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Method for manufacturing thin film transistor using multi-tone mask

  • US 8,980,685 B2
  • Filed: 02/27/2014
  • Issued: 03/17/2015
  • Est. Priority Date: 10/24/2008
  • Status: Active Grant
First Claim
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1. A method for manufacturing a semiconductor device, comprising:

  • forming a gate electrode layer over an insulating surface, wherein the gate electrode layer comprises a stack of a first layer comprising Ti and a second layer comprising Cu;

    forming a gate insulating layer over the gate electrode layer, wherein the gate insulating layer comprises a stack of a silicon nitride layer and a first silicon oxide layer, and the silicon nitride layer covers the second layer;

    forming an oxide semiconductor film over the gate electrode layer;

    forming a conductive film over the gate electrode layer;

    forming a first mask layer over the gate insulating layer, the oxide semiconductor film, and the conductive film;

    forming an oxide semiconductor layer and a conductive layer by etching the oxide semiconductor film and the conductive film with the use of the first mask layer in a first etching step;

    forming a second mask layer by ashing the first mask layer;

    forming an oxide semiconductor layer having a depression, a source electrode layer, and a drain electrode layer by etching the oxide semiconductor layer and the conductive layer with the use of the second mask layer in a second etching step; and

    performing an oxygen radical treatment on the oxide semiconductor layer having the depression,wherein the first mask layer is formed using a light-exposure mask,wherein wet etching in which an etchant is used is employed in the first etching step,wherein dry etching in which an etching gas is used is employed in the second etching step, andwherein the oxide semiconductor layer having the depression includes a region with a smaller thickness than a region overlapping with the source electrode layer or the drain electrode layer.

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