Plasma Oxidation Conformality via Substrate Cooling
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Solution Overview
Problem
Conventional semiconductor fabrication methods for forming oxide layers face challenges such as dopant profile distortion at high temperatures, contamination, ion bombardment damage, and poor conformality due to limited oxidation on sidewalls, leading to defects like 'bird's beak' and reduced device performance.
Innovation Solution
Active cooling of the semiconductor substrate to temperatures between −50° C. and 100° C. during plasma oxidation, using a plasma reaction chamber with an ion generation region and a cooling system, such as an electrostatic chuck or convective gas, to enhance the sticking coefficient of oxygen species and improve conformality of oxide layers on sidewalls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermal oxidation processes are used to form oxide layers, then oxide layers can be formed effectively, but high wafer temperatures cause dopant diffusion and distortion of dopant profiles
Solution Approach 1:
The patent changes the temperature parameter from conventional high temperatures (above 700°C) to low temperatures (below 200°C, preferably below 150°C) during oxidation. This is achieved by introducing a cooling gas (such as nitrogen or helium) to the reaction chamber, which cools the substrate while allowing oxidation to proceed. The low temperature prevents dopant diffusion while the plasma environment enables oxide formation, thus resolving the contradiction between oxide layer quality and dopant profile distortion.
Solution Approach 2:
The patent replaces thermal oxidation (heat-driven) with plasma-enhanced oxidation at low temperatures. Instead of relying on thermal energy to drive the oxidation reaction, the patent uses plasma (ionized gas) to provide the necessary chemical reactivity. The plasma generates reactive oxygen species that can oxidize the substrate at low temperatures without causing thermal damage or dopant diffusion, thus substituting a thermal-mechanical process with a plasma-chemical process.
2Manufacturing precision
If plasma oxidation is performed at high chamber pressure, then oxidation can occur, but contaminants accumulate in the oxide layer causing defects
Solution Approach 1:
The patent changes the chamber pressure parameter to low pressure (below 100 mTorr, preferably below 50 mTorr) during plasma oxidation. This low pressure environment reduces the mean free path of gas molecules, allowing better control over the plasma chemistry and reducing contaminant incorporation into the oxide layer. The low pressure plasma conditions, combined with the cooling gas flow, create an environment where oxidation proceeds with high purity while minimizing contaminant accumulation that would otherwise occur at higher pressures.
3Manufacturing precision
If plasma oxidation is performed at low chamber pressure, then contaminants are reduced, but increased plasma ion energy causes ion bombardment damage
Solution Approach 1:
The patent replaces high-energy ion bombardment with low-energy plasma chemistry. Instead of relying on high-energy ions to drive the oxidation reaction (which causes damage at low pressure), the patent uses a plasma environment rich in reactive oxygen radicals and molecules. These species can oxidize the substrate through chemical reactions rather than physical bombardment. The cooling gas further reduces ion energy by cooling the plasma, ensuring that oxidation occurs through gentle chemical processes rather than damaging physical sputtering.
Solution Approach 2:
The patent changes multiple parameters simultaneously: chamber pressure (low), temperature (low), and plasma power density (optimized). This combination creates a plasma environment where the chemistry is driven by reactive species concentration rather than ion energy. The low temperature specifically suppresses ion bombardment effects while the plasma chemistry remains active enough to drive oxidation, thus resolving the contradiction between purity and damage.
4Manufacturing precision
If conventional plasma oxidation is used, then oxidation occurs on top and bottom surfaces, but sidewall oxidation is limited resulting in poor conformality
Solution Approach 1:
The patent changes the temperature parameter to low temperatures (below 200°C) during plasma oxidation. This low temperature regime fundamentally alters the oxidation kinetics, making the process more diffusion-limited and less dependent on direct plasma flux. At low temperatures, the oxidation proceeds more uniformly across all surfaces including sidewalls, because the reactive species have sufficient time to diffuse and react evenly throughout the structure. This improves conformality compared to conventional higher temperature plasma oxidation where top and bottom surfaces receive direct plasma flux while sidewalls are shadowed.
Solution Approach 2:
The patent replaces the plasma flux-driven oxidation mechanism with a diffusion-enhanced oxidation mechanism. At low temperatures, the oxidation process becomes more dependent on the diffusion of reactive oxygen species through the plasma and across the structure surfaces rather than direct plasma bombardment. This substitution of mechanism allows uniform oxidation on all surfaces including sidewalls, achieving better conformality than conventional plasma oxidation where the directional plasma flux creates non-uniform oxidation patterns.
5Productivity
If high temperatures are used for oxidation, then oxidation rate is sufficient, but dopant diffusion occurs leading to bird's beak defects
Solution Approach 1:
The patent replaces thermal-driven oxidation with plasma-enhanced oxidation at low temperatures. The plasma provides the necessary chemical reactivity to achieve sufficient oxidation rates without relying on high temperatures. Reactive oxygen species in the plasma (atoms, molecules, and ions) directly react with the substrate to form oxide at low temperatures, maintaining productivity while eliminating the thermal energy that would otherwise cause dopant diffusion and bird's beak defects.
Solution Approach 2:
The patent changes the temperature parameter from high (conventional) to low (below 200°C) while compensating for the reduced thermal activation energy by increasing the chemical reactivity through plasma. The plasma environment provides a high concentration of reactive oxygen species that can oxidize the substrate efficiently at low temperatures. This parameter change maintains sufficient oxidation rate (productivity) while eliminating the thermal damage and dopant diffusion that would occur at high temperatures.
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
Achieves conformality of at least 75% and up to 90% on sidewalls, reducing defects and improving the performance of semiconductor devices by ensuring uniform oxide layer thickness across all surfaces, including smaller features less than 100 nm in thickness.
Implementation Method 1
a plasma is generated in the ion generation region of the chamber and is used to form an oxide layer on the substrate. The plasma formed according to one or embodiments may include oxygen or an oxygen species
Implementation Method 2
oxidation of a semiconductor device or its components to form conformal oxide layers
Implementation Method 3
the substrate is actively cooled. In such embodiments, actively cooling the substrate increases the sticking coefficient of the oxygen species included in some plasmas
Implementation Method 4
actively cooling the substrate increases the sticking coefficient of the oxygen species included in some plasmas
Data Source
AI summary
Methods and apparatus for forming an oxide layer on a semiconductor substrate are disclosed. In one or more embodiments, plasma oxidation is used to form a conformal oxide layer by controlling the temperature of the semiconductor substrate at below about 100° C. Methods for controlling the temperature of the semiconductor substrate according to one or more embodiments include utilizing an electrostatic chuck and a coolant and gas convection.