Ultraviolet-erasable nonvolatile semiconductor device

Abstract

An ultraviolet-erasable nonvolatile semiconductor device has a protective film comprised of a silicon nitride film on which is laminated a silicon oxynitride film. The silicon nitride film has a thickness of 1000 or more and 2000 or less and the silicon oxynitride film has a thickness of about 7000 or more. The silicon nitride film and the silicon oxynitride film cooperate to prevent moisture from penetrating into the ultraviolet-erasable nonvolatile semiconductor device. The thickness of the silicon nitride film is set so that the time for erasing data in a nonvolatile semiconductor storage element through irradiation with ultraviolet rays is not increased.

Claims

1. An ultraviolet-erasable nonvolatile semiconductor device, comprising: a semiconductor substrate; an ultraviolet-erasable nonvolatile semiconductor storage element formed in a surface of the semiconductor substrate; a top metal formed on the semiconductor substrate; and a protective film formed on the ultraviolet-erasable nonvolatile semiconductor storage element and the top metal, the protective film comprising a first silicon nitride film, a silicon oxynitride film laminated thereon, a thickness of the silicon oxynitride film being thicker than that of the first silicon nitride film, and a second silicon nitride film laminated on the silicon oxynitride film.

2. An ultraviolet-erasable nonvolatile semiconductor device according to claim 1, wherein the first silicon nitride film has a thickness of 1,000 or more and 2,000 or less.

3. An ultraviolet-erasable nonvolatile semiconductor device according to claim 1, wherein the silicon oxynitride film has a refractive index of from 1.65 to 1.85.

4. An ultraviolet-erasable nonvolatile semiconductor device according to claim 1, wherein the silicon oxynitride film has a thickness of about 7000 or more.

5. An ultraviolet-erasable nonvolatile semiconductor device according to claim 4, wherein the first silicon nitride film has a thickness of 1,000 or more and 2,000 or less.

6. An ultraviolet-erasable nonvolatile semiconductor device according to claim 5, wherein the silicon oxynitride film has a refractive index of from 1.65 to 1.85.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a sectional view of an ultraviolet-erasable nonvolatile semiconductor device.

(2) FIG. 2 is a sectional view of an ultraviolet-erasable nonvolatile semiconductor device.

(3) FIG. 3 is a graph for showing a relationship between a thickness of a silicon nitride film and a time for erasing data in an ultraviolet-erasable nonvolatile semiconductor storage element.

DESCRIPTION OF EMBODIMENTS

(4) In the following, embodiments of the present invention are described with reference to the drawings.

(5) An ultraviolet-erasable nonvolatile semiconductor device is now described. FIG. 1 is a sectional view of the ultraviolet-erasable nonvolatile semiconductor device. FIG. 3 is a graph for showing a relationship between a thickness of a silicon nitride film and a time for erasing data in an ultraviolet-erasable nonvolatile semiconductor storage element.

(6) The ultraviolet-erasable nonvolatile semiconductor device includes a semiconductor substrate 10, a nonvolatile semiconductor storage element 17 formed in the semiconductor substrate 10, a top metal 11 formed on the semiconductor substrate 10, and a protective film formed on the top metal 11. Further, the ultraviolet-erasable nonvolatile semiconductor device includes, in part thereof, a pad opening portion 14 obtained by removing the protective film formed on the top metal 11. In this case, the protective film includes two layers of a silicon nitride film 12 and a silicon oxynitride film 13.

(7) Part of the top metal 11 is exposed from the pad opening portion 14, and necessary signal transmission is performed therewith. The silicon nitride film 12 and the silicon oxynitride film 13 cooperate to prevent moisture from penetrating into the ultraviolet-erasable nonvolatile semiconductor device. As a thickness of the silicon nitride film 12 is increased, ultraviolet rays are more difficult to transmit therethrough, and hence such a thickness is selected with which it is possible to shorten the time for erasing data in the nonvolatile semiconductor storage element 17 through irradiation of the ultraviolet rays.

(8) Through a publicly-known semiconductor manufacturing process, the nonvolatile semiconductor storage element 17 such as an erasable programmable read only memory (EPROM) is formed in the semiconductor substrate 10. After that, an inter-layer insulating film (not shown) and the like are laminated on the resultant, and then the top metal 11 is laminated thereon. After that, as the protective film, the silicon nitride film 12 and then the silicon oxynitride film 13 are laminated thereon. After that, the pad opening portion 14 is formed in part of the protective film formed on the top metal 11.

(9) In this case, the silicon nitride film 12 is formed so as to have a thickness of about 1,000 or more in order to ensure the water resistance. Moreover, as shown in FIG. 3, when the thickness of the silicon nitride film 12 exceeds about 2,000 , the time for erasing data in the ultraviolet-erasable nonvolatile semiconductor storage element is precipitously increased. Thus, it is required that the thickness of the silicon nitride film 12 be set to be about 2,000 or less so that the time for erasing data is not unnecessarily increased. With this, the data in the nonvolatile semiconductor storage element 17 can be erased by the ultraviolet rays even in the manufacturing process.

(10) Moreover, the silicon oxynitride film 13 is formed so as to have a refractive index of from 1.65 to 1.85 and a thickness of about 7,000 or more, and hence the water resistance can be enhanced. Note that, the silicon oxynitride film 13 does not inhibit the entrance of the ultraviolet rays.

(11) With the configuration described above, the ultraviolet-erasable nonvolatile semiconductor device can have the high water resistance and erase the data by the ultraviolet rays within a period of time that allows the mass production.

(12) Note that, in FIG. 1, the silicon oxynitride film 13 is laminated on the silicon nitride film 12. As illustrated in broken lines, the silicon nitride film 12 may be laminated on the silicon oxynitride film 13.

(13) Moreover, as illustrated in FIG. 2, a TEOS film 15 may be added as the protective film between the silicon nitride film and the silicon oxynitride film.

REFERENCE SIGNS LIST

(14) 10 semiconductor substrate 11 top metal 12 silicon nitride film 13 silicon oxynitride film 14 pad opening portion 15 TEOS film 17 nonvolatile semiconductor storage element