Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Electrostatic attraction or piezoelectric
Reexamination Certificate
1997-06-12
2001-10-09
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Electrostatic attraction or piezoelectric
C324S457000
Reexamination Certificate
active
06300756
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a method and apparatus for measuring an electrical charge on a surface, and more particularly to a system of one or more micro-cantilevers for measuring charges on a surface layer on a substrate during semiconductor processing on semiconductor wafers.
2. Related Art
Plasmas are widely used in the semiconductor industry for processing to delineate fine line pattern and deposition at low temperature, e.g. plasma etching. During plasma exposure the wafer is exposed to a bombardment of ions, electron, photons, and x-rays which can lead to a charge build-up on the semiconductor device. Such a charge build-up, known as wafer surface charging, can degrade or destroy the device. If such charges develop, a voltage can develop which could cause irreversible damage to the device, especially metal oxide semi conductor (MOS) gate dielectrics. In recent years, it has been reported that plasma non-uniformity across the wafer is the predominant cause of charging. This non-uniformity can arise from non-uniformities in RF current flow, electron current flow, and ion current flow. Such charging can also arise from handling and/or cleaning a semiconductor device. These problems are becoming more important as gate oxides become thinner, and hence, more vulnerable to surface charging.
It would be beneficial to measure in situ, in a plasma reactor, the charge on a wafer to determine the magnitude of such charges occurring during the manufacturing process. This could lead to improved manufacturing processes. Additionally, if one could measure the charge on a wafer that occurred during the manufacturing process, one may be able to use such measurement as a quality control means, i.e. by discarding chips have too great a charge and therefore, a high likelihood of damage.
Previous efforts in this area have not yielded a suitable method and apparatus for measuring a charge on a wafer during the manufacturing process. One way that has been used in the past to obtain measurements of charge is to attach leads directly to a specimen. Another way of determining charge is to measure degradation of the transistor after processing. Such previous efforts include:
Murakawa, et al., “Mechanism of Surface Charging Effects on etching Profile Defects,” Jpn. J. Appl. Phys., Vol 33 (1994) discloses using a magnet placed under a grounded electrode to create a magnetic field at the wafer center. A probe measures the plasma potential along the wafer. The probe comprises a silicon wafer with an A
1
pad with contacts leading to Cu wires extending out of the chamber to RF chokes and low-pass filters and then to a DC voltmeter. This is not an elegant solution as it requires fishing wires in and out of the reactor chamber.
Another commercially available method of measuring charge comprises a detection device which can be employed outside the reactor chamber after processing of a device is complete. However, this solution is not entirely satisfactory because it measures an accumulated affect over the total processing time and cannot provide specific information about charge development during processing.
None of these previous efforts teach or suggest all of the elements of the present invention, nor do any disclose the benefits and utility of the invention.
OBJECTS AND SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a method and apparatus for measuring charge on a surface.
It is another object of the present invention to provide a method and apparatus for measuring the charged caused by plasma processing of a semi-conductor wafer.
It is another object of the present invention to provide microscopic cantilevers for use in measuring a charge on a surface.
It is an additional object of the present invention to provide a method and apparatus for measuring charge on a semi-conductor surface in situ.
It is even an additional object of the present invention to provide means for measuring charge on a surface by measuring deflection of a cantilever beam.
It is still even an additional object of the present invention to provide a means for measuring a charge on a surface wherein a rigid beam is connected to a flexible bridge so that the surface of the beam does not bend during deflection of the device.
It is still even a further object of the present invention to provide a means for measuring charge on a surface which can map charging across an electrode.
It is still another object of the present invention to utilize a plurality of micro-cantilevers on a wafer to measure surface charging.
It is a further object of the present invention to provide test wafers comprising a plurality of probes for experimental use.
It is also an object of the present invention to provide probes on wafers in combination with actual circuits of chips, which probes do not affect chip performance.
The present invention provides a method and apparatus for measuring a charge on a surface, such as on a semiconductor wafer, arising during plasma processing. Accordingly, such a charge may be measured on an insulating film applied to such a wafer. By the present invention, the charge on such an insulator exposed to plasma is measured in-situ, within the plasma reactor, using micro-cantilevers. The micro-cantilevers include an insulating base positioned on the substrate and a cantilevered beam extending therefrom to over the substrate. The beam is formed of a conductive material. Processing can cause external charges to occur on the beam. A charge on the beam causes an opposite charge to form on the substrate. The opposite charges attract to move or deflect the beam towards the substrate. The amount of movement or deflection corresponds to the magnitude of the charge. This movement or deflection of the beam can be measured to determine the charge by bouncing a light source, such as a laser, off of the cantilevered beam. Alternatively, measuring charge can be performed by allowing the beams to deflect to the point of contact with substrate wherein they stick to the substrate, and the beams can be later inspected to determine charge. In another embodiment, the cantilever includes a flexible bridge interconnected between the base and a rigid beam. In this embodiment, the surface of the beam does not bend. Rather, movement of the beam is accomplished by the bending of the flexible bridge. This allows for easier measurements of the movement of the beam because the surface of the beam remains planar.
REFERENCES:
patent: 3317983 (1967-05-01), De Wit
patent: 4614908 (1986-09-01), Daniele et al.
patent: 4625176 (1986-11-01), Champion et al.
patent: 4835461 (1989-05-01), Snelling
patent: 5517123 (1996-05-01), Zhao et al.
Murakawa et al, “Mechanism of Surface Charging Effects On Etching Profile Defects”, Jpn. J. Appl. Phys, vol. 33, Apr. (1994) pp. 2184-2188.
Lukaszek, et al., “Claim 2: Towards an Industry-Standard Wafer Surface-Charge Monitor”, IEEE/SEMI Advanced Semiconductor Manufacturing Conference (1992) pp 148-152 (month unavailable).
Lukaszek, “Characterization of Wafer Charging in ECR Etching”, 2ndInternational Symposium on Plasma Process-Induced Damage May (1997), pp. 119-122.
Murakawa et al., “Direct Measurement of Surface Charging during Plasma Etching”, Jpn. J. Appl. Phys. vol. 33 May (1994) pp. 4446-4449.
Firebaugh Samara L.
Pangal Kiran
Sturm James C.
Brown Glenn W.
The Trustees of Princeton University
Wolff & Samson
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