Thick PECVD Silicon Dioxide Deposition With Stress-Balancing SiN Layers
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Solution Overview
Problem
Conventional PECVD processes face challenges in depositing thick SiO2 layers without cracking, especially at low temperatures, due to stress buildup, which limits deposition rates and warpage in semiconductor and MEMS applications.
Innovation Solution
A method involving a two-step PECVD process where an intermediate silicon nitride layer is deposited using a silane, nitrogen, and hydrogen or ammonia gas mixture, followed by a TEOS-based silicon dioxide layer using a tetraethyl orthosilicate gas mixture, with specific flow rates and temperatures to achieve compressive and neutral stress, enabling thicker SiO2 deposition without cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional PECVD processes are used to deposit thick SiO2 layers, then deposition rate can be increased, but stress buildup causes cracking and delamination
Solution Approach 1:
The patent divides the single thick SiO2 layer deposition into multiple alternating layers of SiO2 and SiN. Each SiO2 layer is deposited at high rate, followed by a thin SiN layer that provides stress compensation. This segmentation allows the total thickness to exceed 10 μm without cracking, as each individual SiO2 layer remains thin enough to avoid stress-induced failure while the cumulative thickness meets the application requirements.
Solution Approach 2:
The patent creates a composite multilayer structure combining SiO2 and SiN layers. The SiO2 layers provide the required dielectric thickness and electrical properties, while the SiN layers provide mechanical strength and stress compensation. This composite approach allows the system to achieve both high deposition rate (from SiO2) and high reliability (from SiN stress balancing) simultaneously.
2Reliability
If multiple stress balancing layers are used to prevent cracking, then layer integrity is improved, but process complexity increases
Solution Approach 1:
The patent systematically varies key deposition parameters including layer thickness ratios (SiO2:SiN = 5:1 to 20:1), deposition temperatures (200-400°C), and gas flow rates to optimize stress balance. By establishing specific parameter ranges, the process achieves reliable stress compensation without requiring excessive process complexity. The standardized parameter sets enable repeatable results across different wafer batches.
3Productivity
If deposition temperature is increased to improve deposition rate, then productivity increases, but wafer warpage and thermal damage increase
Solution Approach 1:
The patent segments the deposition process into multiple low-temperature cycles rather than one high-temperature process. Each SiO2/SiN layer pair is deposited at moderate temperatures (200-400°C), allowing stress relaxation between layers. This segmentation enables the accumulation of thick total layers without the cumulative thermal budget exceeding wafer tolerance, preventing warpage while maintaining acceptable deposition rates.
Solution Approach 2:
The SiN layers act as thermal buffers in the composite structure. Their different thermal expansion coefficients compared to SiO2 help compensate for thermal stress during deposition and subsequent processing. This composite material approach allows the process to operate at lower temperatures without sacrificing overall productivity, as the SiN layers protect the underlying structure from thermal damage.
4Stress or pressure
If low deposition rate is used to reduce stress, then stress buildup is reduced, but total deposition time increases
Solution Approach 1:
The patent segments the total thickness requirement into multiple thin SiO2 layers separated by SiN layers. Each thin SiO2 layer accumulates minimal stress during deposition, but the segmentation allows rapid deposition of many such layers in sequence. The SiN layers provide stress reset points, enabling the process to maintain low per-layer stress while achieving high total deposition rates that would be impossible with a single slow-deposited thick layer.
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 method allows for the high-rate deposition of TEOS-based silicon dioxide layers exceeding 10 µm thickness at low thermal budgets without cracking, improving adhesion and reducing stress, thus enhancing the deposition process efficiency and substrate integrity.
Implementation Method 1
performing a second deposition step by PECVD to deposit at least one silicon dioxide layer onto the intermediate layer
Implementation Method 2
sustaining a plasma in the chamber from the first gas mixture at a temperature of between about 220°C and about 300°C so as to deposit the intermediate layer onto the substrate
Data Source
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AI summary
A method of depositing silicon dioxide onto a substrate by plasma enhanced chemical vapour deposition (PECVD), a substrate with at least one silicon dioxide layer deposited thereon and a plasma enhanced chemical vapour deposition apparatus for depositing silicon dioxide onto a substrate by plasma enhanced chemical vapour deposition are provided.