JPH1154635A - Manufacturing method of flash memory - Google Patents

Abstract

(57) [Problem] To provide a method of manufacturing a flash memory capable of preventing a step from being generated between a floating electrode and a control electrode and avoiding deterioration of transistor characteristics. SOLUTION: When forming a control electrode 14a by etching a polysilicon film, the cross-sectional shape of the control electrode 14a is made trapezoidal, for example, by increasing the pressure of an etching gas. Thereafter, a protective film 16 made of a silicon oxide film is formed on the side surface of the control electrode 14a, the interlayer insulating film 13 is etched using the control electrode 14a as a mask, and the polysilicon film 12 is further etched to form a floating electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a flash memory having a floating electrode and a control electrode, and more particularly to a method of manufacturing a flash memory in which a floating electrode is formed in a self-aligned manner with respect to a control electrode.

[0002]

2. Description of the Related Art FIGS. 5 to 6 are sectional views showing a conventional method of manufacturing a flash memory in the order of steps. First, FIG.
As shown in FIG. 1A, a gate insulating film 21 is formed on a semiconductor substrate 20 to a thickness of about 100.degree.
A polysilicon film 22 is formed to a thickness of about 1300.degree. Next, an interlayer insulating film (ON
An O film 23 is formed to a thickness of about 300 °, and a polysilicon film 24 is formed on the interlayer insulating film 23 to a thickness of about 1500 °. Then, a photoresist film 25 having a thickness of about 0.76 μm is formed on the polysilicon film 24, and the photoresist film 25 is exposed and developed to be patterned into a predetermined control electrode shape.

Next, as shown in FIG. 5B, a control electrode 24a is formed by plasma etching the polysilicon film 24 using the resist film 25 as a mask. After that, the resist film 25 is removed. Next, as shown in FIG. 6A, the interlayer insulating film 23 is etched using the control electrode 24a as a mask to partially expose the polysilicon film 22. Next, as shown in FIG. 6B, the polysilicon film 22 is etched by changing the etching gas to form the floating electrode 22a in a self-aligned manner with the control electrode 24a.

Next, the control electrode 24a and the floating electrode 22
Using a as a mask, impurities are ion-implanted at a high concentration into the surface layer of the semiconductor substrate 20 to form source / drain regions (not shown).
Is formed in a self-aligned manner with respect to the control electrode 24a and the floating electrode 22a. After that, an insulating film, a wiring (neither is shown) or the like covering these control electrode 24a and floating electrode 22a is formed. Thus, the flash memory is completed.

[0005]

However, the above-described conventional method of manufacturing a flash memory has the following problems. That is, the floating electrode 24a is
It is formed in a self-aligned manner with respect to a. In the etching step for forming the floating electrode 22a, the control electrode 24a
Is side-etched, and as shown in FIG. 7, the width of the control electrode 24a becomes narrower than the width of the floating electrode 22a. Then, when the source / drain regions 27 are formed by ion-implanting impurities into the surface layer of the substrate 20, the impurity ions penetrate the floating electrode 22 a and enter the gate insulating film 21 below the floating electrode 22 a or the semiconductor substrate 20. It is injected into the surface layer and damages the gate insulating film 21 and the surface layer of the substrate 20. Since the damage given to this portion is difficult to recover, the characteristics of the transistor are significantly deteriorated.

An object of the present invention is to provide a method of manufacturing a flash memory which can prevent a step from occurring between a floating electrode and a control electrode and can avoid deterioration of transistor characteristics.

[0007]

The object of the present invention is to form a gate insulating film, a first conductive film, an interlayer insulating film and a second conductive film on a semiconductor substrate in order, Patterning the conductive film, forming a control electrode having a trapezoidal cross-sectional shape, covering the side surface of the control electrode with a protective film, and etching the interlayer insulating film using the control electrode as a mask, Forming a floating electrode by etching the first conductive film using the control electrode as a mask.

Hereinafter, the operation of the present invention will be described. FIG. 1 is a schematic diagram showing the principle of the present invention. In the present invention, first, the gate insulating film 1 and the first
After sequentially forming the conductive film 2, the interlayer insulating film 3, and the second conductive film, the control electrode 4a is formed by patterning the second conductive film. Thereafter, a protective film 6 made of a silicon oxide film, a silicon nitride film, a resist or the like is formed on the side surface of the control electrode 4a. The protective film 6 prevents the control electrode 4a from being side-etched at the time of etching when forming the floating electrode, and prevents a step from occurring between the control electrode 4a and the floating electrode.

If the cross-sectional shape of the control electrode is rectangular, the width of the floating electrode is wider than the width of the control electrode by the thickness of the protective film, and a step is generated between the control electrode and the floating electrode. Resulting in. However, as shown in FIG. 1A, the cross-sectional shape of the control electrode 4a is trapezoidal (a forward tapered shape), and the side surface of the trapezoidal control electrode 4a is
As shown in FIG. 1B, when the first conductor film 2 is etched, the protective film 6 is etched and the film thickness is reduced. The film thickness becomes thin. Thereby, the step between the control electrode 4a and the floating electrode is reduced. Therefore, in the present invention, the cross-sectional shape of the control electrode is trapezoidal.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 2 to 4 are sectional views showing a method of manufacturing a flash memory according to an embodiment of the present invention in the order of steps. First, as shown in FIG.
A gate insulating film 11 is formed on semiconductor substrate 10 to a thickness of about 1000 °, and a polysilicon film 12 is formed on gate oxide film 11 to a thickness of about 1300 °. Thereafter, an interlayer insulating film (ONO film) 13 is formed on the polysilicon film 12 by about 3
It is formed to a thickness of 00 °. Then, the interlayer insulating film 13
A polysilicon film 14 is formed thereon to a thickness of about 1500 °.

Next, a photoresist film 15 is formed on the polysilicon film 14, and this photoresist film 15 is exposed and developed to be patterned into a predetermined control electrode shape. Next, the polysilicon film 14 is dry-etched using the resist film 15 as a mask, and FIG.
The control electrode 14a is formed as shown in FIG. The etching at this time uses, for example, a parallel plate reactor,
The process is performed under the conditions that the F power is 250 W, the pressure is 140 mTorr, the etching gas is HBr, and the gas flow rate is 100 sccm. Generally, when the pressure of the etching gas is increased during the etching of the polysilicon film, the cross section becomes trapezoidal (forward tapered). Further, when the exposure amount at the pattern edge is changed stepwise or continuously when exposing the photoresist film 15, the cross-sectional shape of the developed photoresist film 15 becomes trapezoidal. By etching the polysilicon film 14 using the trapezoidal resist film 15 as a mask, the control electrode 14a can be formed in a trapezoidal shape.

The angle of the side wall of the control electrode 14a is preferably 87 to 88 degrees with respect to the surface of the substrate 10. After forming the control electrode 14a in this way, the resist film 15 is removed.

Next, as shown in FIG. 3A, the interlayer insulating film 13 is etched. The etching at this time uses, for example, a parallel plate reactor, and the RF power is 10
0 W, pressure 70 mTorr, gas CF ₄ , flow rate 120
This is performed under the condition of sccm. Next, the substrate 11 is placed in a vertical diffusion furnace and held at a temperature of about 800 ° C. for 25 minutes (dry oxidation). As a result, as shown in FIG. 3B, the surface of the control electrode 14a is oxidized to form a protective film 16 made of a silicon oxide film having a thickness of about 200 °.

Next, as shown in FIG.
The polysilicon film 12 is etched using the oxide film 16a and the surrounding oxide film 16 as a mask to form the floating electrode 12a in self-alignment with the control electrode 14a. Etching conditions at this time are, for example, using a parallel plate reactor, RF power is 250 W, pressure is 140 mTorr, etching gas is HBr, and gas flow rate is 100 sccm. During this etching, the control electrode 14a is protected by the oxide film 16, and the width of the control electrode 14a is prevented from being reduced by side etching. Further, when the polysilicon film 12 is etched, the protective film 16 is also slightly etched, and in particular, the lower portion of the protective film 16 is thinned by the etching.
The formation of a step between the control electrode 14a and the floating electrode 12a is suppressed (see FIG. 1).

Thereafter, the control electrode 14a and the floating electrode 12
Impurities are ion-implanted into the surface layer of the substrate 10 using a as a mask to form source / drain regions (not shown). Then, after forming an insulating film on the entire surface, selectively forming a contact hole in the insulating film, and forming a conductor film on the entire surface,
Conductor film patterning and wiring (none shown)
To form Thus, a flash memory is manufactured.

In the present embodiment, the control electrode 14a
When the polysilicon film 12 is etched using the mask as a mask, since the surface of the control electrode 14a is covered with the protective film 16 made of a silicon oxide film, the control electrode 14a is protected from plasma when the polysilicon film 12 is etched. Is done. Accordingly, side etching of the control electrode 14a is prevented, and generation of a step between the control electrode 14a and the floating electrode 12a is avoided. Therefore, the floating electrode 1
Damage due to impurity ions is avoided in the portion of the gate insulating film 11 and the substrate 10 below 2a, particularly in the portion between the source and the drain in the surface layer of the semiconductor substrate, and the effect of preventing deterioration of transistor characteristics is obtained. Can be

In the above embodiment, the control electrode 14
A silicon oxide film was formed on the side surface of a to form a protective film.
The protective film may be formed by a silicon nitride film or a resist coating film. The protective film made of a silicon oxide film or a silicon nitride film is formed by plasma CVD (Chemic).
al Vapor Deposition) method. For example, a protective film made of a silicon nitride film is SiH ₂ Cl ₂
+8 NH ₃ gas, the substrate was reduced to 8
It can be formed by holding at a temperature of 00 ° C. for 5 minutes.
When a protective film is formed by a resist coating method, about 2 cc of a resist is dropped on a substrate,
Spin coating is performed at a rotation speed of 0 rpm. In this case, the resist film is made of persulfuric acid (H ₂ O ₂ + H ₂ S) after the formation of the floating electrode.
O ₄ ).

[0018]

As described above, according to the present invention,
The control electrode is formed in a trapezoidal cross-section, and after covering the side surface of the control electrode with a protective film, the first conductive film is etched to form a floating electrode. It can be avoided that a step is formed between the control electrode and the floating electrode due to the etching. Accordingly, it is possible to prevent the gate insulating film below the floating electrode and the surface layer of the substrate from being damaged by impurities, and it is possible to avoid deterioration of transistor characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the principle of the present invention.

FIG. 2 is a cross-sectional view (part 1) illustrating a method of manufacturing the flash memory according to the embodiment of the present invention in the order of steps.

FIG. 3 is a sectional view (part 2) illustrating a method for manufacturing the flash memory according to the embodiment of the present invention in the order of steps.

FIG. 4 is a cross-sectional view (No. 3) illustrating the method of manufacturing the flash memory according to the embodiment of the present invention in the order of steps.

FIG. 5 is a cross-sectional view (part 1) illustrating a conventional method of manufacturing a flash memory in the order of steps;

FIG. 6 is a sectional view (part 2) showing a conventional method of manufacturing a flash memory in the order of steps;

FIG. 7 is a schematic sectional view showing a conventional problem.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gate insulating film 2 1st conductor film 3,13,23 Interlayer insulating film 4a, 14a, 24a Control electrode 6,16 Protective film 10,20 Semiconductor substrate 11,21 Gate insulating film 12,14,22,24 Poly Silicon film 12a, 22a Floating electrode 15 Resist film

Claims (5)

[Claims] A step of sequentially forming a gate insulating film, a first conductive film, an interlayer insulating film and a second conductive film on a semiconductor substrate; and patterning the second conductive film to form a cross-sectional shape. Forming a trapezoidal control electrode; coating a side surface of the control electrode with a protective film; etching the interlayer insulating film using the control electrode as a mask; and forming the first electrode using the control electrode as a mask. Forming a floating electrode by etching the conductive film. 2. The method according to claim 1, wherein the protection film is formed by thermally oxidizing a surface of the control electrode.
3. The method for manufacturing a flash memory according to claim 1. 3. The method according to claim 1, wherein the protection film is formed of a silicon nitride film. 4. The method according to claim 1, wherein the protection film is formed by applying a resist. 5. The method according to claim 1, wherein the protection film is formed by a CVD method.