  Factorization theorems play a crucial role in our understanding of the strong
interaction. For collider processes they are typically formulated at leading
power and much less is known about power corrections in the $\lambda\ll 1$
expansion. Here we present a complete basis of power suppressed operators for a
scalar quark current at $\mathcal{O}(\lambda^2)$ in the amplitude level power
expansion in the Soft Collinear Effective Theory, demonstrating that helicity
selection rules significantly simplify the construction. This basis applies for
the production of any color singlet scalar in $q\bar{q}$ annihilation (such as
$b \bar b \to H$). We also classify all operators which contribute to the cross
section at $\mathcal{O}(\lambda^2)$ and perform matching calculations to
determine their tree level Wilson coefficients. These results can be exploited
to study power corrections in both resummed and fixed order perturbation
theory, and for analyzing the factorization properties of gauge theory
amplitudes and cross sections at subleading power.
