Patent Application
20190351527
The following description relates to methods, devices, and apparatus for preparing abrasive surfaces, including abrasive surfaces that are useful in a pad conditioner for conditioning a chemical-mechanical-planarization pad (CMP pad) used to fabricate microelectronic device or memory substrates, such as a semiconductor or digital memory workpiece.
The electronics, microelectronics, and data storage industries rely on chemical-mechanical-planarization (CMP) techniques for preparing highly planarized or polished surfaces of in-process components of microelectronic and memory device products. Examples of these types of products are modern electronic, microelectronic, magnetic, and optical devices that include microprocessors and other integrated circuits that rely on silicon or another semiconductor material; digital (e.g., solid state and hard disk) memory devices; optical materials and devices; and various other commercial and consumer electronic items. Chemical-mechanical-planarization, as is known, is a process for planarizing or polishing a surface of a workpiece that is being processed for use as a functioning component of one of these types of products. The workpiece (a.k.a. “substrate”) can be an in-process microelectronic, semiconductor, memory storage, or optical device or substrate, among others.
For a typical CMP process, a surface of a CMP pad that contacts a workpiece must be prepared for initial use by “conditioning” the surface. A CMP pad is made of polymeric material that includes small voids or bubbles at the interior, but includes, in an original and unused condition, a thin outer layer of substantially solid polymeric material at each of the two opposed major surfaces of the pad. At a start of use of the CMP pad, the thin layer of non-porous (solid) material at the surface must be removed to expose the interior (porous) portion of the pad that is used during chemical-mechanical-planarization. To remove the thin solid exterior surface layer, a pad conditioner (or “conditioner”) is used to abrasively remove the solid material at the surface to expose the internal polymeric material having bubbles or voids.
After this initial conditioning step, the CMP pad can be used to process workpieces. Over a period of use of the CMP pad, due to wear and accumulation of materials at the surface that occur during chemical-mechanical processing, the quality of the CMP pad surface degrades or otherwise becomes less effective and must be regularly refreshed, i.e., “conditioned.” During use of the CMP pad for processing microelectronic device workpieces, the polishing pad is moved while contacting a workpiece in the presence of a slurry that contains abrasive particles and chemical materials. While used during chemical-mechanical-planarization, the surface of the CMP pad becomes worn or otherwise affected by the abrasive and chemical materials, which may accumulate at the pad surface. The result can be “pad glazing,” which reduces the effectiveness of the CMP pad surface for removing material to planarize or polish a workpiece surface. Additionally, with continued use, a surface of a CMP pad may experience uneven wear, which results in undesired surface irregularities. It becomes necessary to condition the surface of the used CMP pad to restore the surface to a useful form. The process of restoring the pad surface is referred to as pad conditioning. Conditioning a CMP pad may be performed before an initial use of the pad (to remove the outer solid layer), during a polishing process (in-situ conditioning), or between polishing steps (ex-situ conditioning). Conditioning of a CMP pad is essential to prepare or restore a surface of a CMP pad to one that has properties, including frictional properties and surface texture that allow the pad surface to function in a designed and intended manner.
Many examples and varieties of CMP pad conditioners are well known and commercially available. Minimally, a pad conditioner (a.k.a. “conditioner”) includes at least one abrasive surface that can true and dress a surface of a CMP pad when contacted with the abrasive surface, with movement between the abrasive surface of the pad conditioner and the surface of the CMP pad. Example pad conditioners may include abrasive surfaces on one face of the conditioner, and other examples may include abrasive surfaces on two opposed faces. Preferred conditioners may be designed to fit within an opening of a carrier of a CMP tool to allow the conditioner to be placed in the carrier (in place of a workpiece) during a step of conditioning a CMP pad surface. Consistent with these considerations, a large variety of different types of pad conditioners are manufactured, sold, or used for conditioning CMP pads associated with CMP steps applied to different types of workpieces.
According to the present description, Applicant has identified high-precision abrasive surfaces made of high-density silicon carbide. The abrasive surfaces can be used as a surface of a pad conditioner that is optionally and preferably coated with a CVD diamond coating. Preferred high-precision abrasive surfaces used as a surface of a pad conditioner can exhibit useful or desired abrasive properties, including a commercially advantageous level of control over abrasive properties of the pad conditioner, such as an advantageous level of control over abrasive cut rate of a pad conditioner. The improved level of control can be shown as reduced inter-pad variability of cut rate of pads of the invention that are produced to have the same physical features of abrasive surfaces, e.g., the same size, shape, and form of protrusions and the same spacings of protrusions. The improved control of abrasive properties is due to the high level of precision of the physical features of the abrasive surface, such as sizes, shapes, and forms (e.g., angles) of shaped protrusions, and precise spacing of protrusions of a pattern of protrusions on an abrasive surface.
A measure of a pad conditioner is its level of “aggressiveness” in removing material from a CMP pad. A level of aggressiveness of a pad conditioner can be quantified as a “pad cut rate” (PCR), i.e., a rate at which material is removed from CMP pad during a conditioning step. Previous pad conditioners made of shaped surfaces or abrasive-coated surfaces can commonly have a wide range of aggressiveness as measured by pad cut rate. Pad cut rate, even in commercial versions of pad conditioners, has proven difficult to control, meaning that pad cut rate can vary among pad conditioners, even among pad conditioners prepared from the same materials and methods.
Applicant has determined that abrasive surfaces made of high density silicon carbide can be formed into high-precision abrasive surfaces that exhibit desirable or advantageous abrasive properties, including a well-controlled level of abrasive aggressiveness, e.g., predictable, controlled pad cut rate with low inter-pad variability. High density silicon carbide can be effective in increasing control of cut rate of a conditioning pad, because high-density silicon carbide is capable of being formed into an abrasive surface that includes shaped protrusions that have highly precise shapes, highly-precise spacings between protrusions, optionally and preferably a high precision (e.g., low roughness) land surface, or a combination of these.
A high-precision abrasive surface may be formed from high density silicon carbide by use of any suitable technique, e.g., any machining, etching, or cutting technique that provides a desired level of precision of an abrasive surface (e.g., physical features of protrusions and land surfaces). A presently-preferred technique for forming the highly precise shapes and land surfaces is by laser cutting, i.e., by use of a precise and repeatable laser machining process.
In one aspect the invention relates to an abrasive surface that includes a planar land surface and a plurality of high-density silicon carbide protrusions extending from the planar land surface, with the protrusions having high-precision shapes.
In another aspect, the invention relates to a method of forming an abrasive surface on a silicon carbide body. The method includes: from a block of silicon carbide having a high-density silicon carbide surface, removing high-density silicon carbide from the surface to produce a plurality of high density silicon carbide protrusions extending from a planar land surface, the protrusions having high-precision shapes.
In yet another aspect, the invention relates to a method of conditioning a surface of a CMP pad using a CMP tool. The CMP tool includes a rotating platen holding a CMP pad having a top CMP pad surface, and at least one carrier having at least one opening. The method includes placing one or more pad conditioners in the at least one opening, each of the one or more pad conditioners comprising an abrasive surface as described herein. The method also includes providing contact and motion between the abrasive surface and the CMP pad surface.
According to the present description, Applicant has identified high-precision abrasive surfaces made of high density silicon carbide. The abrasive surfaces can be used as a surface of a pad conditioner that is optionally and preferably coated with a CVD diamond coating. Preferred high-precision abrasive surfaces used as a surface of a pad conditioner can exhibit useful or desired abrasive properties, including a commercially advantageous level of control of level of an abrasive property of the pad conditioner, such as an advantageous level of control over abrasive cut rate of a pad conditioner. Improved control of an abrasive property such as cut rate refers to an abrasive property that exhibits a reduced amount of variability, e.g., reduced variability in cut rate between pad conditioners prepared to exhibit a certain cut rate. The improved control of abrasive properties is due to the high level of precision of the physical features of the abrasive surface, such as one or more of: precise sizes, shapes, and forms (e.g., angles) of shaped protrusions; precise spacing of protrusions of a pattern of protrusions on an abrasive surface; a precise level of flatness of a land surface of an abrasive surface; or a combination of these.
The high-precision silicon carbide abrasive surfaces include a planar surface generally extending in an x-y plane, referred to as a “land surface,” and a plurality of high-density silicon carbide protrusions extending from the land surface. The protrusions are made of high density silicon carbide and, due to the high density of the silicon carbide, are capable of being formed into highly-precise (high-precision) shapes; these protrusions may be referred to herein using terms such as “high-precision protrusions.” The land surface can also, preferably, be made of high density silicon carbide, and preferably is integral with the high-density silicon carbide protrusions. The individual high-precision shaped protrusions extend from the land surface in a direction that is perpendicular to the plane of the land surface, and the protrusions can be arranged over the land surface as desired, such as in a high-precision pattern with regular (and advantageously precise) spacings in the x-y plane between the protrusions.
As described, Applicant has identified that high density silicon carbide can be formed into useful or advantageous high-precision shaped abrasive surfaces that include: a high-precision land surface, high-precision three-dimensional protrusions extending from the land surface, high-precision placement of (e.g., spacings between) the protrusions on the land surface, or a combination of these. The shaped protrusions and preferably the land surface are made of high density silicon carbide, which means silicon carbide that has a low porosity or very low porosity, e.g., below 5, 2, or 1 percent porosity. The high-density silicon carbide can also be characterized as having a density of at least 2.5 grams per cubic centimeter. High density silicon carbide, and bodies of high density silicon carbide suitable for use in forming an abrasive surface as described, are commercially available and can be prepared by methods that are well understood by the skilled artisan in the ceramic and silicon carbide arts, including, for example, vapor deposition, sintering, and reaction bonding methods.
While the protrusions are made of high density silicon carbide, and the land surface may also be preferably made of high density silicon carbide, the remaining material of a silicon carbide body (e.g., a silicon carbide “pad” or “segment”) that includes the abrasive surface on one side may be made of high density silicon carbide, or may alternately be made of non-high density (e.g., porous) silicon carbide. For example, a portion of a thickness of a silicon carbide body at a surface that includes the abrasive surface can be made of high density silicon carbide, and a remaining portion of the body (i.e., the balance of the body thickness) can be made of non-high density silicon carbide. A non-high density silicon carbide material may have a porosity, for example, in a range from 10 to 80 percent.
Applicant has determined that an abrasive surface of shaped protrusions extending from a land surface, and being made of high density silicon carbide, can be formed in a manner to exhibit a very high degree of precision of various physical features of the abrasive surface, such as the shape, sizes, forms (e.g., angles), and placement (distance of separation) of the protrusions, as well as flatness of the land surface. The high level of precision of these physical features of the abrasive surface can be particularly useful and advantageous when included as features of an abrasive surface, e.g., of a CMP pad conditioner.
The high-precision abrasive surface can include highly precise physical features of each shaped protrusion, for example as measured by one or more dimension or shape feature of the abrasive surface. Examples of high precision physical features of a protrusion may include (without limitation) one or more of: a height of each protrusion from a land surface; a width of each protrusion at a base; a shape of a tip of each protrusion, such as an angle made between intersecting lines of sidewalls, or a width of a tip; an angle of a sidewall relative to a land surface; a shape of a sidewall of a protrusion, e.g., whether a profile of a sidewall correlates well to a line, as compared to being curved, jagged, or not a close correlation; etc.
Optionally and preferably, the high-precision shaped abrasive surface also includes a highly precise patterned arrangement of the protrusions over the land surface, meaning that the pattern of placement of the protrusions and the spacings between protrusions are highly precise.
Also optionally, the high-precision abrasive surface can include a high-precision land surface, meaning a land surface that has a low variability in height, e.g., a very precise roughness, for example a roughness in a range from 2-10 μm as measured by laser profilometry, and a flatness measured to less than 50 microns.
Example abrasive surfaces as describes include a plurality of individual three-dimensional structures (e.g., protrusions) that extend from a land surface of the silicon carbide body. The three-dimensional protrusions can be integral with the land surface and the silicon carbide body. The protrusions extend from the land surface in a direction that is normal to the x-y plane of the land surface. The three-dimensional structures can be situated on the land surface in a repeating, patterned, un-patterned (e.g., apparently random), or clustered arrangement. Certain preferred three-dimensional structures may be repeating, e.g., patterned, such as in the form of a set of similar and repeating three-dimensional geometric shapes.
Each protrusion can be characterized as having a height measured in a z-direction, the height being measured as a distance from the land surface, in a perpendicular direction, to an upper surface of a protrusion. Each protrusion also includes a width dimension measured at a location where the protrusion meets the land surface, i.e., at a horizontal base of the protrusion. Each protrusion can also include a length dimension that is perpendicular to the width and also in the plane of the land surface.
A shape of a protrusion may be any shape that will be effective for an abrasive surface, e.g., that will be effective as part of an abrasive surface of a pad conditioner for performing a conditioning step as described herein. A specific shape of a protrusion can be any useful or desired three-dimensional shape, which may be selected based on preference, based on a desired application for an abrasive surface (e.g., as a pad conditioner), and based on desired performance such as a desired level of aggressiveness of the abrasive surface. A protrusion may be shaped to include any one or more forms that are rounded, curved, symmetric, asymmetric, angled, cornered, or straight (linear). Example shapes may be pyramidal (with any shape base, e.g., triangular, square, rectangular, pentagonal, hexagonal, octagonal, etc.), conical (with a round or oval base), prism-shaped (e.g., having a geometric cross section and an elongate length), ridged, trapezoid, hemispherical, flat-topped, triangular, hexagonal, octagonal, starburst, zig-zag, square, rectangular, elongate (linear or curved), or a combination of two or more of these, etc.
A dimension or form (e.g., angle, flatness, correspondence to a line, etc.) of a protrusion can be measured by any suitable measurement technique, such as by known laser profilometry techniques. As presented herein, dimensions and forms (e.g., angles) of abrasive surfaces made of high density silicon carbide are capable of being produced with high precision and repeatability over an abrasive surface that includes a plurality of protrusions distributed and spaced over a land surface, e.g., with precision and repeatability that are improved relative to precision and repeatability that has been achieved by forming comparable structures of silicon carbide having a lower density and higher porosity, e.g., above 20 percent porosity. Various techniques can be useful for measuring these dimensions and forms, and various known analytical and statistical methods are available for comparing the precision of abrasive surfaces of the present description to the precision of non-inventive abrasive surfaces.
An improved precision of an abrasive surface of the present description refers to the improved accuracy of size (dimension), form (angle, flatness, correspondence to a line, etc.), or placement of a physical feature (protrusion or land surface) of an abrasive surface. Accuracy in this respect can be assessed in terms of the variability of the size, form, or placement of the physical feature of the abrasive surface. Examples of physical features of an abrasive surface that may be assessed to determine precision of formation and placement of features of an abrasive surface may include (without limitation) any one or more of the following: a dimension of a protrusion, e.g., a height or width of a protrusion; a shape or form of a protrusion, e.g., an angle of a sidewall relative to a land surface; a “width” of a tip of a conical or pyramidal protrusion, meaning the degree to which the tip is rounded as opposed to perfectly sharpened on a minute scale (e.g., on a scale of microns); the degree to which linear (as intended) sidewalls of protrusions correlate to straight lines, as opposed to being curved or lacking strong correlation; distances (in an x-y plane) between similar features of an abrasive surface, e.g., distances between tips, centers, or similar base locations of protrusions (adjacent or non-adjacent protrusions) of a repeating pattern of protrusions.
When measuring a dimension of a protrusion or a dimension of spacings of protrusions to assess precision of dimensions among multiple protrusions of an abrasive surface, the dimension that is measured should be a similar dimension of each protrusion. For measuring spacings, a spacing (distance) can be measured between the same locations of a pair of protrusions and the protrusions should be similarly located as part of a pattern of protrusions of the abrasive surface. For any measurement, the specific dimension or spacing that is measured to assess precision is not a critical feature of a measurement, but the end points of each measurement of a sample of measurements must be consistent between measurements.
As a general matter, a protrusion can have height, width, and length dimensions that are effective to achieve desired abrasion properties of the abrasive surface. The scale of the protrusion dimensions may be on a scale of microns, e.g., tens of microns or hundreds of microns. Example heights of protrusions of various shapes and forms can be in a range from 20 to 100 microns, e.g., from 25 to 75 microns. Example widths at a base of a protrusion (e.g., a diameter of a circular or rounded base) may be in a range from 10 to 200 microns, e.g., from 20 to 150 microns. (A width of a protrusion that includes a circular base can be the diameter of the base. Other width dimensions can also be useful to assess precision of an abrasive surface, such as a dimension of a diagonal of a square or rectangular base.) Example lengths, may vary depending on the type of abrasive surface desired, and may be of a magnitude that is comparable to a width, or greater than or substantially greater than a width, e.g., for an elongate protrusion. Commonly, for individual, non-elongate, protrusions, a length may commonly be in a range that is similar to the magnitude of the width of a protrusion at a base, e.g., in a range from 20 to 1000 microns, e.g., from 25 to 75 microns. In a patterned arrangement of protrusions on an abrasive surface, spacings between a pair of two nearby or adjacent protrusions may vary depending on the type of abrasive surface desired; examples of useful spacings between adjacent protrusions may be, e.g., between 1,000 to 10,000 microns, e.g., from 1,500 to 7,000 microns, or from 2,000 to 6,000 microns.
Improved levels of precision achieved with abrasive surfaces of the present description, relative to otherwise comparable abrasive surfaces made of non-high density silicon carbide, can be shown by measurements and statistical methods that are known by and available to a person of skill in analytical and statistical methods. An improved level of precision achieved by an abrasive structure as described can be demonstrated by showing a statistically-significant improvement (reduction) in variation of a physical feature of an abrasive surface such as one or more of: a dimension, angle, or form of a protrusion; spacings between similar locations of two separate protrusions in a pattern; flatness (e.g., roughness) of a land surface; or any other measurable physical feature.
As one example for demonstrating a useful or improved level of precision that may be achieved by a method or structure of the present description, variability of a physical feature of a sample of protrusions of a single abrasive surface may be stated in terms of standard deviation of the measured values of the sample of physical features. As used herein, the term standard deviation, with reference to a group of measured values (i.e., the “sample standard deviation” as opposed to a “population standard deviation”) (“SD,” also represented by the Greek letter sigma σ or the Latin letter s) is given its ordinary meaning in the field of statistics, i.e., is a calculated value used to quantify the amount of variation or dispersion of a set of data values (measurement values), based on the values of the samples and the total number of values in a sample.
With reference to exemplary values referenced herein for protrusion width (base width), protrusion height, and protrusion spacing, exemplary or preferred standard deviations may be as follows: a preferred standard deviation of a width (a base width) of a protrusion base can be less than 7 μm, e.g., less than 6 μm, or less than 5 μm. A preferred standard deviation of a height of a protrusion can be less than 5.0 μm, e.g., less than 1.2 μm, or less than 1.0 μm. A preferred standard deviation of a spacing between locations of pairs of protrusions can be less than 10 μm e.g., less than 4 μm, or less than 1 μm.
Referring now to
As an example of certain high-precision physical features of an abrasive surface,
A distance (d) or separation between protrusions of an arrangement can be assessed by measuring any two locations of any two protrusions, e.g., a distance between edges of a base on the same side of two conical protrusions. A comparison of the distance measurements, to assess variability, such as to identify a standard deviation, can be made by performing multiple measurements between the same two locations over a sample of pairs of protrusions. As illustrated, a distance d of example abrasive surface 50 can be in a range from 1,000 to 10,000 angstroms, with sample spacings of an abrasive surface having a standard deviation of less than 0.5 angstroms, 0.4 angstroms, or 0.3 angstroms.
An example of a height (h) of a conical protrusion 54 of an abrasive surface 50 can be in a range of from 20 to 100 microns, e.g., from 25 to 75 microns, with a sample of measured heights of an abrasive surface having a standard deviation of less than 1.5 microns, e.g., less than 1.2 microns, or less than 1.0 microns.
An example of a base width (Wb) of a conical protrusion 54 of an abrasive surface 50 can be in a range of from 10 to 200 microns, e.g., from 50 to 150 microns, with a sample of measured base widths of an abrasive surface having a standard deviation of less than 7 microns, e.g., less than 6 microns or less than 5 microns.
An example of an angle (α) formed at an intersection of lines that correspond to two sidewalls (62) of a conical protrusion 54 can be in a range from range from 30 to 70 degrees, e.g., from 40 to 60 degrees, with a sample of measured base angles of an abrasive surface having a standard deviation of less than 5 degrees, e.g., less than 1 degree.
An example of an angle (β) between a sidewall 62 and land surface 56 can be in a range from range from 30 to 70 degrees, e.g., from 40 to 60 degrees, with a sample of measured angles of an abrasive surface having a standard deviation of less than 1, e.g., less than 0.5 degrees, 0.4 degrees, or 0.3 degrees.
An example of a tip width (Wt) of a conical protrusion 54 of an abrasive surface 50 can be in a range of from 10 to 30 microns, with a sample of measured tip widths of an abrasive surface having a standard deviation of less than 5 μm, e.g., less than 2 μm, or less than 1 μm.
As compared to
In contrast,
Various manufacturing methods are available for processing ceramic materials such as silicon carbide to form an abrasive ceramic surface that includes protrusions extending from a land surface. Examples methods include: wire electrical discharge machining (EDM), masked abrasion machining, water jet machining, photo abrasion machining, laser machining, and conventional milling such as by machining, or etching techniques. Any of these techniques may be useful to form three-dimensional surfaces on silicon carbide, including to form high-precision structured abrasive surfaces from high-density silicon carbide. Techniques that are preferred for forming high-precision abrasive surfaces on silicon carbide, as described herein are those that produce abrasive surfaces and protrusions having precision physical features as described herein, with one example of a preferred technique being laser cutting.
Preferred examples of silicon carbide abrasive surfaces as described can be further processed to place a coating of chemical vapor deposited diamond (i.e., “CVD diamond”) on the high-precision silicon carbide abrasive surface. A CVD diamond coating placed over the abrasive surface may be effective to improve performance and useful lifetime of the abrasive surface. Methods of placing a CVD diamond coating onto a surface are known. By one exemplary method, carbon gas is ionized at very high temperatures using microwave power and or electrical power, a hot filament, a laser, an electron beam, or the like, and the ionized carbon deposits onto a substrate (e.g., a three-dimensionally structured surface of a silicon carbide segment as described) as a preferably continuous diamond coating. During this process the substrate can reach temperatures of about 800 degrees Celsius, so the ceramic material of the ceramic segment must be of a type that will withstand this high temperature.
Once formed, a silicon carbide body that includes an abrasive surface as described herein can be incorporated into a pad conditioner as an abrasive silicon carbide “pad,” “segment,” or “insert,” that is attached to a flat and rigid base plate. Example pad conditioner structures include a rigid disk-shaped plate (or base) that supports one or more silicon carbide bodies having a high-precision silicon carbide abrasive surface. The rigid plate includes a top plate surface, a bottom plate surface, and a plate thickness that extends between the top plate surface and the bottom plate surface. One or more silicon carbide segments are attached to the plate to provide the abrasive surfaces.
A preferred conditioner includes a flat, rigid plate (e.g., disk, support, substrate, or the like) to which are attached one or preferably multiple abrasive segments (or “pads” or “conditioning segments”), each of which includes an abrasive surface as described herein, including high density silicon carbide protrusions. An example is shown in
In use, a pad conditioner of the present invention, e.g., pad conditioner 26 of
A pad conditioner as described can exhibit useful abrasive performance, or may preferably exhibit improved abrasive performance as demonstrated by a cut rate that is more precisely controlled (e.g., has reduced variability) relative to a pad conditioner that is otherwise comparable but does not include a high-precision silicon carbide abrasive surface as presently described. It has been found, based on the present description, that a high-precision silicon carbide abrasive surface can be prepared to effect a desired and well-controlled (relative to other pad conditioners) level of aggressiveness of the abrasive surface in terms of cut rate. In comparisons of cut rates of similar CMP pads (pads of similar composition, surface wear, etc.) using similar equipment and conditions (time, temperature, speeds, etc.) of a conditioning step, conditioning pads of the present description can be prepared to have a desired cut rate, with the individual cut rates of multiple such pad conditioner (i.e., the inter-pad variability) showing less variability as compared to pads made using non-inventive abrasive surfaces.
This application claims the benefit under 35 USC 119 of U.S. Provisional Patent Application No. 62/672,938, filed May 17, 2018, the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 62672938 | May 2018 | US |
