Plasma Etching Native Silicon Oxide Selectivity
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Solution Overview
Problem
Current methods for removing native silicon oxide layers from polysilicon surfaces in semiconductor fabrication are inefficient, as they often require costly and hazardous wet etching processes, result in low selectivity over other materials, and can lead to regrowth of native oxides due to exposure to ambient conditions, especially in high-aspect-ratio features.
Innovation Solution
A plasma-based etching process using a hydrogen-based species and a fluorine-based species, such as hydrogen and nitrogen trifluoride, is employed to activate the etchant and remove native silicon oxide layers from polysilicon surfaces, maintaining a low temperature during plasma exposure to minimize damage to surrounding structures and achieving high selectivity over nitride and oxide structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wet etching process is used to remove native oxide, then removal effectiveness is improved, but safety concerns and cost increase
Solution Approach 1:
The patent replaces the wet chemical etching process with a plasma-based etching process. The plasma process uses ionized gas species to remove native oxide through physical and chemical mechanisms, eliminating the need for hazardous liquid chemicals while achieving effective oxide removal through controlled plasma reactions.
Solution Approach 2:
The patent employs an inert plasma environment to perform the etching process. The plasma provides a controlled atmosphere that enables selective oxide removal without requiring contact with hazardous wet chemicals, thereby improving safety while maintaining removal effectiveness.
2Reliability
If wet etching process is used to remove native oxide, then removal is achieved, but selectivity over other materials decreases
Solution Approach 1:
The patent achieves local quality by creating different plasma conditions that selectively affect different materials. By controlling plasma parameters such as power, pressure, and gas composition, the process is optimized to etch native oxide at a high rate while minimizing etching of surrounding nitride and oxide structures, thereby achieving high selectivity.
Solution Approach 2:
The patent utilizes parameter changes in the plasma process to achieve selective etching. By adjusting plasma power, pressure, temperature, and gas flow rates, the etching chemistry is optimized to preferentially remove native oxide while leaving other materials intact, providing the required selectivity for semiconductor fabrication.
3Reliability
If wet etching process is used, then native oxide removal is achieved, but native oxide regrowth occurs due to ambient exposure
Solution Approach 1:
The patent implements a continuous vacuum-based process where the plasma etching of native oxide is performed without breaking vacuum. This eliminates the need to expose the wafer to ambient conditions, preventing oxide regrowth and allowing the process to proceed continuously from oxide removal to subsequent fabrication steps without time loss.
4Productivity
If dry RIE process is used to remove polysilicon, then etch rate is improved, but damage to surrounding structures increases
Solution Approach 1:
The patent applies partial action by using a modified plasma process that provides sufficient ion flux to achieve high etch rates for polysilicon removal, while controlling the ion energy and direction to minimize damage to surrounding structures. The process delivers just enough ion bombardment to maintain high productivity without excessive damage.
Solution Approach 2:
The patent optimizes plasma parameters including power, pressure, and gas composition to achieve the right balance between etch rate and structure damage. By carefully controlling these parameters, the process maintains high polysilicon removal rates while reducing the harmful effects of ion and photon fluxes on surrounding nitride and oxide 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 achieves a high etch rate for polysilicon while minimizing the etch rate of surrounding nitride and oxide structures, ensuring high selectivity and preventing native oxide regrowth, thus improving the efficiency and reliability of semiconductor fabrication processes.
Implementation Method 1
exposing the etchant to a plasma to activate the hydrogen-based species and the fluorine-based species
Implementation Method 2
heating the wafer to a temperature greater than about 60° C. to substantially remove the native silicon oxide layer from the polysilicon layer
Data Source
AI summary
Provided are methods and systems for removing a native silicon oxide layer on a wafer. In a non-sequential approach, a wafer is provided with a native silicon oxide layer on a polysilicon layer. An etchant including a hydrogen-based species and a fluorine-based species is introduced, exposed to a plasma, and flowed onto the wafer at a relatively low temperature. The wafer is then heated to a slightly elevated temperature to substantially remove the native oxide layer. In a sequential approach, a wafer is provided with a native silicon oxide layer. A first etchant including a hydrogen-based species and a fluorine-based species is flowed onto the wafer. Then the wafer is heated to a slightly elevated temperature, a second etchant is flowed towards the wafer, and the second etchant is exposed to a plasma to complete the removal of the native silicon oxide layer and to initiate removal of another layer such as a polysilicon layer.