best way i thickened my back up is with the following:
Deadlift/Rack Pulls
T bar Row/Yates Row
and also Some Rows On Hammer machines.

I always focus on one row always being underhand to get a better stretch and help build lower lats.

ill show u my routine for 2 weeks
Week 1:
Pulldowns 3 sets
T bar row 3 sets
Underhand Yate Rows 3 sets
Deadlifts 4 sets

Week 2:
Weighted Pull ups 3 sets
Bent Over Rows 3 sets
V Bar Pull Downs 3 sets
Hammer Machine Rows 3 sets (Underhand)

I dont like hitting deadlifts every week due to the fact deadlifts i go over 250kg and i wanna make sure i have 110% healed. Also make sure you have mind and muscle connected because alot of people pull with there arms and not with there back or lats. and one more main thing to consider is the negative. stretching it back down is very important.. watch one of dorian yates seminars you will learn a few things on there