Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With rotor
Reexamination Certificate
1999-03-24
2001-06-19
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With rotor
C438S778000
Reexamination Certificate
active
06249117
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of semiconductor fabrication process monitoring and control, and methods therefor, and more particularly, is a device and method that applies to the calibration, monitoring and control of test equipment used on the process line to measure oxide charge including mobile ion contamination.
DESCRIPTION OF THE RELATED ART
Semiconductor wafers undergo a variety of measurements to measure and ensure the suitability of the wafer for further processing. Some of these measurements test for acceptable levels of charge time retention, dopant concentration, leakage and mobile ion concentration. In particular, one of these tests, for the detection of mobile ion concentration and other oxide charge is key to the successful fabrication of integrated circuits upon semiconductor wafers in the process line. The monitoring of mobile ion contaminants such as sodium ions or potassium ions is required to ensure that adequate yields result, and also to ensure that the reliability of the products is maintained at a quality level. Mobile ions are most commonly caused by the atoms of contaminant, or impure, materials. Two examples of major sources of contaminants are sodium and potassium. Sodium may be introduced from quartz ware within oxide furnaces, and it may also be present in chemicals used during the semiconductor manufacturing process such as photoresist solutions. These contaminant ions are of course differentiated from implanted dopant ions such as boron and phosphorus.
In general there are two methods that are routinely used to test for oxide charge, including mobile ion contamination. The first of these methods measures the capacitance-voltage (CV) of metal-oxide-silicon (MOS) structures. The second method measures surface photovoltage (SPV) and oxide surface voltage (Vs) without using a metal contact, and in some cases measures the amount of charge deposited on top of the oxide by a corona-discharge source.
The first measurement method utilizes equipment that is categorized as a contact probe tester to measure the CV. A contact probe tester method utilizes a process in which a voltage is incremented on a MOS electrode upon the surface of a semiconductor wafer using a contact probe, and the corresponding increment in the charge upon the wafer, as measured by a contact probe coulombmeter is monitored.
The second measurement method utilizes equipment that is categorized as a non-contact probe tester. In the non-contact probe tester method a corona gun or wire is used to deposit charges on the dielectric for biasing it. An example of a non-contact probe tester is given in U.S. Pat. No. 5,498,974, and functions as follows: A wafer is charged with a non-contact corona discharge at a positive polarity until a positive dielectric field is developed. A negative, though equal in value, polarity is then applied to the wafer until a negative dielectric field is developed. The amount of corona discharge necessary to change the dielectric field from the positive field to the negative field is measured. This measured charge, Q
m
is noted. Next, an ideal amount of corona discharge necessary to change the dielectric field voltage of a dielectric layer of known thickness from a specific positive dielectric field to a negative, though equal in value, dielectric field is then applied to the wafer. The resultant ideal charge, Q
i
, is then observed. The ideal charge Q
i
is then compared to the measured charge Q
m
. The difference between the measured ideal charge Q
i
and measured charge Q
m
is directly proportional to the amount of mobile ions in the dielectric layer.
There is however, a major area of concern with mobile ion measurement equipment and methods. In order to assure that the readings and measurements obtained by the mobile ion measurement equipment and methods are of high quality, the equipment and methods must be calibrated and verified. There is currently only one common method used for the calibration of mobile ion measurement equipment, and this method is incapable of meeting accepted quality control standards, such as ISO 9000, (International Organization for Standardization (ISO)—Quality management and quality standards assurance. (9000 series)) This method of calibration consists of the production of calibration wafers that have been intentionally contaminated with mobile ions. While the production of calibration wafers, or wafer standards as they are sometimes known, is desirable, these calibration wafers are difficult to produce because the dielectrics of a wafer that have been purposely contaminated with mobile ions tend to be unpredictable and unstable in their use. The unpredictability and instability of the calibration wafers can result in the incorrect calibration of the oxide charge measurement equipment. This may then lead to incorrect assessments of the production line equipment and the wafers in process, which in turn leads to faulty or imperfectly operating semiconductor devices.
A further problem is that in order to control the oxide charge in a semiconductor fabrication line, it is necessary to distinguish between the variables associated with the dielectric layer of a wafer under test and the variables in the tester itself.
Therefore, a need existed for a system and method of producing improved calibration wafers. An additional need existed for a system and method of producing calibration wafers having the properties of predictability and stability in order to ensure the correct assessment of the production line equipment and the wafers in process. A further need existed for a system and method of producing high quality calibration wafers capable of meeting quality control certification. Yet a further need existed for a system and method of producing high quality calibration wafers to enable distinguishing between the variables associated with the dielectric layer of a wafer under test and the variables in the tester itself.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a system and method of producing improved calibration wafers.
Another object of the present invention is to provide a system and method of producing calibration wafers having the properties of predictability and stability in order to ensure the correct assessment of the production line equipment and the wafers in process.
A further object of the present invention is to provide a system and method of producing high quality calibration wafers capable of meeting quality control certification.
An additional object of the present invention is to provide a system and method of producing high quality calibration wafers to enable distinguishing between the variables associated with the dielectric layer of a wafer under test and the variables in the tester itself.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with a preferred embodiment of the present invention a stabilized wafer for monitoring and calibrating oxide charge test equipment is disclosed. The stabilized wafer for monitoring and calibrating oxide charge test equipment comprises; a silicon wafer, a SiO
2
layer upon the silicon wafer, and a phosphosilicate glass layer formed in the SiO
2
layer for providing the stabilized wafer by stabilizing an SiO
2
interface and containing oxygen ions.
In accordance with another embodiment of the present invention a method of constructing and using a stabilized wafer for monitoring and calibrating oxide charge test equipment is disclosed. The method of constructing and using a stabilized wafer for monitoring and calibrating oxide charge test equipment comprises the steps of; providing a stabilized wafer for stabilizing an SiO
2
interface and containing oxygen ions, and using the stabilized wafer for monitoring and calibrating oxide charge test equipment.
In accordance with yet another embodiment of the present invention a method of constructing and using a stabilized wafer for monitoring and calibrating oxide charge test equipment is disclosed. The method of constructing and using a stabilized wafer for monitoring and ca
Koelsch Robert
Koelsch Ronald G.
Kerveros J.
Metjahic Safet
Moy Jeffrey D.
Wafer Standards, Inc.
Weiss Jeffrey
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