Backside Contact Formation Using Shallow Etch and Placeholder Cavities
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Solution Overview
Problem
The integration of backside power delivery networks in semiconductor devices is challenging due to difficulties in forming backside contacts and power rails, particularly in narrow processing windows, leading to variations in epitaxy growth and deep placeholder cavity etches that are hard to achieve.
Innovation Solution
A backside contact patterning method is introduced where the backside placeholder is formed prior to the nanosheet stack, allowing access from the frontside using a shallow etch, and conformal epitaxy is grown to mitigate height variations, enabling robust backside contact formation across varying window sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backside contacts are formed using conventional deep placeholder cavity etches, then power delivery network integration is achieved, but processing difficulty increases significantly in narrow processing windows
Solution Approach 1:
The placeholder structure is formed in advance during frontside processing before the chip is flipped for backside contact formation. This preliminary formation of the placeholder cavity and epitaxial growth platform enables subsequent backside contact etching to be performed as a shallow etch rather than a deep etch, significantly reducing processing difficulty in narrow windows
Solution Approach 2:
The conventional sequence is inverted: instead of forming deep cavities on the backside first and then attempting contact formation, the placeholder is formed on the frontside first, the chip is flipped, and then shallow contact holes are etched through the placeholder to reach the pre-formed epitaxial platform. This inversion transforms an intractable deep etch problem into a manageable shallow etch process
2Reliability
If conventional backside contact formation methods are used, then power delivery is enabled, but variations in epitaxy growth occur that are hard to control
Solution Approach 1:
Epitaxial growth is performed in advance on the frontside of the chip during placeholder formation, creating a pre-formed platform with controlled thickness and composition. This preliminary epitaxial growth occurs under optimized conditions before the chip is flipped, ensuring uniformity and reducing variations that would occur if epitaxy were attempted after backside contact formation
Solution Approach 2:
The placeholder structure serves as an intermediary medium that facilitates controlled epitaxial growth. The placeholder material (typically silicon or silicon-germanium) provides a crystalline template that guides the epitaxial growth of the contact region, ensuring uniform growth characteristics and reducing variations across different processing windows
3Ease of operation
If deep placeholder cavity etches are performed, then backside contact access is achieved, but processing window constraints are violated in narrow windows
Solution Approach 1:
The placeholder cavity is formed in advance with precise dimensions controlled during frontside processing. By pre-defining the cavity depth and dimensions, the subsequent backside contact etch only needs to remove a shallow amount of material to reach the placeholder floor, transforming an impossibly deep etch into a controllable shallow etch that fits within narrow processing windows
Solution Approach 2:
The problem is solved by adding the time dimension through sequential processing: first forming the placeholder cavity to a controlled depth, then flipping the chip, and finally etching through the placeholder from the backside. This temporal sequencing allows the total etch depth to be divided into two manageable stages, each with controllable precision within narrow windows
4Productivity
If backside contacts are formed without preliminary placeholder formation, then processing steps are reduced, but contact formation becomes infeasible in narrow processing windows
Solution Approach 1:
The placeholder formation and epitaxial growth steps are merged into a single integrated process performed during frontside processing. The placeholder structure is formed and epitaxial growth is completed before the chip is flipped, combining what could be separate backside operations into a unified frontside process sequence. This merging reduces the total number of high-precision steps required and eliminates the need for complex backside epitaxial growth equipment
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 relaxes processing constraints, ensures consistent backside contact formation, and prevents shorts, providing a reliable power delivery network even in narrow processing windows.
Implementation Method 1
The backside contact dielectric liner includes an L-shaped spacer having direct contact with a shoulder surface and a sidewall surface of the backside contact
Data Source
AI summary
Embodiments of the present disclosure are directed to processing methods and resulting structures for providing robust backside contacts. In a non-limiting embodiment, a backside contact is electrically coupled to a first source or drain (S/D) region and a frontside contact electrically coupled to a second S/D region. A backside contact dielectric liner wraps around the backside contact. The backside contact dielectric liner includes an L-shaped spacer having direct contact with a shoulder surface and a sidewall surface of the backside contact.