UV lithography (UVL) is a pattern transferring technique in which a pattern of micron to sub-micron resolution is defined in a photoresist. When a photoresist is exposed to light of a specific wavelength it undergoes a change in solubility with respect to a specific chemical solution called the developer.
For UV lithography the wavelength is typically in the near ultraviolet regime of 300-400 nm. If the wavelength is lower than this, it is referred to as deep ultraviolet or even extreme ultraviolet lithography. If the photoresist becomes more soluble after exposure, it is called a positive resist. Likewise, if it becomes less soluble it will be called a negative resist. Photoresist is applied to a substrate by spin coating, this gives a uniform coating with a thickness that can be tuned by the spin speed during application.
Ultraviolet Lithography techniques
There are different techniques within UV lithography for the actual exposure of the pattern onto the photoresist. The most common technique uses a photomask to achieve selective exposure of the pattern. A UV photomask is made from a transparent material, typically fused silica, on which a pattern is defined in an absorbing thin film such as chromium. The photomask is brought into close proximity or even contact with the resist coated substrate using a dedicated exposure system. The substrate is then exposed through the photomask by a UV light source. The UV source consists of a lamp and a filter, such as a Hg-lamp with an i-line notch filter that gives a typical UV source with a wavelength of 365 nm. After exposure the substrate is developed and the pattern is formed.
Maskless Ultraviolet Lithography
Another technique is maskless UV lithography, in which an optical set up is used to direct UV light onto selective areas on the substrate. This replaces the need for a photomask by using a digital micromirror device, where thousands of micromirrors each corresponds to a pixel of the pattern being exposed. The micromirrors can individually be rotated to switch the pixels on and off to expose the desired pattern on the substrate.
The maskless UVL technique is good for rapid prototyping, but the throughput is lower than standard UVL using a photomask.
Both masked and maskless exposure techniques allow for alignment of the exposed pattern to structures on the substrate with a misalignment less than 0.5 µm.
UV lithography and what we can do
NIL Technology offer you both standard and maskless UVL services. Our mask aligners accept both 4” and 6” substrates, have both top and bottom alignment capability, use an exposure wavelength of 365nm, and have a resolution down to 1.5 µm.
We have access to a state of the art maskless aligner with sub-micron resolution, fast exposure and dual wavelength (375 nm or 405 nm) – ideal for rapid prototyping.