WO2000052453A2

WO2000052453A2 - Method for determining the characteristics of a medium

Info

Publication number: WO2000052453A2
Application number: PCT/EP2000/001659
Authority: WO
Inventors: Heinz Schade
Original assignee: Steag Microtech Gmbh
Priority date: 1999-02-28
Filing date: 2000-02-28
Publication date: 2000-09-08
Also published as: WO2000052453A3

Abstract

The aim of the invention is to provide a method for precisely determining the characteristics of a medium, e.g. a medium for treating semiconductor substrates, in a simple and cost-effective manner. To this end, a high-frequency alternating field is produced in the medium. The medium causes an energy loss in the alternating field. The energy loss is measured and the characteristics of the medium are determined according to said energy loss. Characteristics of the medium such as the composition, the concentration of certain ingredients, the degree of purity and similar characteristics can be precisely determined in a simple and cost-effective manner by producing a high-frequency alternating field and by measuring the energy loss. Special, frequency-dependent characteristics of the medium can be determined in the high-frequency alternating field because different components of the medium influence the alternating field at different frequencies and in a different manner.

Description

Method for determining properties of a medium

The present invention relates to an apparatus and a method for determining properties of a medium, e.g. B. liquids, gases and solids, in particular a medium for treating semiconductor substrates.

In the treatment of semiconductor substrates, such as, for example, a chemical coating, an etching treatment or cleaning, media are used whose properties, such as, for example, the concentration or the degree of purity, change over time. For optimal process control and constant treatment success, it is necessary to keep the properties within specified tolerance limits. In the past, different analytical methods were used for this, but some of them were very, time-consuming and associated with high costs and time expenditure.

In a method known from US Pat. No. 5,370,743, the concentration of a cleaner in a cleaning solution is determined as a function of the electrical conductivity of the cleaning solution. This method is limited to measuring the concentration of cleaning solutions. In addition to the concentration of the cleaner, the electrical conductivity also depends on other parameters, such as the temperature or impurities in the cleaning solution. Contamination in particular can influence and falsify the conductivity measurement, so that an exact determination of the concentration is not guaranteed.

Starting from the known method, the present invention is based on the object of a method for determining properties of a medium, in particular a medium for treating semiconductor substances. straten, to create, which enables the determination of properties of a medium with high accuracy in a simple and inexpensive manner.

According to the invention, the object is achieved in a method of the type mentioned at the outset by generating an electromagnetic high-frequency alternating field in the medium, measuring an energy loss caused by the medium in the alternating field and determining the properties of the medium as a function of the energy loss. By using a high-frequency alternating field and measuring the energy loss, properties of the medium, such as the composition, the concentration of certain ingredients, the degree of purity and similar properties, can be determined in a simple and inexpensive manner and with high accuracy. Special, frequency-dependent properties of the medium can be determined in the high-frequency alternating field, since e.g. different components of the medium influence the alternating field differently at different frequencies. This allows a more precise statement about the properties of the medium. Certain parameters, such as the degree of contamination, can be hidden during the determination or specially examined.

According to a particularly preferred embodiment of the invention, the electromagnetic field is generated with a coil. The electromagnetic alternating field is changed by the specific electrical and magnetic properties of the medium under investigation, which makes it possible to draw conclusions about its properties. For example, the energy absorption by the medium being examined is measured with a coil, and the properties of the medium are thereby inferred. In an alternative embodiment, the voltage induced in a further coil is measured, which changes as a function of the medium properties. At least one coil preferably surrounds the medium, so that the medium acts as a coil core. In a further embodiment, the medium is arranged between the coils.

In an alternative embodiment of the invention, the medium to be examined is located between the circuit boards of a capacitor. During the measurement, the energy loss of the alternating electric field applied to the capacitor is preferably determined.

For a good and uniform determination of the properties of the medium, the measuring device is preferably calibrated with a reference sample.

In a preferred embodiment of the invention, the properties of the medium are determined by comparing the energy losses with measurement results of a method carried out in parallel on a reference sample.

For the determination of special properties such. B. the concentration of a medium component, the applied frequency is kept at a fixed constant value. The frequency is chosen so that the interactions of the medium with the high-frequency alternating field at the selected frequency are primarily influenced by the one medium component. To determine several special properties, such as the concentration of several medium components or the degree of contamination, the frequency is switched between at least two specific frequencies. However, the frequency is preferably changed essentially continuously between two frequencies in order to make a frequency-dependent statement about different properties, such as, for example, the concentration of different medium components which influence the interactions of the medium with the high-frequency alternating field at different frequencies. The frequency, an applied voltage and / or the geometry of the measuring device is preferably selected as a function of the properties of the medium to be determined.

In order to compensate for temperature-dependent changes in the measurement results, the temperature of the medium is preferably determined. In order to ensure uniform measurement results, the temperature of the medium is brought to a predetermined temperature in one embodiment of the invention.

The present invention is particularly suitable for determining the properties of media for the treatment of semiconductor wafers, which requires high measurement accuracy. The process is generally applicable to all media used in the chemical industry, e.g. B. liquids, gases and solids, applicable. For example, the method is also suitable for determining the properties of hydraulic fluids in brake systems or the like.

The properties determined by the method according to the invention can, for example, be displayed or used as control parameters within a control loop. For example, the introduction of certain components into the medium can be regulated in order to achieve a predetermined concentration of the medium. Furthermore, the operating temperature, the degree of purity or other parameters could be regulated. In the case of gaseous mixtures in particular, regulation of the pressure is also possible.

Further advantages, features and details of the invention emerge from the following description with reference to the figures; in the figures shows:

1 shows a schematic representation of a device for determining properties of a medium according to the present invention; 2 shows a schematic illustration of an alternative embodiment of a device for determining properties of a medium according to the present invention;

3 shows a schematic illustration of different embodiments of a device for determining properties of a medium.

For the following description it is pointed out that the blocks shown individually in the figures are only shown for a better understanding of the invention. Usually, one or more of these blocks are combined into units. These can be implemented using integrated or hybrid technology or as a program-controlled microcomputer or as part of a program suitable for its control.

The same reference numerals are used in the figures for the same or similar elements. Once the elements have been described, they will be discussed in the further description only to the extent necessary for the understanding of the present invention.

FIG. 1 shows a device 1 for determining properties of a treatment liquid 2, which is contained in a treatment container 3. The treatment container 3 has an inlet opening 6 at a lower area, through which treatment liquid 2 is introduced. The opening 6 is connected via a line 8 to a schematically illustrated liquid supply device 10. The liquid supply device 10 has suitable means, such as a pump, not shown, for conveying the liquid 2 into the treatment container 3. The liquid 2 is, for example, a polishing acid which contains different components, such as sulfuric acid, phosphoric acid and water. Semiconductor wafers are immersed in the liquid for treatment. The different components are present in a predetermined mixture in the liquid feed device 10 and can be introduced into the container 3. Alternatively, the different components can be separately be available and mixed in the liquid supply device 10 or individually introduced into the container 3 and mixed there.

The treatment container 3 has two openings 12, 13 which are connected to one another via a connecting tube, which is referred to below as a sample tube 15. A pump 16 in the sample tube 15 circulates the treatment liquid 2 through the sample tube 15 to ensure that the treatment medium 2 in the container and in the sample tube are the same.

A first coil 18 is provided around the sample tube 15, which is referred to below as the primary coil. A second coil 19 is provided at a defined distance from the primary coil 18, which is referred to below as the secondary coil. The sample tube 15 with the liquid 2 contained therein form the core of the two coils 18, 19. The primary coil 18 is connected to a high-frequency oscillator 21, which applies a high-frequency AC voltage to the coil 18. This generates a high-frequency alternating magnetic field in the area of the primary coil 18 and in particular in the liquid 2.

The secondary coil 19 is connected to an evaluation circuit 23, which measures and evaluates a voltage induced in the secondary coil by the high-frequency alternating magnetic field. The evaluation circuit 23 knows the frequency and voltage applied to the primary coil 18. Interactions between the liquid 2 and the high-frequency alternating magnetic field, in particular the energy losses, can be determined on the basis of the voltage induced in the secondary coil 19. Depending on these energy losses, the evaluation circuit 23 determines the properties of the medium, such as the concentration of a medium component.

The oscillator 21 and the evaluation circuit 23 are part of a control unit 25. The control unit 25 sends, for example, depending on the specific properties, a display signal to a display device 27. The display device 27 is a warning display to an operator The device indicates that the treatment liquid 2 is contaminated or no longer has the required concentration of certain liquid components.

The control device 25 can also send a control signal to the liquid supply device 10 in order to introduce fresh treatment liquid 2, by means of which the old treatment liquid 2 is displaced from the treatment basin 3. In order to allow the old treatment liquid 2 to drain off, the treatment container 3 has an overflow line 30 which is connected to a suitable overflow container 32. As a result, the treatment liquid 2 can be exchanged completely. Alternatively, it is also possible for the control signal from the control device 25 to the liquid supply device 10 to introduce a certain amount of a single one of the liquid components in order to obtain a predetermined concentration of the treatment liquid 2 in the basin 3. The control device 25 also controls a heating device 34 located in the basin 3 and the pump 16. The pump regulates the flow of the treatment medium 2 within the sample tube 15. For example, after introducing a fresh treatment liquid or after introducing a single liquid component, it may be necessary to circulate the liquid 2 in the basin 3 in order to ensure a uniform mixture within the basin to reach. Furthermore, the pump is used to constantly replace the liquid 2 inside the sample tube 15, so that it is ensured that the liquid in the sample tube corresponds to the liquid in the basin 3.

Instead of providing the measuring unit consisting of the primary and secondary coils on a sample tube, it is also possible to arrange them on a riser tube on the outside of the basin 3 or directly inside the basin 3. Depending on the treatment liquid 2, it should be noted that the coils are insulated from the liquid, especially in the case of highly corrosive liquids. A measuring method according to the present invention is briefly described below with reference to FIG.

The treatment basin 3 is filled with treatment liquid 2. The pump 16 circulates the treatment liquid 2 in the sample tube 15. The oscillator 21 applies a high-frequency alternating voltage to the coil 18, so that the coil 18 generates a magnetic high-frequency alternating field in the treatment liquid 2. Depending on the property of the treatment liquid 2 to be determined, a predetermined frequency is selected for the high-frequency alternating field, since different components of the liquid generate different interactions at different frequencies. Instead of a fixed frequency, however, two or more different frequencies or a continuously changing frequency can also be used in order to determine the interactions between the liquid 2 and the field at different frequencies. This enables a comprehensive determination of the properties of the liquid.

A voltage induced in the secondary coil 19 is measured by the evaluation circuit 23. The induced voltage depends on the properties of the liquid 2. If the liquid 2 has a good magnetic coupling, the induced voltage is higher than if it has a bad magnetic coupling. In particular in combination with the choice of frequency, good statements can be made about the properties of the liquid, since certain components in the liquid influence the magnetic coupling at certain frequencies more than other components. The measured voltage at the secondary coil therefore allows conclusions to be drawn about the properties of the liquid. The properties are displayed on the display device 27 and used to control the liquid supply device 10 or the heating device 34.

For the property determination, the evaluation circuit 23 compares the measured variables with previously determined reference variables, which, for. B.- Connect measured voltages at given frequencies with properties of the medium.

FIG. 2 shows an alternative embodiment of the present invention, which has all elements of the exemplary embodiment according to FIG. 1. To avoid repetition, reference is made to the description of FIG. 1. In addition, however, the device according to FIG. 2 has a reference sample tube 40 which is filled with a reference liquid 41. The reference sample tube 40 is surrounded by a reference primary coil 42, which has the same structure as the primary coil 18. The reference sample tube 40 is also surrounded by a reference secondary coil 43, which has the same structure as the secondary coil 19. The coils 42 and 43 are arranged at the same distance as the coils 18 and 19. The reference sample tube 40 has the same cross section as the sample tube 15.

The reference primary coil 42 is connected to the oscillator 21, and the reference secondary coil 43 is connected to the evaluation circuit 23.

2, a high-frequency AC voltage is applied to the reference primary coil 42 and the primary coil 18 via the oscillator 21. The reference primary coil 42 generates a magnetic high-frequency alternating field in the reference liquid 41, and the primary coil 18 also generates a magnetic high-frequency alternating field in the treatment liquid 2. In the reference secondary coil 43 and the secondary coil 19, voltages are induced which by depend on the properties of the reference liquid 41 or the treatment liquid 2. The induced voltages are measured by the evaluation circuit 23 and compared with one another in order to be able to make a statement about the properties of the treatment liquid 2. In this case, it is not necessary to use a look-up table since the evaluation circuit 23 has reference measurement results available. If the measurements deviate too much from each other, a warning signal can be issued are, or the liquid supply device can be controlled in the manner described above.

FIG. 3 also shows a device 1 for determining properties of a liquid 2 located in a treatment basin 3. The structure of the basin 3, the liquid supply device 10, the sample tube 15 and the overflow 30 essentially corresponds to the structure according to FIG However, a sample valve 15 is additionally provided in order to selectively interrupt a flow within the sample tube 15.

In the area of the sample tube 15, three different arrangements for measuring interactions of the treatment liquid 2 with a high-frequency alternating field are provided.

A first of these devices 51, which is shown with solid lines, has a coil 53 which is connected to an oscillator 54. The oscillator is part of a control unit 55, which is connected in a suitable manner to the liquid supply device 10, the heating unit 34 or a display unit, not shown. A high-frequency AC voltage is applied to the coil 53 via the oscillator 54, so that the coil 53 generates a magnetic high-frequency AC field in the region of the coil. A suitable sensor measures the energy consumption of the coil 53, which depends on the interactions of the medium with the field. The measured energy consumption is fed to an evaluation circuit which determines the properties of the liquid 2 on the basis of the energy consumption.

A second device 61 for measuring the properties of the liquid 2, which is represented by a dotted line, has a condenser 63 which is formed by two condenser plates arranged on opposite sides of the sample tube 15. The capacitor is controlled via an oscillator 64 in order to generate an electrical high-frequency alternating field in the medium located between the capacitor plates. A sensor, not shown, measures the energy consumption of the capacitor, ,,.

which allows a conclusion on the interactions of the liquid 2 with the field and thus on the properties of the liquid. A suitable evaluation circuit of the device 61 determines on the basis of the energy consumption and the property of the medium to be determined. The interactions between the liquid and the field in turn depend on the frequency used, which can be selected specifically for the property to be determined.

A third device 71 for determining the properties of the treatment medium 2 has a primary coil 73, which can be controlled via an oscillator 74. The primary coil 73 is arranged on one side of the sample tube 15 such that the coil extends substantially perpendicular to the sample tube 15. On the opposite side of the sample tube 15, a secondary coil 75 is provided, which also extends essentially perpendicular to the sample tube 15. The secondary coil 75 is connected to a suitable evaluation circuit which senses a voltage induced in the secondary coil 75. This device is essentially the same as the structure of the device according to FIG. 1, but the coils 73 and 75 do not surround the sample tube 15, but are arranged on opposite sides of the sample tube 15.

The measuring methods described above are at least partially temperature-dependent. In order to provide temperature compensation, the temperature of the treatment liquid 2 is measured via a suitable temperature sensor and included in the determination of the properties. Of course, the measuring method can also be used for a quick temperature determination.

An alternative embodiment of the invention provides that the treatment liquid 2 does not circulate continuously in the sample tube 15, but is kept stationary in the sample tube 15 during a measuring process. For this purpose, the valve 50 is closed before a measuring process and the pump 16 is switched off. The temperature of the liquid in the sample tube 15 becomes measured via a suitable temperature sensor, and when a predetermined temperature is reached, the measurement method described above is carried out. It is therefore possible that the liquid is always measured at the same temperature. In order to achieve the predetermined temperature, cooling and / or heating elements can be provided in the sample tube 15 or around the tube.

After the measurement, the valve 50 is opened, the liquid is circulated through the pump 16 in the sample tube 15 and the above process is repeated.

The invention has been described above on the basis of preferred exemplary embodiments, but without being restricted to the specifically illustrated exemplary embodiments.

For example, the device according to the invention or the method according to the invention is not limited to treatment liquids for the treatment of semiconductor wafers. Rather, all types of media, such as hydraulic fluids in brake systems, can be examined. The geometry of the respective measuring units, which includes, for example, the coil diameter, the number of windings per coil, the distance between the coils or the distance between the capacitor plates, can be matched to the medium to be examined. Furthermore, the applied voltage and frequency can also be matched to the medium or the property to be examined. The coil or the capacitor can be immersed in the medium to be examined.

Claims

claims

1. Method for determining properties of a medium, e.g. B. a medium for the treatment of semiconductor substrates, characterized by the following process steps:

Generating a high-frequency alternating field in the medium;

- Measuring an energy loss caused by the medium in the alternating field; and

- Determination of the properties of the medium depending on the loss of energy.

2. The method according to claim 1, characterized in that the high-frequency alternating field is generated with a coil.

3. The method according to claim 2, characterized in that the energy consumption of the coil is measured.

4. The method according to claim 2, characterized in that the voltage induced in a further coil is measured.

5. The method according to any one of claims 2 to 4, characterized in that at least one coil surrounds the medium.

6. The method according to claim 4, characterized in that the medium is arranged between the coils or around the coils.

7. The method according to claim 1, characterized in that the high-frequency alternating field is generated in a capacitor, wherein the medium to be examined is located between these circuit boards.

8. The method according to claim 7, characterized in that the energy consumption of the capacitor is measured.

9. The method according to any one of the preceding claims, characterized in that the measuring device is calibrated using a reference sample.

10. The method according to any one of the preceding claims, characterized in that the energy losses are compared with measurement results of a method carried out in parallel on a reference sample.

11. The method according to any one of the preceding claims, characterized in that the applied frequency at a certain constant

Value is held.

12. The method according to any one of claims 1 to 10, characterized in that the frequency is switched between at least two specific frequencies.

13. The method according to any one of claims 1 to 10, characterized in that the frequency is changed substantially continuously between two frequencies.

14. The method according to any one of the preceding claims, characterized in that the frequency (s) is in a range from 1 to 100 MHz, in particular from 1 to 20 MHz.

15. The method according to any one of the preceding claims, characterized in that the frequency, an applied voltage and / or the geometry of the measuring device is selected depending on the properties of the medium to be determined.

16. The method according to any one of the preceding claims, characterized in that the temperature of the medium is determined.

17. The method according to any one of the preceding claims, characterized in that the temperature of the medium is brought to a predetermined temperature.

18. The method according to any one of the preceding claims, characterized in that the temperature of the medium is measured.