Spike Anneal Absorption Control for Semiconductor Thermal Processing
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Solution Overview
Problem
Current spike anneal processes for semiconductor devices face challenges in achieving peak temperature at a short controllable dwell time without using heavily doped substrates or pre-heat thermal treatments, which can degrade resist chemistries or result in inefficient thermal quenching.
Innovation Solution
A method and system that modify absorption properties of specific layers on a substrate, such as using a modified bottom anti-reflective coating (BARC) or resist, to absorb laser energy and achieve rapid heating and cooling, allowing for a spike anneal process that does not rely solely on substrate absorption, thereby controlling temperature and dwell time effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a CO2 laser (10.6 μm wavelength) is used for spike anneal, then free carrier absorption can be induced in heavily doped substrates, but the absorption is limited to the top one-third of the substrate leaving the bottom two-thirds as a cold sink
Solution Approach 1:
The patent modifies the absorption properties of specific layers (such as BARC or resist) to enhance localized heating at the substrate surface while allowing the bulk substrate to remain undoped or lightly doped. This creates a non-uniform absorption distribution where the top layers absorb laser energy preferentially, achieving high peak temperatures locally without requiring the entire substrate to be heavily doped.
Solution Approach 2:
The patent changes the optical absorption parameters of the substrate layers by modifying BARC or resist compositions to have enhanced absorption at the laser wavelength. This parameter change allows the system to achieve efficient energy coupling without relying on heavy substrate doping, thereby resolving the contradiction between achieving high temperature and avoiding complex substrate preparation.
2Use of energy by moving object
If pre-heat thermal treatment is applied to enable free carrier absorption, then absorption can be induced, but resist chemistries are thermally degraded
Solution Approach 1:
The patent applies preliminary modification to the BARC or resist layers to enhance their optical absorption properties before the spike anneal process. This preliminary action allows the layers to absorb laser energy directly during the spike anneal without requiring prior thermal pre-heating, thereby avoiding resist chemistry degradation while still enabling efficient free carrier absorption.
Solution Approach 2:
The patent uses modified BARC or resist layers as intermediary materials that absorb laser energy and transfer it to the substrate. These intermediary layers have enhanced optical absorption properties that allow them to couple laser energy efficiently without requiring high substrate doping or pre-heat treatment, thus protecting the resist chemistry from thermal degradation.
3Reliability
If dwell time is increased to achieve required dopant activation, then activation level improves, but dopant diffusion increases causing higher leakage currents
Solution Approach 1:
The patent employs a periodic or pulsed laser heating approach where the substrate is rapidly heated to high temperature for a very short duration (spike anneal) and then quickly cooled. This periodic thermal action achieves high dopant activation during the brief high-temperature pulse while minimizing dopant diffusion because the total exposure time at elevated temperature is extremely limited.
Solution Approach 2:
The patent utilizes rapid phase transitions in the thermal state of the substrate - quickly transitioning from room temperature to high temperature and then rapidly cooling back. This phase transition approach allows the system to achieve dopant activation during the brief high-temperature phase while the rapid cooling phase prevents excessive dopant diffusion, thereby resolving the contradiction between activation and diffusion.
4Productivity
If peak temperature is increased to enhance dopant activation, then Ion increases, but device functionality may be compromised due to excessive diffusion
Solution Approach 1:
The patent employs dynamic control of the thermal process parameters, specifically using very high heating and cooling rates in a spike anneal regime. This dynamic approach allows the system to reach high peak temperatures that enhance dopant activation efficiency, while the equally rapid cooling that follows limits the total time at high temperature, thereby preventing excessive dopant diffusion and maintaining precise junction depth control.
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 efficient dopant activation with reduced leakage currents and maintains resist chemistry integrity by achieving rapid thermal quenching and precise temperature control, enhancing the scalability of semiconductor device geometries.
Implementation Method 1
A substrate modified with the selected technique of modifying absorption is provided. The spike anneal process is performed on the substrate using the selected heating device and selected spike anneal variables.
Implementation Method 2
Because of the absorption properties of the locally doped or pre-heated surface, the CO2 anneal produces a localized heating within only the top one-third of the substrate, which leaves the bottom two-thirds of the substrate essentially as a cold sink. This cold sink allows for very quick thermal quenching of the elevated temperature induced by the laser exposure
Data Source
AI summary
Provided is a method and system for controlling a spike anneal process on a substrate, comprising selecting one or more objectives, one or more absorbance layers, a technique of modifying absorption of the selected one or more absorbance layers, one or more wavelengths used in a heating device. A substrate modified with the selected technique of modifying absorption is provided. The spike anneal process is performed on the substrate using the selected heating device and selected spike anneal process variables. One or more of the spike anneal process variables, the selected technique of the modifying absorption, the selected one or more wavelengths, and/or the selected heating device are adjusted in order to meet the one or more objectives of the spike anneal process.