Semiconductor device manufacturing: process – With measuring or testing
Reexamination Certificate
1999-12-17
2001-10-16
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
With measuring or testing
C436S016000
Reexamination Certificate
active
06303397
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of semiconductor processing, and, more particularly, to a method for benchmarking measurement tools for measuring an insulation layer on a semiconductor substrate.
BACKGROUND OF THE INVENTION
In the manufacture of a metal oxide semiconductor (MOS) device, an insulation, i.e., a dielectric layer, is formed on a surface of the semiconductor substrate. This insulation layer may be silicon dioxide or silicon nitride, which is typically used as a gate dielectric for the MOS device. For purposes of quality control, the thickness of the insulation layer must be within a specified range. Unfortunately, once the insulation layer is exposed to an ambient environment, a contamination layer is formed on the insulation layer. This contamination layer grows over time to a predicted thickness based upon particles in the ambient environment, as well as the amount of humidity present in the ambient environment.
Measurement tools, such as an ellipsometer, can not distinguish between the insulation layer and the contamination layer because they have similar optical properties. Consequently, an actual thickness of the insulation layer may be within a specified range, yet the measured thickness exceeds this range because of the added thickness of the contamination layer. One approach to this problem is to measure the insulation layer before being exposed to the ambient environment causing the contamination layer to form thereon. However, this is not always practical in manufacturing environments due to limited availability of the measurement tools.
Another approach is to expose or age the insulation layer in the ambient environment so that the contamination layer forms to a predicted level. However, the thickness of the contamination layer may still adversely effect the overall measured thickness of the insulation layer, particularly if the thickness of the contamination layer causes the apparent thickness of the insulation layer to exceed the specified range.
Yet another problem arises in the benchmarking of different measurement tools due to the contamination layer. After the insulation layer has aged, the thickness of the insulation layer is measured using a first measurement tool at a first manufacturing site. Afterwords, the semiconductor substrate may be shipped to a second manufacturing site for further processing. The location of the first and second manufacturing sites may be at respective widely spaced geographic locations. However, a second measurement tool used to measure the same thickness of the insulation layer at the second manufacturing site may not provide the same measured thickness as did the first measurement tool.
This discrepancy in the measured thickness of the insulation layer using the second measurement tool may be caused by a change in the thickness of the contamination layer. That is, if the amount of particles in the ambient environment changes between different manufacturing sites, this is reflected by the thickness of the contamination layer either increasing or decreasing. In other words, the contamination layer may vary over time. In addition, this discrepancy may be caused by the second measurement tool being out of adjustment.
Therefore, there is a need to measure the actual thickness of the insulation layer and not a combined thickness of the insulation and contamination layers so that thin film measurement tools can be benchmarked.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for calibrating thin film measurement tools that overcomes the above described measurement discrepancies associated with the contamination layer when measuring an insulation layer on a semiconductor substrate.
This and other objects, advantages and features in accordance with the present invention are provided by a method for calibrating thin film measurement tools comprising the steps of forming an insulation layer on a semiconductor substrate, and measuring a thickness of the insulation layer using a first measurement tool. The insulation layer is preferably exposed to an ambient environment causing a contamination layer to form thereon.
At least a portion of the contamination layer is removed by preferably heating the semiconductor substrate, and a combined thickness of the insulation layer and the contamination layer is then measured preferably using a second measurement tool. The steps of heating and measuring are preferably repeated until a measurement is obtained indicating that the contamination level has been removed. The measured value of the thickness of the insulation layer using the second measurement tool is then compared to the measured value of the thickness of the insulation layer using the first measurement tool to benchmark the first and second measurement tools.
Once the contamination layer has been removed, an accurate measurement of the insulation layer is performed. Since the first and second measurement tools are preferably at respective widely spaced geographic locations, the thickness of the contamination layer can vary between manufacturing sites due to a change in the amount of particles in the ambient environment, and to the amount of humidity in the ambient environment. Therefore, it is necessary to measure the actual thickness of the insulation layer so that the different measurement tools at the respective manufacturing sites can be benchmarked without being adversely effected by the contamination layer that normally forms on the surface of the insulation layer.
The method preferably further comprises, before the steps of measuring, exposing the insulation layer to an ambient environment causing a contamination layer to form on the insulation layer and heating the semiconductor substrate to remove at least a portion of the contamination layer. The steps of heating and measuring are preferably repeated until a measurement is obtained using the first measurement tool indicating that the contamination layer has been removed. In other words, if the contamination layer is formed at the first manufacturing site before the first measurement tool measures the thickness of the insulation layer, then the step of heating is performed to remove the contamination layer.
The step of heating is preferably performed using a rapid thermal annealing process. The temperature is preferably within a range of about 50 to 600 degree C., and the step of heating is preferably performed within a time period of about 1 second to 10 hours. The contamination layer is thus preferably removed during the step of heating without reoxidizing the insulation layer.
In another embodiment of the invention, the step of heating is performed at least one time for removing the contamination layer. This embodiment preferably includes measuring once a thickness of the insulation layer using the second measurement tool. In other words, the temperature and the time period in which the insulation layer is heated are selected so that the contamination layer is removed without having to repeat the steps of measuring.
REFERENCES:
patent: 5900939 (1999-05-01), Aspnes et al.
patent: 6146541 (2000-11-01), Goldstein et al.
patent: 5-275410-A (1993-10-01), None
Chen Yuanning
Lozada Linette
Ma Yi
Young Roger Morgan
Agere Systems Guardian Corp.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Bowers Charles
Pert Evan
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