Nitrogen or Silicon which element forms only covalent compounds?why

Nitrogen is a non metal. It forms covalent bonds in molecules like NH₃ and also forms ionic bonds with highly electropositive metal that is lithium, Li₃N. While ​silicon is a metalloid. The electronegativity difference between silicon and non-metals such as chlorine is not very high. Because of this, silicon generally forms covalent compounds. 
Thus silicon will have a higher tendency to form covalent compounds than nitrogen.