JPH08330302A - Preparation of silicon oxide film - Google Patents

Abstract

PURPOSE: To provide a method for preparation a highly reliable silicon oxide film in which the E' center is reduced while enhancing the dielectric breakdown strength. CONSTITUTION: In the method for preparing a silicon oxide, film, a silicon oxide film 11 is prepared on a semiconductor substrate 10 and implanted with ions before being heat-treated in an inert atmosphere containing a halogen element. Preferably, the ion species is at least one kind of element selected from a group of silicon, oxygen, nitrogen, arsenic, phosphorus and halogen or a its compound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a silicon oxide film on a semiconductor substrate.

[0002]

2. Description of the Related Art In manufacturing a MOS type semiconductor device,
It is necessary to form a gate oxide film made of a silicon oxide film on the surface of the semiconductor substrate, and it is no exaggeration to say that the characteristics of this silicon oxide film play a role in the reliability of the MOS type semiconductor device. Therefore, the silicon oxide film is always required to have a high breakdown voltage. Various models have been proposed as the dielectric breakdown mechanism of the silicon oxide film, but the general idea is that the electron or hole trap in the silicon oxide film is involved, and in particular, the hole trap of C. Hu et al. The insulation breakdown model by is famous. Regarding this, IC Chen, S. Holland and C. Hu: IEEE Trans.
See Electron Devices, pp413-422, 1985.

When evaluating this hole trap, it is difficult to obtain microscopic information only by electrical measurement.
Light, X-ray, electron spin resonance (Electron Spin Resonanc
There are many research reports using a physical analysis technique such as e, hereinafter abbreviated as ESR). In particular, it is known from the results of ESR analysis that structural defects called E ′ centers exist in the silicon oxide film.

The E'center is a trivalent silicon defect associated with oxygen vacancies and has a form as shown in FIG.
That is, one Si atom is bonded to three O atoms, but a dangling bond exists in such one Si atom. It is known that the E ′ center is increased by injection of holes and irradiation of gamma rays. Figure 5
Shows a model in which E'centers are generated by trapping holes in oxygen vacancies. Further, it is known that the density of the E ′ center has a one-to-one correspondence with the hole trap density obtained from electrical CV (capacitance-voltage) measurement. That is, it is considered that the E ′ center is the hole trap that causes the dielectric breakdown of the silicon oxide film.
The source of Figure 5 is Hideki Sakata and Akira Toriumu,
"Substrate Hole Current Generation and Oxide Brea
kdown in Si MOSFETs under Fowler-Nordheim Electron
Tunneling Injection ", IEDM 93, pp337-340.

[0005]

In order to obtain a highly reliable silicon oxide film having a high breakdown voltage, it is necessary to reduce hole traps which are considered to cause a dielectric breakdown. In order to reduce the hole traps, it is necessary to reduce the E ′ center which is one of the structural defects of the silicon oxide film.

Therefore, an object of the present invention is to provide a method of forming a silicon oxide film having a small number of E'centers, a high breakdown voltage, and a highly reliable silicon oxide film.

[0007]

The method of forming a silicon oxide film according to the present invention for achieving the above object comprises forming a silicon oxide film on a semiconductor substrate and then implanting ions by the ion implantation method. And then heat-treating the silicon oxide film in an inert gas atmosphere containing a halogen element.

In the method for forming a silicon oxide film of the present invention, the ion species in the ion implantation may be any ion species that does not adversely affect the characteristics of the silicon oxide film. , Oxygen, nitrogen,
It is preferably in the form of at least one element selected from the group consisting of arsenic, phosphorus, boron and halogen elements, or a compound composed of such an element.

The projection range of the energy of ion implantation is
It is preferable to select in the silicon oxide film or near the interface between the silicon oxide film and the semiconductor substrate. In addition, the dose amount and energy of ion implantation are 1 ×
It is desirable that the pressure is 10 ^{10 to} 1 × 10 ¹⁶ cm ^-2 , and 1 to 50 keV. The energy of ion implantation is
It may be determined based on the thickness of the silicon oxide film and the type of ion species used.

The method for forming the silicon oxide film may be any method, but it is preferable to use the humidification oxidation method, and the pyrogenic oxidation method is particularly preferable.

As the halogen element contained in the inert gas atmosphere, chlorine, bromine and fluorine can be mentioned, and among them, chlorine is preferable. The form of the halogen element contained in the inert gas is, for example, H
Cl, CCl ₄ , C ₂ HCl ₃ , CH ₂ Cl ₂ , C ₂ H ₃ C
Examples include l ₃ , Cl ₂ , Br ₂ , HBr, NF ₃ and SF ₆ . The content rate of halogen element in the inert gas is
0.001 to 10 based on the form of molecule or compound
%, Preferably 0.005 to 10% by volume, more preferably 0.02 to 10% by volume. For example, when using hydrochloric acid gas, the content rate of hydrochloric acid gas in the inert gas is 0.02
It is desirable to be 10% by volume. Examples of the inert gas may include nitrogen gas and argon gas.

Further, the heat treatment is preferably a furnace annealing treatment. The temperature of the heat treatment is 700 to 1200 ° C,
It is preferably 700 to 1100 ° C.

The semiconductor substrate is not limited to a semiconductor substrate such as a silicon semiconductor substrate itself, but also a semiconductor substrate on which an epitaxial layer, a polycrystalline layer, or an amorphous layer is formed. It means an underlayer on which a silicon oxide film is to be formed, such as a semiconductor layer formed on a layer. The silicon semiconductor substrate is manufactured by the CZ method, M
Any method such as CZ method, DLCZ method and FZ method may be used, or hydrogen annealing may be performed in advance.

The method of forming a silicon oxide film according to the present invention includes, for example, forming a gate oxide film of a MOS type transistor, an interlayer insulating film and an element isolation region, forming a gate oxide film of a top gate type or bottom gate type thin film transistor, and a flash memory. The present invention can be applied to the formation of a silicon oxide film in various semiconductor devices such as the formation of a tunnel oxide film.

[0015]

The operation of the present invention will be described with reference to FIG. Although the silicon oxide film is amorphous, it does not mean that a periodic structure does not exist at all, and four oxygen atoms are locally bonded to one silicon atom as shown in FIG. It is believed to have structure. This also includes oxygen vacancies that cause the E'center. Here, when ions are implanted into the silicon oxide film by the ion implantation method,
The structure of the silicon oxide film becomes more disorderly amorphized. Next, when the silicon oxide film after ion implantation is heat-treated in an inert gas atmosphere containing a halogen element, a structure similar to FIG. 2A is formed again. At this time, if a halogen element is present in the inert gas atmosphere, instead of generating a silicon-silicon bond which becomes an oxygen vacancy,
A strong silicon-chlorine bond is generated ((B) of FIG. 2).
reference). As a result, generation of the E ′ center can be effectively suppressed.

Further, by defining the energy of ion implantation or the dose and energy of ion implantation, the structure of the silicon oxide film can be surely made amorphous.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on embodiments with reference to the drawings.

(Embodiment 1) As shown in the schematic partial cross-sectional view of FIG. 1A, a conventional pyrogenic, which is a kind of humidification oxidation method, is formed on the surface of a semiconductor substrate 10 made of a silicon semiconductor substrate. A silicon oxide film 11 having a thickness of 10 nm was formed by the oxidation method. The substrate temperature in the pyrogenic oxidation method was set to 850 ° C. In order to reduce the effect of microwave dielectric loss that occurs during ESR analysis,
The semiconductor substrate 10 has a resistivity of 1000 Ωcm or more.

Next, as shown in the schematic view of FIG. 1B, silicon ions were implanted into the silicon oxide film by the ion implantation method. The conditions for ion implantation were as follows. The projected range under this ion implantation condition is about 0.011 μm. Ion species: Si ⁺ dose: 1 × 10 ¹³ cm ^-2 Implantation energy: 10 keV

After the ion implantation, as shown in the schematic view of FIG. 1C, the silicon oxide film is heat-treated in a nitrogen gas atmosphere containing 0.1 vol% hydrochloric acid gas using a diffusion furnace. did. The heat treatment conditions were as follows. Substrate temperature: 850 ° C Heat treatment time: 30 minutes

Comparative Example 1 Comparative Example 1 is different from Example 1 in that the heat treatment after ion implantation was performed in a 100% nitrogen gas atmosphere. The resistivity of the silicon semiconductor substrate used, the conditions of the pyrogenic oxidation method, the ion implantation conditions, and the heat treatment conditions were the same as in Example 1.

(Comparative Example 2) Comparative Example 2 is different from Example 1 in that ion implantation was not performed. The resistivity of the silicon semiconductor substrate used, the conditions of the pyrogenic oxidation method and the heat treatment conditions were the same as in Example 1.

[ESR Analysis Method] The silicon oxide films obtained in Example 1, Comparative Example 1 and Comparative Example 2 were analyzed by ESR (electron spin resonance). Three samples each made of a semiconductor substrate on which a silicon oxide film was cut, which was cut into a 6 × 30 mm ² strip shape, were stacked three times and inserted into a sample tube of an analyzer. Using an X-band ESR analyzer (model number: JES-RE2X) manufactured by JEOL Ltd., E under the following conditions
SR analysis was performed. Microwave frequency: about 9 GHz Microwave power: 5 mW Measuring magnetic field: 320 ± 7.5 mT Measuring time constant: 0.03 sec Sample temperature: Room temperature Modulating magnetic field frequency: 100 kHz Modulating magnetic field width: 0.16 mT

[Quantification Result of E'Center Density by ESR Analysis] FIG. 3 shows the ESR spectrum which is the ESR differential signal of the sample obtained in Example 1. The large peaks at both ends of the ESR spectrum are due to Mn ²⁺ having a known spin amount, and the central peaks are the E ′ center and Pb.
At the center (at the interface between the silicon oxide film and the silicon semiconductor substrate or at the cleaved surface of the sample, one Si atom is bonded to three Si atoms, but there is a dangling bond in such one Si atom. It means).
The spin density of the E ′ center to be obtained is Mn with a known spin amount.
^It can be obtained by the area ratio with the ²⁺ peak.

FIG. 4 shows the quantitative results of the E ′ center density in the silicon oxide films obtained in Example 1, Comparative Example 1 and Comparative Example 2.
Shown in It can be seen that in Example 1, the E ′ center density is reduced by one digit or more as compared with Comparative Examples 1 and 2. The reason why the E1 center density of Example 1 is lower than that of Comparative Example 1 is that chlorine is contained in the heat treatment atmosphere after silicon ion implantation, and the oxygen vacancies that cause the E'center are present. It is presumed that this is because chlorine is bonded to form a silicon-chlorine bond. Further, the reason why Example 1 has a lower E ′ center density than Comparative Example 2 is that in Example 1, the structure having oxygen vacancies in the silicon oxide film is once destroyed by the implantation of silicon ions. In Comparative Example 2, it can be inferred that a large amount of oxygen vacancies generated during the formation of the silicon oxide film cannot be reduced only by the bond of chlorine by the heat treatment.

From the above ESR analysis results, it can be seen that the formation of E'centers is dramatically suppressed by the method for forming a silicon oxide film of the present invention.

The present invention has been described above based on the preferred embodiments, but the present invention is not limited to these embodiments. As the wet oxidation method, a conventional wet oxidation method in which water vapor is mixed with a carrier gas such as oxygen, nitrogen, or argon, or dry oxygen is passed through a water bubbler can be employed. Further, the ion implantation conditions of oxygen ions of silicon ions are merely examples, and as other ion species, at least one element selected from the group consisting of oxygen, nitrogen, arsenic, phosphorus, boron and halogen elements, or such The form of a compound composed of elements can be mentioned. Furthermore,
Ion implantation is not limited to once, for example, silicon ions and oxygen ions are continuously implanted, or ion implantation and heat treatment are repeated several times, etc., within a range not departing from the gist of the present invention. The conditions can be changed as appropriate.

[0028]

In the silicon oxide film formed by the method for forming a silicon oxide film of the present invention, generation of E'centers can be effectively suppressed, so that there are few defects and excellent dielectric breakdown voltage characteristics. It is possible to form a silicon oxide film having high reliability.

[Brief description of drawings]

FIG. 1 is a schematic partial cross-sectional view of a semiconductor substrate or the like for explaining a method for forming a silicon oxide film of the present invention.

FIG. 2 is a diagram showing a schematic structure of a silicon oxide film for explaining the operation of the present invention.

FIG. 3 is a diagram showing an ESR spectrum in Example 1.

FIG. 4 ESR of Example 1 and Comparative Examples 1 and 2
It is a figure which shows E'center density calculated | required from the spectrum.

FIG. 5 is a diagram showing a generation model of an E ′ center by hole injection.

[Explanation of symbols]

 10 semiconductor substrate 11 silicon oxide film 12 gate electrode

Claims (9)

[Claims] 1. A silicon oxide film is formed on a semiconductor substrate, ions are injected into the silicon oxide film by an ion implantation method, and then the silicon oxide film is heat-treated in an inert gas atmosphere containing a halogen element. A method for forming a silicon oxide film, comprising: 2. The ion species in the ion implantation is in the form of at least one element selected from the group consisting of silicon, oxygen, nitrogen, arsenic, phosphorus, boron and halogen elements, or a compound composed of such an element. The method for forming a silicon oxide film according to claim 1, wherein 3. The energy of the ion implantation is selected so that the projection range is in the silicon oxide film or near the interface between the silicon oxide film and the semiconductor substrate. A method for forming a silicon oxide film according to item 1. 4. The dose amount and the energy of the ion implantation are 1 × 10 ^{10 to} 1 × 10 ¹⁶ cm ⁻² and 1 to 50 keV, respectively. 2. The method for forming a silicon oxide film as described in 1 above. 5. The method for forming a silicon oxide film according to claim 1, wherein the method for forming the silicon oxide film is a pyrogenic oxidation method. 6. The method for forming a silicon oxide film according to claim 1, wherein the halogen element contained in the inert gas atmosphere is chlorine. 7. The silicon oxide film according to claim 6, wherein the chlorine is in the form of hydrochloric acid, and the concentration of hydrochloric acid contained in the inert gas atmosphere is 0.02 to 10% by volume. Forming method. 8. The method for forming a silicon oxide film according to claim 1, wherein the heat treatment is a furnace annealing treatment. 9. The method for forming a silicon oxide film according to claim 1, wherein the heat treatment is performed at a temperature of 700 to 1100 ° C.