Roughness and Electrical Resistivity of Thin Films Spencer Twining, Marion Titze, Ozgur Yavuzcetin University of Wisconsin – Whitewater, Department of Physics Introduction Thin films are used in many industrial applications including semiconductor technology, optical coatings and sensors. In this project, we created metallic thin films at thicknesses of 200 nanometers (nm) which is a critical thickness for most sensor and semiconductor applications. We then investigated the physical properties (electrical and topographical) to find the optimum application parameters. Conclusion Because of the sensitivity and delicateness of these thin films, the thickness measurements varied drastically. The QCM measured the thicknesses between 160 and 280 nm, while the ranges of the profilometers ranged from 200 to 350 nm. On the other end of the spectrum, the 4-Wire and 2-Wire thicknesses ranged from 6 to 170 nm and from 95 to 130 nm, respectively. Interestingly, the metals with the strongest deviations in measured and calculated thicknesses, tin, aluminum, and silver, are also the three roughest metals, in that order, while copper and nickel, being naturally smoother and having almost negligible roughness, have much more consistent thickness data in comparison. In conclusion, not only does the extreme thinness of these metals affect its physical properties, but also the roughness. The next step in this research is to qualitatively measure the effects of topology on the physical properties of the films. Sheet Resistance: 4-Wire When measuring resistance, one problem that arises is the contact resistance. To remedy this, the 4-Wire measurement technique was used on our test slides. In this process, four probes connected to a source meter made contact with the metallic surface; the outside probes sent current through the metal, while the two inside probes measured voltage. This minimized the effect of the contact resistances, leading to more accurate readings. Resistance was calculated using Ohm’s law, V=IR. Using this resistance, and solving the above equation for t, thickness was calculated based off of the electrical resistance and metallic resistivity ρ. Sheet Resistance: 2-Wire Another technique for measuring accurate resistance is the 2-Wire method. This was done by etching a thin strip into the glass slides and measuring the resistance at 1.00 cm steps with two source meter probes. To minimize the contact resistances, the points were plotted and a line fit was generated. The slope, m, of the line found was put into the above equation, and the following thickness data was found: Profilometer Another thickness measurement was done via profilometer using a micro-needle stylus. Two Tencor profilometers were used: one in Istanbul University, Turkey, and one on the UW-Madison campus. Each profilometer dragged a sensitive stylus across the glass slide, making contact with both the metal film and the exposed glass. From this, we calculated the approximate thicknesses of each metal coating: Acknowledgements 1.Undergraduate Research Program (URP) Grant. 2.UW-W Physics Department 3.iButtonLink LLC, Rob Olson and Dave Hickey Evaporation Thermal evaporation (or physical vapor deposition) technique consisted of heating metals under a vacuum chamber. The target silicon wafers were placed on the stage with a resistor pattern mask, along with a glass slide that was used for testing. The stage was inverted and suspended from the top of the bell. The bell was lowered and the pressure on the inside was reduced to 9x10 -6 Torr. Then, high current was run through the metal, causing the temperature of the metal to increase dramatically. Because of the low pressure and high temperature, the metals evaporated and settled onto the silicon wafers and glass slides. Five source metals were deposited onto five different wafers. The metals used were silver, copper, nickel, aluminum, and tin. The thickness of deposition is measured internally by a quartz crystal monitor (QCM). New corrosion sensor made by iButtonLink that utilizes the thin films from this research The photos to the right show the thermal evaporator used for the depositions in this research. Located at UW- Whitewater in the physics department Data table of 4-wire thickness measurements obtained from the apparatus built for the research Roughness Measurements Samples were scanned and analyzed using the atomic force microscope(AFM) with the ScanAsyst® mode. Measurements of the roughness were determined by using two factors from the NanoScope Analysis software. The first was the maximum vertical distance between the highest and lowest data points, or R max. The second was the root mean square average of height deviations, or R q. This graph shows R max and R q for each metal. The value of R max for tin was several orders of magnitude higher than that of the other metals. Data table of 2-wire thickness measurements obtained from using a source meter on deposited glass slides To the left is a picture of Silver, to the right is a picture of Tin, both taken by the AFM at 5 microns scan windows. The difference in surface roughness is striking.