Conductive Cap Structure for Low-Resistance VTFET Top Contact
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Solution Overview
Problem
Vertical-type field effect transistors (VTFETs) face higher top source/drain (TSD) contact resistance due to smaller TSD region size compared to bottom source/drain (BSD) regions, leading to increased resistance and potential over-gouging during contact element formation, which reduces the epi material and further elevates resistance.
Innovation Solution
Forming an electrically conductive cap on the TSD region using a low-resistance material, such as metal, which increases the contact area and reduces the overall contact resistance by establishing an ohmic connection with the TSD contact element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the TSD region size is reduced to increase device density, then device density is improved, but TSD contact resistance increases
Solution Approach 1:
The patent introduces a vertical conductive cap structure that extends upward from the TSD region, adding a vertical dimension to the contact area. This dimensional transition from horizontal to vertical contact increases the effective contact area without increasing the horizontal footprint, thereby maintaining high device density while reducing contact resistance through enhanced contact geometry.
Solution Approach 2:
The patent employs a composite contact structure consisting of multiple materials: the semiconductor TSD region, a conductive cap material (such as metal or heavily doped semiconductor), and dielectric materials. This composite structure combines the advantages of each material to achieve both small footprint and low contact resistance, with the conductive cap providing low-resistance pathways while the dielectric materials provide isolation and structural support.
2Productivity
If contact element formation is performed on small TSD regions, then device density is improved, but over-gouging occurs during contact element formation
Solution Approach 1:
The conductive cap is formed beforehand on the TSD region before the contact element formation process. This preliminary structure serves as a protective layer and defined contact target, preventing over-gouging during subsequent contact hole etching or contact formation steps. The cap provides a clear etch stop and ensures that contact elements are formed precisely on the intended TSD region without damaging surrounding structures.
Solution Approach 2:
The conductive cap acts as a cushioning layer that protects the underlying TSD region and channel structure from damage during contact element formation. This protective layer absorbs the mechanical and chemical stresses of the fabrication process, preventing over-gouging and ensuring manufacturing precision while maintaining the benefits of small TSD region dimensions.
3Reliability
If the conductive cap material is changed to reduce contact resistance, then TSD contact resistance is improved, but material compatibility and fabrication complexity increase
Solution Approach 1:
The patent reduces contact resistance by changing the electrical parameters of the contact structure through the conductive cap. The cap is formed with materials or doping configurations that provide lower resistance than the native TSD region. This parameter change in electrical conductivity is achieved through controlled material selection and doping levels, balancing resistance reduction with fabrication feasibility.
Solution Approach 2:
The conductive cap is applied locally only to the TSD region where low contact resistance is critical, rather than throughout the entire device. This localized approach reduces fabrication complexity by limiting the scope of additional processing steps to only the necessary areas, while still achieving the desired electrical performance improvement at the contact interface.
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 electrically conductive cap effectively decreases the TSD contact resistance in VTFETs by enhancing the contact area and material conductivity, thereby improving the overall performance of the semiconductor device.
Implementation Method 1
forming an electrically conductive contact via in ohmic connection with the electrically conductive cap to establish an electrically conductive path from the contact via to the bottom source/drain region
Data Source
AI summary
A semiconductor includes a semiconductor substrate having a bottom source/drain region and a vertical semiconductor fin having a bottom end that contacts the semiconductor substrate. The semiconductor device further includes a top source/drain region on a top end of the vertical semiconductor. The top source/drain region is separated from the semiconductor substrate by the vertical semiconductor fin. The semiconductor device further includes an electrically conductive cap on an outer surface of the top source/drain region.