May 31st, 2022
Dry etching is an essential nanofabrication technique in the modern-day manufacturing of miniaturized semiconductor devices. The semiconductors undergo physical bombardment by argon ions in dry-etch chambers for selectively removing masked patterns of semiconductor materials. The atmosphere in dry-etch chambers is highly corrosive and involves halogen-containing gases such as fluorine and chlorine that get broken down by plasma into chemically reactive radicals. The process gases and the removed material pose a potential risk of deposition onto the chamber components such as walls, liners, and process kits.
To meet these challenges, the etch chambers require internal wear and corrosion-resistant coatings to protect them from the corrosive gases that could otherwise prove detrimental to plasma chamber components and their performance. On the other hand, the particle dropout from chamber walls due to ion bombardment also risks contaminating the etched wafer, causing undesirable process drift.
High purity (over 99.9% purity) and homogeneous yttria (short for yttrium oxide, Y2O3) powder is an ideal ceramic coating material for the corrosive environments inside a dry-etch chamber. The coating formed will be both dense and pure which leads to excellent dimensional and chemical stability. Dimensional stability ensures that the physical properties of the coating, such as surface hardness, do not degrade due to repetitive ion bombardment over time.
Impurities in the dry-etch chamber form volatile fluorides that have low boiling points. What makes high purity yttria an unquestionable choice for dry-etch chamber applications is the high boiling point (2230 oC) of YF3, a fluoride compound it forms, compared to other typical fluorides like AlF3 (1297 oC) and ZrF4 (956 °C). The high operating temperatures in chambers result in vapor formation and premature failure of coatings due to the desorption of fluoride particles by ions. Both vapors and spalled coatings contaminate the surface of etched wafers during dry etching. Yttria, being over 99.9% pure with minuscule impurity levels and forming YF3 with a high boiling point, addresses both of these issues simultaneously. Moreover, yttria-based coatings have high sintering resistance and can thus bear thermal cycling that is inevitable inside dry-etch chambers.
The yttria particles possess spherical agglomerate morphology with a typical nominal particle size of 20-53 microns. The strict particle size control ensures complete melting, thus resulting in reduced porosity, smooth surface finish, and optimal deposit efficiency and coating performance. The spherical morphology of these powders results in improved flowability that leads to a more consistent coating process. All these factors significantly add to the overall corrosion and erosion resistance of coatings. A reduced number of pores in the coating layer increases the cohesion strength between atoms, making it difficult for the contamination particles to detach. A smoother surface finish also reduces the effective surface area available for chemical reactions.
Saint-Gobain is committed to continuously developing state-of-the-art industry-leading thermal spray powders to expand our outreach in the semiconductor space. High purity materials possess superior dielectric properties and are sought after as they provide enhanced electrical insulation. Our high purity yttria and alumina-based thermal spray powders are perfectly suited for such applications that require strong dielectric coatings and high resistance against corrosion and erosion. For example, alumina possesses a low dielectric constant, making it a promising material for insulation coatings for high-temperature applications like fusion reactors and bearing components.
Our coating solutions are not only limited to dry-etch chambers. Saint-Gobain also offers cost-effective high purity thermal spray powders to serve other applications in the electronics industry, e.g., coating for electrostatic chucks used in the processing of semiconductor wafers. These powders are based on alumina (Al2O3) and yttria-alumina mixtures (YAG - Yttria-Aluminum-Garnet) and are more cost-effective than yttria. The alumina powders also possesses a spherical morphology and there are a number of different particle size options that can be tailored to the specific application.
Both alumina and YAG do not perform as well as yttria under fluorine-based plasma environments. The fluorine-based radicals react with Al2O3, affecting Al-O bonds. However, the low cost and high mechanical strength of alumina powder make it a good alternative for several ceramic components of high-density plasma chambers. The YAG powder is a purposefully designed, cost-effective hybrid solution that combines the mechanical properties of alumina and the chemical properties of yttria.
Other high-quality thermal spray powders Saint Gobain offers include:
Due to our stringent process control, Saint-Gobain Thermal Spray Powders have minimal impurities and come in custom particle sizes to suit our customer’s tailored needs. Get in touch with our team to learn more about the thermal spray powders we offer.