Phase Change Memory Lower Electrode Contact Formation
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Solution Overview
Problem
Conventional phase change memory devices face challenges in stably forming a lower electrode contact and achieving uniformity due to non-uniform oxide layer deposition and limitations in exposure processes, leading to unstable interfaces and variations in programming current.
Innovation Solution
A method involving the formation of a sacrificial layer and hard mask layer, followed by reactive ion etching to define a contact hole with a reduced size and uniformity, allowing for stable formation of a lower electrode contact and phase change layer interface, using techniques like atomic layer deposition and chemical mechanical polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an oxide layer is formed to delimit a contact hole forming region, then the contact hole region is defined, but the oxide layer is not uniformly deposited causing steps that lead to non-uniform contact holes and unstable lower electrode contact formation
Solution Approach 1:
A planarization layer is formed before the oxide layer to provide a flat surface for uniform oxide deposition. This preliminary action eliminates the step formation issue that would otherwise cause non-uniform contact holes, allowing the oxide layer to be uniformly deposited across the substrate without creating elevation differences.
2Area of moving object
If the diameter of lower electrode contact is reduced below a predetermined diameter, then the contact area is reduced, but the exposure process limitations make it difficult to properly define the contact hole and increase diameter variation
Solution Approach 1:
The contact hole definition process is segmented into multiple sequential steps: first defining a preliminary contact hole region with a first diameter, then defining a final contact hole with a second (smaller) diameter. This segmentation allows each step to be optimized independently, with the first step providing a robust starting point and the second step achieving the precise small diameter required, thereby reducing diameter variation even for contacts below the predetermined diameter.
3Device complexity
If conventional etching processes are used to define contact holes, then the process is simple, but the steps on the oxide layer cause non-uniform etching and unstable lower electrode contact formation
Solution Approach 1:
The planarization layer is formed as a preliminary structure before etching the oxide layer. This planarization layer compensates for the steps created during oxide deposition, providing a uniform etching surface that ensures consistent etching depth and width across all contact holes, thereby improving lower electrode contact stability without adding complex etching procedures.
Solution Approach 2:
The planarization layer acts as an intermediary structure between the substrate and the oxide layer. It mediates the surface uniformity issue by providing a flat platform that allows subsequent layers to be deposited and etched uniformly, thereby transferring the reliability benefit to the lower electrode contact formation without requiring changes to the fundamental etching process.
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 stable and uniform formation of the lower electrode contact, reducing the contact area and programming current variations, thereby enhancing the operational speed and consistency of the phase change memory device.
Implementation Method 1
CMPing the second insulation layer to expose the sacrificial layer of the second stack pattern
Implementation Method 2
performing a first etching the hard mask layer and the sacrificial layer
Data Source
AI summary
A phase change memory device is manufactured by forming a sacrificial layer and a hard mask layer on a lower electrode; performing a first etching these layers and forming on the lower electrode a first stack pattern having a first width less than a width of the lower electrode; performing a second etching the first stack pattern and forming a second stack pattern having a second width less than the first width; forming an insulation to cover the second stack pattern; CMPing the insulation layer to expose the sacrificial layer; removing the sacrificial layer to define a contact hole; forming a lower electrode contact in the contact hole; and forming a phase change layer and an upper electrode on the insulation layer including the lower electrode contact. By manufacturing the phase change memory device in this manner, the size of the contact hole can be decreased and uniformly defined.