Three-dimensional memory device containing a vertical semiconductor channel containing a connection strap and method of making the same

An alternating stack of insulating layers and sacrificial material layers is formed over a substrate. A memory opening is formed through the alternating stack. A memory film is formed in the memory opening. The memory film includes an opening at a bottom portion. A connection strap is formed by performing a selective semiconductor deposition process that grows a strap semiconductor material from a physically exposed surface of an underlying semiconductor material portion through the opening. A vertical semiconductor channel is formed on an inner sidewall of the memory film by non-selectively depositing a semiconductor channel material. The connection strap provides an electrical connection between the underlying semiconductor material portion and the vertical semiconductor channel through the opening in the memory film. The sacrificial material layers are then replaced with electrically conductive layers.