Ultrasonic diamond scrubber unit

Abstract

This invention provides an ultrasonic diamond scriber unit that enables deeper extension of vertical cracks necessary for cleaving workpieces, such as brittle materials, when breaking them into individual pieces. [Solution] A high-rigidity ultrasonic holder, in which a Langevin-type piezoelectric element, a horn, and a cone are fixed by an outer cylinder, is used to amplified vibrations and scribe the cutting edge of a single-crystal diamond tool 4 attached to the tip of the cone. This provides an ultrasonic diamond scriber unit that enables the promotion of vertical crack propagation. Furthermore, in the scribing process of a workpiece 5 such as a brittle material, this ultrasonic diamond scriber unit utilizes ultrasonic vibrations perpendicular to the single-crystal diamond tool 4 to deepen the vertical cracks generated during scribing. The use of ultrasonic waves has the effect of reducing processing resistance due to load, and is expected to result in cleavage with less damage to the workpiece due to cleavage.

Description

Technical Field

[0001] In the mechanical processing method of cutting glass, various ceramics, etc., the method using a conventional carbide wheel is common. This method requires a large load, leaves damage due to stress strain during cutting on the substrate, and causes problems in the quality of the workpiece. Applying ultrasonic vibration to the tool tip or the wheel reduces the cutting load, promotes damage-free cutting, and the extension of vertical cracks.

Background Art

[0002] The cutting method of glass and hard brittle materials is the so-called mechanical scribing method, in which a carbide wheel is loaded with a load on the surface of the workpiece to draw a line, and cracks are generated in the horizontal and vertical directions of the workpiece due to the stress of the surface scoring line to cause splitting. Or the so-called dicing method in which a thin donut-shaped sintered diamond grinding wheel called a blade (outer peripheral blade) is rotated at high speed and cut while spraying water. Furthermore, there is a laser scribing method in which a carbon dioxide laser is linearly transmitted toward the workpiece to continuously drill minute holes for cutting. However, all of these methods have problems of deteriorating the quality of the workpiece. Conventional mechanical scribing applies a load of several newtons to cut, leaving damage as residual stress on the substrate, which causes substrate breakage due to thermal cycling. Dicing generates chips called kerf loss corresponding to the thickness of the outer peripheral blade, and the cutting while spraying water causes problems such as the impact on the environment such as wastewater treatment. Furthermore, spraying water causes problems in the impact on the electric circuit on the substrate. Laser scribing has problems in the poor yield due to the melt adhering to the substrate and the electrodes in the vicinity, which causes problems when mounting chips. Therefore, the ultrasonic-assisted diamond scribing method proposed this time is expected to be a method for solving these problems and to be put into practical use. The ultrasonic diamond scriber unit developed this time is expected to be an epoch-making method for solving problems such as mechanical scribing, laser scribing, and dicing by a wheel.

Summary of the Invention

[0003] The problem that this invention aims to solve is to provide an ultrasonic diamond scriber unit that, when breaking down a workpiece such as a brittle material into individual pieces, uses ultrasonic vibrations perpendicular to a single-crystal diamond tool to continuously transfer indentations, thereby enabling deeper extension of the vertical cracks necessary for fracture of the workpiece. [Means for solving the problem]

[0004] The present invention was made to solve the aforementioned problems, and is an ultrasonic diamond scribing unit that amplifies ultrasonic vibrations generated by a Langevin-type piezoelectric element with a cone and resonates with the tip of a single-crystal diamond tool. This ultrasonic diamond scriber unit applies ultrasonic longitudinal vibrations to a diamond mounted on a shaft, with the tool tip shaped into a cone or pyramidal form, to continuously transfer indentations to the surface of various glass plates, ceramic plates, and compound semiconductor wafers, thereby scribing straight lines and quadratic curves, and promoting the propagation of cracks in the vertical direction for fracture. The diamond can be single-crystal or polycrystalline. Furthermore, having (111) or (110) facets at the tip of the single-crystal diamond is an effective method. [Effects of the Invention]

[0005] According to the ultrasonic diamond scriber unit of the present invention, while vertical crack propagation does not occur in scribing with a diamond tool without the use of ultrasonic vibrations, vertical cracks can be deepened by using ultrasonic vibrations to continuously transfer indentations. [Brief explanation of the drawing]

[0006] [Figure 1] It consists of a transmitter and an ultrasonic diamond scriber unit. [Modes for carrying out the invention]

[0007] As shown in the figure, the ultrasonic diamond scribing unit of this embodiment consists of a transmitter 1, a Langevin-type piezoelectric element 2, a horn 3, and a single-crystal diamond tool 4. A voltage is applied to the Langevin-type piezoelectric element 2 by the transmitter 1, generating ultrasonic vibrations. The generated ultrasonic vibrations are amplified by the horn 3, which is connected to the Langevin-type piezoelectric element 2, and propagated to the single-crystal diamond tool 4 attached to the tip of the horn. The tip of the single-crystal diamond tool 4, which is supported by the ultrasonic vibrations, is brought into contact with the upper surface of the workpiece 5, and the single-crystal diamond tool 4 moves horizontally across the upper surface of the workpiece while applying ultrasonic vibrations in the vertical direction. [Examples]

[0008] As shown in Figure 1, the tip of the single-crystal diamond tool 4 is lowered to the upper surface of the workpiece 5. The depth of digging is set from the position scanned by a non-contact sensor to the Z coordinate of the uneven surface at the separation point, and the depth of digging and movement in the XY direction of the tip of the single-crystal diamond tool 4 are automatically controlled by a program. Depending on the material of the workpiece 5, the depth of digging in the Z direction is changed and the movement speed in the XY direction is determined. When scribing workpieces 5 with smooth surfaces, such as glass (quartz glass, tempered glass, soda glass, glass whose main component is silicon oxide, etc.), ceramic substrates (sapphire (single-crystal alumina) substrates, gallium arsenide single-crystal substrates, etc.), and semiconductor materials (silicon wafers, gallium arsenide wafers, gallium nitride wafers, gallium oxide wafers, aluminum nitride wafers, silicon carbide wafers, etc.), the flatness of the suction table 8 that holds the workpiece 5 is important. With equipment that has sufficient parallelism, it is possible to continuously transfer indentations by using ultrasonic vibrations perpendicular to the single-crystal diamond tool 4 by setting the amount of scribing (position) in the Z direction. Similar results were obtained when using polycrystalline diamond instead of the single-crystal diamond used here. In particular, it was found that with single-crystal diamond, the wear of the tip is reduced and the result is good when the tip has a (111) facet or a (110) facet. On the other hand, in the case of sintered substrates such as ceramic substrates (alumina substrates, alumina-zirconia substrates, silicon nitride substrates, aluminum nitride substrates, silicon carbide substrates, etc.) used as the workpiece material 5, surface irregularities and warping occur due to firing shrinkage during the substrate manufacturing process. Furthermore, when electrodes for mounting semiconductor materials and power / signal circuit wiring are formed on the ceramic substrate, warping occurs due to the difference in thermal expansion coefficients between the ceramic substrate and the electrode material, making it important to follow the irregularities in the Z direction. It is necessary to have a function to detect the position of irregularities on the surface of the workpiece material 5, detect the position where the single-crystal diamond tool 4 contacts the workpiece material 5 and a load is applied, and track the pressing load so that it becomes a constant load to control the position along the Z axis. By incorporating this Z-axis position control function, even when the flatness of the suction table that fixes the workpiece 5 is insufficient, it is possible to continuously transfer indentations onto the single-crystal diamond tool 4 using ultrasonic vibrations perpendicular to the workpiece 5, which has few irregularities. The following shows the results of continuously transferring indentations to various workpiece materials 5 by using the ultrasonic diamond scrubber unit of the present invention and applying ultrasonic vibrations perpendicular to the single-crystal diamond tool 4. As the workpiece material 5, a 0.2 mm thick glass plate was continuously imprinted with a single-crystal diamond tool 4 by using ultrasonic vibrations perpendicular to the single-crystal diamond tool 4 with the ultrasonic diamond scrubber unit of the present invention. The processing conditions were a depth of 0.005 mm in the Z direction and a movement speed of 150 mm per second in the XY direction. Slight traces of the impact points made by the single-crystal diamond tool 4 were observed in the areas where the indentations were imprinted. A flaw detection ink was applied to the areas where the indentations were imprinted, and the propagation of microcracks was observed after cutting. As a result, it was found that microcracks extended to a depth of 0.14 mm, which is approximately 70% of the thickness of the glass plate. Laser microscopy of the surface irregularities revealed a maximum irregularity of 0.035 mm. Furthermore, analysis of the Raman spectrum obtained from the cross-section using Raman spectroscopy showed that no residual stress remained. Similar results were obtained when using polycrystalline diamond instead of single-crystal diamond. In particular, with single-crystal diamond, the presence of (111) or (110) facets at the tip reduced tip wear, resulting in a superior outcome. In conventional scribing methods using diamond wheels, the cut surface has significant irregularities, approximately 0.1 mm. Analysis of the Raman spectrum obtained from the cut surface using Raman spectroscopy revealed that tensile stress remains. If tensile stress remains, microcracks may propagate in the workpiece 5 when stress is applied, potentially leading to failure. In other words, it was found that using the ultrasonic diamond scrubber unit of the present invention and continuously transferring indentations to a single-crystal diamond tool 4 by utilizing ultrasonic vibrations perpendicular to the surface is effective and superior in improving the reliability of power devices. As the workpiece material 5, an alumina substrate with a thickness of 0.38 mm was used with the ultrasonic diamond scrubber unit of the present invention, and indentations were continuously transferred to the single-crystal diamond tool 4 by using ultrasonic vibrations perpendicular to the single-crystal diamond tool 4. The processing conditions were a depth of 0.015 mm in the Z direction and a movement speed of 150 mm per second in the XY direction. Slight traces of the striking points by the single-crystal diamond tool 4 were observed in the areas where indentations were transferred. A flaw detection ink was applied to the areas where indentations were transferred, and the propagation of microcracks was observed after cutting. As a result, it was found that microcracks had penetrated to a depth of 0.27 mm, which corresponds to approximately 70% of the thickness of the alumina substrate. Shape measurement of the surface irregularities of the cut surface using a laser microscope revealed irregularities of up to 0.045 mm. Furthermore, analysis of the Raman spectrum obtained from the cut surface by Raman spectroscopy revealed that no residual stress remained. Similar results were obtained when polycrystalline diamond was used instead of the single-crystal diamond used here. In particular, with single-crystal diamonds, it was found that having a (111) facet or a (110) facet at the tip reduces wear on the tip, resulting in better performance. In conventional scribing methods using diamond wheels, the surface irregularities, including scratches caused by the diamond wheel, are significant, reaching approximately 0.2 mm. Analysis of the Raman spectrum obtained from the surface analysis revealed that tensile stress remains. If tensile stress remains, microcracks may propagate when stress is applied to the workpiece, potentially leading to failure. In other words, it was found that using the ultrasonic diamond scrubber unit of the present invention and continuously transferring indentations to a single-crystal diamond tool 4 by utilizing ultrasonic vibrations perpendicular to the surface is effective and superior in improving the reliability of power devices. As the workpiece material 5, a silicon carbide wafer with a thickness of 0.3 mm was used, and the ultrasonic diamond scrubber unit of the present invention was used to continuously transfer indentations to the single-crystal diamond tool 4 by using ultrasonic vibrations perpendicular to the single-crystal diamond tool 4. The processing conditions were a depth of 0.002 mm in the Z direction and a movement speed of 150 mm per second in the XY direction. Slight traces of the striking points made by the single-crystal diamond tool 4 were observed in the areas where indentations were transferred. A flaw detection ink was applied to the scribed areas, and the propagation of microcracks was observed after cutting. As a result, it was found that microcracks had penetrated to a depth of 0.21 mm, which corresponds to approximately 70% of the thickness of the silicon carbide wafer. Shape measurement of the surface irregularities of the cut surface using a laser microscope revealed irregularities of up to 0.01 mm. Furthermore, analysis of the Raman spectrum obtained from the cut surface by Raman spectroscopy revealed that no residual stress remained. Similar results were obtained when polycrystalline diamond was used instead of the single-crystal diamond used here. In particular, with single-crystal diamonds, it was found that having a (111) facet or a (110) facet at the tip reduces wear on the tip, resulting in better performance. In conventional scribing methods using diamond wheels, the surface irregularities, including scratches caused by the diamond wheel, are significant, reaching approximately 0.2 mm. Analysis of the Raman spectrum obtained from the surface analysis revealed that tensile stress remains. If tensile stress remains, microcracks may propagate when stress is applied to the workpiece, potentially leading to failure. In other words, it was found that using the ultrasonic diamond scrubber unit of the present invention and continuously transferring indentations to a single-crystal diamond tool 4 by utilizing ultrasonic vibrations perpendicular to the surface is effective and superior in improving the reliability of power devices. As the workpiece material 5, an alumina substrate with a thickness of 0.38 mm and copper electrodes formed on both the front and back surfaces was subjected to the ultrasonic diamond scrubber unit of the present invention. Indentations were continuously transferred to the single-crystal diamond tool 4 by using ultrasonic vibrations perpendicular to the single-crystal diamond tool 4. Due to the formation of the copper electrodes, there was a maximum warp of approximately 2 mm, and the machined surface could not be made flat by fixing with the suction table 8 alone. As scribing conditions, the depth of digging in the Z direction was set to 0.015 mm, and the movement speed in the XY direction was set to 150 mm per second. Due to the positioning mechanism using image processing, the scribed area was formed in the center between the electrodes, and traces of the marks made by the single-crystal diamond tool 4 were of almost the same size across the entire surface of the alumina substrate, with only slight scribe marks visible. A flaw detection ink was applied to the scribed area, and the propagation of microcracks was observed after cutting. As a result, it was found that microcracks had penetrated to a depth of 0.27 mm, which corresponds to approximately 70% of the thickness of the alumina substrate. Laser microscopy analysis of the surface irregularities revealed irregularities of up to 0.05 mm. Furthermore, analysis of the Raman spectrum obtained from the surface analysis showed no residual stress. Similar results were obtained using polycrystalline diamond instead of single-crystal diamond. In particular, single-crystal diamond with (111) or (110) facets at the tip showed reduced tip wear, resulting in superior performance. In conventional scribing methods using diamond wheels, the heat treatment required to form the copper electrodes prevented crack propagation in one direction, resulting in unsatisfactory scribing. The present invention's ultrasonic diamond scrubber unit, which utilizes ultrasonic vibrations perpendicular to the single-crystal diamond tool 4 to continuously transfer indentations, proved highly effective. Furthermore, analysis of the Raman spectra obtained by Raman spectroscopy of compound semiconductors scribed using the vibration-assisted scriber apparatus used in this invention confirmed the absence of residual stress. In addition, although very slight compressive stress was observed in the scribed portion, the absence of tensile stress yielded effective results for the device. [Explanation of Symbols]

[0009] 1 Transmitter 2. Langevin type piezoelectric element 3 cones 4 Single Crystal Diamond Tools 5 Work material

Claims

1. An ultrasonic diamond scriber unit characterized by applying ultrasonic longitudinal vibrations to a shaft-mounted diamond with a tool tip shaped into a cone or pyramidal form, continuously transferring indentations to the surface of various glass plates, ceramic plates, and compound semiconductor wafers, thereby scribing straight lines and quadratic curves, promoting the propagation of cracks in the vertical direction, and causing fracture.

2. An ultrasonic diamond scribing unit characterized in that the diamond described in claim 1 above is a single crystal or a polycrystalline diamond.

3. An ultrasonic diamond scribing unit characterized in that the diamond described in claims 1 and 2 is a single crystal and its tip has a (111) facet or a (110) facet.

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