WO2001062441A1

WO2001062441A1 - Mixing device and mixing method

Info

Publication number: WO2001062441A1
Application number: PCT/DE2001/000763
Authority: WO
Inventors: Franz Mayer
Original assignee: Infineon Technologies Ag
Priority date: 2000-02-25
Filing date: 2001-02-26
Publication date: 2001-08-30
Also published as: DE10010287B4; DE10010287A1

Abstract

The mixing devices currently on offer by manufacturers are sophisticated equipment and are therefore expensive. To achieve the thorough mixing of the various components introduced into the mixing container, an impeller is often used to set the liquid(s) in the container in motion, thus blending the components. However, all impeller devices have the inherent problem of requiring the sealing of the shaft feed opening in the mixing container. Said impeller shaft seal generates particles which lead to an unintentional reduction in the quality of the mixture. The aim of the invention is therefore to provide a mixing device for producing suspensions for the chemical-mechanical polishing of wafers. Said device comprises: a mixing container (1) filled with a liquid (2); a liquid jet pump (3) with two inlets (4, 5) and an outlet (6) that is connected to the mixing container (1); at least one system of supply lines (7) for supplying at least one substance (10) to be mixed, one end of said system being connected to one inlet (4, 5) of the liquid jet pump (3); and one system of circulating lines (8), one end of which is connected to the section of the mixing container that is filled with liquid and the other end is connected to the other inlet (5, 4) of the liquid jet pump (3).

Description

description

Mixing device and mixing method

The present invention is directed to a mixing device for the production of suspensions for chemical mechanical polishing of wafers and a method for the production of such suspensions. The invention further relates to a device for the chemical-mechanical polishing of wafers and a method for the chemical-mechanical polishing of wafers.

In the production of microchips, polishing steps are carried out between the individual production steps, in which unevenness on the surface of a wafer or on the surface of the applied layers is removed. For this purpose, the surface of the wafer is moved relative to the surface of a polishing device. A suspension is introduced between the surfaces, which contains particles which mechanically remove the unevenness on the wafer surface through the relative movement of the surfaces. The particles usually consist of silicon dioxide (Si0 ₂ ), aluminum oxide (Al ₃ 0 ₃ ) or cerium oxide (Ce ₂ 0 ₂ ), which have a diameter of the order of 20 nm to 1000 nm. The proportion of particles in the suspension is usually of the order of 1

% By weight to 15% by weight. The liquid phase usually consists of water to which alkaline compounds - such as KOH, NaOH or NH ₂ OH - or acids - such as acetic acid, citric acid or potassium acetate are added to adjust the pH. It may also contain other substances, such as. B. oxidizing agents. The chemicals contained in the liquid phase The surface of the wafer or the layers applied to it is chemically polished.

When manufacturing microchips, high demands are placed on the purity of the process materials used. When producing suspensions for the chemical mechanical polishing of wafers, no contaminants may therefore be entered. If these contaminants come into contact with the wafer during the polishing of the surface, the wafer is contaminated, which leads to an increase in the rejection rate. This means a large financial loss since the production of microchips is very expensive.

Mixing devices for the production of suspensions for the chemical mechanical polishing of wafers are known, for example, from US Pat. No. 5,957,759 and US Pat. No. 5,664,990. These are equipped with a stirrer or a circulating device, for example a pump, in order to produce dispersions, suspensions, mixtures or solutions. As a rule, a liquid is placed in the mixing container and a solid is added or a liquid is added.

The mixing devices currently offered by manufacturers are very demanding in terms of equipment and are therefore correspondingly expensive. To mix well the various components introduced into the mixing container, an agitator is usually used, which sets the liquid (s) in motion by means of shovels, blades, paddles or rods, thus achieving the mixing of the other components added. In one type of known mixing device, the entire mixing container is placed on a scale and the amount of components to be added is determined gravimetrically. However, both the addition of the substances and the actual stirring process lead to shocks which impair the accuracy of the weighing process. Determining the amount of the various components to be added directly in the mixing container is therefore problematic.

Mixing devices in which the components are metered volumetrically are less susceptible to faults than those mentioned above, but generally also require a stirring device in order to accomplish the mixing.

However, all of the stirring devices have the inherent problem that they require a seal on the shaft leadthrough into the mixing container. This agitator shaft seal generates particles that lead to contamination of the suspension for chemical mechanical polishing. In addition, there are often problems with the choice of material for the sealing material, since chemical resistance, abrasion resistance, temperature resistance, etc. cannot be satisfactorily fulfilled by all materials.

It is therefore the object of the present invention to provide a mixing device which enables the production of suspensions for the chemical-mechanical polishing of wafers in a simple manner, wear parts which lead to contamination of the suspension being avoided. This object is achieved according to the invention by a mixing device for producing suspensions for the chemical-mechanical polishing of wafers, comprising a mixing container which is at least partially filled with a liquid, a pump with a first inlet and an outlet which is connected to the mixing container is at least one supply line system for supplying at least one substance to be mixed in, one end of which is connected to the first inlet of the pump, and a circuit line system, one end of which is connected to the part of the mixing container filled with the liquid introduced and which has another end , characterized in that the pump is a liquid pump with a second input which is connected to the other end of the circuit line system.

The invention is based on the principle of using a liquid jet pump for introducing substances to be mixed and for mixing. Such a liquid jet pump (generally also referred to as a water jet pump, if water is used to generate suction) is based on the principle of letting a liquid pass through a nozzle pipe at a certain relatively high speed and providing a suction inlet on the side of the nozzle pipe, from which a substance to be mixed, in the sense of the invention a solid or a liquid, which is entrained by the negative pressure prevailing in the nozzle tube. Due to the swirling of the two liquids or the liquid and the solid in the nozzle pipe of the liquid jet pump, the substances are already mixed for the first time. A

Liquid jet pump has no moving parts and therefore does not require seals for shaft passages that are a source of contamination.

Such a liquid jet pump can be made from resistant materials, e.g. B. glass, ceramic or metal coated with plastic, so that no corrosion of the pump occurs even with prolonged use. As a result, a substantial reduction in the impurities in the suspension can be achieved, and thus also a reduction in the exclusion rate in the manufacture of microchips.

A substance to be mixed in is understood to mean a component of the suspension for chemical mechanical polishing which is to be mixed into the liquid presented. The substance to be mixed in can be solid, liquid or gaseous. Solids, such as the particles of Al ₂ 0 ₃ , Si0 ₂ or Ce ₂ 0 ₃ mentioned above, can be supplied as a gas-solid mixture or, preferably, as a suspension. The alkalis and acids mentioned above are generally supplied as a solution.

The liquid presented is understood to mean a liquid or an already existing suspension which is already in the mixing container and which is supplied to the liquid jet pump via the circuit line system. During the mixing process, there is a shift in the ratio of the liquid and the substance to be mixed in, which naturally increases in its proportion. For the purposes of the present invention, this is also located in the mixing container during the mixing process

Liquid is a liquid, even if it is already approaching the desired end product. One end of the circulatory system must be in constant contact with the liquid in order to be able to convey it and bring it to the liquid jet pump. It is expedient to use gravitation and arrange this end of the feed line system on a bottom of the mixing container. There are two basic options for arranging the supply line system and the circulation line system on the liquid jet pump. On the one hand, it is possible to design a mixing device such that the liquid jet pump has a nozzle inlet for supplying a suction liquid and a suction inlet for sucking in a fluid, the feed line system being connected to the nozzle inlet and the circuit line system being connected to the suction inlet.

In this case, the substance to be mixed in serves to generate the liquid jet, which then entrains the liquid presented. This arrangement of the present invention lends itself particularly well when a large amount of a substance to be mixed is to be introduced into a relatively small amount of the liquid present. The principle of the liquid jet pump means that the liquid entrained by the negative pressure has less volume than the liquid used for entraining and building up the negative pressure. If there were only a few substances to be mixed in, the liquid jet pump would cease its suction effect after a short time, and therefore generally before a good mixing of the liquid and substance to be mixed in was accomplished. The necessary flow of the substance to be mixed in through the liquid jet pump in this embodiment of the invention can take place, for example, through a gravitational gradient between a storage container of the substance to be mixed in and the mixing container. Alternatively, the substance to be mixed in can also be pressed through the liquid jet pump with the aid of a pump. It is also possible for the substance to be mixed in to be a suspension recovered after polishing, which suspension is replenished to its original composition in the mixing device.

As a rule, the inverse arrangement to the one described above will be used. This is characterized in that the liquid jet pump has a nozzle inlet for supplying a suction liquid and a suction inlet for sucking in a fluid, the feed line system being connected to the suction inlet and the circuit line system being connected to the nozzle inlet, and the circuit line system being a pump for generating a flow of the supplied rivers - has enough liquid to suck in the substance to be mixed in at the suction inlet.

With this arrangement, the liquid presented is used to suck in the substance to be mixed. As a result, a pump is required which feeds the liquid from the mixing tank to the liquid jet pump, which is generally located at a higher level.

The pump used for pumping around the liquid presented is preferably a diaphragm pump. Depending on the design of such a diaphragm pump, this also meets the high requirements of the semiconductor industry for the purity of the used Substances because it releases practically no substances into the pumped liquid.

After the substance or substances to be mixed in have been completely added, it may be necessary or desirable to continue mixing the liquid mixture, either to improve the degree of mixing or, for example, to keep the solids content in suspension. For this purpose, in a simple embodiment, it is possible to operate the liquid jet pump further, but empty, so that only air is sucked in or the vacuum is secured by a valve.

In an alternative preferred embodiment, the mixing device furthermore has a bypass line which is connected to the circuit line system and with which the liquid, or the finished suspension for the chemical-mechanical polishing of wafers, can be circulated or mixed for thorough mixing. The bypass line, which is preferably used, leads back into the mixing container and has the effect that the liquid which is drawn in by the pump, or the liquid mixture, is fed under a certain pressure to the mixing container, from which it is removed, at a different point. This leads to a permanent movement of the liquid and thus a permanent mixing.

To support the mixing process, the bypass line can also have a static mixer. Such a static mixer is typically a swirl device within the pipeline that functions as a bypass line. Liquid passing through the mixer speed is set in an additional movement by the swirl device, which improves the mixing.

To control the mixing and admixing process, the circuit line system can furthermore have valves which make it selectively or cumulatively connectable to the liquid jet pump and the bypass line. In this way it can be selected whether the liquid presented is to be passed through the liquid jet pump or through the bypass.

The substance or substances to be mixed in can be provided ready and fed directly to the mixing device via the feed line system. However, it is also possible that the mixing device additionally has a preparation device which is used for the production or other preparation of the substance or substances to be mixed. Therefore, the other end of the feed line system can be connected to at least one preparation device for preparing the substance to be mixed. Such a preparation device can be or have, for example, an agitator for producing solutions, suspensions and / or emulsions.

The preparation device can also have a swirler for producing solid-gaseous mixtures.

While liquid jet pumps have to be operated with a liquid in order to generate a sufficient negative pressure at the nozzle inlet, there is, however, with regard to the sucked-in fluid, that is to say the one to be mixed in the present case

Fabric, greater flexibility. So the one to be seeing substance be liquid, for example a solution, a solid suspension or a liquid emulsion. However, the substance to be mixed in can also be an aerosol, that is to say a mixture of liquid droplets in a gas. The use of an aerosol lends itself, for example, to non-water-soluble liquids which are only to be added to the liquid mixture in smaller amounts. It is possible here to convert the liquid into a droplet form in air by means of a suitable preparation device, which can then be sucked in by the liquid jet pump. It is even possible that the substance to be mixed in is a solid-gaseous mixture. For this purpose, a swirler can be used which is able, for example, to swirl a pulverulent substance in air or in another suitable gas in such a way that a kind of smoke or a dust cloud arises, which in turn can be sucked in by the liquid jet pump. Finally, the substance to be mixed in can be a gas and / or gas mixture.

The polishing device is not particularly limited per se. Conventional polishing devices for polishing wafers can be used. As examples, the polishing devices described in the aforementioned U.S. Patents 5,957,759 and 5,664,990 can be carried out. The feed line is preferably connected either to the circulatory system or to the mixing container of the mixing device. If necessary, a pump can also be provided in the feed line. The invention is further directed to a method for producing suspensions for the chemical-mechanical polishing of wafers with the following steps:

- Sucking in a liquid from a mixing container;

Supplying the presented liquid to a liquid jet pump;

Sucking in a substance to be mixed in through the flow of the liquid presented through the liquid jet pump; and

Feeding the mixture of the two liquids created in the liquid jet pump to the mixing container.

This method essentially reflects the use of the mixing device according to the invention described above. For this reason, all of the advantages and aspects of the mixing device mentioned apply equally to the method, so that reference is made in full to the mixing device described above.

As already explained, it may be necessary to circulate the liquid mixture or the liquid introduced before or after adding the substance to be mixed in, in order either to further improve the degree of mixing or to obtain a uniform mixing. Accordingly, the method according to the invention preferably has the further steps for circulating the liquid mixture before and / or after the entire substance to be mixed is sucked in: Sucking the liquid mixture and / or the liquid presented from the mixing container;

Feeding the liquid mixture and / or the liquid presented to a bypass line and - returning the liquid mixture and / or the liquid presented from the bypass line to the mixing container.

This mixing method therefore uses a bypass line already mentioned above. It is preferable to switch back and forth between the supply of the liquid or the liquid mixture to the liquid jet pump or the supply to the bypass line by means of valves.

It is also possible that before and / or after the entire substance to be mixed is sucked in, the method has the further steps for circulating the liquid mixture:

Sucking the liquid mixture and / or the liquid presented from the mixing container; - Feeding the liquid mixture and / or the submitted liquid to the liquid jet pump;

Passing the liquid mixture and / or the presented liquid through the liquid jet pump; and

Returning the liquid mixture and / or the liquid present to the mixing container.

In this preferred embodiment of the method, therefore, no bypass line is used, but simply the circuit which runs via the liquid jet pump is used to circulate the liquid mixture or the liquid introduced. The suction of the liquid presented is preferably done with a pump. This pump can for example, as already stated above, a diaphragm pump.

The substance to be mixed can in turn be liquid, an aerosol, a solid-gaseous mixture or a gas or. Gas mixture, as already explained above.

The circulation of the liquid supplied via a water jet pump causes the components to be mixed in to be introduced and at the same time mixed. The individual units required are customary and tried and tested and only have to be functionally correctly arranged. The manufacturing costs are comparatively cheap; as well as the construction costs, since no special know-how is required. Another advantage is the lower susceptibility to faults, lower operating costs and high availability. The use of suitable diaphragm pumps also has the advantage that no particles can be generated.

The wafers polished using the suspension produced according to the method described above show a lower susceptibility to faults or a lower failure rate is achieved. The invention therefore also relates to a method for chemical-mechanical polishing of wafers, a suspension for the chemical-mechanical polishing of wafers being produced by the method described above and the surface of a wafer or one applied to the wafer with the suspension Coating is polished.

Preferred exemplary embodiments of the present invention are to be illustrated schematically below, with on reference is made to the accompanying drawings, in which:

FIG. 1 shows a mixing device in a first embodiment of the present invention; and

FIG. 2 shows a further, more complex mixing device according to a preferred embodiment of the present invention.

The mixing device shown in FIG. 1 has a mixing container 1 in which a liquid 2 is placed. The water jet pump 3 shown here just above the liquid surface can also be arranged outside the actual mixing container 1. The liquid jet pump 3 has a nozzle inlet 4 and a suction inlet 5, as well as an outlet 6, through which both liquids that have entered the inlet, or liquid and solid or the like, together leave the liquid jet pump 3 again. In the embodiment shown, a liquid 10 to be mixed is used to operate the liquid jet pump 3, which liquid is fed from a storage container 9 to the nozzle inlet 4 via a feed line system 7, here a simple downpipe. A valve or the like (not shown) can also be provided to regulate the flow. The liquid to be mixed in flowing through the nozzle inlet 4 generates a negative pressure at the suction inlet 5, which leads to the liquid 2 being introduced being sucked out of the mixing container 1 via the circuit line system 8 and being mixed with the liquid 10 to be mixed in the liquid jet pump 3. This very simple embodiment of the present invention works without pumps and only as long as the liquid 10 to be mixed in sufficient pressure is present to generate a flow at the nozzle inlet 4, which is able to suck in liquid at the suction inlet 5. The mixing container 1 is connected to a feed line 16 in which a pump 18 is provided. With this, the finished suspension for the chemical mechanical polishing of wafers is fed to a polishing device 19 with which the wafers are polished.

Figure 2 shows a further preferred embodiment of a mixing device according to the present invention. Same

Features of the invention are provided with the same reference numerals. In this example of a mixing device according to the invention, the circuit line system 8 is connected to the nozzle inlet 4 of the liquid jet pump 3. This has the advantage that, using a pump 11 in the circuit line system 8, a practically unlimited circulation of the liquid 2 through the liquid jet pump is possible. The feed line system 7 is therefore connected to the suction inlet 5 of the liquid jet pump 3, so that the substance to be mixed is in turn entrained by the negative pressure in the liquid jet pump 3. In this embodiment, a bypass line 12 is also provided, which connects the circuit line 8 again directly to the mixing container 1, so that circulation past the liquid jet pump 3 is possible. Valves 13 and 14 can be used to switch between the two alternative routes. A simultaneous or simultaneous partial opening of the two valves is of course also possible according to the invention.

The drawing also shows a preferred embodiment, in which a discharge system 15 and an associated Ges valve 17, for example, the ready mixed suspension for the chemical-mechanical polishing of wafers can be removed from the mixing container 1 and fed to a feed line 16. The suspension in turn is fed to a polishing device 18, in which wafers are polished using the suspension. In principle, buffer tanks (not shown) can also be provided in the feed line 16, in which the suspension is temporarily stored.

Claims

claims

1. Mixing device for the production of suspensions for chemical-mechanical polishing of wafers, comprising - a mixing container (1) which is at least partially filled with a liquid; a pump (3) with a first inlet (5) and an outlet (6) which is connected to the mixing container (1); at least one feed line system (7) for feeding at least one substance (10) to be mixed, one end of which is connected to the first inlet (5) of the pump (3); and a circulation line system (8), one end of which is connected to the part of the mixing container (1) which is filled with the liquid introduced and which has another end; characterized in that the pump (3) is a liquid pump (3) with a second inlet (4) which is connected to the other end of the circuit line system (8).

2. Mixing device according to claim 1, characterized in that the second inlet (4) of the liquid jet pump (3) has a nozzle inlet (4) for supplying the liquid and the first inlet (5) of the liquid jet pump (3) has a suction inlet (5) Sucking in the substance to be mixed.

3. Mixing device according to claim 1, characterized in that the liquid jet pump (3) has a nozzle inlet (4) for supplying a suction liquid and a suction inlet (5) for sucking in a fluid, the feed line system (7) with the suction inlet (5) and the circulation line system (8) with the nozzle inlet (4) is connected and the circuit line system (8) has a pump (11) for generating a flow of the liquid which is sufficient to suck in the substance (10) to be mixed in at the suction inlet (5).

4. Mixing device according to claim 3, characterized in that the pump (11) is a diaphragm pump.

5. Mixing device according to claim 3 or 4, characterized in that it further comprises a bypass line (12) which is connected to the circuit line system (8) and with which the liquid (2) can be circulated for thorough mixing or is circulated.

6. Mixing device according to one of claims 3 to 5, characterized in that the bypass line (12) has a static mixer.

7. Mixing device according to one of claims 3 to 6, characterized in that the circuit line system (8) further comprises valves (13, 14) which make it alternatively connectable to the liquid jet pump (3) and the bypass line (12).

8. Mixing device according to one of claims 1 to 7, characterized in that the other end of the feed line system is connected to at least one preparation device (9) for preparing the substance (10) to be mixed.

9. Mixing device according to claim 8, characterized in that the preparation device (9) has an agitator for the production of solutions, suspensions and / or emulsions.

10. Mixing device according to claim 8 or 9, characterized in that the preparation device (9) has a swirler for producing solid-gaseous mixtures.

11. Device for the chemical-mechanical polishing of wafers, comprising a mixing device for producing suspensions for the chemical-mechanical polishing of wafers according to one of claims 1 to 10, a polishing device and a feed line provided between the mixing device and the polishing device ( 16), with which the suspension for chemical-mechanical polishing of wafers is fed from the mixing device to the polishing device.

12. The device for chemical mechanical polishing of wafers according to claim 11, wherein the feed line (16) is connected to the circuit line system (8).

13. The device for chemical mechanical polishing of wafers according to claim 11, wherein the feed line (16) is connected to the mixing container.

14. Device for the chemical mechanical polishing of wafers according to one of claims 11 to 13, wherein a pump is provided in the feed line (16).

15. A process for the production of suspensions for chemical mechanical polishing of wafers, comprising the following steps:

- Sucking in a liquid (2) from a mixing container (1);

- supplying the liquid (2) to a liquid jet pump (3);

- Sucking in a substance to be mixed (10) through the

Flow of the liquid (2) through the liquid jet pump (3); and

- Feed the mixture of the two liquids created in the liquid jet pump (3) to the mixing tank (1).

16. The method according to claim 15, characterized in that it has the further steps for circulating the liquid mixture before and / or after the entire substance (10) to be mixed in:

- Sucking the liquid mixture and / or the liquid (2) from the mixing container (1);

- Feeding the liquid mixture and / or the submitted liquid (2) to a bypass line (12); and - Returning the liquid mixture and / or the liquid (2) from the bypass line (12) to the mixing container (1) •

17. The method according to any one of claims 15 or 16, characterized in that it has the further steps for circulating the liquid mixture before and / or after the entire substance (10) to be mixed in:

- Feeding the liquid mixture and / or the submitted liquid (2) to the liquid jet pump (3);

- Passing the liquid mixture and / or the submitted liquid (2) through the liquid jet pump (3); and

- Returning the liquid mixture and / or the submitted liquid (2) to the mixing container (1).

18. A method for chemical-mechanical polishing of wafers, a suspension for the chemical-mechanical polishing of wafers being produced by the method according to one of claims 15 to 17 and with the suspension being applied to the surface of a wafer or to the surface of the wafer Coating is polished.