Method for fabricating semiconductor memory device

1. A method for fabricating a semiconductor memory device in which a logic circuit and a nonvolatile memory are provided on a semiconductor substrate, the method comprising the steps of:

forming a trench in the semiconductor substrate and burying an insulating film in the trench, thereby forming an isolation region;

forming a protective film made of an insulating material over the semiconductor substrate in a logic circuit region where the logic circuit is to be formed and a nonvolatile memory region where the nonvolatile memory is to be formed;

selectively introducing impurity ions in part of the semiconductor substrate in the logic circuit region;

removing the protective film formed over the logic circuit region;

forming a first conductive film on the semiconductor substrate in the nonvolatile memory region after the step of forming the isolation region has been performed and before the step of forming the protective film is performed; and

forming a second conductive film on the protective film after the step of forming the protective film has been performed,

wherein the step of introducing the impurity ions is performed before the step of removing the protective film is performed, and

the protective film serves as an insulating film for insulating the first conductive film and the second conductive film from each other.

2. The method of claim 1 , wherein the protective film is made of a material having a lower etching rate with respect to hydrofluoric acid than that of the insulating film buried in the trench.

3. The method of claim 1 , wherein the protective film is made of a material having a lower etching rate with respect to a mixed solution including ammonia water and hydrogen peroxide than that of the insulating film buried in the trench.

4. The method of claim 1 , wherein the protective film is a single layer of either a silicon nitride film or a silicon oxynitride film.

5. The method of claim 1 , wherein the protective film is a multilayer film made of a plurality of insulating films including at least one of a silicon nitride film and a silicon oxynitride film.

6. The method of claim 5 , wherein the multilayer film is a stack of a silicon oxide film, either a silicon nitride film or a silicon oxynitride film, and a silicon oxide film.

7. The method of claim 5 , wherein the step of introducing the impurity ions includes a first impurity introducing step for forming a well and a second impurity introducing step for controlling a threshold voltage, and

the method further comprises the step of selectively removing at least one of the plurality of insulating films before the second impurity introducing step is performed.

8. A method for fabricating a semiconductor memory device in which a logic circuit and a nonvolatile memory are provided on a semiconductor substrate, the method comprising the steps of:

forming a trench in the semiconductor substrate and burying an insulating film in the trench, thereby forming an isolation region;

forming a protective film made of an insulating material over the semiconductor substrate in a logic circuit region where the logic circuit is to be formed and a nonvolatile memory region where the nonvolatile memory is to be formed;

selectively introducing impurity ions in part of the semiconductor substrate in the logic circuit region; and

removing the protective film formed over the logic circuit region,

wherein the step of introducing the impurity ions is performed before the step of removing the protective film is performed,

the protective film formed over the nonvolatile memory region is to serve as a trap film that accumulates charge in a memory formed in the nonvolatile memory region, and

the protective film is made of a material having a lower etching rate with respect to hydrofluoric acid than that of the insulating film buried in the trench.

9. A method for fabricating a semiconductor memory device in which a logic circuit and a nonvolatile memory are provided on a semiconductor substrate, the method comprising the steps of:

forming a trench in the semiconductor substrate and burying an insulating film in the trench, thereby forming an isolation region;

forming a protective film made of an insulating material over the semiconductor substrate in a logic circuit region where the logic circuit is to be formed and a nonvolatile memory region where the nonvolatile memory is to be formed;

selectively introducing impurity ions in part of the semiconductor substrate in the logic circuit region; and

removing the protective film formed over the logic circuit region,

wherein the step of introducing the impurity ions is performed before the step of removing the protective film is performed,

the protective film formed over the nonvolatile memory region is to serve as a trap film that accumulates charge in a memory formed in the nonvolatile memory region, and

the protective film is made of a material having a lower etching rate with respect to a mixed solution including ammonia water and hydrogen peroxide than that of the insulating film buried in the trench.

10. A method for fabricating a semiconductor memory device in which a logic circuit and a nonvolatile memory are provided on a semiconductor substrate, the method comprising the steps of:

forming a trench in the semiconductor substrate and burying an insulating film in the trench, thereby forming an isolation region;

forming a protective film made of an insulating material over the semiconductor substrate in a logic circuit region where the logic circuit is to be formed and a nonvolatile memory region where the nonvolatile memory is to be formed;

selectively introducing impurity ions in part of the semiconductor substrate in the logic circuit region; and

removing the protective film formed over the logic circuit region,

wherein the step of introducing the impurity ions is performed before the step of removing the protective film is performed,

the protective film formed over the nonvolatile memory region is to serve as a trap film that accumulates charge in a memory formed in the nonvolatile memory region, and

the protective film is a multilayer film made of a plurality of insulating films including at least one of a silicon nitride film and a silicon oxynitride film.

11. The method of claim 10 , wherein the multilayer film is a stack of a silicon oxide film, either a silicon nitride film or a silicon oxynitride film, and a silicon oxide film.

12. The method of claim 10 , wherein the step of introducing the impurity ions includes a first impurity introducing step for forming a well and a second impurity introducing step for controlling a threshold voltage, and

the method further comprises the step of selectively removing at least one of the plurality of insulating films before the second impurity introducing step is performed.