A polishing apparatus includes a rotatable head body having a pressing surface, a retainer ring configured to press a polishing surface while rotating together with the head body, a stationary ring, local load applying devices configured to apply a local load to the stationary ring, and a controller. The local load applying devices include a first pressing member and a second pressing member connected to the stationary ring. The first pressing member is disposed in the upstream side of the retainer ring in the traveling direction of the polishing surface, and the second pressing member is disposed in the downstream side. The controller calculates the inclination angle of the stationary ring based on a measured value of the height of at least one of the first pressing member and the second pressing member.

According to one example, a CNC machine tool system may perform error compensation for improving the accuracy of the geometry (or form) of a machined workpiece to, for example, better than 2 micrometers. To do so, a first machined workpiece may be created using the CNC machine tool system. The CNC machine tool system may create the machined workpiece by jig grinding. Following the creation of the first machined workpiece, metrology of the workpiece error may then be performed on the machined workpiece. The metrology of the workpiece error may be used to create a corrected toolpath trajectory for re-machining. This corrected toolpath trajectory may then be utilized by the CNC machine tool system to machine a second machined workpiece having a geometry (or form) with an accuracy of, for example, better than 2 micrometers.

According to one example, a CNC machine tool system may perform error compensation for improving the accuracy of the geometry (or form) of a machined workpiece to, for example, better than 2 micrometers. To do so, a first machined workpiece may be created using the CNC machine tool system. The CNC machine tool system may create the machined workpiece by jig grinding. Following the creation of the first machined workpiece, metrology of the workpiece error may then be performed on the machined workpiece. The metrology of the workpiece error may be used to create a corrected toolpath trajectory for re-machining. This corrected toolpath trajectory may then be utilized by the CNC machine tool system to machine a second machined workpiece having a geometry (or form) with an accuracy of, for example, better than 2 micrometers.

A grinding apparatus includes a chuck table that holds a wafer on a holding surface; a grinding unit that has a spindle unit in which a spindle with an annular grindstone mounted to a tip thereof is rotatably supported and that grinds the wafer by use of the grindstone; a grinding feeding mechanism that puts the grinding unit into grinding feeding in a grinding feeding direction perpendicular to the holding surface; a first height gauge that measures the height of the holding surface; a second height gauge that measures the height of an upper surface of the wafer; and a calculation section that calculates the difference between the height of the holding surface and the height of the upper surface of the wafer, as the thickness of the wafer. In the grinding apparatus, the first height gauge and the second height gauge are disposed in the grinding unit.

Examples are directed to an approach to specifying design guidelines for fabricating a free-form optical component, and methods of fabricating the free-form optical components. In one example, a family of optical prescriptions is created, and a fabricator may manufacture the free-form optical element to any selected prescription within the family. According to certain examples, the series of prescriptions in the family each describe a very similar optical surface providing the same or similar optical performance, and are layered relative to one another such that the thickness of the optical element at any point is slightly less for each subsequent surface defined by the next prescription in the series.

Examples are directed to an approach to specifying design guidelines for fabricating a free-form optical component, and methods of fabricating the free-form optical components. In one example, a family of optical prescriptions is created, and a fabricator may manufacture the free-form optical element to any selected prescription within the family. According to certain examples, the series of prescriptions in the family each describe a very similar optical surface providing the same or similar optical performance, and are layered relative to one another such that the thickness of the optical element at any point is slightly less for each subsequent surface defined by the next prescription in the series.

A method of thinning a wafer includes measuring an initial thickness of the wafer. The method further includes calculating a polishing time using the initial thickness. The method further includes polishing the wafer for a first duration equal to the polishing time to obtain a polished wafer. The method further includes measuring a polished thickness of the polished wafer. The method further includes calculating an etching time using the polished thickness. The method further includes etching the polished wafer for a second duration equal to the etching time to obtain an etched wafer, wherein the wafer has a total thickness variation of less than or equal to 0.15 μm after etching the polished wafer.

A method of thinning a wafer includes measuring an initial thickness of the wafer. The method further includes calculating a polishing time using the initial thickness. The method further includes polishing the wafer for a first duration equal to the polishing time to obtain a polished wafer. The method further includes measuring a polished thickness of the polished wafer. The method further includes calculating an etching time using the polished thickness. The method further includes etching the polished wafer for a second duration equal to the etching time to obtain an etched wafer, wherein the wafer has a total thickness variation of less than or equal to 0.15 μm after etching the polished wafer.

An output of an eddy current sensor includes an impedance component. A film thickness measuring apparatus obtains film thickness information from the impedance component. Using a non-linear function between the film thickness information and the film thickness, the film thickness is obtained from the film thickness information. When a resistance component and a reactance component of the impedance component are associated with respective axes of a coordinate system having two orthogonal coordinate axes, the film thickness information is a reciprocal of a tangent of an impedance angle which is an angle formed by a straight line connecting a point on the coordinate system corresponding to the impedance component and a predetermined reference point, and a predetermined straight line.

An output of an eddy current sensor includes an impedance component. A film thickness measuring apparatus obtains film thickness information from the impedance component. Using a non-linear function between the film thickness information and the film thickness, the film thickness is obtained from the film thickness information. When a resistance component and a reactance component of the impedance component are associated with respective axes of a coordinate system having two orthogonal coordinate axes, the film thickness information is a reciprocal of a tangent of an impedance angle which is an angle formed by a straight line connecting a point on the coordinate system corresponding to the impedance component and a predetermined reference point, and a predetermined straight line.