the amount of back lash is controlled by cutting the worm gear to the master worm. and in addition the pattern is verified.
specify on the print the amount of backlash required. just remember that to little backlash and the combination can bind up.
so if this is low RPM then it is possible for tighter backlash requirements.also the gear set will require tighter dimensional geometric tolerance. and must be cut as a set.

Mfgenggear

Okay but is backlash affected by number of starts?

no it does not, it adjusted as it is cut. is it for high speed(RPM)? if so there it is give and take.
what is the application, being it requires multiple start will require more backlash. because if it's function.
but like I said it is controlled while it is cut. and required tighter AGMA class.

Mfgenggear

Thanks Mfgengear,
I am looking for a robotic application with speed of worm being in the range of 10,000 rpm and worm gear in range of 200-400 rpm.

Backlash in a worm/gear system can be affected by the number of starts of the worm.
As the number of starts increases, the quality level also needs to increase. This is because if there are any errors in the indexing/spacing/lead variations between each start, that'll quickly take-up any backlash in the system.
Generally it is wise to increase the backlash tolerance as the number of starts increase.