JPS61287274A - Manufacture of semicondutor memory device - Google Patents

Abstract

PURPOSE:To prevent a memory retaining characteristic from deteriorating by forming an Si oxide film on an Si nitride film, and then forming the second Si nitride film by a vapor-phase growing method based on a plasma exciting reaction of Si compound and ammonia. CONSTITUTION:Source and drain regions 2, 3 are formed on an N-type Si substrate 1, an Si dioxide film 4 is formed, and a hole is then opened. Then, an extremely thin Si dioxide film 5 of a gate insulating film is formed in the hole. Thereafter, after the first Si nitride film 6 is formed on the film 5, the film 6 is thermally oxidized to form an Si dioxide film 7. Subsequently, after a contacting hole is formed, a gate electrode 8 is formed. Thereafter, a plasma Si nitride film 9 is formed by a plasma vapor-phase growing method of silane gas and ammonia gas. Then, a protective film 10 is formed to manufacture a P-channel aluminum gate MONOS type semiconductor memory device. A semiconductor memory device of excellent memory retaining characteristic with less memory characteristic deterioration can be obtained by the above manufacturing method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to non-volatile performance, particularly memory retention, in a semiconductor memory device comprising a MONO8 (metal-silicon oxide film-silicon nitride film-silicon oxide film-semiconductor) type field effect transistor. The present invention relates to a method of manufacturing a high performance semiconductor memory device with excellent characteristics.

BACKGROUND OF THE INVENTION Conventionally, as a type of semiconductor memory device, a MNOS (metal-silicon nitride film-silicon oxide film-semiconductor) structure, in which a silicon nitride film is grown on a thin silicon dioxide film and a metal electrode is formed on top of the silicon nitride film, has been used. Non-volatile storage devices are well known. In recent years, in order to reduce the programming voltage of this MNO3 type semiconductor memory device, the silicon nitride film of the gate insulating film is thinned and at the same time thermal oxidation is performed on the silicon nitride film. MONO8 with a silicon oxide film formed on the film (metal - silicon oxide film - silicon nitride film - silicon oxide film - semiconductor)
A semiconductor memory device with this structure has been put into practical use.

Problems to be Solved by the Invention In the manufacturing method of the MONO9 semiconductor memory device described above, a high temperature of 900° C. or higher is usually required when thermally oxidizing a silicon nitride film to form silicon oxide. This causes a change in the film quality of the silicon nitride film, resulting in a problem of deterioration of memory characteristics, particularly memory retention characteristics.

N0NO8 type semiconductor memory devices are similar to conventional MNOS type semiconductor memory devices in that ultra-thin oxide film is applied from the semiconductor side to traps distributed at the interface between a silicon nitride film and an ultra-thin silicon oxide film, or in the bulk of the silicon nitride film. The tunneling injection of charge through the silicon film and its accumulation change the threshold voltage (vth) of the transistor, thereby storing information. Therefore, ensuring the memory retention characteristics is the biggest challenge, and the deterioration of the memory retention characteristics when thermally oxidizing the silicon nitride film is the biggest practical problem.

The purpose of the present invention was made in view of such problems, and
The present invention provides a manufacturing method for realizing a high-performance semiconductor memory device comprising MONO3 type field effect transistors, which has excellent non-volatile performance, particularly excellent memory retention characteristics.

Means for Solving the Problems In order to achieve the above object, the present invention provides a method of forming a second silicon oxide film on a silicon nitride film, and then forming a gas based on a plasma-excited reaction between a silicon compound such as silane and ammonia. This method is characterized in that the second silicon nitride film is formed by a phase growth method.

Functional experiments have shown that the deterioration of memory retention characteristics caused by high-temperature heat treatment after forming a silicon nitride film, which is a gate insulating film, strongly depends on the formation conditions of the silicon nitride film. It has become clear that memory retention characteristics deteriorate when heat treatment is performed at a temperature higher than that temperature.

In addition, after forming the second silicon oxide film, which is the gate insulating film, a second silicon nitride film is formed using a vapor phase growth method based on a plasma-excited reaction between a silicon compound such as silane gas and ammonia gas, thereby improving memory characteristics. It was discovered that excellent memory retention characteristics with little deterioration could be obtained, and furthermore, it was discovered that further effects can be obtained by performing heat treatment at a temperature higher than the formation temperature after forming the second silicon nitride film. .

Example Hereinafter, specific examples will be described using the drawings.

FIGS. 1A to 1C are diagrams showing a cross-sectional structure of a semiconductor device in order of steps in an embodiment of the manufacturing method of the present invention.

In FIG. 1d, a source region 2 and a drain region 3 are formed on an N-type silicon substrate 1 using a thermal oxidation technique and an impurity selective diffusion technique, and a silicon dioxide film 4 is formed using a thermal oxidation technique. , holes are formed in predetermined portions using phosphorography and etching techniques. Next, an extremely thin silicon dioxide film 5 serving as a gate insulating film is formed in this opening.

In this example, the thickness of the extremely thin silicon dioxide film serving as the tunneling medium was set to about 20 people.

Next, as shown in FIG. 1, the silicon dioxide film 6 is
After a first silicon nitride film 6 is formed thereon using a vapor growth technique, the silicon nitride film 6 is thermally oxidized to form a silicon dioxide film 7. In this embodiment, the silicon nitride film 6
The formation of silane (SiH) gas and ammonia (NH
3) Using a low-pressure vapor phase growth method that utilizes chemical reactions with gas,
It was applied under the conditions of SOO℃NH3/51H4=10, and the film thickness was about 250 mm.

The silicon dioxide film 7 was oxidized at 900C in a water vapor atmosphere and had a thickness of about 20 layers.

Next, after forming a contact hole using lithography technology, as shown in FIG. . Thereafter, a plasma silicon nitride film 9 is formed by plasma vapor phase epitaxy based on a plasma-excited reaction between silane gas and ammonia gas. In this example, the plasma silicon nitride film 9 was formed using an RF output of 100 W and a gas pressure of 0.5 To.
rr, temperature 30oC, gas flow ratio NH3/5iH4=2
Approximately 1,000 people were formed under these conditions.

Next, by forming the protective film 10, the P channel A2 gate MONO8 type semiconductor memory device shown in FIG. 1C can be manufactured.

FIG. 2 shows an example of the memory retention characteristics of the semiconductor device structure obtained by the above method. The horizontal axis is the threshold voltage immediately after writing and erasing, and the vertical axis is the electrode attenuation rate accumulated at that time (
aVth/&log t;vth; L threshold voltage, t: time). The smaller the slope of the straight line in this figure, the better the memory retention characteristics are. The memory retention characteristics (straight line 11) of the semiconductor memory device manufactured by the manufacturing method of the present invention have a smaller slope than the conventional characteristics (straight line 12) when the plasma silicon nitride film is not grown, and exhibit excellent memory retention. It can be seen that it has certain characteristics.

Further, FIG. 3 shows the effect of the heat treatment temperature after growing the second silicon nitride film. As shown in FIG. 3, the heat treatment temperature is the second silicon nitride film growth temperature (3 in this example).
00°C) or higher was found to be even more effective.

In this example, the case where a P channel type semiconductor memory device was manufactured using an N type silicon substrate was explained.
Needless to say, it can be used in a channel type MONOS, and it can also be used in a case where a high melting point metal such as a polycrystalline silicon film is used as the gate electrode. It is also possible to use the second silicon nitride film as a protective film.

Effects of the Invention As described above, according to the present invention, in the manufacturing method of a MONO3 type semiconductor memory device, the heat treatment performed when forming a silicon dioxide film on a silicon nitride film is caused by a plasma excitation reaction caused by silane and ammonia. By applying the 9 second silicon nitride film by vapor phase growth based on the method, and further performing heat treatment at a temperature higher than the growth temperature, it is possible to fabricate an extremely excellent semiconductor memory device with little deterioration in memory retention characteristics. This greatly contributes to improving the performance of MONO3 type semiconductor memory devices.

[Brief explanation of the drawing]

FIG. 1 is a step-by-step sectional view of an embodiment of the present invention, and FIGS. 2 and 3 are characteristic diagrams of a device obtained in the embodiment of the present invention and a conventional device. 1...Silicon substrate, 2,3...Source, train region, 4,5,7...Silicon oxide film, 6゜9...Silicon nitride Membrane, 8...
...Aluminum electrode, 10...Protective film.

Claims (1)

[Claims] a step of forming an ultrathin first silicon dioxide film that can serve as a tunneling medium for electrons or holes on the surface of a semiconductor substrate of one conductivity type; a step of forming a first silicon nitride film on the silicon dioxide film; In the method of manufacturing a semiconductor memory device, the method includes at least the steps of forming a second silicon oxide film on the first silicon nitride film and depositing a gate electrode on the second silicon oxide film. A semiconductor memory device comprising the step of forming a second silicon nitride film by a vapor phase growth method based on a plasma-excited reaction between a silicon compound such as silane and ammonia after forming a second silicon oxide film. Production method.