Self-Aligned Refractory Contacts for Semiconductor Devices
Solution Overview
Problem
The challenge in semiconductor device fabrication lies in the difficulty of achieving stable refractory metal contacts on highly doped regions without damaging the underlying semiconductor lattice, particularly when the activation anneal temperature exceeds the material's dissociation temperature, making it hard to remove the capping layer and align the metal contacts accurately.
Innovation Solution
A method is developed where ions of a first conductivity type are implanted into a semiconductor layer, and metal layers are formed on these implanted regions. These regions and metal layers are annealed simultaneously to activate the ions and create self-aligned ohmic contacts, using refractory metals like Ti, TiW, Mo, Ta, W, WSi, Re, Nb, TiWN, NiSi, and TiSi, which can withstand high temperatures and provide improved contact resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If activation anneal temperature is increased to activate implanted ions, then doping effectiveness is improved, but semiconductor lattice damage worsens
Solution Approach 1:
The patent divides the thermal processing into two distinct stages: first forming the metal contact layer at lower temperature to establish initial contact, then performing a second anneal at higher temperature to activate dopants. This segmentation allows each process to occur at optimal temperature without compromising the other, resolving the contradiction between achieving effective doping and preventing lattice damage.
Solution Approach 2:
The metal contact layer is formed beforehand before the high-temperature dopant activation anneal. This preliminary action creates a protective and conductive layer that can withstand the subsequent high-temperature processing, enabling effective dopant activation while the pre-formed metal structure protects the semiconductor lattice from excessive damage.
2Manufacturing precision
If conventional separate processes are used for dopant activation and metal contact formation, then process control is improved, but fabrication complexity worsens
Solution Approach 1:
The patent combines dopant activation and metal contact formation into a single annealing process. By merging these two functions into one thermal treatment step, the process achieves both dopant activation and contact formation simultaneously, reducing fabrication complexity while maintaining precise control through optimized annealing parameters.
Solution Approach 2:
The annealing process is designed to perform multiple functions: activating implanted dopants, forming ohmic contacts, and repairing lattice damage. This multi-functional approach eliminates the need for separate processing steps, simplifying the fabrication workflow while maintaining manufacturing precision through carefully controlled annealing conditions.
3Ease of manufacture
If standard metal contacts are used on highly doped regions, then contact formation is simplified, but contact stability worsens
Solution Approach 1:
The patent employs refractory metal materials (such as tungsten, molybdenum, or titanium) that combine high melting points with good electrical conductivity. These composite material properties enable the contacts to withstand high-temperature annealing processes while maintaining stable electrical connection to highly doped regions, resolving the contradiction between ease of formation and long-term stability.
Solution Approach 2:
The invention changes the material parameters of the contact layer by selecting refractory metals with specific properties (high melting point, chemical stability, electrical conductivity). This parameter change allows the contacts to remain stable during high-temperature dopant activation while maintaining ease of formation through standard deposition techniques.
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 simplifies the fabrication process by enabling simultaneous annealing and self-alignment of ohmic contacts, reducing contact resistivity and ensuring the stability of semiconductor devices, particularly suitable for Group III-nitride semiconductor devices.
Implementation Method 1
Ion implantation is a well-known method of doping a semiconductor layer with impurities. In an ion implantation process, ionized impurity atoms are accelerated under high vacuum through an electric field towards a target layer, where they become implanted.
Implementation Method 2
Typically, after impurities are implanted into a semiconductor layer, the implanted impurities may be annealed at a high temperature, this may be called an activation anneal. An activation anneal may repair damage caused by the implantation of high-energy ions into the semiconductor lattice.
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 1E~1F
AI summary
Methods of forming semiconductor devices are provided by forming a semiconductor layer on a semiconductor substrate. A mask is formed on the semiconductor layer. Ions having a first conductivity type are implanted into the semiconductor layer according to the mask to form implanted regions on the semiconductor layer. Metal layers are formed on the implanted regions according to the mask. The implanted regions and the metal layers are annealed in a single step to respectively activate the implanted ions in the implanted regions and provide ohmic contacts on the implanted regions. Related devices are also provided.