JP3087189B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device in which the breakdown voltage of an oxide film is increased to prevent occurrence of dielectric breakdown of the oxide film even when an electric field is applied for a long time, thereby improving long-term reliability. About the method.

[0002]

2. Description of the Related Art With the advancement of computer systems in recent years, it has been demanded that LSIs, which are the brains of such systems, have higher reliability. In particular, various measures have been taken since the occurrence of dielectric breakdown in the insulating film in the semiconductor element during long-term operation is fatal to the system.
Typically, efforts are made to clean the LSI manufacturing process and to prevent impurities at the particle level or the atomic level from entering the insulating film.

In general, when fabricating a MOS structure of a semiconductor device, a gate oxide film and a storage capacitor oxide film are formed by a heat treatment in an oxygen atmosphere, and a polycrystalline S
An electrode such as i (polysilicon) is deposited. However,
As the element is miniaturized, the electric field applied to the oxide film becomes higher, and dielectric breakdown is more likely to occur.

[0004] One of the causes of dielectric breakdown is heavy metal impurities taken into the oxide film. A typical mechanism of dielectric breakdown caused by heavy metal impurities will be described with reference to FIG. FIG. ₂ shows a structure in which an SiO ₂ oxide film 32 is formed on a Si substrate 31 and a polycrystalline Si electrode layer 33 is formed thereon. First, FIG. 3A shows that heavy metal (M) taken in oxide film 32 is deposited in the form of free metal atoms in the precipitate 34 in the film.
In this case, the substrate 34 and the electrode 3 are
3 is a dielectric breakdown caused by a short circuit. The occurrence of precipitation in the oxide film depends on the solid solubility of the heavy metal element in the oxide film. A metal having a low solid solubility in an oxide film, for example, Fe in SiO ₂ is easily precipitated, which causes a reduction in the pressure resistance of the SiO ₂ film.

Next, in the case of FIG. 1B, the heavy metal (M) taken in the oxide film 32 is combined with oxygen of SiO ₂ of the oxide film 32 when subjected to a heat treatment in a subsequent step. To form a metal oxide (MO) 35, resulting in Si atoms 36
Is swept out and becomes excessively present in the oxide film 32, causing dielectric breakdown. For impurity metals (Al, Fe, Cu, Ni, Co, Cr, Mn), which are generally problematic, this binding / sweeping-out reaction occurs as follows.

4 / 3Al + SiO ₂ → 2 / 3Al ₂ O ₃ + Si 3 / 2Fe + SiO ₂ → 1 / 2Fe ₃ + Si 4Cu + SiO ₂ → 2Cu ₂ O + Si 2Ni + SiO ₂ → 2NiO + Si 2Co + SiO ₂ → 2CoO + Si 4 / 3Cr + SiO ₂ → 2 / 3Cr ₂ O ₃ + Si ₂ Mn + SiO ₂ → 2Mn + Si The Si atoms swept out by the above reaction increase the conductivity of the oxide film and lower the breakdown voltage strength.

Therefore, in order to reduce heavy metal contamination, it is necessary to purify gases, chemicals and materials used to prevent the adhesion of contaminants, and to remove the adhered contaminants by washing. I have.

[0008]

However, in order to prevent contaminants from adhering, it is necessary to purify the entire system including the apparatus, and it is not desirable to clean the apparatus simultaneously with the action of removing the contaminants. Etching is involved. As described above, in order to obtain an oxide film with a low withstand voltage, a great deal of investment, time, and effort are required to prevent the adhesion of contaminants. In addition, it is necessary for the operator to control the amount of etching of the surface for cleaning having an effect of removing contamination, and it is necessary to consider the difficulty of causing surface shape disorder.

An object of the present invention is to provide a method of manufacturing a semiconductor device capable of forming an oxide film which is less likely to cause dielectric breakdown without requiring a large investment, labor and time, and without an undesirable etching action. I do.

[0010]

In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention comprises forming an oxide film as a gate oxide film or a storage capacitor oxide film on a semiconductor substrate. And applying 10 ¹² cm ^-2 to the oxide film.
A step of implanting oxygen ions at a dose of more than 10 ¹⁶ cm ^-2 and then performing a heat treatment to convert free metal atoms present in the oxide film into oxides.

[0011]

According to the present invention, oxygen is introduced into an oxide film by ion implantation, and then heat treatment is performed to convert free metal atoms present as impurities in the oxide film into oxides, and at the same time, the semiconductor elements are converted into atoms. And (B) the short-circuit effect due to the precipitation of the free impurity metal and (B) the short-circuit effect due to the swept-out semiconductor atoms.

FIG. 2 is a schematic view illustrating the principle of the present invention, taking an oxide film made of SiO ₂ as an example. First, as shown in FIG. 2A, oxygen (O) is introduced into the SiO ₂ film by ion implantation, and the introduced oxygen (O) is introduced into the SiO ₂ network where the impurity metal element (M) exists. ) Is added.

By performing heat treatment from this state, the metal element (M) forms a metal oxide (MO) as shown in FIG. At this time, the SiO ₂ of the oxide film is S
It is maintained in the form of an oxide without being swept out as an i atom. In this oxide formation reaction, the metal element M is Al, F
In the case of e, Cu, Ni, Co, Cr, and Mn, the following occurs respectively.

4/3 Al + SiO ₂ + O ₂ → 2/3 Al ₂ O ₃ + SiO ₂ 3 / 2Fe + SiO ₂ + O ₂ → 1 / 2Fe ₃ + SiO ₂ 4Cu + SiO ₂ + O ₂ → 2Cu ₂ O + SiO ₂ 2Ni + SiO ₂ + O ₂ → 2NiO + SiO ₂ 2Co + SiO ₂ + O ₂ → 2CoO + SiO ₂ 4 / 3Cr + SiO ₂ + O ₂ → 2 / 3Cr ₂ O ₃ + SiO ₂ 2Mn + SiO ₂ + O ₂ → 2Mn + SiO ₂ Thus, both the impurity metal in the oxide film and the SiO ₂ constituting the oxide film are both oxides. Since it exists in the form, no precipitation of free metal atoms and no short-circuiting action by the swept-out semiconductor atoms occur as in the related art.

The dose by oxygen ion implantation is 10 ¹³ to
It is appropriate to be about 10 ¹⁵ cm ^-2 . At 10 ¹² cm ^-2 or less, a clear effect is not recognized, and at 10 ¹⁶ cm ^-2 or more, defects in the oxide film increase and recovery becomes difficult even by heat treatment, which is not preferable. It is appropriate that the heat treatment performed after the oxygen ion implantation be performed at a temperature of 900 ° C. or lower. 10
In a heat treatment of 00 ° C. or more, the SiO ₂ surface and Si / Si
The effect is lost due to the roughening of the O ₂ interface. The lower limit of the heat treatment temperature does not need to be particularly determined, and can be appropriately set within a range where the effect is recognized at a temperature of 900 ° C. or less.
A heat treatment time of about 10 to 30 minutes is sufficient. Usually, an inert gas atmosphere such as a nitrogen gas atmosphere is used as the heat treatment atmosphere.

Hereinafter, the present invention will be described in more detail by way of examples.

[0017]

1A to 1C, an example in which an SiO ₂ film is processed according to the present invention will be described. First, as shown in FIG. 1A, a P-type (100) Si wafer 11 is formed.
Was heat-treated in a dry oxygen atmosphere at 1000 ° C. to form an oxide film (SiO ₂ film) 12 having a thickness of 20 nm on the surface.

Next, as shown in FIG.
O_TwoOxygen ions 13 were implanted into the film 12. Ion implantation strip
The subject is an irradiation angle of 7 °, an implantation energy of 4 keV, and a dose amount.
10 ¹³cm^-2Met. The injected oxygen is shown in FIG.
As shown, SiO_TwoIn the vicinity of the center of the film thickness of the film 12, Rp (min.
It is present in the film 12 in a state having a cloth peak) 14. acid
After implantation of elementary ions, 800 in an electric furnace and in a nitrogen gas atmosphere.
A heat treatment was performed at 10 ° C. for 10 minutes.

An example of the measurement result of the tunnel leak current of the MOS structure manufactured by performing the above processing is described in Fowler.
FIG. 4 shows a -Nordheim plot. For comparison, the figure also shows the results of a sample without oxygen ion implantation and a sample without ion implantation. In the figure, E on the horizontal axis indicates the applied electric field intensity, and J on the vertical axis indicates the measured current density. The linearity of the Fowler-Nordheim plot indicates that a tunnel current is flowing in the oxide film.

From the results shown in the figure, when the processing according to the present invention was performed, the electric field intensity E = 10 MV / cm (1 / E in the figure).
= 1 × 10 ⁻⁷ cm / V), the current value is reduced to about ３ as compared with the case without the treatment, and it can be seen that the leak resistance is remarkably improved. FIG. 5A is a histogram of the breakdown voltage of the 180 MOS diodes manufactured by performing the above-described processing, and FIG. 5B is a histogram of a comparative example in which the processing of the present invention is not performed. 10
The non-defective product having a withstand voltage of MV / cm or more was improved to 93% by performing the treatment of the present invention, while the comparative example without treatment was 69%.

[0021]

As described above, according to the present invention,
By performing the oxygen ion implantation and the heat treatment, it is possible to manufacture a semiconductor device in which the breakdown voltage strength of the oxide film is increased without requiring a large investment, labor and time, and without an undesirable etching action.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a process for performing an oxide film treatment according to the present invention.

FIG. 2 is a schematic diagram showing, at an atomic level, a structure of an oxide film after oxygen ion implantation and subsequent heat treatment are performed according to the present invention.

FIG. 3 is a cross-sectional view schematically showing a mechanism in which dielectric breakdown of an oxide film occurs due to a metal element taken into the oxide film.

FIG. 4 shows the behavior of a tunnel leak current of a MOS structure fabricated by performing oxygen ion implantation and subsequent heat treatment on an oxide film according to the present invention, as compared with a conventional MOS structure fabricated without oxygen ion implantation and oxygen ion implantation. 7 is a graph showing a comparison with a MOS structure manufactured without heat treatment.

FIG. 5 is a graph showing the appearance frequency of the breakdown voltage strength of a MOS diode manufactured by performing oxygen ion implantation and subsequent heat treatment on an oxide film according to the present invention, as compared with a conventional case in which oxygen ion implantation is not performed.

[Explanation of symbols]

11 ... P-type (100) Si wafer 12 ... oxide film (SiO ₂ film) 13 ... oxygen ion beam 14 ... distribution peak position 21 ... Si atoms 22 ... oxygen atom 23 ... metal atom of oxygen injected into the oxide film 12 DESCRIPTION OF SYMBOLS 31 ... Si substrate 32 ... Oxide film (Si film) 33 ... Polycrystalline Si film (polysilicon film) 34 ... Deposited metal (M) 35 ... Metal oxide (MO) 36 ... Sweeped Si atoms

Claims (2)

(57) [Claims] A gate oxide film or accumulation on a semiconductor substrate
Forming an oxide film as a capacitor oxide film, and oxide film to 10 ¹² cm ^-2 to exceed 10 ¹⁶ cm ^-2 than the dough
A method of manufacturing a semiconductor device, comprising the step of: converting a free metal atom present in an oxide film into an oxide by performing a heat treatment after implanting oxygen ions in a small amount . 2. The method according to claim 1, wherein a dose of said oxygen ion implantation is 1
0 ¹³ ~10 ¹⁵ cm ^-2 and then, the method of manufacturing a semiconductor device according to claim 1, characterized in that the heat treatment at 900 ° C. or lower.