JP2853791B2 - Method for manufacturing 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 of manufacturing a semiconductor memory device, and more particularly to a method of forming an oxide film capable of improving the insulation of a floating gate.

[0002]

^2. Description of the Related Art As a semiconductor memory device having a floating gate, a nonvolatile memory such as an EPROM or an E ² PROM is known. The operation of the nonvolatile memory will be described with reference to the drawings.

FIG. 3A shows the structure of an E ² PROM. A gate oxide film 14 is provided on a p-type silicon substrate 2. On the gate oxide film 14, a gate structure
28, polysilicon floating gate 22,
An inter-gate insulating film 24 and a control gate 26 made of polysilicon are sequentially formed. Also, a p-type silicon substrate 2
Inside, an n ^{+ type} source 6 and an n ^{+ type} drain 8 are provided. During the n ⁺ -type source 6 and the n ⁺ -type drain 8 is channel forming region 7.

When a voltage of 20 V is applied to the control gate 26 while the n ⁺ -type drain 8 of this memory is kept at 0 V, a strong electric field is generated in the gate oxide film 14 and electrons in the channel forming region 7 are transferred to the floating gate 22 Be drawn in. Thereby, the gate threshold voltage Vth for turning on this transistor increases.

On the other hand, when the polarity of the electric field is reversed by changing the voltage applied to the memory, the electrons held in the floating gate 22 are extracted to the silicon substrate 2 side. As a result, the gate threshold voltage Vth decreases. That is,
A binary state is stored depending on whether the gate threshold voltage Vth is high or low. As described above, in the nonvolatile memory, data is written or erased by the flow of electrons into or out of the floating gate 22.

Accordingly, in a nonvolatile memory,
The floating gate 22 needs to be insulated so that electrons do not inadvertently enter or leave the floating gate 22.
For this reason, when manufacturing a nonvolatile memory, after forming the gate structure 28 shown in FIG. 3A, this was heat-treated in an oxygen atmosphere. By this heat treatment, as shown in FIG. 3B, a silicon oxide film 40 derived from polysilicon is formed on the surface of the floating gate 22, and functions as an insulating film.

[0007]

However, the conventional method for manufacturing a semiconductor memory device as described above has the following problems.

The thermal oxidation of the polysilicon constituting the floating gate 22 and the control gate 26 is difficult to proceed in a portion near the gate oxide film 14 and the inter-gate insulating film 24. Therefore, the silicon oxide film 40 is formed near these films. It was thin. For this reason, at a fine level, the electrons held in the floating gate 22 escape from the thin portion of the silicon oxide film 40 (on the side of the gate oxide film 14) to the silicon substrate 2, and the data holding capability (retention) of the memory element is reduced. ).

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a semiconductor memory device which can solve the above-mentioned problems, improve the insulation of a floating gate, and improve the data retention ability.

[0010]

Method of manufacturing SUMMARY OF THE INVENTION The semiconductor memory device according to claim 1, the vapor deposition to the gate structure on the surface
Thermal oxidation after forming the first surface oxide film
The floating gate on the surface of the gate structure
Second surface oxide film formed child fine Control Rugate
And features.

According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor storage device.
The first surface oxide film is made of TEOS (tetraethoxy
(Silane) as a raw material .

[0012]

[0013]

According to the manufacturing method of the first aspect, the surface of the gate structure
After forming the first surface oxide film by vapor phase growth method,
Float on the gate structure surface by thermal oxidation
Second surface acid Ingugeto and Control Rugate
An oxide film is formed. As a result, an oxide film having higher insulating properties is formed.

According to a second aspect of the present invention, the first surface is provided.
The oxide film is made of TEOS (tetraethoxysilane)
It is formed as. Thereby, the gate structure surface
The above first surface oxide film is more uniformly formed due to the excellent coverage of TEOS.

[0015]

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a semiconductor memory device according to one embodiment of the present invention will be described with reference to the drawings. As a semiconductor memory device having a floating gate, E ² PR
OM shall be manufactured.

First, as shown in FIG. 1A, a p-type silicon substrate 2 is oxidized to form a silicon oxide film 4 on the upper surface.
After element isolation is performed by the LOCOS (Local Oxidation of Silicon) method to form the element isolation region 10 and the element formation region 12 in FIG. 1B, boron ions are ion-implanted to adjust the channel concentration (channel ion implantation). . Next, the surface of the element formation region 12 is heat-treated to form a gate oxide film. In order to form an electrode, polysilicon as a material of a floating gate is deposited on the entire surface of the structure to form a first polysilicon layer 16.

Further, an ONO film 18 as an inter-gate insulating film is formed on the surface of the first polysilicon layer 16, and polysilicon as a control gate material is deposited on the entire surface of the structure on the ONO film 18. As a second polysilicon layer 20, the structure shown in FIG. 1C is obtained.

Next, a resist is applied on the second polysilicon layer 20 and patterned into a shape of a gate electrode. Etching is performed using the resist as a mask, and as shown in FIG.
22, a gate structure 28 comprising an ONO film inter-gate insulating film 24 and a control gate 26 made of a second polysilicon layer is obtained.

A surface oxide film is formed on the surface of the apparatus shown in FIG. 2A by a vapor phase growth method. The vapor phase growth is LP-CVD
The reaction is performed at 700 ° C. using an apparatus, and TEOS (tetraethoxysilane) is introduced at 80 ml / min using N ₂ as a carrier gas. As a result, as shown in FIG. 2B, a surface oxide film 30 as a first silicon oxide film is formed with a thickness of 300 Å on the entire surface of the device.

Thereafter, the apparatus shown in FIG. 2B is heat-treated in an oxygen atmosphere. This heat treatment allows the floating gate 22
A silicon oxide film 32 (second silicon oxide film) formed by oxidizing polysilicon as a gate material is formed on the side surface of the control gate 26 on the side of the surface oxide film 30 (FIG. 2C).

In this state, after forming a source and a drain in the element forming region 12, an interlayer film is provided, an Al wiring is formed, and a memory element is obtained by covering with an passivation film.

In this embodiment, an E ² PROM is manufactured as a semiconductor memory device having a floating gate, but another semiconductor memory device may be manufactured.

In this embodiment, the vapor phase growth method for forming a surface oxide film is performed at 700 ° C. using TEOS with N ₂ as a carrier gas, but may be performed under other conditions. .

[0025]

According to the manufacturing method of the first aspect, the gate structure
Forming a first surface oxide film on the surface by vapor phase epitaxy
After that, thermal oxidation is performed to remove the gate structure surface.
Low coating gates and Control Rugate second
Since a surface oxide film is formed, an oxide film having higher insulating properties is formed. Therefore, the insulating property of the floating gate is improved, and the data holding ability of the memory element can be further improved.

In the manufacturing method according to claim 2, the first surface
The oxide film is made of TEOS (tetraethoxysilane)
The first table on the gate structure surface is formed as
The surface oxide film is more uniformly formed by the excellent coverage of TEOS. Therefore, the insulating property of the floating gate is further improved, and the data holding ability of the memory element can be further improved.

[0027]

[Brief description of the drawings]

FIG. 1 is a diagram showing a method of manufacturing a semiconductor memory device according to one embodiment of the present invention.

FIG. 2 is another diagram showing the method of manufacturing the semiconductor memory device according to one embodiment of the present invention;

FIG. 3 is a diagram showing a method of manufacturing a semiconductor memory device according to a conventional method.

[Explanation of symbols]

 22 ... Floating gate 24 ... Inter-gate insulating film 26 ... Control gate 30 ... Surface oxide film 32 ... Silicon oxide film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/8247 H01L 21/316 H01L 29/788 H01L 29/792 H01L 29/43

Claims (2)

(57) [Claims] A floating gate;
Insulating film formed on a floating gate and the interlayer insulating film
Gate and a Control Rugate formed on the film
A method for manufacturing a semiconductor memory device having a structure, comprising: forming a first surface acid on a surface of a gate structure by vapor phase epitaxy;
After forming the oxide film, thermal oxidation is performed to form the gate structure.
Floating gate and control gate on the surface of the structure
Forming a second surface oxide film on the substrate . 2. A method for manufacturing a semiconductor memory device according to claim 1, wherein
And the first surface oxide film is made of TEOS (tetraethoxy
Silane) as a raw material .