# Patent

## Title
Method of cleaning semiconductor wafer

## Abstract

The present application discloses a method of cleaning a semiconductor wafer by mounting a wafer to a chuck, positioning a gas guard, defining therein a chamber having an open bottom, immediately above the layer of water, spraying de-ionized water onto the wafer while rotating the chuck at a location outside the chamber when the wafer is mounted to the chuck, to thereby form a layer of water on the wafer, and spraying a cleaning gas from a gas spraying unit disposed above said chuck through the chamber and into the layer of water to thereby cause the cleaning gas to dissolve in the layer of water, and at the same time moving the chamber across a surface of the wafer, to thereby clean the wafer, wherein said gas spraying unit includes a gas injection tube oriented to inject the cleaning gas towards the wafer mounted to the chuck, and the gas guard connected to the gas injection tube.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a divisional of application Ser. No. 10/017,415, filed Dec. 18, 2001, and now U.S Pat. No. 6,860,277, which is incorporated herein by reference in its entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor wafer cleaning apparatus. More particularly, the present invention relates to a single type of semiconductor wafer cleaning apparatus and to a method of cleaning a semiconductor wafer using the same.
2. Description of the Related Art
In general, semiconductor wafer cleaning apparatuses include batch and single types. In the batch type of semiconductor wafer cleaning apparatus, several semiconductor wafers are cleaned simultaneously. Although the production efficiency of the batch type of semiconductor cleaning apparatus is high, the cleaning efficacy is low. On the contrary, in the single type of semiconductor wafer cleaning apparatus, the production efficiency is low, and the cleaning efficacy is high. When manufacturing highly-integrated semiconductor devices it is important that the semiconductor wafer be very clean at several stages in the process. Thus, the single type of semiconductor wafer cleaning apparatus is preferred over the batch type.
Also, ozone (O3) has been used to increase the cleaning efficacy of conventional semiconductor wafer cleaning apparatuses. Semiconductor wafer cleaning apparatuses using ozone (O3) include a normal bath type of semiconductor wafer cleaning apparatus that uses a solution containing ozone (O3), a spray type of semiconductor wafer cleaning apparatus that uses ozone (O3) in a gaseous state, and a vapor type of semiconductor wafer cleaning apparatus that uses a mixture of vapor and ozone (O3).
In the bath type of semiconductor wafer cleaning apparatus, the cleaning solution is saturated when the concentration of the ozone (O3) is in the range of 10–20 ppm at room temperature. Thus, it is difficult to use ozone (O3) in high concentrations and at high temperatures in a bath type of semiconductor wafer cleaning apparatus. In the spray type semiconductor wafer cleaning apparatus, a semiconductor wafer is rotated while de-ionized water is sprayed to form a layer of water thereon. Subsequently, the ozone (O3) concentration in the layer of water is increased by spraying ozone (O3) into the chamber, whereby the semiconductor wafer is cleaned. However, in the spray type semiconductor wafer cleaning apparatus, the thickness of the water layer as a means of diffusing the ozone (O3) is proportional to the rate of rotation of the semiconductor wafer. Accordingly, the spray nozzle must be complex so that the ozone (O3) can be sprayed uniformly over the entire surface of the semiconductor wafer. In the vapor type of semiconductor wafer cleaning apparatus, ozone (O3) and vapor are mixed, and the mixture is sprayed onto a semiconductor wafer. In this way, the ozone (O3) is diffuses into vapor molecules attached to the semiconductor wafer, whereby the ozone (O3) concentration can be increased by tens of thousands of ppm. However, in the vapor type of semiconductor wafer cleaning apparatus, the ozone (O3) is used under high pressure in a sealed chamber, and vapor adheres to sides of the chamber.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the problems, disadvantages and limitations of the prior art. More specifically, it is a first object of the present invention to provide a single type of semiconductor wafer cleaning apparatus having a simple structure, capable of producing a cleaning solution having a high concentration of ozone (O3), and capable of producing other various cleaning solutions. It is likewise a second object of the present invention to provide a method of cleaning a semiconductor wafer with a high degree of efficacy.
To achieve the first object, the single type of semiconductor wafer cleaning apparatus includes a rotary chuck on which a wafer is mounted, a de-ionized water supply means for supplying de-ionized water onto the wafer to form a layer of water on the wafer, and a gas spray unit disposed above the chuck and including a gas injection tube for spraying gases including a cleaning gas onto the layer of water, and a gas guard extending from the gas injection tube and forming a small chamber in which the gas is sprayed onto the layer of water.
Preferably, the gas spray unit can be moved forward and backward and to the right and left relative to the wafer. The gas guard has a frusto-conical portion through which exhaust holes are formed. A megasonic transducer is attached to the gas spraying unit for transmitting supersonic waves into the layer of water via the gas guard.
The apparatus further includes gas supply means for supplying gases to the gas injection tube. The gases can include ozone (O3), hydrofluoric acid (HF), ammonia (NH3), carbon dioxide (CO2), sulfur oxide (SO2), hydrogen (H2), nitrogen (N2), argon (Ar), isopropyl alcohol (IPA), or a combination of these gases. The gas supply means preferably includes a mixer for mixing a plurality of the gases.
In order to achieve the second object, a method of cleaning a semiconductor wafer includes steps of mounting a wafer to a rotary chuck within a chamber, spraying de-ionized water onto the wafer while rotating the chuck to form a layer of water on the wafer, providing a gas guard defining a chamber having an open bottom just over the layer of water on the wafer (e.g., 2–4 mm from the water layer), and spraying a cleaning gas through the chamber and onto the layer of water whereupon the cleaning gas dissolves in the water and produces a cleaning solution having a high concentration of the cleaning gas.
The gas spray and gas guard can be moved across the surface of the wafer to “scan” the layer of water with the spray of cleaning gas. Preferably, the internal pressure of the chamber formed by the gas guard is maintained between 1–2 atm. Subsequently, a drying gas is injected into the layer of water on the cleaned wafer, whereby the wafer is dried (the water layer is evaporated). The gas for drying the water layer is preferably isopropyl alcohol (IPA).



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention will become more apparent by referring tot he following detailed description of the preferred embodiments thereof made with reference to the attached drawings, of which:
FIG. 1 is a schematic diagram of a single type of semiconductor wafer cleaning apparatus according to the present invention;
FIG. 2 is a schematic of a portion of the single type of semiconductor wafer cleaning apparatus of FIG. 1 showing a gas spraying unit thereof in more detail;
FIG. 3 is a plan view of that portion of the single type of semiconductor wafer cleaning apparatus shown in FIG. 2;
FIG. 4 is an enlarged schematic diagram of the gas spraying unit;
FIG. 5 is a perspective view of a gas guard of the gas spraying unit; and
FIG. 6 is a flow chart of a preferred embodiment of a method of cleaning a semiconductor wafer according to the present invention.



DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described more fully with reference to the accompanying drawings.
Referring now to FIGS. 1 and 2, a single type of semiconductor wafer cleaning apparatus according to the present invention includes a chamber 11 into which a wafer 23 is loaded, a rotatable chuck 11a disposed in the chamber 11 and to which the wafer 23 is mounted, and a de-ionized water supplying means for supplying de-ionized water onto the wafer from the side(s) of the chamber 11. The de-ionized water supplying means includes de-ionized water supply sources D1 and D2, valves V5 and V6, and at least one and preferably, two or more, de-ionized water supply lines 13a and 13b. 
The semiconductor wafer cleaning apparatus also includes a gas spraying unit 15 for spraying gas towards the wafer, and a gas supply means for supplying gases to the gas spraying unit 15. The gas supply means includes gas supply sources G, a gas line 17a, valves V1 through V4 and V7 through V9, mass flow controllers MFC1 through MFC5, gas measuring gauges M1 and M2, and a mixer 17b. For ease of explanation, only four gas supply sources G1 through G4 are illustrated although more may be provided. The mixer 17b mixes gases supplied from the gas supply sources G1 through G4 and supplies the mixed gases to the gas spraying unit 15. Gases not used among the gases supplied from the gas supply sources G1 through G4 are exhausted by a vacuum pump 21.
The gas supply sources G1 through G4 can be sources of ozone (O3), hydrofluoric acid (HF), ammonia (NH3), carbon dioxide (CO2), sulfur oxide (SO2), hydrogen (H2), nitrogen (N2), argon (Ar), or isopropyl alcohol (IPA). The gases supplied by the gas supply means include a cleaning gas (for example, ozone (O3), hydrofluoric acid (HF), ammonia (NH3), sulfur oxide (SO2), carbon dioxide (CO2), and hydrogen (H2)), a carrier gas (for example, nitrogen (N2) and argon (Ar)), and a dry gas (for example, IPA).
Although the chamber 11 and the gas spraying unit 15 are shown in FIG. 1 as separated from each other, the gas spraying unit 15 can be installed inside the chamber 11. In either case, the crux of the single type of semiconductor wafer cleaning apparatus has a simple structure comprised of the gas spraying unit 15, the gas supply means, and the de-ionized water supply means.
Referring now to FIGS. 2 and 3, de-ionized water is supplied from the de-ionized water supplying lines 13a and 13b onto the wafer 23, thereby forming a layer of water 25 on the wafer. The gas spraying unit 15 includes a gas injection tube 15a and a gas guard 15b. The gas injection tube 15a, in turn, comprises a plurality of nozzles N, e.g. a first nozzle N1 and a second nozzle N2. The gas guard 15b defines a small chamber 27 open just above the surface of the wafer 23 mounted to the rotatable chuck 11a. More specifically, the gas guard 15b is attached to the gas injection tube 15a and extends therefrom to a location close to the surface of the water layer 25. For example, the gas guard is positioned so that the distance between the water layer 25 and the bottom of the gas guard 15b is in the range of 2–4 mm. The gas injection tube 15a and the gas guard 15b are formed of Teflon®, stainless steel, gold (Au), or platinum (Pt).
A first gas G1 and a second gas G2 are injected into the gas injection tube 15a, but other gases may be injected into the gas injection tube 15a, as well. For example, the first gas G1 and the second gas G2 may be ozone (O3), hydrofluoric acid (HF), ammonia (NH3), carbon dioxide (CO2), sulfur oxide (SO2), hydrogen (H2), nitrogen (N2), argon (Ar), isopropyl alcohol (IPA) or a combination of the same. The first gas G1 and the second gas G2 are injected via the first nozzle N1 and the second nozzle N2, respectively. As best shown in FIGS. 4 and 5, the gas guard 15b has a frusto-conical portion having upper and lower openings, with the upper opening being smaller than the lower opening. The gas guard 15b further includes a guide member e extending radially outwardly from the bottom of the frusto-conical portion.
As described above, in the single type of semiconductor wafer cleaning apparatus, a small chamber 27 is formed by the gas guard 15b close to the water layer 25. The distance between the water layer 25 and the bottom of the gas guard 15b is in the range of 2–4 mm. In addition, the gas spraying unit 15 comprising the gas injection tube 15a and the gas guard 15b can be moved forward and backward and to the right and to the left, that is, in X and Y directions over the wafer 23, as shown in FIG. 3, while in contact with the layer of water 25 on the wafer 23. Any suitable X-Y driving mechanism 16, known per se, can be connected to the gas injection tube 15a for this purpose. Gases issuing from the gas injection tube 15a reduce the thickness of the water layer 25 under the gas injection tube 15a, whereupon the diffusion barrier layer 33 becomes thin. In the case in which the distance between the water layer 25 and the bottom of the gas guard 15b is in the range of 2–4 mm, the diffusion barrier layer 33 can be made as thin as several hundreds of micrometers.
Referring again to FIG. 4, the gas guard 15b has exhaust holes 31 extending therethrough. The holes 31 define paths through which the air in the small chamber 27 is released, and through which a small quantity of cleaning gas is continuously emitted. Also, the pressure in the small chamber 27 is maintained higher than atmospheric pressure, for example, is maintained between 1–2 atm, by the holes 31. With the interior of the chamber 27 at such a pressure, the atmosphere will not flow back into the gas injection tube 15a. The size and number of holes 31 can be selected based on the volume of the small chamber 27 and the amount of cleaning gas emitted by the gas injection tube 15a. 
The cleaning gas (or mixed gas) supplied from the first nozzle N1 and the second nozzle N2 of the gas injection tube 15a, for example, ozone (O3) gas, is sprayed onto the water layer 25 at the bottom of the small chamber 27 and dissolves in the water layer. In this case, the cleaning gas (or mixed gas) has a high partial pressure and the diffusion barrier layer 33 is also thin. Therefore, a large amount of the cleaning gas is dissolved in the water layer 25. The gas spraying unit 15 is scanned across the wafer 23 in the X and Y directions while such a cleaning solution having a high concentration of cleaning gas (for example, a cleaning solution having a high ozone concentration) is produced. Accordingly, impurities are readily removed from the wafer 23. The scanning speed and number of gas spraying units 15 are determined depending on the solubility and etching rate of the gas.
Furthermore, a megasonic transducer 29 is attached to the gas spraying unit 15, thereby finely vibrating the gas spraying unit 15. Accordingly, the supersonic waves are transmitted onto the water layer 25 via the gas guard 15b, thereby facilitating the cleaning of the wafer 23. in particular, the supersonic waves facilitate the removal of particles from the wafer 23.
FIG. 6 is a flow chart of a method of cleaning a semiconductor wafer using the single type of semiconductor wafer cleaning apparatus according to the present invention. In this method, a wafer 23 is loaded onto a rotary chuck 11a (step 100). Subsequently, de-ionized water DI is sprayed onto the wafer, thereby forming a water layer 25 (step 110). The temperature of the de-ionized water is 10–50° C. The chuck 11a is continuously rotated during this water layer-forming process at a rate set according to the amount of de-ionized water being sprayed.
Next, a small chamber 27 is formed over the water layer 25 (step 120). The pressure in the small chamber is maintained between 1–2 atm. The distance between the bottom of the gas guard 15b and the water layer 25 is set to be in the range of 2–4 mm. More specifically, the gas spraying unit 15 can be lowered towards the wafer, or the gas spraying unit 15 can be moved laterally over the wafer from a previous position at which the unit was at the desired level above the wafer.
Alternatively, the de-ionized water can be supplied onto the wafer after the gas spraying unit has been positioned over the wafer. In any case, once the water layer is formed, the small chamber 27 is formed over the water layer 25 by the gas guard 15b of the gas spraying unit 15.
Subsequently, the gas spraying unit 15 is moved to the right and to the left and forward and backward while a cleaning gas, for example, ozone (O3) gas, is sprayed by the gas spraying unit 15. As a result, the cleaning gas is dissolved in the water layer (step 130). The cleaning gas is formed of a gas selected from ozone (O3), hydrofluoric acid (HF), ammonia (NH3), carbon dioxide (CO2), sulfur oxide (SO2), hydrogen (H2), or a combination of these gases. As described above, the cleaning gas is under high pressure in the small chamber 27, whereby the cleaning gas dissolves into the water layer 25 at a high concentration. Thus, when the gas spraying unit 15 is scanned across the wafer surface, i.e., when the wafer surface on which the water layer 25 has been formed has been scanned with cleaning gas under high pressure, impurities on the wafer are removed effectively. The scanning speed and the number of nozzles N used are determined depending on the solubility and etching rate of the cleaning gas. Of course, during the cleaning process, as occasion demands, the megasonic transducer 29 attached to the gas spraying unit 15 can be activated whereupon supersonic waves are transmitted onto the water layer, thereby increasing the cleaning effect.
Next, the water layer on the cleaned wafer is dried (step 140). The water layer is dried by spraying isopropyl alcohol (IPA) onto the rotating wafer using the gas spraying unit 15. Therefore, that segment of the method from the cleaning step to the drying step can be performed in the same chamber 11.
The rate of rotation of the chuck is set at 5–100 rpm throughout the cleaning step 120, and at 5–1500 rpm during the subsequent IPA drying step 130.
As described above, the present invention can produce a cleaning solution having a high concentration of ozone (O3). Cleaning a wafer using a cleaning solution having a high concentration of a cleaning gas enhances the cleaning efficacy. Furthermore, the megasonic transducer attached to the gas spraying unit can be used to transmit supersonic waves into the water layer, thereby further improving the cleaning efficacy. Also, that period of the method from the cleaning step to the drying step can be performed in one chamber. The single type semiconductor wafer cleaning apparatus thus has a simple structure comprising a gas spraying unit made up of a gas injection tube and a gas guard, a gas supplier, and a de-ionized water supplier.
Finally, although the present invention has been shown and described with reference to the preferred embodiment thereof, various changes in form and details, as will become apparent to those of ordinary skill in the art, may be made thereto without departing from the true spirit and scope of the invention as defined by the appended claims.

## Claims

1. A method of cleaning a semiconductor wafer, comprising:
mounting a wafer to a chuck;
spraying de-ionized water onto the wafer while rotating the chuck, to thereby form a layer of substantially only water on a surface of the wafer;
positioning a gas guard, defining therein a chamber having an open bottom, immediately above the layer of water; and
spraying a cleaning gas through the chamber and into the layer of substantially only water to thereby cause the cleaning gas to dissolve in the layer of water, and at the same time moving the chamber across the surface of the wafer, to thereby clean the wafer.

2. The method of claim 1, wherein the cleaning gas is selected from the group of gases consisting of ozone (O3), hydrofluoric acid (HF), ammonia (NH3), carbon dioxide (CO2), sulfur oxide (SO2), hydrogen (H2), and a combination of the gases.

3. The method of claim 1, wherein said positioning of the gas guard comprises maintaining the bottom of the gas guard at a distance of 2–4 mm above the layer of water while the cleaning gas is sprayed.

4. The method of claim 1, wherein a pressure within the chamber is maintained between 1–2 atm.

5. The method of claim 1, wherein the chuck is rotated at 5–100 rpm from the time the layer of water is formed through the time the cleaning gas is sprayed.

6. The method of claim 1, and further comprising subsequently injecting a drying gas onto the layer of water on the cleaned wafer, to thereby dry the cleaned wafer.

7. The method of claim 6, wherein the drying gas is isopropyl alcohol.

8. The method of claim 7, wherein the chuck is rotated at 5–1500 rpm while the wafer is being dried by the isopropyl alcohol.

9. A method of cleaning a semiconductor wafer, comprising:
mounting a wafer to a chuck;
spraying de-ionized water onto the wafer while rotating the chuck, to thereby form a layer of water on a sufface of the wafer;
subsequently moving a gas guard, defining therein a chamber having an open bottom, to a position immediately above the layer of water; and
spraying a cleaning gas through the chamber and into the layer of water to thereby cause the cleaning gas to dissolve in the layer of water, and at the same time moving the chamber across the surface of the wafer, to thereby clean the wafer.

10. The method of claim 9, wherein the cleaning gas is selected from the group of gases consisting of ozone (O3), hydrofluoric acid (HF), ammonia (NH3), carbon dioxide (CO2), sulfur oxide (SO2), hydrogen (H2), and a combination of the gases.

11. The method of claim 9, and further comprising subsequently injecting a drying gas onto the layer of water on the cleaned wafer, to thereby dry the cleaned wafer.

12. The method of claim 11, wherein the drying gas is isopropyl alcohol.

13. A method of cleaning a semiconductor wafer, comprising:
mounting a wafer to a chuck;
positioning a gas guard, defining therein a chamber having an open bottom, immediately above a surface of the wafer;
subsequently spraying deionized water onto the surface of the wafer at a location outside of the chamber defined by the gas guard to thereby form a layer of water on the wafer; and
spraying a cleaning gas through the chamber and into the layer of water to thereby cause the cleaning gas to dissolve in the layer of water, and at the same time moving the chamber across the surface of the wafer, to thereby clean the wafer.

14. The method of claim 13, wherein the cleaning gas is selected from the group of gases consisting of ozone (O3), hydrofluoric acid (HF), ammonia (NH3), carbon dioxide (CO2), sulfur oxide (SO2), hydrogen (H2), and a combination of the gases.

15. The method of claim 13, and further comprising subsequently injecting a drying gas onto the layer of water on the cleaned wafer, to thereby dry the cleaned wafer.

16. The method of claim 15, wherein the drying gas is isopropyl alcohol.