Multi-step Quartz Etching for Photomask Uniformity Control
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Solution Overview
Problem
Conventional quartz etching processes exhibit RIE lag and non-uniformity, particularly for features with critical dimensions less than 5 μm, leading to suboptimal etch uniformity and sidewall angles, which hampers the production of small critical dimension features in photomasks.
Innovation Solution
A multi-step etching process utilizing a first step with a fluorocarbon and chlorine-containing process gas, followed by a second step with another fluorocarbon process gas, in a controlled plasma environment, to achieve improved etch uniformity and reduced RIE lag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional single-step quartz etching processes are used, then the etching process is simple and fast, but etch uniformity deteriorates and RIE lag occurs between features of different critical dimensions
Solution Approach 1:
The etching process is divided into multiple sequential steps, each with specific gas compositions and process parameters. The first step uses a fluorocarbon-based plasma to etch quartz, followed by a second step with adjusted gas composition to complete the etch. This segmentation allows optimization of each step for uniformity while managing overall process complexity.
2Manufacturing precision
If conventional quartz etching processes are used, then the process is straightforward, but microtrenching and non-uniformity occur in features with critical dimensions less than 5 μm
Solution Approach 1:
The patent modifies process parameters including gas composition (fluorocarbon to chlorine ratio), RF power levels, and pressure conditions across different etching steps. These parameter changes are specifically tuned to eliminate microtrenching and achieve uniform etching in sub-5 μm features while maintaining reasonable process complexity.
3Manufacturing precision
If conventional etching processes are used, then the process duration is short, but RIE lag causes different vertical etch rates for features of different widths
Solution Approach 1:
The etching process employs periodic alternation between different plasma chemistries and power levels. The first etching step uses one gas composition and power setting, then transitions to a second step with different parameters. This periodic action allows the process to address RIE lag by adjusting conditions mid-process, though it increases total etching time.
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
The method enhances etch uniformity, reduces RIE lag, and improves sidewall angle control, enabling the production of features with sub-5 μm critical dimensions, thereby improving the fabrication of phase shifting photomasks.
Implementation Method 1
In one etch process, known as dry etching, reactive ion etching (RIE), or plasma etching, a plasma is used to enhance a chemical reaction and etch the exposed quartz area of the mask.
Implementation Method 2
In one etch process, known as dry etching, reactive ion etching (RIE), or plasma etching, a plasma is used to enhance a chemical reaction and etch the exposed quartz area of the mask.
Data Source
AI summary
Methods for etching quartz are provided herein. In one embodiment, a method of etching quartz includes providing a film stack on a substrate support disposed in a processing chamber, the film stack having a quartz layer partially exposed through a patterned layer; and etching the quartz layer of the film stack in a multi-step process including a first step of etching the quartz layer utilizing a first process gas comprising at least one fluorocarbon process gas and a chlorine-containing process gas; and a second step of etching the quartz layer utilizing a second process gas comprising at least one fluorocarbon process gas.