JPH02130963A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve writing/erasing characteristics while improving yield and reliability of an MNOS semiconductor device by forming a nitride film by using cryooptical CVD process. CONSTITUTION:MNOS memory cell according to the invention includes silicon oxide film 3 formed on a part of a P-type semiconductor substrate 2 where a channel is to be formed, the substrate 2 having an N<+> type diffused layer 1 for providing source and drain. A silicon nitride film 4 is formed on the film 3 and a gate electrode 5 is further formed thereon. The element thus produced is isolated from other circuit elements by an oxide film 9 and a P<+> type channel stopper 10. The silicon nitride film 4 is formed by the following method. The substrate 2 is heated within a reaction chamber to a temperature of 400 deg.C or below and the reaction chamber is exhausted. Reaction gas consisting of disilane and ammonium is supplied into the reaction chamber and irradiated with light from a mercury lamp. The nitride film 4 is formed on the oxide film 3 by radical reaction and the nitride film 4 thus formed is lamp annealed. The writing/erasing characteristics can be improved in this manner.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a technique that is effective when applied to the formation of a semiconductor integrated circuit, and more specifically, to a technique that is applied to the formation of an MNOS type semiconductor device. Concerning effective techniques.

[Prior art] Regarding MNOS type semiconductor devices, for example,
It is described on pages 67 to 79 of "Nikkei Microdevices" published by Nikkei McGraw-Hill on March 1, 2017. An overview of an example of this MNOS type semiconductor device is as follows.

That is, this MNOS type semiconductor device has a structure in which the gate oxide film of the MOSFET is replaced with a double layer structure of an extremely thin oxide film and a nitride film.

More specifically, this MNOS type semiconductor device has a thin silicon oxide film (SiO2 with a thickness of 2 nm or less) on a portion corresponding to a channel of a semiconductor substrate on which a diffusion layer (source/drain) is formed. is formed, a silicon nitride film (sxxN4) with a thickness of 30 to 50 nm is formed thereon, and a gate electrode made of polycrystalline silicon is further provided thereon.

In this MNOS type semiconductor device, writing is performed by applying a high voltage between the gate electrode and the semiconductor substrate and sending electrons or holes through a thin silicon oxide film from the semiconductor substrate to the silicon nitride film by tunneling. It has become.

The threshold voltage vth can be changed by this writing.

By the way, conventionally, the silicon nitride film in the above-mentioned MNOS type semiconductor device is formed by a low pressure CVD method under high temperature heating. That is, after forming a thin silicon oxide film on a semiconductor substrate, the semiconductor substrate is heated to a high temperature of 750°C or higher by high frequency induction heating, etc., and a reactive gas (NH,...
S i H2C11,) was introduced into the reactor and the following equation (1
) A silicon nitride film is formed on a thin silicon oxide film.

1ONH, +3SiH, CQ, -+Si, N, +6NH
4CQ +6H, = (1) After forming the silicon nitride film, hydrogen annealing is performed to control the trap sites and prevent leakage of charge to the gate electrode.

[Problems to be Solved by the Invention] However, when an MNOS type semiconductor device manufactured by the above technique was studied, the following was found.

In other words, since the silicon nitride film is formed under high-temperature heating, the silicon oxide film underlying the silicon nitride film grows due to the entrained oxygen, and the increased oxide film thickness prevents charge tunneling. may not be possible.

In addition, since the semiconductor substrate is exposed to high temperatures, damage (crystal defects) may remain on the semiconductor substrate, and diffusion layers such as source/drain may expand more than necessary, reducing the yield and reliability of semiconductor devices. do.

Note that the temperature during hydrogen annealing must be higher than the temperature during silicon nitride film formation, and this work is dangerous.

In addition, a silicon nitride film was formed using various methods.
When NOS type semiconductor devices were manufactured and the relationship between dangling bonds, which serve as trap sites, and device characteristics was investigated using ESR (electron spin resonance), the following was found.

That is, the charge storage capacity depends on the amount of dangling bonds in the silicon nitride film in the vicinity of the silicon oxide film, and the larger the amount of dangling bonds in the portion, the larger the charge storage capacity.

Further, leakage of charge toward the gate electrode side depends on the amount of dangling bonds in the silicon nitride film in the vicinity of the gate electrode, and the larger the amount of dangling bonds in the portion, the greater the leakage.

The present invention has been made based on the above problems and findings, and is capable of improving write/erase (W/E) characteristics, increasing charge retention capacity, and improving charge retention characteristics, yield, and reliability. Its main purpose is to provide semiconductor technology.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for Solving the Problems] Representative inventions disclosed in this article will be summarized as follows.

That is, the first invention is such that the nitride film of the MNOS type semiconductor device is formed by a low temperature photo-CVD method, and then annealed.

Further, in a second invention, a nitride film is formed by photo-CVD while the semiconductor substrate temperature is maintained at 400° C. or lower, and then annealing is performed.

Furthermore, a third invention is the seventh aspect of the first or second invention.
Lamp annealing or laser annealing is used as the annealing.

[Function] According to the first to third inventions described above, the nitride film is exposed to low-temperature light C.
Since it is formed by the VD method, a natural oxide film is not formed on the oxide film underlying the nitride film, and the tunneling of charges is not inhibited.
W/E) characteristics can be improved. Furthermore, since the semiconductor substrate itself is not damaged and the diffusion layer is not expanded more than necessary, yield and reliability can be improved.

In addition, since an amorphous nitride film is formed and contains a large amount of dangling bonds and unbonded hydrogen, it is possible to control the amount of dangling bonds with high precision through subsequent annealing. Become. In other words, by expelling hydrogen, the amount of dangling bonds in the nitride film can be increased near the oxide film, while it can be reduced near the gate electrode. As a result, it is possible to increase the load holding capacity, improve charge holding characteristics, and reduce leakage current.

[Example] Hereinafter, an example of a semiconductor memory device according to the present invention will be described.

FIG. 1 shows a longitudinal cross-sectional view of an MNOS memory cell according to an embodiment of the invention.

The MNOS memory cell of this embodiment has a thickness of 1.5 to 2.5 degrees above the channel portion of the P type semiconductor substrate 2 on which the N+ diffusion layer 1, which becomes the source/drain, is formed. A silicon oxide film 3 with a thickness of 20 to 30 nm is formed on it.
A silicon nitride film 4 is formed thereon, and a gate electrode 5 made of polycrystalline silicon is further formed thereon.

In FIG. 1, reference numeral 6 represents a source/drain electrode, and this picture electrode 6 is insulated and isolated from the gate electrode 5 via a thick silicon oxide film 7. 8 is an insulating film between the eyebrows.

FIG. 2 also shows a vertical cross-sectional view of the MNOS memory cell in the direction perpendicular to FIG. The elements are separated by 10.

Here, the silicon nitride film 4 is formed as follows.

That is, the semiconductor substrate 2 is installed in a reaction chamber, and the semiconductor substrate 2 is
is heated to a temperature below 400°C. After evacuating the reaction chamber in this state, reaction gases of disilane (Si2H6) and ammonia (NH3) are supplied, and a mercury lamp is irradiated. Then, the reaction gas undergoes a radical reaction as shown in the following equation (2): 6 disilane (s iz Hz) + ammonia (NH,) → silicon nitride film (S
)+・++ (2) However, 5izNyHz means a silicon nitride film containing a large amount of hydrogen (H). Also, z,
x and y satisfy the condition z<xty.

Then, the silicon oxide film 3 is formed by the above radical reaction.
A silicon nitride film 4 is formed thereon. This silicon nitride film 4 contains many dangling bonds and unbonded hydrogen (not shown).

Thereafter, lamp annealing is performed at, for example, 800° C. to LOOO° C. for about 10 seconds. Note that laser annealing may be used as the annealing in this case, whereby unbonded hydrogen in the silicon nitride film 4 is expelled, and the amount of dangling bonds in the silicon nitride film 4 is controlled by the hydrogen.

According to the MNOS memory cell configured as described above, the following effects can be obtained.

That is, according to the MNOS memory cell of the above embodiment, since the silicon nitride film 4 is formed by the low-temperature photoCVD method, no natural oxide film is formed on the silicon oxide film 3 that is the base of the silicon nitride film 4. , write/erase (W/E) due to the effect that charge tunneling is not inhibited.
The characteristics can be improved. Furthermore, since the semiconductor substrate 2 itself is not damaged and the source/drain diffusion layer 1 is not expanded more than necessary, yield and reliability can be improved.

Furthermore, since the silicon nitride film 4 formed by low-temperature photo-CVD is in an amorphous state, it contains a large amount of dangling bonds and unbonded hydrogen. It becomes possible to control the amount of dangling bonds with high precision. In other words, by expelling hydrogen, the silicon nitride film 4
The amount of dangling bonds inside can be increased near the silicon oxide film 3, while it can be reduced near the gate electrode 5. As a result, it is possible to increase the charge retention capacity, improve charge retention characteristics, and reduce leakage current. This point will be explained in detail next.

That is, the amount of dangling bonds in the film formed by low-temperature photo-CVD method is I
The amount of dangling bonds in the conventional method (5
X10''''(aI+-')), and the amount of unbonded hydrogen contained in the silicon nitride film 4 is also larger than in the past.

If annealing is performed in this state, the hydrogen in the silicon nitride film 4 is easily expelled, and during the annealing, the hydrogen acts to eliminate the dangling bonds.

Therefore, the amount of dangling bonds in the silicon nitride film 4 can be reduced as it goes upward. This means that the amount of dangling bonds in the silicon nitride film 4 can be increased in the vicinity of the silicon oxide film 3 and decreased in the vicinity of the gate electrode 5, and as a result, the charge retention capacity can be increased and the leakage current can be reduced. become. Furthermore, the fact that the amount of dangling bonds in the silicon nitride film 4 can be increased near the silicon oxide film 3 means that trap sites are formed at deep levels.

As a result, the charge retention characteristics can be improved. Note that the annealing treatment in this case can be performed at high temperature and in a short time, so that the semiconductor substrate 2. Diffusion/l! 31 will not be adversely affected.

Furthermore, since lamp annealing or laser annealing is used as annealing, the amount of dangling bonds can be highly controlled by controlling the time or scanning speed.

Furthermore, since a radical reaction is utilized, surface reaction characteristics are improved, and as a result, step coverage can also be improved.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor.

In the above embodiments, a P-type substrate is used as the semiconductor substrate 2, but an N-type substrate may also be used. However, in this case, electrons will be trapped within the silicon nitride film 4.

In the above embodiment, disilane was used as one of the reaction gases, but other higher-order silanes may be used.

It is also possible to use the MNOS configured as described above as a capacitor.

[Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly explained below.

That is, the nitride film of the MNOS type semiconductor device is formed by low-temperature optical CVD.
Since the nitride film is formed using a method and then annealed, a natural oxide film is not formed on the oxide film underlying the nitride film, and charge tunneling is not inhibited, resulting in improved write/erase (W/E) characteristics. This will lead to improvements.

Further, since the semiconductor substrate itself is not damaged and the diffusion layer is not expanded more than necessary, yield and reliability can be improved.

Furthermore, since an amorphous nitride film can be formed and contains a large amount of dangling bonds and unbonded hydrogen, it is possible to control the amount of dangling bonds with high precision through subsequent annealing. Become. In other words, by expelling hydrogen, the amount of dangling bonds in the nitride film can be increased near the oxide film, while it can be reduced near the gate electrode. As a result, 1! It is possible to increase the load holding capacity, improve charge holding characteristics, and reduce leakage current.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an MNOS memory cell obtained by applying the present invention, and FIG. 2 is a longitudinal sectional view of the MNOS memory cell in a direction perpendicular to FIG. 1. 2...Semiconductor substrate, 3...Silicon oxide film, 4
P: Silicon nitride film, 5: Gate electrode.

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor device, characterized in that when forming a nitride film in an MNOS type semiconductor device, the nitride film is formed by a low-temperature photo-CVD method, and then annealed. . 2. The method of manufacturing a semiconductor device according to claim 1, wherein the nitride film is formed while the temperature of the semiconductor substrate is maintained at 400° C. or lower. 3. The method of manufacturing a semiconductor device according to claim 1 or 2, wherein lamp annealing or laser annealing is used as the annealing.