Monolithic Lens Formation via Two-Stage Dry Etching
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Solution Overview
Problem
Conventional processes for forming a monolithic lens on semiconductor materials face challenges in transcribing convex photoresist patterns due to surface damage from RF plasma, leading to difficulties in achieving desired curvature and optical dimensions.
Innovation Solution
A method involving the formation of an intermediate layer and a mask layer with a convex shape, where the convex shape is transcribed through dry-etching in two stages to create a monolithic lens with adjustable curvature, using specific etching conditions to control the etching rates and selectivities between the mask layer, intermediate layer, and semiconductor material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a convex photoresist pattern is directly transcribed on the semiconductor material, then the lens formation process is simplified, but the photoresist surface is damaged by RF plasma causing transcription failure
Solution Approach 1:
An intermediate layer is introduced between the photoresist mask layer and the semiconductor material. This intermediate layer acts as a mediator that protects the photoresist surface from RF plasma damage while still allowing the convex pattern to be transcribed. The intermediate layer absorbs the harmful plasma effects and enables successful pattern transfer to the semiconductor material without compromising photoresist integrity.
2Strength
If hard baked photoresist is used for the mask layer, then the photoresist is more durable, but the convex shape curvature is limited
Solution Approach 1:
The invention changes the etching parameters by using inductively coupled plasma (ICP) with specific gas compositions (CF4, O2, and CH4) and power settings. This allows the convex pattern to be transcribed with greater curvature than what is achievable with the hard baked photoresist alone. The parameter changes in the etching process enable the intermediate layer to be shaped with the desired curvature, which is then transferred to the semiconductor material.
3Productivity
If the etching rate of the intermediate layer is increased, then the transcription speed is improved, but the curvature control of the processed intermediate layer is reduced
Solution Approach 1:
The etching process is performed in two distinct stages with different gas compositions and parameters. The first stage uses CF4 and O2 gases with specific flow rates to achieve the initial transcription of the convex pattern. The second stage introduces CH4 gas to enhance the etching rate while maintaining curvature control. This periodic change in etching conditions allows both high productivity and precise curvature control.
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 allows for the formation of a monolithic lens with optionally selected curvature, avoiding surface degradation and heating issues, and enabling precise optical dimensions, even when starting with hard baked photoresist with limited curvature.
Implementation Method 1
inductively coupled plasma to transcribe a convex shape of the mask layer on the intermediate layer
Implementation Method 2
first transcribing the convex shape of the mask layer on the intermediate layer to from a processed intermediate layer with a semispherical shape by etching the mask layer and the intermediate layer
Implementation Method 3
second transcribing the semispherical shape of the processed intermediate layer on the semiconductor material to form the monolithic lens
Implementation Method 4
the second transcription of the convex shape of the processed intermediate layer to the convex shape of the lens is also carried out by dry-etching
Data Source
AI summary
A process to form a lens on a semiconductor material is disclosed. The process includes steps of: forming double layers of an intermediate layer on the semiconductor material and a mask layer made of hard-baked photoresist on the semiconductor substrate; the first transcribing the convex shape of the mask layer on the intermediate layer; and the second scribing the convex shape of the intermediate layer on the semiconductor material.