Method for fabricating semiconductor devices

A method for fabricating a semiconductor device comprising the steps of:

• providing a semiconductor substrate formed with n and p type wells and element-isolating films;
• forming gate oxide films on the n and p type wells, respectively;
• forming a polysilicon film over the entire exposed upper surface of the resulting structure obtained after the formation of the gate oxide films;
• forming a first photoresist film pattern on a portion of the polysilicon film disposed over the n type well;
• implanting first impurity ions having an n type conductivity in a portion of the polysilicon film disposed over the p type well by use of the first photoresist film pattern as a mask;
• removing the first photoresist film pattern, and forming a second photoresist film pattern on the portion of the polysilicon film disposed over the p type well;
• implanting first impurity ions having a p type conductivity in the portion of the polysilicon film disposed over the n type well by use of the second photoresist film pattern as a mask;
• removing the second photoresist film pattern, and forming a third photoresist film pattern on the portions of the polysilicon film respectively disposed over the n and p type wells;
• implanting second impurity ions having the p type conductivity in the polysilicon film by use of the third photoresist film pattern as a mask;
• removing the third photoresist film pattern, and annealing the resulting structure, thereby forming p.sup.+ source/drain in the n type well;
• selectively removing the polysilicon film, thereby forming n and p type gate electrodes;
• forming a fourth photoresist film pattern on the exposed surface of the gate oxide film disposed over the n type well;
• and
• implanting second impurity ions having the n type conductivity in an exposed surface portion of the p type well, thereby forming n.sup.+ source/drain.