${\mathrm{SiO}}_2$ is a solid while ${\mathrm{CO}}_2$ is a gas, this is because

Solid ${\mathrm{SiO}}_2$ has a three dimensional net work structure whereas ${\mathrm{CO}}_2$ contains discrete molecules.

${\mathrm{SiO}}_2$ contains weak vander Waal attraction while ${\mathrm{CO}}_2$ contains strong covalent bonds

Both contain strong covalent bonds

Both contain weak vander Waal attraction