Method for real-time in-situ monitoring of a trench formation process
First Claim
1. A method for real-time and in-situ monitoring of trench depth and silicon dioxide redeposited layer thickness parameters during a trench formation process on a silicon wafer comprising the steps of:
- a) placing the wafer in an evacuated reaction chamber of an etching apparatus;
b) using an oxygen-comprising plasma to etch a desired pattern of trenches in at least a portion of said wafer such that a silicon dioxide layer is redeposited during trench formation;
c) illuminating an area of said portion with a light beam including at least one first radiation wavelength to produce a reflected interferometric light beam;
d) applying the reflected light to a spectrometer to generate a primary signal;
e) processing said primary signal to extract a first secondary signal having a low frequency component and a second secondary signal having a higher frequency component, wherein said first secondary signal is representative of a deposition rate of said silicon dioxide layer, and said second secondary signal is representative of an etch rate of said trenches;
f) monitoring said silicon dioxide layer deposition with said first secondary signal and a depth of said trenches with said second secondary signal; and
,g) in response to said monitoring, stopping the etching when a desired final trench depth has been attained or upon detecting an anomaly in said silicon dioxide layer deposition.
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Abstract
In the manufacturing of 16 Mbit DRAM chips, the deep trench formation process in a silicon wafer by plasma etching is a very critical step when the etching gas includes 02. As a result, the monitoring of the trench formation process and thus the etch end point determination is quite difficult. The disclosed monitoring method is based on zero order interferometry. The wafer is placed in a plasma etcher and a plasma is created. A large area of the wafer is illuminated through a view port by a radiation of a specified wavelength at a normal angle of incidence. The reflected light is collected then applied to a spectrometer to generate a primary signal S of the interferometric type. Next, this signal is applied in parallel to two filters. A low-pass filter produces a first secondary signal S1 that contains data related to the deposition rate and the redeposited layer thickness. A band-pass filter produces a second secondary signal S2 that contains data related to the trench etch rate and depth. The band-pass filter is centered around the fundamental frequency of the interferometry phenomenon. These filtered signals are monitored as standard and the trench formation parameters such as the SiO2 redeposited layer thickness and the trench depth are accurately measured in real time to allow an accurate determination of the etch end point. It is worthwhile to have the optical emission of the plasma viewed by another spectrometer to generate a second primary signal S* that is used to validate the parameter measurements.
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Citations
12 Claims
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1. A method for real-time and in-situ monitoring of trench depth and silicon dioxide redeposited layer thickness parameters during a trench formation process on a silicon wafer comprising the steps of:
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a) placing the wafer in an evacuated reaction chamber of an etching apparatus; b) using an oxygen-comprising plasma to etch a desired pattern of trenches in at least a portion of said wafer such that a silicon dioxide layer is redeposited during trench formation; c) illuminating an area of said portion with a light beam including at least one first radiation wavelength to produce a reflected interferometric light beam; d) applying the reflected light to a spectrometer to generate a primary signal; e) processing said primary signal to extract a first secondary signal having a low frequency component and a second secondary signal having a higher frequency component, wherein said first secondary signal is representative of a deposition rate of said silicon dioxide layer, and said second secondary signal is representative of an etch rate of said trenches; f) monitoring said silicon dioxide layer deposition with said first secondary signal and a depth of said trenches with said second secondary signal; and
,g) in response to said monitoring, stopping the etching when a desired final trench depth has been attained or upon detecting an anomaly in said silicon dioxide layer deposition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification