Selective Amorphisation for Transistor Source Drain Doping
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Solution Overview
Problem
Existing methods for doping source and drain regions of transistors on semiconductor-on-insulator substrates face challenges in achieving selective amorphization and recrystallization without damaging the crystalline structure, particularly when trying to minimize thermal budget and maintain performance.
Innovation Solution
A method involving selective amorphization of a second semiconductor layer with respect to a first crystalline semiconductor layer, followed by thermal annealing for recrystallization and dopant activation, using specific semiconductor materials and parameters to define a precise interface and enable efficient doping close to the channel zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ion implantation is performed over the whole thickness of source and drain blocks to dope them, then doping is achieved, but the crystalline structure is damaged and becomes amorphous, making monocrystalline recrystallisation impossible
Solution Approach 1:
The source and drain blocks are divided into two distinct zones: an upper zone that is amorphized by ion implantation for doping, and a lower zone that maintains its crystalline structure. This segmentation allows the upper zone to be doped while the lower zone serves as a crystalline seed for recrystallisation, resolving the contradiction between achieving doping and preserving crystalline structure.
Solution Approach 2:
Different regions of the source and drain blocks are given different properties: the upper region near the gate is made amorphous for effective doping, while the lower region near the substrate maintains crystalline structure to enable recrystallisation. This local differentiation allows simultaneous achievement of doping effectiveness and crystalline structure preservation.
2Stability of the object's composition
If a thick crystalline seed layer is conserved near the insulating layer to enable recrystallisation of the upper amorphous zone, then recrystallisation is possible, but the doping efficiency is reduced due to the distance from the channel
Solution Approach 1:
Instead of requiring a thick crystalline seed layer, the invention uses a thin crystalline layer at the bottom of the source and drain blocks. Ion implantation is performed with sufficient energy to amorphize the upper portion while leaving the thin lower crystalline layer intact. This partial amorphization approach enables both recrystallisation and close proximity to the channel, improving doping efficiency.
3Stability of the object's composition
If high thermal budget is used for recrystallisation, then complete recrystallisation is achieved, but transistor performances are deteriorated
Solution Approach 1:
The invention changes the thermal parameters by using low-temperature recrystallisation (below 650°C) made possible by the presence of the crystalline seed layer. The crystalline structure provided by the seed layer enables recrystallisation to proceed at lower temperatures than would be required for complete recrystallisation from an entirely amorphous state, thus preserving transistor performance while achieving the desired crystalline structure.
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 allows for improved doping of source and drain regions with reduced access resistances, enabling the production of transistors with enhanced performance while minimizing thermal budget and maintaining crystalline structure integrity.
Implementation Method 1
making amorphous and doping the second layer by means of one or more implantation(s), the amorphisation being a selective amorphisation of the second semiconductor material
Implementation Method 2
these implantations having a tendency to damage the crystalline structure of the doped semiconductor material and to make it amorphous
Implementation Method 3
carrying out a recrystallisation of the second layer and an activation of dopants by means of at least one thermal annealing
Implementation Method 4
a recrystallisation leading to an activation of the dopants in the amorphous semiconductor material may then be carried out at low temperature
Data Source
AI summary
Method including the steps consisting in:forming source and drain semiconductor blocks comprising a first layer based on a first crystalline semiconductor material surmounted by a second layer (16) based on a second crystalline semiconductor material different from the first semiconductor material,making amorphous and selectively doping the second layer (16) by means of one or more implantation(s),carrying out a recrystallisation of the second layer and an activation of dopants by means of at least one thermal annealing.