JP2660297B2 - Method for manufacturing silicon oxide film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a silicon oxide film. More specifically, the present invention relates to a method for manufacturing a silicon oxide film by a plasma CVD method using an organic silane and an oxygen gas or a nonmetal oxide gas.

[Prior art] Conventionally, a silicon oxide film used for a gate insulating film or a passivation film of a thin film transistor is formed by a so-called CVD method using a silane-based gas and a nonmetal oxide gas. Have been. For example, a glow discharge region is formed in a decompression container, and a mixed gas of a monosilane gas and a laughing gas (dinitrogen monoxide gas) is introduced into the container to form a silicon oxide film on a substrate.

[Problems to be Solved by the Invention] The characteristics required of this type of silicon oxide film used for the gate insulating film, the passivation film, and the like of the thin film transistor as described above include a high withstand voltage and a hysteresis characteristic such as polarization. Small, little charge accumulation, small refractive index, and the like.

However, a silicon oxide film formed by a conventional plasma CVD method using an organic silane and a non-metal oxide gas cannot satisfy characteristics required for use as a gate insulating film of a thin film transistor. This is mainly because hydrocarbon groups and hydroxyl groups generated during the reactive growth of the silicon oxide film remain in the silicon oxide film.

That is, when a hydrocarbon group remains in the silicon oxide film, the refractive index of the silicon oxide film increases. Further, when hydroxyl groups remain in the silicon oxide film, problems such as low dielectric strength in the silicon oxide film, large hysteresis characteristics such as polarization, and large accumulation of electric charge occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a silicon oxide film that can solve the above-mentioned conventional problems.

[Means for Solving the Problems] That is, the gist of the first means adopted to achieve the object of the present invention is that a plasma region is formed in a reduced-pressure vessel and a hydrocarbon group is contained in the vessel. In a method of introducing an organic silane and an oxygen gas or a non-metal oxide gas and forming a silicon oxide film on a substrate in the plasma region, an organic silane containing a hydrocarbon group and an oxygen gas or The component ratio of oxygen atoms to silicon atoms in the mixed gas with non-metal oxide gas is 100
As described above, the present invention provides a method for manufacturing a silicon oxide film, wherein the number of hydrocarbon groups in the film is reduced.

In addition, the gist of the second means is a method of heating the substrate to a temperature of 330 ° C. or higher in the method of manufacturing a silicon oxide film.

[Operation] FIG. 1 shows the composition ratio of oxygen atoms / silicon atoms in the mixed gas introduced into the decompression vessel and the ratio (α) of the hydrocarbon groups remaining in the formed silicon oxide film to the Si—O groups.
₆ is a graph showing an example of the relationship between _{Si—CH 3} / α _{Si—O 2} ), and the relationship between the same composition ratio and the refractive index of the formed silicon oxide film. The present invention has been made by focusing on the facts shown in this graph.

That is, when a silicon oxide film is formed by a CVD method using an organic silane and an oxygen gas or a nonmetal oxide gas, when the component ratio of oxygen atoms to silicon atoms contained in the mixed gas is changed, FIG. As shown by the solid line, the composition ratio between the hydrocarbon group and the Si—O group remaining in the formed silicon oxide film changes. As is clear from this graph, when the component ratio of oxygen atoms to silicon atoms in the mixed gas is less than 100, hydrocarbon groups remain in the formed silicon oxide film, and the Si-O
The ratio to group decreases sharply as the ratio of oxygen atoms increases. Then, when the above composition ratio reaches and exceeds 100, no hydrocarbon groups remain in the silicon oxide film.

Further, in a range where the hydrocarbon groups remain in the silicon oxide film, that is, in a range where the component ratio of oxygen atoms to silicon atoms in the mixed gas is less than 100, the refractive index of the formed silicon oxide film is As shown by the dotted line in FIG. 1, the oxygen / silicon composition ratio decreases as the ratio increases, and when the component ratio of oxygen atoms to silicon atoms in the mixed gas reaches 100, the refractive index becomes about 1.46. It keeps constant at the same refractive index. Therefore, as in the first means of the present invention, by maintaining the component ratio of oxygen atoms to silicon atoms contained in the mixed gas at 100 or more, hydrocarbon groups in the formed silicon oxide film are reduced. To maintain the refractive index at the lowest value.

Next, FIG. 2 shows that when a silicon oxide film is formed by a CVD method using an organic silane and an oxygen gas or a nonmetal oxide gas, the substrate temperature and the silicon oxide film in the formed silicon oxide film are changed. The relationship between the ratio of the remaining hydroxyl groups to the Si-O groups (α _OH / α _Si-O ) is shown by a solid line, and the relationship between the substrate temperature and the interface state amount (N _rb ) of the silicon oxide film is shown by a dotted line. The relationship between the temperature and the hysteresis of the silicon oxide film is indicated by an alternate long and short dash line, and the relationship between the substrate temperature and the breakdown voltage of the silicon oxide film is indicated by an alternate long and two short dashes line. The substrate temperature is / K
Are shown in units of.

As shown in FIG. 2, the substrate temperature was 330 ° C. (1 / T = 1.66 ×
Within a range less than 10 ^-3 ), the hydroxyl groups remaining in the formed silicon oxide film gradually decrease with an increase in temperature, and the hydroxyl groups do not remain when the substrate temperature is 330 ° C. or higher. Also, when the substrate temperature is lower than 330 ° C., the interface state amount (N _rb ) and the hysteresis amount of the silicon oxide film rapidly decrease from a high value as the substrate temperature rises, and the substrate temperature becomes 330 ° C. Above, the low value changes at the bottom. At the same time, the withstand voltage of the silicon oxide film also increases rapidly when the substrate temperature is 330 ° C. or lower.
At 30 ° C., the pressure resistance reaches 3 × 10 ⁶ v / cm and saturates. The present invention pays attention to this fact and proposes that the substrate temperature at the time of forming the silicon oxide film be 330 ° C. or higher.

[Embodiment] Next, an embodiment of the present invention will be described in detail with reference to FIG.

(Example 1) The silicon substrate 1 was organically cleaned, the oxide film on the surface was removed with 1% hydrofluoric acid, washed with pure water, and then water was removed by nitrogen blow to remove the plasma CVD shown in FIG. It was fixed to the substrate holder 2 in the apparatus. The inside of the vacuum container 1 was depressurized by the exhaust device 4, and the substrate 1 was heated to 350 ° C. by the substrate heater 6. An laughing gas was supplied at a flow rate of 450 sccm from the laughing gas introduction system 5b and monomethylsilane was supplied at a flow rate of 1.5 sccm from the monomethylsilane gas introducing system 5a into the pressure reducing container 1, and these were mixed by a gas mixer 5c. Then, it was introduced into the reduced pressure vessel 1. The composition ratio of oxygen atoms / silicon atoms of the mixed gas in the depressurized container 1 thus adjusted is
300. At this time, the pressure in the container 1 was 1 Torr.

The RF power source 3 applies 13.56 MHz RF power to parallel plate electrodes at 200 mmφ and 25 mm intervals so that the difference between the traveling wave and the reflected wave becomes 15 W, causing a glow discharge and plasma CVD on the silicon substrate 1. To form a silicon oxide film. Then, when the thickness of the silicon oxide film becomes 1000 angstroms, the power supply from the RF power source 3 is stopped, and the temperature of the substrate 1 is cooled down to room temperature while the vacuum vessel 1 is maintained in a vacuum. Then, the substrate 1 was taken out of the vacuum container 1.

The infrared absorption of the silicon oxide film thus obtained was measured, and the remaining amount of hydrocarbone groups contained in the film was determined as follows:
It was 0 when calculated as the ratio to the amount of Si-O groups. Also, when the refractive index was measured by an ellipsometer, 1.
46.

For comparison, the flow rate of monomethylsilane gas was set to 1.5 s.
While maintaining a constant ccm, the flow rate of laughing gas is 0-600sc
cm, and the composition ratio of oxygen atoms / silicon atoms in the mixed gas in the vacuum vessel 1 is changed in the range of 0 to 400, and a silicon oxide film is formed on the silicon substrate 1 in the same manner. Filmed. The remaining amount and the refractive index of the hydrocarbone groups contained in the silicon oxide thin film thus obtained were determined.

FIG. 1 shows the results in relation to the composition ratio of oxygen atoms / silicon atoms in the mixed gas. That is, the first
In the figure, the ratio of the amount of hydrocarbon groups contained in the silicon oxide film to the amount of Si—O groups and the refractive index are plotted on the vertical axis, and the composition of oxygen atoms relative to silicon atoms contained in the mixed gas of monomethylsilane and laughing gas is shown. The ratio is shown on the horizontal axis.
As described above, by setting the component ratio of oxygen atoms to silicon atoms of the mixed gas to 100 or more, the hydrocarbon groups remaining in the silicon oxide film can be reduced to almost 0, and the refractive index of the film can be reduced to about 0. Can be maintained at the lowest value of 1.46.

(Example 2) The infrared absorption of the silicon oxide film obtained in the same manner as in Example 1 was measured, and the amount of hydroxyl groups contained in the film was calculated as a ratio to the amount of Si-O groups. In addition, a dot electrode made of a 500-Å-thick Ni film was formed by a vacuum evaporation method to form a MOS structure, and the breakdown voltage between the substrate and the dot electrode was measured. Furthermore, when the amount of interface state and the magnitude of hysteresis of CV characteristics were measured using this MOS structure, the breakdown voltage was 1.0 × 10 ⁶ V / cm, and the amount of interface charge (N _rb )
Was 3.5 × 10 ¹¹ , and the amount of hysteresis was 0.

For comparison, a silicon oxide film was formed on the silicon substrate 1 in the same manner while changing the substrate temperature from 200 ° C. to 400 ° C. Then, in the same manner as described above, the ratio of the amount of hydroxyl groups to the amount of Si—O groups contained in the film, the breakdown voltage, the amount of interface state, and the hysteresis of the CV characteristic of the film were measured.

The result is shown in FIG. The figure shows the breakdown voltage, interface state amount,
With the hysteresis of the CV characteristic on the vertical axis, the substrate temperature is 1 / T (1
0−3 / K) on the horizontal axis. As described above, by setting the substrate temperature to 330 ° C. or higher (1 / T = 1.66 × 10 ⁻³ K), the amount of hydroxyl groups remaining in the silicon oxide film can be reduced to almost zero, and the withstand voltage of the film can be reduced. And the interface state amount and CV characteristics can be reduced.

In addition, the raw materials, conditions, and the like shown in each of the above-described examples are merely examples, and the present invention can be implemented with various changes. The main ones are listed below.

(A) The organic silane in the present invention has an alkyl group containing no O as a substituent. In the above embodiment, monomethylsilane is used as such an organic silane, but instead of this, dimethylsilane, trimethylsilane, tetramethylsilane, and an organic silane in which the methyl group of the organic silane is another alkyl group are used. The same result can be obtained by using. However, when the organic silane is not a gas, it is necessary to mix the organic silane with a nonmetal oxide gas by a method of converting the organic silane into a gas or by atomizing.

(B) In the above embodiment uses the laughing gas as non-metal oxide gas, O _x gases such as oxygen Alternatively, HO _x gases such as water vapor, the CO _x gas, etc., such as dioxide oxygen Equivalent results can be obtained when used.

(C) In the above embodiment, a parallel plate type plasma CVD apparatus is used. However, instead of this, another type of CVD apparatus capable of decomposing non-metal oxide gas and organosilane by glow discharge is used. Equivalent results can be obtained when used.

(D) The film forming conditions such as film forming pressure, RF power, RF frequency, total flow rate of non-metal oxide gas and organic silane, electrode area and electrode spacing are also controlled by glow discharge. As long as it can be decomposed, changing it appropriately does not lose the function and effect of the present invention.

[Effects of the Invention] As described above, according to the present invention, a silicon oxide film having high withstand voltage, low hysteresis characteristics such as polarization, and low charge accumulation can be obtained. Therefore, a silicon oxide film having characteristics necessary for use as a gate insulating film, a passivation film, and the like of a thin film transistor can be manufactured by a plasma CVD method using organosilane and oxygen gas or nonmetal oxide gas. Become.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the amount of hydrocabone groups contained in a film and the refractive index of the composition ratio of oxygen atoms to silicon atoms contained in a mixed gas of organosilane and nonmetal oxide gas. is there. FIG. 2 is a graph showing the breakdown voltage, the amount of interface state, and the magnitude of the hysteresis of the CV characteristic with respect to the substrate temperature. FIG. 3 is a conceptual diagram showing a plasma CVD apparatus used in the embodiment of the present invention. In the figure, 1 is a vacuum container, 2 is a substrate holder, 3 is an RF power source,
Reference numeral 4 denotes an exhaust device, 5a denotes a monomethylsilane gas introduction system, 5b denotes a laughing gas introduction system, 5c denotes a gas mixer, and 6 denotes a substrate heater.

Continuation of front page (72) Inventor Takashi Yoshimi 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Yuden Co., Ltd. (72) Inventor Hideyo Iida 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Yuden Co., Ltd. (72) Inventor Kiyohiro Kondo 2-6-1 Otemachi, Chiyoda-ku, Tokyo Shin-Etsu Chemical Co., Ltd. (72) Inventor Satoshi Okazaki 2-3-1 Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Judge Kunio Kobayashi Judge, Functional Materials Research Laboratory Judge, Yoshihiro Samura Judge, Yuko Matsuda (56) References JP-A-64-50429 (JP, A) JP-A-1-243553 (JP, A)

Claims (2)

(57) [Claims] 1. A plasma region is formed in a reduced pressure vessel, and an organic silane containing a hydrocarbon group and an oxygen gas or a nonmetal oxide gas are introduced into the vessel, and a silicon oxide film is formed on a substrate in the plasma region. In the method of forming, by making the component ratio of oxygen atoms to silicon atoms of a mixed gas of an organic silane containing a hydrocarbon group and an oxygen gas or a non-metal oxide gas introduced into the decompression container to 100 or more, A method for producing a silicon oxide film, wherein the number of hydrocarbon groups in the film is reduced. 2. A method for manufacturing a silicon oxide film according to claim 1, wherein the hydroxyl group in the film is reduced by heating the temperature of the substrate to 330 ° C. or higher.