Etch Process Input and Output Parameters

1. Etch Process Input and Output Parameters

2. Inputs Process Outputs Control parameter1 Quality parameter1 Process Model Control parameter2 Quality parameter2 Control parameter3 Process Modeling • how to use input parameters to achieve desired output parameters Relation between inputs and outputs

3. Input Parameters • Pressure • RF power • Gas Flow Rates • Temperature • Gap distance

4. Output Parameters • Etch rate • Uniformity • Vertical profile • Selectivity

5. Etch Rate • How fast the film material is etched per minute. • Unit: nm/min

6. Uniformity Center vs. Edge • Etch rate is not the same everywhere. • Desire uniformity, all features finish etching at the same time, else some will be under-retched while others are already over-etcher. • Center to edge difference: caused by electric field strength difference, gas flow rate difference. • Etcher rate sampled at sites across the wafer. Stand deviation is used to measure variation. The larger the variation the worse the uniformity.

7. Uniformity small vs. large features • Small feature vs. large feature difference; a deep and narrow feature can be difficult to etch—slower than wider features.

8. Vertical Profile • Isotropic vs. anisotropic: isotropic means same etch rate in all directions. • higher density circuits make deep and narrow features desirable. Anisotropic Isotropic

9. Selectivity • Selectivity: etching only the target material not others. For example, if my etch rate for SiO2 is much larger than SiN4, then it will only etch the SiO2 film not the layer underneath. SiO2 Si3N4—etch stop layer