JP2009280417A - Anode-joinable ceramic composition for low temperature sintering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide LTCC (low temperature co-fired ceramic), and to provide an anode-joinable ceramic composition for low temperature sintering even if a glass component is reduced. <P>SOLUTION: Disclosed is a ceramic composition for low temperature sintering comprising movable ion-containing anode-joinable glass powder and ceramic powder, and having purity and a composition with which the ceramic powder does not form a reaction crystal phase with a glass component upon sintering. The ceramic powder is preferably composed of a mixture of ceramic powder whose thermal expansion coefficient is higher than that of the glass of the glass powder and ceramic powder whose thermal expansion coefficient is lower than that of the glass of the glass powder. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ceramic composition for low-temperature sintering capable of anodic bonding, a green sheet made of the composition, a sintered substrate that can be used for a through wiring board formed by molding and sintering the composition, and the like The present invention relates to a MEMS (Micro Electro Mechanical Systems) element formed by wafer level packaging using a through wiring substrate.

  In anodic bonding, glass containing alkali metal, such as borosilicate glass, is in contact with silicon and heated to a temperature at which alkali metal ions such as sodium in the glass can easily move. This is a method of joining glass and silicon by connecting a side to a negative electrode and applying a DC voltage of about several hundred to 1,000 volts. Non-bridging oxygen ions generated when alkali metal ions move to the negative electrode side and silicon are electrostatically attracted to form a chemical bond at the glass-silicon interface, resulting in a strong and reliable bond, and a pressure sensor It is often used as a mounting technology for sensors and acceleration sensors.

Many MEMS devices are manufactured with die level packaging. This packaging method is manufactured by the following process.
1. The MEMS element manufactured in the wafer state is diced into individual pieces.
2. The separated MEMS elements are mounted one by one on a mounting substrate to which a bonding material is applied, and bonded by heat treatment or the like.
3. Since the MEMS element has a movable part and is affected by moisture and particles, a lid is mounted on the mounting substrate and hermetically sealed.

  Die level packaging not only has many processes, but flowing a MEMS element having a fragile structure such as a movable part without protection causes a decrease in yield. Further, the package requires a considerably larger size than the MEMS device, which is not preferable from the viewpoint of miniaturization and low profile. Moreover, the package cost accounts for nearly 80% of the MEMS device cost, which is said to be an obstacle to popularization.

Wafer level packaging has been proposed and actively developed as a solution. This packaging method is manufactured by bonding a wafer-state MEMS element to a mounting substrate as it is, and then dicing into individual pieces. The process is minimally simplified and the package dimensions can be made the same as the chip.
In order to manufacture a MEMS device by this wafer level packaging, a through wiring is required on the mounting substrate. This is because it is necessary to take out the electrode on the mounting substrate side bonded to the electrode of the MEMS device to the back surface. As the through wiring board material, a glass or silicon having a through hole and filled with a conductive material is used.

  Although the drilling used for drilling glass has a good hole shape, there is a limit to the refinement of the hole size and pitch, and there is a limit to the number of holes because the number of holes in the wafer cannot be reduced. In addition, although sand blasting can simultaneously process many holes at the same time, the hole shape is poor and the hole size and pitch are limited. Although through wiring processing is performed after drilling, a complicated process is required. In an example that is put into practical use, finishing is performed in the order of metallization treatment of the hole side surface, insertion of a conductive metal core material, pouring of a brazing material, and mirror polishing. Cost is high and there is a limit to miniaturization and large diameter.

  Silicon can be drilled with a deep RIE apparatus, but the Deep RIE apparatus is very expensive and takes a long processing time. Through-hole wiring boards are made in the same complicated process as glass after hole processing. It is finished in the order of oxidation treatment for insulation, seed layer formation for electroplating, hole filling by electroplating, and mirror polishing. In addition, since anodic bonding cannot be performed, the silicon MEMS wafer is bonded to the silicon MEMS wafer by plasma metal activation or room temperature bonding. However, the bonding apparatus is quite expensive and takes a long time for bonding. Although a fine substrate can be made, the problem is that it requires considerable capital investment and the cost is high.

As a multilayer wiring board, a low temperature co-fired ceramic (LTCC) substrate is widely known. The LTCC substrate is generally a paste containing a conductor using a green sheet made by adding an organic binder to a mixed material in which glass or the like is added to a ceramic material, and through-holes are formed in the sheet to connect up and down. Are printed in the through holes and on the surface of the green sheet, and then these green sheets are accurately stacked, laminated by heating and pressurizing, and then fired.
Since drilling in the LTCC substrate can be performed on the green sheet by punch pins or laser processing, it is easy and has high mass productivity. Also, conductor filling into the perforated green sheet can be easily performed by screen printing, which is a general-purpose technique.
Although multilayer wiring is difficult with glass or silicon, the LTCC substrate is manufactured by stacking a number of green sheets, so that it can be easily formed into a multilayer substrate. Since rewiring design is possible in the inner layer, it is not necessary to care about the position of the electrode pad on the MEMS chip side and the position of the electrode pad on the secondary mounting side, and the degree of freedom in wiring design is increased. If necessary, it is possible to increase the functionality by incorporating passive components such as capacitors and coils, as is often used in LTCC substrates. Thus, it is considered that the LTCC substrate is easy to manufacture and can be reduced in cost as compared with glass and silicon, which are currently used MEMS through wiring electrode substrate materials.
However, the thermal expansion coefficient is not consistent with silicon, or the only bonding method with silicon is the use of inclusions such as solder, brazing material, glass, and organic adhesives. It was difficult to adopt from a viewpoint.

  Patent Document 1 discloses a glass ceramic (LTCC) capable of anodic bonding with silicon, specifically, a low-temperature sintered ceramic using a glass powder containing an alkali metal and a ceramic powder made of alumina, cordierite and / or silica glass. Is described. As the glass powder, borosilicate glass containing about 2.6% of Na component is used, and the thermal expansion coefficient is 3.4 ppm / ° C. which is almost equivalent to silicon. The composition is borosilicate glass: 60 to 70 wt%, alumina: 10 to 20 wt%, cordierite or silica glass: 8 to 25%, and the content of Na component is 1.5% or more.

WO2005 / 042426

Anodic bonding is a technique that can bond not only silicon but also GaAs, Kovar, Al, Ti, and the like, and a more versatile low-temperature ceramic composition is desired. Moreover, the glass used for LTCC is expensive, and its usage should be as small as possible from the viewpoint of strength and thermal conductivity.
Accordingly, an object of the present invention is to provide a porcelain composition used for a low-temperature sintered substrate from which a through wiring substrate can be easily produced, and capable of anodic bonding and having a glass component as small as possible. is there.

In the low-temperature sintering porcelain composition containing glass and ceramics that can be anodically bonded, the present inventors consider that a composition that does not hinder the anodic bondability of glass is important, and that such a composition is obtained by sintering glass to ceramics. It should be able to maintain an amorphous state without reacting with the material, and if a reaction product (reaction crystal phase) between glass and ceramics or impurities is generated by sintering, it acts as a mobile ion during anodic bonding It has been found that since the alkali metal ions are fixed in the crystal, the junction current does not flow and anodic bonding is not sufficiently performed.
In addition, since anodic bonding is a solid-solid direct bonding, it is important that the porcelain composition used has similar thermal expansion properties to the material of the other party to be anodic bonded, and therefore the thermal expansion of glass composition is higher than that of glass powder. It has been found that the physical properties of thermal expansion can be easily adjusted by combining a large ceramic material and a small ceramic material.

That is, the present invention has the following configuration.
[1] For low-temperature sintering, comprising an anodic bondable glass powder containing mobile ions and a ceramic powder, wherein the ceramic powder has a purity and composition that does not form a reaction crystal phase with a glass component during sintering. Porcelain composition.
[2] The porcelain composition according to 1 above, wherein the ceramic powder is a mixture of a ceramic powder having a larger thermal expansion coefficient than a glass powder glass and a ceramic powder having a smaller thermal expansion coefficient.
[3] The porcelain composition according to 2, wherein the ceramic powder is a mixture of alumina powder and cordierite powder.
[4] The porcelain composition according to any one of the above items 1 to 3, wherein the movable ions are sodium ions or lithium ions.
[5] 55 to 60% by weight of glass powder containing 2 to 5% by weight of Na ₂ O, 8 to 25% by weight of alumina powder, and 18 to 34% by weight of cordierite powder % Or less of the porcelain composition for low-temperature sintering.
[6] The composition is expressed by mass% of the oxide. Al ₂ O ₃ : 21 to 33%
SiO _2: 55~65%
B ₂ O _3: 5~7%
MgO: 2-5%
Na ₂ O: 1-3%
6. The porcelain composition according to 5 above.
[7] A green sheet comprising the porcelain composition according to any one of 1 to 6 and an organic binder.
[8] A sintered substrate obtained by molding and firing the porcelain composition according to any one of 1 to 6, and having a thermal expansion coefficient of 3.0 to 4.0 ppm / ° C.
[9] A through wiring substrate using one or a plurality of the green sheets as described in 7 above.
[10] A MEMS element formed by anodically bonding the through wiring substrate according to 9 and a silicon wafer on which the MEMS element is formed, and then dicing.

The present invention also provides the following method.
[11] A method for screening a ceramic composition for low-temperature sintering for anodic bonding, comprising a substrate formed by molding and firing a ceramic composition comprising glass powder and ceramic powder containing movable ions and anodic bonding, and silicon A method of screening a composition that achieves a predetermined bonding degree by changing the purity, blending ratio and / or type of ceramic powder based on the degree of bonding when anodic bonding is performed.
[12] The screening method according to 11 above, wherein the amount of the glass powder blended is 65% by mass or less.

The glass powder used in the present invention is not particularly limited as long as it can be anodically bonded, and can be widely used including commercially available ones. The glass powder capable of anodic bonding contains mobile ions, and examples of the mobile ions include alkali metal ions such as sodium ions and lithium ions. Although the amount of mobile ions is related to other compositions, it is usually preferably about 2 to 6% by mass in the glass and about 1 to 3% by mass in the total inorganic matter.
As an example of glass, for example, borosilicate glass (chemical _{composition: SiO 2 -B 2 O 3 -Na} 2 O), etc. _{SiO 2 -B 2 O 3 -Li 2} O and the like.

Examples of the ceramic powder used in the present invention include alumina powder, cordierite powder, zirconia powder, steatite powder, forsterite powder, zircon powder, and the like, which can be used alone or in combination of two or more. However, it is necessary not to include a component (including impurities) that forms a reaction crystal phase with a glass component during sintering. When the amount of the component capable of forming the reaction crystal phase is increased, the anodic bonding strength is reduced or the bonding cannot be performed unless a large amount of glass powder is used.
Taking cordierite powder as an example, cordierite powder is often synthesized from natural raw materials, but when it is mixed and fired with glass powder under the influence of impurities contained, a reaction crystal phase is likely to be formed. Therefore, it is preferable to use cordierite powder synthesized from purified raw material powder.

  The composition of the glass powder and the ceramic powder is not limited as long as it does not form a reaction crystal phase with the glass component at the time of sintering. From the viewpoint of reducing the amount of glass, the glass amount is 65% by mass or less in the total inorganic matter. Is preferable, more preferably 60% by mass or less, and particularly preferably less than 60% by mass. As a result, the mixing ratio of the ceramic powder is relatively increased. The ceramic powder does not contribute to the anodic bonding, and the ceramic portion becomes an unbonded portion in the anodic bonding, and the anodic bonding becomes difficult to be performed as the mixing ratio of the ceramic powder increases. In the present invention, various kinds of materials, compositions, and amounts of impurities are selected so that the composition can sufficiently perform anodic bonding even in such a range.

Further, in anodic bonding, due to problems such as misalignment due to thermal expansion with the counterpart material, the thermal expansion behavior of the ceramic composition for the sintered substrate of the present invention is required to approximate the thermal expansion behavior of the counterpart material. . Also from that viewpoint, the kind and amount of the ceramic powder are adjusted as the composition of the composition of the present invention. Specifically, the composition of the present invention is preferably adjusted so that the coefficient of thermal expansion of the material after molding and firing is within 0.5% of the coefficient of thermal expansion of the counterpart material. When the counterpart material is silicon, the thermal expansion coefficient of the composition of the present invention is preferably 3.0 to 4.0 ppm / ° C, more preferably 3.2 to 3.8 ppm / ° C, and particularly preferably 3.2. 3.5 ppm / ° C.
As a method for adjusting the coefficient of thermal expansion of the composition of the present invention, as a ceramic powder, a mixture of a ceramic powder having a thermal expansion coefficient larger than that of glass of glass powder and a ceramic powder having a small thermal expansion coefficient is used. This can be easily done by adjusting.
In this specification, the thermal expansion coefficient is measured based on a differential expansion method using a quartz (SiO ₂ ) standard sample.

The case where alumina powder and cordierite powder are used as ceramic powder will be described below as an example of the composition of the present invention.
The glass powder preferably contains 2% by mass or more and 5% by mass or less of a mobile ion component such as Na ₂ O, and the glass powder is preferably 53% by mass or more and 62% by mass or less, more preferably based on the amount of all inorganic substances. Is used in an amount of 55% by mass to 60% by mass. When the amount of the glass powder is increased, there are problems such as economical disadvantages and insufficient strength. If the amount of mobile ions is too small, the bonding strength at the time of anodic bonding is weak, and if it is too large, there is a concern that the insulating property will be lowered.
5-30 mass% is preferable with respect to the quantity of all the inorganic substances, and, as for the compounding quantity of an alumina powder, More preferably, it is 8-25 mass%. If the amount of alumina powder is too small, the thermal expansion coefficient is too low, and if it is too large, the thermal expansion coefficient is too large.
The blending amount of the cordierite powder is preferably 15 to 36% by mass, more preferably 18 to 34% by mass with respect to the total amount of inorganic substances. If the amount of cordierite powder is too small, the thermal expansion coefficient becomes too large, and if too much, the thermal expansion coefficient becomes too low.

  These powders only have to have a particle size suitable for the application. For example, the average particle size (D50) may be 0.05 to 10 μm, preferably 0.5 to 5 μm.

When the obtained composition is expressed by mass% of the oxide, for example, it is as follows.
Al ₂ O ₃ : 21 to 33%
SiO _2: 55~65%
B ₂ O _3: 5~7%
MgO: 2-5%
Na ₂ O: 1-3%

The porcelain composition described above can be made into a green sheet by combining with an organic binder.
The production of the green sheet of the present invention can be performed by a conventional method. For example, after adding a solvent such as toluene and isopropyl alcohol to a predetermined mixed powder of glass powder and ceramic powder and dispersing in a ball mill, the total of inorganic powder Add 1 to 20 parts by weight of an organic binder such as polyvinyl alcohol and 1 to 10 parts by weight of a plasticizer (for example, dibutyl phthalate) to 100 parts by weight, and further add a dispersing agent or the like as needed to produce a slurry. To do. The obtained slurry is formed into a sheet by a forming method such as a doctor blade method and dried to obtain a green sheet. The thickness of the green sheet may be designed according to the application and the like, but is usually about 80 to 150 μm.

  The obtained green sheet is punched by punching or the like, and then printed with a circuit and filled with a conductive paste into the drilled via hole. Conventional processing such as binder processing and baking processing is performed to obtain a through wiring substrate. The firing is performed at the same time that the green sheet and the conductor are fired at a low temperature of 950 ° C. or lower.

The obtained through wiring substrate can be formed into a MEMS device by performing anodic bonding with a silicon wafer on which various MEMS elements are formed, followed by dicing. Manufacture and anodic bonding of a silicon wafer on which a MEMS element is formed can be performed by conventional methods.
The thermal expansion coefficient of the substrate is adjusted to 3.0 to 4.0 ppm / ° C. when the anodic bonding partner material is silicon. This adjustment can be performed by selecting the material of the ceramic powder as described above.
Here, silicon has been presented as a material for anodic bonding, but the composition of the present invention can be a porcelain composition that can be bonded to GaAs, Kovar, Al, Ti, and the like.

  The present invention also provides a method for easily screening the composition of a low-temperature sintering porcelain composition comprising glass powder and ceramic powder. Whether or not anodic bonding is possible can be judged based on the degree of bonding when anodic bonding with a specific counterpart material is actually performed. If it is insufficient, the purity of the ceramic powder is improved, or various blending ratios are changed. To do. This method can be suitably used for examining the composition of a porcelain composition having a particularly small amount of glass powder, and in particular, a composition in which the blending amount of the glass powder is 65% by mass or less, further less than 60% by mass. Suitable for screening.

Glass commercially available as a glass capable of anodic bonding (SiO _2: 81.9 to 82.4 wt%, Al ₂ O _3: 2.9~3.2 _{wt%, B 2 O 3: 10.5~11} . 0% by mass, Na ₂ O: 3.9 to 4.7% by mass, K ₂ O, Fe ₂ O ₃ , CaO, and MgO are all 0.1% or less) with an average particle size (D50) of 0.6 The mixture was pulverized to ˜2.5 μm, and alumina powder having an average particle diameter of 1 to 3 μm and cordierite powder (glass recrystallization type) having an average particle diameter of 1 to 3 μm were mixed at a blending ratio shown in Table 1. Table 2 shows the obtained mixture in terms of mass% of oxide. A solvent such as toluene and isopropyl alcohol was added to the mixture and dispersed in a ball mill, and then polyvinyl alcohol as a binder and dibutyl phthalate (DBP) as a plasticizer were added to prepare a slurry. The obtained slurry was formed into a sheet by a doctor blade method and dried to obtain a green sheet having a thickness of 125 μm.

This was cut into a predetermined size, laminated into 8 layers, and then fired in the atmosphere at 835 ° C. or 850 ° C. for 1 hour to produce a low-temperature sintered substrate. The thermal expansion coefficient and water absorption rate of the obtained substrate were measured and are shown in Table 1. Here, the thermal expansion coefficient was measured based on a differential expansion method using a quartz (SiO ₂ ) standard sample, and the water absorption was measured based on the Archimedes method.

This substrate was cut into 20 mm □ by dicing and mirror-polished to about 3 nmRa. On this hot plate where the substrate and silicon were heated to 400 ° C., anodic bonding was performed by applying a DC voltage (600 VDC) so that silicon became a positive electrode and the substrate became a negative electrode. A resistance element for voltage detection was inserted on the anodic junction circuit, and the voltage applied to the resistance element was monitored to check how the junction current changed with the junction time. An anodic bonding current equivalent to that of the glass substrate and silicon flowed.
The obtained bonded body was scratched with glass and divided by hand, and the fracture surface was observed with SEM. Silicon and the low-temperature sintered substrate had a continuous fracture surface. It was observed that

Claims (10)

  A ceramic composition for low-temperature sintering, comprising a glass powder containing movable ions and an anodic bondable ceramic powder, wherein the ceramic powder has a purity and composition that does not form a reaction crystal phase with a glass component during sintering. .   The porcelain composition according to claim 1, wherein the ceramic powder is a mixture of a ceramic powder having a larger thermal expansion coefficient than a glass of glass and a ceramic powder having a smaller thermal expansion coefficient.   The porcelain composition according to claim 2, wherein the ceramic powder is a mixture of alumina powder and cordierite powder.   The porcelain composition according to any one of claims 1 to 3, wherein the movable ions are sodium ions or lithium ions. 55 to 60% by weight glass powder containing 2 to 5% by weight of Na ₂ O, 8 to 25% by weight alumina powder, and 18 to 34% by weight cordierite powder A porcelain composition for low-temperature sintering characterized by the above. The composition is expressed as mass% of oxide. Al ₂ O ₃ : 21 to 33%
SiO _2: 55~65%
B ₂ O _3: 5~7%
MgO: 2-5%
Na ₂ O: 1-3%
The porcelain composition according to claim 5.   A green sheet comprising the porcelain composition according to any one of claims 1 to 6 and an organic binder.   A sintered substrate obtained by molding and firing the porcelain composition according to any one of claims 1 to 6, and having a thermal expansion coefficient of 3.0 to 4.0 ppm / ° C.   A through wiring substrate using one or a plurality of the green sheets according to claim 7.   The MEMS element formed by carrying out anodic bonding of the penetration wiring board of Claim 9, and the silicon wafer in which the MEMS element was formed, and dicing.