| 摘要 |
A method and structure, particularly relevant to forming a narrow gate of a pseudomorphic high electron mobility transistor (PHEMT), are presented. The method involves forming a narrow gate by first forming a thin protective layer (18) and etch stop layer (20) over the donor layer (16). The contact layers (22, 24) are etched through with high selectivity, stopping on the etch stop layer (20). A second etch is performed highly selective to the etch stop layer (20). The resultant tapered opening is filled with electrode material (30) and the contact layers (22, 24) are etched. A resultant structure typified by a preferred embodiment of the method is GaAs substrate (12); an InGaAs channel layer (14) over the substrate; a doped A1GaAs barrier layer (16) over the channel layer; a GaAs protective layer (18) disposed on the donor layer (16); an InGaP etch stop layer (20) disposed over the protective layer (18); and a GaAs source and drain contact layer (22, 24) disposed over the etch stop layer (20). The combination of a high selectivity etch stop overlying a protective layer allows the narrow gate electrode shape to be formed by a two-step wet etch with wide process window, thus eliminating damage associated with a dry etch, and also eliminates the need for channel current measurement during a less selective etch process.
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