Contact Structure Reliability via Metal Silicide Etch Selectivity
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Solution Overview
Problem
Conventional semiconductor manufacturing processes for forming contact structures between polysilicon lines and active semiconductor regions often result in increased leakage currents and short circuits due to process variability and reduced etch control, especially in aggressively scaled devices with feature sizes below 100 nm.
Innovation Solution
Enhancing etch selectivity by providing metal silicide at the contact region during the etch process and using a test structure to monitor and evaluate the manufacturing sequence, thereby reducing the probability of creating short circuits and leakage paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional etch processes are used to form contact structures in aggressively scaled devices, then manufacturing complexity is reduced, but etch control deteriorates leading to increased leakage currents and short circuits
Solution Approach 1:
The method performs preliminary doping of the semiconductor layer before etching to create a dopant-rich region that will serve as an etch stop. This preliminary action ensures that when the etch process reaches this region, it automatically stops due to the changed etch characteristics, preventing over-etching and potential short circuits without requiring complex real-time monitoring or multiple etch steps.
Solution Approach 2:
The etch process incorporates feedback through the dopant-rich region that provides inherent etch stop characteristics. As the etch progresses, it automatically detects the change in material properties when reaching the dopant-rich region, which has different etch rates, thereby self-regulating the etch depth and preventing penetration into the active region that would cause leakage paths.
2Ease of manufacture
If conventional contact structures are formed without enhanced etch control, then manufacturing process is simpler, but reliability deteriorates due to leakage paths and short circuits
Solution Approach 1:
The dopant-rich region is formed in advance through selective doping before the contact etch process. This preliminary doping action creates a built-in etch stop mechanism that prevents the etch from penetrating too deep into the semiconductor layer, thereby preventing short circuits and leakage paths without adding complex monitoring or control steps during the etching itself.
Solution Approach 2:
The dopant-rich region acts as an intermediary layer between the contact opening and the active semiconductor region. This intermediary region has modified etch characteristics that cause the etch process to stop at its boundary, thereby mediating the etch depth control and preventing direct connection between the contact and the active region that would create leakage paths.
3Productivity
If feature sizes are reduced below 100 nm to increase device density, then productivity is improved, but manufacturing precision deteriorates due to reduced etch control
Solution Approach 1:
The method changes the physical and chemical parameters of the semiconductor layer by introducing a dopant-rich region with elevated dopant concentration. This parameter change modifies the etch characteristics of the material, creating a distinct etch stop layer that provides precise depth control during contact formation, which is critical when working with aggressively scaled feature sizes below 100 nm where traditional etch control becomes difficult.
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 significantly reduces the likelihood of leakage paths and short circuits, enhancing the reliability and yield of contact structures by improving etch control and process robustness.
Implementation Method 1
Since metal silicide may have a significantly increased etch resistivity with respect to the contact etch chemistry compared to doped silicon material, etching into the depth of the active region upon opening the contact etch stop layer may be substantially avoided or at least significantly reduced.
Implementation Method 2
defining a dopant profile in the active region
Data Source
AI summary
By forming a direct contact structure connecting, for instance, a polysilicon line with an active region on the basis of an increased amount of metal silicide by removing the sidewall spacers prior to the silicidation process, a significantly increased etch selectivity may be achieved during the contact etch stop layer opening. Hence, undue etching of the highly doped silicon material of the active region would be suppressed. Additionally or alternatively, an appropriately designed test structure is disclosed, which may enable the detection of electrical characteristics of contact structures formed in accordance with a specified manufacturing sequence and on the basis of specific design criteria.