Modern IC processing utilizes a technique called oxygen precipitation to getter metallic contami- nants out of...

 

Transcribed Image Text:

Modern IC processing utilizes a technique called oxygen precipitation to getter metallic contami- nants out of a thin layer at the top surface of the wafer. It is in this so-called denuded zone, where the devices are fabricated. Typically, the denuded zone is thin and is characterized by a fairly long lifetime, while the rest of the wafer where oxygen precipitation has taken place exhibits much lower lifetimes. The denuded zone results in device reverse-bias leakage currents that are much reduced. The change in lifetime in the wafer presents an interesting problem for the computation of the current injected downward in a bulk p+-n diode, as sketched in the figure below. SOBOT RY X₁ << Ln1 -- X₂ >> Ln2 No solem toz enoitq i suntedisalo No p ranno YÜstend palub and Volote n Denuded zone TELO (2) mif dong() (5) Oxygen precipitated region DE40 ogerior a vigas ang a) soresb upala pdt datolaylaviatiluu Make the following assumptions. The doping level is the same in both regions of the n substrate. The junction depth of the p+ region and its associated depletion region are much thinner than x₁, the denuded zone thickness. x, is much shorter than the local diffusion length Lh1. The thickness of the oxygen precipitated region x₂ is much longer than the local diffusion length Ln2- (a) Sketch the shape of the excess hole concentration in the n region in forward bias. (b) Derive an expression for the hole current density injected into the n-type substrate in forward bias in terms of the hole diffusion length in the oxygen precipitated region, Lh2, the denuded zone thickness, x₁, and the usual parameters. Modern IC processing utilizes a technique called oxygen precipitation to getter metallic contami- nants out of a thin layer at the top surface of the wafer. It is in this so-called denuded zone, where the devices are fabricated. Typically, the denuded zone is thin and is characterized by a fairly long lifetime, while the rest of the wafer where oxygen precipitation has taken place exhibits much lower lifetimes. The denuded zone results in device reverse-bias leakage currents that are much reduced. The change in lifetime in the wafer presents an interesting problem for the computation of the current injected downward in a bulk p+-n diode, as sketched in the figure below. SOBOT RY X₁ << Ln1 -- X₂ >> Ln2 No solem toz enoitq i suntedisalo No p ranno YÜstend palub and Volote n Denuded zone TELO (2) mif dong() (5) Oxygen precipitated region DE40 ogerior a vigas ang a) soresb upala pdt datolaylaviatiluu Make the following assumptions. The doping level is the same in both regions of the n substrate. The junction depth of the p+ region and its associated depletion region are much thinner than x₁, the denuded zone thickness. x, is much shorter than the local diffusion length Lh1. The thickness of the oxygen precipitated region x₂ is much longer than the local diffusion length Ln2- (a) Sketch the shape of the excess hole concentration in the n region in forward bias. (b) Derive an expression for the hole current density injected into the n-type substrate in forward bias in terms of the hole diffusion length in the oxygen precipitated region, Lh2, the denuded zone thickness, x₁, and the usual parameters.