Mixed SOI Substrate Formation Without Boundary Bulge
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Solution Overview
Problem
The existing SOI gate-last process experiences a bulge formation at the boundary between the SOI and silicon substrate areas due to epitaxial silicon growth, leading to silicon peeling and uneven BARC thickness, which affects the product yield.
Innovation Solution
A method involving depositing mask silicon oxide and nitride layers, followed by photolithography and dry etching to remove these layers, oxidizing the silicon surfaces to form protective silicon oxide, and then depositing supplementary silicon oxide to prevent epitaxial growth on the SOI area sidewalls, ensuring a flush surface during epitaxial silicon growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If epitaxial silicon growth is performed to make the silicon substrate area grow flush with the SOI area, then the surface flatness is improved, but a bulge is formed at the boundary between SOI and silicon substrate due to epitaxial growth on exposed side surfaces
Solution Approach 1:
The patent applies preliminary action by forming a protective oxide layer on the SOI side surface before performing epitaxial silicon growth. This protective layer is created through thermal oxidation in advance, preventing silicon from the SOI area from undergoing unwanted epitaxial growth during the subsequent epitaxial process, thereby avoiding boundary bulge formation while still achieving surface flatness
Solution Approach 2:
The protective oxide layer acts as an intermediary barrier between the silicon substrate and the epitaxial growth environment. This intermediary layer prevents direct contact between the silicon atoms and the SOI side surface, blocking the epitaxial growth pathway and preventing the formation of bulges at the boundary region
2Device complexity
If the SOI area sidewall is exposed during epitaxial silicon growth, then the growth process is simplified, but silicon peeling and uneven BARC thickness occur due to bulge formation
Solution Approach 1:
The protective oxide layer is formed in advance on the SOI side surface before epitaxial growth, creating a barrier that prevents silicon peeling and ensures uniform BARC thickness. This preliminary protective measure maintains device structure integrity without significantly complicating the overall growth process
Solution Approach 2:
The protective oxide layer serves as a cushioning barrier that prevents the harmful effects of epitaxial growth on the SOI side surface. By providing this protective cushion beforehand, the patent prevents silicon peeling and ensures uniform BARC deposition, thereby maintaining device reliability
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 bulge formation at the boundary, maintains the device structure integrity, and enhances product yield by forming STI at the boundary, thus optimizing the substrate formation process.
Implementation Method 1
depositing a layer of mask silicon oxide 4 on an SOI silicon wafer, and then depositing a layer of mask silicon nitride 5
Implementation Method 2
depositing a layer of mask silicon oxide 4 on an SOI silicon wafer, and then depositing a layer of mask silicon nitride 5
Implementation Method 3
performing dry etching to remove the mask silicon nitride 5, the mask silicon oxide 4, SOI 3 and BOX 2 above the substrate silicon 1 in the silicon substrate area
Implementation Method 4
oxidizing silicon on an upper surface of the substrate silicon 1 in the silicon substrate area and a side surface of an SOI area to form protective silicon oxide 7
Implementation Method 5
performing epitaxial silicon 9 growth to enable the upper surface of the substrate silicon 1 in the silicon substrate area to grow flush with an upper surface of SOI 3 in the SOI area
Data Source
AI summary
The present application discloses a method for forming a mixed substrate. By optimizing the process flow, adding a silicon oxide sidewall process and covering an SOI area sidewall after dry etching with protective silicon oxide, epitaxial silicon growth on the SOI area sidewall is prevented, so that a bulge is prevented from being formed at a boundary between an SOI area and a silicon substrate area when the silicon substrate area is formed on an SOI silicon wafer. At the same time, since STI is eventually formed at the boundary between the SOI area and the silicon substrate area, the actual structure of a device formed on the mixed substrate remains basically unchanged, thus improving the product yield. The method for forming the mixed substrate is particularly suitable for an SOI gate-last process.