In an embodiment, the present invention discloses a stackable substrate carrier for scalably storing, transporting or processing multiple substrates. The present substrate carriers can be stacked side-by-side by an attaching mechanism, forming an integrated carrier with double, triple or multiple capacity. The attaching mechanism comprises a locking mechanism to secure the substrate carriers together, engaged by mating two substrate carriers, together with an additional rotating or translating action of the two substrate carriers. Alternatively, the locking mechanism can be engaged by pressing two substrate carriers against each other, using friction to keep the carriers together. Other locking mechanism can also be used, such as hooks or latches.