Isotropic Silicon Dummy Etching Using NF3 and H2 Plasma
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Solution Overview
Problem
Conventional methods for removing silicon dummy structures from substrates, such as those used in semiconductor processing, face challenges in achieving infinite selectivity to silicon dioxide and silicon nitride without damaging other structures or leaving residue, especially as feature scaling continues, and the post-etch clean processes can cause additional damage to the SiO2 layer.
Innovation Solution
An inductively coupled plasma etching process using nitrogen trifluoride (NF3) and molecular hydrogen (H2) plasma is employed to isotropically etch silicon dummy structures with infinite selectivity to silicon dioxide and silicon nitride, followed by the use of solvents like sulfuric acid and hydrogen peroxide to remove etch byproducts without damaging the remaining structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wet etching is used to remove silicon dummy structures, then selectivity to silicon dioxide and silicon nitride is improved, but residue is left on the substrate
Solution Approach 1:
The patent changes the etching parameters by transitioning from wet etching to plasma etching with specific gas compositions (CHF3, CF4, SF6 mixed with O2 or H2), transforming the etching mechanism to achieve both high selectivity and complete residue removal through isotropic etching with controlled byproduct formation
Solution Approach 2:
The patent uses composite plasma chemistry combining multiple gases (fluorocarbon compounds for etching + oxygen or hydrogen for byproduct management) to create an etching process that simultaneously achieves selectivity, anisotropy control, and residue-free cleaning
2Object-generated harmful factors
If plasma etching is used to remove silicon dummy structures, then residue is reduced, but byproduct deposition damages the SiO2 layer
Solution Approach 1:
The patent optimizes plasma parameters including gas composition ratios (CHF3:O2 or CF4:H2 or SF6:O2), pressure, and power levels to control the etching chemistry, achieving a balance where silicon is etched efficiently while byproduct deposition on SiO2 is minimized through controlled isotropic etching
Solution Approach 2:
The patent introduces oxygen or hydrogen as a mediator gas that reacts with silicon etch byproducts to form volatile compounds, preventing excessive byproduct accumulation and damage to the SiO2 layer while maintaining etching effectiveness
3Productivity
If feature size is reduced for scaling, then device density is improved, but residue removal becomes more difficult
Solution Approach 1:
The patent adjusts plasma etching parameters (gas flow rates, pressure, power) to achieve isotropic etching with controlled mean free path, enabling complete residue removal from high-aspect-ratio and tightly-spaced structures that result from feature scaling
Solution Approach 2:
The patent replaces mechanical scraping or aggressive chemical mechanical polishing with plasma-based isotropic etching, using controlled chemical reactions and ion bombardment to remove residue from scaled features without physical contact that could damage delicate structures
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 effectively removes silicon dummy structures with minimal residue and no additional damage to SiO2 or Si3N4, ensuring precise and residue-free etching while maintaining the integrity of the substrate.
Implementation Method 1
supplying nitrogen trifluoride and molecular hydrogen gas to the processing chamber; striking plasma in the processing chamber; and etching the dummy structure
Implementation Method 2
The processing chamber is an inductively coupled plasma processing chamber
Implementation Method 3
The solvent includes water. The solvent includes a mixture of sulfuric acid and hydrogen peroxide
Data Source
AI summary
Systems and methods for etching a substrate include arranging a substrate including a first structure and a dummy structure in a processing chamber. The first structure is made of a material selected from a group consisting of silicon dioxide and silicon nitride. The dummy structure is made of silicon. Carrier gas is supplied to the processing chamber. Nitrogen trifluoride and molecular hydrogen gas are supplied to the processing chamber. Plasma is generated in the processing chamber. The dummy structure is etched.