SiC etching is an integral component of power devices and microsystems fabrication. Achieve a high etch rate without degrading surface quality can be challenging due to silicon carbide’s hardness and chemical stability, however.
Process parameters have an immense effect on surface morphology, sidewall inclination angle of MESA structures and trench structures, as well as on microtrenches after etching.
Chemical Etching
Chemical etching involves bathing a metal sheet in chemicals to strip away part of its surface. A variety of factors affect the rate and efficiency of chemical etching processes, including concentration, temperature and agitation – accurate control over these variables ensures high-quality and precise results.
Before etching metal sheets, they must first be thoroughly cleaned using acetone, ethyl alcohol and deionized water in ultrasonic baths – this sets the stage for the complex chemical reactions necessary to alter their structures. Next comes an application of photoresist that captures any desired patterns or designs before being exposed to ultraviolet (UV) light using a special mask as part of this intricate process.
UV light-induced chemistry induces dramatic transformations in materials. Chemical reactions etch away metal sheets beneath photoresist, revealing intricate designs etched onto its surface. Together, art and science come together in this exquisite display that shapes materials’ paths toward becoming meticulously designed final products.
Experiments were performed using 6H-SiC substrates covered with 1 um thick chromium masks with windows of different geometries and linear sizes, measuring root mean square roughness with an atomic force microscope at five locations for each sample. As pressure increased from 8 to 30 millitorr, etching rates steadily declined due to decreased fluxes of reactive fluorine ions reaching the SiC surface.
Plasma Etching
Plasma etching is an indispensable tool for producing precise and high-resolution features on different substrate materials. The choice and mixture of gas (etchant) in the plasma determines its rate, selectivity and profile as an etched surface; its ions may either physically sputter away atoms from substrate surfaces or provide energy that drives chemical reactions on them.
Different combinations of gases and plasma parameters have been investigated to achieve optimal plasma etching results. Particularly, using SF6 + O2 plasma has proven highly successful for almost vertical etch profiles with heights up to 87deg; on the other hand BCl3 plasma produces structures which may not be as deep and feature an inclination angle of 40deg [23].
Another key parameter in plasma generation is RF power: higher power facilitates faster removal of volatile reaction products from the surface of etching areas and improved selectivity, while temperature of substrate holders also plays a part; as substrate surface temperatures increase, so too does etching rate and selectivity; however, this effect is limited by certain values of DC bias voltage; beyond which chemical reactions take over control over etching rates as their concentration relates to silicon-carbon interactions.
Chemical Vapor Deposition (CVD) Etching
In this process, a high-temperature CVD reactor is utilized to form a silicon carbide film on the surface of a base material. Silane or chlorosilane precursors typically serve as reactants in this reaction process.
MTS (methyltrichlorosilane) serves as a precursor for making silicon carbide films, and requires both silicon and carbon to create its crystalline form, along with chlorine for chlorination purposes to facilitate formation of this film. A hydrogen carrier gas must also be provided in order to break down MTS into intermediate species that contain both silicon and chlorine before reacting with silicon in a surface reaction and producing new silicon carbide layers.
CVD silicon carbide coatings are durable, high-performance thin film surfaces designed to be applied over a range of substrates. Ideal for coating precision surfaces that demand high adhesion such as those found on high resolution computers or precision machines. You can apply them on ceramics, glass, metals and alloys including threaded areas or intricate surfaces such as seals.
CVD silicon carbide is widely used in semiconductor industry applications such as focus rings for plasma etching equipment. Due to its low chemical and electrical reactivity as well as superior thermal and electrical properties, CVD silicon carbide makes for an excellent material choice in such applications. Furthermore, CVD silicon carbide’s uniform heating can improve processing chamber temperatures while helping minimize waste created during an etching process – saving both chemicals and waste resources during this process.
Physical Etching
Physical etching involves the removal of material from silicon carbide (SiC) surfaces through chemical reactions and physical sputtering, producing vertical sidewall features which are easier to align during subsequent processing steps or final device applications. Etching can be controlled in several ways including substrate biasing, gas pulsing and endpoint detection while the choice of etch gas affects its profile, slant angle and surface morphology characteristics.
An ICP-RIE system can be used to physically etch SiC. As its target material, this typically takes the form of a hard mask with various geometries and line widths patterned into it. A plasma containing reactive species is then used to chemically etch SiC before its ions accelerate towards substrate to physically remove material via chemical reaction as well as physical sputtering processes; then finally the mask is removed before repeating this cycle.
As part of the etch process, nonvolatile chemical compounds may deposit on the surface being etched. When combined with scratches on the substrate surface, these contaminants often lead to what’s known as “micro-mask effect”, compromising the quality of resulting structures and potentially hindering performance.
To evaluate the influence of temperature on SiC etching behavior, several control experiments were carried out. 6H-SiC wafers were mounted onto chromium masks featuring windows of different geometry and line width, and measurements taken with both a scanning electron microscope (ZISS AURIGA 60) and contact stylus profilometry system (“Dektak 150 Surface Profiler”, Veeco Instrument.
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