Photolithography and nanolithography:

Also known as 'optical lithography'. Photolithography is a process used in micro fabrication which is the removal of thin films selectively (or the bulk of a substrate). Utilizing a light to transfer a geometric pattern from a photo mask to a light-sensitive chemical on the substrate. Moreover is a process by which patterns on a semiconductor material can be defined using light. A series of chemical treatments then engraves the exposure pattern into the material underneath the photo resist. In a complex integrated circuit, a wafer will go through the photolithographic cycle up to 50 times.

However a group of scientists at the National Institute of Standards and Technology (NIST) have made the first direct measurements of the infinitesimal expansion and collapse of thin polymer films used in the manufacture of advanced semiconductor devices. It ís a matter of only a couple of nanometers, but it can be enough to impact the worldwide chip manufacturing in the forthcoming years and could affect the development of new technology in this area. Also these NIST measurements, revealed in a detailed paper that it offers a new insight into the complex chemistry that enables mass production of very powerful integrated circuits.

These circuits are named 'transistor gates' and are the smallest critical features found in the most advanced memory or processor chips. Gate length is near to 45 nanometers, and the industry is aiming for 32-nanometer gates. To develop modern microprocessors, manufacturers use 'photolithography', the highest technology in the nano-scale dimension of printing technology. The semiconductor wafer is coated with a thin film of photo resist, a polymer-based formulation, and exposed with a desired pattern using masks and short wavelength light (193 nm). The light changes the solubility of the exposed portions of the resist, and a developer fluid is used to wash the resist away, leaving the pattern which is used for further processing.

Photolithography utilizes the machine to do all this and is called a 'stepper'. Basically this technology was created to reproduce engraving and photographs and then make printing plates. Since 1960's, Photolithography has been a perfect way to produce massively integrated circuits and computer chips. The exposure systems normally produce an image on the wafer using a photo mask. The light shines through the photo mask, which blocks it in some parts and lets it pass in others. Maskless lithography projects a precise beam directly onto the wafer without using a mask, but it is not commonly used in commercial processes. Exposure systems may be classified by the optics that transfers the image from the mask to the wafer. In the case of Nanolithography we are talking almost about the same.
The differences are that the aforementioned is lithography at the nanometer scale and refers the developing of structures in the nano scale, that is patterns with at least one lateral dimension between the size of an individual atom and approximately 100 nm. This technology is commonly used during the fabrication of leading-edge semiconductor integrated circuits. Now Nanolithography is a very active technology for the research realm in the academic and industrial areas.

Nanolithography techniques:

There are many techniques and uses for Nanolithography. For instance we have the 'X-ray lithography' which can be extended to an optical resolution of 15nm through the use of a short wavelength of 1 nm for the illumination and it's implementation is based on the proximity printing approach. Other techniques of Nanolithography include the 'Fresnel diffraction' that is a clear mask feature that is "demagnetized" by proximity to a wafer that is set near to a "Critical Condition". This Condition determines the mask-to-wafer Gap and depends on both the size of the clear mask feature and on the wavelength. This method is simple because it requires no lenses.

Future Uses of Nanolithography:

The future use of Nanolithography is attached to the current uses and the techniques applied with this technology. The utilization of self-assembled nanolayers in nanosphere lithography will be one of the most important bottom-up methods. The complexity of these methods and techniques is increasing constantly which is why the capacity to operate them, the knowledge and research need to be updated too. Also the study of nanotechnology applications in this field is an area scientists are giving ongoing considerations for further investigations.

Author: HÈctor Nicol·s Suero
Nanovip Staff Writer