Etching Endpoint Control via Optical Reflection for Mask Uniformity
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Solution Overview
Problem
In semiconductor device manufacturing, the etching process for shallow trench isolation (STI) often results in non-uniform film thickness of the hard mask layer, leading to irregularities in the buried oxide film and potential residue issues during chemical mechanical polishing (CMP), due to indiscriminate time-based endpoint control in the break-through step.
Innovation Solution
An etching method and apparatus that monitor the thickness of the mask layer in real-time using optical measurements and spectral reflectance, allowing precise control of the etching process to maintain uniform film thickness, and subsequently, uniform trench depth, by terminating the etching when predetermined thickness or depth values are reached.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If time-based endpoint control is used in the break-through step, then the etching process is simple to control, but the film thickness of the mask layer becomes non-uniform
Solution Approach 1:
The patent applies feedback control by monitoring the reflected light intensity during the etching process. The end point detection system continuously measures the light reflected from the mask layer surface, and when the reflected light intensity reaches a predetermined threshold, the etching process is automatically terminated. This feedback mechanism ensures uniform mask layer thickness while maintaining operational simplicity.
Solution Approach 2:
The patent replaces the time-based mechanical control system with an optical detection system. Instead of relying on predetermined etching time, the system uses optical reflection measurements to detect the etching end point. This substitution of mechanical timing with optical sensing achieves both precision and ease of operation.
2Productivity
If the end point of the break-through step is controlled indiscriminately based on time, then the etching process is efficient, but the residual film thickness of the mask becomes non-uniform
Solution Approach 1:
The feedback control system monitors the etching process in real-time by measuring reflected light intensity. When the mask layer thickness reaches the desired residual thickness, the system automatically stops etching. This prevents over-etching and ensures uniform residual film thickness while maintaining high productivity through automated control.
Solution Approach 2:
The etching process is self-regulating through the optical detection system. The system automatically detects when the etching should stop based on the reflected light characteristics, eliminating the need for external timing control and ensuring consistent results without manual intervention.
3Manufacturing precision
If an end point detection layer is prepared in the mask, then the film thickness uniformity can be maintained, but the number of processes increases
Solution Approach 1:
The patent extracts the end point detection function from a separate detection layer and integrates it into the existing mask layer. By utilizing the optical reflection properties of the mask layer itself, the system eliminates the need for additional detection layers and processes, achieving both precision and process simplicity.
Solution Approach 2:
The mask layer serves dual functions: as the protective mask during etching and as the end point detection medium. The same mask layer material provides both the masking function and the optical reflection characteristics needed for end point detection, eliminating the need for separate detection layers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures uniformity in the mask layer thickness and trench depth, preventing residue generation and improving the precision of the STI process, thereby enhancing the consistency and quality of the semiconductor device manufacturing.
Implementation Method 1
a film thickness measuring unit for measuring a thickness of the mask layer
Implementation Method 2
a plasma source for generating a plasma; a processing chamber for performing an etching processing on the substrate by using the plasma
Data Source
AI summary
An etching method capable of controlling the film thickness of a hard mask layer uniformly is provided. A plasma etching is performed on a native oxide film by using an etching gas containing, for example, CF4 and Ar while a thickness of a silicon nitride film is being monitored and the etching is finished when the thickness of the silicon nitride film reaches a predetermined value. Then, a plasma etching is performed on a silicon substrate by employing an etching gas containing, for example, Cl2, HBr and Ar and using the silicon nitride film as a mask while a depth of a trench is being monitored and the etching is finished when the depth of the trench reaches a specified value.