Lithography

Lithography is the gating function in the development of new CMOS manufacturing processes. While all semiconductor manufacturers are dependent on the same available lithography tools, the ways of using those tools vary depending on the expertise and requirements of the manufacturer.

At Texas Instruments, we have a long history of innovation in lithography. Our expertise allows us to develop leading-edge processes with the right balance of performance, cost and power consumption for our customers.

As the critical dimensions of transistors get smaller, it becomes increasingly difficult to focus light on the areas of the chip where the photoresist must be exposed. Today's argon-fluorine (ArFl) lithography tools, which provide light at a wavelength of 193 nm, are used to pattern critical dimensions as small as 37 nm—five times smaller than the light wave that forms it.

Obviously, we have to maintain tight control of these critical dimensions so that the transistors formed are consistent in their scaling. Embedded phase shifting within the reticule enables us to focus light at sub-wavelength dimensions. Models built using our experience with the process allow us to employ optical proximity correction (OPC) to ensure that the effect of exposure is uniform across the wafer. We are also developing reticule enhancements, such as sub-resolution assist features for stricter process margins, as we enter volume production.

These types of improvements drive up the cost of making reticules. As a result, it is no longer economical to make numerous versions in developing the right set of reticules for a new product. Instead, we are learning to build the complexities required of deep-submicron lithography into the reticule from the very beginning. This process keeps time and expense to a minimum.

With an eye to the future, we anticipate the availability of the next generation of 193 nm immersion lithography tools. These tools place a thin layer of liquid between the lens and the wafer to increase the refractive index of the lithography tool, making even smaller transistor feature sizes possible. TI believes 193nm immersion can carry the industry through the 45nm and 32nm nodes. Beyond 32 nm, 157 nm immersion or extreme ultraviolet (EUV) are being explored. Electron beam projection printing is also likely to become important as the alternative technology matures. For Texas Instruments’ R&D, the key issue with these tools, as with other fundamental process developments, is how we can use them to build products with the right mix of performance, low cost and power efficiency for our customers.