Plasma Cleaning of CMOS Image Sensor Substrates
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Solution Overview
Problem
Existing methods for forming CMOS image sensors face challenges in removing fluorine residual components post-etching without damaging the device, as wet etching can dissolve adhesive agents and heat treatment can damage the unit pixels.
Innovation Solution
A method involving plasma etching using a mixture of CF series gas and inert gas to clean the substrate after the etching step, effectively removing fluorine residual components without causing damage to the silicon layer or the unit pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wet etching is performed to remove fluorine residual component, then the fluorine residual component is removed, but the adhesive agent bonding the substrate and support substrate dissolves
Solution Approach 1:
The patent changes the etching method from wet etching to plasma etching, altering the chemical and physical parameters of the cleaning process. Plasma etching uses reactive ions and radicals in a controlled vacuum environment to remove fluorine residues without dissolving the adhesive agent, thus resolving the contradiction between effective residue removal and adhesive integrity
Solution Approach 2:
The patent replaces the chemical-based wet etching process with a plasma-based physical-chemical process. Plasma etching utilizes ion bombardment and chemical reactions in a plasma state to selectively remove fluorine-containing residues while being controllable enough to preserve the adhesive agent bonding the substrate to the support substrate
2Manufacturing precision
If heat treatment is performed to vaporize fluorine residual component, then the fluorine residual component is removed, but the unit pixels are damaged
Solution Approach 1:
The patent changes the temperature parameter of the cleaning process by replacing heat treatment with plasma etching. Plasma etching operates at lower temperatures compared to heat treatment methods, effectively removing fluorine residues through chemical reactions and ion bombardment without subjecting the unit pixels to damaging high temperatures
Solution Approach 2:
The patent substitutes thermal energy-based heat treatment with plasma-based energy delivery. The plasma process uses ion kinetic energy and reactive chemical species to remove fluorine residues, replacing the thermal mechanism that causes damage to sensitive unit pixels with a more selective and gentler physical-chemical process
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 prevents the degradation of electrical characteristics in CMOS image sensors by efficiently removing fluorine residues while maintaining the integrity of the device components.
Implementation Method 1
an etching step of etching the substrate by plasma via a mask having a predetermined pattern formed at a back surface side of the silicon layer of the substrate
Implementation Method 2
a cleaning step of cleaning the substrate by plasma using cleaning gas obtained by mixing CF series gas and inert-gas
Implementation Method 3
cleaning the substrate by plasma using cleaning gas obtained by mixing CF series gas and inert-gas
Data Source
AI summary
A method of forming a pattern on a silicon layer of a substrate, to be processed, wherein a semiconductor device is formed at a front surface side of the substrate that is supported by a support substrate at the front surface side, includes an etching step of etching the substrate by plasma via a mask having a predetermined pattern formed at a back surface side of the silicon layer of the substrate; and a cleaning step of cleaning the substrate by plasma using cleaning gas obtained by mixing CF series gas and inert-gas, after the etching step.