JP4831581B2 - Low loss dielectric material for high frequency, its manufacturing method and member - Google Patents

Description

  The present invention relates to a high-frequency low-loss dielectric material. More specifically, the present invention relates to a novel high-frequency low-loss dielectric material that satisfies both requirements of low dielectric loss and high thermal conductivity, its members, and the like. It is about. The present invention provides a high-frequency low-loss dielectric material used in a plasma processing apparatus member, for example, a semiconductor manufacturing apparatus, a liquid crystal manufacturing apparatus, etc., which is mainly used in an apparatus that generates plasma using a high frequency such as microwaves. To do.

  In recent years, microwave plasma processing apparatuses have been frequently used mainly for CVD, etching, and resist processes in semiconductor and liquid crystal thin film manufacturing. In these devices that generate plasma using a high frequency such as a microwave, a member made of a material having a high frequency permeability is used. These members are required to have high thermal conductivity (low dielectric constant, low dielectric loss) and high thermal conductivity in order to eliminate the temperature distribution in the member and improve the uniformity of the reaction.

Regarding high-frequency permeability, for example, silica glass is excellent because of its low dielectric constant and low dielectric loss, but its thermal conductivity is as low as ˜2 W · m ⁻¹ · K ^−1, and does not satisfy the requirements as a member. High-purity alumina ceramics also have a low dielectric loss, but have a low thermal conductivity of ˜30 W · m ⁻¹ · K ⁻¹ and do not meet the requirements. In contrast, aluminum nitride has a very high thermal conductivity of ~ 160 W · m ⁻¹ · K ⁻¹ , but cannot satisfy the requirement because it has a dielectric loss of 10 ⁻³ or more.

On the other hand, silicon nitride (Si ₃ N ₄ ) is known as a ceramic that is remarkably superior in heat resistance, thermal shock resistance, and mechanical strength compared to the above ceramics, and has a high thermal conductivity of 100 W · m ⁻¹ · K ⁻¹ or higher. Si ₃ N ₄ having a rate has also been developed. In addition, with respect to the dielectric loss of Si ₃ N ₄ , research has been conducted for the purpose of reducing the dielectric loss of silicon nitride having excellent mechanical strength in order to provide reliability of the high-frequency introduction window material. .

As a prior cited document, for example, a low dielectric loss of 10 ⁻⁴ or less at 10 GHz has been achieved so far as there is a report example of a low dielectric loss high-frequency introduction window material using silicon nitride. However, in order to satisfy the above-described requirements, a dense Si ₃ N ₄ that has a low dielectric loss and a high thermal conductivity has been hardly studied so far.

So far, as a prior art, for example, a molar ratio of Group 3a compound (RE ₂ O ₃ ) and SiO _{2 in} the periodic table, and a composition having (RE ₂ O ₃ / SiO ₂ ) of 0.1 to 0.67 has been proposed. It is reported that it is promising as a low dielectric loss silicon nitride material (Patent Document 1).

In addition, regarding the thermal conductivity of the silicon nitride sintered body to which the Group 3a compound of the periodic table is added, as the RE ₂ O ₃ / SiO ₂ ratio increases to ˜1, the dissolved oxygen in the silicon nitride grains is reduced. It has been reported that the thermal conductivity is improved to about 100 W · m ⁻¹ · K ⁻¹ (Non-patent Document 1).

From these findings, it is difficult to improve the thermal conductivity of the low dielectric loss silicon nitride having a composition reported so far, and the thermal conductivity of the commercially available low dielectric loss silicon nitride material is 60 W · m ^−1.・ It remains at around K- ¹ .

  On the other hand, high thermal conductivity of silicon nitride is performed, for example, by adding a rare earth oxide for promoting high thermal conductivity and an Mg element compound as a sintering aid for promoting densification (Non-patent Document 2). ).

However, it has been reported that the dielectric loss at 9.1 GHz of silicon nitride added with 6.6 mol% of MgO and sintered is as large as 2 × 10 ⁻³ (Non-patent Document 3). It has been considered that alkaline earth metals such as Mg and Ca and alkali metals such as Na and K adversely affect the dielectric loss of silicon nitride.

  Further, for example, in the above-mentioned patent document (Japanese Patent Laid-Open No. 10-134956), these alkali metal compounds and alkaline earth metal compounds are not preferable and do not exist as much as possible in order to reduce the dielectric loss. It has been needed. That is, silicon nitride using an alkaline earth metal as a sintering aid is dense and has high thermal conductivity, but it is expected that it is difficult to reduce dielectric loss.

In the case of adding a Group 3a compound of the periodic table without using an alkaline earth metal, as previously indicated, the prior art document (Journal of American Ceramics Society, Vol. 83 (2000), pp. 1985-1992). ), It has been reported that the thermal conductivity is improved as RE ₂ O ₃ / SiO ₂ increases to ˜1, but with this composition, it has so far been made sufficiently dense only by gas pressure sintering. Is difficult and exhibits poor sinterability.

This is because when the RE ₂ O ₃ / SiO ₂ ratio is ˜1, the liquid phase formation temperature due to the reaction of RE ₂ O ₃ and SiO ₂ is high, and the sintering temperature is lower than that of the composition with a small ratio. This is because the amount of liquid phase generated in the vicinity is small.

  For this reason, it is difficult to obtain a dense sintered body without using hot isostatic pressing (hot press sintering), which is expensive to manufacture, and is not suitable for industrial production of low-loss dielectric materials. As a matter of fact, the dielectric properties of this composition region have not been investigated.

Japanese Patent Laid-Open No. 10-134956 Journal of American Ceramics Society, Volume 83 (2000), pp. 1985-1992. Journal of the Ceramic Society of Japan, Vol. 109, No. 12 (2001), pp. 1046-1050 Journal of Nuclear Materials, 155-157 (1988), pp. 372-377.

Under such circumstances, the present inventors have developed a high-frequency low-loss dense dielectric material that satisfies the requirements of both low dielectric loss and high thermal conductivity in view of the above-described conventional technology. As a result of earnest research as a target, the content of the Group 3a element compound in the periodic table contained in the silicon nitride sintered body is controlled to a specific amount, and the densification of the sintered body is promoted. By crystallizing the phase, the dielectric loss at 2 GHz and 3 GHz can be reduced to 2 × 10 ⁻⁴ or lower, and the thermal conductivity can be increased to 90 W · m ⁻¹ · K ⁻¹ or higher. It has been found that the material is suitable as a lossy dense ceramic dielectric material, and has led to the present invention.

The present invention comprises a silicon nitride sintered body mainly composed of silicon nitride and containing a group 3a element compound of periodic table and impurity oxygen, and a crystal grain boundary in the sintered body is crystallized, and 2 GHz. An object of the present invention is to provide a high-frequency low-loss dense dielectric material having a dielectric loss at 3 GHz of 2 × 10 ⁻⁴ or less and a thermal conductivity of 90 W · m ⁻¹ · K ⁻¹ or more.

The present invention for solving the above-described problems comprises the following technical means.
(1) It is a dense sintered body having a relative density of 97% or more, composed of a silicon nitride sintered body mainly composed of silicon nitride, containing a Group 3a element compound of the periodic table and impurity oxygen, and has a relative density of 97% or more. in the dielectric loss is less than 2 × ^{10 -4,} and the thermal conductivity of a low-loss dielectric material for high have higher frequency than 90W · ^{m -1} · ^K -1,
1) The ratio of Group 3a element compound (RE) in the periodic table contained in the sintered body is at least 16% by weight in terms of oxide (RE ₂ O ₃ ), and contains a silicon oxynitride compound crystal phase And 2) the low-loss dielectric material for high frequency, wherein the silicon oxynitride compound is a compound represented by RE ₄ Si ₂ N ₂ O ₇ .
( 2 ) The low-loss dielectric material for high frequencies according to (1), wherein the grain boundary phase in the sintered body is mainly composed of a RE-Si-O-N compound and is crystallized.
( 3 ) The high-frequency low-loss dielectric material according to (1), wherein the Al content is 0.1% by weight or less in terms of oxide (Al ₂ O ₃ ).
( 4 ) A member made of the high-frequency low-loss dielectric material according to any one of (1) to ( 3 ), wherein the member is a high-frequency transmitting member applied to an electrical component manufacturing apparatus A high-frequency transmitting member.
( 5 ) The member for high frequency transmission according to ( 4 ), wherein the member is a member for high frequency transmission applied to a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus.
( 6 ) A method for producing the material according to (1) above,
Abundance of the periodic table group 3a element compound is at least 7 mol% in terms of oxide, the molar ratio of silicon oxide _{(SiO 2) (RE 2 O} 3 / SiO 2) is 1.0 to 1 By using a starting material in the range of .5, molding and firing ,
1) The ratio of Group 3a element compound (RE) in the periodic table contained in the sintered body is at least 16% by weight in terms of oxide (RE ₂ O ₃ ), and contains a silicon oxynitride compound crystal phase 2) A method for producing a low-loss dielectric material for high frequency, wherein the silicon oxynitride compound produces a compound represented by RE ₄ Si ₂ N ₂ O ₇ .
( 7 ) The method for producing a high-frequency low-loss dielectric material as described in ( 6 ) above, wherein a molded body having a relative density of 52% or more is produced by isostatic pressing at least 400 MPa and fired.

Next, the present invention will be described in more detail.
The present invention relates to a high-frequency low-loss dielectric material satisfying both low dielectric loss and high thermal conductivity, which is mainly composed of silicon nitride, and contains silicon nitride based on Group 3a element compound of periodic table and impurity oxygen It is a dense sintered body made of a sintered body and having a relative density of 97% or more, dielectric loss at 2 GHz and 3 GHz is lower than 2 × 10 ⁻⁴ , and thermal conductivity is from 90 W · m ⁻¹ · K ⁻¹ It is characterized by being high.

In the present invention, the proportion of the Group 3a element compound (RE) in the periodic table contained in the sintered body is at least 16% by weight in terms of oxide (RE ₂ O ₃ ), and the silicon oxynitride compound crystal phase , The silicon oxynitride compound is a compound represented by RE ₄ Si ₂ N ₂ O ₇ , and the group 3a element of the periodic table contained in the sintered body is Yb, Y, Dy, A preferred embodiment is that it is Er, Tm, Lu, or Sc, and that the grain boundary phase in the sintered body is mainly composed of a RE-Si-O-N compound and is crystallized.

The high-frequency low-loss dense dielectric material according to the present invention is mainly composed of silicon nitride, and contains impurity oxygen and Group 3a elements of the periodic table as components other than silicon nitride. . Here, impurity oxygen means impurity oxygen inevitably contained in the silicon nitride raw material, or intentionally added silicon oxide (SiO ₂ ).

The group 3a element of the periodic table is a component added as a sintering aid, and examples thereof include Yb, Y, Dy, Er, Tm, Lu, or Sc. These Periodic Table Group 3a elements are suitably 7 mol% or more in terms of oxides as starting materials, and the amount of the above-mentioned impurity oxygen in terms of SiO ₂ is such that the RE ₂ O ₃ / SiO ₂ molar ratio is 1 ~ 1.5 is suitable.

In this composition region, the generation temperature of the liquid phase due to the reaction of RE ₂ O ₃ and SiO ₂ is high, and the generation amount of the liquid phase in the vicinity of the sintering temperature is reduced compared to the composition having a small ratio. Until now, it has been difficult to achieve sufficient densification using gas pressure sintering.

  However, an important point in the production of the low-loss dielectric material according to the present invention is that the relative density of the molded body is increased to 52% or more by setting the press pressure of the cold isostatic press as high as 400 MPa or more. Thus, it has been clarified that, even in a composition having a relatively small amount of liquid phase generation near the sintering temperature, densification with a relative density of 97% or more can be achieved by low-pressure gas pressure sintering.

Furthermore, in the low dielectric loss material of the present invention, it is also important that the grain boundary phase in the silicon nitride sintered body is crystallized. As a cause of the influence of the grain boundary phase, when the grain boundary phase is vitrified, it is expected that the dielectric loss of the grain boundary phase increases. Here, the grain boundary phase is a portion other than the silicon nitride crystal phase, and mainly contains silicon (Si), the Group 3a element (RE) of the periodic table, oxygen and nitrogen, and mainly RE-Si-O. -N compound. As the crystal phase, it is desirable to deposit the RE ₄ Si ₂ N ₂ O ₇ phase.

Moreover, as a cation impurity in a sintered compact which has a big influence on dielectric loss, it is preferable that aluminum (Al) in a sintered compact is 2 weight% or less in oxide conversion amount. On the other hand, from the viewpoint of thermal conductivity, it is known that even if the Al content is very small, it is known that the thermal conductivity is remarkably lowered, and it is desirable that the Al element in the sintered body is further reduced. . According to the prior art literature, it has been reported that the addition of only 1 mol% Al ₂ O ₃ reduces the thermal conductivity by about 35%. When the Al ₂ O ₃ abundance is in the range of 0 to 1 mol%, it is assumed that the thermal conductivity decreases linearly with respect to the abundance, and the reduction rate of the thermal conductivity is considered to be within 5%. Then, it is desirable that the amount of Al ₂ O ₃ is 0.1% by weight or less (Journal of Materials Research, Vol. 13 (1998), pp. 3473-3477).

  As a method for producing the low-loss dielectric material of the present invention, a compound such as an oxide of a group 3a element of the periodic table is added to a silicon nitride raw material, and after mixing this, a high-pressure cold of 400 MPa or more After forming with a hydrostatic press to a relative density of 52% or more, firing is performed using a graphite resistance furnace or the like that is free from Al element contamination.

  Firing is required to be performed under conditions that can suppress decomposition of silicon nitride in nitrogen, and is performed by a known firing method such as nitrogen gas pressure sintering or hot isostatic pressing. As the sintering temperature, although it depends on the composition, it is fired in a temperature range of 1600 to 2000 ° C. so that a relative density of 97% or more is achieved.

The dielectric material produced as described above is a dense sintered material having a dielectric loss of 2 × 10 ⁻⁴ or less at a high frequency of 2 GHz and 3 GHz and a thermal conductivity of 90 W · m ⁻¹ · K ⁻¹ or more. It is a ligation. Therefore, the dielectric material of the present invention is a material suitable for use in an apparatus that performs processing by generating plasma using a high frequency of 2.45 GHz, for example, in a semiconductor manufacturing process. By using it, not only the high frequency can be sufficiently transmitted, but also the temperature distribution of the treatment material is flattened and the uniform reaction is promoted, so that the yield of the product can be improved.

The present invention has the following effects.
(1) Low loss dense dielectric for high frequency with high thermal conductivity and low dielectric loss having dielectric loss at 2 GHz and 3 GHz of 2 × 10 ⁻⁴ or less and thermal conductivity of 90 W · m ⁻¹ · K ⁻¹ or more Material can be provided.
(2) The dielectric material of the present invention is suitably used in an apparatus that performs processing by generating plasma using a high frequency of 2.45 GHz, for example, in a semiconductor manufacturing process.
(3) By using the dielectric material of the present invention, not only can a high frequency be sufficiently transmitted, but the temperature distribution of the treatment material is flattened to promote a uniform reaction, and the yield of products can be improved.
(4) The dielectric material is generally expected to be excellent in thermal shock resistance because of its high thermal conductivity, but by using the dielectric material of the present invention, the thermal shock resistance is improved and the length of the member is increased. Use under severer conditions such as life extension and rapid temperature rise and fall is possible.
(5) Since the dielectric material of the present invention is mainly composed of silicon nitride having excellent mechanical characteristics, the mechanical characteristics are improved by using the dielectric material of the present invention, and the strength is improved even in a thin member. Thus, the weight of the member can be reduced.
(6) According to the manufacturing method of the present invention, a dielectric material can be manufactured only by gas pressure sintering without using hot press sintering, which is expensive to manufacture, and a heat treatment step for crystallization of the grain boundary glass phase is performed. Since it is not necessary, the manufacturing cost can be reduced.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited at all by the following examples.

As raw materials, a high-purity silicon nitride raw material (total amount of transition metal impurities of 100 ppm or less) produced by an imide decomposition method and having an α ratio of 95% or more, and a fine powder having a purity of 99.9% or more as Group 3a oxide of the periodic table Yb ₂ O ₃ was used. As shown in Table 1, the amount of Yb ₂ O ₃ powder added was set at five levels of 0.5, 1, _{2, 3} , 5, and 7 mol%. After weighing the powder so as to have these compositions, it was put in a silicon nitride pot and wet mixed in a planetary ball mill with a rotation speed of 280 rpm for 1 hour using a silicon nitride ball and a methanol solvent.

The obtained slurry was transferred to an eggplant flask, dried by a rotary evaporator for about 30 minutes, and then dried in a vacuum dryer at 110 ° C. for 24 hours. Next, mesh # 60 was screened. The obtained powder was filled into a rubber bag, and formed into a cylindrical shape having a diameter of 13 mm and a length of about 100 mm by a hydrostatic pressure press of 441 MPa (4.5 ton / cm ² ) to obtain a sample for firing.

As a comparison, a molded body using a 118 MPa (1.2 ton / cm ² ) isostatic press was also produced and fired. The relative density of the molded body was 47 to 50% when the press pressure was 118 MPa, but was 52 to 57% when the press pressure was 441 MPa, depending on the composition, compared with the molded body having a press pressure of 118 MPa. Was clearly rising.

  A firing sample was buried in a BN fired crucible covered with BN packing powder, and this crucible was set in a graphite resistance furnace. Firing was performed in 9 atm nitrogen at 1900 ° C. for 3 hours to produce a sintered body.

  The obtained sintered body was cut and processed into a 1.5 mm × 1.5 mm × 75 mm elongated prism as a dielectric property measurement sample by surface grinding. In addition, a pellet sample having a diameter of 9 mm and a thickness of 3 mm was prepared as a sample for measuring thermal conductivity by using cylindrical grinding or the like. Two to three measurement samples were prepared from each sample.

Using these samples, the bulk density was determined by the Archimedes method. Assuming that the added Yb ₂ O ₃ and SiO ₂ remain as they are, the relative density was calculated by dividing the bulk density by the theoretical density calculated from the added auxiliary agent amount.

  The dielectric loss was measured at a resonance frequency of 2 GHz and 3 GHz by a perturbation method using a cylindrical cavity resonator after sufficiently drying the sample. The thermal conductivity was measured by a laser flash method after the pellet sample surface was coated with gold by an ion sputtering apparatus and then coated with carbon with a carbon spray.

  In any measurement, the measurement was repeated three times for one sample, and the average of the three measurement values was obtained. And the measured value of each sample used the average value of 2-3 samples. However, measurements were not performed on samples that were sintered after being hydrostatically pressed at a pressure of 118 MPa and were insufficiently densified with a relative density of 90% or less.

Crystal phases other than the silicon nitride crystal phase were identified by X-ray diffraction. An ICP analysis was performed on the sample cut from the center of the sintered sample, which was molded at a hydrostatic press pressure of 441 MPa, and the amount of Yb was quantified and converted to the weight percent of Yb ₂ O ₃ . The results are shown in Table 1.

As is clear from Table 1, the sample having a hydrostatic press pressure of 441 MPa showed a higher relative density in any composition than the sample having a press pressure of 118 MPa. In particular, Sample No. with a Yb ₂ O ₃ / SiO ₂ ratio of 0.5 or more. In the samples 4, 5, and 6, when the press pressure was 441 MPa, a remarkable densification promoting effect of about 10% was observed, and the amount of Yb ₂ O ₃ added was 7 mol%. In the 12 samples, a dense body having a relative density of 97% or more was obtained.

The values in Table 1 (Yb ₂ O ₃ content) in which the abundance of the Yb element obtained by ICP emission analysis of the sintered body is expressed in terms of weight% in terms of oxide are calculated from the Yb ₂ O ₃ addition amount. It was confirmed that the added Yb element remained almost equal to the value.

Looking at the dielectric loss of each sample, the smallest sample _Yb 2 _{O 3} amount No. Although the dielectric loss of 1 and 7 was as small as 1 to 2 × 10 ⁻⁴ , the dielectric loss tended to increase gradually as the Yb ₂ O ₃ addition amount increased to 1 to 2 mol%.

However, when the added amount of Yb ₂ O ₃ is increased to 3, 5 mol%, the dielectric loss tends to decrease, and the sample No. 7 with the added amount of Yb ₂ O ₃ is 7 mol%. In the case of 12, a dielectric loss of 2 × 10 ⁻⁴ or less was achieved. The thermal conductivity increases monotonously as Yb ₂ O ₃ / SiO ₂ increases, and a high thermal conductivity of 90 W · m ⁻¹ · K ⁻¹ or higher is obtained when the amount of Yb ₂ O ₃ added is 7 mol%. I was able to. Similar results were obtained when other Group 3a element compounds of the periodic table were used.

As described above in detail, the present invention relates to a high-frequency low-loss dielectric material, a manufacturing method thereof, and a member. According to the present invention, the dielectric loss is excellent at 2 × 10 ⁻⁴ or less even at a high frequency of 2 GHz and 3 GHz. It is possible to provide a low-loss dense dielectric material that exhibits high thermal conductivity and at the same time. By using the high-frequency low-loss dielectric material of the present invention, the temperature distribution is uniform and the uniformity of the processing reaction can be ensured, and as a result, the yield of products such as semiconductors can be improved. The present invention is a high-frequency, low-loss, dense dielectric with high thermal conductivity and low dielectric loss that has a dielectric loss of 2 × 10 ⁻⁴ or less at 2 GHz and 3 GHz and a thermal conductivity of 90 W · m ⁻¹ · K ⁻¹ or more. It is useful for providing body materials and members thereof.

Claims (7)

It consists of a silicon nitride sintered body mainly composed of silicon nitride, containing a group 3a element compound of the periodic table and impurity oxygen, and is a dense sintered body having a relative density of 97% or more, and dielectric loss at 2 GHz and 3 GHz. there 2 × ¹⁰ lower than ^-4, and a high have low loss dielectric materials for high frequency than the thermal conductivity of 90W · ^{m -1} · ^K -1,
1) The ratio of Group 3a element compound (RE) in the periodic table contained in the sintered body is at least 16% by weight in terms of oxide (RE ₂ O ₃ ), and contains a silicon oxynitride compound crystal phase And 2) the low-loss dielectric material for high frequency, wherein the silicon oxynitride compound is a compound represented by RE ₄ Si ₂ N ₂ O ₇ .   The low-loss dielectric material for high frequency according to claim 1, wherein the grain boundary phase in the sintered body is mainly composed of a RE-Si-O-N compound and is crystallized. Al content, in terms of oxide is 0.1 wt% or less _(Al 2 _{O 3),} the high frequency low loss dielectric material of claim 1. A member made of the high frequency low loss dielectric material according to any one of claims 1 to 3, the high frequency transmission member which is a member for radio frequency transmission to be applied to the manufacturing apparatus of the electrical components. The high frequency transmission member according to claim 4 , wherein the member is a high frequency transmission member applied to a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus. A method for producing the material of claim 1, comprising:
Abundance of the periodic table group 3a element compound is at least 7 mol% in terms of oxide, the molar ratio of silicon oxide _{(SiO 2) (RE 2 O} 3 / SiO 2) is 1.0 to 1 By using a starting material in the range of .5, molding and firing ,
1) The ratio of Group 3a element compound (RE) in the periodic table contained in the sintered body is at least 16% by weight in terms of oxide (RE ₂ O ₃ ), and contains a silicon oxynitride compound crystal phase 2) A method for producing a low-loss dielectric material for high frequency, wherein the silicon oxynitride compound produces a compound represented by RE ₄ Si ₂ N ₂ O ₇ . The method for producing a high-frequency low-loss dielectric material according to claim 6 , wherein a molded body having a relative density of 52% or more is produced by isostatic pressing at least 400 MPa and fired.