SOI Wafer Bonding via Surface Activation and Thermal Detachment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The bonding of different substrates with varying thermal expansion coefficients, such as silicon and sapphire, leads to thermal strain, detachment, and crystal defects due to incomplete bonding and stress during heat treatment in existing SOI wafer production methods.
Innovation Solution
A method involving surface activation treatment, bonding at a first temperature of 175°C to 225°C, grinding or etching the silicon wafer, and subsequent heating at a second temperature of 225°C to 400°C to achieve mechanical detachment at the hydrogen ion-implanted layer, thereby preventing thermal strain and improving film uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-temperature heat treatment (around 500°C) is performed after bonding in the SOITEC process to generate microcavities for silicon wafer separation, then the silicon film is successfully transferred to the handle wafer, but wafer cracking occurs due to large difference in thermal expansion coefficients between the silicon wafer and handle wafer (quartz or sapphire)
Solution Approach 1:
The patent performs surface activation treatment on both the handle wafer and donor wafer surfaces before bonding. This preliminary action creates highly reactive surface states that enable strong bonding at lower temperatures (200-400°C), avoiding the need for high-temperature heat treatment after bonding that causes thermal expansion mismatch cracking. The activated surfaces form strong chemical bonds immediately upon contact, eliminating the harmful thermal stress cycle.
2Strength
If the SiGen process uses plasma treatment to activate wafer surfaces for stronger bonding, then bonding strength is improved, but the bonded wafers still require heating at 250°C or higher which causes wafer damage and untransferred portions due to thermal expansion differences
Solution Approach 1:
The patent changes the bonding temperature parameter to a lower range (200-400°C) compared to conventional processes. By combining surface activation treatment with this optimized temperature parameter, the process achieves strong bonding without the thermal damage caused by higher temperature heating. The activation treatment enables bonding at temperatures below 400°C, preventing warpage and detachment while maintaining strong bonding strength.
3Reliability
If multiple heat treatment steps (room temperature bonding, low-temperature heat treatment, grinding, and high-temperature heat treatment at 900°C or higher) are performed to complete SOS bonding, then bonding is achieved, but multiple misfit dislocations and cracks are included in the silicon film layer due to weak bonding and stress during temperature changes
Solution Approach 1:
The patent performs surface activation treatment before bonding to create strong chemical bonds at the interface. This preliminary action ensures that when subsequent heat treatment and grinding steps are performed, the bonded wafers remain firmly attached without relative displacement. The activated surfaces maintain bonding strength throughout the processing sequence, preventing misfit dislocations and cracks in the final silicon film.
Solution Approach 2:
The patent maintains continuous strong bonding throughout the entire processing sequence by using surface activation. Unlike conventional methods where bonding strength is insufficient during intermediate steps, the activated surfaces ensure continuous adhesion during heat treatment, grinding, and cooling, preventing any separation or displacement that would cause defects in the silicon film.
4Manufacturing precision
If hydrogen ion implantation is used to create a transfer interface at 400°C to 600°C, then fine microcavities form for detachment, but bonding of different substrates with weak bonding strength causes surface displacement during temperature rise and fall
Solution Approach 1:
The patent performs surface activation treatment before bonding to establish strong bonding strength from the outset. This preliminary action ensures that when hydrogen ion implantation and subsequent heat treatment are performed, the bonded wafers maintain strong adhesion and do not experience surface displacement. The activation treatment creates a robust bond that can withstand the thermal cycling required for microcavity formation and detachment.
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 method produces SOI wafers with uniform silicon film thickness and prevents thermal strain, detachment, and cracking, ensuring strong bonding without warpage or detachment issues due to thermal expansion differences.
Implementation Method 1
a single crystal silicon wafer into which a hydrogen ion has been implanted to form a hydrogen ion-implanted layer in advance
Implementation Method 2
both a surface of a handle wafer and a surface of a donor wafer into which hydrogen ions have been implanted in advance in the same manner as in the above process, are subject to a plasma treatment so as activate the surfaces
Implementation Method 3
bonding the hydrogen ion-implanted surface to the surface of the insulator wafer to obtain bonded wafers; heating the bonded wafers at a first temperature; heating the bonded wafers thus ground and/or etched at a second temperature which is higher than the first temperature
Implementation Method 4
performing detachment at the hydrogen ion-implanted layer by applying a mechanical impact to the hydrogen ion-implanted layer of the bonded wafers thus heated at the second temperature
Data Source
Figure 1
AI summary
[PROBLEM] Provided is a method for producing an SOI wafer which the method can prevent occurrence of thermal strain, detachment, crack and the like attributed to a difference in thermal expansion coefficients between the insulating substrate and the SOI layer and also improve the uniformity of film thickness of the SOI layer. [MEANS FOR SOLVING THE PROBLEM] Provided is a method for producing an SOI wafer comprising steps of: performing a surface activation treatment on at least one of a surface of an insulator wafer and a hydrogen ion-implanted surface of a single crystal silicon wafer having a hydrogen ion-implanted layer; bonding the hydrogen ion-implanted surface to the surface of the insulator wafer to obtain bonded wafers; heating the bonded wafers at a first temperature; grinding and/or etching a surface of a single crystal silicon wafer side of the bonded wafers thus heated so as to thin the single crystal silicon wafer of the bonded wafers; heating the bonded wafers thus ground and/or etched at a second temperature which is higher the first temperature; and performing detachment at the hydrogen ion-implanted layer by applying a mechanical impact to the hydrogen ion-implanted layer of the bonded wafers thus heated at the second temperature.