Patent DE-102007013058-A1 (DE)
Title: Method for simultaneous double-side grinding of semiconductor wafers, comprises moving the wafer freely into a recess of a circulating disk, and processing the wafer between two rotating circular working disk components
Inventor: PIETSCH GEORG
IPC: B24B37/04
Filed: 2007-03-19
Abstract: The method for simultaneous double-side grinding of semiconductor wafers, comprises moving the wafer freely into a recess of a circulating disk (13), which is rotatably movable by a shifting device and is moved on a cycloidic trajectory, and processing the wafer between two rotating circular working disk components (1, 4). The working disks have working layers (11, 12), which contain bounded abrasive medium. The shape of working gap formed between the disks is determined during the grinding process and the shape of the working surface of the working disk is modified mechanically or thermally. The method for simultaneous double-side grinding of semiconductor wafers, comprises moving the wafer freely into a recess of a circulating disk (13), which is rotatably movable by a shifting device and is moved on a cycloidic trajectory, and processing the wafer between two rotating circular working disk components (1, 4). The working disks have working layers (11, 12), which contain bounded abrasive medium. The shape of a working gap formed between the working disks is determined during the grinding process and the shape of the working surface of the working disk is modified mechanically or thermally as a function of measured geometry of the working gap in such a way that the working gap has a given form. The working gap is regulated in such a way that the amount of the ratio of the difference between the maximum and minimum width of the working gap to width of the working disks is 50 ppm during 10% of the material removal. The ratio of the difference of the widths of the working gap at the outside edge and at the inner edge to width of the working disks is 0-50 ppm. The working disk contains a device for changing the temperature of the working disk. The shape of the working gap is regulated so that the temperature of the working disk and the shape of the working surface are changed. The temperature of the working disk is changed by the temperature and/or the flow rate of a cooling agent introduced during the treatment in the working gap. The working disk is mechanically deformed by a hydraulic adjustment device or by piezoelectrically, magnetostrictively or electro-dynamically positioning elements. The shape of the working gap is regulated via the pressure in the hydraulic adjustment device or via the electrical voltage or the electric current in the position elements. The width of the working gap is determined at two points by contact-less distance measuring sensors in the working disk with a distance sensor near internal edge and another distance sensor near the outside edge of the working disk. During grinding, the temperature in the working gap is measured at two points and the shape of the working gap is measured by comparing the measured temperature profile in the working gap with the temperature profile measured before beginning the grinding and by the shapes of the working gap measured for these temperature profiles. A prediction of the deformation of the working gap takes place by comparing the measured temperature profile in the working gap with the temperature profile measured before beginning the grinding and by the shapes of the working gap measured for these temperature profiles. The prediction of the deformation is used for a fast regulation of the shape of the working gap. The measurement of the width of the working gap is used for controlling the actual shape of the working gap and for the compensation of a possible drift of the shape of the working gap for a slow regulation. The regulation of the shape of the working gap takes place in an automatic control loop. The difference of the widths of the working gap at the inside and at the outside edge of the working disk represents the controlled variable, the temperature of the working disk of the correcting variable and the temperatures of the variable disturbances measured in the working gap. The temperature of the working disk is influenced by the temperature or the flow rate of a cooling lubricant introduced during the treatment in the working gap. The working disk contains a hydraulic adjustment device. The maximum of the overflow in radial direction is more than 0-20% of the diameter of the disk. The overflow is defined as the length measured related to the working disks. The circulating disk consists of a first and a second material that is completely or partly coated with the first material. The first material has a high abrasion resistance. The circulating disk has a coating from the first material and a core from the second material that possesses a higher modulus of elasticity than the first material. The second material is a metal, steel or a fiber-reinforced plastic. The first material is a non-strengthened plastic. The coating is applied on the core by the process of separation, dipping, spraying, submerging, heating or heat sticking, chemical sticking, sintering or positive connection. The coating consists of individual points or strips, which are inserted by adding or pressing, injection molding or sticking into suitable drillings of the core. The coating is replaced after wear of the core and a new coating from the first material is applied and the core is reused. The core consists of a thin outer ring of the circulating disk. The ring comprises a tooth system of the circulating disk for the activation through the shifting device. The first material is connected with the core by positive connection, sticking or injection molding. The first material has recesses for the semiconducting wafer. The first material causes a grinding of the abrasive medium in the working layer. The grinding takes place by releasing free hard materials from the first material of the circulating disk. The hard materials are softer than the abrasive medium. The hard material is soft or its grain size is small so that the material does not increase the roughness and damage depth of the surface of the wafers.