Method of producing bonded wafer and bonded wafer

1. A method of producing a bonded wafer by bonding a support substrate wafer and an active layer wafer with an insulating film therebetween, comprising:

a polycrystalline silicon deposition step of depositing a polycrystalline silicon layer on the support substrate wafer on the bonding surface side;

a polycrystalline silicon layer polishing step of polishing a surface of the polycrystalline silicon layer using a polishing cloth:

an insulating film formation step of forming the insulating film on at least one of a bonding surface of the support substrate wafer and a bonding surface of the active layer wafer; and

a bonding step of bonding the polished surface of the polycrystalline silicon layer of the support substrate wafer and the active layer wafer with the insulating film therebetween,

wherein when an amount of depression of the polishing cloth is defined as:

Amount of depression (μm)=Thickness of polishing cloth (μm)×Compression ratio (%/(N/cm 2 ))×Load (N/cm 2 ),

the amount of depression of the polishing cloth is 50 μm to 90 μm, and a surface hardness (ASKER C) of the polishing cloth is 50 to 60.

2. The method of producing a bonded wafer, according to claim 1 , wherein the polishing cloth is a suede pad composed of a base and a nap layer.

3. The method of producing a bonded wafer, according to claim 2 , wherein the thickness of the base is 0.15 mm to 0.20 mm.

4. A bonded wafer comprising a polycrystalline silicon layer deposited on a support substrate wafer,

wherein the polycrystalline silicon layer has a thickness variation Δt of 5% or less, and

the support substrate wafer has a GBIR of 0.2 μm or less and an SFQR of 0.06 μm or less after the polycrystalline silicon layer is polished.