Technology
Manufacturing Transistors Despite Their Infinitesimal Size
Manufacturing Transistors Despite Their Infinitesimal Size
Transistors, the fundamental building blocks of modern electronics, are incredibly small, often measuring just a few nanometers in size. Despite their infinitesimal dimensions, the manufacturing process for these devices is a highly complex and precise endeavor. This article explores the intricacies of how transistors are made, focusing on modern techniques such as ion implantation, photolithography, and Extreme Ultra Violet (EUV) lithography.
Overview of Transistor Manufacturing Process
Manufacturing modern transistors involves a series of advanced techniques, including ion implantation, photolithography, and etching, to create the precise layers and features necessary for transistor operation. Key steps include the deposition and patterning of materials onto the silicon wafer, followed by etching to define the transistor's structure.
Photolithography Techniques
Photolithography is one of the most critical steps in the transistor manufacturing process. It involves the use of light to transfer patterns onto a silicon wafer. In modern production, excimer lasers are often employed, with masks that are usually four times larger than the actual devices. An optical path through a reduction lens reduces the size of the pattern on the wafer. However, with the advent of EUV lithography, this process has become significantly more complex.
EUV lithography, which operates at a wavelength of 13 nanometers, is a game-changer in semiconductor manufacturing. This technique uses a tin vapor atmosphere and a reflective mask, with pre-distorted masks to accommodate varying distances from the wafer. The use of EUV lithography is particularly important for creating features smaller than the wavelength, a challenge in conventional excimer laser lithography, which operates at 248 and 193 nanometers.
FinFET Fabrication Process
Fabricating a FinFET, a type of transistor that significantly improves performance and reduces power consumption, involves a series of precise manufacturing steps:
Step 1: Channel Doping
Before the etch step, the wafer must be prepared with appropriate doping. For a FinFET, the channel dopant is applied in a very thin layer on the surface. This is typically achieved using ion implantation, where a specific energy ion beam (usually 10 to 100KV) drives the dopant to a precise depth.
Step 2: Fin Formation
The top surface layer is the channel, and the remaining silicon is etched away, leaving only the Fin structure. This is accomplished through a process called Reactive Ion Etching (RIE) in a plasma chamber with low pressure gas. The etching angle is carefully controlled to achieve the desired vertical sides.
Step 3: Gate Oxide Formation
After the etch, the gate oxide is formed. This step is crucial, as the oxide must be a precise thickness without any defects to ensure the transistor functions correctly. The oxide is thicker outside the Fin to prevent short circuits and maintain the transistor's integrity.
Step 4: Gate Polysilicon Deposition
The gate polysilicon is then deposited in a thin stripe. This step is critical for the proper electrical functioning of the FinFET.
Step 5: Source and Drain Contacts
Finally, the source and drain contacts are applied, which are typically at a distance from the cross-sectional view shown.
Conclusion
While the process of manufacturing modern transistors is highly complex, it is evolving rapidly, with advances in EUV lithography pushing the boundaries of what is possible. As the semiconductor industry continues to innovate, the future of electronics will undoubtedly rely on these precise and efficient manufacturing processes.