Fluid viscosity control during wafer bonding

A system for bonding wafers, the system comprising:

• a first wafer holder to hold a first wafer having a first surface;
• a second wafer holder to hold a second wafer having a second surface, wherein the second surface is to be held at a distance from the first surface wherein the distance is to be in a range of 30 microns and 150 microns;
• a wafer deformer to deform a portion of the first wafer to contact the second wafer;
• a chamber housing both the first wafer holder and the second wafer holder and having a fluid inlet port therein;
• a valve fluidly coupled to the fluid inlet port;
• and
• a controller controllably coupled to the valve and the wafer deformer, the controller to provide a first signal to the valve to supply a fluid between the first surface and the second surface, wherein the fluid has a viscosity greater than a viscosity of air at standard ambient temperature and pressure, and to provide a second signal to the wafer deformer to deform the first wafer;
• wherein the wafer deformer comprises a first heating element, wherein the controller is controllably coupled to the first heating element, and the controller is to provide a third signal to the first heating element to heat the fluid.