Mechanical Properties of Silicon Carbide Wafer Coatings

Single crystal silicon carbide (c-SiC) wafers are widely used in the production and manufacturing of microelectronic devices such as integrated circuits (IC) or photovoltaic (PV) cells. Most wafers are formed from highly pure single crystals and can range in size from 25.4 mm to 300 mm. The wafer acts as the substrate for the micro-devices that are fabricated in, and over, the wafer. Doping or ion implantation, photolithographic patterning, deposition of different materials, and etching are all examples of the many micro-fabrication process steps a wafer can go through.

The fabrication process for microelectronic devices can have over 300 different processing steps and can take anywhere from six to eight weeks. During this process, the wafer substrate must be able to withstand the extreme conditions of manufacturing, since a failure at any step would result in the loss of time and money. The hardness, adhesion/scratch resistance and COF/wear rate of the wafer must meet certain requirements in order to survive the conditions imposed during the manufacturing and application process to ensure a failure will not occur.

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Five indents were made per sample in order to calculate an average Vickers Hardness, Hardness (GPa) and Young’s Modulus. The load vs depth curves that each indent made were analysed in order to assure appropriate initial point of contact and unloading curve slope. The data below clearly shows a higher average hardness for the Control coating versus the Au Alloy Coating and a higher Young’s Modulus for the Au alloy coating than the Control coating.

The NANOVEA Mechanical Tester’s Micro module demonstrates reproducibility and precise indentation at low levels. The controlled and closely monitored environment allows the measurement of hardness to be used as a quantitative value for comparing a variety of samples. This test also shows that it can measure other characteristics, such as Young’s modulus and maximum depth. Here we have shown the ability to control the specific load being applied to test the thin coatings on top of silicon carbide wafers.

The cohesive failure (A) and adhesive failure (B) of the coatings are reported as the load at which these phenomena occur. The data shows that the Au alloy coating has a higher cohesive and adhesive strength than the control coating. Three scratches were performed for each sample and a graph containing the load, depth and frictional force are shown as well as a full-length image for one of the scratches to visually show the failures.

It is important to mention that the repeatability of the scratches can vary due to the uniformity of the coating and substrate.

The NANOVEA Mechanical Tester’s ability to apply a wide range of loads allows the user to produce repeatable low to high load scratches on a material. This ability is valuable for the wafer industry because manufacturers of these wafers can see at which loads the coating will fail.

The following data sets represent the tribology study and tests performed on the Au and Control coating with the NANOVEA Mechanical Tester. Linear reciprocating scratch tests were performed on both coatings with the same testing parameters in order to compare the COF and wear rate of each. The wear rate for Au alloy coating was greater than the wear rate for the control coating. However, the average COF was the same for both coatings. The wear rate was calculated by scanning the post worn area with the NANOVEA 3D profilometer and calculating the volume loss.

The NANOVEA Mechanical Tester’s micro module is able to not only apply progressive loads but constant loads as well in order to perform tribological studies on thin wafer coatings. By using the same testing parameters, the user is able to compare various materials in order to see how they will perform. The sensitivity that the instrument has allows us to see even the smallest COF values and wear rates.

In conclusion, it was shown that the NANOVEA Mechanical Tester’s micro module with its unmatchable load range (0.003 to 20N and 0.03 to 200N) can fully test coatings using nanoindentation to micro scratch and wear levels. Many other tests could be performed such as controlled fracture toughness and yield strength measurements among many others all on a single system.