JP3433016B2 - Manufacturing method of nonvolatile semiconductor memory device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-volatile semiconductor memory device, and more specifically, to improve the erasing characteristic of information stored in a split gate type flash memory.

[0002]

2. Description of the Related Art A method of manufacturing a split gate type flash memory which is a non-volatile semiconductor memory device according to a conventional example will be described below with reference to the drawings. This split gate type flash memory is a flash memory in which a control gate 7 is formed from an upper portion to a side portion of a floating gate 5 via an insulating film 6 as shown in FIG.

In order to form this, first, as shown in FIG. 13, a gate insulating film 2 made of a SiO 2 film and a polysilicon film 3 are sequentially formed on a semiconductor substrate 1, and LOCOS oxidation is performed on the polysilicon film 3. The film 4 is formed. Next, FIG.
As shown in FIG. 5, the polysilicon film 3 is etched and removed using the LOCOS oxide film 4 as a mask to form the floating gate 5.

Then, the insulating film 2 is isotropically etched with a hydrofluoric acid-based etching solution so as to be etched and removed so as to remain only just under the floating gate, and then an insulating film made of a thermal oxide film is formed as shown in FIG. The film 6 is formed. Then, a polysilicon film is formed on the insulating film 6 and is patterned so as to remain from the upper part to the side parts of the floating gate 5 to form a control gate 7. The floating gate 5 and the control gate 7 thus formed are formed. Is used as a mask to implant impurities into the semiconductor substrate 1 to form the source / drain regions 8 and 9. As a result, a split gate type flash memory as shown in FIG. 16 is formed.

In the split gate flash memory described above, a program is written by turning on a transistor of a memory cell to be written (hereinafter referred to as a selected cell) and injecting electrons into the floating gate 5. Was there.

[0006]

According to the conventional method of manufacturing a nonvolatile semiconductor memory device, as shown in FIG. 14, the polysilicon film 3 is etched and removed using the LOCOS oxide film 4 as a mask, and the floating gate 5 is removed. By forming the above, a sharp portion is formed at the upper corner portion of the floating gate 5 to facilitate the concentration of an electric field and improve the electron erasing efficiency.

However, the angle of the above-mentioned sharp portion is
Since it is determined by the conditions at the time of oxidation, in order to improve the erasing efficiency, there is no choice but to control with other parameters such as thinning the insulating film 6, applying a high voltage, adjusting the ion implantation amount, and the like. . Therefore, it is an object of the present invention to provide a method for manufacturing a non-volatile semiconductor memory device that increases the degree of freedom in designing the angle of the sharp portion of the floating gate.

[0008]

Therefore, according to the present invention, the LOCOS oxide film 13 is formed on the semiconductor substrate 11, and the LOCOS oxide film 13 is formed.
By removing the OS oxide film 13, the stepped portion 11A is formed on the substrate 11.
Then, a gate insulating film 14 and a polysilicon film 15 are sequentially formed on the entire surface, and a LOCOS oxide film 18 is formed on the polysilicon film 15 in the step portion 11A. Next, the polysilicon film 15 is etched and removed using the LOCOS oxide film 18 as a mask, and the step portion 1
By using the slope of the stepped portion 11A in 1A, the floating gate 19 having an acute pointed portion 19A is formed.

Further, a LOCOS oxide film 33 is formed on the semiconductor substrate 31 so as to sandwich the floating gate formation region, and the LOCOS oxide film 33 is removed so that the floating gate formation region becomes higher than other regions. After forming the portion 31A, a gate insulating film 34 and a polysilicon film 35 are sequentially formed on the entire surface, and a LOCOS oxide film 38 is formed on at least the polysilicon film 35 on the step portion 31A. Next, the LOCOS oxide film 38
Is used as a mask to etch the polysilicon film 35.
The floating gate 39 having an obtuse sharp point 39A is formed on the stepped portion 31A by utilizing the slope of the stepped portion 31A.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for manufacturing a nonvolatile semiconductor memory device of the present invention will be described below. A nonvolatile semiconductor memory device according to one embodiment of the present invention is characterized in that a control gate 21 is formed from an upper portion to a side portion of a floating gate 19 via an insulating film 20 as shown in FIG. It is a split gate type flash memory.

First, as shown in FIG. 1, the SiN film 12 having an opening formed on the semiconductor substrate 11 is used as a mask to perform thermal oxidation at a temperature of about 900 ° C. to form a LOCOS (Local) in the opening of the SiN film 12. Oxidation of Silicon) oxide film 13 is formed. Next, the SiN film 12 and LOCO
By removing the S oxide film 13, a step portion 11A is formed on the semiconductor substrate 11 as shown in FIG.

Subsequently, as shown in FIG. 3, a gate insulating film 14 made of a SiO 2 film is formed by dry oxidation at about 900 ° C. to form a polysilicon film 15 having a film thickness of about 1500 Å. Then, a SiN film 16 is formed on the polysilicon film 15.
Is deposited, and an opening 17 is formed in a region below the stepped portion 11A at least, and then the polysilicon film 15 is thermally oxidized at a temperature of about 900 ° C. to form an opening in the SiN film 16 as shown in FIG. A LOCOS oxide film 18 is formed on 17.

Next, using the LOCOS oxide film 18 as a mask, as shown in FIG. 5, Cl 2 gas with a flow rate of 80 sccm and O 2 gas with a flow rate of 5 sccm are used, and the pressure is 5 mTo.
The remaining polysilicon film 15 is etched and completely removed under the conditions of rr, PF power of 50 W and magnetron of 250 mA to form the floating gate 19. At this time, the angle of the sharp portion 19A formed at the corner portion of the floating gate 19 uses the slope of the step portion 11A formed on the semiconductor substrate 11 to form, for example, a LOCOS oxide film under the same oxidizing conditions as the conventional one. Even if it does, it can be formed with a sharper angle than the angle of the sharp portion of the conventional floating gate shown in FIG. For example, about 3 steps
At 00Å (LOCOS film about 500Å), an acute angle of about 5 degrees is obtained.

Next, after removing the first gate insulating film 14 formed in a region other than the region immediately below the floating gate 19 using a hydrofluoric acid-based etching solution, the entire surface is about 950.
By thermal oxidation at a temperature of ° C, a thermal oxide film having a film thickness of about 250Å is formed, and an insulating film 20 integrated with the insulating film 14 and the LOCOS oxide film 18 is formed as shown in FIG.

Next, a polysilicon film and a WSix film are sequentially formed in the order of about 1500 Å and about 1500 Å, respectively, and the control gate 21 is formed by patterning the floating gate 19 so as to remain from the upper portion to the side portions thereof. By implanting impurities into the semiconductor substrate 11 using the control gate 21 as a mask to form the source / drain regions 22 and 23, a split gate type flash memory as shown in FIG. 7 is formed.

As described above, by forming the floating gate 19 on the step portion 11A formed on the semiconductor substrate 11, for example, even if a LOCOS oxide film for forming the floating gate is formed under the same oxidizing condition as the conventional one. By the slope of the stepped portion 11A, the sharp portion can be formed at an acute angle, and by making the acute angle, electric field concentration is more likely to occur, and a lower voltage plate can be supported.

Another embodiment of the present invention will be described with reference to FIGS. First, as shown in FIG. 8, the SiN film 32 formed on the floating gate formation region on the semiconductor substrate 31 is used as a mask for thermal oxidation at a temperature of about 900 ° C., and the region not masked by the SiN film 32. Then, a LOCOS (Local Oxidation of Silicon) oxide film 33 is formed.

Next, by removing the SiN film 32 and the LOCOS oxide film 33, a step 31A higher than the other regions is formed in the floating gate formation region on the semiconductor substrate 31, as shown in FIG. Then, as shown in FIG. 10, a gate insulating film 34 made of a SiO2 film is formed to a thickness of about 900.
A polysilicon film 35 having a thickness of about 1500 Å is formed by dry oxidation at ℃. Then, the polysilicon film 3
5, a SiN film 36 is deposited on the upper surface of the SiN film 5, and an opening 37 is formed in a layer below the SiN film 36 in a region including at least the step portion 31A. Then, as shown in FIG.
Thermally oxidize at a temperature of ℃ to LOC the opening 37 of the SiN film 36.
An OS oxide film 38 is formed.

Next, using the LOCOS oxide film 38 as a mask, as shown in FIG. 12, Cl 2 having a flow rate of 80 sccm is used.
Gas, O2 gas with a flow rate of 5 sccm, pressure of 5 mT
The remaining polysilicon film 35 is etched and completely removed under the conditions of orr, PF power 50 W, and magnetron 250 mA to form the floating gate 39.

At this time, the angle of the sharp portion 39A formed at the corner of the floating gate 39 is determined by the semiconductor substrate 31.
By utilizing the slope of the step portion 31A formed above, for example, even if the LOCOS oxide film is formed under the same oxidation condition as the conventional one, the angle becomes obtuse as compared with the angle of the sharp portion of the conventional floating gate shown in FIG. Can be formed. For example, a 300 Å step makes an obtuse angle of about 7 degrees.

Thereafter, similarly to the first embodiment described above, an insulating film covering the floating gate 39 is formed, and a control gate is formed from the upper part to the side part of the floating gate 39, and the floating gate 39 and Impurities are implanted into the semiconductor substrate 31 using the control gate as a mask to form source / drain regions, whereby a split gate flash memory is formed.

As described above, in the nonvolatile semiconductor memory device of the other embodiment, the floating gate 39 is formed in the step portion 31A formed on the semiconductor substrate 31, so that, for example, under the same oxidizing condition as the conventional one. Even if the LOCOS oxide film for forming the floating gate is formed, the sharp portion of the floating gate can be formed at an obtuse angle due to the slope of the step portion 31A.

As described above, according to the present invention, conventionally, the angle of the sharp portion of the floating gate is restricted by the condition at the time of oxidation, but by applying the present invention, the angle of the sharp portion can be freely set.

[0024]

As described above, according to the present invention, the floating gate is formed in the step portion formed on the semiconductor substrate.
Since the angle of the sharp portion of the floating gate can be freely set by utilizing the slope of the stepped portion, the present invention is applied without the angle of the sharp portion being restricted by the condition at the time of oxidation as in the conventional case. This increases the degree of freedom in designing the angle of the sharp portion.

[Brief description of drawings]

FIG. 1 is a first cross-sectional view showing a method for manufacturing a nonvolatile semiconductor memory device according to an embodiment of the present invention.

FIG. 2 is a second cross-sectional view showing the method for manufacturing the nonvolatile semiconductor memory device in the embodiment of the present invention.

FIG. 3 is a third cross-sectional view showing the method for manufacturing the nonvolatile semiconductor memory device in the embodiment of the present invention.

FIG. 4 is a fourth cross-sectional view showing the method of manufacturing the nonvolatile semiconductor memory device in the embodiment of the present invention.

FIG. 5 is a fifth cross-sectional view showing the method for manufacturing the nonvolatile semiconductor memory device in the embodiment of the present invention.

FIG. 6 is a sixth cross-sectional view showing the method for manufacturing the nonvolatile semiconductor memory device in the embodiment of the present invention.

FIG. 7 is a seventh cross-sectional view showing the method for manufacturing the nonvolatile semiconductor memory device in the embodiment of the present invention.

FIG. 8 is a first cross-sectional view showing the method of manufacturing a nonvolatile semiconductor memory device according to another embodiment of the present invention.

FIG. 9 is a second cross-sectional view showing the method of manufacturing a nonvolatile semiconductor memory device according to another embodiment of the present invention.

FIG. 10 is a third cross-sectional view showing the method of manufacturing the nonvolatile semiconductor memory device according to another embodiment of the present invention.

FIG. 11 is a fourth cross-sectional view showing the method of manufacturing a nonvolatile semiconductor memory device according to another embodiment of the present invention.

FIG. 12 is a fifth cross-sectional view showing the manufacturing method of the nonvolatile semiconductor memory device in another embodiment of the present invention.

FIG. 13 is a first cross-sectional view showing the method of manufacturing the conventional nonvolatile semiconductor memory device.

FIG. 14 is a second cross-sectional view showing the method of manufacturing the conventional nonvolatile semiconductor memory device.

FIG. 15 is a third cross-sectional view showing the method of manufacturing the conventional nonvolatile semiconductor memory device.

FIG. 16 is a fourth cross-sectional view showing the method of manufacturing the conventional nonvolatile semiconductor memory device.

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/8247 H01L 27/115 H01L 29/788 H01L 29/792

Claims (2)

(57) [Claims] 1. A first selective oxide film is formed on a semiconductor substrate.
And the step of removing the first selective oxide film to remove the substrate
After forming a step on the gate, a gate insulating film and a policy are formed on the entire surface.
A recon film is sequentially formed, and at least the inside of the step portion is
Step of forming second selective oxide film on polysilicon film
And using the second selective oxide film as a mask,
Etching and removal of the con-
Using a slop of the part, a float having an acute pointed part.
The step of forming an ingate and oxidizing the entire surface
An insulating film was formed so as to cover the rotating gate.
Later on from the top of the floating gate to the sides
A step of forming a control gate;
Impure using nggate and control gate as a mask
Injecting a substance into the substrate to form a source / drain region
Non-volatile semiconductor memory characterized by including the steps of:
Device manufacturing method. 2. A floating gate type on a semiconductor substrate.
Step of forming first selective oxide film so as to sandwich the formed region
And removing the first selective oxide film to remove the floatein.
Stepped portion so that the gate formation area is higher than other areas
Gate insulating film and polysilicon film over the entire surface after forming
Are sequentially formed, and at least the polysilicon on the step portion is formed.
Forming a second selective oxide film on the conductive film;
The polysilicon film is etched using the selective oxide film of No. 2 as a mask.
On the stepped portion by stitching and removal.
A floating gate having an obtuse sharp point
And the step of forming the insulating film by oxidizing the entire surface
From the top to the side of the floating gate.
Forming a control gate, and the above floate
Impurities with masks of gugget and control gate
Are implanted into the substrate to form a source / drain region.
Nonvolatile semiconductor memory device characterized by having
Manufacturing method.