Apparatus and method for reducing substrate thickness and surface roughness

Abstract

To provide precise control of RST and thickness variation for surfaces of substrates which exhibit incoming non-uniformity from thinning processes.SOLUTION: An apparatus comprises: a plasma chamber; a plasma generation device; a substrate support disposed within the plasma chamber; one gas inlet for introducing gas or gas mixture into the plasma chamber; a plasma-controlling structure configured to control the distribution of plasma; and a controller. The controller is configured to: generate the plasma within the plasma chamber from the gas or gas mixture; receive a measured variation in a thickness of a substrate, a measured average substrate thickness, a target variation in the thickness of the substrate and a target average substrate thickness; and generate an etch routine that provides the target variation in the thickness of the substrate and a target average substrate thickness on the basis of the measured variation in the thickness and the measured average substrate thickness.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for thinning a substrate and reducing surface roughness.The present invention also relates to a method for thinning a substrate. [Background technology]

[0002] The technical and economic challenges of classical two-dimensional "Moore's Law" scaling are increasing for advanced technology nodes, e.g., nodes below 5 nm. As a result, greater consideration is being given to three-dimensional heterogeneous integration schemes, where dies are attached together in an integrated package to provide improved system performance. In many cases, these 3D schemes require that the thickness of the dies be reduced, or typically thinned from an original wafer thickness of about 775 μm to a thickness of less than 100 μm, to facilitate integration into the heterogeneous package. For example, average substrate thicknesses of less than 5 μm are being considered for 3D heterogeneous integration schemes. Although semiconductor thinning is an established technology, such reduction in die thickness presents new challenges that must be addressed to make these integration schemes commercially viable.

[0003] Conventional thinning of semiconductor wafers after device fabrication is typically accomplished by two main processes. First, the thickness of the semiconductor wafer is reduced by grinding the backside of the semiconductor wafer (i.e., the side of the wafer that is not processed to form devices) to remove the bulk of the unwanted semiconductor material. Second, the semiconductor wafer is then subjected to chemical mechanical polishing (CMP) to remove a few microns of material, reduce the surface roughness of the ground wafer, or smooth the ground wafer. These thinning methods are potentially followed by wet etching and / or plasma etching steps to relieve stresses in the wafer. Each of these steps typically removes a smaller amount of material to achieve a smoother and / or more uniform surface with reduced surface roughness. The thickness variation across the wafer, or the difference between the thickest and thinnest points of the wafer, is often defined in terms of total thickness variation (TTV), while the average (or mean) wafer thickness is specified as the residual silicon thickness (RST). However, the TTV is determined by the difference between the most prominent or thickest point of a substate and the most recessed or thinnest point of the substrate. Thus, TTV can only reflect the extremes of thickness variation, and not the distribution or spread of thickness variation across the substrate. A low TTV value is expected to correspond to a low variation in thickness across the substrate, while a high TTV value is not illustrative of the thickness variation of the substrate as a whole. For example, a substrate may have portions with significant local variations in substrate thickness, such as through large peaks and valleys on the substrate surface, while the remainder of the substrate is quite uniform. Although such a substrate has a high TTV value, this does not represent the distribution of thickness variation across the substrate.

[0004] Fusion or hybrid bonding schemes for die-to-wafer (D2W) and wafer-to-wafer (W2W) attachment require a highly uniform surface with low TTV and very low defects. For example, when sub-500 nm interconnects are required for backside power delivery, it is expected that sub-micron diameter through-silicon vias (TSVs) will be required. This imposes practical limitations on the final RST and TTV of the thinned substrate in order to maintain a practical aspect ratio for the TSVs when the final wafer thickness is reduced to around 1 μm.

[0005] Conventional thinning processes require improvement to meet the needs of these new applications. For example, if a CMPed wafer has a TTV of 7 μm and a thickness of 30 μm, but a target TTV of 1 μm for a wafer with a RST of 5 μm, a significant change in the relative thickness uniformity or thickness of the substrate is required. Currently, such a change in the relative thickness uniformity of the substrate cannot be achieved by grinding and CMP, either alone or in combination. Thus, a process is needed to reduce the surface roughness of the surface of the substrate that can achieve these lower target TTV and RST values.

[0006] Variability in TTV and RST non-uniformity from grinding and CMP tools is also a practical consideration, as the consumables in these systems change over time, and thus the resulting profiles of substrates subjected to these thinning methods change over time. Any subsequent smoothing steps must therefore account for these variations. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-110217 A Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, what is needed is a smoothing process that can provide precise control of RST and thickness variations for a surface of a substrate that exhibits non-uniformities from the thinning process that are substantially greater than would be acceptable for a target average substrate thickness. [Means for solving the problem]

[0009] The present invention, in at least some of its embodiments, seeks to address at least some of the problems, desires and needs set forth above.

[0010] According to a first aspect of the present invention there is provided an apparatus for thinning a substrate and reducing surface roughness comprising: Plasma chamber; a plasma generating device for maintaining a plasma in the plasma chamber; a substrate support disposed within the plasma chamber for supporting the substrate; at least one gas inlet for introducing a gas or gas mixture into the plasma chamber; at least one plasma control structure configured to control a distribution of plasma within the plasma chamber; controller. The controller is generating a plasma in a plasma chamber from a gas or gas mixture; receiving a measured variation in substrate thickness, a measured average substrate thickness, a target variation in substrate thickness, and a target average substrate thickness; generating a generated etch routine that provides a target variation in thickness of the substrate and a target average substrate thickness based on the measured thickness variation and the measured average substrate thickness; Based on the generated etch routine, controlling at least one plasma control structure within the plasma chamber in accordance with the generated etch routine.

[0011] The inventors have found that controlling the plasma distribution using at least one plasma control structure, such as a movable annular ring (typically referred to as a uniformity ring), has the most significant effect on the radial distribution of the plasma generated in the plasma chamber from any of the most frequently adjusted etching parameters. This means that a controller configured to control at least one plasma control structure in the plasma chamber according to a generated etching routine while a plasma is generated in the plasma chamber can provide an unprecedented level of control over the etching of the substrate, which can take into account existing thickness variations of the substrate and provide precise control of the average substrate thickness and substrate thickness variations.

[0012] The controller may be configured to control at least one of a position, an orientation, or a configuration of the at least one plasma control structure to control a distribution of the plasma in the plasma chamber.

[0013] The at least one plasma-control structure may include at least one annular ring structure. The at least one annular ring structure may be movable along an axis perpendicular to the substrate support. The at least one annular ring structure may include a uniformity ring. The annular ring structure may include a wafer edge protection (WEP) structure. The at least one annular ring structure may include one or more combinations of uniformity rings and WEP structures.

[0014] The substrate support may include a conductive structure. The substrate support may comprise a dielectric electrostatic chuck (ESC). Alternatively, the substrate support may include a metal platen. The substrate support is configured to be supplied with an RF electrical signal having RF bias power from a suitable power source. The RF bias power may have a frequency of 2-20 MHz, preferably 13.56 MHz.

[0015] The plasma generator can be an inductively coupled plasma generator. The controller can be configured to control operation of at least one of the at least one gas inlet, the plasma generator, the substrate support, and the power supply.

[0016] According to a second aspect of the present invention there is provided a method for thinning a substrate and reducing surface roughness, the method comprising the steps of: measuring a variation in substrate thickness and an average substrate thickness to provide a measured variation in substrate thickness and a measured average substrate thickness; defining a target variation in substrate thickness and a target average substrate thickness; generating a generated etch routine, the generated etch routine configured to etch the generated etch profile onto a substrate to achieve a target variation in thickness of the substrate and a target average substrate thickness; loading a substrate into a plasma chamber of a plasma etching apparatus and positioning the substrate on a substrate support; Introducing a gas or gas mixture into the plasma chamber through at least one gas inlet; generating a plasma from a gas or gas mixture in a plasma chamber using a plasma generating device; · controlling a plasma in the plasma chamber using the controller to etch the substrate according to the generated etching routine to generate a smoothed substrate.

[0017] The step of controlling the plasma in the plasma chamber using the controller includes the controller controlling at least one plasma control structure in the plasma chamber according to the generated etch routine to achieve a target variation in substrate thickness and a target average substrate thickness, the at least one plasma control structure configured to control a distribution of plasma in the plasma chamber.

[0018] The inventors have arrived at the present invention by generating a generating etch routine that accounts for not only a target variation in substrate thickness and a target average substrate thickness, but also existing variations in substrate thickness prior to plasma etching, and controlling at least one plasma control structure in a plasma chamber in accordance with the generated etch routine. Substrates can be etched in a manner that significantly increases the uniformity of the etched substrate over known methods, while providing high precision over final average substrate thickness and uniformity.

[0019] The portion of the substrate that is etched by the plasma generated in the plasma chamber is preferably not covered or otherwise masked by a mask layer. Preferably, the portion of the substrate that is etched by the plasma generated in the plasma chamber does not include any deposition layer or deposits on the surface of the substrate or have any features formed on the surface of the portion of the substrate.

[0020] Controlling the plasma in the plasma chamber may include controlling at least one of a position, an orientation, and a configuration of at least one plasma control structure. The at least one plasma control structure may include at least one annular ring structure. The at least one annular ring structure may be movable along an axis perpendicular to the substrate support. During controlling the plasma in the plasma chamber using the controller, the controller may control the at least one annular ring structure to move along an axis perpendicular to the substrate support.

[0021] The at least one annular ring structure may include a uniformity ring. The at least one annular ring structure may include a wafer edge protection (WEP) structure. The substrate may be a semiconductor substrate. The semiconductor substrate may be a silicon, silicon carbide or compound semiconductor substrate. The silicon substrate may be a silicon wafer.

[0022] The measured variation in thickness of the substrate may include a two-dimensional representation of the surface profile of the substrate or a three-dimensional representation of the surface profile of the substrate. The measured variation in thickness of the substrate may include a two-dimensional representation of the surface profile of the substrate. The measured variation in thickness of the substrate may include a three-dimensional representation of the surface profile of the substrate.

[0023] The step of loading the substrate into the plasma chamber may be performed prior to the steps of measuring the variation in substrate thickness and the average substrate thickness, defining the target variation in substrate thickness and the target average substrate thickness, and generating the generated etch routine, or the step of loading the substrate into the chamber may be performed after any one of the steps of measuring the variation in substrate thickness and the average substrate thickness, defining the target variation in substrate thickness and the target average substrate thickness, and generating the generated etch routine.

[0024] The step of generating the generated etch routine may include combining at least two predefined etch routines to generate the generated etch profile, each of the at least two predefined etch routines configured to etch a respective predefined etch profile onto the substrate. Each of the at least two predefined etch routines may be associated with a respective set of etch parameters implemented to achieve the respective predefined etch profile. Each set of etch parameters may include at least one of a position, an orientation, and a configuration of at least one plasma control structure within the chamber. The set of etch parameters may further include at least one of the following: the pressure in the chamber during plasma etching; and / or a flow rate of a gas or gas mixture through at least one gas inlet during plasma etching; and / or power supplied to the plasma generating device during plasma etching; and / or ·Power delivered to the substrate support during plasma etching.

[0025] The set of etching parameters may further include a temperature of the substrate.The set of etching parameters may further include a frequency of the power supplied to the plasma generator and / or the substrate support.

[0026] The at least two predefined etch routines may include a first predefined etch routine configured to etch a first predefined etch profile onto the substrate and a second predefined etch routine configured to etch a second predefined etch profile onto the substrate. And, the generated etch routine includes a combination of the first predefined etch routine and the second predefined etch routine such that a set of etch parameters associated with the generated etch routine is a combination of a first set of etch parameters associated with the first predefined etch routine and a second set of etch parameters associated with the second predefined etch routine. The at least two predefined etch routines may include two or more predefined etch routines, for example, the at least two predefined etch routines may include a first predefined etch routine, a second predefined etch routine, and a third predefined etch routine. The set of etch parameters associated with the generated etch routine is a respective combination of the respective sets of etch parameters associated with each of the respective predefined etch routines. In other words, in the above embodiment, the set of etching parameters associated with the generated etching routine is a combination of a first set of etching parameters associated with a first predetermined etch routine, a second set of etching parameters associated with a second predetermined etch routine, and a third set of etching parameters associated with a third predetermined etch routine.

[0027] In embodiments where the generated etch routine includes a first etch routine and a second etch routine, the generated etch routine can include performing the first predefined etch routine for a first duration followed by performing the second predefined etch routine for a second duration. In embodiments where the generated etch routine includes more than two etch routines, the generated etch routine can include performing each predefined etch routine for its respective duration. Each predefined etch routine, including the first predefined etch routine and the second predefined etch routine, can be performed sequentially. The second predefined etch routine can be performed immediately after the first predefined etch routine without breaking the vacuum conditions in the chamber. Alternatively, the generated etch routine can include a vacuum break between the first predefined etch routine and the second predefined etch routine.

[0028] Generating the generated etch profile may include determining, for each value of the first duration and the second duration, a predicted variation in substrate thickness following the generated etch profile and / or a predicted average substrate thickness following the generated etch profile. Then, selecting the respective value of the first duration and the second duration that corresponds to the variation in substrate thickness following the generated etch profile and / or the predicted average substrate thickness following the generated etch profile that is closest to the target variation in substrate thickness following the generated etch profile and / or the target average substrate thickness following the generated etch profile. The first duration and the second duration may be expressed as a ratio.

[0029] According to a third aspect of the present invention there is provided a method of reducing a thickness of a substrate, the method comprising at least one of the following steps: a. grinding the substrate by relative movement between the substrate and a grinding surface to remove material from the substrate; and / or b. removing material from a substrate by chemical mechanical polishing (CMP), the CMP comprising contacting the substrate with a polishing pad and a CMP composition, and creating relative motion between the polishing pad and the substrate while maintaining a portion of the CMP composition in contact with the substrate between the pad and the substrate; and further comprising the step of reducing the surface roughness of the substrate by carrying out the method of the second aspect of the invention.

[0030] The method may comprise the successive steps of grinding the substrate, removing material from the substrate by CMP and the method according to the second aspect of the invention.

[0031] Although the invention has been described above, the invention extends to any inventive combination of the features set out above or in the following description, drawings or claims. For example, any feature disclosed in relation to one aspect of the invention may be combined with any feature disclosed in relation to any of the other aspects of the invention.

[0032] Whenever reference is made herein to "comprising" or "including" and similar terms, the invention is understood to also include more restrictive terms such as "consisting of" and "consisting essentially of." [Brief description of the drawings]

[0033] [Figure 1] 4 is a flow chart of method steps according to a second aspect of the invention; [Figure 2A] 1 shows a representation of a part of an exemplary apparatus according to a first aspect of the present invention. [Figure 2B] 1 shows a representation of a part of an exemplary apparatus according to a first aspect of the present invention. [Diagram 3] 1 shows a plot of the surface profile of an exemplary silicon wafer after CMP. [Figure 4A]1 shows a plot of a first predetermined etch profile for a first predetermined etch routine. [Figure 4B] 4 shows a plot of a simulated surface profile after performing a first predetermined etching routine on the surface profile of the wafer shown in FIG. 3. [Figure 5A] 4 shows a plot of a second predetermined etch profile for a second predetermined etch routine. [Figure 5B] 4 shows a plot of a simulated surface profile after performing a second predetermined etching routine on the surface profile of the wafer shown in FIG. 3. [Figure 6] 4 shows a simulated surface profile of the surface profile shown in FIG. 3 after performing a first predetermined etch routine and a second predetermined etch routine for the same amount of time (1:1 ratio) for each of the first predetermined etch routine and the second predetermined etch routine. [Figure 7] 4 shows a plot of the projected TTV of the surface profile shown in FIG. 3 as a function of the ratio of the duration of the first predetermined etch routine to the duration of the second predetermined etch routine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] In the following description, examples were performed on an inductively coupled plasma (ICP) based SPTS Rapier (RTM) XE plasma etch tool available from SPTS Technologies Limited (Newport, South Wales, UK). However, the method of the present invention can be performed on alternative plasma etch tools, preferably other ICP-based etch tools. Although the examples use 300 mm silicon wafers, the method of the present invention may be applied to different substrate materials and geometries.

[0035] Where the same reference numbers are used in different Figures and / or embodiments, the features to which they relate correspond to substantially identical features.

[0036] A method for thinning a substrate and reducing surface roughness according to an exemplary embodiment of the present invention is shown in the flow chart of FIG. 1. The method of this embodiment is described in the context of a substrate that has undergone a prior treatment to reduce the thickness of the substrate, such as grinding and / or chemical mechanical polishing (CMP). However, the method of the exemplary embodiment may be equally applied to a substrate that does not have a prior treatment to reduce the thickness of the substrate. The portion of the substrate that is processed using the method of the exemplary embodiment is usually the backside of the substrate, and therefore typically does not have any features formed on the front side of the substrate, or any layers, such as mask layers, formed on the front side of the substrate. Typically, the substrate material that is etched is "homogeneous" in that it does not exhibit significant variations in microstructure that would etch differently upon exposure to plasma. However, the method of the exemplary embodiment of the present invention may be equally applied to "heterogeneous" substrate materials, although it is expected that there will be greater variations between the expected surface profile of the substrate after plasma etching and the actual surface profile obtained.

[0037] The method of the exemplary embodiment of the present invention may be performed in a plasma etching apparatus comprising a plasma chamber, a substrate support for supporting a substrate in the plasma chamber, at least one gas inlet for introducing a gas or gas mixture into the plasma chamber, a plasma generating device for generating plasma in the plasma chamber, a controller, and at least one plasma control structure in the plasma chamber.

[0038] In a measuring step 101, the variation in thickness of the substrate and the average substrate thickness are measured to provide a measured variation in thickness of the substrate and a measured average substrate thickness. The variation in thickness is typically measured as a line scan across at least the radius of the substrate. This is likely to be sufficient when the substrate is expected to exhibit radial symmetry in its thickness variation. However, the line scan may be performed across a larger portion of the substrate. For example, a line scan may be performed across the diameter of the substrate. This is particularly useful when the substrate is not expected to exhibit radial symmetry in its thickness variation. Multiple line scans may also be performed across multiple sections of the substrate to provide a more accurate measurement of the thickness variation. The method of measurement is also not limited to line scans and may be performed by other methods known in the art, such as optical interferometry. The measuring step 101 may be performed in a plasma etching apparatus by a measuring device controlled by a controller, and the measured variation in thickness of the substrate and the measured average substrate thickness may be stored in a memory of the controller of the plasma etching apparatus. However, the measuring step 101 may be performed by any device capable of obtaining the measured variation in thickness of the substrate and the measured average substrate thickness.

[0039] An example of a measured thickness variation is shown in FIG. 3. The thickness variation is measured by performing a series of measurements, in this case 103 measurements, over the diameter of a 300 mm wafer. As is evident from FIG. 3, the measurement of the substrate in the measurement step 101 allows not only to measure the thickness variation, i.e. the local changes on the surface of the substrate, but also the overall thickness of the substrate over the measured section. This allows the determination of an average substrate thickness, which is particularly useful when attempting to significantly reduce the thickness of the substrate or to thin the substrate, as well as when attempting to reduce the variation in the thickness or surface roughness of the substrate. Also evident from FIG. 3, the measurement of the thickness variation is not limited to the overall variation in thickness encompassed by the TTV value, but also to the distribution of the thickness variation over the substrate.

[0040] In the exemplary embodiment shown in Figure 3, the substrate is subjected to both a grinding process and a CMP process, which results in a significant reduction in the average substrate thickness at the center of the substrate (i.e., the absolute value of the radial distance is small) and a less significant reduction in the average substrate thickness at the periphery of the substrate (i.e., the absolute value of the radial distance is large). The grinding and CMP processes also result in significant variation in substrate thickness across the diameter of the substrate.

[0041] Once the variation in thickness of the substrate and the average substrate thickness are measured, a target variation in thickness of the substrate and a target average substrate thickness are defined in a definition step 102. The target variation in thickness of the substrate can be expressed in several forms. The target variation in thickness can be expressed as a total thickness variation (TTV), where it is expected that a low TTV value would correspond to a low variation in thickness across the substrate. However, the target variation in thickness can also be expressed as a representation of the distribution of the variation in thickness of the substrate. This distribution can be shown as a two-dimensional or three-dimensional representation of the surface profile of the substrate. Similarly, the target average substrate thickness can be expressed in several forms, but typically, in the manufacture of silicon wafers, the target average substrate thickness is expressed as a residual silicon thickness (RST). In the exemplary embodiment shown in FIG. 3, the TTV of the substrate is 2.8 μm and the RST is 26 μm. In the present embodiment, the target RST is 2.00 μm and the target TTV is 2.00 μm. Thus, in addition to reducing the surface roughness of the substrate (i.e., reducing the TTV value), a reduction in the average thickness of the substrate (i.e., reducing the RST) is also required.

[0042] The target variation in substrate thickness and the target average substrate thickness may be applied over the entire surface of the substrate. Alternatively, the target variation in substrate thickness and the target average substrate thickness may be applied to a subsection of the surface of the substrate. For example, in an exemplary embodiment, the target RST and target TTV are applied to the majority of the substrate, but it is desirable to have a slightly thicker region at the periphery of the substrate, also known as the edge exclusion region. The edge exclusion region of a semiconductor wafer is typically not used during device manufacturing. This is especially true when manufacturing wafers for use in fusion hybrid bonding, since particle control is critical to the success of the bonded die, and the edge of the wafer can be a significant source of particulate matter. The same principle may be true when the wafer is etched in an apparatus using a WEP structure, since the edge of the wafer is not exposed to the plasma and therefore is not etched. In an exemplary embodiment, an edge exclusion region of about 2 mm radial distance around the periphery of the wafer is desirable. The average substrate thickness, and possibly the thickness variation, in this edge exclusion region may be greater than that over the remainder of the substrate. Thus, the RST and TTV values ​​for the entire surface of the substrate are higher than the RST and TTV values ​​for the surface of the substrate that does not include this edge exclusion region. Thus, the target variation in substrate thickness and the target average substrate thickness may be defined for the entire substrate, for a region of the substrate that does not include the edge exclusion region, or even for the edge exclusion region itself.

[0043] In one embodiment, the defining step 102 may be performed in a plasma etching apparatus, and the target variation in substrate thickness and the target average substrate thickness may be stored in a memory of a controller.

[0044] In the generating step 103, a generated etch routine is generated to achieve the target variation in thickness and the target average substrate thickness of the substrate. The generated etch routine is configured to etch a generated etch profile for a substrate that will achieve the target variation in thickness and the target average substrate thickness. In other words, the generated etch routine, when implemented in a plasma etching apparatus, is configured to etch a substrate such that the substrate has a target variation in thickness and a target average substrate thickness. This is achieved by a generated etch profile, or a measure of the predicted removal of substrate material across the surface of the substrate under conditions in the plasma etching apparatus. This generated etch profile is achieved by carefully controlling conditions in the plasma etching apparatus as part of the generated etch routine, which causes preferential plasma etching of the substrate in areas that require more substrate material to be removed to meet the target average substrate thickness and the target variation in thickness, and causes inhibition of plasma etching of the substrate in areas that require less substrate material to be removed to meet the target average substrate thickness. As a result, after etching according to the generated etch routine, the substrate will have an average substrate thickness and a profile with a thickness variation that is approximately the same as the target value set in the defining step 102 of the method.

[0045] The generated etch routines can include at least one predefined etch routine, each of the at least one predefined etch routines configured to etch a predefined etch profile on the substrate. The predefined etch profile can be determined from experimental data obtained from previous plasma etches. These previous plasma etches are preferably performed on substrates similar to the substrate being processed, with standardized starting parameters to obtain the most accurate picture of the effect of the predefined etch profile. For example, the predefined etch profile can be obtained by plasma etching an unthinned silicon wafer, typically having a uniform thickness and a small TTV of about 1 μm or less. The plasma etch can be performed for a specific period of time using specific etching parameters, such as chamber pressure, applied RF power, gas mixture composition, and gas flow rates, to generate an etched surface. The profile of the etched surface can then be used as the predefined etch profile for the silicon wafer under these etching conditions.

[0046] The set of etching parameters associated with each of the at least one predetermined etching routine may include at least one of a position, an orientation, and a configuration of the at least one plasma control structure in the plasma chamber. The position of the at least one plasma control structure may be adjusted in any manner known in the art, for example, by raising and lowering the at least one plasma control structure relative to the substrate support or the entire plasma chamber. The orientation of the at least one plasma control structure may be adjusted in any manner known in the art, for example, by rotating the at least one plasma control structure about an axis. The configuration of the at least one plasma control structure may be adjusted in any manner known in the art, for example, by extending or retracting the at least one plasma control structure in the plasma chamber, or by changing a dimension. The change in the position, orientation, or configuration of the at least one plasma control structure may be effected by any known means of controlling the position, orientation, or configuration. For example, the at least one plasma control structure may be mounted on at least one actuator, and the position of the at least one plasma control structure may be adjusted by the controller by extending or retracting the actuator.

[0047] The at least one predefined etch routine may be stored in a database or other means of collating data. Once generated, the generated etch routine may also be stored in a database or other means of collating data, so that the generated etch routine can be used as a predefined etch routine for subsequent wafer processing. The generating step 103 may be performed in a plasma etching apparatus, and the generated etch routine and the associated set of etching parameters may be stored in a memory in the controller. Alternatively, the generated etch routine may be generated in a separate apparatus and introduced into the memory of the controller for control of etching of the substrate in a subsequent plasma etching step. If the generating step 103 is performed in a plasma etching apparatus, the controller may comprise a memory configured to store the database or other means of collating data with which the at least one predefined etch routine is stored. Alternatively, the database or other means of collating data including the at least one predefined etch routine may be stored in a separate storage medium and introduced into the memory of the controller for control of etching of the substrate in a subsequent plasma etching step.

[0048] The step of generating the generated etch routine may include combining at least two predefined etch routines to generate the generated etch profile. Each of the at least two predefined etch routines is configured to etch a respective predefined etch profile on the substrate, and the generated etch profile is a result of the combination of the respective predefined etch profiles. Each of the at least two predefined etch routines is associated with a respective set of etch parameters implemented to achieve the respective predefined etch profile. Each set of etch parameters may include at least one of a position, an orientation, and a configuration of at least one plasma control structure in the plasma chamber. The set of etch parameters may include a pressure in the plasma chamber during the plasma etch, a flow rate of a gas or gas mixture through at least one gas inlet during the plasma etch, a power supplied to a plasma generator during the plasma etch, a power supplied to a substrate support during the plasma etch, and may further include at least one of a temperature of the substrate, a frequency of the power supplied to the plasma generator and / or the substrate support.

[0049] In one embodiment, the at least two predefined etch routines include a first predefined etch routine configured to etch a first predefined etch profile into the substrate and a second predefined etch routine configured to etch a second predefined etch profile into the substrate, and the generated etch routine includes a combination of the first predefined etch routine and the second predefined etch routine such that a set of etch parameters associated with the generated etch routine is a combination of the first set of etch parameters associated with the first predefined etch routine and the second set of etch parameters associated with the second predefined etch routine.

[0050] The combination of the first and second predetermined etch routines may be a simultaneous combination of the two routines such that the set of etch parameters associated with the generated etch routine is an interpolation between values ​​of the first set of etch parameters associated with the first predetermined etch routine and values ​​of the second set of etch parameters associated with the second predetermined etch routine. For example, in an embodiment in which the plasma control structure is an annular ring, the first set of etch parameters includes an annular ring positioned 1 cm above the substrate support and the second set of etch parameters includes an annular ring positioned 5 cm above the substrate support. The set of etch parameters associated with the generated etch routine may include an annular ring positioned 1 cm to 5 cm above the substrate support.

[0051] Alternatively, the combination of the first and second predetermined etch routines in the generated etch routine may include performing the first predetermined etch routine for a first duration followed by performing the second predetermined etch routine for a second duration. The first predetermined etch routine may be performed for the first duration immediately prior to the second predetermined etch routine such that there is no interruption in the vacuum conditions in the chamber between the first and second predetermined etch routines. Alternatively, there may be a vacuum break between the first and second predetermined etch routines.

[0052] In an exemplary embodiment for a wafer having the profile shown in FIG. 3, a first predetermined etch routine ("A-Routine") having a corresponding first predetermined etch profile ("A-Profile") and a second predetermined etch routine ("B-Routine") having a corresponding second predetermined etch profile ("B-Profile") were selected to generate an etch routine. In the A-Routine, the plasma control structure is an annular ring, and the annular ring is configured in a "raised" position, with the annular ring positioned above the surface of the substrate support. The A-Profile is shown in FIG. 4A, with a corresponding plot of a simulated surface profile of the wafer after performing the A-Routine shown in FIG. 4B. The expected final average thickness is 2.04 μm, with an expected TTV for the entire substrate of 2.04 μm and an expected TTV for 2 mm edge exclusion regions at both ends of the substrate of 4.75 μm. As seen in FIG. 4A, the A-Profile shows a greater removal of substrate material at the periphery of the substrate, which causes a corresponding, greater decrease in thickness at the periphery of the simulated surface profile in FIG. 4B. In fact, in Figure 4B, the predicted rate of substrate material removal is so great that the substrate thickness at the periphery is predicted to be negative. In practical terms, this corresponds to a complete removal of substrate material and a corresponding reduction in the radius of the substrate. This also contributes to the predicted variation in substrate thickness, indicated by the higher TTV values ​​in the 2 mm edge exclusion region.

[0053] The B profile is shown in FIG. 5A with a corresponding plot of a simulated surface profile of a wafer after performing the B routine shown in FIG. 5B. In the B routine, the plasma control structure is an annular ring, the annular ring is configured in a "down" position, and the annular ring is positioned above the surface of the substrate support. The expected final average thickness is 1.95 μm, the expected TTV for the entire substrate is 1.95 μm, and the expected TTV for the 2 mm edge exclusion regions at both ends of the substrate is 5.86 μm. As seen in FIG. 5A, the B profile shows a reduction in the removal of substrate material at the periphery of the substrate, which causes a corresponding, smaller reduction in thickness at the periphery of the simulated surface profile in FIG. 5B.

[0054] Thus, the etch profile generated is expected to include a combination of A and B profiles between the profiles shown in Figures 4A and 5A, producing a surface profile for the wafer between the profile shown in Figure 4B and the profile shown in Figure 5B.

[0055] In one embodiment, the step 103 of generating the generated etch profile includes determining, for each value of the first duration and the second duration, a predicted variation in the thickness of the substrate following the generated etch profile and / or a predicted average substrate thickness following the generated etch profile. Then, selecting a respective value of the first duration and the second duration corresponding to the variation in the thickness of the substrate following the generated etch profile and / or a predicted average substrate thickness following the generated etch profile that is closest to the target variation in the thickness of the substrate following the generated etch profile and / or a target average substrate thickness following the generated etch profile. Preferably, the step 103 of generating the generated etch profile includes determining, for each value of the first duration and the second duration, a predicted variation in the thickness of the substrate following the generated etch profile and a predicted average substrate thickness following the generated etch profile. Then, selecting a respective value of the first duration and the second duration corresponding to the variation in the thickness of the substrate following the generated etch profile and a predicted average substrate thickness following the generated etch profile that is closest to the target variation in the thickness of the substrate following the generated etch profile and a target average substrate thickness following the generated etch profile. The first duration and the second duration can be expressed as a duration ratio. The selection process may then include determining a predicted variation in substrate thickness following the etch profile and a predicted average substrate thickness for multiple values ​​of the duration ratio, and selecting the duration ratio corresponding to the predicted variation in substrate thickness and the predicted average substrate thickness following the etch profile that most closely matches the target variation in substrate thickness and the target average substrate thickness set in the determining step.

[0056] For example, in an exemplary embodiment for a wafer having the profile shown in Figure 3, a 1:1 ratio of the A routine corresponding to Figures 4A and 4B and the B routine corresponding to Figures 5A and 5B is predicted to produce a surface profile of the substrate as shown in Figure 6. This corresponds to the substrate being etched under the A routine for a first duration, followed by etching under the B routine for a second duration, the first duration and the second duration being equal. The predicted surface profile has a predicted average substrate thickness of 2.00 μm and a predicted TTV of 2.15 μm. This meets the target average substrate thickness, but the predicted TTV is greater than the target TTV of 2.00 μm.

[0057] A set of predicted TTV values ​​for different duration ratios of the first and second predetermined profiles is shown in FIG. 7. As can be seen from FIG. 7, the lowest TTV value is obtained with a duration ratio of 4:5, i.e., the second duration is 1.25 times longer than the first duration. In this scenario, the predicted average substrate thickness is 2.00 μm and the predicted TTV is 2.08 μm. This is closer to the target variation of substrate thickness, and therefore, the 4:5 duration ratio would be selected in preference to the 1:1 duration ratio.

[0058] If the generating step 103 is performed in a plasma etching apparatus, the controller may comprise a calculation unit configured to determine, for each value of the first duration and the second duration, a predicted variation in thickness of the substrate following the generated etch profile and / or a predicted average thickness of the substrate following the generated etch profile, and select the respective value of the first duration and the second duration corresponding to the variation in thickness of the substrate following the generated etch profile and / or the predicted average substrate thickness following the generated etch profile that is closest to the target variation in thickness of the substrate following the generated etch profile and / or the target average substrate thickness following the generated etch profile.

[0059] After the generating step 103, the substrate is loaded into a plasma chamber of a plasma etching apparatus and placed on a substrate support in a loading step 104. However, if at least one of the measuring step 101, the defining step 102 or the generating step 103 is performed in a plasma etching apparatus, the loading step 104 may be performed before any of the measuring step 101, the defining step 102 or the generating step 103. In a preferred embodiment, the loading step 104 is performed prior to all of the measuring step 101, the defining step 102 and the generating step 103, and each of the measuring step 101, the defining step 102 and the generating step 103 is performed in a plasma etching apparatus. Given that the thickness of the substrate can be significantly thinned, down to the order of 1 μm, the substrate is preferably attached to a carrier wafer or other carrier, for example a carrier wafer formed of silicon or glass, to facilitate handling of the substrate. The substrate may be bonded to the carrier wafer or other carrier by an adhesive to secure the substrate.

[0060] Once the measuring step 101, the defining step 102, the generating step 103, and the loading step 104 have been performed, regardless of the order in which they are performed, a gas or gas mixture is introduced into the plasma chamber through at least one gas inlet in a gas introducing step 105. The introduced gas or gas mixture is then ignited by a plasma generating device in a generating step 106.

[0061] Once the plasma is generated, the controller controls the plasma in the plasma chamber in a control step 107 to etch the substrate according to the generated etching routine to generate a smoothed substrate. In the control step 107, the controller controls at least one plasma control structure in the plasma chamber according to the generated etching routine to achieve a target variation in substrate thickness and a target average substrate thickness, the at least one plasma control structure being configured to control the distribution of the plasma in the plasma chamber. The plasma control structure may be any physical component, at least partially within the plasma chamber, that interacts with the generated plasma to modify the etching profile of the plasma on the substrate. For example, the plasma control structure may comprise at least one annular ring structure, which may comprise a uniformity ring and / or a WEP structure, which may be movable along an axis perpendicular to the substrate support. In this case, the control step 107 may include moving the at least one annular ring structure along an axis perpendicular to the substrate support according to the generated etching routine. In an exemplary embodiment, the controller is configured to move the annular ring between an "up" position and a "down" position corresponding to the A profile and the B profile while executing the generated etching profile. Although the at least one plasma control structure is described herein primarily as a plasma control structure that can change its position, orientation, or configuration to control the plasma distribution, the at least one plasma control structure is not limited to this embodiment. For example, the at least one plasma control structure can comprise a component configured to impose a magnetic and / or electric field in the plasma chamber, such as a static conductive grid in the plasma chamber, or a stationary ring in the plasma chamber that is activated by a bias voltage, an electromagnet, or any other component known to controllably change the plasma distribution between the plasma source and the wafer surface. Each of these plasma control structures can be present individually or in combination to enable control of the plasma distribution according to an etching routine generated to achieve a target variation in substrate thickness and a target average substrate thickness.

[0062] During the control step 107, the average thickness and thickness variation of the substrate can be monitored using known measurement techniques. For example, a near infrared (NIR) interferometer can be used to measure the average thickness and thickness variation of the substrate during or at the end of the etching process to ensure that the process is performing as expected.

[0063] The generated etch profile is executed, and once the target average substrate thickness and target variation in substrate thickness are achieved, the plasma etch process may be stopped and the smoothed and thinned substrate may then be removed from the plasma etcher (step 108).

[0064] The method of the second aspect of the invention provides a much higher degree of control over the surface profile of the substrate, even when starting with a substrate having a high degree of surface roughness, and can provide a uniform substrate surface. This control is provided by the generation of a tailored generated etch profile that takes into account the initial surface of the substrate, and precise control of the etch environment within the plasma by control of at least one plasma control structure that affects the behavior of the plasma, and therefore the resulting etch profile.

[0065] The method of the second aspect of the invention may be performed on an otherwise unprocessed substrate by itself, or as part of an overall method of reducing the thickness of the substrate, as described in the third aspect of the invention. In the third aspect of the invention, the method of the second aspect of the invention may be performed after at least one of grinding the substrate to remove material from the substrate by relative movement between the substrate and a grinding surface, and / or removing material from the substrate by CMP. CMP involves contacting the substrate with a polishing pad and a CMP composition, and causing relative movement between the polishing pad and the substrate while maintaining a portion of the CMP composition in contact with the substrate between the pad and the substrate. In one embodiment, both grinding and CMP may be performed on the substrate before the method of the second aspect of the invention. In the third aspect of the invention, the method of the second aspect of the invention is used to reduce the roughness introduced during the grinding and / or CMP steps, as well as the surface roughness that was initially present, to a target value, and to reduce the average substrate thickness to a target value. This provides a much greater degree of control over the surface profile of the substrate, and can provide a uniform substrate surface, even when starting from a substrate with a high degree of surface roughness.

[0066] FIG. 2A shows a cross section of a lower plasma chamber assembly 7 of a plasma etching apparatus according to an exemplary embodiment of the invention. The plasma etching apparatus comprises a plasma chamber, at least one gas inlet for introducing a gas or gas mixture into the plasma chamber, and a plasma generating device, in this case a dual concentric ICP plasma source. In operation, a substrate 1, i.e. a wafer, to be thinned is loaded through a slot 2 and placed on a substrate support 3, which in this embodiment is an electrostatic chuck (ESC). The plasma chamber is evacuated through an opening 4. A plasma control structure 5 is disposed within the plasma chamber. In this embodiment, the plasma control structure is an annular ring structure including an annular ring, sometimes known as a uniformity ring. The annular ring 5 is disposed around the wafer 1 and can be automatically raised and lowered from the surface of the ESC. The annular ring 5 surrounds the wafer 1 and is movable along an axis perpendicular to the ESC. A dual concentric ICP plasma source (not shown) is disposed above a ceramic interface plate 6. In FIG. 2A, the annular ring 5 is disposed on the ESC. In FIG. 2B, the maximum movement of the annular ring 5 is shown, where the annular ring 5 is proximate to the interface plate 6. Adjustment of the position of the annular ring 5 is provided by an actuator controlled by a controller (not shown). The controller is configured to control the position of the annular ring 5 during plasma etching of the substrate according to the generated etch routine. To generate the generated etch routine, the controller is configured to receive a measured variation in the thickness of the substrate, a measured average substrate thickness, a target variation in the thickness of the substrate and a target average substrate thickness, and generate a generated etch routine from these data, which provides a target variation in the thickness of the substrate and a target average substrate thickness based on the measured variation in the thickness and the measured average substrate thickness. The generated etch routine may be generated in the manner described above with respect to the exemplary method of the present invention.

[0067] The controller is also configured to control at least one gas inlet, the dual concentric ICP plasma source, and the ESC in a manner known in the art. An RF electrical signal having RF power can be provided to the substrate support by a power source (not shown). The RF electrical signal can also be controlled by the controller.

[0068] Once the wafer 1 is loaded into the plasma chamber and the controller generates or receives the generated etching routine, a gas or gas mixture is introduced into the plasma chamber through at least one gas inlet and a plasma is generated from the gas or gas mixture by the dual concentric ICP sources to etch the wafer according to the generated etching routine.

[0069] Some etching applications require a WEP structure instead of or in addition to a uniformity ring to protect the edge region of the substrate from harsh plasma etching conditions. The WEP structure covers the edge region of the substrate without contacting the substrate, shielding the edge region from the plasma. For example, the WEP structure may have an inner diameter of about 297 mm (i.e., 3 mm less than the diameter of a 300 mm wafer). In this example, the WEP structure covers an edge region about 1.5 mm wide around the periphery of the wafer. The WEP structure may also be movable along an axis perpendicular to the ESC, and adjustment of the position of the WEP structure may be provided by an actuator controlled by the controller.

[0070] The annular ring structure can be made of a dielectric material, such as a ceramic material. In one embodiment, the annular ring structure can comprise a uniformity ring stacked on top of a WEP structure. However, in other embodiments, the annular ring structure can be a uniformity ring or a WEP structure. The annular ring structure can cover the edge region of the substrate and can be spaced apart from the edge region of the substrate to protect the edge region of the substrate from plasma conditions during the etching process.

[0071] The annular ring structure may have a front surface that faces (is typically exposed to) the plasma during the plasma etching process. In the illustrated embodiment, the front surface is the surface of the annular ring 5 that faces the plasma during the plasma etching process. The front surface may be formed in any particular shape. The annular ring structure may also include a back surface that faces away from the plasma during the plasma etching process. In the embodiment of FIG. 2A, the back surface of the annular ring 5 is in partial contact with the surface of the ESC 3 that supports the wafer 1. [Explanation of symbols]

[0072] 1 substrate (wafer), 2 slot, 3 substrate support (electrostatic chuck (ESC)), 4 aperture, 5 plasma control structure (annular ring).

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