Backside Contact Doping for Low-Resistance Source/Drain Sidewalls
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Solution Overview
Problem
Conventional contact schemes for semiconductor devices, particularly for multigate devices like GAA and CFETs, face challenges in reducing contact resistance (Rc) due to misalignment issues, shadowing effects, and thermal limitations, especially when forming backside contacts.
Innovation Solution
A method involving the formation of trenches, deposition of a temporary material, and plasma doping at room temperature or higher to increase ion concentration along the source/drain epitaxial layer, followed by thermal activation, to create conformally doped sidewalls and reduce Rc, suitable for both frontside and backside contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ion implantation is used for backside contact formation, then contact resistance can be reduced, but the process becomes complex and alignment precision deteriorates due to misalignment between MSW contact and BSCON
Solution Approach 1:
The patent performs frontside doping on the source/drain epitaxial layer before forming the backside contact. This preliminary doping action ensures that when the backside contact is subsequently formed and connected to the source/drain region, the contact resistance is already optimized due to the pre-established high dopant concentration at the interface.
Solution Approach 2:
The patent uses the frontside source/drain epitaxial layer as a template or copy of the desired doped structure. By doping the epitaxial layer conformally on the frontside, the same doping pattern and concentration profile are replicated at the backside contact interface, ensuring low contact resistance without requiring complex backside alignment procedures.
2Reliability
If conventional ion implantation is used for backside contact formation, then contact resistance can be reduced, but manufacturing precision deteriorates due to alignment issues
Solution Approach 1:
The doping operation is performed in advance on the frontside when the source/drain epitaxial layer is accessible and can be precisely patterned. This eliminates the need for subsequent alignment-critical doping steps at the backside, as the doping pattern is already established before the backside contact formation process begins.
Solution Approach 2:
Instead of doping the backside contact from the backside (which would require precise alignment), the patent inverts the approach by doping the source/drain epitaxial layer from the frontside. This reverses the conventional sequence and makes the doping operation independent of backside contact alignment, thereby improving manufacturing precision.
3Reliability
If metal sidewall contacts are used to enlarge contact area, then resistance effects are reduced, but doping becomes difficult due to shadowing effect from large aspect ratio
Solution Approach 1:
Instead of attempting to dope the backside contact through the metal sidewall structure (which suffers from shadowing effects), the patent inverts the approach by doping the source/drain epitaxial layer from the frontside before metal sidewall formation. This eliminates the shadowing problem entirely, as the doping occurs when the epitaxial layer is exposed and accessible from the frontside.
Solution Approach 2:
The doping of the source/drain epitaxial layer is performed as a preliminary step before forming the metal sidewall contacts. This timing ensures that the epitaxial layer can be doped conformally without obstruction, and the doped structure is subsequently enclosed by the metal sidewalls, achieving both easy doping and low contact resistance.
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 achieves reduced contact resistance, minimizes doping-induced defects, and enhances device performance by allowing conformal doping without AR limitations, suitable for both frontside and backside contacts, especially beneficial for backside contacts with thermal budget constraints.
Implementation Method 1
performing an implant by directing ions to the source/drain epitaxial layer after filling the recess with the temporary material, wherein the implant increases an ion concentration along a surface of the source/drain epitaxial layer
Implementation Method 2
followed by thermal activation
Data Source
AI summary
Approaches herein relate to methods for forming self-aligned backside contacts and metal sidewall contacts in a semiconductor device. One method may include forming a plurality of alternating first layers and second layers atop a base layer, forming a trench in the plurality of alternating first layers and second layers, and forming a source/drain epitaxial layer along a sidewall of the trench. The method may further include forming a recess in the base layer by extending the trench into the base layer following formation of the source/drain epitaxial layer, filling the recess with a temporary material, and performing an implant by directing ions to the source/drain epitaxial layer after filling the recess with the temporary material, wherein the implant increases an ion concentration along an outer surface of the source/drain epitaxial layer.