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FEOL (Front End of Line: substrate process, the first half of wafer processing)
3. Gate oxidation and gate formation

How a semiconductor wafer is made

This step is most important from the viewpoint of transistor characteristics.
A gate oxide film greatly influences the performance and reliability of a transistor, and should therefore be a high-density thin film uniformly distributed over the wafer surface.
Since the size of the gate formed may also greatly influence the performance of the transistor, strict dimensional control is necessary in both photo resist patterning and gate etching.
Gate electrodes are formed of polysilicon (polycrystalline silicon) by CVD.

3-1. Gate oxidation

Gate oxidation

The silicon surface is cleaned through chemical treatment, and then oxidized, forming a gate oxide film. The thickness and quality of this oxide film has a major effect on transistor performance and reliability, and thus it must be a thin, high-density film with a uniform distribution.


3-2. Polysilicon growth

Polysilicon growth

Polysilicon (polycrystalline silicon) to be the gate electrode is formed using the CVD method.


3-3. Formation of gate resist pattern

Formation of gate resist pattern

Gate resist pattern is formed.


3-4. Gate etching

Gate etching

Using the gate resist pattern as a mask, the gate is formed by etching the polysilicon and gate oxide film. After etching, the resist pattern is removed. Gate dimensions have a major effect on transistor performance, and thus strict dimensional control is needed in both gate resist patterning and gate etching.

Process Flow

FEOL (Front End of Line: substrate process, the first half of wafer processing)
| 1. Isolation | 2. Well and channel formation | 3. Gate oxidation and gate formation
| 4. LDD formation | 5. Side wall spacers | 6. Source/drain | 7. Silicide | 8. Dielectric film |
9. Contact holes |

BEOL (Back End of Line: interconnect process, the second half of wafer processing)
| 10. Metal-1 | 11. Metal-2 |

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