JPS62230059A - Formation of semiconductor storage device - Google Patents

Abstract

PURPOSE:To prevent rewriting number from decreasing due to the generation of a recombination unit in a region where a stress concentration feasibly occurs by forming a trap layer TL as a gate insulating film and a dielectric film of the lower side of the layer TL by an optical CVD method. CONSTITUTION:A P10 channel forming region is formed on a substrate 1 in an N-channel IGF. A first dielectric film 3-1 is made of a silicon nitride film, and its average thickness is 300Angstrom . Further, a TL 3-2 formed on the film is formed to have 30-2000Angstrom of average thickness such as 100Angstrom by the optochemical reaction of a silicon semiconductor. Moreover, the upper surface is formed to have 500-1000Angstrom of thickness of a second dielectric film 3 by an optical CVD method. Then, a gate electrode 6 is formed, and then a source 7 and a drain 8 are formed by a self-aligning method of an N-type low impurity density region 7-1 and an N<-> type high impurity density region 7-2. Thus, rewriting number can be increased by 10<2>-10<3> times as large as conventional IGF.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to an insulated gate field effect semiconductor memory device (I
The present invention relates to a manufacturing method for forming a first dielectric film constituting a gate insulating film and a charge trapping center above the dielectric film by a CVO method using a photochemical reaction (referred to as GF).

"Conventional technology" When trying to create non-volatile memory using IGF, MNO
S (gate electrode-silicon nitride silicon monoxide-silicon semiconductor substrate), MMCO3 (gate electrode-silicon nitride film-semiconductor cluster or film-silicon oxide film-silicon semiconductor substrate), MNCNOS (gate electrode-silicon nitride film'- Many substrates are known, such as clusters or films of semiconductors (silicon nitride, silicon monoxide, silicon semiconductor substrates). Furthermore, a method is known in which a thin silicon oxide film is formed on this silicon semiconductor using a hydrochloric acid oxidation method that causes less deterioration. Typical examples thereof include the inventor's patent [Semiconductor Memory Device, Japanese Patent Publication No. 50-36955J, and the inventor's paper Ceramic Bulletin Vol. 164.
No. 12 (1985) 1585-1589 rMe
tal-Insulator-3emiconduct
or (Fulrath Award Paper)j.

``Problems to be Solved by the Invention'' However, there has been a demand for an improvement in the number of rewrites of such nonvolatile memories for the purpose of application to IC cards. However, this number of rewrites is lXIO3~3Xl
Up to O" times, and no means have been found so far to increase the number beyond that. However, for IC cards etc.
It was required to be able to be rewritten more than 'times.

“Good” if the rate of change from the initial value is within 10%
Based on this standard, a known method for increasing the number of rewrites is to transform a silicon oxide film in close contact with a semiconductor substrate into silicon nitride in ammonia at a high temperature of 1150 to 1200°C. Alternatively, a silicon nitride film of 20 to 100% can be formed by directly nitriding the semiconductor substrate itself at a similar temperature.
A method of forming it to the thickness of a person is known. Then, by using this silicon nitride, MMCNO3, MNCNS
structure can be obtained.

However, such high-temperature treatment induces stacking faults in the junctions provided in the substrate and promotes re-diffusion of impurities, resulting in deterioration of the substrate material and
It must be said that this is insufficient.

In order to solve these problems, the present invention uses a photo-CVD method to form a stable first dielectric film that does not cause any damage to the underlying silicon oxide film or silicon semiconductor substrate. It was forced upon me. Furthermore, this first dielectric film has a 10 to 5
Since it is extremely thin, the charge trapping center layer (hereinafter referred to as trap layer, TL) is further laminated on top of this layer.
) is also intended to be formed by the photo-CVD method. Then, by forming a second dielectric film on this by a plasma CVD method, a photo CVD method, etc., preferably a photo CVD method, MIzTLI+S (gate electrode - second dielectric film) is formed.
The present invention aims to obtain a structure (dielectric film-charge trapping center layer-first dielectric film-semiconductor substrate). And ItTLh
A floating charge trapping center layer (hereinafter referred to as FTL) is obtained by the laminated structure. Further, this TL is made of a cluster or thin film of a semiconductor such as a silicon semiconductor, or a layer having a semiconductor dangling bond. In particular, the first dielectric film is made of silicon nitride, and these are coated on a semiconductor substrate or on a blocking layer previously formed on this semiconductor, such as a two-layer film (I , -TL).

"Function" By making this first dielectric film and TL using the optical CVO method, the formation temperature can be reduced to 700°C or less, generally 300 to 300°C.
The temperature can be set at 500° C., and a nitride having no silicon clusters in the formed film and having almost no dangling bonds stoichiometrically can be produced.

In addition, since the first dielectric film is a high-quality insulating film that does not damage the underlying substrate or the bonding provided inside it, and is made at low temperatures, no residual strain is imparted to the interface with the semiconductor substrate. . As a result, it is possible to prevent a decrease in the number of write operations due to the generation of recombination portions in areas where such stress concentration is likely to occur.

Because of these characteristics, it has become possible to withstand up to 10 hours of rewriting. Furthermore, such a stacked structure is a short channel MIS with a channel length of 1μ or less.
, Fl! Even in T, patterning of VLSI can be handled without any problems.

Example 1 FIG. 1 shows a longitudinal cross-sectional view of the IGF of the present invention.

In the drawing: substrate (1), field insulator (2).

First dielectric film (3-1>, TL (3-2),
It has an FTL (3) made of a second dielectric film (3-3) as a gate insulator.

Gate electrode (6), source (7), drain (7”),
It consists of a channel cut (9) and a channel forming region (10).

The drawing shows an N-channel IGF with P(1) on the substrate (1).
0), and the channel length is 1.5μ.
The channel width was 10μ. The gate electrode was made of titanium silicide. The first dielectric film (3-1) is made of a silicon nitride film,
Its average thickness had 30 people. Before forming silicon nitride using this photo-CVD method, the substrate is held at a temperature of 300 to 500°.
In an oxygen or ammonia atmosphere, ultraviolet light with a wavelength of 185 nm is irradiated to remove organic matter and other contaminants from the surface, and an extremely thin silicon oxide film or silicon nitride film is formed by solid-vapor phase oxidation or nitridation. It may also be used as a blocking layer.

Furthermore, the TL (3-2) above it is made of silicon semiconductor with an average thickness of 30 to 2000, for example, 100 by photochemical reaction.
Formed to the thickness of a person. Furthermore, the upper surface is coated with a second dielectric film (3
) was formed to a thickness of 500 to 1000 layers by photo-CVD. Next, a gate electrode is formed, and then a source (
7), the drain (8) is connected to the N-type low impurity concentration region (7-1
) and N-type lower impurity concentration region 7-2) were fabricated by the self-line method.

In such a structure, the gate voltage is set to ±25V by 100μ.
The pulse width of seconds was repeatedly rewritten. As a result, a threshold voltage of ±7v could be obtained. Even when the value was repeated 1×10 h, there was only a rate of change of about 7χ from the initial value, and the rewriting life was 10'' to 10' times longer than that of the conventional IGF.

Example 2 The silicon nitride film of the present invention (
Details of the fabrication of SiJ4) and Si clusters or films are described.

In FIG. 2, a silicon substrate (1) having a surface to be formed
is held in a holder (1') and provided close to a halogen heater (13) (the top surface of which is water-cooled (31)) in the reaction chamber (12). The reaction chamber (12), the light source chamber (35) in which the ultraviolet light source was disposed, and the heating chamber (30) in which the heater (13) was disposed were maintained at approximately the same degree of vacuum of 10 torr or less. . For this purpose, a gas (nitrogen, argon or ammonia) that does not interfere with the reaction (28
This was achieved by supplying air to (36) from ) or exhausting air from (36'').Also, the light source chamber (35) and reaction chamber (12) were There is a nozzle (3) on the upper side of this window (40).
4), and this nozzle is equipped with ammonia (NHi) used in the photo-CVD method and nitrogen fluoride (NHi) used in plasma etching.
The nozzle (34°) for NF3) is oriented downward (facing the window) (32) for 5i2H used in the production of 5iJ4.
b+5iJb+5i3H, the nozzle (34°) has its ejection port facing upward (towards the substrate) (33).

This nozzle (34) uses a high frequency power source (15) (frequency: 13.56 MHz) to remove unnecessary materials formed on the window (40) by plasma etching after forming a film by photo-CVD. ) is one of the electrodes.

A heater (29) was provided to prevent reactive gas from entering the light source chamber due to backflow when the light source chamber was evacuated.

This traps the components of the reactive gas that become solid after decomposition, allowing only the gas to enter.

Regarding movement, a load-lock system was used to prevent pressure differences from occurring. First, the board (1) is placed in the preliminary room (14).
, holder (1゛), board and board support (1")
(to efficiently conduct heat to the substrate), and after evacuating, open the gate valve (16) and open the reaction chamber (
12), and the gate valve (16) was closed to partition the reaction chamber (12) and preliminary chamber (14) from each other.

The doping system (37) includes a valve (22), a flow meter (
21), the reactive gas forming the solid product after the reaction was supplied to the reaction chamber (12) from (23) i (24), and the reaction gaseous products were supplied from (25) and (26) to the reaction chamber (12). . The pressure in the reaction chamber is controlled using a control valve (
17), a turbo molecular pump (PG550 manufactured by Osaka Vacuum Co., Ltd. was used) (1B), and a rotary pump (19) for exhaustion.

The exhaust system (38) is connected to the preliminary chamber (14) by the cock (20).
When vacuuming the chamber, open that side and open the reaction chamber (12
) side is closed. Furthermore, when evacuating the reaction chamber, the reaction chamber was opened and the preliminary chamber side was closed.

Then, the substrate was inserted into the reaction chamber as shown.

The degree of vacuum in this reaction chamber was set to 10-' torr or less. Thereafter, nitrogen was introduced from (28) and a reactive gas was further introduced into the reaction chamber from (37) to form a film.

The light source for the reaction was a low-pressure mercury lamp (34), water-cooled (31”).
has been established. The ultraviolet light source is a low-pressure mercury lamp (185 nm).

There are 16 lamps (luminous length: 40 cm, irradiation intensity: 15 mW/cm", lamp power: 40 W) that emit light at a wavelength of 254 nm.

This ultraviolet light passes through quartz (40), which is a transparent shielding plate, and irradiates onto the formation surface (1) of the substrate (1) in the reaction chamber (12).

The heater (13) was of the "deposition up" type and was located above the reaction chamber to avoid flakes from adhering to the surface to be formed and causing pinholes.

The reaction chamber is made of stainless steel, and both the light source chamber and heating chamber (30) are evacuated to maintain a pressure difference of 10 torr.
The following was made. As a result, the present invention does not have the disadvantage of not being able to withstand pressure when the area of the quartz plate is increased for irradiation of a large area, as shown in the conventional example. That is, the ultraviolet light source is also kept under vacuum in a stainless steel container surrounding a light source chamber and a reaction chamber that are kept under vacuum. For this reason, 5
inch or 6 inch wafer size instead of 30
Substrates as large as cm x 3 ocm can also be produced without any industrial problems.

In the case of the drawing, the effective area to be formed is 30cm x 30cr
a, and five boards (1) with a diameter of 5 inches are placed in a holder (1).
The substrate was heated by a halogen heater (13) to a predetermined temperature ranging from room temperature to 500°C.

An experimental example of FTL is shown below. Experimental example Si2H6,5
izF6 or St 38B was connected to (23) and 3cc
/min. 30cc/ of ammonia from (25)
Supplied in minutes. Then, they receive 185 nm light from the ultraviolet light source (34) and are photolyzed without using mercury, reacting with ammonia, and forming Si, N, and a coating on the surface of the substrate (1). Ta. That is, after processing the underlying semiconductor or the exposed semiconductor surface as shown in FIG. 1, silicon nitride could be formed thereon to a thickness of 20 to 200, typically 30 to 50. .

Further, the entire structure was evacuated to form a TL thereon.

Next, 5izH was supplied from (23) at 5 cc/min. Then, 5izH6 decomposes without using mercury in the light source chamber and forms silicon semiconductor clusters (average film thickness 3o~1
00 people, silicon is formed in island shapes, forming a cluster structure). Or the average thickness is 200~
It becomes a membranous state with 2,000 people. It is also possible to obtain a mixture of 100 to 200 people. A semiconductor formation rate of 6 persons/min (pressure: 3 torr, temperature: 350° C.) was achieved. In this way, the TL (FIG. 1 (3-2)) was formed.

Since this semiconductor has a high absorption of ultraviolet light, a second dielectric film (
In order to form Figure 1 (3-2)), plasma CVD is used.
It must be formed by law. For this, NH3/5
It is sufficient to set itHb≧50 and apply high frequency plasma of 13.56 MHz to form a predetermined thickness.

□Thereafter, as shown in Example 1, IGF was prepared using this FTL.

After film formation, regarding the optical CVO device shown in FIG.
Plasma etching of window (40) from (26) with NF3
was supplied to perform a plasma reaction. The window (4o) is thus cleaned and the second FTL formation operation can be performed.

Even if this FTL formation was repeated 10 times, the same film thickness could be obtained under the same conditions.

r effect" As is clear from the above description, in the present invention, the TL as a gate insulating film and the first dielectric film below it (on the substrate side) are formed using a photo-CVD method.

As a result, there was little damage to the substrate, and the TL could be formed at a predetermined distance from the semiconductor surface. In particular, even though such a silicon nitride film is formed at a temperature of 300 to 500° C., the 5i-N bonds are not broken, so it has the great advantage that no deterioration occurs due to rewriting.

Further, in the present invention, when the channel forming region is made of silicon, a two-layer film of silicon oxide and a nitride film is excellent as the gate insulator. However, in the case of m-v compounds such as GaAs and InP, these semiconductors and silicon oxide react and deteriorate during high-temperature operation tests, so it was preferable to use only Si+Na. That is, Si3N may be directly brought into close contact with the semiconductor to form a gate electrode structure.

The dielectric strength voltage of the insulating film is 3.3.
5.times.10'V/cm had a breakdown voltage 3.5 times higher than I.times.106V/cm of silicon nitride produced by plasma CVD.

Furthermore, even if a voltage corresponding to an electric field of ±3X10'ν/cn+ is applied, the change in threshold voltage is ±0°2ν.
I only drifted within the following range.

From this, if such a silicon nitride film is used as the first dielectric film between the semiconductor substrate and the TL, dangling bonds will not occur as a result of rewriting information, and 10' or more You can expect more rewrites.

The present invention utilizes the fact that such a high quality silicon nitride film can be produced by the 1cvo method.

In addition, in order not to damage the silicon nitride film, the TL on top of it is also formed by photo-CVD. As described above, the method of the present invention has achieved 106 things that were previously impossible.
For the first time, it has become possible to rewrite data twice or more.

In the experimental example described above, an excimer laser (wavelength: 100 to 400 nm) was used as the light source for optical CVD, instead of a low-pressure mercury lamp.
m) It goes without saying that an argon laser, a nitrogen laser, etc. may also be used.

[Brief explanation of drawings]

FIG. 1 shows an insulated gate field effect semiconductor device of the present invention. FIG. 2 shows a CVO device using the present invention.

Claims (1)

[Claims] 1. In a floating charge trapping center layer provided by laminating a first dielectric film, a charge trapping center layer, and a second dielectric film as a gate insulating film in an insulated gate field effect semiconductor memory device. A method for manufacturing a semiconductor memory device, comprising forming a first dielectric film and a charge trapping center layer by a photovapor phase reaction method. 2. A method for manufacturing a semiconductor memory device according to claim 1, characterized in that a blocking layer is formed on a semiconductor substrate, and a floating charge trapping center layer is formed on the blocking layer. 3. The method of manufacturing a semiconductor memory device according to claim 1, wherein the first dielectric film is made of silicon nitride. 4. A method for manufacturing a semiconductor memory device according to claim 1, wherein the charge trapping center layer is a layer made of a semiconductor thin film or cluster, or a layer containing semiconductor dangling bonds.