Selective Si Plasma Etching with Ge Passivation for Nanosheet Stacks
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Solution Overview
Problem
Conventional plasma etching techniques face challenges in selectively etching silicon (Si) layers relative to germanium (Ge) layers in semiconductor fabrication, particularly in forming nanowires or nanosheets for 3D vertical structures, due to insufficient control over native oxide layers and passivation layer formation, leading to surface roughness and gouging of Ge-containing layers.
Innovation Solution
A two-step plasma process is employed, where a first plasma step modifies the surfaces by removing native oxide layers and forming a passivation layer on Ge-containing layers, followed by a second plasma step that selectively etches Si layers while inhibiting etching of Ge layers, using a controlled gas injection timeline to ensure passivation layer formation and maintain selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional plasma etching is used to etch Si layers, then etching speed is improved, but selectivity between Si and Ge layers deteriorates due to insufficient passivation layer formation
Solution Approach 1:
A preliminary plasma treatment step is performed before the main etching process to form a passivation layer on Ge-containing layers. This preliminary action prepares the surface by removing native oxide and creating a protective layer that will prevent Ge etching during subsequent high-speed Si etching, thus enabling both high productivity and high selectivity
Solution Approach 2:
The patent employs different plasma parameters (gas composition, power, pressure) for different process steps. The first plasma step uses parameters optimized for passivation layer formation, while the second step uses parameters optimized for high-speed Si etching. This parameter change allows the system to achieve both selective Ge protection and high Si etching speed
2Productivity
If plasma power is increased to improve etching rate, then productivity is improved, but surface roughness and gouging of Ge layers worsen
Solution Approach 1:
The etching process is segmented into distinct steps with different power levels and gas compositions. The first step uses lower power for controlled passivation layer formation, while the second step uses higher power for rapid Si etching. This segmentation allows high etching rates to be achieved without causing surface roughness or Ge layer gouging, as the protective passivation layer is already in place
Solution Approach 2:
The first plasma step performs a preliminary anti-action by forming a protective passivation layer on Ge-containing layers before the high-power etching step. This preliminary protection prevents the harmful effects of high power (surface roughness and gouging) from affecting the Ge layers during the high-productivity etching phase
3Loss of time
If native oxide layer is not removed before etching, then processing time is reduced, but etching uniformity and selectivity deteriorate
Solution Approach 1:
The patent merges the native oxide removal and passivation layer formation into a single integrated plasma step. This combined step achieves both functions simultaneously, maintaining etching uniformity and selectivity without requiring separate processing steps, thus minimizing the loss of time while preserving manufacturing precision
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 improves surface roughness and local uniformity, reduces gouging of Ge-containing layers, and maintains selectivity during the etching process, enhancing the formation of indents in the film stack for nanowire devices.
Implementation Method 1
modifying, in a first plasma step, exposed surfaces of the first Ge-containing layer, the second Ge-containing layer, and the first Si layer by exposing the exposed surfaces to a first plasma
Implementation Method 2
removing at least a portion of a native oxide layer (NOL) from the exposed surfaces of the first Si layer
Implementation Method 3
forming a passivation layer on the exposed surfaces of the first Ge-containing layer and the second Ge-containing layer
Implementation Method 4
forming a passivation layer on the exposed surfaces of the first Ge-containing layer and the second Ge-containing layer
Implementation Method 5
etching, using a second plasma, the first Si layer to form an indent in the film stack
Implementation Method 6
The second plasma selectively etches the Si layers
Implementation Method 7
The passivation layer inhibits etching of the first Ge-containing layer and the second Ge-containing layer
Data Source
AI summary
In certain embodiments, a method of processing a semiconductor substrate includes positioning a semiconductor substrate in a plasma chamber of a plasma tool. The semiconductor substrate includes a film stack that includes silicon layers and germanium-containing layers in an alternating stacked arrangement, with at least two silicon layers and at least two germanium-containing layers. The method includes exposing, in a first plasma step executed in the plasma chamber, the film stack to a first plasma. The first plasma is generated from first gases that include nitrogen gas, hydrogen gas, and fluorine gas. The method includes exposing, in a second plasma step executed in the plasma chamber, the film stack to a second plasma. The second plasma is generated from second gases comprising fluorine gas and oxygen gas. The second plasma selectively etches the silicon layers.