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
-
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.
-
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.
-
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.
-
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.
-
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
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:
- Match the LIST-I with LIST-IIChoose the correct answer from the options given below:
LIST-I LIST-II A. Shallow trench isolation (STI) I. Low static power dissipation B. Junction isolation II. High static power dissipation C. CMOS technology III. High component density D. Bipolar IC technology IV. Low component density Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Impurity diffusion in semiconductor essentially needs very high temperature.
Reason R: Diffusivity of impurity atoms is negligibly small at room temperature.
In the light of the above statements, choose the most appropriate answer from the options given below
- In particle beam lithography, the resolution depends upon :
When silicon dioxide of thickness d is grown, the Silicon consumed is :
