Plasma etching endpoint detection using multiple wavelengths for small open-area wafers

Abstract

This article proposes a new approach for etch endpoint detection of small open area wafers. The traditional endpoint detection technique uses a few manually selected wavelengths, which are adequate for large open areas. As the integrated circuit devices continue to shrink in geometry and increase in device density, detecting the endpoint for small open areas presents a serious challenge to process engineers. In this work, a high-resolution optical emission spectroscopy (OES) system is used to provide the necessary sensitivity for detecting subtle endpoint signals. Principal component analysis is used to analyze the OES data and extract key components that capture the endpoint signal. Data analysis from many wafers shows that the endpoint pattern in the principal components is repeatable. Two methods are used to select wavelengths so as to improve reliability and reduce susceptibility to noise. The first method is to remove those spectrum windows that contain no endpoint information. The second method is to use a “sphere” criterion to select the most relevant wavelengths. The final endpoint algorithm using a much-reduced number of wavelengths shows more distinguishable and reliable endpoint features.

Actinometric Investigation of In-Situ Optical Emission Spectroscopy Data in SiO2Plasma Etch

“…OES measures the optical emission intensity from the glow discharge of reactive species of plasma and it provides useful information about the plasma physics and chemistry. The most well-known application of OES is end-point-detection (EPD) in etching by tracing one or more specific wavelengths and these wavelengths correspond to the etch by-products along time [5]. Moreover, it is also reported that OES can be utilized as a useful tool for in-situ real-time process fault detection and classification [6].…”

Matrix Factorisation Techniques for Endpoint Detection in Plasma Etching

“…Variance scaling can be used to eliminate the effect of non-uniformity, but this in turn leads to the amplification of noise on small magnitude signals. This is a particularly severe problem with OES data as some channels are predominately background noise, hence, in practice variance scaling is not recommended [5].…”

“…In [3] PCA is applied for spatial characterisation of the wafer state. In [2] and [5] it is exploited for endpoint detection, while in [4] the focus is on fault detection.…”

“…The main technique employed to date in this regard has been Principal Components Analysis (PCA). The literature on PCA applications in semiconductor manufacturing research is rather numerous, see for example [2], [3], [4] and [5]. In [3] PCA is applied for spatial characterisation of the wafer state.…”

Real-time In-situ Plasma Etch Process Monitoring for Sensor Based-Advanced Process Control

“…The most widely utilized in-situ sensor is optical emission spectroscopy (OES) for endpoint detection and FDC as well [5][6]. OES can provide much of information including plasma properties and process chemistries, but it is limited in the speed of data acquisition due to the large dimensionality.…”