Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-01-04
2001-06-19
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S630000
Reexamination Certificate
active
06247368
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates, in general, to the field of semiconductor manufacture. In particular, it relates to monitoring the presence of a semiconductor wafer during post chemical mechanical polishing (CMP) processing.
2. Description of Related Art
Fabrication of semiconductor integrated circuits (IC) is a complicated multi-step process for creating microscopic structures with various electrical properties to form a connected set of devices. As the level of integration of ICs increases, the devices become smaller and more densely packed, requiring more levels of photolithography and more processing steps. As more layers are built up on the silicon wafer, problems caused by surface non-planarity become increasingly severe and can impact yield and chip performance. During the fabrication process, it may become necessary to remove excess material in a process referred to as planarization.
A common technique used to planarize the surface of a silicon wafer is chemical mechanical polishing (CMP). CMP involves the use of a polishing pad affixed to a circular polishing table and a holder to hold the wafer face down against the rotating pad. A slurry containing abrasive and chemical additives are dispensed onto the polishing pad.
The wafer and polishing pad rotate relative to each other. The rotating action along with the abrasive and chemical additives of the slurry results in a polishing action that removes material from the surface of the wafer. Protrusions on the surface erode more efficiently than recessed areas leading to a flattening or planarization of the wafer surface. Following CMP, the wafer must be cleaned of any CMP and slurry residue. Any residue remaining on the wafer can cause shorts in the IC devices.
The wafers are loaded into a wet processing station such as that shown in
FIG. 1
, and submerged in a water bath. The processing station contains a wafer transporter having a track which moves the wafers by means of a water jet pushing the wafers along the track. The wafers are then pushed into a cassette-like holder having horizontal slots for each wafer. The holder is motorized moving vertically to receive the wafer in the slot as it is being shot off the wafer transporter.
One or more sensors are used to track the presence of the wafers along the wafer transporter and prior to being inserted into the slots of the wafer holder.
Prior art methods employ sensors to track the presence of the wafers which utilize interruption of a signal path, for example, optical sensors using fiber optics. However, the optical sensors have proven unreliable due to film build-up, wafer color/hue variations, light refraction, sensing distance, bubble interference in water tracks, and other wet environment associated problems. These “false” sense events result in wafer breakage due to the inability of the sensor to correctly detect the presence of the wafer. The wafer breaks apart as the timing between the transport track and the holder are not in sync. Lost tool production in stopping the process adds to the already high cost of semiconductor wafer fabrication.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a non-optical sensor which overcomes the problems of false sensing.
It is another object of the present invention to provide a sensor which is sustainable for use in a wet environment without regard to slurry contamination or CMP residue.
A further object of the invention is to provide a method of sensing a semiconductor wafer in a CMP processing station.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a semiconductor post-polishing processing apparatus comprising a wet processing station; a wafer transport track leading from the wet processing station; and a non-optical sensor for detecting the presence or position of semiconductor wafers within the station of the processing apparatus.
Preferably, the non-optical sensor of the semiconductor post-polishing processing apparatus emits and detects sound waves. More preferably, the non-optical sensor of the semiconductor post-polishing processing apparatus comprises a piezo element. The sound waves are emitted and reflected back to the sensor to determine the presence or position of semiconductor wafers within the station of the processing apparatus. Most preferably, the non-optical sensor of the semiconductor post-polishing processing apparatus emits sound waves in a frequency range of about 175 to 200 kHz, and most preferably at a frequency of about 190 kHz. Alternatively, the non-optical sensor of the semiconductor post-polishing processing apparatus may comprise a mechanical sensor attached to the wafer transport track.
In another aspect, the present invention relates to a post-planarization processing system for semiconductor wafers comprising at least one processing station; a transport system for transporting the wafers within the processing stations in a wet environment; a non-optical sensing means for sensing the presence of the wafers along the transporter; and an end station located at the end of the transport system comprising a holder having a plurality of horizontal slots for individual placement of the wafers adapted for placement of each wafer in a slot as they leave the transport system.
The sensing means comprises a transducer capable of emitting sound waves and a detector for detecting reflection of the sound waves when there is a wafer present on the transport system. Preferably, the transducer is a piezo element. The post-planarization processing system may further include a processor for producing a signal when the presence of a wafer is not detected by the sensing means.
In still yet another aspect, the present invention relates to a method of detecting the presence or position of a semiconductor wafer in a post-polishing apparatus comprising the steps of: providing a post-polishing apparatus having a wet environment; providing a semiconductor wafer situated in the post-polishing apparatus within the wet environment; emitting an acoustic wave; reflecting the acoustic wave to produce an electrical signal; processing the electrical signal resulting from the wave reflection; and comparing the electrical signal with a threshold signal to determine the presence and position of the semiconductor wafer.
Preferably, the emitter and detector of the post-polishing apparatus used in the method of detecting the presence or position of a semiconductor wafer is a piezo element operating at a frequency range of about 175 to 200 kHz, and most preferably at a frequency of about 190 kHz.
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Cline Scott R.
Kalvaitis Willi O.
Lebel Richard J.
McKinney Charles A.
Nadeau Douglas P.
DeLio & Peterson LLC
International Business Machines - Corporation
Larkin Daniel S.
Miller Rose M.
Peterson Peter W.
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