CBRAM Silver Deposition via Displacement and Diffusion Control
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Solution Overview
Problem
Current methods for fabricating conductive bridge random access memory (CBRAM) cells using physical vapor deposition result in uncontrolled silver diffusion, leading to variability in memory cell operation and difficulties in removing silver from unwanted areas.
Innovation Solution
The method involves selective deposition of silver using a displacement process and the formation of a diffusion control layer comprising cobalt, tungsten, rhenium, or molybdenum with additional elements like boron and phosphorus, along with a barrier layer to control silver diffusion, reducing process steps and enhancing controllability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If physical vapor deposition (PVD) is used to deposit silver, then silver can be deposited onto the chalcogenide material, but silver diffuses rapidly and uncontrollably into the chalcogenide during deposition
Solution Approach 1:
A diffusion control layer comprising cobalt, tungsten, rhenium, or molybdenum with additional elements like boron and phosphorus is introduced as an intermediary between the silver layer and the chalcogenide material. This intermediate layer allows controlled diffusion of silver ions during subsequent thermal processing while preventing uncontrolled rapid diffusion that occurs with direct PVD deposition onto the chalcogenide.
Solution Approach 2:
The invention changes the physical and chemical parameters of the diffusion control layer by selecting specific materials (cobalt, tungsten, rhenium, or molybdenum with boron and phosphorus) and controlling its thickness (5-50 nm). These parameter changes enable controlled silver diffusion at elevated temperatures while maintaining manufacturing precision.
2Quantity of substance
If PVD process is used for silver deposition, then silver can be formed in the memory cell, but removal of silver from unwanted areas becomes difficult
Solution Approach 1:
The diffusion control layer serves as a selective barrier that allows silver to diffuse into the chalcogenide material during controlled thermal processing while preventing silver from diffusing into unwanted areas. This intermediary layer provides spatial control over silver distribution, making it easier to manage silver placement and removal compared to uncontrolled PVD deposition.
Solution Approach 2:
The diffusion control layer is formed in advance before silver deposition, establishing predetermined diffusion pathways and barriers. This preliminary action allows silver to be deposited more easily knowing that the diffusion control layer will subsequently guide its movement, and facilitates easier removal of excess silver since the diffusion control layer defines the boundaries of acceptable silver distribution.
3Quantity of substance
If uncontrolled silver diffusion occurs during PVD, then silver is deposited into the chalcogenide, but significant variability in memory cell operation results from cell to cell
Solution Approach 1:
The diffusion control layer acts as a mediator that standardizes silver diffusion across all memory cells. By providing a uniform intermediate layer with controlled composition and thickness, silver diffusion proceeds through the same pathway and resistance in each cell, eliminating the cell-to-cell variability that occurs with direct uncontrolled diffusion during PVD.
Solution Approach 2:
The invention changes the diffusion parameters by introducing a layer with specific material composition (cobalt, tungsten, rhenium, or molybdenum with boron and phosphorus) and controlled thickness (5-50 nm). These parameter changes create consistent diffusion characteristics across all memory cells, improving operational reliability by reducing variability.
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 allows for the formation of CBRAM devices with improved controllability and integration, suitable for 45 nm nodes and beyond, minimizing variability and simplifying the fabrication process.
Implementation Method 1
forming a second conductive layer in the opening by displacement by immersion, wherein the second conductive layer comprises bridging material
Implementation Method 2
silver diffuses rapidly into the chalcogenide during the PVD step itself and thus the silver diffusion is largely uncontrolled
Data Source
AI summary
A method for making a semiconductor device (10) includes providing an interconnect layer (14) over an underlying layer (12), forming a first insulating layer (16) over the interconnect layer, and forming an opening (18) through the insulating layer to the interconnect layer. A first conductive layer (24) is formed over the interconnect layer and in the opening. This is performed by plating so it is selective. A second conductive layer (28) in the opening is formed by displacement by immersion. This is performed after the first conductive layer has been formed. The result is the second conductive layer is formed by a selective deposition and is effective for providing it with bridging material. A layer of bridgeable material (34) is formed over the second conductive layer and in the opening. A third conductive layer (42) is formed over the bridgeable material. The semiconductor device may be useable as a conductive bridge memory device.