Hi Rishika,
If you are using Process Framework which uses utilities guided processes to create contract.
In this case you can remove the switch group assignment from process configuration which will stop the switch document creation.
If you are using custom program to create contracts then have a look at the class: CL_CRM_ISU_SWTMSG_API -> CREATE_NEW_SWTMSG_BY_ITEM & CREATE_NEW_SWTMSG_BY_KEY. These methods gets called when system tries to create switch in ISU from CRM side.
Also the BADI: CRM_ISU_IL_SWTMSG will help you to meet your requirement.
I did this in one of my previous projects but don't remember the exact change.
Regards,
Naresh