*2.4.2 Spin coating and lithography for wafer-level deposition*

Spin coating is a common technique widely used in microelectronic industry for applying resins in thin film form to silicon wafers. Its primary advantage over other methods is its ability to quickly and easily produce very uniform films.

*Polyimide in Electronics: Applications and Processability Overview DOI: http://dx.doi.org/10.5772/intechopen.92629*


### **Table 2.**

*Main radicals for diamines (*reproduced from *[8]).*

**Figure 5.**

*Industrial scale polyimide film stretching manufacturing from PAA precursors (*reproduced and modified from *[9]).*

When the solution of PAA containing NMP solvent is spun at high speeds, the centrifugal force enables to cover the substrate (see **Figure 6**). Spin coating results in a PAA thin film ranging from a few microns to a few tens of microns in thickness depending on coating parameters. The thickness of the final film is determined by the spinning speed, surface tension, and viscosity of the solution. The solvent is removed partly during the spinning process due to evaporation and partly by subsequent baking at elevated temperatures during imidization.

Many experiments have confirmed a mathematical model for photoresist deposition where the thickness variation versus the spin speed is like ω�0.5 [11]. In the

### **Figure 6.**

*(a) Industrial polyimide spin-coating process on 8*00*-wafer scale from PAA precursor solution. (b) Polyimide thickness as a function of spin speed and time* (reproduced from *[11]).*
