Method of drying wafers

A new method and apparatus is provided for the cleaning and drying of a wafer. An IPA vapor is created using an ultrasonic nebulizer that can be operated at a relatively low temperature. The water and the IPA that is used by the cleaning and drying process will be heated and evaporated using energy supplied by a microwave source of energy.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method and apparatus for the drying of wafers.

(2) Description of the Prior Art

In the creation of semiconductor devices, these devices are typically created in or on the surface of a semiconductor wafer. After the process of creating the devices in or on the surface of the wafer and also during intervening processing steps, the need arises for drying the surface of the wafer. One of the conventional methods that is used for this purpose is the application of a cascade rinse whereby the wafer is placed into a water supply that is provided in an inner chamber while the rinsing water is transferred from an outer chamber to the inner chamber. This causes problems of water purity since there is an interconnect between the various chambers of the rinsing apparatus. Further, even after the process of cleaning the wafer has been completed, the wafer must as yet be dried, which may again be a source of introducing foreign matter (contaminants) onto the surface of the wafer.

Other methods employ the quick insertion of the wafer into a tank containing water in order to remove contaminants and other impurities in one, quick operation. Since particles that need to be removed from a surface must at times be agitated before the particle is loosened from the surface and can then be removed, this method of wafer cleaning has also proven to be not satisfactory.

Yet another method relies on spinning the wafer at high speed while water is applied to the surface of the wafer. Dislodged particles are in this manner removed from the surface of the wafer by centrifugal force, a step of drying the wafer can be applied as part of this sequence. This method requires rather complex supporting tools and equipment and, due to the violent nature of the process, the degree of particle removal is difficult to control.

Yet another method uses an isopropyl alcohol (IPA) vapor dryer or a full displacement IPA dryer. These methods typically require large amounts of IPA in order to achieve drying the wafer satisfactorily. In addition, to completely dry a wafer using this method requires a large drying time, adding to product costs. Also, the method of IPA vapor dry requires a high temperature of in excess of 200 degrees C. adding to the thermal budget of the process.

There is therefore a need in the industry to provide a method of cleaning and drying wafers that is cost-effective (low thermal requirements and limiting the need for a cleaning agent such as IPA) and that is simple to operate (low equipment cost). The invention provides such a method by reducing the temperature that is required to dry a wafer while heating and the drying of the wafer will be achieved using energy from a microwave source.

SUMMARY OF THE INVENTION

A principle objective of the invention is to provide a cost-effective method and apparatus for the cleaning and drying of a wafer.

Another objective of the invention is to limit the thermal budget that is required for the cleaning and drying of a wafer.

Yet another objective of the invention is to provide a method and apparatus for cleaning and drying a wafer that requires a limited amount of cleaning agent.

A still further objective of the invention is to provide a method and apparatus for cleaning and drying a wafer that can be completed in a relatively short period of time.

In accordance with the objectives of the invention a new method and apparatus is provided for the cleaning and drying of a wafer. An IPA vapor is created using an ultrasonic nebulizer that can be operated at a relatively low temperature. The water and the IPA that is used by the cleaning and drying process will be heated and evaporated using energy supplied by a microwave source of energy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 , there is shown a cross section of the microwave-drying chamber with the ultrasonic nebulizer of the invention. Highlighted in FIG. 1 are:

10 , the microwave drying chamber of the invention

14 , a wafer being processed

15 , a wafer positioning barrier or stop

16 , a first entry port of the microwave drying chamber 10 ; supplied through first entry port 16 is the cleaning agent which typically comprises IPA, the IPA may be mixed with DI water up to a percentage of the total cleaning agent

18 , a second entry port of the microwave drying chamber 10 ; supplied through second entry port 18 is an inert gas such as N 2

20 , the drain of the microwave drying chamber 10

22 , an exhaust vent of the microwave drying chamber 10

24 , the top cover of the microwave drying chamber 10 .

The processing sequence of the invention can be explained using the following FIGS. 2-5 .

It must be pointed out that the invention is not limited to using N 2 as an inert gas but can equally apply other inert gasses such as Ne, Kr, Xe, CO, CO 2 , He, Ar, N 2 and mixtures thereof.

FIG. 2 represents the first processing step of the invention. Shown is the cross section of the microwave drying chamber with the ultrasonic nebulizer while IPA, possibly mixed with DI water, is dispensed in the form of vapor spray 26 into the microwave drying chamber 10 by the ultrasonic nebulizers 12 . The processing sequence that is executed under this step is as follows:

1. the wafer 14 is loaded into the microwave drying chamber 10

2. the top cover 24 is placed on top of the microwave drying chamber

3. exhaust 22 and the second entry port 18 are closed

4. IPA is supplied, possibly mixed with DI water, to the ultrasonic nebulizers 12 ; the microwave energy that is present inside the microwave drying chamber 10 converts the supplied IPA, possibly mixed with DIW, into a spay 26 of IPA vapor, possibly mixed with DI water vapor; the combined activity of supplying IPA, possibly mixed with DI water and energizing the microwave-energy is to continue for at least 30 seconds

5. discontinue the supply of IPA, possibly mixed with DI water

6. open exhaust 22 and the second port of entry 18 , allowing inert gas to enter the microwave drying chamber 10 , thereby removing IPA vapors, possibly mixed with DIW vapors, from the microwave drying chamber 10 .

FIG. 3 represents the second processing step of the invention, shown is the cross section of the microwave-drying chamber with the ultrasonic nebulizer of the invention while microwave energy 28 is applied by the microwave energy supply unit 29 . The microwave energy 28 in this case has a major energy transfer with the surface of the wafer 14 , heating the wafer 14 and most importantly the surface of the wafer 14 , drying the surface of wafer 14 as a consequence.

FIGS. 4 and 5 show details of two types of ultrasonic nebulizers 12 that can be used by the invention. These nebulizers are well known in the art and are not part of the invention.

Specifically highlighted in the cross section of a first type of nebulizer as shown in FIG. 4 are:

30 , a reservoir or tank that contains the IPA, possibly mixed with DIW that is used for the cleaning/drying process of the invention

32 , the entry port to reservoir 30 ; IPA, possibly mixed with DIW is entered into reservoir 30 through this entry port

34 , a concentric plastic ring into which is used to house unit

36 , a nozzle through which IPA, possibly mixed with DIW, exits the reservoir 30 in direction 37

38 , a piezoelectric vibrator that has as function to increase evaporation (breaking up in smaller droplets) of the IPA, possibly mixed with DIW that exits reservoir 30

40 the vibration horn of the piezoelectric vibrator 38

41 , a supporting surface for the piezoelectric vibrator 38

42 , the surface area of the piezoelectric vibrator 39 where the mist of IPA, possibly mixed with DIW, is essentially formed

44 , the mist of IPA, possibly mixed with DIW that exists the ultrasonic nebulizer 12 .

Specifically highlighted in the cross section of a second type of nebulizer as shown in FIG. 5 are:

46 , a supply reservoir that can be supplied with IPA, possibly mixed with DIW via either

48 , a first entry port into vessel 46 , or

50 , a second alternate entry port into vessel 46

52 , the direction in which IPA, possibly mixed with DIW, is fed to the distribution nozzle

54 , the IPA, possibly mixed with DIW, before evaporation and distribution

56 , a housing for components of the nebulizer

58 , a screen or vibration plate through which the IPA, possibly mixed with DIW, passes

62 , small openings through the piezoelectric vibrator through which the IPA, possibly mixed with DIW, passes

64 , a mist of vaporized IPA, possibly mixed with DIW, after the IPA, possibly mixed with DIW, is ejected from the nebulizer.

A modification of the microwave-drying chamber with the ultrasonic nebulizer of the invention is shown in cross section in FIG. 6 . This cross section shows a modified mounting position of the nebulizers 12 whereby the nebulizers have been mounted external to the microwave drying chamber 10 of the invention. The mist of IPA, possibly mixed with DIW, in this case emanates essentially from the sidewalls of the microwave-drying chamber 10 .

It must further be pointed out that, although the drawings have shown the presence of one wafer inside the microwave drying chamber 10 , the invention is not limited to processing only one wafer at a time but can readily be altered, by altering the dimensions of the microwave drying chamber 10 , to accept more than one wafer for simultaneous processing of a multiplicity of wafers during one processing sequence. Dimensional modification of the microwave drying chamber 10 is, for this kind of application, essentially limited to extending the height of the microwave drying chamber so that a cassette of wafers can be entered at one time into the microwave drying chamber 10 for cleaning and drying.

The essential steps of the invention can be summarized as follows:

1. the IPA vapor, possibly mixed with DIW, is generated by an ultrasonic nebulizer inside a microwave drying chamber

2. the IPA vapor, possibly mixed with DIW, will be deposited on the surface of the wafer

3. the IPA vapor, possibly mixed with DIW, will be heated and evaporated from the surface of the wafer by applying microwave energy to the wafer and to the IPA vapor, possibly mixed with DIW, that has been deposited on the surface of the wafer.