Photolithography is the pioneering technique used to generate functional patterns on various substrates. Precision microfabrication often occurs at scales and levels of throughput that conventional machining paradigms cannot achieve. No mechanical tools can etch microelectronics for complex devices like integrated circuits, optical components, and bio-sensors. Photolithography, meanwhile, is perfectly suited to the task.
An Overview of Semiconductor Manufacturing
Semiconducting materials form the backbone of modern electronics. Since the mid-1960s, engineers have been generating transistors and microelectronic elements using silicon. Silicon was then a novel material with wholly unique conductive properties; offering variable resistance to allow optimal current flow. Various other semiconductors have since been developed, including aluminum nitride, germanium, and zinc oxide–but they are all manufactured via the same general workflow.
A single crystal ingot is grown epitaxially using the Czochralski method, or perhaps the float-zone technique, and wafers are mechanically extracted. Here is a general workflow that may be followed to yield an optimized functional substrate:
- Start by cleaning the wafers with chemical agents to avoid contamination
- Use sputtering, electrodeposition or chemical vapor deposition to help thin film deposition occur on the wafer
- Particles are removed through post-deposition cleaning with brushes or a Nanospray
- Resist is added to the wafer, and it is spun to create a uniform layer
- Ultraviolet radiation is used on the resist layer to create a structural change
- Developer is added to the wafer to show the thin film
- Etching is undertaken using chemicals to dissolve the layer
- To add semiconducting properties to the silicon substrate, impurities are placed into the wafers
- Heat is used to activate the implanted ions
- Resist is then removed using chemicals or through ashing
- The wafer is assembled into a product
How is Photolithography Used in Semiconductor Manufacturing?
The primary purpose behind semiconductor lithography is to add a pattern to the surface of a wafer. If you are trying to remember its purpose, consider its name’s roots, “lithos” and “grapha,” which translate to writing on a stone.
Using a coating, exposure, and development process, a pattern can be etched perfectly and help provide a higher resolution of miniature semiconductors. The process goes as follows:
- The substrate is prepared with a photo-resistant material to create a layer
- Imaging systems and photolithography are used to align a substrate and photomask under UV light to create a unique pattern
- A final pattern is revealed through post-baking and hard-baking before the photo resistant material is dissolved
If you want to use photolithography at a smaller scale, you can use immersion lithography to create a smaller technological product. This is where purified water, at 1.44 of a refraction index, is pushed into the spaces in the wafer, essentially becoming a lens. From here, semiconductors can be created that are sized at under 40 nanometers:
To create a more intrinsic pattern, multiple patterning can also be used to divide a circuit pattern and create a density that is low enough to be printed into the system. Both of these types of lithography can be used in conjunction with semiconductor manufacturing.
Are you ready to use photolithography in semiconductor manufacturing?
Photolithography offers a fantastic opportunity to create incredibly complicated circuit patterns on a semiconductor. Not only does this make them more precise when they are optically transferred, but the etching process allows for perfect alignment on the wafer even when they are mass-produced.
Now that technologies are becoming more advanced, and there is a greater need for miniaturization and multiple patterning to create advanced systems, you should consider incorporating photolithography into your semiconductor manufacturing.