Shield gate trench MOSFET manufacturing method

Abstract

The invention discloses a shield gate trench MOSFET manufacturing method. Gate structure forming comprises steps: a hard mask layer is formed, and a gate forming area is defined; a semiconductor substrate is etched to form a deep trench; thermal oxidation is carried out to form a bottom oxidation layer; source polysilicon is formed; back etching of the polysilicon is carried out, and thus, the source polysilicon is flush with the top surface of the hard mask layer, a source polysilicon lateral extension part is formed outside the opening of the bottom oxidation layer and the top part of the bottom oxidation layer inside the opening of the hard mask layer; the hard mask layer is removed to form a top convex structure of the source polysilicon; the source polysilicon lateral extension part serves as a self-alignment mask to etch the bottom oxidation layer to form top trenches and inter-polysilicon isolation oxidation layers at two side surfaces of the source polysilicon; a gate dielectric layer is formed on the side surface of the top trench; and the top trench is filled to form a polysilicon gate, and chemical mechanical polishing is carried out. Thus, while the threshold voltage of the device is reduced, the gate source electric leakage of the device is reduced.

Description

technical field [0001] The invention relates to a method for manufacturing a semiconductor integrated circuit, in particular to a method for manufacturing a shield gate (Shield Gate Trench, SGT) deep trench MOSFET. Background technique [0002] Such as Figure 1A to Figure 1N As shown, it is a schematic diagram of the device structure in each step of the manufacturing method of the existing shielded gate trench MOSFET; this method adopts a bottom-up method to form a deep trench separated side gate structure with a shielded gate, including the following steps: [0003] Step 1, such as Figure 1A As shown, a semiconductor substrate such as a silicon substrate 101 is provided; a hard mask layer 102 is formed on the surface of the semiconductor substrate 101, and the hard mask layer 102 can be an oxide layer, or an oxide layer plus a nitride layer. [0004] Such as Figure 1B As shown, the hard mask layer 102 is then etched by a photolithography process to define a gate format...

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Problems solved by technology

[0019] It can be seen from the above that the above-mentioned polysilicon gate with sidewall polysilicon structure is a deep trench gate MOSFET device with a separated side gate structure with a shielded gate, or a shielded gate trench MOSFET with a left and right structure, which is used in the existing formation process method Bottom-up process implementation approach, consisting of Figure 1G As shown, it can be seen that the gate oxide layer 106a and the isolation dielectric layer of the shield gate, that is, the polysilicon isolation dielectric layer 106b, are formed at the same time, so that the gate oxide layer 106a determines the gap between the deep trench gate, that is, the polysilicon gate 107, and the shield gate, that is, the source polysilicon 105. When the thickness of the gate oxide layer 106a is relatively thin, it is easy to cause leakage between the gate and the source, which restricts the application of this structure in devices with low threshold voltage or turn-on voltage.

It can be seen that in order to obtain a low threshold voltage device, a thinner gate oxide layer 106a is required, and a thinner gate oxide layer 106a will simultaneously reduce the thickness of the inter-polysilicon isolation dielectric layer 106b to increase the leakage between the gate and source , so the existing method cannot solve the contradiction between lowering the threshold voltage and reducing the gate-source leakage

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