Influence of Fabrication Process Parameters and Material Properties on Process Yield Performance on RF and Microwave Thin Film based Termination Resistors

Abstract

Ever-rising pressure of improving frequency domain performance of RF and Microwave components to improve the signal integrity as well as to reduce component package size consistently challenge design engineers not only with signal integrity and size constraints, but also the power integrity and thermal constraints concurrently. To achieve excellent signal and power integrity performance for microwave frequency application, components need to have superior voltage standing wave ratio (VSWR) characteristics as well as outstanding power handling capability. Addition to the brilliant component performance, manufacturers need to achieve excellent fabrication yield performance to keep the project viable. Process engineers face many challenges on each fabrication steps, which could significantly degrade the fabrication yield. Few challenges could originate from material sets, while others could arise from the process variations. In this work, we extensively studied the influence of many different parameters that considerably diminish the fabrication yield performance. We analyzed different parameters to design RF and Microwave termination resistors using thin film materials. One of the essential parameters, which significantly reduce the fabrication yield, is the inconsistency of surface roughness throughout the wafer. We studied the variations of the thin film materials microstructure and the sensitivity of film resistivity in response to surface roughness inconsistency. We experimented anneal drift of the material and effects of the temperature compensation of resistor (TCR) due to substrate surface roughness and existence of powder contamination on the surface. We compared Lapped and As-Fired substrates roughness and researched the inconsistence roughness effects on the thin film material. We studied the deposition rate of sputtered copper over the life of the target, from machine to machine and across the pallet, and analyzed the effects on the thin film material component. We studied the moisture related long time drift based on electro migration effect and the temperature dependence drift based on the materials sheet resistance. We analyzed the alteration of current density due to thin film resistor trimming and yield loss due to resistor value tolerance and trim variation by studying the sensitivity of the resistor area variation through trimming process. By analyzing different fabrication factors and material parameter properties, we realized the fact that most sensitive parameter that degrades the process yield is the existence of inconsistent surface roughness throughout the substrate. Based on the research study, we developed high power RF and Microwave 50 ohm termination resistors with excellent fabrication process yield performance.