Continuous Plasma Etching for Smooth Semiconductor Trench Profiles
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Solution Overview
Problem
The Bosch process for anisotropically etching semiconductor wafers results in uneven surfaces due to its cyclic nature, leading to scalloping and side wall roughening, and is sensitive to temperature and parameter changes, making it difficult to achieve accurate and reproducible deep etch features.
Innovation Solution
A continuous plasma etching method using a mixture of halogen gases, halocarbons, and nitrogen compounds to selectively remove passivation material from the closed end of etch features while maintaining it on the sidewalls, preventing undercutting and promoting smooth, anisotropic profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the Bosch process uses cyclic etch and deposition steps to etch deep features, then the anisotropic etching is achieved, but uneven surfaces with scalloping and side wall roughening occur
Solution Approach 1:
The patent applies a continuous plasma etching process instead of cyclic steps, maintaining constant passivation material deposition on sidewalls while removing it from the base. This continuous action eliminates the scalloping effect caused by repeated deposition and removal cycles, producing smooth sidewalls while maintaining anisotropic etching.
Solution Approach 2:
The patent creates different conditions at different locations within the etch feature: passivation material is continuously removed from the base (closed end) while being maintained on the sidewalls. This spatial differentiation allows selective etching at the base while protecting sidewalls, achieving both precision and smoothness.
2Reliability
If the Bosch process uses cyclic deposition steps to maintain anisotropic etching, then sidewall protection is improved, but the process becomes sensitive to temperature and parameter changes
Solution Approach 1:
The continuous plasma process maintains constant passivation material deposition, eliminating the sensitivity to timing and parameter changes inherent in cyclic processes. The continuous nature provides inherent stability against temperature and parameter fluctuations while maintaining reliable sidewall protection.
3Duration of action of stationary object
If lower wafer temperatures are used to improve mask life, then mask durability increases, but excessive polymer growth causes grass formation at the base
Solution Approach 1:
The patent creates local differences in passivation material behavior: at lower temperatures, polymer deposits heavily on the base (causing grass formation) but this is continuously removed by the plasma. On sidewalls, the polymer is maintained at controlled thickness. This local differentiation allows low temperature operation with extended mask life without grass formation problems.
Solution Approach 2:
The patent converts the harmful grass formation effect into a beneficial one: the excessive polymer deposition at the base is continuously removed by the plasma, and this same plasma maintains sidewall protection. The continuous process transforms what would be a defect into a self-correcting mechanism.
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 method reduces side wall roughness and scalloping, improves control over the etching process, and allows for deeper etch features with smoother profiles, enhancing the manufacturability of silicon trench etched wafers and enabling higher integration levels in ASIC circuitry.
Implementation Method 1
forming a plasma of the etching mixture in the environment for etching the wafer
Implementation Method 2
Ions entering the dark space sheath of the etching plasma are accelerated by the sheath field and impact onto the substrate at an angle substantially normal to the wafer plane increasing the anisotropic etching
Implementation Method 3
at least one passivation component for depositing passivation material on the wafer
Implementation Method 4
at least one passivation material removal component for removing passivation material deposited on a wall of a closed end of an etch feature of the wafer
Data Source
AI summary
A method for anisotropically plasma etching a semiconductor wafer is disclosed. The method comprises supporting a wafer in an environment operative to form a plasma, such as a plasma reactor, and providing an etching mixture to the environment. The etching mixture comprises at least one etch component, at least one passivation component, and at least one passivation material removal component.