JPH01108776A - Manufacture of semiconductor storage device - Google Patents

Abstract

PURPOSE:To increase tunneling injection efficiency without deteriorating storage hold characteristics, and enable stably forming an insulating film turning to a tunneling medium, with excellent controllability, by oxidizing the surface of a polycrystalline silicon film, and forming thickly an insulating film turning to a tunneling medium. CONSTITUTION:On a P-type silicon substrate 1, is formed a polycrystalline silicon film, which is etched to leave a part 2 turning to a tunneling region. Phosphorus is selectively doped in the polycrystalline silicon film, and at the same time, N-type diffusion layers 3, 4 are formed. By oxidizing the surfaces of the silicon substrate 1 and the polycrystalline silicon film, a gate insulating film 5 and a tunneling insulating film 6 on the polycrystalline silicon film are formed. After a conductive polycrystalline silicon film is formed on the gate insulating film 5 and the insulating film 6, a floating electrode 7 is formed by photo etching treatment. Thereon an oxide silicon film is formed, and then a conductive polycrystalline silicon film is formed. This film is subjected to photo etching, and a control gate electrode 9 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of Application The present invention aims to improve the performance of the memory characteristics of a semiconductor memory device consisting of a floating gate field effect transistor, and can stably obtain the memory characteristics. This relates to a manufacturing method.

Conventional technology Conventionally, electrically eraseable ROM (EEPRO)
M；Electrically Erasable a
As one of the ndProgrammable ROM),
2. Description of the Related Art Semiconductor memory devices having a floating gate structure in which writing and erasing are performed by tunneling injection are well known.

This floating gate type semiconductor memory device tunnels charges through a thin insulating film formed on a diffusion layer, accumulates charges in a floating gate electrode further formed on the insulating film, and raises the threshold voltage of the transistor. The principle is to memorize information by changing the

An example of a conventional manufacturing method for manufacturing such a floating gate type semiconductor memory device is shown in FIG.

As shown in FIG. 3a, a thick oxide film 1o which will become a gate insulating film is formed on the surface of a P-type silicon substrate 1. Next, after forming N-type diffusion layers 3 and 4 by ion implantation, a part of the silicon oxide film 1° is selectively removed to form an opening, and a thin oxide film that can serve as a tunneling medium is inserted into the opening. A silicon film 11 is formed (FIG. 3b). Next, Figure 3C
As shown in the floating gate electrode 7. By forming the silicon oxide film 8 and the control gate electrode 9 (FIG. 3C), a floating type semiconductor memory device is formed. Note that the thin oxide film 11, which can serve as a tunneling medium, has a normal programming voltage (16 to 20
For the purpose of obtaining a sufficient tunneling current in (v), it is necessary to set the film thickness to an extremely thin thickness of about 100%. On the other hand, the silicon oxide film 1o that becomes the gate insulating film is
It is necessary to form the layer to a thickness (approximately 60.0 mm) so that tunneling injection from the semiconductor substrate does not occur. Therefore, conventionally, after first forming a silicon oxide film 10 that will become a gate insulating film, the silicon oxide film 1o formed in a predetermined portion that will become a tunneling region is etched to form an opening. A method has been adopted in which a thin silicon oxide film 11 that can serve as a tunneling medium is formed in the portion.

Problems to be Solved by the Invention Incidentally, in order to realize a lower programming voltage, which has been increasing in demand in recent years, it is necessary to reduce the thickness of the thin silicon oxide film 11, which serves as the tunneling medium, to an extremely thin thickness of 100 Å or less. However, with conventional manufacturing methods, it is extremely difficult to stably form a thin silicon oxide film of 100 Å or less with good controllability, which poses a major practical problem. Furthermore, if the thickness of the silicon oxide film 11 is made extremely thin, such as 1.08 or less, the discharge speed of the charges stored in the floating gate electrode 7 will be fast, resulting in a disadvantage that the memory retention characteristics will be deteriorated.

An object of the present invention is to increase the tunneling injection efficiency without deteriorating the memory retention characteristics of a floating gate semiconductor memory device, and to form an insulating film that serves as a tunneling medium stably with good controllability. The objective is to provide a manufacturing method that allows for

Means for Solving the Problems The manufacturing method of the present invention which can achieve the above object includes a step of forming first and second regions of opposite conductivity types in a spaced manner on the surface layer of a semiconductor substrate of one conductivity type. forming a gate insulating film on a channel region sandwiched between the first and second regions; a step of forming a polycrystalline silicon film doped with impurities; a step of oxidizing the surface layer of the polycrystalline silicon film to form an insulating film that will become a tunneling medium; floating electrode on top of the membrane,
This method is characterized by comprising a step of laminating an insulating film and a control electrode.

Function: In the manufacturing method of the present invention, an insulating film that becomes a tunneling medium is formed by oxidizing a polycrystalline silicon film, and this insulating film can generate a sufficient tunneling current at a normal programming voltage (15 to 20 V). The film thickness required to obtain
(person) can be made thicker. Therefore, the controllability of the thickness of the insulating film serving as the tunneling medium becomes extremely high. Furthermore, even if the insulating film that serves as the tunneling medium is made thinner in order to increase the tunneling injection efficiency, the film thickness will be much thicker than that which can be achieved using conventional methods (approximately 100 layers), so memory retention No deterioration of properties occurs.

Further, since the thickness of the gate insulating film on the channel is normally used by about 600 people, if the formation conditions are appropriately selected, it is possible to form the gate insulating film and the insulating film to serve as the tunneling medium at the same time.

Although the tunneling injection mechanism of the insulating film, which is formed by oxidizing the polycrystalline silicon film and becomes the tunneling medium, is not clear, it is thought that the quality of the insulating film and the surface condition of the polycrystalline silicon are largely related. It will be done.

Example Specific embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a step-by-step sectional view showing an embodiment of the manufacturing method of the present invention.

First, as shown in FIG. 1a, a polycrystalline silicon film is formed on a P-type silicon substrate 1 to a thickness of about 100 mm by a low pressure vapor phase growth method based on a thermal decomposition reaction of silane. Further, etching is performed so as to leave only a predetermined portion 2 that will become a tunneling region.

Next, as shown in FIG. 1, phosphorus ions are selectively implanted by an ion implantation method to dope phosphorus into the polycrystalline silicon film 2, and at the same time form N-type diffusion layers 3 and 4. . In this example, in order to implant phosphorus ions not only into the polysilicon film 2 but also into the silicon substrate directly under the polysilicon film 2, the ion implantation conditions were set to an acceleration voltage of 100 KeV and a dose of 1. ×1o15c##
Ion implantation was performed using the following settings.

Next, as shown in FIG. 1C, the surfaces of the silicon substrate 1 and the polycrystalline silicon film are oxidized by a normal thermal oxidation method to form the gate insulating film 5 on the channel region and the tunneling insulating film on the polycrystalline silicon film. A film 6 is formed. In this example, a gate insulating film 6 with a thickness of 500 mm and an insulating film 6 serving as a tunneling medium with a thickness of 700 mm were simultaneously formed by oxidation in a steam atmosphere at 100° C.

Next, a conductive polycrystalline silicon film is formed on the gate insulating film 6 and the insulating film 6 serving as the tunneling medium to a thickness of about 500 mm by vapor phase growth, and then a well-known photoetching process is performed. A floating gate electrode 7 made of a polycrystalline silicon film is formed by applying a polycrystalline silicon film, and a silicon oxide film is further formed on the floating gate electrode by a normal thermal oxidation method so that the film thickness on the floating gate electrode is about 100 m. After this, a conductive polycrystalline silicon film is formed to a thickness of about 40 µm by vapor phase growth, and a well-known photoetching process is applied to this to form a control gate electrode 9 made of a polycrystalline silicon film. By forming this, a floating gate type semiconductor memory device shown in FIG. 1d is completed.

In this embodiment, a case was shown in which the insulating film 46 serving as a tunneling medium and the gate insulating film 5 were formed at the same time.
As shown in the figure, after forming the gate insulator g5, an opening is formed in a predetermined portion that will become the tunneling region, a polycrystalline silicon film 2 is buried in this opening, and then a layer is formed on the polycrystalline silicon film. It goes without saying that the insulating film 6 may be oxidized to serve as a tunneling medium.

As is clear from the detailed description of the invention, according to the manufacturing method of the present invention, it is possible to make the insulating film that serves as the tunneling medium thicker than in the past. Thickness can be easily controlled. Furthermore, even if the insulating film that serves as the tunneling medium is made thinner in order to achieve a lower program voltage, this film can be thicker than before, so the voltage can be reduced while maintaining memory retention characteristics. It is also possible to achieve the effect of greatly contributing to improving the performance of floating gate type semiconductor memory devices.

[Brief explanation of the drawing]

FIG. 1 is a step-by-step sectional view showing one embodiment of the method for manufacturing a semiconductor memory device of the present invention, and FIG. 2 shows the structure of a semiconductor memory device formed by another embodiment of the method for manufacturing a semiconductor memory device of the present invention. The cross-sectional views and FIG. 3 are step-by-step cross-sectional views for explaining the conventional manufacturing method. 1... P-type silicon substrate, 2... Polycrystalline film, 3° 4... N-type diffusion layer, 5, 8...
...Silicon oxide film, 6...Insulating film serving as a tunneling medium, 7...Floating electrode, 9
・・・・・・Control electrode. Figure 1/-P-type silicon substrate 9-/control electrode Figure 2

Claims (3)

[Claims] (1) A step of forming first and second regions of opposite conductivity types in a surface layer of a semiconductor of one conductivity type, and forming a gate insulator on a channel region sandwiched between the first and second regions. a step of forming a polycrystalline silicon film doped with an impurity of a conductivity type opposite to that of the semiconductor substrate at a predetermined portion on the surface of the first or second region; The present invention is characterized by comprising a step of forming an insulating film to serve as a tunneling medium on the film, and a step of stacking and forming a floating electrode, an insulating film, and a control electrode on the gate insulating film and the insulating film to serve as a tunneling medium. A method for manufacturing a semiconductor memory device. (2) The method for manufacturing a semiconductor memory device according to claim 1, wherein the insulating film serving as the tunneling medium is formed by oxidizing a polycrystalline silicon film. (3) The method for manufacturing a semiconductor memory device according to claim 1, wherein a gate insulating film and an insulating film serving as a tunneling medium are formed at the same time.