Oxide Semiconductor Transistor Etching Selectivity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in manufacturing transistors with oxide semiconductor films is the difficulty in achieving high selectivity during etching of electrode layers, leading to defective shapes and electrical characteristics, especially when the oxide semiconductor film thickness is small, resulting in exposure of underlying layers and potential disconnection of gate insulating films.
Innovation Solution
A method involving the formation of a single-layer metal film over an oxide semiconductor film with a crystal structure, followed by multiple etching steps and wet etching using dilute hydrofluoric acid to create a thin region as the channel formation area, reducing electric-field concentration and enhancing the reliability of the transistor by forming electrodes with projecting portions and using oxygen-excess regions in the insulating films to supply oxygen efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If electrode layer etching is performed with conventional methods, then the electrode layer can be formed, but the oxide semiconductor film may be partly removed or defective shapes may occur due to insufficient etching selectivity
Solution Approach 1:
A protective film is introduced as an intermediary layer between the oxide semiconductor film and the electrode layer. This protective film has high etching selectivity compared to the electrode layer, allowing the electrode layer to be etched without damaging the underlying oxide semiconductor film. The protective film acts as a buffer that protects the sensitive oxide semiconductor film during the etching process.
Solution Approach 2:
The protective film is formed in advance before the electrode layer etching process. This preliminary action ensures that the oxide semiconductor film is protected before any etching occurs, preventing potential damage from the outset. The protective film is strategically placed and formed with appropriate thickness to withstand the subsequent etching process.
2Productivity
If the oxide semiconductor film thickness is reduced to improve device performance, then higher integration and better electrical characteristics are achieved, but the film becomes more susceptible to damage during etching
Solution Approach 1:
The protective film serves as a cushioning layer that absorbs and protects the thin oxide semiconductor film during the etching process. By providing this protective barrier in advance, the thin film is shielded from the harsh etching conditions, preventing accidental removal or damage that would otherwise occur with reduced film thickness.
3Reliability
If the electrode layer completely covers the oxide semiconductor film to improve contact, then electrical connection is enhanced, but electric field concentration occurs at the edges causing reliability issues
Solution Approach 1:
The electrode layer is designed with different coverage characteristics in different regions. It completely covers the oxide semiconductor film in the channel formation region to ensure good electrical connection, but has reduced or no coverage in the end portions to minimize electric field concentration. This local differentiation of coverage quality optimizes both electrical connection and field distribution.
4Ease of manufacture
If conventional etching methods are used to form source and drain electrodes, then the basic transistor structure is achieved, but defective shapes and openings in the oxide semiconductor film occur
Solution Approach 1:
The protective film serves as a mediator that enables the etching process to proceed without causing defects. It allows the source and drain electrodes to be properly formed while preventing the oxide semiconductor film from developing defective shapes or openings, thus maintaining both ease of manufacture and shape accuracy.
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 the electrical characteristics and reliability of the transistor by reducing electric-field concentration, preventing disconnection of gate insulating films, and ensuring stable performance even with thin oxide semiconductor films, while also providing a normally-off transistor with enhanced resistance to external electric fields.
Implementation Method 1
exposing the oxide semiconductor film to dilute hydrofluoric acid with a concentration higher than 0.0001% and lower than or equal to 0.25% to reduce a thickness of an exposed portion of the oxide semiconductor film
Implementation Method 2
using oxygen-excess regions in the insulating films to supply oxygen efficiently
Data Source
AI summary
Provided is a method for manufacturing a transistor by which the defective shape of a semiconductor device is prevented in the case where a source electrode layer and a drain electrode layer are formed on an oxide semiconductor film. A source electrode layer and a drain electrode layer are formed each having a cross-sectional shape with which disconnection of a gate insulating film is unlikely to occur even when the gate insulating film over the source electrode layer and the drain electrode layer has a small thickness. An oxide semiconductor film having a crystal structure over an insulating surface is formed; an electrode layer on the oxide semiconductor film is formed; and a thickness of an exposed portion of the oxide semiconductor film is reduced by exposing the oxide semiconductor film to dilute hydrofluoric acid with a concentration higher than 0.0001% and lower than or equal to 0.25%.