JPH05190862A - Method of manufacturing nonvolatile semiconductor memory device - Google Patents

Abstract

(57) [Summary] (Modified) [Structure] Select gate electrode 5 formed on semiconductor substrate 1 via gate oxide film 2 and floating gate electrode 11 formed on the side wall of select gate electrode A method for manufacturing a non-volatile semiconductor memory device including a transistor, the step of depositing a nitride film 7 on a semiconductor substrate on which a select gate electrode is formed via a gate oxide film to cover a side wall portion of the select gate electrode, A step of forming an oxide film 8 on the entire surface of the semiconductor substrate, a step of stacking a nitride film on the oxide film to form a nitride film sidewall insulating film 9 on the side wall of the select gate electrode, a nitride film sidewall insulating film being interposed. A method for manufacturing a non-volatile semiconductor memory device, which includes the step of forming a floating gate electrode. [Effect] It becomes possible to stabilize the characteristics of the memory cell by reducing the film thickness of the insulating film between the select gate electrode and the floating gate electrode.

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 nonvolatile semiconductor memory device, and more particularly to a method for manufacturing a nonvolatile semiconductor memory device suitable for high integration.

[0002]

2. Description of the Related Art Conventionally, a nonvolatile semiconductor memory device has been proposed in which a polysilicon side wall formed on a side wall portion of a select gate electrode of a transistor forming a semiconductor memory device is used as a floating gate electrode. The semiconductor memory device is manufactured by forming a floating gate electrode on the side wall of the select gate electrode via an insulating film, as shown below.

A method of manufacturing the semiconductor memory device thus manufactured will be described with reference to FIGS. In FIGS. 3 and 4, reference numeral 21 denotes a silicon substrate, and a gate insulating film, for example, 150, is formed on the surface of the silicon substrate 21.
After forming the SiO ₂ film 22 of about Å, the thickness is 3000 Å
Polysilicon 23 with a thickness of about 2000Å and NS
G24 is stacked and the select gate electrode 33 is formed by patterning by a photolithography process. At this time, simultaneously with the patterning of the select gate electrode 33,
The SiO ₂ film 22 on the silicon substrate 21 around the select gate electrode 33 is etched, and the film thickness of the SiO ₂ film 22 on the silicon substrate 21 around the select gate electrode 33 becomes about 50 Å. Furthermore, by photolithography, for example, A
s is ion-implanted to form a source region (see FIG. 3).
(A)).

Then, the silicon substrate 21 and
SiO on the select gate electrode 33 ₂Form the film 26
It At this time, a film of about 150 Å is formed on the silicon substrate 21.
Thick SiO₂The film 26 is formed, and this Si
O₂The film 26 is a select gate electrode 3 which will be formed in a later step.
Of the SiN film 27, which is the side wall insulating film of the side wall 3
It becomes an oxide film that acts as a stopper during etch back (Fig. 3).
(B)).

On the SiO ₂ film 26, 400 Å
The SiN film 27 is laminated to a certain extent (FIG. 3C), and the SiN film 27 is etched back by anisotropic etching to form the sidewall insulating film while leaving the SiN film 27 on the side wall of the select gate electrode 33. Yes (Fig. 4
(D)). Then, the S formed on the silicon substrate 21
After removing the iO ₂ film 22, the silicon substrate 2 is further removed.
1. A SiO ₂ film 28 of about 90 Å is formed as a tunnel oxide film on the select gate electrode 33 and the SiN film 27 (FIG. 4E).

Subsequently, about 4500 Å of polysilicon is laminated, and the SiN film 27 and SiO ₂ are formed on the side wall of the select gate electrode 33 by anisotropic etching similar to the above.
After forming the floating gate electrode 29 via the films 26 and 28, the drain region 31 is formed by ion-implanting phosphorus, for example, using the select gate electrode 33 and the floating gate electrode 29 as a mask. Then, on the silicon substrate 21, the select gate electrode 33, and the floating gate electrode 29, an ONO (Oxide-Nitride-Oxide) film 30 as an interlayer insulating film and polysilicon for the program gate electrode 32 are laminated (FIG. 4F). ), And patterning the program gate electrode 32 in a photolithography process.

[0007]

In the method of manufacturing a nonvolatile semiconductor memory device described above, the SiN sidewall insulating film 27 is formed between the select gate electrode 33 and the floating gate electrode 29. This SiN
The sidewall insulating film 27 is formed by etching back the SiN film 27 laminated on the semiconductor substrate 1 and the select gate electrode 33, but prevents the semiconductor substrate 1 itself from being etched when the SiN film 27 is etched back. Therefore, the oxide film 22 serving as a stopper is required on the semiconductor substrate 1. To etch back the SiN film 27 having a desired thickness, a SiO ₂ film 2 of about 150 Å is used as a stopper.
2 must be formed, but in order to secure the SiO ₂ film 22 of that thickness on the semiconductor substrate 1, after patterning the select gate electrode 33, the thickness of the SiO ₂ film 22 is changed by oxidizing again. Must be secured. At the time of this oxidation, at the same time, the polysilicon forming the select gate electrode 33 is also oxidized and thickly oxidized to 300 to 400 Å. Therefore, the film thickness of the insulating film between the select gate electrode 33 and the floating gate electrode 29 is increased, and a gap is formed between the channels formed between the select gate electrode 33 and the floating gate electrode 29. There is a problem that the read current is reduced.

The present invention has been made in view of the above problems, and it is possible to stabilize the characteristics of the memory cell by controlling the film thickness of the insulating film between the select gate electrode and the floating gate electrode. It is an object of the present invention to provide a method for manufacturing a semiconductor memory device.

[0009]

According to the present invention, a select gate electrode is formed on a semiconductor substrate via a gate oxide film, and a floating gate electrode is formed on a side wall of the select gate electrode. In a method of manufacturing a nonvolatile semiconductor memory device including a transistor,
(i) depositing a nitride film on the semiconductor substrate on which the select gate electrode is formed via the gate oxide film, and covering the sidewall of the select gate electrode, (ii) over the entire surface of the semiconductor substrate Forming an oxide film, (iii) further forming a nitride film on the oxide film to form a nitride film side wall insulating film on the side wall of the select gate electrode, (iv) the nitride film side wall Provided is a method for manufacturing a nonvolatile semiconductor memory device, including the step of forming a floating gate electrode via an insulating film.

In the present invention, the nitride film can be formed by a known method such as a CVD method, and the film thickness of the nitride film formed when covering the side wall of the select gate electrode is about 50 to 100Å. The thickness of the nitride film for forming the sidewall insulating film is preferably about 350 to 400Å. Further, the oxide film can be formed by a known method, for example, thermal oxidation or the like.
It is preferable that the oxide film formed after the sidewall of the select gate electrode is covered with the nitride film is about 250 to 300Å.

Further, the covering of the side wall of the select gate electrode with the nitride film and the formation of the side wall insulating film of the nitride film on the side wall of the select gate electrode can be carried out by a known anisotropic etching method. The oxide film formed as the gate oxide film on the entire surface of the semiconductor substrate and the oxide film formed after the sidewall of the select gate electrode is covered with the nitride film act as a stopper when the nitride film is etched.

The select gate electrode formed in the present invention preferably has a two-layer structure in which NSG is laminated on polysilicon, and the floating gate electrode is preferably formed of polysilicon.

[0013]

According to the method described above, after covering the side wall portion of the select gate electrode with the nitride film, an oxide film having a constant film thickness serving as a stopper for etching performed for forming the SiN sidewall insulating film is formed on the semiconductor substrate and Since it is formed on the select gate electrode, it is possible to easily control the film thickness of the oxide film on the side wall of the select gate electrode as compared with the case where an oxide film serving as a stopper is directly formed on the semiconductor substrate and the select gate electrode. You can

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a nonvolatile semiconductor memory device according to the present invention will be described with reference to FIGS. It should be noted that although the case where the p-type semiconductor substrate is used is described in the present embodiment, the same applies to the case where the n-type semiconductor substrate is used, and the present invention extends to these. ..

In FIGS. 1 and 2, reference numeral 1 denotes a silicon substrate. After forming a SiO ₂ film 2 of about 150 Å as a gate insulating film on the surface of the silicon substrate 1, a polysilicon of about 3000 Å is formed. 3 and thickness 20
The NSG 4 having a thickness of about 00Å is stacked, and the select gate electrode 5 is formed by patterning by a photolithography process. At this time, simultaneously with the patterning of the select gate electrode 5, SiO ₂ film 2 on the silicon substrate 1 of the select gate electrode 5 peripheral portion is etched, SiO ₂ film 2 film on the silicon substrate 1 of the select gate electrode 5 periphery The thickness is about 50Å. Further, by photolithography, for example, As is ion-implanted into one of the select gate electrodes 5 at 2.5 × 10 ¹⁵ cm ^-2 and 50 keV,
A source region is formed (FIG. 1A).

Then, a SiN film 7 of about 100 Å is deposited on the silicon substrate 1 and the select gate electrode 5 (FIG. 1 (b)), and the SiN film 7 is etched back by anisotropic etching. 5 The side wall portion is covered with the SiN film 7 (FIG. 1C). further,
A SiO ₂ film 8 of about 100 Å is formed on the silicon substrate 1, the select gate electrode 5 and the SiN film 7 by oxidation. In this case, it becomes possible to SiO ₂ film 8 having a thickness of about 150Å is formed on the silicon substrate 1 is formed, the SiO ₂
The film 8 serves as an oxide film that serves as a stopper at the time of etching back the SiN film 9, which is a sidewall insulating film on the sidewall of the select gate electrode 5 formed in a later step (FIG. 1D).

Then, a SiN film 9 of about 400 Å is laminated on the SiO ₂ film 8 as an insulating film (see FIG. 2).
(E)), SiN by anisotropic etching similar to the above
By etching back the film 9, a sidewall insulating film is formed from the SiN film 9 on the sidewall of the select gate electrode 5 (FIG. 2F). Then, after removing the SiO ₂ film 2 formed on the silicon substrate 1, a SiO ₂ film 10 of about 90 Å is further formed as a tunnel oxide film on the silicon substrate 1, the select gate electrode 5 and the SiN film 9. FIG. 2 (g)).

Subsequently, polysilicon is laminated in a thickness of about 4500 Å, and the SiN films 7 and 9 and SiO ₂ are formed on the side wall of the select gate electrode 5 by anisotropic etching similar to the above.
After the floating gate electrode 11 is formed through the films 8 and 10, using the select gate electrode 5 and the floating gate electrode 11 as a mask, for example, As
0 keV, 3.0 × 10 ¹⁵ cm ^-2 , and phosphorus at 30 ke
The drain region 14 is formed by ion implantation with V at 2.0 × 10 ¹⁴ cm ^-2 . Then, on the silicon substrate 1, the select gate electrode 5, and the floating gate electrode 11, polysilicon for an ONO film 12 and a program gate electrode 13 is laminated as an interlayer insulating film (FIG. 2 (h)), and a program is performed in a photolithography process. The gate electrode 13 is patterned.

[0019]

According to the method of manufacturing a semiconductor memory device of the present invention, after the sidewall of the select gate electrode is covered with the nitride film, it serves as a stopper for etching performed to form the SiN sidewall insulating film. Since an oxide film having a film thickness is formed on the semiconductor substrate and the select gate electrode, the oxide film on the sidewall of the select gate electrode is compared with the case where the oxide film serving as a stopper is directly formed on the semiconductor substrate and the select gate electrode. The film thickness of can be easily controlled. Therefore, by reducing the thickness of the insulating film between the select gate electrode and the floating gate electrode,
It is possible to reduce the gap generated between the channels formed between the select gate electrode and the floating gate electrode, prevent the read current from decreasing, and stabilize the characteristics of the memory cell. .

[Brief description of drawings]

FIG. 1 is a process chart showing an embodiment of a method for manufacturing a nonvolatile semiconductor memory device according to the present invention.

FIG. 2 is a process drawing showing an example of a method for manufacturing a nonvolatile semiconductor memory device according to the present invention.

FIG. 3 is a process drawing showing an example of a conventional method for manufacturing a nonvolatile semiconductor memory device.

FIG. 4 is a process drawing showing an example of a conventional method for manufacturing a nonvolatile semiconductor memory device.

[Explanation of symbols]

1 Silicon substrate (semiconductor substrate) 2 SiO ₂ film (gate oxide film) 5 Select gate electrode 7 SiN film (nitride film) 8 SiO ₂ film (oxide film) 9 SiN film (sidewall insulating film) 11 Floating gate electrode

Claims (1)

[Claims] 1. A nonvolatile semiconductor memory device including a transistor including a select gate electrode formed on a semiconductor substrate via a gate oxide film, and a floating gate electrode formed on a sidewall of the select gate electrode. In the manufacturing method, (i) a step of depositing a nitride film on the semiconductor substrate on which the select gate electrode is formed via the gate oxide film to cover the side wall portion of the select gate electrode, (ii) the semiconductor Forming an oxide film on the entire surface of the substrate, (iii) further forming a nitride film on the oxide film, and forming a nitride film sidewall insulating film on the select gate electrode sidewall part, (iv) And a step of forming a floating gate electrode with a nitride film sidewall insulating film interposed therebetween.