Laser Annealing Apparatus with Cyclic Delay Unit
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Solution Overview
Problem
Conventional single- and double-pulse laser annealing methods face inefficiencies in energy utilization and temperature maintenance, leading to suboptimal annealing effects due to excessive reflection and temperature fluctuations during the annealing process.
Innovation Solution
A laser annealing apparatus and method that splits a single-pulse laser beam into multiple pulsed beams with controlled time delays and energy ratios, using a cyclic delay unit and optical module to maintain substrate temperature around the melting point, preventing excessive reflection and ensuring efficient energy absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a single-pulse or double-pulse laser annealing method is used to heat the silicon surface, then the annealing temperature can be raised, but the laser energy utilization efficiency decreases due to increased reflection from liquid silicon
Solution Approach 1:
The invention divides a single laser pulse into multiple sub-pulses (at least two) with different time delays. The first sub-pulse heats the silicon surface to annealing temperature, while subsequent sub-pulses provide supplemental heating to maintain temperature and compensate for energy loss from reflection, thereby improving overall energy utilization efficiency while achieving the required annealing temperature
Solution Approach 2:
The first sub-pulse is designed to preheat the silicon surface to the annealing temperature range before the subsequent sub-pulses arrive. This preliminary heating action establishes the base temperature, and the delayed sub-pulses then supplement the energy to overcome reflection losses and maintain the temperature throughout the annealing process
2Duration of action of stationary object
If the time delay between laser pulses is extended to allow temperature maintenance, then the annealing duration increases, but the temperature may drop below the required annealing threshold
Solution Approach 1:
The invention employs periodic sub-pulses with optimized time delays between them. The first sub-pulse initiates heating, and subsequent sub-pulses are timed to arrive at optimal intervals to maintain the temperature above the annealing threshold throughout the process, ensuring both sufficient duration and temperature maintenance
3Reliability
If the laser energy is increased to maintain temperature above melting point, then the annealing effectiveness improves, but the reflection from liquid silicon doubles, further reducing energy absorption
Solution Approach 1:
The invention acknowledges that some reflection is inevitable when silicon melts, but converts this potential harm into a benefit by using the reflected energy timing information to optimize sub-pulse sequencing. The sub-pulses are timed to arrive when the silicon is in a state that maximizes absorption, and the cumulative effect of multiple sub-pulses overcomes the reflection loss, achieving reliable annealing without excessive single-pulse energy that would cause problematic reflection
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 enhances laser energy utilization efficiency and annealing effectiveness by maintaining the substrate temperature within the desired range for a sufficient duration, improving upon existing methods by reducing reflection and thermal radiation issues.
Implementation Method 1
a laser beam generator for providing a stable single-pulse laser beam
Implementation Method 2
an optical module for converging one or more of the plurality of pulsed laser beams on a substrate
Implementation Method 3
a cyclic delay unit for splitting the single-pulse laser beam into a plurality of pulsed laser beams
Data Source
AI summary
A laser annealing apparatus includes: a laser beam generator for providing a stable single-pulse laser; a cyclic delay unit (300) for splitting the single-pulse laser into several pulsed lasers; an optical module for converging one or more of the pulsed lasers on a substrate (204); and a movable stage (500) for providing the substrate (204) with movement in at least one degree of freedom. A laser annealing method includes: providing a stable single-pulse laser; splitting the single-pulse laser into several pulsed lasers according to a delay requirement and an energy ratio; and irradiating a substrate (204) successively with one or more of the pulsed lasers to keep a surface temperature of the wafer around the melting point or around a needed annealing temperature for a sufficiently long time during the annealing process, thus resulting in an improvement in both the laser energy utilization efficiency and effect of the annealing process.