All SF-100 systems provide users with the ability to manipulate materials using light. The mercury arc lamp provides optical energy at g-line (435nm), h-line (405nm), and i-line (365nm) wavelengths, which are projected onto substrate materials in user designed patterns using the SF-100 XPRESS's patented technology. The most common application of SF-100 systems is to transfer micro patterns onto a substrate. This pattern transfer technique is called Photolithography. Standard photolithography process steps are detailed below.
Step 1 : Photoresist Coating
A substrate, an object onto which the image is transferred or projected, is coated with photoresist, a liquid polymeric material. The photoresist is the material that the image will be transferred to during the photolithography process. The coating process is typically performed by spinning the substrates at speeds between 1000 and 5000 rpm. Photoresist is deposited onto the substrate surface during this dynamic movement to ensure even coating over the entire substrate surface. Another alternative is to employ dry film photoresists which can be laminated into place to create the photopatternable surface.
A substrate coated with photoresist
Step 2: Exposure
Once the substrate has been coated with photoresist, the substrate is then exposed on an exposure tool. This is the process step that the SF-100 performs. In standard processes, the system shines light through a glass plate which is partially coated with chrome. This plate, termed a photomask or mask, has the master image of the device on it. By shining light through it and onto the substrate, individual areas of the photoresist are selectively exposed to light. This exposure causes a chemical change in the photoresist. The SF-100 is able to perform this process step without the need for a photomask, providing the user many financial and technical benefits over conventional technieques. After exposure, the photoresist that was exposed to light changes chemically on the substrate.
The photoresist coated substrate after exposure
Step 3: Development
Once exposed, the substrate is then immersed in a developer solution. Developer solutions are typically aqueous and will dissolve away areas of the photoresist that were exposed to light. Therefore, after successful development, the photoresist is patterned with the master image that was provided by the user.
After development, the resist pattern is observed on the substrate
Step 4: Hardbake
After development, the substrate is baked in an oven or hot plate at temperatures between 100-120C. This is needed to drive off liquids that may have been absorbed on the substrate and to crosslink the remaining photoresist. Crosslinking the polymer increases mechanical and chemical stability of the material, allowing it to be used in further substrate processing.
After hardbaking the patterned substrate is chemically stable and ready for future processing