Arrange the given process steps in sequence for self-aligned gate formation. A. Thermal oxidation to grow gate oxide. B. Polysilicon deposition C. Photolithography using gate mask D. Etching of polysilicon and oxide E. Source/drain diffusion Choose the correct answer from the options given below:
Self-Aligned Gate Formation Sequence Explained
The formation of a self-aligned gate in semiconductor manufacturing involves a specific order of steps to ensure the gate electrode correctly defines the source and drain regions. Here's the breakdown of the correct sequence:
Step-by-Step Process
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Step A: Thermal Oxidation
The process begins with growing a thin layer of silicon dioxide (SiO₂) on the silicon wafer. This layer serves as the gate oxide, providing electrical insulation between the silicon substrate and the gate electrode.
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Step B: Polysilicon Deposition
Next, a layer of heavily doped polysilicon (polycrystalline silicon) is deposited uniformly over the entire wafer, covering the gate oxide. This material will form the gate electrode.
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Step C: Photolithography
Photolithography using a specific gate mask is performed. This step transfers the pattern of the gate onto the polysilicon layer, defining its dimensions and location.
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Step D: Etching
An etching process removes the unwanted portions of the polysilicon layer and the underlying gate oxide that are not protected by the patterned photoresist. This step defines the actual gate structure.
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Step E: Source/Drain Diffusion/Implantation
Finally, the source and drain regions are created. The previously formed gate electrode acts as a mask during the doping process (either diffusion or ion implantation) for the source and drain areas. This self-alignment is crucial for device performance.
Therefore, the correct sequence for self-aligned gate formation is A, B, C, D, E.
Important Questions from Semiconductor Process Flow
Which one of the following processes is preferred to form the gate dielectric (SiO2) of MOSFETs?
Arrange the following in the correct sequence of steps for MOS fabrication
A. Wafer formation
B. Photolithography
C. Oxidation
D. Gate and source/drain formation
E. Metallization
Choose the correct answer from the options given below:Which of the following statements are true for optical photoresists
A. Solubility of a photo-resist changes on exposure to light in developer solution.
B. Solubility of a photo-resist does not change on exposure to light in developer solution.
C. A negative photo-resist on exposure to light becomes less soluble in developer solution.
D. A positive photo-resist on exposure to light becomes more soluble in developer solution.
Choose the correct answer from the options given below:- In particle beam lithography, the resolution depends upon :
A. For impurity diffusion in semiconductor, concentration gradient is the only essential requirement.
B. Annealing is a mandatory step after ion-implantation.
C. Wet etching is normally anisotropic
D. High temperature is required for the growth of $SiO_2$ because oxidation reaction takes place at high temperature
E. Bird's beak formation is a characteristic of LOCOS isolation
Choose the correct answer from the options given below:
