Phase Change Memory Cell Void Elimination via Rapid Thermal Anneal
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Solution Overview
Problem
Phase change memory cells often contain voids in the crystalline phase change material, leading to erratic properties and uniformity issues due to shrinkage and expansion during cell construction.
Innovation Solution
A method involving rapid thermal anneal to melt and re-crystallize the phase change material, using a thermally insulating layer and capping layer to direct heat and cool the material, causing voids to migrate away from the switching region, which are then removed through chemical mechanical polish, resulting in a substantially void-free phase change layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase change material is deposited and crystallized during cell construction, then the crystalline phase is formed for data storage, but voids form throughout the material due to shrinkage and expansion
Solution Approach 1:
The patent applies a preliminary rapid thermal anneal process after depositing the phase change material but before final cell construction. This anneal melts the material and allows controlled re-crystallization, preventing void formation in the switching region before the material is fully integrated into the cell structure.
Solution Approach 2:
The patent utilizes rapid changes in temperature parameters through the rapid thermal anneal process. By quickly heating to melt the phase change material and then controlling the cooling rate, the material re-crystallizes without forming voids, transforming the physical state from amorphous to crystalline while eliminating defects.
2Manufacturing precision
If rapid thermal anneal is applied to melt and re-crystallize phase change material, then voids are eliminated and uniformity is improved, but additional processing steps and time are required
Solution Approach 1:
The patent combines the void-elimination anneal process with the existing phase change material deposition and crystallization sequence. By integrating the rapid thermal anneal into the overall cell construction workflow and using the same thermal processing equipment, the method eliminates voids without requiring separate dedicated equipment or completely independent process steps.
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
The approach ensures a void-free crystalline phase change material, enhancing the uniformity and reliability of phase change memory cells by eliminating voids and stabilizing electrical resistance.
Implementation Method 1
rapid thermal anneal heats the phase change material so that it melts
Implementation Method 2
the bottom electrode causes the voids in the phase change material to migrate away from the switching region of the phase change layer as the phase change material re-crystallizes
Implementation Method 3
the phase change material re-crystallizes from the bottom electrode upward
Data Source
AI summary
A phase change memory cell with substantially void free crystalline phase change material. An example memory cell includes a substrate and a bottom electrode carried by the substrate. The bottom electrode is a thermal conductor. A phase change layer includes phase change material. The phase change layer is void free within a switching region when the phase change material is in a crystalline phase. A top electrode is positioned over the phase change layer.