Patent Application
20080318496
1. Field of the Disclosure
The present application is generally directed to single crystal substrates and methods of finishing such substrates.
2. Description of the Related Art
Semiconducting components based on single crystal nitride materials of Group-III and Group-V elements are ideal for devices such as light-emitting diodes (LED), laser diodes (LD), displays, transistors and detectors. In particular, semiconductor elements utilizing Group-III and Group-V nitride compounds are useful for light emitting devices in the UV and blue/green wavelength regions. For example, gallium nitride (GaN) and related materials such as AlGaN, InGaN and combinations thereof, are the most common examples of nitride semiconductor materials in high demand.
However, manufacturing boules and substrates of some semiconducting materials, such as nitride semiconducting materials has proven difficult for a multitude of reasons. Accordingly, epitaxial growth of semiconducting materials on foreign substrate materials is considered a viable alternative. Substrates including SiC (silicon carbide), Al2O3 (sapphire or corundum), and MgAl2O4 (spinel) are common foreign substrate materials.
Such foreign substrates have a different crystal lattice structure than nitride semiconducting materials, particularly GaN, and thus have a lattice mismatch. Despite such mismatch and attendant problems such as stresses and defectivity in the overlying semiconductor materials layer, the industry continues to develop substrate technology to improve viability for semiconductor applications. There is current interest in large surface area, high quality substrates, particularly sapphire substrates. However, challenges remain with the production of high quality substrates in larger sizes.
According to a first aspect, a method of changing the crystallographic orientation of a single crystal body is provided that includes the steps of characterizing a crystallographic orientation of the single crystal body and calculating a misorientation angle between a select crystallographic direction of the single crystal body and a projection of the crystallographic direction along a plane of a first exterior major surface of the single crystal body. The method further includes removing material from at least a portion of the first exterior major surface to change the misorientation angle.
According to another aspect, a method for crystallographically re-orienting a single crystal body is provided which includes characterizing the single crystal body by correlating a crystallographic orientation of the single crystal body to the orientation of an initial first exterior major surface of the body, and removing material from said initial first exterior major surface to define a modified first exterior major surface that is non-parallel to the initial first exterior major surface to change the crystallographic orientation of the single crystal body.
According to another aspect, an apparatus for changing the crystallographic orientation of a single crystal body is provided that includes a stage configured to hold a single crystal body, the stage comprising interval tilt capabilities about at least one axis and a x-ray gun directed at the stage and a x-ray detector positioned to detect x-rays diffracted from the single crystal body. The apparatus further includes a grinding wheel configured to overlie and engage a single crystal body overlying the stage, the grinding wheel rotatable around an axis and translatable in a direction along the axis.
According to another aspect, an system for completing angled material removal operations on a single crystal body is provided that includes a characterization module having an x-ray gun directed at a characterization stage, an x-ray detector positioned to detect x-rays diffracted from a single crystal body overlying the characterization stage, and an output configured to provide characterization data based on crystallographic orientation of the single crystal body gathered from the diffracted x-rays at the x-ray detector. The system further includes a processing stage having a first actuator having an input to receive a control signal and configured to adjust the orientation of the processing stage for an angled material removal operation based upon the control signal. Further included is a data processing module having an input coupled to the output of the characterization module configured to receive the characterization data, the data processing module having an output coupled to the input of the first actuator to provide a control signal based upon a comparison between the characterization data and predefined crystallographic orientation.
The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.
The use of the same reference symbols in different drawings indicates similar or identical items.
Referring to
In particular reference to planarizing the side surface of the sheet, planarizing can include a material removal process. A suitable planarizing process includes a grinding process, such as a coarse grinding process, or a fine grinding process. According to one particular embodiment, planarizing a side surface of a sheet includes a coarse grinding process using a fixed abrasive, and notably a bonded abrasive grinding wheel.
Generally, the single crystal body includes an inorganic material. Suitable inorganic materials can include oxides, nitrides, carbides, and combinations thereof. In one particular embodiment, the single crystal body includes a metal oxide, including for example, aluminum oxide or compound oxides, and combinations thereof. More particularly, the single crystal body is a sapphire body, comprising only alumina.
As described below, sapphire single crystal materials have multiple crystallographic planes and corresponding directions. In reference to particular orientations of the sapphire single crystal bodies, typical planes within said sapphire body include a c-plane, r-plane, n-plane, a-plane, and m-plane. Depending upon the desired application of the single crystal body, certain orientations are desirable.
The sheet of single crystal material can have generally polygonal shapes, and in particular generally rectangular portions, and as such have dimensions of length, width, and thickness. Typically, the length is the longest dimension, having a dimension equal to and oftentimes greater than the width or thickness. The width of the sheet is typically the second largest dimension, and is typically greater than the thickness. The thickness is the smallest dimension, and is typically less than the length and width. Generally, the length of the sheet is not less than about 7.5 cm. According to other embodiments, the length of the sheet is greater, such as not less than about 25 cm, or not less than about 50 cm, not less than about 75 cm, or even not less than about 100 cm. Generally, the length of the sheet of single crystal material is not greater than about 200 cm.
The width of the sheet of single crystal material is generally not less than about 7.5 cm. Other embodiments may utilize sheets having greater widths, such as not less than about 10 cm, or not less than about 15 cm, or even not less than about 20 cm. Generally, the width of the single crystal sheets is not greater than about 50 cm.
As described previously, the thickness is generally the smallest dimension, and as such, the single crystal sheet typically has a thickness that is not less than 0.5 mm prior to processing. Other embodiments can utilize sheets of greater thickness, such as sheets having a thickness not less than about 1 mm, or not less than 2 mm, or even not less than about 5 mm. Generally, the thickness of the sheet of single crystal material is not greater than about 20 mm.
After planarizing a first side surface of the sheet at step 101, it will be appreciated that the opposing opposite side surface of the sheet of single crystal material may also be planarized. As such, this planarization step typically includes the same processes as used to planarize the first side of the sheet, and particularly, a grinding process.
Referring again to
After characterizing the side surface of the sheet at step 103, the process can continue by removing material from the side surface of the sheet to align the side surface of the sheet with the identified reference plane, at step 105. Removing material from the side surface of the sheet can include typical abrasive processes, such as grinding, and particularly a coarse grinding or fine grinding process. According to a particular embodiment, a suitable grinding process includes use of a fixed abrasive, such as a grinding wheel.
Moreover, upon identification of a reference plane, the sheet can be angled such that during removal of the material, the material is removed such that the side surface of the sheet is aligned with the reference plane identified. Such a process is suitable for orientation of the side of the sheet, and if so chosen, upon removal of smaller pieces of single crystal material from the sheet, such as a disk, such disks are properly oriented with respect to the identified reference plane.
After removing material from the side of the sheet at step 105, the process continues by removing a skin layer from an initial first exterior major surface and an initial second exterior major surface of the sheet at step 107. As described above, typically the sheet can have a generally polygonal contour having opposing and generally rectangular major surfaces, those being the first exterior major surface and the second exterior major surface. Removal of the skin layer at step 107 can include generally abrasive processes, such as grinding processes, and particularly, a fine grinding process. Generally, the removal of the skin layer includes removal of not greater than about 2 mm of material from the initial first exterior major surface and the initial second exterior major surface. It will be appreciated, that all of the above processes described thus far, notably step 101, step 103, step 105, and step 107 can be completed on single sheets of single crystal material, or alternatively, may be may be completed on multiple sheets. Additionally, such steps may be interchanged.
After removing the skin layer at step 107, the process continues by characterizing the initial first exterior major surface at step 109. According to one embodiment, such characterization can be carried out via diffraction techniques, such as for example x-ray diffraction. In particular, characterizing the initial first exterior major surface can include correlating a crystallographic orientation of the single crystal body to the orientation of the initial first exterior major surface. That is, the overall orientation of particular crystallographic planes and directions of the single crystal body can be compared to the orientation of the initial first exterior major surface. In completing such characterization, typically one or more selected crystallographic planes are identified and compared to the plane defined by the first initial exterior major surface, and in doing so one or more misorientation angles are identified. As used herein, the term “misorientation angle,” is defined as the angle between a direction which is normal to a select crystallographic plane within the single crystal body and a selected projection of the corresponding crystallographic direction along the surface of the first exterior major surface or second exterior major surface.
In further describing the crystallographic orientation of the single crystal body, the term, “tilt angle” is also used herein. As such, the tilt angle is a specific term which describes the angle formed between the vector normal to the surface of the single crystal body and a direction normal to a selected crystallographic plane that describes the general orientation of the single crystal body. For example, in the particular context of a sapphire single crystal, the first exterior major surface of the single crystal body may have a generally c-plane orientation. Therefore, the tilt angle describes only the relationship between the vector normal to the crystallographic c-plane and the vector normal to the surface of the single crystal body. Typically, this c-plane orientation is not precisely coplanar with the first exterior major surface of the body and, notably, the c-plane is oriented such that it is tipped toward another crystallographic plane (e.g., the m-plane, a-plane). In fact, c-plane orientation can include a manufactured or intentional tilt angle of the generally planar surface from the c-plane in a variety of directions. For the purposes of clarity, the tilt angle is only a measurement using the vector normal to the surface of the single crystal body, whereas the misorientation angle may describe the angle between a projection (i.e., normal to the plane or within the plane) of the single crystal body and a direction normal to any one of numerous selected crystallographic directions. As such the misorientation angle and the tilt angle may be the same angle when referencing the selected crystallographic plane that describes the general orientation of the single crystal body.
In one particular embodiment, the single crystal body is a sapphire single crystal body having a generally c-plane orientation which is tilted away from the c-plane at a tilt angle of not greater than about 5.0°. Other embodiments may use a sapphire single crystal having a c-plane orientation wherein the tilt angle away from the c-plane is not greater than about 3°, such as not greater than about 2°, or even not greater than about 1°. Typically, the tilt angle is not less than about 0.02°, or not less than 0.05°. Moreover, it will be noted that in some applications, a certain degree of tilt angle is desirable, that is, such that the c-plane is intentionally non co-planar with the first exterior major surface of the body.
After characterizing the initial first exterior major surface at step 109, the process continues at step 111 by removing material from said initial first exterior major surface to define a modified first exterior major surface. Notably, the plane defined by the modified first exterior major surface is non-parallel to the plane defined by the initial first exterior major surface. Thus, the material removal process of step 111 can include removing material from the initial first exterior major surface at an angle. That is, the surface of the single crystal body is tilted or angled during the material removal process. Such a process facilitates crystallographically reorienting the single crystal body, and also redefining misorientation angles.
According to one embodiment, the material removal process can be completed via a grinding process, particularly an angled grinding process. In one particular embodiment, and as will be illustrated in further embodiments, during the grinding process the single crystal body can be fixed in a tilted position, along one or more axes, relative to a grinding surface to effectuate an angled grinding operation. Alternatively, the grinding surface may be tilted along one or more axes relative to the surface of the single crystal body.
During the angled material removal operation, a direction normal to the initial first exterior major surface of the single crystal body can define a first axis, and a direction normal to the grinding surface can define a second axis. This angle between the first axis and second axis also defines the angle between the initial first exterior major surface and the grinding surface during the material removal operation. As such, because the initial first exterior major surface is angled relative to the grinding surface, the first axis and second axis are angled relative to each other and thus not coaxial. Typically the angle between the axes is not greater than about 30°, and more typically, not greater than about 15°. Other embodiments utilize less angle during grinding, such as not greater than about 10°, or not greater than about 5°, or even not greater than about 1°.
By way of clarification, abrasives generally can be categorized as free abrasives and fixed abrasives. Free abrasives are generally composed of abrasive grains or grits in powder form, or particulate form in a liquid medium that forms a suspension. Fixed abrasives generally differ from free abrasives in that fixed abrasives utilize abrasive grits within a matrix of material that fixes the position of the abrasive grits relative to each other. Fixed abrasives generally include bonded abrasives and coated abrasives. An example of a coated abrasive is sandpaper; coated abrasives are typically planar sheets (or a geometric manipulation of a planar sheets to form a belt, flaps, or like), that rely on a flexible substrate on which the grits and various size and make coats are deposited. In contrast, bonded abrasives generally do not rely upon such a substrate, and the abrasive grits are fixed in position relative to each other by use of a matrix bond material in which the grits are distributed. Such bonded abrasive components are generally shaped or molded, and heat treated at a cure temperature of the bond matrix (typically above 750° C.) at which the bond matrix softens, flows, and wets the abrasive grits, and cooled. Various three dimensional forms may be utilized, such as annular, conical, cylindrical, frusto-conical, various polygons, and may form as grinding wheels, grinding blocks, grinding bits, etc. Particular grinding processes described herein utilize fixed abrasive components in the form of bonded abrasives.
According to the embodiment, the material removal process includes a coarse grinding process. Generally, the coarse grinding process can utilize a fixed coarse abrasive that includes coarse abrasive grains in a bond material matrix. The coarse abrasive grains can include conventional abrasive grains such as crystalline materials or ceramic materials including alumina, silica, silicon carbide, zirconia-alumina and the like. In addition to or alternatively, the coarse abrasive grains can include superabrasive grains, including diamond, and cubic boron nitride, or mixtures thereof. Particular embodiments take advantage of superabrasive grains. Those embodiments utilizing superabrasive grains can utilize non-superabrasive ceramic materials such as those noted above as a filler material.
In further reference to the coarse abrasive, the coarse abrasive grains can have a mean particle size of not greater than about 300 microns, such as not greater than about 200 microns, or even not greater than about 100 microns. According to a particular embodiment, the mean particle size of the coarse abrasive grains is within a range of between about 2.0 microns and about 300 microns, such as within a range of between about 10 microns and 200 microns, and more particularly within a range of between about 10 microns and 100 microns. Typical coarse grains have a mean particle size within a range of about 25 microns to 75 microns.
As described above, the coarse abrasive includes a bond material matrix. Generally, the bond material matrix can include an organic or inorganic material. Suitable organic materials can include materials such as resins. Suitable inorganic materials can include ceramics, glasses, metals, or metal alloys. Suitable ceramic materials generally include oxide, carbides and nitrides. Particularly suitable glass materials can include oxides. Suitable metals include iron, aluminum, titanium, bronze, nickel, silver, zirconium, alloys thereof and the like. In one embodiment, the coarse abrasive includes not greater than about 90 vol % bond material, such as not greater than about 85 vol % bond material. Typically, the coarse abrasive includes not less than about 30 vol % bond material, or even not less than about 40 vol % bond material. In a particular embodiment, the coarse abrasive includes an amount of bond material within a range of between about 40 vol % and 90 vol %. Examples of particular abrasive wheels include those described in U.S. Pat. No. 6,102,789; U.S. Pat. No. 6,093,092; and U.S. Pat. No. 6,019,668, incorporated herein by reference.
Generally, the coarse grinding process includes providing an unfinished single crystal body on a holder and rotating the single crystal body relative to a coarse abrasive surface. In one particular embodiment, the grinding wheel can have an abrasive rim extending around the periphery of an inner wheel of the grinding wheel. The single crystal body can be rotated relative to the grinding wheel, and such rotation can be in the same direction of the rotation of the grinding wheel or the opposite direction relative to the rotation of the grinding wheel, while grinding is effected due to the offset rotational axes. According to one embodiment, the grinding process includes rotating the abrasive wheel at a speed of greater than about 2000 revolutions per minute (rpm), such as greater than about 3000 rpm, such as within a range of 3000 to 6000 rpm. Typically, a liquid coolant is used, including aqueous and organic coolants.
In a particular embodiment, a self-dressing coarse abrasive surface is utilized. Unlike many conventional fixed abrasives, a self-dressing abrasive generally does not require dressing or additional conditioning during use, and is particularly suitable for precise, consistent grinding. In connection with self-dressing, the bond material matrix may have a particular composition, porosity, and concentration relative to the grains, to achieve desired fracture of the bond material matrix as the abrasive grains develop wear flats. That is, the bond material matrix fractures as wear flats develop due to increase in loading force of the matrix. Fracture desirably causes loss of the worn grains, and exposes fresh grains and fresh cutting edges associated therewith. In particular, the bond material matrix of the self-dressing coarse abrasive can have a fracture toughness less than about 6.0 MPa-m1/2, such as less than about 5.0 MPa-m1/2, or particularly within a range of between about 1.0 MPa-m1/2 and 3.0 MPa-m1/2.
Generally, a self-dressing coarse abrasive partially replaces the bond material with pores, typically interconnected porosity. Accordingly, the actual content of the bond material is reduced over the values noted above. In one particular embodiment, the coarse abrasive has a porosity not less than about 20 vol %, such as not less than about 30 vol %, with typical ranges between about 30 vol % and about 80 vol %, such as between about 30 vol % to about 70 vol %. According to one embodiment, the coarse abrasive includes about 50 vol % to about 70 vol % porosity. It will be appreciated that, the porosity can be open or closed, and in coarse abrasives that have a greater percentage of porosity, generally the porosity is open, interconnected pores. The size of the pores can generally be within a range of sizes between about 25 microns to about 500 microns, such as between about 150 microns to about 500 microns. The foregoing pore-related values and those described herein are made in connection with various components pre-machining or pre-grinding.
According to one embodiment, the coarse abrasive grain content is confined in order to further improve self-dressing capabilities. For example, the coarse abrasive contains not greater than about 50 vol %, not greater than 40 vol %, not greater than 30 vol %, such as not greater than about 20 vol %, or even not greater than about 10 vol % coarse abrasive grains. In one particular embodiment, the coarse abrasive includes not less than about 0.5 vol % and not greater than about 25 vol % coarse abrasive grains, such as within a range of between about 1.0 vol % and about 15 vol % coarse abrasive grains, or particularly within a range of between about 2.0 vol % and about 10 vol % coarse abrasive grains.
During the angled material removal process utilized for crystallographic reorientation, generally not less than about 200 microns of material are removed from the first exterior major surface to define the modified first exterior major surface. Other embodiments may remove a greater amount of material depending upon the desired orientation, such as not less than about 300 microns, or not less than about 400 microns of material. Typically, the amount of material that is removed to define the modified first exterior major surface is not greater than about 700 microns. It will be appreciated that when referring to the amount of material removed, because the angled material removal process is capable of removing different amounts of material from different portions of the surface, such values represent the greatest amount of material removed from a portion of the surface of the single crystal body.
After completing the angled material removal process to define a modified first exterior major surface at step 111, the process continues at step 113 by characterizing the initial second exterior major surface. As described above, generally the initial second exterior major surface has an opposing major plane or surface of the first exterior major surface. Characterization of the initial second exterior major surface, may be carried out in accordance with process described above with relation to characterization of the initial first exterior major surface. Alternatively, characterization of the initial second exterior major surface may be an optional process as the crystallographic orientation of the single crystal body may be known through the characterization of the initial first exterior major surface, and the misorientation angle can be calculated and adjusted based upon the initial characterization.
Accordingly, after the optional characterization of the initial second exterior major surface at step 113, the process continues at step 115 by removing material from said initial second exterior major surface to define a modified second exterior major surface. As will be appreciated, the removal of material from the initial second exterior major surface to define a modified second exterior major surface can include those processes as described above in accordance with step 111. Notably, the single crystal body can be angled relative to a grinding surface such that material is removed at an angle from the initial second exterior major surface to define a modified second exterior major surface, thereby crystallographically reorienting the single crystal body and changing the misorientation angle.
In particular reference to the misorientation angles, generally before undertaking the removal of material from both initial first and initial second exterior major surfaces, the misorientation angles of the single crystal body are generally greater than about 0.05°. According to one embodiment, the misorientation angles are greater prior to the material removal process, such as greater than about 0.1°, or greater than about 0.2°, or even greater than about 0.3°. Still, after performing the material removal process to define modified surfaces and complete the crystallographic reorientation, the misorientation angle can be reduced, such that the misorientation is not greater than about 0.05°. Other embodiments have misorientation angles which are less after material removal, such as not greater than about 0.04°, not greater than about 0.03°, or even not greater than about 0.02°.
As such, the removal of material to define the modified first exterior major surface and the modified second exterior major surface generally changes the one or more misorientation angles by a delta (Δ) of not less than about 0.01°. Other embodiments are capable of changing the misorientation angle by a greater delta, such as not less than about 0.05°, or not less than 0.1°, or not less than about 0.2°, or even not less than about 0.5°. Generally, the change to the one or more misorientation angles is not greater than about 10°, and more particularly, not greater than about 5°.
Referring again to
One or more disks may be removed from the larger sheet of single crystal material. A disk generally describes a single crystal article having a substantially circular outer periphery and a first major surface and a second major surface with side surfaces extending between and joining the first major surface and second major surface. It will be appreciated, that such disks can form wafers, that is, a disk may be one wafer, or alternatively, a disk may be later processed to form a plurality of wafers.
It will be appreciated that prior to removing the disks or after removing the disks, the remaining single crystal bodies can undergo further processing to make the articles suitable for use. Typically, further processing can include additional grinding processes, such as a fine grinding operation, lapping operation or polishing operation. During such a fine grinding operation, the scratches formed during a previous coarse grinding operation, such as the angled material removal operation, are removed. As such, the fine grinding operation removes not greater than about 200 microns of material. Other fine grinding operations may remove less, such as not greater than about 100 microns, or not greater than about 50 microns, or even not greater than about 25 microns. Generally, however, the fine grinding operation removes not less than about 10 microns of material.
Typically, after such finishing operations the single crystal bodies can also be subjected to a stress relief process. Such processes may include an etching or annealing process. Moreover, further processing may be undertaken, such as polishing to ensure proper geometries. Typically, such polishing operations include use of a free abrasive, such as a CMP process.
Referring to
In particular reference to the geometry of a disk, generally the disk has a substantially circular outer periphery. Moreover, the disk generally has a diameter of not less than about 7.5 cm. According to another embodiment, the diameter of the disk may be greater, such as not less than about 8 cm or 9 cm or even not less than about 10 cm. Typically, the diameter of the disk is not greater than about 30 cm.
Generally, the thickness of a disk is not greater about 10 mm before removing material. Other embodiments, may utilize a disk having a thinner profile, such that the thickness is not greater than about 5 mm, or not greater than about 2.5 mm or even not greater than about 0.5 mm prior to removal of material from both major exterior surfaces.
Referring to
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In particular reference to the types of single crystal materials, according to one embodiment, a suitable single crystal body for crystallographic reorientation can include a sapphire single crystal. As such,
For further clarity
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Generally, the characterization module 701 includes a x-ray gun and a x-ray detector oriented around a characterization stage for characterizing a single crystal body. Upon characterization of the single crystal body, the characterization module generates characterization data 707 particular to the single crystal body and can provide the characterization data 707 to the data processing module 703. The characterization data 707 typically includes data relevant to the orientation of the crystal. According to one embodiment, the characterization data 707 can include data that relates the physical orientation of the single crystal body as determined by its physical exterior surfaces to a crystallographic orientation. In one particular embodiment, the characterization data 707 includes information relevant to identifying a reference plane within the single crystal body. In another embodiment, the characterization data 707 can include information relevant to misorientation angles with respect to an initial major first exterior surface of the single crystal body.
The data processing module 703 receives the characterization data 707 and generates a control signal for controlling the angled material removal operation at a select processing stage. Because multiple angled material removal operations can be implemented by the system, such as for example an angled material removal operation to form a reference plane or an angled material removal operation to change misorientation angles on an initial first exterior major surface, the data processing module 703 can be used to generate different control signals. Such control signals can then be sent to the appropriate processing stages (e.g., either 705 or 711) to carry out the appropriate operation.
For example, in one embodiment the data processing module 703 receives characterization data 707 from the characterization module 701 and processes the characterization data 707 to generate a control signal which represents an error between the current orientation of the single crystal body and the desired orientation based upon a predetermined crystallographic orientation. The control signal is sent to the processing stage to adjust the orientation of the processing stage. As such, in one particular embodiment, the control signal 709 includes data which is sent to the first processing stage 705 which is suitable for completing an angled material removal process on the first exterior major surface of the single crystal body to change at least one misorientation angle. Alternatively, in another embodiment, the data processing module 703 provides a control signal 713 to the second processing stage 711 which includes data suitable for completing an angled material removal operation on a side surface of the single crystal body to define a reference plane or “flat”. Notably, such processes are different and can require different processing stages as well as different control signals since in one operation the first exterior major surface of the single crystal body is being processed, while in the other operation, the side surfaces of the single crystal body are being processed.
Generally, processing of the characterization data 707 by the data processing module 703 can be accomplished via hardware, firmware, or software. For example, the data processing module may include a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), or computer programmable software, or a combination thereof.
Referring to
As illustrated, the processing stage 809 includes an actuator 811 which has an input connected to the data processor 807 for receiving the control signal 815. Upon receiving the control signal 815, the actuator adjust the orientation of the processing stage 809 and an overlying single crystal body 813 relative to a grinding surface 817 based upon the control signal 815. According to one embodiment, the actuator 811 can control the tilt of the processing stage 809 around a first axis that is in the plane defined by the major surface of the processing stage 809. According to another embodiment, the processing stage 809 includes more than one actuator to control the motion of the processing stage 809 in multiple directions. As such, in one embodiment, another actuator is used to control the tilt of the processing stage 809 in a second axis that is generally orthogonal to and in the same plane as the first axis. According to another embodiment, the processing stage 809 can include another actuator configured to receive a control signal from the data processor 807, such that the actuator is configured to rotate the processing stage in the plane of the major surface of the processing stage.
As will be appreciated, multiple control signals can be sent to multiple actuators to control the motion of the processing stage in multiple directions. As such, the data processor 803 and processing stage 809 can include additional or intervening components, such as multiplexers and digital logic circuits beyond those illustrated. Moreover, while such embodiments have demonstrated changing the angle of the processing stage 809 relative to a grinding surface 817, such controls can be used to change the angle of the grinding surface 817 relative to the processing stage 809, or alternatively, such controls can be used to control both the grinding surface and the processing stage 809.
Table 1 below provides data for 21 samples formed according to the following processing procedures. Twenty one, single crystal sapphire disks are cored from multiple larger single crystal sapphire sheets grown via a EFG method. Each of the grown single crystal sheets have a misorientation of approximately +/−0.5 degrees from a selected crystallographic orientation; typically a generally c-plane orientation. Each of the sheets are first visually inspected for defects, and inspected using polarized light, and then using x-ray characterization methods. After inspection of the sheets, each sheet is mapped and marked for the coring operation and removal of single crystal sapphire disks. Generally, 4 single crystal disks are removed from each single crystal sheet.
After the coring operation, each of the single crystal disks are inspected and ground to diameter of about 2 inches. Each single crystal disk is cleaned and characterized using x-ray diffraction to determine the orientation of a particular reference plane which will correspond to the reference flat. After identification of the selected reference plane, for example the a-plane within the sapphire single crystal disks, the flat is formed on the single crystal disk using a surface grinder.
After forming the flat, a single crystal disk is wax mounted onto a flat plate and cleaned via a grinding of a first exterior major surface. After cleaning the sample, the single crystal disk is characterized using x-ray diffraction and the orientation of the first exterior major surface relative to a predetermined crystallographic orientation is calculated. The single crystal disk is secured to a sine plate and the orientation of the single crystal disk relative to a grinding surface is adjusted so that the single crystal disk is angled with respect to a grinding surface. The single crystal disk undergoes an angled grinding operation. Generally, the grinding operation for each of the listed samples below is between about half an hour and about 2 hours, depending upon the correction required.
After the angled grinding operation, the first exterior major surface of each of the single crystal disks is characterized using x-ray diffraction. During characterization, certain misorientation angles of the single crystal disks are measured and recorded. If necessary, the single crystal disks undergo the angled grinding operation again for further correction. After processing the first exterior major surface, the disks are flipped over, and the second exterior major surface is corrected using the same process as used on the first exterior major surface.
After adjusting the orientation of the second exterior major surface, each of the samples are double-sided lapped and cleaned. The side surfaces of each of the single crystal disks are edge-ground, and the disks are cleaned again, annealed, polished, cleaned, and inspected again.
Table 1 above illustrates the 21 samples processed according to the procedures described above. Each of the sapphire samples has a generally c-plane orientation. Misorientation angles relative to the a-axis and the m-axis corresponding to crystallographic planes within the sapphire single crystal disks are measured and provided above. Notably, the average misorientation angles of the 21 samples relative to the a-axis and m-axis is low (less than about 0.05 degrees). Moreover, as the original orientation of the single crystal sheets was +/−0.5 degrees within a selected crystallographic direction. After the grinding operation, the misorientation angles with respect to the a-axis and the m-axis have average values of −0.04 degrees and 0.01 degrees respectively illustrating a crystallographic reorientation. Additionally, the combined angle of the 21 samples has an average value of 0.1 illustrating a close crystallographic orientation, closer than +/−0.5 degrees. Also, the combined angle misorientation of each of the single crystal disks on a wafer-to-wafer comparison is reduced, as the standard deviation of the 21 samples is 0.05 degrees. The maximum and minimum values with respect to the angles measured also illustrate a reduction in the misorientation.
The embodiments described herein provide notable advantages. The embodiments herein describe characterization methods, orientation processes and procedures, and particular grinding processes and articles, all of which in combination facilitate crystallographically reorienting single crystal bodies. Moreover, such combination of methods are scalable as some processes herein are suitable for processing large sheets of single crystal material, while alternatively, certain combinations of processes are suitable for processing individual disks or wafers of single crystal materials. In particular, the embodiments herein facilitate post-growth crystallographic reorientation of single crystal bodies which is particularly desirable for reducing scrap and improving the quality of devices formed thereon. Moreover, the processes provided herein facilitate manufacturers mobility as single crystal bodies can be engineered and adjusted to end user specifications for particular applications after the single crystal article has been grown.
The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.
The present application claims priority from U.S. Provisional Patent Application No. 60/946,104, filed Jun. 25, 2007, entitled “Methods Of Crystallographically Reorienting Single Crystal Bodies,” naming inventors Brahmanandam V. Tanikella, Christopher Arcona, David Gindhart, Christopher D. Jones, and Matthew A. Simpson, and U.S. Provisional Patent Application No. 60/974,008, filed Sep. 20, 2007, entitled “Methods Of Crystallographically Reorienting Single Crystal Bodies,” naming inventors Brahmanandam V. Tanikella, Christopher Arcona, David Gindhart, Christopher D. Jones, and Matthew A. Simpson, of which both applications are incorporated by reference herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60946104 | Jun 2007 | US | |
| 60974008 | Sep 2007 | US |
