JPS59120217A - Method for filtering wax - Google Patents

Abstract

PURPOSE:To easily filter wax kept relatively high in viscosity and to easily and certainly remove a fine particulate solid, by filtering molten wax by a filter medium consisting of filter layers respectively made of porous ceramics and different in pore sizes and a support layer integrally formed so as to be superposed to said filter layers. CONSTITUTION:The whole of a filter apparatus 1 is heated to about 100- 200 deg.C corresponding to the kind of wax by a heater 34 and the wax 18 stored in a crucible 17 in a molten state is sent into pores 20 of tubular filter media 4, 5, 6 through an orifice 10. After the pores 20 are filled with the molten wax 18, pressurized inert gas (e.g., pressurized N2-gas) is introduced into the upper part of the chamber 19 in the crucible 17 under pressure from an inlet 21. As a result, filtering pressure is imparted by pressure difference between chambers 19, 20 provided to both sides of the filter layer 16 in addition to the own wt. of the molten wax 18. In this case, wax 28 other than solid impurities having high melting temps. is rapidly introduced into a chamber 30 through the filter and further accumulated in the chamber 29 of a crucible 27. Because filtering is performed by the ceramic media 4-6 each high in mechanical strength during this time, high viscosity wax can be also filtered within a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of filtering molten wax, and more specifically, wax that is normally in a solid state or a highly viscous state at room temperature,
The present invention relates to a method of filtering the wax used for fixing the semiconductor wafer to a polishing plate to remove and purify contaminant particles when polishing, lapping, or mirror-finishing the surface of the semiconductor wafer (hereinafter simply referred to as polishing).

Conventionally, polytetrafluoroethylene filtration membranes or sintered metal filtration media have been used to filter this wax.

By the way, wax for fixing semiconductor wafers is easily deteriorated by oxidation at temperatures far above its softening or melting temperature, so when the wax is filtered to remove solid impurities from the wax, the temperature of the wax is softened. It must be suppressed to a level higher than the melting temperature. As a result, the semiconductor wafer fixing wax must be treated in a relatively highly viscous state.

However, when trying to filter highly viscous wax under pressure using a polytetrafluoroethylene filtration membrane, the filtration layer deforms due to its flexibility and viscoelasticity, and the size of the filtration pores decreases. For example, there was a risk that it would be difficult to perform filtration.

On the other hand, sintered metal filtration media has relatively large filtration pores and can remove particulate matter with a particle size of about 1 μm or more through filtration without being too difficult, and is suitable for use with wax for fixing semiconductor wafers. Filtering ζ is not necessarily preferable either. Furthermore, conventional sintered metal filtration media has pores of substantially uniform size along its thickness, and the entire pores are formed to function as a filtration layer. Furthermore, in order to impart appropriate mechanical strength to the filtration media, it was necessary to make the filtration layer considerably thicker, and it was necessary to apply a large amount of pressure to filter the highly viscous wax.

The present invention has been made in view of the above points, and its purpose is to not only easily filter semiconductor wafer fixing wax until it has a relatively high viscosity, but also to obtain a solid product with extremely small particle size. It is an object of the present invention to provide a wax filtration method capable of easily and reliably removing wax.

This purpose, according to the present invention, is achieved by heating the wax to a molten state, and forming a filter layer made of porous ceramic, and a filter layer formed integrally with the filter layer by overlapping it with the filter layer. This is achieved by a wax filtration method characterized in that the molten wax is filtered through a filtration media comprising a support layer made of porous ceramic having large pores.

In this specification, the term "wax for fixing semiconductor wafers" refers to the wax used to polish the surface of flat semiconductor wafers cut out with various crystal planes depending on the type of semiconductor and the use of the semiconductor wafer to eliminate warpage, distortion, etc. A wax that is used to fix semiconductor wafers to polishing plates when finishing surfaces with small thickness, small thickness unevenness, and high flatness.

This wax is in a highly viscous state that can be considered solid or substantially solid at the temperature used for fixing, for example at room temperature. Waxes include not only esters of fatty acids and higher-hydric alcohols or dihydric alcohols that are not bathed in water, but also waxes such as wood waxes made of aliphatic carbides (paraffins) with high melting points, and petroleum waxes. A wax or the like may be used, and a chemical mixture may be used, but the softening or melting temperature is high enough to prevent softening by heating during polishing (e.g., 60°C or higher, preferably 80°C or higher), and it is difficult to apply to the polishing plate. It is preferable that the range of melting temperature is small enough to uniformly soften during application, and the thermal conductivity is high. Such waxes include refined paraffin, shellac,
There are pine resin (mixed with olive oil), sealing wax and beeswax mixture, etc.

A molten state refers to a state in which the material has substantially fluidity, and a state in which the viscosity is approximately 1×10 poise or less.

The ceramic constituting the filtration media may be not only oxides of metals such as alumina, but also nitrides, carbides, etc., or mixtures thereof. Further, the filtration layer and the support layer may be made of different ceramics.

The porous ceramic support layer is preferably made of a sintered body of alumina particles of similar particle size, and has a thickness that provides sufficient mechanical strength to the ff3 media to withstand the filtration pressure; As long as the support layer has pores that can reduce the pressure loss when relatively high viscosity molten wax filtered through the filtration layer to the same level or less as the pressure loss in the filtration layer, it can be freed from ceramic particles of various sizes etc. The filtration layer made of porous ceramic is preferably as thin as possible to perform filtration, and is preferably fixed to the support layer by sintering. It is preferable that the pores of the filtration layer have a smaller pore diameter and a smaller variation in pore diameter.

For example, according to the method disclosed in Japanese Patent Application Laid-Open No. 57-7J604, porous alumina particles having pores of 15 to 20 μm are formed as a support l-, and the pore size is gradually formed on one surface of the support layer. When an alumina slip layer with a particle size range adjusted to reduce the particle size is deposited at least twice and fired as a single piece (in this case, a temporary layer with a thickness of about 102 m and an average filtration pore diameter of about 0.2 μm is formed). be done.

In addition, the outer diameter formed in this way is 1! llu+, inner diameter 1
In a filtration media that has a filtration layer of about 10 μm on the inner circumference of a support layer of 5 mm, the radial crushing strength measured in a ring with a length of 151 m reaches 74 owy/ciζ, and the filtration media is sufficient for a filtration pressure of about 10 atm. I could endure it.

The filtration media may be formed by forming a temporary layer on the outer periphery of a tubular support layer, or may be formed by forming a filtration layer on the inner and outer peripheries, or may be formed by at least one of a flat support layer and a curved support layer. A filtration layer may be formed on one of the surfaces.

Next, a filtration device 1 according to a preferred embodiment for carrying out the wax filtration method according to the present invention will be explained based on FIGS. 1 and 2. FIG.

In the figure, 2 is a filter body made of alumina. , 5.6, and supports 7, 8 which fix both ends of the tubular filtration media 4, 5.6 to both ends of the case 3.

The upper support part 7 has an alumina support frame part 9 that is airtightly fitted to the upper end of the case 3, and a hole that communicates with the upper end opening of each of the filtration media 4, 5.6. Overmedia 4゜5
．． It consists of a partition plate part 11 made of alumina, the ends of which are hermetically fitted. Lower 1tl + support part 8 is 30mm
] Support frame part 12 on the back of alumina airtightly fitted to the F end, and alumina with a hole 13 fixed in the center and a lower end opening of the filtration media liquid-tightly sealed via a packing 14a. It consists of a partition plate part 14 made of

The case 3 and the support portion 7.8 may be made of another ceramic instead of alumina, or may be made of metal or other material as long as it can withstand the temperature of the molten wax as the filtered material, for example, about 100 to 200°C. It may be made of other materials such as plastic.

The case 3 may have a rectangular cylindrical shape instead of a cylindrical shape. Note that a through hole may be provided in the upper part of the peripheral wall of the case 3.

The filtration media 4 is integrally fixed to a support layer 15 made of a relatively thick tubular alumina sintered body with a relatively large pore diameter and high mechanical strength, and an inner wall of the support layer 15. The filtration layer 16 is made of a thin tubular alumina sintered body with small pore diameters. The pore diameter of the support layer 15 is about 10 to 30 μm and the thickness is about 1.5 to 2 μm, and the average pore diameter of the filtration Jfj 16 is 1.0 to 0.1 μm.
about μm, preferably about 0.5 to 0.1 μm,
The thickness is about 100 to 20 μm, preferably 40 to 20 μm.
It is about m. The filtration media 5 and 6 are constructed similarly to the filtration media 4.

Note that the support layer 15 may be composed of a plurality of layers, and may be formed, for example, so that the pores of the radially outer layer ai+41 have a larger hole diameter. Support layer 15 and filtration layer 16
It is not necessary that the boundary between the filtration layer 16 and the filtration layer 16 be clearly defined, and it is sufficient that the 7 filtration layers that filter the molten wax and the support layer 15 that mechanically supports the filtration layer 16 are formed aesthetically.

Note that the number of tubular filtration media provided in the main body 2 may be 1 to 2, or 4 or more.

F cooperates with the main body 2 to melt the wax 1 in a molten state.
It is a crucible for accommodating 8, and chamber 1 in crucible 17
9 is connected to the bottom of the crucible 17 (via the hole 10 located therein) to the columnar hole 20 of the tubular filtration media 4, 5.6. 7
A tube 22 for introducing pressurized inert gas, having an inlet 21 at the top, extends at the upper end.

23 is a band engaged with the support frame portion 9 of the support portion 7; 24;
Push up the upper part 25 of the band 23 to remove the band 23.
This is a tightening screw for engaging the crucible 17 with the support frame 9 and fixing the crucible 17 to the filter main body 2.

27 is fixed to the filter main body 2 by the support part 8, and P
: A crucible for accommodating the molten wax 28 after iM, and the chamber 29 in the crucible 27 is connected to the space inside the case 3 around the tubular filtration media 4, 5.6 through the hole 13 located at the top of the crucible 27. It is connected to 30.

Reference numeral 31 denotes a pedestal, and the pedestal 31 supports a filter 33 consisting of the crucible 27, the filter main body 2, and the crucible 17 at the bottom 32 of the crucible 27 and the support frame portion 12 of the support portion 8.

7 34 is a heater that heats the crucible 1τ and the filter B2. Note that the heater 34 may be used to heat only the crucible 17 and the filter body 2.

In the filtration device 1 constructed as described above, wax filtration is performed as follows.

First, screw the screw 24 into the crucible 17 side and
The lower end engaging portion 3 is disengaged from the support frame portion 9 of the filter body 2, and the crucible 17 is removed.

Next, the wax, which is in a substantially solid state as a whole and contains high melting point impurity components to be removed by filtration, is left in a lump or crushed into pieces and placed on the partition plate 11 constituting the bottom wall of the crucible 17. , the crucible 17 is placed over the crucible 17, and the annular lower edge of the crucible 17 is pressed against the partition plate portion 11 via the packing using the band 23 and the screw 2+ to seal the chamber 19.

Next, the entire filtering device 1 is heated to an appropriate temperature of about 100 to 2008 C depending on the type of wax using a furnace or heater 34. This temperature is kept within a range that can avoid deterioration of the wax due to oxidation, thermal decomposition, etc., and is usually about 180 to 200°C at the most.

If there is a risk that the wax 18 may be oxidized by this heating, fill the device 1 with an inert gas such as nitrogen gas or make the device 1 substantially evacuated before heating. You can leave it there.

Due to the heating in the heater 34, the wax 18 in the crucible 17 becomes molten and passes through the holes 10 into the holes 20 of the tubular filter media 4, 5.6.

After the holes 20 are filled with molten wax, the gas introduction tube 21
A pressurized inert gas, such as pressurized nitrogen gas or pressurized argon gas, is fed into the upper part of the chamber 19 in the crucible 17 via the crucible 17 . As a result, in addition to the weight of the molten wax 18, filtration pressure is applied by the pressure difference between the chambers 19 and 30 on both sides of the filtration layer 16, and the wax 28 other than solid impurities with a high melting temperature is quickly transferred to the filtration layer 16. It passes through the chamber 3o, passes through the hole 13, and accumulates in the chamber 29 of the crucible 27. In the apparatus 1, since filtration is performed using ceramic filtration media 4, 5.6 with high mechanical strength, the pressurized air pressure can be increased, and even wax 18 with high viscosity can be filtered in a short time.

In addition, in the apparatus 1, since the filtration layer 16 is thin and filtration is performed using the filtration media 4, 5.6 with low pressure loss, if the viscosity of the wax 18 is not so thin, additional filtration pressure is applied by pressurized gas. Filtration can be performed relatively quickly even without feeding.

At the end of said filtration, the pressurized gas passes through the filtration layer 16 and enters the chamber 30, so that filtration is carried out by the weight of the wax 18. Note that if a through hole is provided in the upper part of the peripheral wall of the case 3 and pressurized air pressure is continuously introduced from the pipe 22, the filtration pressure τ can be applied by gas until the filtration is completed.

When substantially all of the wax 18 has been filtered, the device 1 is moved downward relative to the heater 34 so that at least the lower end 32 of the device-1 is located outside the heater 34, and the handle 31ar and turn-C crucible are moved. The lower end opening of 27 is opened and the filtered molten wax 28 is taken out.

The wax 28 thus obtained contains 1
Solids with a particle size of, for example, 1 μm or more are considered virtually non-remaining.

In FIGS. 3 and 4, a table '□ of a semiconductor wafer 35 is shown.
A portion of a polishing device 36 for polishing the surface of a wafer 35 for surface finishing is shown.

In the polishing device 36, 37 is a polishing cloth 381
has a fixed horizontal surface 39 and axis 4
0□ 1 is a turntable configured to rotate in the direction A, and 41 is configured to rotate in the direction B around an axis 42, and a turntable configured to press in the direction C. Surface 43 is turntable 3
The polishing plate is mounted on the main body of the device 36 so as to be kept parallel to the surface 39 of the polishing plate 7.

44, the semiconductor wafer 35 is placed on the surface 43 of the polishing plate 41;
This is a layer of wax 28 that is fixed to the surface.

When fixing a semiconductor wafer 35 cut out along an appropriate crystal plane depending on the type of semiconductor and the application of the semiconductor wafer to the surface 43 of the polishing plate 41 with wax 28,
The heated and melted wax 28 is applied to a predetermined portion of the surface 43 of this polishing plate 410, and the applied molten wax 28 is
A semiconductor wafer 35 is placed on the plate 1-41, and when the wax 28 cools and solidifies, the wafer 35 is pressed onto the plate 1-41.

The wafer 35 is fixed to the plate 41 by the wax layer 44 that is formed when the thin liquid layer of the wax 28 solidifies, but the wax 28, in the 1'8 molten state, has large solid particles of, for example, over 1 μm. Because it does not contain impurities, the wax layer 44 is extremely thin (for example, 1
The thickness is uniform (~10 μm: jA degrees), and the machine part 45 of the G1 semiconductor wafer 35 can be positioned parallel to the surface 43 of the polishing plate 41 with high precision.

In this manner, the surface 468 of the semiconductor wafer 35 fixed to the polishing plate 41 via the wax layer 44
The wafer 35 is polished by polishing with the polishing cloth 38 of G.
The surface 46 of can be parallelized with high accuracy to the surface 45,
Moreover, it becomes one plane with high flatness.

The wafer thus obtained is suitable for use as a wafer for monolithic integrated circuits, etc., which requires finishing accuracy of lapping or polishing to have irregularities within 1 μm or parallelism on both surfaces.

Example filtration device 1: Tubular 7 filtration media 4 and 1iiJ-like filtration media with both ends open (1 hole 19 mm, inner core 15 m, length 70 mm, 1 filtration layer 1. 1.
difference? 1'') 10μms+!'iB hole?-¥=0.
1 to 0.9 μm) of one i:ii mouth and sealed with a pigeon's imum] 14 vessels (+' A wax for fixing or bonding semiconductor wafers (for example, (-6++ melt wax') or "Botomax", commercially available) was filtered with a vertical surface of about 2,500 mm.

For filtration, first, the solid wax was crushed and placed in a tubular filter, and the entire /J''i filter was heated in a constant temperature bath. This wax was bath-melted at about 85°C. At this time, the wax was approximately 45 mm deep in the tubular υj filter.

When the temperature of the wax was set to 90°C, 4 waxes were observed to come out from the tube wall of the I:5M tube, but due to the large wax occupancy, only one wax actually flowed out. is.

The temperature of the wax was maintained at 110'C, the weight of the wax was kept at 110'C, the weight of wax/wax was low, and 10 cc of σj1 was obtained in about 5 cycles of C1.

- On the other hand, add the same ¥3 note to the song, '7'/''bu,
If the temperature is 2'λ at 130 °C,
Once's fortune telling is 4Σ(this IJ(doshi0)
At zero time, the F:J level was 10 cc fcfiQ.

I am in charge of the work of Ito in 11!2.
56 Self (:: i) ``1・j'' [reverse the tube to the 140 end] ・Jll through the tube] pressurized one force゛--2
7. -1. (This 2
When applying a constant pressure of 00'F, i, 1,2-L, 10 cc of filtered wax was obtained in 20 minutes at a wax temperature of 130C.

In the above, when the wax before filtration was observed under a metallurgical microscope, there were 2 particles/ci on the surface of the molten wax with a particle size of about 20 μm (approximately 1 particle with a particle size of about 1 μm or more).
However, in the molten wax of the filter, no particles with a particle size of about 20 μm'n were observed, and only about 5 particles/ff1) with a particle size of about 1 to 3 μm were observed.
Only about IL was observed, and when this p-super wax is used for fixing a semiconductor wafer, it can be considered that there is virtually no possibility that particles larger than 1 μm will be present between the wafer and the polishing plate.

As described above, in the wax filtration method according to the invention I, the wax is heated to a molten state, and a porous ceramic filtration layer is superimposed on the filtration layer to support the filter, Since the molten wax is filtered through a filter consisting of a support layer made of porous ceramic having pores larger than the filtration layer, the wax used for fixing semiconductor wafers can be kept at a relatively high viscosity. Not only can it be easily filtered, but even extremely small-sized solids can be easily and reliably removed.

8. The method of the present invention can also be applied to the filtration of other waxes for fixing semiconductor wafers that require filtration of solids, similar to Nox.

[Brief explanation of the drawing]

Fig. 1 shows the wax filtration method according to the present invention; Fig. 3 is an explanatory diagram showing a part of the semiconductor wafer surface polishing apparatus using the wax obtained by the method of the present invention; and Fig. 4 shows the apparatus shown in Fig. 3. FIG. 4.5.6...Filtration media, 15...
・Support layer, 16...Filtration layer, 18, 28.44
...Wax, 34...--Heater, 35
・・・・・・Semiconductor wafer. Representative Patent Attorney Y Imamura

Claims (1)

[Claims] Wax is heated to a molten state, and a filtration layer made of porous ceramic, which is superimposed on the filtration layer to support the filtration layer, and has pores larger than the filtration layer. 1. A wax filtration method comprising filtering the molten wax using a filtration media comprising a support layer made of high quality ceramic.