In Richard III, Act I, scene 3, lines 245-246 Queen Margaret tells Elizabeth that:
The day will come that thou shalt wish for me
To help thee curse this poisonous bunch-back'd toad.
and indeed, in In Act IV, Scene IV, lines 79-81 Queen Elizabeth does so curse Richard:
O, thou didst prophesy the time would come
That I should wish for thee to help me curse
That bottled spider, that foul bunch-back'd toad!
according to Wikipedia, in the second Quarto, the last line read "hunch-back'd", but it is retained as above in the texts I've found.
Also, in Henry VI, part 3, act III, scene 2, lines 1648-1650, Richard (here still called Gloucester), laments his looks:
To shrink mine arm up like a wither'd shrub;
To make an envious mountain on my back,
Where sits deformity to mock my body;
So it is pretty clear Shakespeare thought of him as a hunchback.