Low-Temperature SOI Substrate Bonding with Metal Gettering
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Solution Overview
Problem
SOI substrates are susceptible to metal contamination during the production process, particularly due to the accumulation of metal impurities at the bonding interface during low-temperature plasma-treatment, which conventional cleanliness measures cannot adequately address.
Innovation Solution
A method involving ion-implantation of hydrogen ions on a silicon substrate, followed by plasma-treatment and bonding with an insulator substrate at low temperature, mechanical delamination of the silicon film, and a heat-treatment at 600°C to 1250°C to getter metal impurities to the surface region, using a mixed gas atmosphere of oxidizing and inert gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If plasma-treatment is performed to secure bonding strength at low temperature, then bonding strength is improved, but metal impurities accumulate at the bonding interface at high density
Solution Approach 1:
The patent applies preliminary action by performing ion implantation of hydrogen or helium ions into the silicon substrate before plasma treatment and bonding. This pre-treatment creates a modified layer that will later serve as a gettering region to capture metal impurities, thereby preventing their harmful accumulation at the bonding interface while still allowing low-temperature plasma bonding to proceed.
Solution Approach 2:
The patent converts the harmful effect of metal impurity accumulation into a beneficial outcome by using the plasma treatment process itself to activate the ion-implanted layer, which then acts as a gettering mechanism. The same plasma environment that causes impurity accumulation also activates the implanted ions to form a region that preferentially attracts and traps these impurities, transforming the problem into a solution.
2Object-affected harmful factors
If conventional cleanliness measures are taken to reduce metal contamination, then environmental cleanliness is improved, but metal impurities still accumulate during plasma-treatment
Solution Approach 1:
The patent introduces an intermediary substance (ion-implanted hydrogen or helium layer) that acts as a mediator between the plasma treatment process and the silicon substrate. This intermediary layer preferentially attracts and traps metal impurities during plasma treatment, preventing them from accumulating at the bonding interface, thereby making conventional cleanliness measures sufficient rather than inadequate.
Solution Approach 2:
The patent transforms the unavoidable metal impurities generated during plasma treatment from a harmful contaminant into a beneficial effect by using the ion-implanted layer as a gettering region. The impurities are not prevented from forming, but are instead directed to accumulate in a controlled region away from the bonding interface, where they can be later removed.
3Temperature
If bonding is performed at low temperature, then thermal damage is reduced, but metal impurities are prone to accumulate in the bonding interface
Solution Approach 1:
The patent applies preliminary action by implanting ions into the silicon substrate before low-temperature bonding. This creates a modified layer that will subsequently serve as a gettering region to capture metal impurities that accumulate during the low-temperature plasma bonding process, thereby enabling both low-temperature bonding and impurity control.
Solution Approach 2:
The patent converts the harmful accumulation of metal impurities during low-temperature plasma bonding into a beneficial outcome by using the ion-implanted layer as a gettering mechanism. The low-temperature plasma process that causes impurity accumulation also activates the implanted ions to form a region that selectively traps these impurities, transforming the problem into a solution.
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
Enables bonding at low temperatures while significantly reducing metal contaminants in the SOI film, resulting in a cleaner substrate with improved performance and reduced parasitic capacitance.
Implementation Method 1
ion-implanting for forming a hydrogen-ion implanted layer to a main surface of a silicon substrate
Implementation Method 2
a surface treatment for performing a plasma-treatment on at least one of a main surface of an insulator substrate and the main surface of the silicon substrate
Implementation Method 3
the SOI substrate is subjected to a heat-treatment at a temperature of 600°C to 1250°C so that metal impurities accidentally mixed into an interface of the SOI film and the insulator substrate and into the SOI film in such a step as the plasma-treatment are gettered to a surface region of the silicon film
Implementation Method 4
a heat-treatment of the SOI substrate at a temperature of 600°C to 1250°C
Data Source
Figure 1(A)~1(G)
Figure 2(A)~2(C)
AI summary
An object of the present invention is to provide a method by which bonding at a low temperature is possible and an amount of metal contaminants in an SOI film is decreased. An embodiment of the present invention is realized in the following manner. A single crystal silicon substrate 10 surface-activated by a plasma-treatment and a quartz substrate 20 are bonded together at a low temperature, to which an external impact is given to mechanically delaminate silicon film from a single crystal silicon bulk thereby obtaining a semiconductor substrate (SOI substrate) having a silicon film (SOI film) 12. Next, the SOI substrate is subjected to a heat-treatment at a temperature of 600°C to 1250°C so that metal impurities accidentally mixed into an interface of the SOI film and the quartz substrate and into the SOI film in such a step as a plasma-treatment are gettered to a surface region of the silicon film 12. Then, in the end, a surface layer (gettering layer) of the silicon film 12 of the SOI substrate after the heat-treatment is removed to finally prerare an SOI film 13 and a semiconductor substrate (SOI substrate) is obtained.