(A) Field of the Invention
The present invention relates to a method for preparing a gate oxide layer, and more particularly, to a method for preparing a gate oxide layer capable of preventing the incremental increase in thickness of the gate oxide layer at the edge of an active area.
(B) Description of the Related Art
In conventional semiconductor fabrication processes, the local oxidation of silicon (LOCOS) or shallow trench isolation (STI) is widely adopted to electrically isolate electronic elements on the wafer so as to avoid shorts circuit caused by the interference of electronic elements. As the field oxide layer formed by LOCOS occupies a larger area on the wafer and meanwhile the bird's beak phenomenon occurs, current advanced semiconductor fabrication processes often adopt STI to electrically isolate the electronic elements.
One aspect of the present invention provides a method for preparing a gate oxide layer, which uses an implanting process to implant nitrogen-containing dopants into the silicon substrate of the active area, in which nitrogen-containing dopants can inhibit the reaction rate of the thermal oxidation to prevent the gate oxide layer having a greater thickness at the edge of the active area than at the center of the active area.
A method for preparing a gate oxide layer according to this aspect of the present invention first forms a mask layer having at least one opening on a semiconductor substrate, and performs an anisotropic dry etching process to form a trench in the semiconductor substrate below the opening, wherein the trench surrounds an active area. A wet etching process is carried out to enlarge the opening to expose a portion of the semiconductor substrate at the sides of the trench, i.e., to expose the edge of the active area, and an implanting process is then performed to implant nitrogen-containing dopants into the semiconductor substrate below the opening. Subsequently, the mask layer is removed to expose the semiconductor substrate in the active area, and a first thermal treating process is performed to form a gate oxide layer on the upper surface of the semiconductor substrate in the active area.
The nitrogen-containing dopants can inhibit the thermal oxidation rate of the semiconductor substrate during the first thermal treating process, and the nitrogen-containing dopants are selectively implanted into the semiconductor substrate at the sides of the trench, i.e., into the edge of the active area. Consequently, when the thermal treating process is carried out to form the gate oxide layer, the oxidation rate of the semiconductor substrate at the sides of the trench is slower, i.e., the oxidation rate at the edge of the active area is slower, while the oxidation rate at the center of the active area is relatively faster, thus preventing the gate oxide layer having a larger thickness at the edge of the active area than at the center of the active area.
The objectives and advantages of the present invention will become apparent upon reading the following description and upon reference to the accompanying drawings in which:
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The nitrogen-containing dopants 40′ can inhibit the thermal oxidation rate of the semiconductor substrate 32 during the thermal treating process, and the nitrogen-containing dopants 40′ are selectively implanted into the semiconductor substrate 32 at the sides of the trench 40, i.e., into the edge of the active area 50. Consequently, when the thermal treating process is carried out to form the gate oxide layer 48, the oxidation rate of the semiconductor substrate 32 at the sides of the trench 40 is slower, i.e., the oxidation rate at the edge of the active area 50 is slower, while the oxidation rate in the center of the active area 50 is relatively faster, thus preventing the gate oxide layer 48 having a greater thickness at the edge of the active area 50 than in the center of the active area 50.
The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.
Number | Date | Country | Kind |
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095139293 | Oct 2006 | TW | national |