JP3818402B2 - Nonvolatile semiconductor memory device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nonvolatile semiconductor memory device that stores information by trapping charges at a trap level at the interface between a nitride film and an oxide film, and a method for manufacturing the same.
[0002]
[Prior art]
As a type of nonvolatile semiconductor memory device that can rewrite information electrically and retain information even when the power is turned off, it traps charges at the trap level that exists at the interface between the insulating film and the oxide film. There is a nonvolatile semiconductor memory device that stores information by shifting the threshold voltage of a transistor.
[0003]
This nonvolatile semiconductor memory device is called a MIOS (Metal Insulator Oxide Semiconductor) type or a MOIOS (Metal Oxide Insulator Oxide Semiconductor) type, but a nitride film is mainly used as an insulating film. In particular, it is called MNOS type or MONOS type.
[0004]
FIG. 2 shows a conventional example of a MONOS type nonvolatile semiconductor memory device. In this conventional example, a tunnel SiO ₂ film 11 having a thickness of ₂ nm, a SiN film 12 having a thickness of 8 nm, and a SiO ₂ having a thickness of 4 nm are formed on a Si substrate (not shown). A film 13 is sequentially stacked, and a polycrystalline Si film (not shown) as a gate electrode is formed on the SiO ₂ film 13.
[0005]
[Problems to be solved by the invention]
However, in the MNOS type and MONOS type non-volatile semiconductor memory devices, the area per bit, the SiN film 12 and the like are increased in accordance with the miniaturization for increasing the capacity and the low voltage operation for reducing the power consumption. The thickness is decreasing. As a result, the area of the interface between the SiN film 12 and the SiO ₂ films 11 and 13 is reduced and the amount of trap levels contained in the SiN film 12 is also reduced, thereby reducing the amount of trapped charges and improving the memory retention characteristics. It was falling.
[0006]
[Means for Solving the Problems]
A nonvolatile semiconductor memory device according to the present invention is a nonvolatile semiconductor memory device that stores information by trapping charges at a trap level at an interface between a nitride film and an oxide film. The nitride film includes an oxide film. The oxide film is characterized by spreading discretely along the interface .
[0007]
A method for manufacturing a nonvolatile semiconductor memory device according to the present invention is a method for manufacturing a nonvolatile semiconductor memory device that stores information by trapping charges at a trap level at an interface between a nitride film and an oxide film. An oxide film is formed in the nitride film by oxygen ion-implanted in the form of dots .
[0008]
In the nonvolatile semiconductor memory device according to the present invention, since the nitride film includes the oxide film, the area of the interface between the nitride film and the oxide film is large compared with the same planar area, and the trapped charge amount There are many. In addition, since many deep trap levels due to oxygen in the nitride film are formed, the trapped charges are not easily released spontaneously.
[0009]
Further, Runode oxide film in the nitride film stretches discretely along their interface, even a content of the oxide in the nitride film are the same, it is wider area of the interface between the nitride film oxide film More trapped charge .
[0010]
In the method for manufacturing a nonvolatile semiconductor memory device according to the present invention, an oxide film is formed in the nitride film. Therefore, when the same planar area is compared, the area of the interface between the nitride film and the oxide film is increased. The amount of trapped charges can be increased. In addition, since many deep trap levels due to oxygen in the nitride film are formed, it is possible to make it difficult to spontaneously release the trapped charges.
[0011]
In addition, when an oxide film is formed in the nitride film, oxygen can be ion-implanted into the nitride film in the form of dots to form an oxide film that spreads discretely along the interface with the nitride film. Even if the amount of oxygen to be injected is the same, the area of the interface between the nitride film and the oxide film can be further widened to further increase the amount of trapped charges.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, first and second embodiments of the present invention will be described with reference to FIG. In the first embodiment, for example, a gas of O ₂ / N ₂ = 300 SCCM / 10 SLM is supplied to a resistance heating type heat treatment furnace to dilute and oxidize a Si substrate (not shown), thereby forming a surface of the Si substrate. A SiO ₂ film 11 having a thickness of 2 nm is formed.
[0013]
Next, for example, an NH ₃ / SiH ₂ Cl ₂ = 2000 SCCM / 50 SCCM gas is supplied to a resistance heating type low pressure CVD apparatus at 70 Pa, and deposition is performed at 760 ° C. for 2 minutes to form a SiN film having a thickness of 3 nm. 14 is formed on the SiO ₂ film 11. Note that when a Si substrate is inserted into the CVD furnace with a load lock mechanism provided in the low-pressure CVD apparatus, vacuum transfer is performed, and a high-purity gas is used so that oxygen and hydrocarbons are converted into SiN film 14. Try to avoid mixing in as much as possible.
[0014]
Further, since the deposition temperature is relatively high, the mixing of hydrogen into the SiN film 14 is relatively suppressed. Under the above conditions, it is possible to form the SiN film 14 having a uniform film quality, a dense film and few impurities and structural defects. In such a SiN film 14, there is little leakage current through impurities and structural defects, and the memory retention characteristics can be improved.
[0015]
Next, for example, a gas of N ₂ O / SiH ₂ Cl ₂ = 200 SCCM / 1000 SCCM is supplied at 70 Pa to a resistance heating type low pressure CVD apparatus, and deposition is performed at 800 ° C. for 5 minutes to obtain SiO 2 having a thickness of 1 nm. _Two films 15 are formed on the SiN film 14. Then, a SiN film 16 having a thickness of 3 nm is formed on the SiO ₂ film 15 under the same conditions as when the SiN film 14 is formed.
[0016]
Thereafter, a SiO ₂ film 13 having a thickness of 4 nm is formed on the SiN film 16 under the same conditions as those for forming the SiO ₂ film 15 except that the deposition time is set to 20 minutes. Further, a gate electrode or the like is formed by a conventionally known process to complete the nonvolatile semiconductor memory device.
[0017]
The SiO ₂ films 11, 13, 15 and the SiN films 14, 16 are macroscopically amorphous, but microscopically all have a regular structure, and there is a crystal at the interface between them. A structural defect such as a lattice is generated, and a trap level due to the structural defect is formed.
[0018]
It has also been reported that deep trap states are formed due to oxygen in the nitride film (VJ Kapoor and SBBibyk, “Energy distribution and electron trapping defects in thick-oxide MNOS structures”, in “The Physics of MOS Insulators ", edited by G. Lucousky et al. (Pergamon, New York, 1980) p. 117), this deep trap level at the interface between the SiO ₂ films 11, 13, 15 and the SiN films 14, 16 Is also formed.
[0019]
In addition, since a larger amount of energy is required for the charge trapped in the deep trap level to escape from it, the charge trapped in the deep trap level is difficult to be spontaneously released. This means that information once stored is not easily lost, and this also improves the memory retention characteristics.
[0020]
Next, a second embodiment will be described. Also in the second embodiment, prior to the deposition of the SiN film 16, for example, NH ₃ is supplied at 1 SLM to a lamp heating type heat treatment apparatus, and the surface of the SiO ₂ film 15 is heated at 1000 ° C. for 1 minute. Except for performing thermal nitridation, substantially the same steps as those in the first embodiment are performed.
[0021]
When such thermal nitridation is performed, surface roughness of the SiN film 16 due to migration of deposited species on the surface of the SiO ₂ film 15 at the initial deposition stage is suppressed during the subsequent deposition of the SiN film 16. As a result, a more uniform SiN film 16 having a more uniform film quality can be formed, and the memory retention characteristics can be further improved.
[0022]
In the first and second embodiments described above, as shown in FIG. 1, only the single-layer SiO ₂ film 15 is included between the SiN films 14 and 16, but the SiN film and the SiO2 film are not included. _A plurality of SiO ₂ films may be included between the SiN films in a state where the _two films are alternately stacked.
[0023]
In the first and second embodiments described above, the SiN films 14 and 16 and the SiO ₂ films 13 and 15 on the SiO ₂ film 11 are all formed by deposition. For example, the surface of the SiN film 14 is thermally oxidized. Thus, the SiO ₂ film 15 may be formed, or the SiO ₂ film 15 may be formed by performing heat treatment after ion implantation of a large amount of oxygen into the SiN films 14 and 16.
[0024]
Further, when oxygen is ion-implanted into the SiN films 14 and 16, if the ion implantation is not performed on the entire surface of the SiN films 14 and 16, but is performed in a dot-like manner, the interface with the SiN films 14 and 16 is followed. Since the SiO ₂ film 15 spreading discretely can be formed, even if the amount of oxygen to be ion-implanted is the same, the area of the interface between the SiN films 14 and 16 and the SiO ₂ film 15 can be further increased, and the trap charge can be increased. The amount can be increased further.
[0025]
【The invention's effect】
In the nonvolatile semiconductor memory device according to the present invention, the amount of trapped charges is large compared with the same planar area, and the trapped charges are not easily released spontaneously, so that the memory retention characteristics are excellent even when miniaturized. Yes.
[0026]
Further, the oxide film of the nitride film is not spread discretely along their interface, since the amount of trapped charge more often, memory retention characteristics are more excellent.
[0027]
In the method of manufacturing a nonvolatile semiconductor memory device according to the present invention, the amount of trapped charges can be increased compared to the same planar area, and the trapped charges can be made difficult to be spontaneously released. Even if manufactured, a nonvolatile semiconductor memory device having excellent memory retention characteristics can be manufactured.
[0028]
Furthermore, by ion implantation of oxygen into a point-like on the nitride film during the formation of the oxide film on the nitride film, it is possible to further increase the trapped charge amount, the non-volatile semiconductor memory retention characteristics are more excellent A storage device can be manufactured.
[Brief description of the drawings]
FIG. 1 is a side sectional view of an essential part of first and second embodiments of the present invention.
FIG. 2 is a side cross-sectional view of a main part of a conventional example of the present invention.
[Explanation of symbols]
11, 13, 15 SiO ₂ film 14, 16 SiN film

Claims (2)

In a nonvolatile semiconductor memory device that stores information by trapping charges at a trap level at the interface between a nitride film and an oxide film,
The nitride film includes an oxide film ,
A non-volatile semiconductor memory device characterized in that the oxide film spreads discretely along the interface . In a method for manufacturing a nonvolatile semiconductor memory device that stores information by trapping charges at a trap level at an interface between a nitride film and an oxide film,
A method of manufacturing a nonvolatile semiconductor memory device, comprising forming an oxide film in the nitride film by oxygen ion-implanted in the form of dots in the nitride film .

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