SiGe Stack Etching with Plasma Pretreatment for High Selectivity
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Solution Overview
Problem
Existing methods for selectively etching silicon germanium (SiGe) layers in a stack of silicon (Si) and SiGe layers face challenges such as silicon loss at low flow rates and degraded selectivity at high flow rates, leading to inefficiencies in etch rate and selectivity.
Innovation Solution
A substrate processing method that involves plasma pretreatment with a halogen component, followed by etching with an etch gas, to enhance the reactivity of SiGe layers selectively, thereby increasing the etch rate and maintaining high selectivity even at low flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low flow rate conditions are used for selective etching of SiGe layers, then selectivity is maintained, but etch rate decreases and silicon loss increases
Solution Approach 1:
The patent applies plasma pretreatment to the SiGe layer surface before etching to modify the surface properties and increase reactivity. This preliminary action enables faster etching rates during the subsequent etching step while maintaining selectivity, as the pretreated surface is more reactive to the etch gas. The pretreatment step prepares the surface in advance to overcome the low etch rate problem without sacrificing selectivity.
Solution Approach 2:
The patent changes the surface state parameter of the SiGe layer through plasma pretreatment, transforming it from a low-reactivity state to a high-reactivity state. This parameter change in surface reactivity allows the etching process to proceed at higher rates while maintaining the selective removal of SiGe over Si, effectively resolving the contradiction between etch rate and selectivity.
2Reliability
If extended exposure to etch gas is used under low flow rate conditions, then selectivity is maintained, but silicon loss increases due to F and/or Cl fume levels
Solution Approach 1:
Plasma pretreatment is applied before etching to modify the SiGe surface, making it more reactive. This preliminary modification reduces the required etching time, thereby limiting the exposure duration to etch gas. The reduced exposure time minimizes silicon loss and harmful fume generation while maintaining selectivity through the enhanced surface reactivity.
Solution Approach 2:
The patent rushes through the etching process by utilizing the pretreated high-reactivity surface, completing the etching in a shorter time. This rapid completion reduces the duration of harmful gas exposure, thereby minimizing silicon loss and fume generation while achieving the desired selective etching result.
3Productivity
If high flow rate and high pressure conditions are used for etching, then etch rate increases, but SiGe etch selectivity degrades
Solution Approach 1:
The plasma pretreatment step is applied before etching to selectively modify the SiGe surface, enhancing its reactivity. This preliminary action creates a surface state that is highly responsive to etch gas, enabling fast etching rates even at lower flow rates and pressures. The selectivity is preserved because the pretreatment selectively activates SiGe surfaces, and subsequent etching proceeds rapidly without requiring high flow rate conditions that would compromise selectivity.
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
The method effectively increases the etch rate of SiGe layers while maintaining high selectivity relative to silicon, addressing the inefficiencies of existing methods and improving processing efficiency.
Implementation Method 1
modifying the surface of the SiGe layers by plasmaizing a pretreatment gas
Implementation Method 2
the surface of the SiGe layer may be modified with the halogen component in step (a)
Implementation Method 3
etching SiGe layers using an etch gas
Data Source
AI summary
A substrate processing method of selectively etching silicon germanium layers laterally in a stack in which silicon layers and silicon germanium layers are alternately stacked on a substrate is disclosed. The substrate processing method includes steps of (a) modifying the surface of the SiGe layers by plasmaizing a pretreatment gas and (b) etching the silicon germanium layers using etch gas. Preferably, the step of removing native oxide from a side of a stack in which the silicon layers and the silicon germanium layers are alternately stacked may be further included before step (a).