The process flow of SOI (Silicon On Insulator) wafer.

The process flow of SOI (Silicon On Insulator) wafer.

 

 

SOI wafer (Silicon-On-Insulator) is a semiconductor material that forms an ultra-thin silicon layer on an insulating layer through a special process. Its unique sandwich structure significantly enhances device performance.

 

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The SOI wafer consists of three layers:

1. Top Silicon (Device Layer): The thickness ranges from tens of nanometers to several micrometers, used for manufacturing transistors and other devices.

2. Buried Oxide (BOX): The middle silicon dioxide insulating layer (thickness approximately 0.05-15μm) isolates the device layer from the substrate, reducing parasitic effects.

3. Substrate Silicon: The bottom silicon layer (thickness 100-500μm) provides mechanical support.

 

According to the fabrication process technology, the mainstream process routes of SOI wafers can be classified into: SIMOX (Separation by Implantation of Oxygen), BESOI (Bonding and Etching of SOI), and Smart Cut (Smart Separation Technology).

 

 

 

SIMOX (Separation by Implantation of Oxygen) involves implanting high-energy oxygen ions into a silicon wafer to form a buried silicon dioxide layer, followed by high-temperature annealing to repair lattice defects. The core of this process is the direct ion implantation of oxygen to form the buried oxide layer.

 

 

 

BESOI (Bonding and Etching of SOI) involves bonding two silicon wafers together, then thinning one of them through mechanical grinding and chemical etching to form the SOI structure. The core of this process is bonding + thinning.

 

 

Smart Cut technology involves implanting hydrogen ions to form a separation layer. After bonding, thermal treatment causes the silicon wafer to separate along the hydrogen ion layer, resulting in an ultra-thin silicon layer. The core of this process is hydrogen implantation and separation.

 

 

Currently, there is another technology called SIMBOND (Oxygen Implantation Bonding Technology), developed by Soitec. This technology is essentially a process that combines both oxygen implantation isolation and bonding techniques. In this process, the implanted oxygen serves as a thinning barrier, while the actual buried oxide layer is a thermally grown oxide layer. As a result, it simultaneously improves parameters such as the uniformity of the top silicon and the quality of the buried oxide layer.

 

 

SOI wafers manufactured using different technological routes have different performance parameters, making them suitable for various application scenarios.

 

Technology	Top Layer Thickness Range	Buried Oxide Layer Thickness	Uniformity (±)	Cost	Application Areas
SIMOX	0.5-20um	0.3-4m	0.5um	Medium-High	Power Devices, Model Circuits
BESOI	1-200um	0.3-4um	250nm	Low	Automotive Electronics, Photonics
Smart Cut	0.075-1.5um	0.05-3um	12.5nm	Medium	5G Frequency, Millimeter-Wave Chips
SIMBOND	0.075-3um	0.05-3um	12.5nm	High	High-End Devices, Filters

 

 

 

Here is a summary table of the core performance advantages of SOI wafers, combining their technical characteristics and practical application scenarios. Compared to traditional bulk silicon, SOI offers significant advantages in the speed-power consumption balance. (PS: The performance of 22nm FD-SOI is close to FinFET, with a 30% cost reduction.)

 

Performance Advantages	Technology Route	Specific Performance	Typical Application Areas
Low Power Consumption	Buried Oxide (BOX) Isolation	Turning on at 15%~30%, power consumption 20%~50%	5G base stations, high-speed integrated circuits
High Breakdown Voltage	High Breakdown Voltage Device	High breakdown voltage, up to 90% or more, extended service life	Power modules, high voltage devices
High Thermal Conductivity	High Thermal Conductivity Device	Thermal resistance 3-5 times lower, reduced thermal resistance	Heat dissipation devices, high performance chips
High Electromagnetic Compatibility	High Electromagnetic Compatibility Device	Resistant to external electromagnetic interference	Electronic devices sensitive to electromagnetic interference
High Temperature Resistance	High Temperature Resistance	Thermal resistance above 30%, working temperature 15~25°C	14nm CPU, LED lights, power systems
Excellent Design Flexibility	Excellent Design Flexibility	No additional assembly process, reduces complexity	High precision devices, power sensors
Excellent Electrical Performance	Excellent Electrical Performance	Electrical performance reaches 100mA	Electric vehicles, solar cells

 

 

 

 

To sum it up simply and bluntly, the main advantages of SOI are: it runs faster and consumes less power. Due to these performance characteristics, SOI has a wide range of applications in fields that require excellent frequency and power consumption performance. As shown below, based on the market share of SOI in various application fields, RF and power devices account for the vast majority of the SOI market.

 

 

 

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