Methods and system for cleaning semiconductor wafers

Abstract

A method for cleaning semiconductor substrate without damaging patterned structure on the substrate using ultra/mega sonic device comprising applying liquid into a space between a substrate and an ultra/mega sonic device; setting an ultra/mega sonic power supply at frequency f.sub.1 and power P.sub.1 to drive said ultra/mega sonic device; before bubble cavitation in said liquid damaging patterned structure on the substrate, setting said ultra/mega sonic power supply at frequency f.sub.2 and power P.sub.2 to drive said ultra/mega sonic device; after temperature inside bubble cooling down to a set temperature, setting said ultra/mega sonic power supply at frequency f.sub.1 and power P.sub.1 again; repeating above steps till the substrate being cleaned. Normally, if f.sub.1=f.sub.2, then P.sub.2 is equal to zero or much less than P.sub.1; if P.sub.1=P.sub.2, then f.sub.2 is higher than f.sub.1; if the f.sub.1<f.sub.2, then, P.sub.2 can be either equal or less than P.sub.1.

Claims

1. An apparatus for cleaning a semiconductor wafer comprising features of patterned structures, the apparatus comprising: a wafer holder configured to hold the semiconductor wafer; an inlet configured to apply liquid on the semiconductor wafer; a transducer configured to deliver acoustic energy to the liquid; a power supply of the transducer; and a controller for the power supply comprising a timer, the controller being configured to control the transducer based on the timer to: deliver acoustic energy to the liquid at a first frequency and a first power level for a predetermined first time period, and deliver acoustic energy to the liquid at a second frequency and a second power level for a predetermined second time period, wherein the controller is configured to alternately apply the first and second time periods one after another for a predetermined number of cycles, wherein the first and second time periods, the first and second power levels, and the first and second frequencies are determined such that no feature is damaged as a result of delivering the acoustic energy.

2. The apparatus of claim 1, wherein the wafer holder comprises a rotating chuck.

3. The apparatus of claim 1, wherein the wafer holder comprises a cassette submerged in a cleaning tank.

4. The apparatus of claim 1, wherein the inlet comprises a nozzle.

5. The apparatus of claim 1, wherein the transducer is connected to the inlet and imparts acoustic energy to the liquid flowing through the inlet.

6. The apparatus of claim 1, wherein bubble implosion does not occur in the first time period.

7. The apparatus of claim 1, wherein the second power level is lower than the first power level.

8. The apparatus of claim 7, wherein the second power level is zero.

9. The apparatus of claim 1, wherein the second frequency is higher than the first frequency.

10. The apparatus of claim 1, wherein acoustic energy in the second time period is in antiphase to acoustic energy in the first time period.

11. The apparatus of claim 1, wherein the first frequency is equal to the second frequency, while the first power level is higher than the second power level.

12. The apparatus of claim 1, wherein the first frequency is higher than the second frequency, while the first power level is higher than the second power level.

13. The apparatus of claim 1, wherein the first frequency is lower than the second frequency, while the first power level is equal to the second power level.

14. The apparatus of claim 1, wherein the first frequency is lower than the second frequency, while the first power level is higher than the second power level.

15. The apparatus of claim 1, wherein the first frequency is lower than the second frequency, while the first power lever is lower than the second power level.

16. The apparatus of claim 1, wherein the first power level rises during the first time period.

17. The apparatus of claim 1, wherein the first power level falls during the first time period.

18. The apparatus of claim 1, wherein the first power level both rises and falls during the first time period.

19. The apparatus of claim 1, wherein the first frequency changes from a higher value to a lower value during the first time period.

20. The apparatus of claim 1, wherein the first frequency changes from a lower value to a higher value during the first time period.

21. The apparatus of claim 1, wherein the first frequency changes from a lower value to a higher value and then back to the lower value during the first time period.

22. The apparatus of claim 1, wherein the first frequency changes from a higher value to a lower value and then back to the higher value during the first time period.

23. The apparatus of claim 1, wherein the first frequency is set as f.sub.1 first, f.sub.3 later and f.sub.4 at last during the first time period, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

24. The apparatus of claim 1, wherein the first frequency is set as f.sub.4 first, f.sub.3 later and f.sub.1 at last during the first time period, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

25. The apparatus of claim 1, wherein the first frequency is set as f.sub.1 first, f.sub.4 later and f.sub.3 at last during the first time period, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

26. The apparatus of claim 1, wherein the first frequency is set as f.sub.3 first, f.sub.4 later and f.sub.1 at last during the first time period, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

27. The apparatus of claim 1, wherein the first frequency is set as f.sub.3 first, f.sub.1 later and f.sub.4 at last during the first time period, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

28. The apparatus of claim 1, wherein the first frequency is set as f.sub.4 first, f.sub.1 later and f.sub.3 at last during the first time period, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

29. The apparatus of claim 1, wherein the second frequency is zero and the second power level remains a constant positive value during the second time period.

30. The apparatus of claim 1, wherein the second frequency is zero and the second power level remains a constant negative value during the second time period.

31. The apparatus of claim 1, wherein the features comprise vias or trenches having depth to width ratios of at least 3.

32. The apparatus of claim 1, wherein a device manufacturing node of the semiconductor wafer is no more than 16 nanometers.

33. The apparatus of claim 1, wherein the wafer holder is further configured to rotate the wafer with respect to the transducer as acoustic energy is delivered.

34. The apparatus of claim 1, wherein the features are not damaged by expansion of bubbles in the first time period.

35. The apparatus of claim 1, wherein temperatures inside bubbles decrease in the second time period.

36. The apparatus of claim 35, wherein temperatures inside the bubbles decrease to near a temperature of said liquid in the second time period.

37. The apparatus of claim 1, wherein the first time period is shorter than 2,000 times of a cycle period of the first frequency.

38. The apparatus of claim 1, wherein the first time period is shorter than ((T.sub.i−T.sub.0−ΔT)/(ΔT−δT)+1)/f.sub.1, where T.sub.i is an implosion temperature, T.sub.0 is a temperature of the liquid, ΔT is a temperature increase after one time of compression, δT is a temperature decrease after one time of expansion, and f1 is the first frequency.

39. A controller for a power supply of a transducer comprising a timer, the controller being configured to control the transducer based on the timer to: deliver acoustic energy to liquid applied on a semiconductor wafer at a first frequency and a first power level for a predetermined first time period; and deliver acoustic energy to the liquid at a second frequency and a second power level for a predetermined second time period, wherein the controller is configured to alternately apply the first and second time periods one after another for a predetermined number of cycles, wherein the first and second time periods, the first and second power levels, and the first and second frequencies are determined such that no feature is damaged as a result of delivering the acoustic energy.

40. The controller of claim 39, wherein bubble implosion does not occur in the first time period.

41. The controller of claim 39, wherein the second power level is lower than the first power level.

42. The controller of claim 41, wherein the second power level is zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A-1B depict an exemplary wafer cleaning apparatus using ultra/mega sonic device;

(2) FIGS. 2A-2G depict variety of shape of ultra/mega sonic transducers;

(3) FIG. 3 depicts bubble cavitation during wafer cleaning process;

(4) FIGS. 4A-4B depict a transit cavitation damaging patterned structure on a wafer during cleaning process;

(5) FIGS. 5A-5C depict thermal energy variation inside bubble during cleaning process;

(6) FIGS. 6A-6C depict an exemplary wafer cleaning method;

(7) FIGS. 7A-7C depict another exemplary wafer cleaning method;

(8) FIGS. 8A-8D depict another exemplary wafer cleaning method;

(9) FIGS. 9A-9D depict another exemplary wafer cleaning method;

(10) FIGS. 10A-10B depict another exemplary wafer cleaning method;

(11) FIGS. 11A-11B depict another exemplary wafer cleaning method;

(12) FIGS. 12A-12B depict another exemplary wafer cleaning method;

(13) FIGS. 13A-13B depict another exemplary wafer cleaning method;

(14) FIGS. 14A-14B depict another exemplary wafer cleaning method;

(15) FIGS. 15A-15C depict a stable cavitation damaging patterned structure on a wafer during cleaning process;

(16) FIG. 16 depicts another exemplary wafer cleaning apparatus using ultra/mega sonic device; and

(17) FIG. 17 depicts an exemplary wafer cleaning apparatus using ultra/mega sonic device;

(18) FIGS. 18A-18C depict another exemplary wafer cleaning method;

(19) FIG. 19 depicts another exemplary wafer cleaning method;

DETAILED DESCRIPTION

(20) FIGS. 1A to 1B show a wafer cleaning apparatus using a ultra/mega sonic device. The wafer cleaning apparatus consists of wafer 1010, wafer chuck 1014 being rotated by rotation driving mechanism 1016, nozzle 1012 delivering cleaning chemicals or de-ionized water 1032, and ultra/mega sonic device 1003 and ultra/mega sonic power supply. The ultra/mega sonic device 1003 further consists of piezoelectric transducer 1004 acoustically coupled to resonator 1008. Transducer 1004 is electrically excited such that it vibrates and the resonator 1008 transmits high frequency sound energy into liquid. The bubble cavitation generated by the ultra/mega sonic energy oscillates particles on wafer 1010. Contaminants are thus vibrated away from the surfaces of the wafer 1010, and removed from the surfaces through the flowing liquid 1032 supplied by nozzle 1012.

(21) FIGS. 2A to 2G show top view of ultra/mega sonic devices according to the present invention. Ultra/mega sonic device 1003 shown in FIG. 1 can be replaced by different shape of ultra/mega sonic devices 3003, i.e. triangle or pie shape as shown in FIG. 2A, rectangle as shown in FIG. 2B, octagon as shown in FIG. 2C, elliptical as shown in FIG. 2D, half circle as shown in FIG. 2E, quarter circle as shown in FIG. 2F, and circle as shown in FIG. 2G.

(22) FIG. 3 shows a bubble cavitation during compression phase. The shape of bubbler is gradually compressed from a spherical shape A to an apple shape G, finally the bubble reaches to an implosion status I and forms a micro jet. As shown in FIGS. 4A and 4B, the micro jet is very violent (can reaches a few thousands atmospheric pressures and a few thousands ° C.), which can damage the fine patterned structure 4034 on the semiconductor wafer 4010, especially when the feature size t shrinks to 70 nm and smaller.

(23) FIGS. 5A to 5C show simplified model of bubble cavitation according to the present invention. As sonic positive pressure acting on the bubble, the bubble reduces its volume. During this volume shrinking process, the sonic pressure P.sub.M did a work to the bubble, and the mechanical work converts to thermal energy inside the bubble, therefore temperature of gas and/or vapor inside bubble increases.

(24) The idea gas equation can be expressed as follows:
p.sub.0v.sub.0/T.sub.0=pv/T  (1),

(25) where, p.sub.0 is pressure inside bubbler before compression, v.sub.0 initial volume of bubble before compression, T.sub.0 temperature of gas inside bubbler before compression, p is pressure inside bubbler in compression, v volume of bubble in compression, T temperature of gas inside bubbler in compression.

(26) In order to simplify the calculation, assuming the temperature of gas is no change during the compression or compression is very slow and temperature increase is cancelled by liquid surrounding the bubble. So that the mechanical work w.sub.m did by sonic pressure P.sub.M during one time of bubbler compression (from volume N unit to volume 1 unit or compression ratio=N) can be expressed as follows:

(27) $\begin{array}{cc}\begin{array}{c}{w}_m={\int }_0^{x_0-1}\mathrm{pSdx}={\int }_0^{x_0-1}\left(S\left(x_0{p}_0\right)\text{/}\left(x_0-x\right)\right)\mathrm{dx}={\mathrm{Sx}}_0{p}_0{\int }_0^{x_0-1}\mathrm{dx}\text{/}\left(x_0-x\right)\\ =-{\mathrm{Sx}}_0{p}_0\ln \left(x_0-x\right){.Math.}_0^{x_0-1}={\mathrm{Sx}}_0{p}_0\ln \left(x_0\right)\end{array}& \left(2\right)\end{array}$
Where, S is area of cross section of cylinder, x.sub.0 the length of the cylinder, p.sub.0 pressure of gas inside cylinder before compression. The equation (2) does not consider the factor of temperature increase during the compression, so that the actual pressure inside bubble will be higher due to temperature increase. Therefore the actual mechanical work conducted by sonic pressure will be larger than that calculated by equation (2).

(28) If assuming all mechanical work did by sonic pressure is partially converted to thermal energy and partially converted mechanical energy of high pressure gas and vapor inside bubble, and such thermal energy is fully contributed to temperature increase of gas inside of bubbler (no energy transferred to liquid molecules surrounding the bubble), and assuming the mass of gas inside bubble staying constant before and after compression, then temperature increase ΔT after one time of compression of bubble can be expressed in the following formula:
ΔT=Q/(mc)=βw.sub.m/(mc)=βSx.sub.0p.sub.0 ln(x.sub.0)/(mc)  (3)
where, Q is thermal energy converted from mechanical work, βratio of thermal energy to total mechanical works did by sonic pressure, m mass of gas inside the bubble, c gas specific heat coefficient. Substituting β=0.65, S=1E−12 m.sup.2, x.sub.0=1000 μm=1E−3 m (compression ratio N=1000), p.sub.0=1 kg/cm.sup.2=1E4 kg/m.sup.2, m=8.9E−17 kg for hydrogen gas, c=9.9E3 J/(kg ° k) into equation (3), then ΔT=50.9° k.
The temperature T.sub.1 of gas inside bubbler after first time compression can be calculated as
T.sub.1=T.sub.0+ΔT=20° C.+50.9° C.=70.9° C.  (4)

(29) When the bubble reaches the minimum size of 1 micron as shown in FIG. 5B. At such a high temperature, of cause some liquid molecules surrounding bubble will evaporate. After then, the sonic pressure become negative and bubble starts to increase its size. In this reverse process, the hot gas and vapor with pressure P.sub.G will do work to the surrounding liquid surface. At the same time, the sonic pressure P.sub.M is pulling bubble to expansion direction as shown in FIG. 5C, therefore the negative sonic pressure P.sub.M also do partial work to the surrounding liquid too. As the results of the joint efforts, the thermal energy inside bubble cannot be fully released or converted to mechanical energy, therefore the temperature of gas inside bubble cannot cool down to original gas temperature T.sub.0 or the liquid temperature. After the first cycle of cavitation finishes, the temperature T.sub.2 of gas in bubble will be somewhere between T.sub.0 and T.sub.1 as shown in FIG. 6B. Or T.sub.2 can be expressed as
T.sub.2=T1−δT=T.sub.0+ΔT−δT  (5)

(30) Where δT is temperature decrease after one time of expansion of the bubble, and δT is smaller than ΔT.

(31) When the second cycle of bubble cavitation reaches the minimum bubble size, the temperature T3 of gas and or vapor inside bubbler will be
T3=T2+ΔT=T.sub.0+ΔT−δT+ΔT=T.sub.0+2ΔT−δT  (6)

(32) When the second cycle of bubble cavitation finishes, the temperature T4 of gas and/or vapor inside bubbler will be
T4=T3−δT=T.sub.0+2ΔT−δT−δT=T.sub.0+2ΔT−2δT  (7)

(33) Similarly, when the nth cycle of bubble cavitation reaches the minimum bubble size, the temperature T.sub.2n-1 of gas and or vapor inside bubbler will be
T.sub.2n-1=T.sub.0+nΔT−(n−1)δT  (8)

(34) When the nth cycle of bubble cavitation finishes, the temperature T.sub.2n of gas and/or vapor inside bubbler will be
T.sub.2n=T.sub.0+nΔT−nδT=T.sub.0+n(ΔT−δT)  (9)

(35) As cycle number n of bubble cavitation increase, the temperature of gas and vapor will increase, therefore more molecules on bubble surface will evaporate into inside of bubble 6082 and size of bubble 6082 will increase too, as shown in FIG. 6C. Finally the temperature inside bubble during compression will reach implosion temperature T.sub.i (normally T.sub.i is as high as a few thousands ° C.), and violent micro jet 6080 forms as shown in FIG. 6C.

(36) From equation (8), implosion cycle number n.sub.i can be written as following:
n.sub.i=(T.sub.i−T.sub.0−ΔT)/(ΔT−δT)+1  (10)

(37) From equation (10), implosion time τ.sub.i can be written as following:

(38) $\begin{array}{cc}\begin{array}{c}{\tau }_i=n_i{t}_1=t_1\left(\left(T_i-T_0-\Delta T\right)\text{/}\left(\Delta T-\delta T\right)+1\right)\\ =n_i\text{/}{f}_1=\left(\left(T_i-T_0-\Delta T\right)\text{/}\left(\Delta T-\delta T\right)+1\right)\text{/}{f}_1\end{array}& \left(11\right)\end{array}$
Where, t.sub.1 is cycle period, and f.sub.1 frequency of ultra/mega sonic wave.

(39) According to formulas (10) and (11), implosion cycle number n.sub.i and implosion time τ.sub.i can be calculated. Table 1 shows calculated relationships among implosion cycle number n.sub.i, implosion time τ.sub.i and (ΔT−δT), assuming Ti=3000° C., ΔT=50.9° C., T.sub.0=20° C., f.sub.1=500 KHz, f.sub.1=1 MHz, and f.sub.1=2 MHz.

(40) TABLE-US-00001 TABLE 1 ΔT-δT (° C.) 0.1 1 10 30 50 n.sub.i 29018 2903 291 98 59 τ.sub.i (ms) 58.036 5.806 0.582 0.196 0.118 f.sub.1 = 500 KHz τ.sub.i (ms) 29.018 2.903 0.291 0.098 0.059 f.sub.1 = 1 MHz τ.sub.i (ms) 14.509 1.451 0.145 0.049 0.029 f.sub.1 = 2 MHz

(41) In order to avoid damage to patterned structure on wafer, a stable cavitation must be maintained, and the bubble implosion or micro jet must be avoided. FIGS. 7A to 7C shows a method to achieve a damage free ultra or mega-sonic cleaning on a wafer with patterned structure by maintaining a stable bubble cavitation according to the present invention. FIG. 7A shows waveform of power supply outputs, and FIG. 7B shows the temperature curve corresponding to each cycle of cavitation, and FIG. 7C shows the bubble size expansion during each cycle of cavitation. Operation process steps to avoid bubble implosion according to the present invention are disclosed as follows:

(42) Step 1: Put ultra/mega sonic device adjacent to surface of wafer or substrate set on a chuck or tank;

(43) Step 2: Fill chemical liquid or gas (hydrogen, nitrogen, oxygen, or CO.sub.2) doped water between wafer and the ultra/mega sonic device;

(44) Step 3: Rotate chuck or oscillate wafer;

(45) Step 4: Set power supply at frequency f.sub.1 and power P.sub.1;

(46) Step 5: Before temperature of gas and vapor inside bubble reaches implosion temperature T.sub.i, (or time reach τ.sub.1<τ.sub.i as being calculated by equation (11)), set power supply output to zero watts, therefore the temperature of gas inside bubble start to cool down since the temperature of liquid or water is much lower than gas temperature.

(47) Step 6: After temperature of gas inside bubble decreases to room temperature T.sub.0 or time (zero power time) reaches τ.sub.2, set power supply at frequency f.sub.1 and power P.sub.1 again.

(48) Step 7: repeat Step 1 to Step 6 until wafer is cleaned.

(49) In step 5, the time τ.sub.1 must be shorter than τ.sub.i in order to avoid bubble implosion, and τ.sub.i can be calculated by using equation (11).

(50) In step 6, the temperature of gas inside bubble is not necessary to be cooled down to room temperature or liquid temperature; it can be certain temperature above room temperature or liquid temperature, but better to be significantly lower than implosion temperature T.sub.i.

(51) According to equations 8 and 9, if (ΔT−δT) can be known, the τ.sub.i can be calculated. But in general, (ΔT−δT) is not easy to be calculated or measured directly. The following method can determine the implosion time τ.sub.i experimentally.

(52) Step 1: Based on Table 1, choosing 5 different time τ.sub.1 as design of experiment (DOE) conditions,

(53) Step 2: choose time τ.sub.2 at least 10 times of τ.sub.1, better to be 100 times of τ.sub.1 at the first screen test

(54) Step 3: fix certain power P.sub.0 to run above five conditions cleaning on specific patterned structure wafer separately. Here, P.sub.0 is the power at which the patterned structures on wafer will be surely damaged when running on continuous mode (non-pulse mode).

(55) Step 4: Inspect the damage status of above five wafers by SEMS or wafer pattern damage review tool such as AMAT SEM vision or Hitachi IS3000, and then the implosion time τ.sub.i can be located in certain range.

(56) Step 1 to 4 can be repeated again to narrow down the range of implosion time τ.sub.i. After knowing the implosion time τ.sub.i, the time τ.sub.1 can be set at a value smaller than 0.5 τ.sub.i for safety margin. One example of experimental data is described as following.

(57) The patterned structures are 55 nm poly-silicon gate lines. Ultra/mega sonic wave frequency was 1 MHz, and ultra/mega-sonic device manufactured by Prosys was used and operated in a gap oscillation mode (disclosed by PCT/CN2008/073471) for achieving better uniform energy dose within wafer and wafer to wafer. Other experimental parameters and final pattern damage data are summarized in Table 2 as follows:

(58) TABLE-US-00002 TABLE 2 Process Power Number of CO.sub.2 conc. Time Density Cycle τ.sub.1 τ.sub.2 Damage Wafer ID (18 μs/cm) (sec) (Watts/cm2) Number (ms) (ms) Sites #1 18 60 0.1 2000 2   18    1216 #2 18 60 0.1  100 0.1 0.9   0

(59) It was clear that the τ.sub.1=2 ms (or 2000 cycle number) introduced as many as 1216 damage sites to patterned structure with 55 nm feature size, but that the τ.sub.1=0.1 ms (or 100 cycle number) introduced zero (0) damage sites to patterned structure with 55 nm feature size. So that the τ.sub.i is some number between 0.1 ms and 2 ms, more detail tests need to be done to narrow its range. Obviously, the cycle number related to ultra or mega sonic power density and frequency, the larger the power density, the less the cycle number; and the lower the frequency, the less the cycle number. From above experimental results, we can predict that the damage-free cycle number should be smaller than 2,000, assuming the power density of ultra or mega sonic wave is larger than 0.1 watts or cm.sup.2, and frequency of ultra or mega sonic wave is equal to or less than 1 MHz. If the frequency increases to a range larger than 1 MHz or power density is less than 0.1 watts/cm.sup.2, it can be predicted that the cycle number will increase.

(60) After knowing the time τ.sub.1, then the time τ.sub.2 can be shorten based on similar DEO method described above, i.e. fix time τ.sub.1, gradually shorten the time τ.sub.2 to run DOE till damage on patterned structure being observed. As the time τ.sub.2 is shorten, the temperature of gas and or vapor inside bubbler cannot be cooled down enough, which will gradually shift average temperature of gas and vapor inside bubbler up, eventually it will trigger implosion of bubble. This trigger time is called critical cooling time. After knowing critical cooling time τ.sub.c, the time τ.sub.2 can be set at value larger than 2τ.sub.c for the same reason to gain safety margin.

(61) FIGS. 8A to 8D show another embodiment of wafer cleaning method using a ultra/mega sonic device according to the present invention. The method is similar to that shown in FIG. 7A, except in step 4 setting ultra/mega sonic power supply at frequency f.sub.1 and power with changing amplitude of waveform. FIG. 8A shows another cleaning method of setting ultra/mega sonic power at frequency f.sub.1 and power with increasing amplitude of waveform in step 4. FIG. 8B shows another cleaning method of setting ultra/mega sonic power supply at frequency f.sub.1 and power with decreasing amplitude of waveform in step 4. FIG. 8C shows another cleaning method of setting ultra/mega sonic power supply at frequency f.sub.1 and power with decreasing first and increasing later amplitude of waveform in step 4. FIG. 8D shows further another cleaning method of setting ultra/mega sonic power at frequency f.sub.1 and power with increasing first and decreasing later amplitude of waveform in step 4.

(62) FIGS. 9A to 9D show another embodiment of wafer cleaning method using a ultra/mega sonic device according to the present invention. The method is similar to that shown in FIG. 7A, except in step 4 setting ultra/mega sonic power supply at changing frequency. FIG. 9A shows another cleaning method of setting ultra/mega sonic power supply at frequency f.sub.1 first then frequency f.sub.3 later, f.sub.1 is higher than f.sub.3 in step 4. FIG. 9B shows another cleaning method of setting ultra/mega sonic power supply at frequency f.sub.3 first then frequency f.sub.1 later, f.sub.1 is higher than f.sub.3 in step 4. FIG. 9C shows another cleaning method of setting ultra/mega sonic power supply at frequency f.sub.3 first, frequency f.sub.1 later and f.sub.3 last, f.sub.1 is higher than f.sub.3 in step 4. FIG. 9D shows another cleaning method of setting ultra/mega sonic power supply at frequency f.sub.1 first, frequency f.sub.3 later and f.sub.1 last, f.sub.1 is higher than f.sub.3 in step 4.

(63) Similar to method shown in FIG. 9C, the ultra/mega sonic power can be set at frequency f.sub.1 first, at frequency f.sub.3 later and at frequency f.sub.4 at last in step 4, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

(64) Again similar to method shown in FIG. 9C, the ultra/mega sonic power can be set at frequency f.sub.4 first, at frequency f.sub.3 later and at frequency f.sub.1 at last in step 4, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1

(65) Again similar to method shown in FIG. 9C, the ultra/mega sonic power can be set at frequency f.sub.1 first, at frequency f.sub.4 later and at frequency f.sub.3 at last in step 4, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

(66) Again similar to method shown in FIG. 9C, the ultra/mega sonic power can be set at frequency f.sub.3 first, at frequency f.sub.4 later and at frequency f.sub.1 at last in step 4, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

(67) Again similar to method shown in FIG. 9C, the ultra/mega sonic power can be set at frequency f.sub.3 first, at frequency f.sub.1 later and at frequency f.sub.4 at last in step 4, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

(68) Again similar to method shown in FIG. 9C, the ultra/mega sonic power can be set at frequency f.sub.4 first, at frequency f.sub.1 later and at frequency f.sub.3 at last in step 4, where f.sub.4 is smaller than f.sub.3, and f.sub.3 is smaller than f.sub.1.

(69) FIGS. 10A to 10B show another method to achieve a damage free ultra/mega-sonic cleaning on a wafer with patterned structure by maintaining a stable bubble cavitation in according to the present invention. FIG. 10A shows waveform of power supply outputs, and FIG. 10B shows the temperature curve corresponding to each cycle of cavitation. Operation process steps according to the present invention are disclosed as follows:

(70) Step 1: Put ultra/mega sonic device adjacent to surface of wafer or substrate set on a chuck or tank;

(71) Step 2: Fill chemical liquid or gas doped water between wafer and the ultra/mega sonic device;

(72) Step 3: Rotate chuck or oscillate wafer;

(73) Step 4: Set power supply at frequency f.sub.1 and power P.sub.1;

(74) Step 5: Before temperature of gas and vapor inside bubble reaches implosion temperature T.sub.i, (total time τ.sub.1 elapse), set power supply output at frequency f.sub.1 and power P.sub.2, and P.sub.2 is smaller than P.sub.1. Therefore the temperature of gas inside bubble start to cool down since the temperature of liquid or water is much lower than gas temperature.

(75) Step 6: After temperature of gas inside bubble decreases to certain temperature close to room temperature T.sub.0 or time (zero power time) reach τ.sub.2, set power supply at frequency f.sub.1 and power P.sub.1 again.

(76) Step 7: repeat Step 1 to Step 6 until wafer is cleaned.

(77) In step 6, the temperature of gas inside bubble can not be cooled down to room temperature due to power P.sub.2, there should be a temperature difference ΔT.sub.2 existing in later stage of τ.sub.2 time zone, as shown in FIG. 10B.

(78) FIGS. 11A to 11B show another embodiment of wafer cleaning method using a ultra/mega sonic device according to the present invention. The method is similar to that shown in FIG. 10A, except in step 5 setting ultra/mega sonic power at frequency f.sub.2 and power P.sub.2, where f.sub.2 is lower than f.sub.1 and P.sub.2 is less than P.sub.1. Since f.sub.2 is lower than f.sub.1, the temperature of gas or vapor inside bubble increasing faster, therefore the P.sub.2 should be set significantly less than P1, better to be 5 or 10 times less in order to reduce temperature of gas and or vapor inside bubble.

(79) FIGS. 12A to 12B show another embodiment of wafer cleaning method using a ultra/mega sonic device according to the present invention. The method is similar to that shown in FIG. 10A, except in step 5 setting ultra/mega sonic power at frequency f.sub.2 and power P.sub.2, where f.sub.2 is higher than f.sub.1, and P.sub.2 is equal to P.sub.1.

(80) FIGS. 13A to 13B show another embodiment of wafer cleaning method using a ultra/mega sonic device according to the present invention. The method is similar to that shown in FIG. 10A, except in step 5 setting ultra/mega sonic power at frequency f.sub.2 and power P.sub.2, where f.sub.2 is higher than f.sub.1, and P.sub.2 is less than P.sub.1.

(81) FIGS. 14A-14B shows another embodiment of wafer cleaning method using a ultra/mega sonic device according to the present invention. The method is similar to that shown in FIG. 10A, except in step 5 setting ultra/mega sonic power at frequency f.sub.2 and power P.sub.2, where f.sub.2 is higher than f.sub.1, and P.sub.2 is higher than P.sub.1. Since f.sub.2 is higher than f.sub.1, the temperature of gas or vapor inside bubble increasing slower, therefore the P2 can be slightly higher than P1, but must make sure the temperature of gas and vapor inside bubbler decreases in time zone τ.sub.2 comparing to temperature zone τ.sub.1, as shown in FIG. 14B

(82) FIGS. 4A and 4B show that patterned structure is damaged by the violent micro jet. FIGS. 15A and 15B show that the stable cavitation can also damage the patterned structure on wafer. As bubble cavitation continues, the temperature of gas and vapor inside bubble increases, therefore size of bubble 15046 also increases as shown in FIG. 15A. When size of bubble 15048 becomes larger than dimension of space W in patterned structure as shown in FIG. 15B, the expansion force of bubble cavitation can damage the patterned structure 15034 as shown in FIG. 15C. Another cleaning method according to the present invention are disclosed as follows:

(83) Step 1: Put ultra/mega sonic device adjacent to surface of wafer or substrate set on a chuck or tank;

(84) Step 2: Fill chemical liquid or gas doped water between wafer and the ultra/mega sonic device;

(85) Step 3: Rotate chuck or oscillate wafer;

(86) Step 4: Set power supply at frequency f.sub.1 and power P.sub.1;

(87) Step 5: Before size of bubble reaches the same dimension of space W in patterned structures (time τ.sub.1 elapse), set power supply output to zero watts, therefore the temperature of gas inside bubble starts to cool down since the temperature of liquid or water is much lower than gas temperature;

(88) Step 6: After temperature of gas inside bubble continues to reduce (either it reaches room temperature T.sub.0 or time (zero power time) reach τ.sub.2, set power supply at frequency f.sub.1 power P.sub.1 again;

(89) Step 7: repeat Step 1 to Step 6 until wafer is cleaned;

(90) In step 6, the temperature of gas inside bubble is not necessary to be cooled down to room temperature, it can be any temperature, but better to be significantly lower than implosion temperature T.sub.i. In the step 5, bubble size can be slightly larger than dimension of patterned structures as long as bubble expansion force does not break or damage the patterned structure. The time τ.sub.1 can be determined experimentally by using the following method:

(91) Step 1: Similar to Table 1, choosing 5 different time τ.sub.1 as design of experiment (DOE) conditions,

(92) Step 2: choose time τ.sub.2 at least 10 times of τ.sub.1, better to be 100 times of τ.sub.1 at the first screen test

(93) Step 3: fix certain power P.sub.0 to run above five conditions cleaning on specific patterned structure wafer separately. Here, P.sub.0 is the power at which the patterned structures on wafer will be surely damaged when running on continuous mode (non-pulse mode).

(94) Step 4: Inspect the damage status of above five wafers by SEMS or wafer pattern damage review tool such as AMAT SEM vision or Hitachi IS3000, and then the damage time τ.sub.i can be located in certain range.

(95) Step 1 to 4 can be repeated again to narrow down the range of damage time τ.sub.d. After knowing the damage time τ.sub.d, the time τ.sub.1 can be set at a value smaller than 0.5 τ.sub.d for safety margin.

(96) All cleaning methods described from FIGS. 7 to FIG. 14 can be applied in or combined with the method described in FIG. 15.

(97) FIG. 16 shows a wafer cleaning apparatus using a ultra/mega sonic device. The wafer cleaning apparatus consists of wafer 16010, wafer chuck 16014 being rotated by rotation driving mechanism 16016, nozzle 16064 delivering cleaning chemicals or de-ionized water 16060, ultra/mega sonic device 16062 coupled with nozzle 16064, and ultra/mega sonic power supply. Ultra/mega sonic wave generated by ultra/mega sonic device 16062 is transferred to wafer through chemical or water liquid column 16060. All cleaning methods described from FIGS. 7 to FIG. 15 can be used in cleaning apparatus described in FIG. 16.

(98) FIG. 17 shows a wafer cleaning apparatus using a ultra/mega sonic device. The wafer cleaning apparatus consists of wafers 17010, a cleaning tank 17074, a wafer cassette 17076 holding the wafers 17010 and being held in the cleaning tank 17074, cleaning chemicals 17070, a ultra/mega sonic device 17072 attached to outside wall of the cleaning tank 17074, and a ultra/mega sonic power supply. At least one inlet fills the cleaning chemicals 17070 into the cleaning tank 17074 to immerse the wafers 17010. All cleaning methods described from FIGS. 7 to FIG. 15 can be used in cleaning apparatus described in FIG. 17.

(99) FIGS. 18A to 18C show another embodiment of wafer cleaning method using a ultra/mega sonic device according to the present invention. The method is similar to that shown in FIG. 7A, except in Step 5: Before temperature of gas and vapor inside bubble reaches implosion temperature T.sub.i, (or time reach τ.sub.1<τ.sub.i as being calculated by equation (11)), set power supply output to a positive value or negative DC value to hold or stop ultra/mega sonic device to vibrate, therefore the temperature of gas inside bubble start to cool down since the temperature of liquid or water is much lower than gas temperature. The positive value of negative value can be bigger, equal to or smaller than power P.sub.1.

(100) FIG. 19 shows another embodiment of wafer cleaning method using a ultra/mega sonic device according to the present invention. The method is similar to that shown in FIG. 7A, except in Step 5: Before temperature of gas and vapor inside bubble reaches implosion temperature T.sub.i, (or time reach τ.sub.1<T.sub.i as being calculated by equation (11)), set power supply output at the frequency same as f.sub.1 with reverse phase to f.sub.1 to quickly stop the cavitation of bubble. Therefore the temperature of gas inside bubble start to cool down since the temperature of liquid or water is much lower than gas temperature. The positive value of negative value can be bigger, equal or less than power P.sub.1. During above operation, the power supply output can be set at a frequency different from frequency f.sub.1 with reverse phase to f.sub.1 in order to quickly stop the cavitation of bubble.

(101) Generally speaking, an ultra/mega sonic wave with the frequency between 0.1 MHz˜10 MHz may be applied to the method disclosed in the present invention.

(102) Although the present invention has been described with respect to certain embodiments, examples, and applications, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the invention.