Undoped SOI Substrate Fabrication for RF Applications
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Solution Overview
Problem
The existing process for fabricating FDSOI semiconductor-on-insulator substrates for radiofrequency applications leads to a reduction in electrical resistivity of the carrier substrate due to dopant diffusion from the donor substrate, causing significant electrical losses, especially in high-frequency mmWave applications.
Innovation Solution
A process involving the formation of an undoped semiconductor epitaxial layer on a p-doped seed substrate, with an electrically insulating layer and selective etching, to prevent dopant diffusion during the Smart Cut™ layer transfer, maintaining high resistivity of the carrier substrate near the bonding interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional donor substrate with dopants is used in the Smart Cut process, then the layer transfer can be achieved, but dopant diffusion occurs into the carrier substrate causing reduced electrical resistivity
Solution Approach 1:
The donor substrate is segmented into two distinct parts: a dopant-free epitaxial layer that is transferred to the carrier substrate, and a doped seed substrate that remains separate. This segmentation prevents dopant diffusion into the carrier substrate while maintaining the benefits of the Smart Cut process for precise layer transfer.
Solution Approach 2:
The dopants are extracted from the transferred layer by using an undoped epitaxial layer instead of a doped bulk substrate. The dopants remain confined to the seed substrate, which is separated from the carrier substrate after layer transfer, thus removing the harmful dopant diffusion effect.
2Manufacturing precision
If high-temperature finishing treatment is applied to smooth the transferred layer, then surface roughness is reduced, but dopant diffusion is enhanced
Solution Approach 1:
A dopant barrier structure is created beforehand during the epitaxial growth process, positioning undoped regions between the seed substrate and the bonding interface. This pre-established barrier cushions against dopant diffusion during subsequent high-temperature finishing treatments, allowing surface smoothing without compromising electrical resistivity.
3Reliability
If an undoped epitaxial layer is used instead of a doped bulk substrate, then dopant diffusion is prevented, but additional fabrication steps are required
Solution Approach 1:
The doping parameter is changed during the epitaxial growth process by controlling precursor flow rates and temperature profiles to create undoped or lightly-doped regions. This parameter control during manufacturing achieves the desired dopant distribution without requiring additional complex post-processing steps.
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 effectively maintains the high electrical resistivity of the carrier substrate, reducing electrical losses and ensuring the substrate's suitability for radiofrequency applications, particularly in the mmWave frequency band.
Implementation Method 1
forming an undoped semiconductor epitaxial layer on a p-doped seed substrate... to prevent dopant diffusion during the Smart Cut™ layer transfer
Implementation Method 2
an ion species implantation is performed, using, for example, hydrogen and/or helium ions, through the electrically insulating layer 10, so as to form a weakened area 11
Implementation Method 3
the donor substrate 1 thus implanted is bonded to a carrier substrate 2 by way of the electrically insulating layer
Implementation Method 4
the donor substrate 1 is detached along the weakened area 11, resulting in the thin layer 12 being transferred to the carrier substrate 2
Implementation Method 5
a finishing process called 'batch anneal,' which is a lengthy, high-temperature smoothing process that is advantageously carried out in a furnace... at a temperature between 1150 and 1200° C. for a duration of several minutes
Data Source
AI summary
A method for fabricating a semiconductor-on-insulator substrate for radiofrequency applications, comprises:forming a donor substrate through epitaxial growth of an undoped semiconductor layer on a p-doped semiconductor seed substrate;forming an electrically insulating layer on the undoped epitaxial semiconductor,implanting ion species through the electrically insulating layer, so as to form, in the undoped epitaxial semiconductor layer, a weakened area defining a semiconductor thin layer to be transferred,providing a semiconductor carrier substrate having an electrical resistivity greater than or equal to 500 Ω·cm,bonding the donor substrate to the carrier substrate via the electrically insulating layer, anddetaching the donor substrate along the weakened area of embrittlement so as to transfer the semiconductor thin layer from the donor substrate to the carrier substrate.