SOI Imager Structure With Rear Oxide Bow Compensation
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Solution Overview
Problem
Semiconductor on insulator (SOI) type structures, particularly for front side imagers, face challenges in maintaining flatness during epitaxial deposition of monocrystalline silicon-germanium (SiGe) layers, leading to deformation and handling issues due to stress-induced bow, which is difficult to manage with conventional industrial tools.
Innovation Solution
A semiconductor on insulator type structure with a silicon oxide layer on the rear side to compensate for the mechanical stress induced by the SiGe layer, allowing for epitaxial growth while maintaining structural flatness, comprising a semiconductor support substrate, an electrically insulating layer, and a monocrystalline SiGe active layer with controlled germanium content and thickness to enhance near-infrared absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monocrystalline silicon-germanium (SiGe) layer is deposited on SOI structure to improve near-infrared absorption, then sensitivity in near infrared region is improved, but stress-induced bow deformation increases making the structure difficult to handle
Solution Approach 1:
A compensating layer is deposited on the rear side of the support substrate before or during the SiGe epitaxy process to pre-counteract the stress-induced bow deformation. This preliminary anti-action prevents the structure from developing excessive bow, maintaining flatness within 250 μm and enabling handling with conventional industrial tools while preserving the near-infrared sensitivity improvement from the SiGe layer.
2Reliability
If SiGe layer thickness is increased to enhance near-infrared absorption, then absorption coefficient improves, but stress-induced bow deformation increases
Solution Approach 1:
The compensating layer on the rear side is designed with specific thickness and material properties to counteract the stress from thicker SiGe layers. This allows the front side SiGe layer to achieve the necessary thickness for high near-infrared absorption while the rear compensating layer prevents excessive bow, maintaining the structure within acceptable flatness tolerances.
Solution Approach 2:
By changing the parameters of the compensating layer (thickness, material composition, deposition temperature), the stress compensation can be optimized for different SiGe layer thicknesses. This enables flexible design where the SiGe layer thickness can be increased for better absorption while the compensating layer parameters are adjusted to maintain flatness.
3Reliability
If epitaxial deposition of SiGe is performed on SOI structure, then crystalline quality is maintained, but stress-induced deformation occurs
Solution Approach 1:
The compensating layer is introduced as a counterbalancing element that offsets the stress from the SiGe epitaxial layer. This allows the epitaxial deposition to proceed with maintained crystalline quality while the compensating layer prevents the stress from translating into excessive bow deformation, keeping the structure within 250 μm flatness tolerance.
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
The solution enables the epitaxial growth of SiGe on SOI structures without significant deformation, allowing for improved light absorption in the near-infrared region while maintaining compatibility with existing manufacturing methods and crystalline quality, facilitating the production of flat substrates suitable for industrial handling.
Implementation Method 1
the thickness of the oxide layer being chosen to compensate the bow induced by the mechanical stress between the active layer and the support substrate during cooling of the structure after the formation by epitaxy of at least a part of the active layer on the support substrate
Implementation Method 2
monocrystalline silicon-germanium (SiGe) is another material that could be considered for the active layer, because it advantageously has a coefficient of absorption in the near infrared that increases with increasing germanium content thereof
Data Source
AI summary
A semiconductor on insulator type structure, which may be used for a front side type imager, successively comprises, from its rear side to its front side, a semiconductor support substrate, an electrically insulating layer and an active layer comprising a monocrystalline semiconductor material. The active layer is made of a semiconductor material having a state of mechanical stress with respect to the support substrate, and the support substrate comprises, on its rear side, a silicon oxide layer, the thickness of the oxide layer being chosen to compensate bow induced by the mechanical stress between the active layer and the support substrate during cooling of the structure after the formation by epitaxy of at least a part of the active layer on the support substrate.