Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
2000-09-08
2002-07-30
Powell, William A. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C156S345420, C216S002000, C216S038000, C216S084000, C216S088000, C438S008000, C438S745000
Reexamination Certificate
active
06426296
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an end-point detector and a method for quickly and accurately measuring a change in thickness in semiconductor and other wafers during chemical-mechanical polishing (CMP) of the wafer.
2. Background Information
The prior art discloses methods and apparatus for removing material by chemical-mechanical polishing (CMP) from the surface of a wafer in the production of ultra-high density integrated circuits. In a typical process, a wafer is pressed against a polishing pad in the presence of a slurry under controlled chemical, pressure, velocity, and temperature conditions. The slurry solution generally contains small, abrasive particles that abrade the surface of the wafer and chemicals that etch and/or oxidize the surface of the wafer. The polishing pad is generally a planar pad made from a porous material such as blown polyurethane. Thus, when the pad and/or the wafer moves with respect to the other, material is removed from the surface of the wafer by the abrasive particles (mechanical removal) and by the chemicals in the slurry (chemical removal).
Microsensor technology is heavily dependent on precision wafer thickness control during fabrication. Poor thickness control has resulted in deviation in predicted system functionality. Inconsistent reproducibility of sensor functionality has also been partially attributed to the lack of precision control of wafer thickness. The existence and seriousness of the problem has remained a major area of research.
The prior art discloses various methods and apparatus for obtaining a wafer of a desired thickness at the completion of the process. U.S. Pat. No. 4,793,895 to Kaanta, et al., for example, discloses an apparatus and method for monitoring the conductivity of a semiconductor wafer during the course of a polishing process. A polishing pad that contacts the wafer has an active electrode and at least one passive electrode, both of which are embedded in the polishing pad. A detecting device is connected to the active and passive electrodes as the wafer is lapped by the polishing pad. The etch end-point of the wafer is determined as a function of the magnitude of the current flow.
U.S. Pat. No. 5,242,524 to Leach, et al. discloses an apparatus for remotely detecting impedance adapted for use on a polishing machine wherein the end point of polishing for removing a surface layer during the processing of semiconductor substrates is detected. A first stationary coil having a high permeability core is wound having an air gap and an AC voltage is applied to the stationary coil to provide a magnetic flux in the air gap. A second coil is mounted for rotation on the polishing table, in a position to periodically pass through the air gap of the stationary coil as the table rotates. The second coil is connected at its opposite ends to contacts which are embedded in the surface of the polishing wheel. The contacts are positioned to engage the surface of the substrate being polished and provide a load on the second rotating coil when it is in the air gap of the stationary coil, will perturb the flux field therein as a function of the resistance of the load caused by the contacts contacting either a conducting surface or a non-conducting surface. This perturbance of the flux field is measured as a change in the induced voltage in the stationary cell which is converted to a signal processed to indicate the end point of polishing, the end point being when a metallic layer has been removed to expose a dielectric layer or when a dielectric layer has been removed to expose a metallic layer.
U.S. Pat. No. 5,433,651 to Lustig, et al. discloses an in-situ chemical mechanical polishing (CMP) process monitor apparatus for monitoring a polishing process during polishing of a workpiece in a polishing machine, the polishing machine having a rotatable polishing table provided with a polishing slurry, is disclosed. The apparatus comprises a window embedded within the polishing table, whereby the window traverses a viewing path during polishing and further enables in-situ viewing of a polishing surface of the workpiece from an underside of the polishing table during polishing as the window traverses a detection region along the viewing path. A reflectance measurement means is coupled to the window on the underside of the polishing table for measuring a reflectance measurement means providing a reflectance signal representative of an in-situ reflectance, wherein a prescribed change in the in-situ reflectance corresponds to a prescribed condition of the polishing process.
U.S. Pat. No. 5,667,629 to Pan, et al. discloses an apparatus and method for determination of the end-point for chemical-mechanical polishing of a layer of dielectric material formed on an integrated circuit wafer. A first voltage is generated which is proportional to the current supplying electrical power to the electric motor driving the polishing mechanism. The current is proportional to the rate of removal of dielectric material by the polishing process. The integral over time of the first voltage, which is proportional to the amount of dielectric material and is a function of the age of the polishing pad. When the integral over time of the first voltage is less than the reference voltage the polishing continues. When the integral over time of the first voltage is equal to the reference voltage or becomes larger than the reference voltage the polishing is stopped.
U.S. Pat. No. 5,777,739 to Sandhu, et al. discloses an end-point detector and a method for quickly and accurately measuring the change in thickness of a wafer in chemical-mechanical polishing processes. The end-point detector has a reference platform, a measuring face, and a distance measuring device. The reference platform is positioned proximate to the wafer carrier, and the reference platform and measuring device are positioned apart form one another by a known, constant distance. The measuring face is fixedly positioned with respect to the wafer carrier at a location that allows the measuring device engage the measuring face when the wafer is positioned on the reference platform. Each time the measuring device engages the measuring face with respect to the measuring device. The displacement of the measuring face is proportional to the change in thickness of the wafer between measurements.
U.S. Pat. No. 6,015,754 to Mase, et al. discloses an apparatus used to subject a target surface of a semiconductor wafer to a polishing treatment, by moving the target surface and a polishing surface of a polishing cloth relative to each other while supplying a polishing cloth relative to each other while supplying a polishing liquid between the target surface and the polishing surface. Electric resistance is measured between pairs of measuring points arranged on opposite sides of dicing lines on the target surface, while subjecting the target surface to the polishing treatment. The polishing treatment is caused to be ended by comparing detected values of a changing rate in measured values of the electric property with a reference value set to correspond to an end point of the polishing treatment.
Such prior art of thickness control during lapping and polishing involves intermittent stopping of the lapping process to measure the thickness by various means. Other methods include capacitive sensing, slurring monitoring, and optical measurement. In the case of reactive ion etching, end-point detection using optical emission spectroscopy has been employed as a method.
The main disadvantages of the prior art include the time wasted during intermittent lapping and stopping, lack precision of measurement, involve considerable measurement complexity and have attendant high costs.
SUMMARY OF THE INVENTION
It is an objective of this invention to provide a precision thickness capability during lapping and polishing of semiconductor wafers and other wafers such as dielectric wafers.
It is a further objective of the present invention to provide automatic control features in the lappin
Powell William A.
Stone Kent N.
The United States of America as represented by the Administrator
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