JP2010129739A - Nonvolatile semiconductor storage device and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MONOS type flash memory securing a required amount of electric charge stored sites in an electric charge stored film. <P>SOLUTION: The nonvolatile semiconductor storage device includes source-drain regions 10a, 10b formed by spacing apart from each other on the surface of a semiconductor layer 10, a tunnel insulating film 11 arranged on the semiconductor layer 10 between the source-drain regions 10a, 10b, an insulating electric charge stored film 12 arranged on the tunnel insulating film 11 and containing an isotope having a ratio different from an isotope ratio in a natural state, a block insulating film 14 arranged on the electric charge stored film 12, and a control gate electrode 15 arranged on the block insulating film 14. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nonvolatile semiconductor memory device and a manufacturing method thereof.

  There are many non-volatile storage devices including those in the research stage even when the power is turned off, but at present, non-volatile semiconductor storage devices (flash memories) have the largest market scale. Semiconductor circuits have been miniaturized year by year, and semiconductor memory devices have also been increased in capacity. Flash memory is no exception, and miniaturization is progressing, but the application of a structure having a block insulating film and a charge storage portion called a MONOS (metal / oxide / nitride / oxide / semiconductor) type is being studied. .

Also in the flash memory having a structure called the MONOS type, as the miniaturization progresses, the charge storage film as a memory portion is becoming thinner. Conventionally, SiN has been used as the charge storage film (see, for example, Patent Document 1). However, the electrical defect density of SiN is not sufficient, and a particularly thin SiN charge storage film cannot store sufficient charges.
JP 2004-71877 A

  Patent Document 1 discloses the use of a high dielectric constant film as a charge storage film, but it goes without saying that there are various barriers for incorporating a new material into a complicated LSI process. In particular, it is extremely difficult to create a material that contains stable electrical defects that should become charge storage sites even after heat treatment at a high temperature required in an LSI process. A method for increasing the density of electrical defects from a completely new viewpoint is desired.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a nonvolatile semiconductor memory device including a charge storage film having electrical defects stably at high density even after heat treatment of an LSI process, and its manufacture Is to provide a method.

  The present invention provides a source region and a drain region formed on a surface of a semiconductor layer so as to be separated from each other, a tunnel insulating film provided on the semiconductor layer between the source region and the drain region, and the tunnel insulating film An insulating charge storage film containing an isotope in a ratio different from an isotope ratio in a natural state, a block insulating film provided on the charge storage film, and on the block insulating film There is provided a nonvolatile semiconductor memory device comprising a control gate electrode provided.

  The present invention also provides a source region and a drain region formed on the surface of a semiconductor layer, a tunnel insulating film provided on the semiconductor layer between the source region and the drain region, and the tunnel An insulating charge storage film containing an isotope generated by the decay of unstable nuclides provided on the insulating film; a block insulating film provided on the charge storage film; and on the block insulating film There is provided a nonvolatile semiconductor memory device comprising a control gate electrode provided.

  The present invention also includes a step of forming a tunnel insulating film on the semiconductor layer, a step of forming a charge storage film containing unstable nuclides on the tunnel insulating film, and a block insulating film formed on the charge storage film. And a method of forming a control gate electrode on the block insulating film. A method of manufacturing a nonvolatile semiconductor memory device is provided.

  The present invention also includes a step of forming a tunnel insulating film on the semiconductor layer, a step of forming a film containing unstable nuclides on the tunnel insulating film, and a first covering the film containing unstable nuclides. And a step of forming a block insulating film on the charge storage film, and a step of forming a control gate electrode on the block insulating film. A method for manufacturing a semiconductor memory device is provided.

  The present invention also includes a step of forming a tunnel insulating film on a semiconductor layer, a step of forming a charge storage film on the tunnel insulating film, a step of forming a block insulating film on the charge storage film, There is provided a method for manufacturing a nonvolatile semiconductor memory device, comprising: forming a control gate electrode on a block insulating film; and injecting unstable nuclides into the charge storage film.

  According to the present invention, it is possible to provide a nonvolatile semiconductor memory device including a charge storage film having electrical defects stably at a high density even after heat treatment of an LSI process, and a manufacturing method thereof.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
[Structure of nonvolatile semiconductor memory device]
FIG. 1 is a cross-sectional view showing the structure of the nonvolatile semiconductor memory device according to this embodiment.

  As shown in FIG. 1, the nonvolatile semiconductor memory device of this embodiment has a MONOS type structure. That is, source and drain regions 10a and 10b are formed on the surface of the silicon substrate 10 apart from each other, and a channel region 10c is formed between the source and drain regions 10a and 10b. A tunnel insulating film 11, a lower charge storage film 12a, an upper charge storage film 12b, a block insulating film 14, and a control gate electrode 15 are sequentially formed on the channel region 10c. The block insulating film is an insulating film that blocks the flow of charges between the charge storage film and the control gate electrode. The charge storage film 12 is composed of the lower charge storage film 12a and the upper charge storage film 12b. The charge storage film 12 has an electrical defect site as a site for storing charges, and charges can be stored at these sites. Information can be stored by the difference in charge accumulation state in the charge storage film 12. A write voltage is applied to the control gate electrode 15 to inject charges into the charge storage film 12 through the tunnel insulating film 11, and writing is performed. A read voltage is applied to the control gate electrode 15 to perform reading.

Here, as the tunnel insulating film 11, for example, a film of SiO ₂ , SiON, HfSiON, HfAlO, LaAlO ₃ , La ₂ Hf ₂ O ₇ , or PrO _x (where x is in the range of 1.5 ≦ x ≦ 2.0), or These laminated films can be used. The charge storage films 12a and 12b include SiN _x , AlO _y , SiAlO, SiO _z , HfON, HfSiON, ZrON, ZrSiON, where x, y, and z are 0 <x ≦ 1.33, 1.0 ≦ y ≦ 1.5, 1.0 ≦ z ≦ 2.0) or a laminated film thereof can be used. The charge storage film is insulative and needs to be a material other than a metallic electrical conductor and capable of trapping charges. The materials of the charge storage films 12a and 12b may be the same or different. As the block insulating film 14, for example, an oxide containing rare earth such as SiO ₂ , Al ₂ O ₃ , or lanthanum aluminate can be used. Furthermore, as the control gate electrode 15, for example, Si doped with a low resistance, or a metal such as Al or W can be used. The materials of the tunnel insulating film, charge storage film, block insulating film, and control gate electrode are not essential to the present invention, and other types of films can be used.

An isotope 13 generated by the decay of unstable nuclides is present at and near the interfaces of the charge storage film 12a and the charge storage film 12b. The concentration of the isotope 13 is, for example, 1 × 10 ¹⁰ / cm ² or more and 1 × 10 ¹³ / cm ² or less, but is not limited to this range. What is important in the present embodiment is that the ratio of the isotope 13 is higher than that in the natural state. Here, the isotope ratio in the natural state is the isotope ratio in the solar system that can be experimentally verified by mankind, and is 0.01% except for a few exceptional environments where enrichment occurs due to natural phenomena. It is known that the ratio will be constant within the solar system. As an environment in which enrichment occurs due to a natural phenomenon, for example, the Okuro natural reactor and oxygen in the atmosphere of Venus are known. The use of raw materials mined from such a very few exceptional environments is usually not profitable industrially, so the possibility of such a case can be ruled out by common sense. The values of isotope ratios in these exceptional environments are known individually, and the reason why they differ from normal isotope ratios is due to the raw materials collected in these exceptional environments, or the manufacture according to this patent. It is very difficult to think that it is difficult to judge whether the method is adopted.

The type of isotope is not limited. For example, in the case of Si, the ratio of the stable isotope is ²⁸ Si: ²⁹ Si: ³⁰ Si = 92.23: 4.67: 3.10 in the natural state. In the nonvolatile semiconductor memory device of this embodiment, the ratio of ²⁸ Si is relatively higher than this ratio. For example, if limited to only one atomic layer at the interface, the ratio of ²⁸ Si increases from 92.23% of the natural isotope ratio and increases in the range of about 92.23% + 0.0025% to 92.23% + 2.5%. As will be described later, in order to obtain this stable isotope ratio, for example, ²⁸ Mg is used as an unstable nuclide as a raw material, and a method of generating an isotope by its decay can be employed. When a relatively light isotope is contained in the charge storage film in an abundance ratio higher than the abundance ratio in the natural state in this way, the charge collision cross section is slightly increased by decreasing the mass ratio with the electrons. This has the advantage that the trap characteristics are improved. In addition, there is an advantage that the mass of the device becomes light, which is advantageous for consumers.

Further, in the present embodiment, a relatively heavy isotope may be included in the charge storage film at a higher abundance ratio than the abundance ratio in the natural state, in which case there is an advantage that deterioration at high temperature is reduced, This is advantageous for devices used in high temperature environments. Examples of such applications include those for automobile control equipment. In the natural state, the Hf isotope ratio is ¹⁷⁴ Hf: ¹⁷⁶ Hf: ¹⁷⁷ Hf: ¹⁷⁸ Hf: ¹⁷⁹ Hf: ¹⁸⁰ Hf = 0.16: 5.12: 18.60: 27.10: 13.74: 35.20, for example, ¹⁷⁴ Hf: ¹⁷⁶ Hf: ¹⁷⁷ Hf: ¹⁷⁸ Hf: ¹⁷⁹ Hf: ¹⁸⁰ Hf = 0.16: 5.07: 18.15: 26.44: 15.84: 34.34 The ratio of heavy isotopes increases. In order to obtain this stable isotope ratio, for example, ¹⁷⁹ Lu having a half-life of about 5 hours can be used as an unstable nuclide as a raw material, and an isotope can be generated by its decay.

  The nonvolatile semiconductor memory device of this embodiment is characterized in that a linear locus generated by the decay of unstable nuclides is formed in the charge storage film 12a and the charge storage film 12b. An example of a fission track in which this locus is enlarged by etching with a dilute hydrofluoric acid solution or the like is shown in FIG. 2 (a) and 2 (b) are plan views schematically showing fission tracks appearing on the film surface after etching. FIG. 2A shows that a linear locus appears as a linear fission track by etching, and the fission track may be radial. FIG. 2B shows an elongated hole-like fission track opened obliquely with respect to the film surface. The shape of these fission tracks and the shape of the trajectory differ depending on the unstable nuclide used.

The trajectory of the present embodiment is generated by the decay of unstable nuclides as will be described later, and corresponds to an electrical defect site (charge storage site). A large amount of charge can be stored in the portion of the charge storage film where the locus is formed. The size of the locus generated by the decay of the unstable nuclide is, for example, 0.5 nm or more and 5 nm or less, and the density is, for example, 1 × 10 ¹⁰ / cm ² or more and 1 × 10 ¹³ / cm ² or less. There is no. In addition, the existence range of the locus is, for example, a film thickness range of 1 nm or more and 10 nm or less, and there is almost no influence on components other than the charge storage film of the nonvolatile semiconductor memory device.

[Method of Manufacturing Nonvolatile Semiconductor Memory Device]
Next, a method for manufacturing the nonvolatile semiconductor memory device of this embodiment will be described. FIG. 3 is a process cross-sectional view illustrating the method for manufacturing the nonvolatile semiconductor memory device of this embodiment.

  First, as shown in FIG. 3A, the surface of the single crystal silicon substrate 10 having the (100) plane is treated with dilute hydrofluoric acid to peel off the natural oxide film on the surface of the substrate 10, and after the peeling. A tunnel insulating film 11 is formed on the surface of the substrate 10. Further, a charge storage film 12 a is formed on the tunnel insulating film 11.

Next, as shown in FIG. 3A, a film 13a containing unstable nuclides is formed on the charge storage film 12a by a film forming method that causes little damage to the underlying film, such as a vacuum deposition method, a sputtering method, or a CVD method. Form. The unstable nuclides and their types will be described later. For example, ⁹³ Y can be used as the unstable nuclide, and for example, a ZrO ₂ film can be used as the film 13a containing the unstable nuclide. The types of unstable nuclides and production methods will be described in detail later. Further, as shown in FIG. 3B, a charge storage film 12b is formed on the charge storage film 12a so as to cover the film 13a containing unstable nuclides. The unstable nuclides of the film 13a containing the unstable nuclides are diffused into the charge storage films 12a and 12b by the heat treatment performed normally thereafter, and the unstable nuclides 13b are mixed into the charge storage films 12a and 12b. Can do. The concentration of the unstable nuclide 13b in the charge storage films 12a and 12b is controlled by adjusting the film thickness of the charge storage films 12a and 12b and the film 13a containing the unstable nuclide, and adjusting the heat treatment temperature and heat treatment time. can do. The film thickness of the charge storage film 12a and the film thickness of the charge storage film 12b may be substantially the same. However, when the film thickness of the charge storage film 12a is smaller than the film thickness of the charge storage film 12b, the vicinity of the tunnel insulating film 11 is used. Therefore, it is possible to generate more charge storage sites, and it is possible to suppress erroneous writing due to parasitic capacitance between adjacent cells by lowering the charge center position.

  Thereafter, as shown in FIG. 3B, a block insulating film 14 and a conductive film to be the control gate electrode 15 are sequentially formed on the charge storage film 12b. Next, as shown in FIG. 3C, the stacked body including the tunnel insulating film 11, the charge storage films 12a and 12b, the block insulating film 14, and the conductive film to be the control gate electrode 15 is patterned by lithography and etching. Further, source / drain regions are formed on the surface of the silicon substrate 10 on both sides of the stacked body by heat treatment for impurity ion implantation and activation.

  Such heat treatment reduces the number of electrical defect sites (charge storage sites) in the charge storage films 12a and 12b, but the unstable nuclide 13b in the charge storage films 12a and 12b gradually collapses after the subsequent semiconductor manufacturing process. By doing so, it is possible to generate charge storage sites. The unstable nuclide 13b changes to the isotope 13 in FIG. 1 by decay.

[Types of unstable nuclides]
Here, the unstable nuclide of this embodiment will be described in more detail.

  The half-life of the unstable nuclide used in this embodiment is preferably a short-lived nuclide of 1 minute or more and 1 year or less. In the case of an ultra-short-lived nuclide having a half-life of less than 1 minute, the unstable nuclide decays before undergoing the heat treatment necessary for the LSI manufacturing process, and the effect of controlling the amount of electrical defects is poor. For long-lived nuclides whose half-life exceeds one year, the reliability of the product is reduced due to the structural life of parts other than the charge storage film of the nonvolatile semiconductor memory device and other LSI parts. Since the pace at which performance improves is on a yearly basis, it is difficult to make it industrially viable. On the other hand, there is no problem even if an ultrashort-lived nuclide having a half-life of less than 1 minute is mixed with a nuclide produced by the decay of a short-lived nuclide having a half-life of 1 minute to less than 1 year.

For example, ¹¹ C, ¹³ N, ¹⁴ O, ¹⁵ O, ¹⁷ F, ¹⁸ F, ²⁴ Ne, ²⁴ Na, ²⁷ Mg, ²⁸ Mg, ²⁸ Al, ²⁹ Al, ³⁰ P , ³¹ Si, ³² P, ³⁵ S, ³⁷ S, ³⁷ Ar, ³⁸ S, ³⁸ Cl, ³⁸ K, ³⁹ Cl, ³⁹ Ar, ⁴¹ Ar, ⁴² K, ⁴³ K, ⁴³ Sc, ⁴⁴ K, ⁴⁴ Sc, ⁴⁵ K, ⁴⁵ Ti, ⁴⁶ Sc, ⁴⁷ K, ⁴⁷ Sc, ⁴⁷ V, ⁴⁸ Sc, ⁴⁸ V, ⁴⁸ Cr, ⁴⁹ K, ⁴⁹ Sc, ⁴⁹ V, ⁴⁹ Cr, ⁵¹ Ti, ⁵¹ Cr, ⁵¹ Mn, ⁵² Ti, ⁵² V, ⁵² Mn, ⁵² Fe, ⁵³ V, ⁵⁴ Mn, ⁵⁵ Cr, ⁵⁶ Cr, ⁵⁶ Mn, ⁵⁶ Co, ⁵⁶ Ni, ⁵⁷ Mn, ⁵⁷ Co, ⁵⁷ Ni, ⁵⁸ Co, ⁵⁹ Fe, ⁶⁰ Cu, ⁶⁰ Zn , ⁶¹ Fe, ⁶¹ Co, ⁶¹ Cu, ⁶¹ Zn, ⁶² Co, ⁶² Cu, ⁶² Zn, ⁶³ Zn, ⁶⁴ Cu, ⁶⁵ Ni, ⁶⁵ Zn, ⁶⁵ Ga, ⁶⁶ Ni, ⁶⁶ Cu, ⁶⁶ Ga, ⁶⁶ Ge, ⁶⁷ Cu, ⁶⁷ Ga, ⁶⁷ Ge, ⁶⁸ Ga, ⁶⁸ Ge, ⁶⁹ Zn, ⁶⁹ Ge, ⁷⁰ Ga, ⁷⁰ As, ⁷¹ Zn, ⁷¹ Ge, ⁷¹ As, ⁷¹ Se, ⁷² Zn, ⁷² Ga, ⁷² As, ⁷² Se, ^{73 Ga, 73 As, 73 Se} , 74 As, 75 Ge, 75 Se, 76 As, 76 Br, 76 Kr, 77 Ge, 77 As, 77 Br, 77 Kr, 78 Ge, 78 As, 78 Br, 79 Kr , ⁷⁹ Rb, ⁸⁰ Br, ⁸⁰ Sr, ⁸¹ Se, ⁸² Br, ⁸² Rb, ⁸² Sr, ⁸³ Rb, ⁸³ Sr, ³⁴ Se, ⁸⁴ Br, ⁸⁴ Rb, ⁸⁵ Sr, ⁸⁵ Y, ⁸⁵ Zr, ⁸⁶ Rb, ⁸⁶ Y, ⁸⁶ Zr, ⁸⁷ Y, ⁸⁷ Zr, ⁸⁸ Kr, ⁸⁸ Rb, ⁸⁸ Y, ⁸⁸ Zr, ⁸⁹ Kr, ⁸⁹ Rb, ⁸⁹ Sr, ⁸⁹ Zr, ⁸⁹ Nb, ⁹⁰ Y, ⁹⁰ Nb, ⁹⁰ Mo, ⁹¹ Sr, ⁹¹ Y, ⁹¹ Nb, ⁹¹ Mo, ⁹² Sr, ⁹² Y, ⁹³ Sr, ⁹³ Y, ⁹⁴ Sr , ⁹⁴ Y, ⁹⁴ Tc, ⁹⁴ Ru, ⁹⁵ Y, ⁹⁵ Zr, ⁹⁵ Nb, ⁹⁵ Tc, ⁹⁵ Ru, ⁹⁶ Nb, ⁹⁶ Tc, ⁹⁷ Zr, ⁹⁷ Nb, ⁹⁸ Ru, ⁹⁹ Rh, ⁹⁹ Pd, ¹⁰⁰ Rh, ¹⁰⁰ Pd, ¹⁰¹ Mo, ¹⁰¹ Tc, ¹⁰² Mo, ¹⁰² Tc, ¹⁰³ Mo, ¹⁰³ Tc, ¹⁰³ Ru, ¹⁰³ Pd, ¹⁰⁴ Tc, ¹⁰⁴ Ag, ¹⁰⁴ Cd, ¹⁰⁵ Ru, ¹⁰⁵ Rh, ¹⁰⁵ Ag, ¹⁰⁵ Cd, ¹⁰⁶ Ag, ¹⁰⁶ In, ¹⁰⁷ Cd, ¹⁰⁷ In, ¹⁰⁸ Ru, ¹⁰⁸ Ag, ¹⁰⁸ In, ¹⁰⁹ Pd, ¹¹⁰ In, ¹¹⁰ Sn, ¹¹¹ Pd, ¹¹¹ Ag, ¹¹¹ In, ¹¹¹ Sn, ¹¹² Pd, ¹¹² Ag, ¹¹² In, ¹¹³ Pd , ¹¹³ Ag, ¹¹³ Sn, ¹¹⁴ In, ¹¹⁵ Sb, ¹¹⁶ Sb, ¹¹⁶ Te, ¹¹⁷ Cd, ¹¹⁷ In, ¹¹⁷ Sb, ¹¹⁸ Cd, ¹¹⁸ Sb, ¹¹⁸ Te, ¹¹⁹ Sb, ¹¹⁹ Te, ¹¹⁹ I, ¹²⁰ Sb, ¹²⁰ I, ¹²⁰ Xe, ¹²¹ Sn, ¹²¹ Te, ¹²¹ I, ¹²¹ Xe, ¹²² Sb, ¹²² I, ¹²² Xe, ¹²³ Sn, ¹²⁴ Sb, ¹²⁴ I, ¹²⁵ I, ¹²⁵ Xe, ¹²⁵ Cs, ¹²⁶ Sb, ¹²⁶ I, ¹²⁶ Cs, ¹²⁶ Ba, ¹²⁷ Sn, ¹²⁷ Sb, ¹²⁷ Te, ¹²⁷ Xe, ¹²⁷ Cs, ¹²⁷ Ba, ¹²⁸ Sn, ¹²⁸ Sb, ¹²⁸ I, ¹²⁸ Cs, ¹²⁸ Ba, ¹²⁹ Cs, ¹²⁹ Ba, ¹³⁰ Sb, ¹³⁰ I ^{, 130 Cs, 131 Sb, 131} Te, 131 I, 131 Cs, 131 Ba, 132 Te, 132 I, 132 Cs, 132 La, 133 Te, 133 I, 133 Xe, 134 Te, 1 ³⁴ I, ¹³⁴ La, ¹³⁴ Ce, ¹³⁵ La, ¹³⁵ Ce, ¹³⁶ I, ¹³⁶ Cs, ¹³⁶ La, ¹³⁶ Pr, ¹³⁸ Xe, ¹³⁸ Cs, ¹³⁸ Pr, ¹³⁸ Nd, ¹³⁹ Cw, ¹³⁹ Ba, ¹³⁹ Ce, ¹³⁹ Pr , ¹³⁹ Nd, ¹⁴⁰ Cs, ¹⁴⁰ Ba, ¹⁴⁰ La, ¹⁴⁰ Pr, ¹⁴⁰ Nd, ¹⁴¹ Ba, ¹⁴¹ La, ¹⁴¹ Ce, ¹⁴¹ Nd, ¹⁴² Ba, ¹⁴² La, ¹⁴² Pr, ¹⁴² Sm, ¹⁴³ La, ¹⁴³ Ce, ¹⁴³ Pr, ¹⁴³ Pm, ¹⁴³ Sm, ¹⁴⁴ Ce, ¹⁴⁴ Pr, ¹⁴⁴ Pm, ¹⁴⁴ Gd, ¹⁴⁵ Ce, ¹⁴⁵ Pr, ¹⁴⁶ Pr, ¹⁴⁶ Eu, ¹⁴⁶ Gd, ¹⁴⁹ Nd, ¹⁴⁹ Pm, ¹⁴⁹ Eu, ¹⁵⁰ Pm, ¹⁵² Pm, ¹⁵³ Pm, ¹⁵³ Sm, ¹⁵³ Gd, ¹⁵³ Tb, ¹⁵⁴ Pm, ¹⁵⁵ Tb, ¹⁵⁵ Dy, ¹⁵⁶ Sm, ¹⁵⁶ Eu, ¹⁵⁶ Tb, ¹⁵⁷ Eu, ¹⁵⁸ Eu, ¹⁵⁸ Ho, ¹⁵⁸ Er, ¹⁵⁹ Gd, ¹⁵⁹ Dy, ¹⁵⁹ Ho , ¹⁵⁹ Er, ¹⁶⁰ Tb, ¹⁶⁰ Ho, ¹⁶⁰ Er, ¹⁶¹ Gd, ¹⁶¹ Tb, ¹⁶¹ Ho, ¹⁶¹ Er, ¹⁶¹ Tm, ¹⁶² Gd, ¹⁶² Tb, ¹⁶² Ho, ¹⁶² Tm, ¹⁶³ Tb, ¹⁶⁴ Tb, ¹⁶⁴ Ho, ¹⁶⁴ Tm, ¹⁶⁴ Yb, ¹⁶⁵ Dy, ¹⁶⁵ Er, ¹⁶⁵ Tm, ¹⁶⁵ Yb, ¹⁶⁶ Dy, ¹⁶⁶ Ho, ¹⁶⁶ Tm, ¹⁶⁶ Yb, ¹⁶⁷ Dy, ¹⁶⁷ Ho, ¹⁶⁷ Tm, ¹⁶⁷ Yb, ¹⁶⁸ Ho, ¹⁶⁸ Tm, ¹⁶⁹ Er, ¹⁶⁹ Yb, ¹⁶⁹ Lu, ¹⁶⁹ Hf, ¹⁷⁰ Tm, ¹⁷⁰ Lu, ¹⁷⁰ Hf, ¹⁷¹ Lu, ¹⁷¹ Hf, ¹⁷² Er, ¹⁷² Tm, ¹⁷² Lu, ¹⁷³ Er, ¹⁷³ Tm, ¹⁷⁴ Tm, ¹⁷⁵ Yb, ¹⁷⁵ Hf, ¹⁷⁵ Ta , ¹⁷⁵ W, ¹⁷⁶ Ta, ¹⁷⁶ W, ¹⁷⁷ Yb, ¹⁷⁷ Lu, ¹⁷⁷ Ta, ¹⁷⁷ W, ¹⁷⁸ Yb, ¹⁷⁸ Lu , ¹⁷⁸ Ta, ¹⁷⁸ W, ¹⁷⁹ Lu, ¹⁸⁰ Ta, ¹⁸⁰ Re, ¹⁸¹ Hf, ¹⁸¹ W, ¹⁸¹ Re, ¹⁸¹ Os, ¹⁸² Ta, ¹⁸² Re, ¹⁸² Os, ¹⁸³ Hf, ¹⁸³ Ta, ¹⁸³ Re, ¹⁸³ Os, ^{184 Ta, 184 Re, 185 Ta,} 185 W, 185 Os, 185 Ir, 186 Ta, 186 Re, 186 Ir, 186 Pt, 187 Ir, 187 Pt, 188 W, 188 Re, 188 Ir, 188 Pt, 189 W, ¹⁸⁹ Re, ¹⁸⁹ Ir, ¹⁸⁹ Pt, ¹⁸⁹ Hg, ¹⁹⁰ W, ¹⁹⁰ Re, ¹⁹⁰ Ir, ¹⁹¹ Os, ¹⁹¹ Pt, ¹⁹¹ Au, ¹⁹¹ Hg, ¹⁹² Ir, ¹⁹² Au, ¹⁹² Hg, ¹⁹³ Os, ¹⁹⁴ Ir, ¹⁹⁴ Au , ¹⁹⁵ Ir, ¹⁹⁵ Au, ¹⁹⁵ Hg, ¹⁹⁵ Pb, ¹⁹⁶ Au, ¹⁹⁶ Pb, ¹⁹⁷ Pt, ¹⁹⁷ Hg, ¹⁹⁷ Tl, ¹⁹⁷ Pb, ¹⁹⁸ Au, ¹⁹⁸ Tl, ¹⁹⁸ Pb, ¹⁹⁹ Pt, ¹⁹⁹ Au, ¹⁹⁹ Tl, ¹⁹⁹ Pb, ²⁰⁰ Pt, ²⁰⁰ Au, ²⁰⁰ Tl, ²⁰⁰ Pb, ²⁰⁰ Bi, ²⁰¹ Tl, ²⁰¹ Pb, ²⁰¹ Bi, ²⁰² Tl, ²⁰³ Hg, ²⁰³ Pb, ²⁰³ Bi, ²⁰⁴ Bi, ²⁰⁵ Hg, ²⁰⁶ Hg, ²⁰⁶ Tl, ²⁰⁶ Bi, ²⁰⁶ Po, ²⁰⁶ At, ²⁰⁷ Tl, ²⁰⁸ Tl, ²⁰⁹ Tl, ²⁰⁹ Pb, ²¹⁰ Bi, ²¹⁰ Po, ²¹¹ Pb, ²¹¹ Bi, ²¹¹ Po, ²¹⁵ At, ²¹⁵ Po, ²¹⁵ Bi, ²¹⁹ Rn, ²¹⁹ At , ²²³ Ra, ²²³ Fr, ²²⁷ Th, ²¹² Po, ²¹² Bi, ²¹² Pb, ²¹⁶ Po, ²²⁰ Rn, ²²⁴ Ra, ²¹³ Po, ²¹³ Bi, ²¹⁷ At, ²²¹ Fr, ²²⁵ Ac, ²²⁵ Ra it can.

Among these short-lived nuclides, they are harmless to unstable nuclides that decay into charge storage films such as O, N, Si, Zr, and Hf and elements that constitute semiconductors, or semiconductors such as rare gases. The use of unstable nuclides that decay into elements is particularly desirable in that the effort to build a process that suppresses the diffusion of stable isotopes after decay is minimized. For example, ²⁸ Mg, ³⁸ S, ³⁸ Cl, ⁸² Br, ⁸² Sr, ⁸³ Rb, ⁸³ Sr, ⁹² Sr, ⁹² Y, ⁹³ Y, ¹²⁸ Ba, ¹²⁹ Cs, ¹²⁹ Ba, ¹³¹ Cs, ¹³¹ Ba, ¹³² Te, ¹³² I, ¹⁷⁶ Ta, ¹⁷⁷ Yb, ¹⁷⁷ Lu, ¹⁷⁷ Ta, ¹⁷⁷ W, ¹⁷⁸ Yb, ¹⁷⁸ Lu, ¹⁷⁸ Ta, ¹⁷⁸ W, ¹⁷⁹ Lu, and the like. For example, when the charge storage film is HfO ₂ , an unstable nuclide such as ¹⁷⁶ Ta may be used and a stable isotope such as ¹⁷⁶ Hf may be generated by decay.

Among these nuclides that are short-lived nuclides and whose elements after decay are harmless to semiconductors, nuclides having a half-life of 8 hours to 30 days are particularly preferred in the process. For example, ²⁸ Mg (half-life 21 hours), ³² P (half-life 14 days), ⁸² Br (half-life 1.4 days), ⁸² Sr (half-life 26 days), ⁸³ Sr (half-life 1.4 days), ⁹³ Y (half-life) period 10 hours), ¹²⁸ Ba (half-life 2.4 days), ¹²⁹ Cs (half-life 1.3 days), ¹²⁹ Ba (collapse from ¹²⁹ Cs to ¹²⁹ Xe (half-life 1.3 days) half-life 2 hours short-lived intermediate in the nuclide), ¹³¹ Cs (9. 6 days), ¹³¹ Ba (12 days), ¹³² Te (3 days), ¹⁷⁶ Ta (8 hours), ¹⁷⁶ W (collapse from ¹⁷⁶ Ta to ¹⁷⁶ Hf (half-life 8 hours) in short-lived intermediates nuclide half life 2 hours), ¹⁷⁷ Ta (2 days), ¹⁷⁸ W (22 days) is particularly preferred. Among these, ²⁸ Mg is preferable because the element after collapse is ²⁸ Si and has a particularly small influence on a semiconductor integrated circuit containing silicon as a main component.

  In addition, the half-life is h, the number of integrated cells in the memory chip is n, the flat band voltage shift amount required by the retention characteristics of the memory chip is Vfbs, the flat band window of the memory chip is Vfbw, and the charge storage film starts to be formed The manufacturing time from the end of the product inspection to the end of the memory chip is defined as p. All flat band windows Vfbw are caused by unstable nuclides introduced by the method of this embodiment, and all flat band voltage shifts Vfbs are caused by unstable nuclides remaining in the product in the method of this embodiment. Approximately, the amount Rr of short-lived nuclides introduced into the charge storage film and the various amounts Rr of short-lived remaining after the product inspection are completed in one memory cell. The relational expression / Ri = Vfbs / Vfbw is established. Considering the requirement that there should not be one defective cell among all the cells in the memory chip, this ratio (Rr / Ri) is further reduced to a value of (Vfbs / Vfbw) × (1 / n). become. This is because if the probability that a failure occurs in one memory cell is x, the probability that a failure occurs in n memory cells is nx, which is multiplied by n. n. If this value is written using the half life h and the production time p, it is (p / h) to the power of (1/2), so (Vfbs / Vfbw) × (1 / n) ≧ ((1/2) (P / h)) is established. The right side of this relational expression is the ratio of the ratio of unstable nuclides that remain even after the production time has elapsed and the ratio of unstable nuclides that have formed a flat band voltage window. The maximum value of this ratio is The ratio between the maximum retention voltage value allowable in the product and the flat band window width necessary for writing / erasing in the product. The actual retention voltage may be less than or equal to the maximum allowable voltage value used in this estimation. From the above relational expression, the relational expression h ≦ p / (ln ((Vfbs / Vfbw) × (1 / n)) / ln (1/2)) is required for the half-life.

According to this relational expression, assuming that a 100 Gbit memory chip is manufactured and Vfbs = 0.1 V, Vfbw = 20 V, and ²⁸ Mg (half-life 21 hours) is used, from the start of fabrication of the charge storage film It is sufficient that the time p until the end of product inspection is 39 days. This estimate is limited when the multi-level memory cell is required because the required specifications for the retention characteristics of the flat band shift are strict, but if it is a binary memory cell of 0 or 1, the flat band shift Can be relatively large, which has the advantage that the time p from the start of film formation to the end of product inspection can be shortened.

  The product inspection is also a safety, health and environmental inspection. That is, a standard that does not affect even a very delicate ultra-highly integrated memory device exceeds a standard that does not affect the human body or the like. Short-lived nuclides used for product production remain below natural radiation levels that are negligible for safety, health and the environment after product inspection.

[Method of producing unstable nuclides]
As the above-mentioned method of generating unstable nuclides, for example, fission reaction, fusion reaction, nuclear fragmentation reaction caused by collision of high energy particles such as protons, deuterons, tritium nuclei, helium trinuclear and lithium nuclei with atomic nuclei. Etc. can be used. In addition, it is also possible to employ a neutron absorption reaction in which particles having no charge, for example, particles such as neutrons are absorbed by the nucleus.

For example, a ^{30 Si (γ, 2p) 28} Mg reaction of irradiating gamma rays ³⁰ Si. This reaction formula shows that the nuclide ³⁰ Si in front of the parenthesis absorbs the left particle γ, that is, gamma ray (photon) in the parenthesis, and the inside of the nucleus is activated, and the right particle p in the parenthesis p It means that the nuclide ²⁸ Mg after the parenthesis is generated by releasing one. The same applies to the reaction formula described later. Other, it may also be mentioned a method of obtaining a ^{26 Mg (3H, p) 28} Mg reaction ²⁸ Mg, such as by implanting three hydrogen atoms to ²⁶ Mg. Further, after purification of the fission product ⁹⁰ Sr contained in the spent fuel of a nuclear reactor, also include a method for obtaining a ⁹⁰ Sr is ⁹⁰ Sr (β, ^ν) wait to beta decay spontaneously ⁹⁰ Y react by ⁹⁰ Y It is done.

  The unstable nuclides generated in this way are chemically separated, for example, using a solution and precipitation, using a column, or using a radioisotope (RI) beam in an electric quadrupole field in a vacuum. Separation is performed by a method of separating by mass / charge ratio by passing through, and necessary unstable nuclides are purified. It goes without saying that nuclides that do not harm the final LSI product need not be separated in this purification. For example, to briefly describe a method of extracting from a solution, in order to extract fission products in spent fuel, the spent fuel is dissolved with an acid or the like, and various ions are precipitated by various precipitation reactions. Magnesium is an ion that remains in the solution to the end together with sodium, etc., but separates by separating only magnesium using a reaction that precipitates magnesium with, for example, ammonium phosphate, against a mixed solution of ions such as sodium that do not precipitate to the end. There is a technique like this. The purified nuclide can be included in the target by, for example, directly irradiating the sputtering target with an RI beam separated by an electric quadrupole electric field. Alternatively, it is possible to drive into the raw material used for vacuum deposition by the same method. Further, it can be included in the raw material of the CVD method by being implanted into the raw material when the organometallic compound as the raw material of the CVD method is produced. These may be introduced into a charge storage film deposition apparatus to prepare for the deposition of the film 13a containing unstable nuclides.

[Safety during manufacturing process]
It has been described that the safety related to the radioactivity level of the device itself manufactured by the manufacturing method of the present embodiment has no problem as described above. On the other hand, it goes without saying that sufficient attention must be paid to the safety of factory workers during the process of manufacturing the device. The film forming apparatus usually has a strong and thick outer wall made of SUS material in order to maintain a vacuum or the like, and therefore, there is little leakage of radioactivity to the outside of the film forming apparatus. However, since the window portion may be a portion that leaks radioactivity, it is necessary to use a window material made of a material that blocks radioactivity, such as lead glass.

  In addition, it is necessary to devise a method in which exhaust or waste water from a manufacturing apparatus using unstable nuclides is once adsorbed to a detoxification column or the like at a sufficient rate and does not leak unstable nuclides to the outside. It is necessary to wait until the radioactivity from the unstable nuclide is sufficiently attenuated by leaving the abatement column or the like adsorbing the unstable nuclide for about the product inspection time described above. If the abatement column is replaced immediately after use, there is a risk that the operator will be exposed to the explosion. Therefore, for example, two types of abatement columns are prepared, and after using one of the column abatement columns, as described above, it is left without using these abatement columns for about the product inspection time, and the radioactivity is reduced. Replace the column after it has decayed sufficiently. On the other hand, while the detoxification column is not used, it is possible to maintain high productivity by continuing production with the other type of detoxification column.

  In order to prevent human error, it is desirable to attach a small radioactivity measuring device or the like and an interlock that cannot be maintained unless the radioactivity is sufficiently attenuated. Such maintenance is not limited to the abatement column. Since all production equipment after the process of introducing unstable nuclides has a danger of radioactivity, it is necessary to provide an interlock that forcibly waits until the radioactivity is sufficiently attenuated before maintenance.

(Second Embodiment)
FIG. 4 is a process cross-sectional view illustrating the method for manufacturing the nonvolatile semiconductor memory device of this embodiment. Parts corresponding to the components in FIG. 3 are denoted by the same reference numerals. The manufacturing method of this embodiment is different from the manufacturing method of the first embodiment in that a film containing an unstable nuclide is formed between the charge storage film and the tunnel insulating film.

  That is, as shown in FIG. 4A, the tunnel insulating film 11 is formed on the surface of the single crystal silicon substrate 10 as in the first embodiment. Next, a film 13a containing unstable nuclides is formed on the tunnel insulating film 11 by a film forming method such as a vacuum evaporation method, a sputtering method, or a CVD method that causes little damage to the underlying film. Thereafter, the nonvolatile semiconductor memory device shown in FIG. 4C is manufactured in the same manner as in the first embodiment. The unstable nuclide 13b is changed to the isotope 13 by the decay as in the first embodiment.

  According to this embodiment, the same effect as that of the first embodiment can be obtained. In the case of an element structure in which the block insulating film is omitted, an unstable nuclide is introduced at a position in the charge storage film 12 close to the interface between the charge storage film 12 and the tunnel insulating film 11, so that the control gate electrode 15 side is reached. Leakage current can be suppressed.

(Third embodiment)
FIG. 5 is a process cross-sectional view illustrating the method for manufacturing the nonvolatile semiconductor memory device of this embodiment. Parts corresponding to the components in FIG. 3 are denoted by the same reference numerals. The manufacturing method of this embodiment is different from the manufacturing method of the first embodiment in that an unstable nuclide is included in the charge storage film by an ion implantation method.

  That is, as shown in FIG. 5A, the tunnel insulating film 11 and the charge storage film 12 are formed on the surface of the single crystal silicon substrate 10 by using the same method as in the first embodiment. Further, as shown in FIG. 5B, a block insulating film 14 and a conductive film to be the control gate electrode 15 are sequentially formed on the charge storage film 12 as in the first embodiment.

Next, as shown in FIG. 5B, unstable nuclides are introduced into the charge storage film 12 at a density of, for example, about 10 ¹¹ atoms / cm ² by ion implantation of unstable nuclides. By this ion implantation method, some unstable nuclides may be introduced into the conductive film to be the tunnel insulating film 11, the block insulating film 14, or the control gate electrode 15. There is no problem if the thickness of the tunnel insulating film or the block insulating film is such that the leakage current is sufficiently small. In this embodiment, the ion implantation is performed after the conductive film to be the control gate electrode 15 is formed. However, before the block insulating film 14 is formed after the charge storage film 12 is formed, or the block insulating film 14 is formed. Then, before forming the conductive film to be the control gate electrode 15, ion implantation of unstable nuclides may be performed. If ion implantation is performed before the block insulating film 14 is formed, the content of unstable nuclides in the block insulating film 14 can be reduced, and the effect of suppressing leakage current in the block insulating film 14 is increased. For the ion implantation of unstable nuclides shown in the present embodiment, a technique in which an RI beam is directly implanted is also possible.

Here, the thickness of the tunnel insulating film 11 and the block insulating film 14 must have a margin. That is, when the thickness of the tunnel-insulating film 11 or the block insulating film 14 where there is no defect is insufficient, the retention characteristics deteriorate. For example, when a SiO ₂ film is used as the tunnel insulating film 11, it is desirable that a defect-free film thickness of about 4 nm or more exists. Since the block insulating film 14 is often much thicker than the tunnel insulating film 11, this restriction is more relaxed and does not pose any problem if it is manufactured normally.

  The film thickness of the charge storage film is preferably 20 nm or less. If the thickness exceeds 20 nm, the actual film thickness of the storage film becomes thicker than the size of the miniaturized memory element in the in-plane direction, so that the element becomes elongated in the film thickness direction, making processing difficult. Therefore, a problem arises in robustness.

  Thereafter, the nonvolatile semiconductor memory device shown in FIG. 5C is manufactured in the same manner as in the first embodiment. The unstable nuclide 13b is changed to the isotope 13 by the decay as in the first embodiment.

  According to this embodiment, the same effect as that of the first embodiment can be obtained. In addition, if a technique such as direct ion implantation of the RI beam is used, it is possible to obtain an effect that the number of steps that must be taken care of against radioactive contamination is drastically reduced.

  In addition, this invention is not limited to the said embodiment. The example of the present invention is an invention related to the elemental technology in the memory cell, and does not depend on the connection method of the memory cell at the circuit level. Therefore, in addition to the NAND type nonvolatile semiconductor memory, the NOR type, the AND type, DINOR-type non-volatile semiconductor memory, two-tra type flash memory that combines the advantages of NOR-type and NAND-type, and three-tra-NAND type having a structure in which one memory cell is sandwiched between two select transistors It is also applicable to. The present invention can also be applied to a flash memory having an architecture having both a NAND type interface and a NOR type high reliability and high speed read function.

  Moreover, in the said embodiment, although the example which used the surface part of the silicon substrate was shown as a semiconductor layer of this invention, it is not restricted to this, The silicon layer etc. of a SOI (Silicon On Insulator) substrate are used as a semiconductor layer. Alternatively, a semiconductor material other than silicon may be used. Further, the present invention is applicable not only to semiconductor devices but also to devices that are essential for accumulating electric charges in electrical defects, such as memory devices and switching devices.

  In addition, the present invention is not limited to the above-described embodiments and examples as they are, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments and examples. For example, you may delete some components from all the components shown by embodiment and an Example. Furthermore, you may combine suitably the component covering different embodiment and an Example.

1 is a cross-sectional view showing a structure of a nonvolatile semiconductor memory device according to a first embodiment. The schematic diagram which shows the example of a fission track. Process sectional drawing explaining the manufacturing method of the non-volatile semiconductor memory device of 1st Embodiment. Process sectional drawing explaining the manufacturing method of the non-volatile semiconductor memory device of 2nd Embodiment. Process sectional drawing explaining the manufacturing method of the non-volatile semiconductor memory device of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Silicon substrate 10a, 10b Source region and drain region 10c Channel region 11 Tunnel insulating film 12, 12a, 12b Charge storage film 13 Isotope 13a Film containing unstable nuclide 13b Unstable nuclide 14 Block insulating film 15 Control gate electrode

Claims (10)

A source region and a drain region formed on the surface of the semiconductor layer, a tunnel insulating film provided on the semiconductor layer between the source region and the drain region, and provided on the tunnel insulating film; An insulating charge storage film containing an isotope ratio different from the isotope ratio in the natural state, a block insulating film provided on the charge storage film, and a control provided on the block insulating film A nonvolatile semiconductor memory device comprising: a gate electrode; The nonvolatile semiconductor memory device according to claim 1, wherein the isotope is generated by decay of an unstable nuclide, and a half-life of the unstable nuclide is 1 minute or more and 1 year or less. A source region and a drain region formed on the surface of the semiconductor layer, a tunnel insulating film provided on the semiconductor layer between the source region and the drain region, and provided on the tunnel insulating film; An insulating charge storage film containing an isotope generated by the decay of an unstable nuclide, a block insulating film provided on the charge storage film, and a control gate electrode provided on the block insulating film And a non-volatile semiconductor memory device. 4. The nonvolatile semiconductor memory device according to claim 3, wherein a half-life of the unstable nuclide is 1 minute or more and 1 year or less. 5. The nonvolatile semiconductor memory device according to claim 2, wherein the charge storage film includes a linear defect due to the decay of the unstable nuclide. Forming a tunnel insulating film on the semiconductor layer; forming a charge storage film containing unstable nuclides on the tunnel insulating film; forming a block insulating film on the charge storage film; Forming a control gate electrode on the insulating film. A method for manufacturing a nonvolatile semiconductor memory device. Forming a tunnel insulating film on the semiconductor layer; forming a film containing unstable nuclides on the tunnel insulating film; and forming a first charge storage film so as to cover the film containing unstable nuclides And a step of forming a block insulating film on the charge storage film, and a step of forming a control gate electrode on the block insulating film. . The nonvolatile semiconductor memory according to claim 7, further comprising a step of forming a second charge storage film on the tunnel insulating film before the step of forming the film containing the unstable nuclide. Device manufacturing method. Forming a tunnel insulating film on the semiconductor layer; forming a charge storage film on the tunnel insulating film; forming a block insulating film on the charge storage film; and controlling on the block insulating film A method for manufacturing a nonvolatile semiconductor memory device, comprising: forming a gate electrode; and injecting an unstable nuclide into the charge storage film. The method further comprises: patterning at least the charge storage film; and forming a source region and a drain region separately on the surface of the semiconductor layer on both sides of the patterned charge storage film. A method for manufacturing a nonvolatile semiconductor memory device according to claim 6.

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