Metal Gate Oxidation Control via Selective Wet Process
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Solution Overview
Problem
Conventional selective oxidation processes in semiconductor device fabrication damage metal gate patterns and fail to control the thickness of the gate oxide layer effectively, especially for smaller gate lengths, leading to increased resistance and potential punch-through failures.
Innovation Solution
A method involving the deposition of a capping layer, followed by selective wet oxidation using a partial pressure of H2O and H2 in an H2-rich atmosphere, which reduces the oxidation of metal layers and selectively oxidizes silicon, thereby minimizing damage and preventing punch-through.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dry oxidation process is used to perform gate polysilicon reoxidation, then the damage caused by dry etching can be corrected, but the exposed surface of the tungsten layer may be oxidized, resulting in reduced effective sectional area of the gate and increased resistance
Solution Approach 1:
The patent applies selective oxidation conditions that create different oxidation behaviors in different regions. The H2-rich atmosphere with controlled H2O partial pressure enables selective oxidation of polysilicon while protecting tungsten layers from oxidation, achieving local quality differentiation in the oxidation process
Solution Approach 2:
The patent changes the oxidation parameters by using H2-rich atmosphere with controlled H2O partial pressure instead of conventional dry oxidation conditions. This parameter change shifts the oxidation mechanism to preferentially oxidize polysilicon while preventing tungsten oxidation, resolving the contradiction between damage correction and resistance control
2Productivity
If the gate length is reduced to increase integration density, then the signal delay can be decreased, but the selective oxidation process may result in a dramatic increase in the thickness of the gate oxide layer due to the bird's beak effect
Solution Approach 1:
The patent changes the oxidation parameters by using H2-rich atmosphere with controlled H2O partial pressure, which fundamentally alters the oxidation mechanism. This parameter change eliminates the bird's beak effect that plagues conventional oxidation processes, enabling precise gate oxide thickness control even at reduced gate lengths
Solution Approach 2:
The patent applies preliminary protective measures by using the H2-rich atmosphere before oxidation occurs, which prevents the formation of the bird's beak effect from the outset. This preliminary anti-action approach counteracts the tendency toward oxide thickness variation that would otherwise occur during the oxidation process
3Object-affected harmful factors
If conventional selective oxidation is performed to reduce damage to the metal gate pattern, then the oxidation of metal layers may be reduced, but the thickness of the gate oxide layer cannot be controlled effectively, leading to potential punch-through failures
Solution Approach 1:
The patent changes the oxidation parameters by using H2-rich atmosphere with controlled H2O partial pressure, which simultaneously achieves selective oxidation protection for metal layers and precise control of gate oxide thickness. This dual control resolves the contradiction between reducing metal oxidation and preventing punch-through failures
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 reduces damage to the metal gate pattern edges and lowers the occurrence of punch-through failures by controlling the oxidation of the gate oxide layer, maintaining the resistance and vertical profile of the gate line.
Implementation Method 1
Selective oxidation is carried out to reduce damage caused by the etching process for forming the metal gate pattern. Both the oxidation rates for silicon and polysilicon and the ratios of those rates can vary depending on the particular oxidation process employed.
Implementation Method 2
Selective oxidation using a partial pressure ratio of H2O and H2 in an H2-rich wet oxidation process may oxidize a polysilicon layer and a silicon substrate and may reduce the oxidation of the metal layers included in the metal gate pattern.
Implementation Method 3
A metal gate material layer may be deposited on a substrate, e.g., a silicon substrate
Data Source
AI summary
A method of fabricating a semiconductor device having a metal gate pattern is provided in which capping layers are used to control the relative oxidation rates of portions of the metal gate pattern during a oxidation process. The capping layer may be a multilayer structure and may be etched to form insulating spacers on the sidewalls of the metal gate pattern. The capping layer(s) allow the use of a selective oxidation process, which may be a wet oxidation process utilizing partial pressures of both H2O and H2 in an H2-rich atmosphere, to oxidize portions of the substrate and metal gate pattern while suppressing the oxidation of metal layers that may be included in the metal gate pattern. This allows etch damage to the silicon substrate and edges of the metal gate pattern to be reduced while substantially maintaining the original thickness of the gate insulating layer and the conductivity of the metal layer(s).