international patent application WO9411944.

[0052] The plate is also considered to be floating or connected to ground.

[0053] The capacitance formed by each electrical element with the portion of the plate facing it is considered to be identical for all electrodes. Each electrode is considered to be supplied with the same voltage in absolute value.

[0054] To measure the impact of the different cases on the minimum clamping force, the clamping tension is considered to be already optimized / maximized for the electrostatic chuck. For each case, the minimum clamping force is compared to the maximum clamping force F calculated when all electrodes are energized and when the insert is referenced to 0V, providing a clamping pressure "Pserrage".

[0055] In the first case, corresponding to a monopolar chuck: - if the plate is not connected to a reference voltage, the plate floats at the same voltage as the electrode, leading to a lack of clamping and significant charge transfer, and - if the circuit board is connected to a reference voltage: - if this reference voltage "Vref" is lower than the maximum AC voltage "Vac", there is a point where the electrode has the same voltage as the reference voltage during polarity reversal, leading to a lack of clamping, - if this reference voltage is higher than the Vac voltage (or lower than the minimum voltage), the average voltage difference is not zero, leading to charge migration - furthermore, the wafer undergoes significant fluctuations in clamping force, which can generate significant defects on the underside of the wafer as well as the emission of particles, - moreover, the clamping tension is very low: because Vserrage / d is already optimized such that Vserrage = Vref + Vac (for Vref > Vac), then the minimum clamping force is Vmin = Vref-Vac, corresponding to a value of little interest to competent people in the field.

[0056] In the second case, corresponding to a bipolar chuck: - If the polarity of electrodes 1 and 2 is reversed simultaneously, there is a point where no voltage flows through the two electrodes, leading to a lack of clamping. - if the polarity of electrodes 1 and 2 is not reversed simultaneously, there is a moment during the tightening cycle in which the two electrodes present the voltage Vserrage: - If the plaque is not referenced, the plaque is lost. - if the insert is referenced, it is not lost but the theoretical floating tension of the insert moves from +Vserrage to -Vserrage, leading to a significant charge transfer to the insert - moreover, the dielectric above an electrode is stressed to a value equal to 2 x Vserrage, which can lead to a critical malfunction of the chuck - finally, when an electrode is at OV, the actual clamping force corresponds to half of the maximum force of the desired clamping force: Fmin = Fserrage / 2.

[0057] In the third case, corresponding to a three-pole chuck: - in the case where the electrodes are reversed at different times: - when one of the three electrodes is at 0V, the clamping force is at two-thirds of the maximum clamping force, - the theoretical floating voltage of the plate varies from +1 / 3 of Vserrage to -1 / 3 of Vserrage, leading to a significant charge transfer to the plate if this plate is referenced, - if the plaque is not referenced: - The wafer voltage varies from +1 / 3 of Vserrage to -1 / 3 of Vserrage, which can be a significant problem (for ion implementation, for example). Furthermore, the voltage difference between the electrode and the wafer is 4 / 3 of Vserrage, i.e., one-third more than the optimized Vserrage voltage, leading to the need to implement an adapted Vserrage voltage corresponding to 75% of the preferred Vserrage voltage. - the maximum clamping force corresponds to Fmin = 2 / 3 x ¾ Fserrage = % Fserrage when an electrode is at 0V, - In the case where two electrodes are reversed simultaneously, in addition to the problems identified above, the clamping force Fmin corresponds to half the theoretical clamping force Fserrage if the insert is referenced; otherwise, the insert is lost.

[0058] In the fourth case, corresponding to a four-pole chuck: - when the polarity of the electrodes is reversed in pairs: - The theoretical float voltage of the wafer is fixed at 0V, such that there is no difference between referenced and unreferenced wafer voltages, - when a pair of electrodes is at 0V, the actual clamping force Fmin is half the theoretical clamping force Fserrage, - when the polarity of the electrodes is not reversed in pairs: - there is a moment in which three electrodes share the same polarity, leading to an evolution of the theoretical float voltage of the plate between + 1 / 2 and -1 / 2 Vserrage, - if the plate is referenced, the minimum clamping force during polarity reversal corresponds to Fmin = 0.75 x Fserrage, - if the plaque is not referenced: - the minimum clamping force when three electrodes share the same polarity corresponds to Fmin = 0.75 x Fserrage, - In addition, the voltage difference between the electrode and the plate will be 1.5 Vserrage, i.e. 50% more than the optimized Vserrage value, which could lead to damage to the system and therefore to an adaptation of the clamping voltage to 2 / 3 of Vserrage, leading to obtaining a minimum clamping force of Fmin = 0.75 x 2 / 3 Fserrage = 0.5 Fserrage.

[0059] In the fifth case, corresponding to a hexapolar chuck: - when the polarity of the electrodes is reversed in pairs (case described in international patent application WO9411944): - the theoretical floating voltage of the wafer remains stable at 0V and - when a pair of electrodes is at 0V, the clamping force corresponds to 2 / 3 of the maximum clamping force, - when the polarity of the electrodes is not reversed in pairs: - there is a moment in which four electrodes share the same polarity, leading to an evolution of the theoretical float voltage of the plate between +1 / 3 and -1 / 3 Vserrage, - if the plate is referenced, the minimum clamping force during polarity reversal corresponds to Fmin = 0.83 x Fserrage, and the plate is traversed by a significant current, - if the plaque is not referenced: - the minimum clamping force when three electrodes share the same polarity corresponds to Fmin = 0.81 x Fserrage, - moreover, the voltage difference between the electrode and the plate will be 1.5 Vserrage, i.e. 50% more than the optimized Vserrage value, which could lead to damage to the system and therefore to an adaptation of the clamping voltage to 2 / 3 of Vserrage, leading to obtaining a minimum clamping force of Fmin = 0.81 x 0.75 Fserrage = 0.61 Fserrage.

[0060] Thus, there is no solution which satisfies the previously stated constraints satisfactorily. Summary of the invention

[0061] The present invention aims to remedy all or part of these drawbacks.

[0062] To this end, according to a first aspect, the present invention relates to an electrostatic clamping device for a support plate comprising a dielectric material, which comprises: - at least two electrodes configured to generate an electrostatic attractive force on the support plate and - a dynamic polarity control device for each electrode, configured to control, for each electrode, the establishment of a stable state among: - a state of positive polarity, - a state of negative polarity and - a neutral polarity state, said control element being configured so that at least one electrode among the set of electrodes is in a neutral polarity state while at least one other electrode is in a positive or negative polarity state.

[0063] These provisions confer several advantages to the clamping device: - the clamping force is increased compared to devices with a similar number of electrodes used, - the transfer of charges to the plate is minimized, - the theoretical floating voltage of the plate is also limited and - the electrical stress on the dielectric is limited, reducing the aging of this dielectric.

[0064] Conceptually, the present invention aims to, instead of implementing a sinusoidal or square polarity reversal sequence between the powered electrodes, integrate a stable state corresponding to zero voltage (and therefore neutral polarity) into a reversal sequence.

[0065] Several use cases can thus be implemented from this general inventive concept.

[0066] Thus, in certain variants, a single electrode can be fixed at a voltage of zero volts rather than a pair (in a hexagonal configuration for example).

[0067] Polarity change profiles can vary in form, aiming in some cases to reduce or eliminate the theoretical floating voltage excursion of the packet or to reduce or eliminate the clamping force excursion.

[0068] In particular embodiments, the control element is configured to, for each electrode, control the successive establishment of a stable state among: - a first state of positive or negative polarity, - a second state of neutral polarity, then

[0069] - a third state of polarity respectively negative or positive depending on the first polarity state controlled.

[0070] In particular embodiments, the control element is configured to control the simultaneous change of state of a number of electrodes less than the total number of electrodes.

[0071] In particular embodiments, the device of the present invention comprises an odd number of electrodes greater than 1.

[0072] In particular embodiments, the device which is the subject of the present invention comprises three electrodes.

[0073] In particular embodiments, the device which is the subject of the present invention comprises five electrodes.

[0074] In particular embodiments, the control element is configured to, during a transient state of polarity change, control the voltage of each electrode in this transient state so that the sum of the products of the current through an electrode and the capacitance formed locally by the electrode-plate couple is equal to zero during the duration of the transient state.

[0075] In particular embodiments, the control element is configured to, during a transient state of polarity change, control the voltage of each electrode in this transient state so that the sum of the products of the capacitance formed locally by the electrode-plate couple and the square of the voltage difference between the upstream and downstream stable states of the transient state is equal to a constant during the duration of the transient state.

[0076] In particular embodiments, the variation of voltage and / or current during a transient state is limited to a predetermined limit value.

[0077] In particular embodiments, the control element is configured to command, for at least two electrodes, the execution of a polarization sequence according to an identical sequencing pattern.

[0078] In particular embodiments, the control element is configured to control, for at least one electrode, the execution of a periodic polarization sequence.

[0079] In particular embodiments, the control element is configured to control, for at least one electrode, the execution of a polarization sequence in which the duration of at least two stable states is identical.

[0080] In particular embodiments, the control element is configured to control, for at least one electrode, the execution of a polarization sequence in which the duration of at least two stable states is identical.

[0081] In particular embodiments, the control element is configured to command, successively to different neighboring electrodes, the establishment of a stable state of neutral polarity.

[0082] In particular embodiments, the control element is configured to command, successively to different non-neighboring electrodes, the establishment of a stable state of neutral polarity.

[0083] According to a second aspect, the present invention relates to an electrostatic clamping method for a support plate comprising a dielectric material, which comprises: - a step of generating an electrostatic attractive force by at least two electrodes on the support plate and - a dynamic polarity control step for each electrode, to control, for each electrode, the establishment of a stable state among: - a positive polarity state, - a state of negative polarity and - a state of neutral polarity, at least one electrode among the set of electrodes being established in a neutral polarity state while at least one other electrode is in a positive or negative polarity state during the dynamic polarity control step. Brief description of the figures

[0084] Other advantages, purposes and particular features of the invention will become apparent from the following non-limiting description of at least one particular embodiment of the device and method of the present invention, with reference to the accompanying drawings, in which:

[0085] [Fig. 1] schematically represents a particular embodiment of an electrostatic chuck as implemented by the present invention,

[0086] [Fig.2] schematically represents an electrical circuit equivalence of a assembly comprising an electrostatic chuck and an insert,

[0087] [Fig.3] schematically represents how a force is generated clamping based on the electrostatic forces of each electrode of an electrostatic chuck,

[0088] [Fig.4] schematically represents a particular embodiment of the device object of the present invention,

[0089] [Fig.5] represents, schematically and in the form of a flowchart, a succession of a particular step in the process that is the subject of the present invention,

[0090] [Fig.6] schematically represents a sequence of variation of stable states for an electrode,

[0091] [Fig.7] schematically represents a first sequence of state variations stable for three electrodes,

[0092] [Fig.8] schematically represents a second sequence of state variation stable for three electrodes,

[0093] [Fig.9] schematically represents a first sequence of state variation stable for six electrodes,

[0094] [Fig. 10] schematically represents a pattern of transient state variation of polarity variation, and

[0095] [Fig. 11] schematically represents three electrode support layers of electrostatic mandrels. Description of the implementation methods

[0096] The present description is given by way of non-limiting grammar, each feature of an embodiment being able to be advantageously combined with any other feature of any other embodiment.

[0097] It should be noted from the outset that the figures are not to scale.

[0098] As can be understood from reading the present description, various concepts The inventive features can be implemented by one or more methods or devices described below, several examples of which are provided herein. The actions or steps performed in implementing the method or device can be ordered in any appropriate manner. Consequently, it is possible to construct embodiments in which the actions or steps are performed in a different order than that illustrated, which may include performing certain acts simultaneously, even if they are presented as sequential acts in the illustrated embodiments.

[0099] The expression "and / or", as used in this document, shall be understood as meaning "either or both" of the elements thus joined, that is, elements that are present conjunctively in some cases and disjunctively in others. Multiple elements listed with "and / or" shall be interpreted in the same way, that is, "one or more" of the elements thus joined. Other elements may also be present, other than those specifically identified by the "and / or" clause, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, a reference to "A and / or B", when used in conjunction with an open language such as "including", may refer, in one embodiment, to A only (possibly including elements other than B); in another embodiment, to B only (possibly including elements other than A); in yet another embodiment, to A and B (possibly including other elements); etc.

[0100] As used herein in the description, "or" should be understood inclusively.

[0101] As used in this description, the expression "at least one," with reference to a list of one or more elements, is to be understood as meaning at least one element chosen from one or more elements in the list of elements, but not necessarily including at least one of each element specifically enumerated in the list of elements and not excluding any combination of elements in the list of elements. This definition also allows for the optional presence of elements other than the elements specifically identified in the list of elements to which the expression "at least one" refers, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B", or, equivalently, "at least one of A and / or B") may refer, in one embodiment, to at least one, possibly including more than one, A, without B present (and possibly including elements other than B); in another embodiment, to at least one, possibly including more than one, B, without A present (and possibly including elements other than A); in yet another embodiment, to at least one, possibly including more than one, A, and at least one, possibly including more than one, B (and possibly including other elements); etc.

[0102] In the description below, all transitive expressions such as "comprising", "including", "carrying", "having", "containing", "implying", "holding", "composed of", and others, are to be understood as open, that is, as meaning including but not limited to. Only the transitive expressions "consisting of" and "consisting essentially of" are to be understood as closed or semi-closed transitive expressions, respectively.

[0103] In this description, a "stable polarity state" is defined as a polarity state corresponding to a predetermined target state and maintained for a comparatively long time compared to a "transient polarity state" corresponding to the necessary voltage variation between two target states. In a transient polarity state, a voltage value is maintained for a short time compared to a voltage value implemented in a stable polarity state.

[0104] Figure 4, which is not to scale, shows a schematic view of one embodiment of the device 400 that is the subject of the present invention. This electrostatic clamping device 400 for a support plate comprising a dielectric material comprises:

[0105] - at least two electrodes, 405 and 410, configured to generate an attractive force electrostatic discharge on the support plate and - a dynamic polarity control device 415 for each electrode, configured to control, for each electrode, the establishment of a stable state among: - a positive polarity state, - a state of negative polarity and - a neutral polarity state, said control element being configured so that at least one electrode among the set of electrodes is in a neutral polarity state while at least one other electrode is in a positive or negative polarity state.

[0106] The electrodes, which may be two or more in number, and preferably an odd number, such as three or five, are made from any conductive material commonly used for electrostatic chuck electrodes. Such materials are widely known in the field of electrical chucks and are not described here. Similarly, variations in the structure and dimensions of the electrodes are widely known in the field of electrostatic chucks.

[0107] For the present invention, any structure and any size of electrode can be implemented.

[0108] The objective of the electrodes is to achieve a clamping force on the plate, as illustrated opposite [Fig.3].

[0109] Although the other ordinary components of an electrostatic mandrel are not shown in [Fig. 4], their presence can be implicitly deduced from the content of Figures 1, 2, and 3. [Fig. 4] shows an electrostatic mandrel viewed from above, and the relative positioning of the various electrodes is clearly indicated. [Fig. 11] shows further variations in the layer of electrically insulating material that supports the electrodes and allows the passage of thermal coupling gas.

[0110] With regard to [Fig. 4], the electrostatic mandrel shown comprises five electrodes, 405, 410, 420, 425, and 430. All the electrodes may be identical. In some variants, at least one electrode has a surface area with dimensions different from at least one other electrode. In some variants, at least one electrode is made of a material different from at least one other electrode.

[0111] Similarly, a dielectric material separating the plate from the electrodes can be homogeneous with respect to each electrode or have distinct local characteristics.

[0112] Similarly, each electrode can be supplied with the same electrical voltage or at least one electrical voltage used for at least one electrode can be different from at least one other electrical voltage used for at least one other electrode.

[0113] The control unit 415 corresponds, for example, to a programmable logic controller (PLC) or a microcontroller or microprocessor configured to execute a set of computer instructions corresponding to a software program, said software comprising instructions for controlling the variation of the voltage polarity of at least one electrode.

[0114] The exact nature of the control organ 415 is widely known in the field of semiconductor manufacturing and this nature is not limiting for the implementation of the present invention.

[0115] The control element 415 is defined by its functional role, this role consisting at a minimum of organizing the variation of voltage polarity for the electrodes so as to respond to the different constraints mentioned in the discussion of the prior art.

[0116] Thus, the control unit 415 is configured to control, for each electrode, a voltage application corresponding to +Vserrage, 0V or -Vserrage for a given electrode.

[0117] Preferably, the control member 415 is configured to control an evolution according to a predetermined tightening sequence 600 corresponding to a succession of variations in the voltage of an electrode, as shown in [Fig. 6]. Such a repeatable sequence corresponds, for example, to: - a positive polarity state, - a neutral polarity state, - a negative polarity state and then - a neutral polarity state.

[0118] Such a sequence can be carried out periodically, at a frequency, for example of 50Hz, 1Hz, 0.1Hz or 0.016Hz (corresponding to a period of one minute).

[0119] In [Fig.7], we observe the stacking of 600 sequences as illustrated in [Fig.6] and applied in a phase-shifted manner to three electrodes. In this configuration, at any given instant, two electrodes are supplied with reversed polarity while one electrode is not supplied.

[0120] In [Fig. 7], we observe the stacking of variants of 600 sequences as illustrated in [Fig. 6] and applied in a phase-shifted manner to three electrodes. In this configuration, the neutral polarity state is of shorter duration than the other polarity states.

[0121] Thus, in particular embodiments, the control member 415 is configured to, for each electrode, control the successive establishment of a stable state among: - a first state of positive or negative polarity, - a second state of neutral polarity, then - a third state of polarity respectively negative or positive depending on the first polarity state commanded.

[0122] In particular embodiments, such as that shown in [Fig.4], the device 400 comprises five electrodes sequentially brought to a neutral polarity state. Such a bringing to a neutral polarity state can be organized step by step, i.e. in the order of electrodes 405, 410, 420, 425 then 430, or in a star pattern, i.e. by skipping one electrode at a time, corresponding to the order of electrodes 405, 420, 430, 410 and 425.

[0123] Fig. 9 represents the realization of different variation sequences for a device comprising six electrodes.

[0124] In particular embodiments, the control member 415 is configured to control the simultaneous change of state of a number of electrodes less than the total number of electrodes.

[0125] This number of electrodes changing state is, for example, an even number. This number of electrodes can correspond to all electrodes except one.

[0126] In particular embodiments, the control member 415 is configured to, during a transient state of polarity change, control the voltage of each electrode in this transient state so that the sum of the products of the current through an electrode (corresponding to the theoretical float voltage of the paddle) and the capacitance formed locally by the electrode-plate couple is equal to zero during the duration of the transient state.

[0127] This particular embodiment is represented by the following equation:

[0128] £.CV=0

[0129] In particular embodiments, the following equation is verified only for two electrodes changing polarity simultaneously:

[0130]

[0131] In variants of these particular embodiments, the other electrodes remain at the same voltage during the change of polarity of the two electrodes.

[0132] In variants of these particular embodiments, the voltage of the others is optimized to maximize the minimum clamping force during the change of polarity of the two electrodes.

[0133] In particular embodiments, the control member 415 is configured to, during a transient state of polarity change, control the voltage of each electrode in this transient state so that the sum of the products of the capacitance formed locally by the electrode-plate couple and the square of the voltage difference between the upstream and downstream stable states of the transient state is equal to a constant during the duration of the transient state.

[0134] This particular embodiment is represented by the following equation:

[0135] ££.7 V2 = constant

[0136] In particular embodiments, the following equation is verified only for two electrodes changing polarity simultaneously:

[0137] £,Cv2; = constant ll

[0138] In variants of these particular embodiments, the other electrodes remain at the same voltage during the change of polarity of the two electrodes.

[0139] In variants of these particular embodiments, the voltage of the others is optimized to, during the change of polarity of the two electrodes, reduce the floating voltage excursion of the plate.

[0140] In particular embodiments, the variation of voltage and / or current during a transient state is limited to a predetermined limit value.

[0141] Thus, as can be understood, in variants, the voltage change profile of a transient state can be linear or not and over a more or less long determined duration.

[0142] In [Fig.10], we observe different corresponding variation profiles: - to a linear variation, - to a linear variation for which the voltage of the electrode not changing state is adapted so as to minimize the theoretical floating voltage of the wafer and - to four limited variations, according to different parameters, in the maximum speed of voltage variation to avoid damaging the system.

[0143] Figure 5 schematically illustrates a succession of specific steps in implementing the method 500, which is the subject of the present invention. This method 500 for electrostatic clamping of a support plate comprising a dielectric material comprises: - a step 505 of generating an electrostatic attractive force by at least two electrodes on the support plate and - a step 510 for dynamically controlling the polarity of each electrode, to control, for each electrode, the establishment of a stable state among: - a state of positive polarity, - a state of negative polarity and - a state of neutral polarity, at least one electrode among the set of electrodes being established in a neutral polarity state while at least one other electrode is in a positive or negative polarity state during the dynamic polarity control step.

Claims

Demands

1. Electrostatic clamping device (400) for a support plate comprising a dielectric material, characterized in that it comprises: - at least two electrodes (405, 410) configured to generate an electrostatic attractive force on the support plate and - a dynamic polarity control element (415) for each electrode, configured to control, for each electrode, the establishment of a stable state among: - a positive polarity state, - a negative polarity state and - a neutral polarity state, said control element being configured so that at least one electrode among all the electrodes is in a neutral polarity state while at least one other electrode is in a positive or negative polarity state.

2. Device (400) according to claim 1, wherein the control member (415) is configured to, for each electrode, control the successive establishment of a stable state among: - a first state of positive or negative polarity, - a second state of neutral polarity, then - a third state of negative or positive polarity respectively according to the first polarity state controlled.

3. Device (400) according to any one of claim 1 or 2, wherein the control member is configured to control the simultaneous change of state of a number of electrodes less than the total number of electrodes.

4. Device (400) according to any one of claims 1 to 3, which comprises an odd number of electrodes greater than 1.

5.

6. Device according to claim 4, which comprises three electrodes. Device (400) according to claim 4, which comprises five electrodes (405, 410, 415, 420, 425).

7. A device (400) according to any one of claims 1 to 6, wherein the control member (415) is configured to, during a transient state of polarity change, control the voltage across each electrode in that transient state such that the sum of the products of the current through an electrode and the capacitance formed locally by the electrode-plate pair is equal to zero during the duration of the transient state.

8. Device (400) according to any one of claims 1 to 6, wherein the control member (415) is configured to, during a transient state of polarity change, control the voltage of each electrode in that transient state such that the sum of the products of the capacitance formed locally by the electrode-plate pair and the square of the voltage difference between the upstream and downstream stable states of the transient state is equal to a constant during the duration of the transient state.

9. Device (400) according to claim 8, wherein the variation of voltage and / or current during a transient state is limited to a predetermined limit value.

10. Device (400) according to any one of claims 1 to 9, wherein the control member (415) is configured to command, for at least two electrodes, the execution of a polarization sequence according to an identical sequencing pattern.

11. Device (400) according to any one of claims 1 to 10, wherein the control member (415) is configured to command, for at least one electrode, the execution of a periodic polarization sequence.

12. Device (400) according to any one of claims 1 to 11, wherein the control member (415) is configured to control, for at least one electrode, the execution of a polarization sequence in which the duration of at least two stable states is identical.

13. Device (400) according to any one of claims 1 to 12, wherein the control member (415) is configured to control, for at least one electrode, the execution of a polarization sequence in which the duration of at least two stable states is identical.

14. Device (400) according to any one of claims 1 to 13, wherein the control member (415) is configured to command, successively to different neighboring electrodes, the establishment of a stable state of neutral polarity.

15. Device (400) according to any one of claims 1 to 13, wherein the control member (415) is configured to command, successively to different non-neighboring electrodes, the establishment of a stable state of neutral polarity.

16. Method (500) for electrostatic clamping of a support plate comprising a dielectric material, characterized in that it comprises: - a step (505) of generating an electrostatic attractive force by at least two electrodes on the support plate and - a step (510) of dynamically controlling the polarity of each electrode, to control, for each electrode, the establishment of a stable state among: - a state of positive polarity, - a state of negative polarity and - a state of neutral polarity, at least one electrode among all the electrodes being established in a state of neutral polarity while at least one other electrode is in a state of positive or negative polarity during the step of dynamic polarity control.

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