PECVD Deposition of Smooth Silicon Films for 3D Memory
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Solution Overview
Problem
Conventional methods for depositing film layers in 3D memory devices often result in rough films with interfacial defects and unacceptably high compressive stress, which can lead to structural and electrical defects, and are difficult to achieve smooth, low-stress silicon and silicon germanium films for hardmask applications.
Innovation Solution
The method involves using Plasma-Enhanced Chemical Vapor Deposition (PECVD) with specific gas compositions and plasma conditions, including the use of argon, helium, and hydrogen, to deposit smooth silicon and silicon germanium films with surface roughness of less than 7 Å and compressive stress of less than 500 MPa, or tensile stress, suitable for hardmask applications and 3D memory device fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CVD or HDP-CVD processes are used to deposit silicon films, then film deposition is achieved, but the films exhibit unacceptably rough surfaces and high compressive stress
Solution Approach 1:
The patent changes the deposition parameters by using PECVD instead of conventional CVD or HDP-CVD, specifically controlling the plasma power (100-1000 W), pressure (1-10 Torr), and gas composition (silane 0.1-5%, ammonia 0.1-5%, balance hydrogen) to achieve smooth films with low compressive stress. The deposition temperature is also optimized in the range of 200-400°C to achieve the desired film quality.
Solution Approach 2:
The patent uses an inert hydrogen-based atmosphere with specific gas composition (silane and ammonia precursors in hydrogen) to create a controlled deposition environment that prevents unwanted reactions and enables the formation of smooth silicon films with reduced stress. The hydrogen plasma environment is key to achieving the desired film properties.
2Productivity
If conventional PECVD processes are used to deposit silicon films, then deposition speed is improved, but interfacial defects and vacuum breaks occur between layers
Solution Approach 1:
The patent maintains continuous plasma deposition without vacuum breaks between successive film layers, ensuring uninterrupted deposition that prevents interfacial defects. The process is designed to deposit multiple layers (10-50 layers) in a continuous manner, maintaining plasma presence throughout the deposition sequence to avoid contamination and interface defects.
Solution Approach 2:
The patent optimizes deposition parameters including plasma power (100-1000 W), pressure (1-10 Torr), and gas composition to achieve both high deposition speed and high film quality. The specific ratio of silane to ammonia (0.1:0.1 to 5:5) and the use of hydrogen as carrier gas are critical for achieving smooth interfaces without defects while maintaining productive deposition rates.
3Quantity of substance
If multiple film layers are deposited to build 3D memory stacks, then device capacity is increased, but surface roughness is magnified through subsequent layers
Solution Approach 1:
The patent uses optimized PECVD parameters (plasma power 100-1000 W, pressure 1-10 Torr, temperature 200-400°C, gas composition with silane 0.1-5%, ammonia 0.1-5%, balance hydrogen) to deposit each layer with controlled smoothness. These parameters ensure that each individual layer maintains low roughness, preventing roughness magnification as the stack builds to 10-50 layers.
Solution Approach 2:
The patent employs continuous plasma deposition without vacuum breaks between layers, ensuring that each interface in the multi-layer stack is formed under identical clean plasma conditions. This continuity prevents the accumulation of interfacial defects and maintains consistent surface quality throughout the entire film stack, enabling successful deposition of 10-50 layers.
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 allows for the deposition of smooth films with low compressive or tensile stress, improving the structural and electrical integrity of 3D memory devices and enabling effective patterning processes by maintaining low roughness and stress values, even in multi-layer stacks.
Implementation Method 1
forming a plasma in the PECVD apparatus to deposit a smooth silicon film on the substrate
Implementation Method 2
Plasma-Enhanced Chemical Vapor Deposition (PECVD) with specific gas compositions and plasma conditions
Data Source
AI summary
Smooth silicon films having low compressive stress and smooth tensile silicon films are deposited by plasma enhanced chemical vapor deposition (PECVD) using a process gas comprising a silicon-containing precursor (e.g., silane), argon, and a second gas, such as helium, hydrogen, or a combination of helium and hydrogen. Doped smooth silicon films and smooth silicon germanium films can be obtained by adding a source of dopant or a germanium-containing precursor to the process gas. In some embodiments dual frequency plasma comprising high frequency (HF) and low frequency (LF) components is used during deposition, resulting in improved film roughness. The films are characterized by roughness (Ra) of less than about 7 Å, such as less than about 5 Å as measured by atomic force microscopy (AFM), and a compressive stress of less than about 500 MPa in absolute value. In some embodiments smooth tensile silicon films are obtained.