Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
2001-02-06
2001-11-20
Banks, Derris H. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S041000
Reexamination Certificate
active
06319093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to chemical-mechanical planarization or polishing (CMP) tools and, more particularly, to a system and method, which combine work-piece film measurements with a spin-dry process.
2. Description of the Related Art
Briefly, the chemical mechanical polishing process requires that a workpiece be held, with the desired coated surface face down, on a polishing pad supported on a rotating table, in the presence of an abrasive slurry. A chemical mechanical polishing machine (unit) can include a single rotating polishing plate and a smaller diameter rotating wafer carrier to which a wafer (or wafers) is (are) mounted. The wafer carrier is held above the polishing plate, in either a stationary fixed position or oscillating back and forth in a predetermined path, while both polishing plate and wafer carrier are rotated about their respective center axes. A slurry, consisting of an abrasive suspension with or without an etching reagent, is fed onto the polishing plate during polishing of the wafer. The slurry, also referred to as a carrier liquid, can be selected to include an etchant for the coating being planarized and for not substantially attacking other materials involved in the process. The slurry is further fed between the polishing plates to polish and flush away the material removed from the semiconductor wafer. Current CMP tools are built with a constrained processing sequence whereby wafers are loaded from a cassette, polished, rinsed, cleaned, dried and unloaded. In some cases there are multiple polish steps where a wafer is polished first in one polishing medium, rinsed, polished in a second medium, rinsed, cleaned, dried and unloaded.
In particular, when using various CMP polishing tools in processing a wafer where a sufficient amount of surface films has been polished (removed by grinding), the wafer is rinsed and cleaned to remove slurry and then dried in a spin-dry process using a CMP spin-dry tool. Further, when a CMP process polishes transparent materials such as oxides and nitrides in addition to metals, the process is typically controlled by performing an optical film thickness measurement. For example, back end silicon dioxide layers are typically polished from a starting thickness of 20000 angstroms to a final thickness of 10000 angstroms. To control the process, wafers have to be removed periodically from the spin dryer and measured on an optical film thickness measurement tool that examines the film reflectivity spectrum across a range of optical wavelengths to determine the thickness of material from the optical fringe pattern. Thickness measurements are typically made at many points on the wafer (usually six or more). The deviation of this thickness value from a desired value is used to adjust the polish time for subsequent wafers up or down to assure that they are polished to the correct thickness.
The measurement of thin films on semiconductor and other micro-manufactured parts is typically performed by an optical interference technique in which the reflectance or transmission properties are measured using an optical probe using a separate apparatus. Then, the acquired spectrum is analyzed with a computer program referred to as a “recipe” using known film properties and physics to solve for unknown properties such as film thickness, density etc. For ideal films having one or more perfectly flat layers, these measurements are straight forward and well documented.
However, prior to the invention, there has been no effective structure or operation that minimizes the number of steps or machines used to perform this process, which is slow and expensive since wafers being processed must be manually loaded into a stand alone optical film thickness measurement tool. This represents significant delay between the time the wafer is polished and the time the film thickness measurement is completed. Where precise control is essential, the process is halted until the thickness measurement results are known. This causes both the introduction of additional errors due to tool drift during idle time and cost in terms of process cycle time.
In addition, known processes have had to stop processing and determine variations of thickness of a wafer being processed to determine whether the CMP polishing unit is operating within acceptable tolerances to control basic thickness of the resultant polished films on the wafer. When the CMP polishing unit is in need of maintenance and/or out of tolerance, this state of operation incurs processing error, thus additional unwanted processing expense. This is generally caused by the CMP polishing pads wearing out and in need of replacement, and the polishing tool often needs to be calibrated and adjusted. Mechanical part wear and failure is evident when examining the thickness distribution of a polished wafer. The normal polish distribution on a wafer is a radially symmetric distribution which is typically low in variation magnitude. When the range or distribution of thickness values becomes unusually large, this is interpreted as need for maintenance, which is slow and expensive.
SUMMARY OF THE INVENTION
In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional methods and structures, an object of the present invention is the ability to perform integrated film measurement system with a chemical-mechanical polishing process' spin-dry tool using optical probe(s) mounted in an optical line-of-sight of a surface of a workpiece in the CMP spin-dry tool.
Another object of the invention is to retain the accuracy advantages inherent in optical interference film measurements for performing optical interferometric measurements of film properties in conjunction with established optical detection and signal analysis methods. Also, by doing such measurements, the number of steps involved with a CMP process are minimized, thereby enabling a continuous processing of wafers without need for removal of the wafer from a CMP spin-dry tool to perform thickness/composition measurements.
A further object of the invention is to provide continuous monitoring of operational tolerances of the CMP polishing unit for more cost effective manufacturing of wafers.
One aspect of the present invention provides integration of a thickness measurement probe with an appropriate measurement and processing CMP controller subsystem with a CMP spin-dry tool. By doing so, each wafer can be measured as it comes out of the previous CMP process. Thickness measurement feedback is provided, which controls processing of the wafer and also monitor operational status of the CMP polishing unit prior to completion of the wafer being polished. In so doing, significant cost and cycle time reduction results through the elimination of tool infrastructures and handling by ensuring proper tolerances of the CMP polishing unit are maintained. Additionally, significant control advantage is afforded by having a tighter control loop with more measurements thereby resulting in improved polishing precision. By using an integrated CMP spin dry tool with film thickness measurement system in one system that includes at least two probes, significant cost savings occur.
Further, the present invention includes, in preferred form, a CMP spin-dry tool that has at least two multi-pass optical probes mounted in a hood member that perform measurements of the wafer during a spin-dry process. The probes perform optical thin film thickness and composition measurements, which includes an optical light source for emitting light to the wafer, a detector for detecting the light reflected from the wafer, one of a spectral dispersion element and a filtration element constructed to propagate light from the light source to wafer surface films under examination, and back to the detector such that a given ray of light passes through substantially a same location on the wafer at least two times. The determination of thin film properties of thickness and composition can be measured with inexpensive compact,
Lebel Richard J.
Maurer Frederic
Nadeau Rock
Smith, Jr. Paul H.
van Kessel Theodore G.
Banks Derris H.
International Business Machines - Corporation
McGinn & Gibb PLLC
Walsh, Esq. Robert A.
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