Semiconductor Steep Junctions via Laser Thermal Anneal
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Solution Overview
Problem
Conventional methods for activating implanted dopants in semiconductor devices are inefficient, particularly in achieving steep junctions and deep dopant profiles, as they either affect the entire wafer or have limited melting depth, leading to suboptimal electrical characteristics.
Innovation Solution
A method involving the generation of crystal lattice vacancies in a pretreated section of the semiconductor layer, followed by implantation of dopants and subsequent laser thermal anneal (LTA) to activate the dopants, allowing for deeper and more efficient activation of dopants beyond the typical melting depth, especially using a 308 nm laser beam with antireflective coatings to enhance energy coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional furnace heating techniques are used to activate implanted dopants, then the entire wafer is heated and dopants are activated, but all previously formed structures in the wafer are affected and energy consumption is high
Solution Approach 1:
The patent applies local quality by using laser thermal anneal (LTA) to heat only the specific section of the semiconductor crystal where dopant activation is needed, rather than heating the entire wafer. This localized heating approach activates dopants in the target region while leaving previously formed structures in other areas unaffected, thereby resolving the contradiction between achieving dopant activation and avoiding harmful effects on other wafer regions.
Solution Approach 2:
The patent replaces the conventional furnace heating system with a laser-based thermal anneal system. This substitution allows for precise spatial and temporal control of the heating process, enabling dopant activation in specific regions without affecting the entire wafer, thus eliminating the harmful side effects associated with conventional furnace heating.
2Manufacturing precision
If LTA with 308 nm laser beam is used, then absorption depth is limited to about 10 nm and melting depth is limited to about 500 nm, but this limits the depth of dopant activation
Solution Approach 1:
The patent applies parameter changes by modifying the optical properties of the semiconductor substrate through antireflective coatings. These coatings change the reflection and absorption parameters of the laser beam at the substrate surface, enabling deeper penetration of the 308 nm laser beam and extending the melting depth beyond the typical 500 nm limit, thereby achieving deeper dopant activation while maintaining manufacturing precision.
3Quantity of substance
If ion implantation is used to introduce dopants, then dopant atoms are implanted into the wafer, but crystal lattice damage is caused and dopant atoms are electrically inactive until heating treatment
Solution Approach 1:
The patent applies preliminary action by performing laser thermal anneal immediately after ion implantation to activate the dopant atoms and repair crystal lattice damage. This immediate thermal treatment converts the electrically inactive implanted dopant atoms into electrically active ones by facilitating their incorporation into regular lattice sites, thereby resolving the contradiction between achieving high dopant concentration and ensuring their electrical activity.
Solution Approach 2:
The patent utilizes phase transitions by employing rapid thermal annealing that induces localized melting and subsequent solidification of the semiconductor crystal. This phase transition process effectively repairs implantation-induced lattice damage and activates dopant atoms, transforming them from electrically inactive to electrically active states while maintaining the implanted dopant concentration.
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 enables the activation of implanted dopants to a depth of at least 500 nm, achieving steep dopant density gradients and improved electrical characteristics by transferring dopants to regular lattice sites with reduced energy consumption, while minimizing impact on non-targeted areas of the semiconductor.
Implementation Method 1
A melt section of the semiconductor layer is heated by irradiating the process surface with a laser beam activating the implanted dopants at least in the melt section
Implementation Method 2
Antireflective coatings such that more energy of the laser beam is coupled into the semiconductor substrate
Implementation Method 3
Ion implantation includes ionizing, isolating and accelerating dopant atoms and sweeping an ion beam including the ionized dopant atoms across a wafer surface
Implementation Method 4
crystal lattice vacancies are generated in a pretreated section of the semiconductor layer
Data Source
AI summary
Crystal lattice vacancies are generated in a pretreated section of a semiconductor layer directly adjoining a process surface. Dopants are implanted at least into the pretreated section. A melt section of the semiconductor layer is heated by irradiating the process surface with a laser beam activating the implanted dopants at least in the melt section.