Rough Polysilicon Ion Implantation Annealing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current MEMS device fabrication techniques face challenges in achieving improved performance and reliability due to issues with surface roughness and doping variability, which affect sensor performance and stiction reduction, particularly with the use of polysilicon annealing that degrades roughness and requires tight control of interfacial oxide thickness.
Innovation Solution
The method involves ion implantation of rough polysilicon followed by high temperature annealing to dope the polysilicon, and the introduction of a silicided layer to create a vertical sensing gap, allowing for increased surface roughness and improved doping levels while reducing epitaxial regrowth sensitivity, thereby enhancing sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polysilicon annealing is used to dope the polysilicon, then doping levels are improved, but surface roughness is degraded
Solution Approach 1:
The patent applies preliminary action by performing ion implantation before annealing to introduce dopants into the polysilicon layer. This preliminary doping step ensures that dopants are already present in the polysilicon structure before the annealing process, allowing the annealing to proceed at lower temperatures without causing excessive roughness degradation while still achieving the desired doping levels.
Solution Approach 2:
The patent applies parameter changes by modifying the annealing temperature parameter. Instead of using conventional high-temperature annealing that degrades surface roughness, the patent uses lower temperature annealing (e.g., 400-600°C) combined with ion implantation. This parameter change allows achieving adequate doping levels while preserving surface roughness for stiction reduction.
2Manufacturing precision
If ion implantation is used to dope the polysilicon, then doping levels are improved, but process complexity is increased
Solution Approach 1:
The patent merges the doping process with the existing polysilicon deposition and annealing processes. By combining ion implantation with the standard polysilicon fabrication sequence and using the same annealing step for both doping activation and stress management, the patent avoids adding separate complex doping equipment or processes, thereby limiting the increase in process complexity.
Solution Approach 2:
The patent applies self-service by using the polysilicon layer itself as the target for ion implantation. The existing polysilicon structure serves as both the functional layer and the doping target, eliminating the need for separate substrate preparation or additional doping steps. The ion implantation directly modifies the polysilicon in-situ, simplifying the overall process.
3Productivity
If high temperature annealing is used to dope the polysilicon, then doping efficiency is improved, but epitaxial regrowth sensitivity is increased
Solution Approach 1:
The patent applies preliminary action by pre-forming a protective oxide layer on the polysilicon surface before ion implantation. This preliminary oxide layer acts as a barrier that prevents epitaxial regrowth during the subsequent low-temperature annealing process. The oxide layer is formed in advance and maintains its protective function throughout the doping process, eliminating the need for high-temperature annealing that would trigger epitaxial regrowth.
Solution Approach 2:
The patent uses an oxide layer as an intermediary between the polysilicon surface and the environment during annealing. This intermediary oxide layer blocks the polysilicon from direct contact with the annealing atmosphere that would otherwise cause epitaxial regrowth. The oxide serves as a protective mediator that allows low-temperature processing while preventing harmful epitaxial formation.
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 increases the process window for avoiding epitaxial re-alignment, maintains high active doping levels, and provides improved surface roughness, leading to enhanced sensor performance and reliability by relaxing annealing conditions and using silicidation to create a true metal-metal capacitor.
Implementation Method 1
implanting rough polysilicon on the device layer. Implanting the rough polysilicon can comprise performing ion implantation of the rough polysilicon
Implementation Method 2
performing high temperature annealing. The high temperature can comprise a temperature in a range between around 700 and 1100 degrees Celsius
Implementation Method 3
performing high temperature annealing to dope the polysilicon
Implementation Method 4
introduction of a silicided layer to create a vertical sensing gap
Data Source
AI summary
A modification to rough polysilicon using ion implantation and silicide is provided herein. A method can comprise depositing a hard mask on a single crystal silicon, patterning the hard mask, and depositing metal on the single crystal silicon. The method also can comprise forming silicide based on causing the metal to react with exposed silicon of the single crystal silicon. Further, the method can comprise removing unreacted metal and stripping the hard mask from the single crystal silicon. Another method can comprise forming a MEMS layer based on fusion bonding a handle MEMS with a device layer. The method also can comprise implanting rough polysilicon on the device layer. Implanting the rough polysilicon can comprise performing ion implantation of the rough polysilicon. Further, the method can comprise performing high temperature annealing. The high temperature can comprise a temperature in a range between around 700 and 1100 degrees Celsius.