JP3103646B2 - Alumina veljer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bell jar which is a bell-shaped envelope used for plasma etching of a silicon wafer.

[0002]

2. Description of the Related Art Conventionally, plasma etching of a silicon wafer has been performed using a quartz glass velger.

[0003] That is, a method in which a wafer is placed in a quartz glass belger and a fluoride gas converted into plasma is introduced into the wafer, thereby etching a thin film formed on a silicon wafer. Has been adopted.

[0004] Plasma conversion of fluoride gas is carried out by using Belgian gas.
A method of irradiating a high-frequency microwave to a fluoride gas introduced into the inside, a method of irradiating a fluoride gas in an introduction pipe integrated with a bell jig from the outside and introducing the microwave to a silicon wafer. And so on.

Heretofore, quartz glass has been used exclusively as such a bell jersey. Quartz glass has been widely used as a bell jar because quartz glass has a high purity with a low content of impurities contaminating the wafer and can be easily processed with high heat.

However, a number of problems due to corrosion have previously been pointed out in quartz glass bell jewels. Silicon fluoride formed by the reaction between quartz glass and a fluoride gas has a high vapor pressure and evaporates immediately. Etching of a silicon oxide film or the like has been performed on this principle. -Resulted in various problems. That is, since the component of the conventional silica glass bell jelly is silicon oxide, it has been significantly corroded by the plasma-converted fluoride gas.

[0007] For example, conventional corroding of jewelry is severe and its life is short, and as a result, the cost of etching a wafer is increased. If the quartz glass bell jewel is corroded, there is a problem that a small amount of impurities contained in the quartz glass contaminate the wafer. Further, the conventional one has a productivity problem that a hole is formed in the bell jewel after several hours of etching, and etching cannot be performed continuously for a long time.

Conventionally, corrosion of quartz glass bell jewels has not always proceeded uniformly, and there has been a problem that weak portions are selectively etched and quartz glass which has become fine particles adheres to the wafer.

Further, the silicon fluoride formed by the reaction between the quartz glass and the fluoride gas reacts with oxygen or the like in the mixed gas introduced into the belljar, and becomes an oxide or an oxynitride to form the oxide. -Deposit on the cold part of the enclosure. It has also been pointed out that the deposited material has a different coefficient of thermal expansion from the envelope of the base material, so that it is sometimes peeled off and adhered to the wafer.

In order to solve such a problem, it is conceivable to use alumina ceramic for the bell jar instead of quartz glass. However, alumina ceramic absorbs a lot of microwaves, and the alumina is partially heated and expanded to crack. Have occurred and have been considered difficult to use.
Alumina ceramics have a high impurity concentration and
Has been contaminated, and it has been said that it is difficult to put it to practical use from this aspect.

[0011]

According to the present invention, there is little corrosion due to fluoride gas, a long life, and it is possible to avoid contamination of the wafer, and further, there is little absorption of microwaves, so that cracks can be prevented. The purpose is to obtain an alumina-based bell jig suitable for the property.

[0012]

SUMMARY OF THE INVENTION The present invention relates to an alumina-based material.
In Belger, the alumina ceramic of the substrate is
99.9% or more alumina, SiO_TwoIs not 100ppm
Fully polycrystalline aluminum with less than 50ppm alkali metal oxide
A sintered body having a specific gravity of 3.96 or more and an average crystal grain size of 1
Dielectric loss in microwaves of 0 μm or more and 1 to 10 GHz
n δ is 8 × 10^{- Four} It is characterized by the following
is there.

The base material of the alumina-based bell jar of the present invention is a high-purity alumina-based sintered body having a purity of 99.9% or more.
SiO ₂ less than 100 ppm, alkali metal oxide 50
It consists of less than ppm. This is because the corrosion resistance of alumina ceramics to fluoride gas converted into plasma is proportional to the alumina purity in the alumina ceramics,
In particular, it has been found that Si and alkali metals such as Na and K are greatly affected.

[0014] SiO _{2 in} alumina ceramics
The reason why the content is set to less than 0 ppm is that when the content is more than 100 ppm, SiO ₂ is concentrated at the crystal grain boundaries and reacts with the fluoride gas to evaporate, thereby accelerating the corrosion of the ceramic grain boundaries. The microwave absorption of alumina ceramics is SiO
_2. It is thought to be affected by impurities such as alkali metals. The reason why the content of the alkali metal oxide is set to 50 ppm or less is that
If the alkali metal exceeds this value, the microwave absorption of the alumina ceramics is particularly enhanced, and the energy absorbed by the alumina ceramics raises the temperature of the ceramics to generate cracks in the belliers, thereby causing the belliers to crack.
This is because the long life cannot be achieved. Further, such a rise in temperature promotes a chemical reaction between the fluoride gas and SiO ₂ , and further promotes corrosion.

In order to obtain such a bell jar, predetermined raw materials, for example, 99.9% or more of alumina and 10% of SiO ₂ are used.
A raw material having a content of less than 0 ppm and an alkali metal oxide content of 100 ppm or less may be formed into a bell-jar shape and fired at 1700 ° C. or more in a hydrogen atmosphere or vacuum to obtain polycrystalline alumina.

Furthermore, the specific gravity of the alumina ceramics of the present invention is 3.96 or more. Bell jar
If the number of pores is large, the ratio of a part of the pores exposed to the surface also increases, and there is a possibility that corrosion proceeds through such pores on the surface. In addition, impurities easily accumulate in the pores and become a source of contamination for the syringe wafer. For this reason, it is preferable that the specific gravity of the alumina ceramic is 3.96 or more so that pores are not substantially present on the surface.

Further, since the corrosion of alumina ceramics proceeds from the crystal grain boundaries, it is necessary to use ceramics having few grain boundaries, and the average crystal grain size is set to 10 μm or more. However, if the crystal grain size is too large, there is a problem that the mechanical strength is reduced.
It is preferable that Further, in the present invention, conditions are required for the microwave transmission.

In general, alumina ceramics often become red-heated by microwave irradiation, cracks occur, and are often damaged. Also, even if it does not lead to damage due to cracks,
Such a temperature increase promotes erosion by the plasma-converted fluoride gas. Therefore, a material having high microwave permeability is also desired from the viewpoint of corrosion resistance. Microwave transmission can be expressed as the reciprocal of dielectric loss. The dielectric loss is proportional to the product of the non-dielectric constant and the loss factor tanδ. Alumina ceramics having a smaller impurity have a smaller value of tan δ, but in the present invention, this value is set to 8 × 10 ⁻ which is close to sapphire. ^Four The following values are assumed.

According to the present invention, as described above, alumina is 99.
9% or more, SiO ₂ is less than 100 ppm, alkali metal oxides is not more than polycrystalline alumina sintered body 50 ppm, and a specific gravity of 3.96 or more, an average grain size 10μm or less, 1 to 1
The dielectric loss tanδ at microwave 0GHz is 8 × 10 ^-
Four When the following conditions are satisfied, it has excellent corrosion resistance to fluoride gas, and also has excellent microwave permeability, avoids damage due to heat shock, and can be used for a long time and practical It has been found that a bell jar satisfying the requirements can be obtained.

[0020]

According to the present invention, the lower limit of the average crystal grain size and the upper limit of the dielectric loss are specified with high purity, the contents of SiO ₂ and alkali metal oxides are limited to minute amounts, and the specific gravity is high. Therefore, it is excellent in corrosion resistance, microwave transmission, etc., suppresses heat generation, and can be used for a long time without polluting the wafer.
Can be obtained, whereby the etching cost can be provided at low cost.

[0021]

【Example】

 (Example 1)

FIG. 1 is an explanatory view showing an outline of a plasma etching apparatus using a bell jewel according to the present invention. FIG.
In the figure, reference numeral 1 denotes a gas introduction pipe, which is irradiated with a microwave 2 of 2.4 GHz perpendicular to the gas introduction pipe 1 so that the microwave 2 passes through the gas introduction pipe 1 and reaches the inside 3 of the introduction pipe. Has become. Gas 4 introduced for etching
Was converted into plasma in the introduction tube 1 with CF ₄ + O ₂ , and then sent to the inside 5 of the bell jar 7 to process the wafer 6.

The material of the bell jewel and the gas inlet tube is 2 mm thick and 99.9 purity, fired at 1800 ° C. in a hydrogen atmosphere.
% High-purity alumina ceramics, and the usable time was measured. As a comparative example, a quartz glass having a thickness of 5 mm,
Further, ordinary alumina ceramics having a thickness of 3 mm and a purity of 99.5% were used.

The SiO ₂ purity of each material is 30 ppm for high-purity alumina ceramics, 100% for quartz glass,
The content of alkali metal oxides (Na ₂ O, K ₂ O, etc.) was 45 ppm for high-purity alumina ceramics, 1 ppm or less for quartz glass, and 540 ppm for normal alumina ceramics. . The average crystal grain size was 25 μm for high-purity alumina ceramics and 25 μm for normal alumina ceramics. As a result, the alumina-based bell jewel of the present invention could be used for 600 hours despite its thinnest thickness of 2 mm.

On the other hand, the quartz glass bell jewel has a hole due to corrosion in 20 hours despite its thickness of 5 mm.
At 0 hours, cracks occurred and could not be used. (Example 2)

The purity of alumina ceramics fired in a hydrogen atmosphere was changed (the content of SiO ₂ and NaO ₂ was changed), and an alumina velzier was formed in which the density and the average crystal grain size were changed.

That is, if necessary, SiO ₂ and NaO ₂ are dispersed and added to the raw material powder having a purity of 99.9%, and a slurry obtained by adding an organic binder and ion-exchanged water thereto is sprayed with a spray dryer. Granulated. It is 1.0 with rubber press.
t / cm ² , And then calcined at 1000 ° C., and baked at 1700 to 1800 ° C. for 1 to 8 hours in a steam atmosphere.

The size after firing is 180 mm in diameter and 10 mm in height.
It was a 0 mm hemispherical shape and 2 mm thick. A microwave of 2.45 GHz was irradiated for 100 hours from the top of the bell jewel. Belger surface temperature near the microwave waveguide was measured with a surface thermometer. Berujiya - Some of CF ₄ +
An O ₂ mixed gas was introduced, and a silicon wafer on which an oxide film was formed was placed below the bell jersey.

Further, the same granulated material as described above was used to obtain 10 mm ×
A 10 mm cylindrical molded body was prepared by press molding, calcined under the same conditions as in the above-mentioned bell jewel, and calcined in a hydrogen atmosphere. This was used as a tan δ measurement sample. tanδ is 1
It was measured at 0 GHz by the cylindrical resonance method. Table 1 shows the results.

[0030]

[Table 1]

[0031]

Industrial Applicability The alumina-based bell jewel of the present invention has excellent corrosion resistance to fluoride gas, and also has excellent microwave permeability, so that breakage due to thermal shock can be avoided. Therefore, the bell jewel of the present invention can be used for a long time, and as a result, the etching cost can be reduced. Further, the bell jer according to the present invention is less corroded by the fluoride gas, so that it is possible to prevent impurities from being generated and contaminating the wafer.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an outline of a plasma etching apparatus performed by using an alumina-based bell jewel of the present invention.

[Explanation of symbols]

1 ... Gas introduction pipe, 2 ... Microwave 2,7 ... Bergier, 6 ... Wafer.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Haruji Harada Haruka Onumada, Togane-shi, Chiba Prefecture 1573-8 Inside the Togane Plant of Toshiba Ceramics Co., Ltd. 1573-8 In the Togane Plant of Toshiba Ceramics Co., Ltd. (72) Inventor Kazuto Ando Kazuma Onuma, Togane-shi, Chiba Pref. (JP, A) JP-A-64-56873 (JP, A) JP-A-1-213910 (JP, A) Patent 3029488 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00 C30B 25/08

Claims (1)

(57) [Claims] (1) at least 99.9% of alumina and SiO_TwoIs 1
Less than 00 ppm, alkali metal oxide less than 50 ppm
Crystalline alumina sintered body with specific gravity of 3.96 or more
Induced by microwaves with a crystal grain size of 10 μm or more and 1 to 10 GHz
Electric body loss tanδ is 8 × 10^{- Four} It is characterized by the following
Alumina Belger.