Patent Application
20220032344
The present invention generally relates to method and apparatus for cleaning substrate. More particularly, relates to controlling the bubble cavitation generated by ultra or mega sonic device during the cleaning process to achieve a stable or controlled cavitation on the entire substrate, which removes fine particles efficiently in vias, trenches or recessed areas with high aspect ratio.
Semiconductor devices are manufactured or fabricated on semiconductor substrates using a number of different processing steps to create transistor and interconnection elements. Recently, the transistors are built from two dimensions to three dimensions such as finFET transistors and 3D NAND memory. To electrically connect transistor terminals associated with the semiconductor substrate, conductive (e.g., metal) trenches, vias, and the like are formed in dielectric materials as part of the semiconductor device. The trenches and vias couple electrical signals and power between transistors, internal circuit of the semiconductor devices, and circuits external to the semiconductor device.
In forming the finFET transistors and interconnection elements on the semiconductor substrate may undergo, for example, masking, etching, and deposition processes to form the desired electronic circuitry of the semiconductor devices. In particular, multiple masking and plasma etching step can be performed to form a pattern of finFET, 3D NAND flash cell and or recessed areas in a dielectric layer on a semiconductor substrate that serve as fin for the transistor and or trenches and vias for the interconnection elements. In order to removal particles and contaminations in fin structure and or trench and via post etching or photo resist ashing, a wet cleaning step is necessary. Especially, when device manufacture node migrating to 14 or 16 nm and beyond, the side wall loss in fin and or trench and via is crucial for maintaining the critical dimension. In order to reduce or eliminate the side wall loss, it is important to use moderate, dilute chemicals, or sometime de-ionized water only. However, the dilute chemical or de-ionized water usually is not efficient to remove the particles in the fin structure, 3D NAND hole and or trench and via. Therefore the mechanical force such as ultra or mega sonic is needed in order to remove those particles efficiently. Ultra sonic or mega sonic wave will generate bubble cavitation which applies mechanical force to substrate structure, the violent cavitation such as transit cavitation or micro jet will damage those patterned structures. To maintain a stable or controlled cavitation is key parameters to control the mechanical force within the damage limit and at the same time efficiently to remove the particles. In the 3D NAND hole structure, the transit cavitation may not damage the hole structure, but however, the bubble cavitation saturated inside hole will stop or reduce the cleaning effects.
Mega sonic energy coupled with nozzle to clean semiconductor wafer is disclosed in U.S. Pat. No. 4,326,553. The fluid is pressurized and mega sonic energy is applied to the fluid by a mega sonic transducer. The nozzle is shaped to provide a ribbon-like jet of cleaning fluid vibrating at ultra/mega sonic frequencies for the impingement on the surface.
A source of energy vibrates an elongated probe which transmits the acoustic energy into the fluid is disclosed in U.S. Pat. No. 6,039,059. In one arrangement, fluid is sprayed onto both sides of a wafer while a probe is positioned close to an upper side. In another arrangement, a short probe is positioned with its end surface close to the surface, and the probe is moved over the surface as wafer rotates.
A source of energy vibrates a rod which rotates around it axis parallel to wafer surface is disclosed in U.S. Pat. No. 6,843,257 B2. The rod surface is etched to curve groves, such as spiral groove.
It is needed to have a better method for controlling the bubble cavitation generated by ultra or mega sonic device during the cleaning process to achieve a stable or controlled cavitation on the entire substrate, which removes fine particles efficiently in vias, trenches or recessed areas with high aspect ratio.
One method of the present invention is to achieve a damage free ultra/mega-sonic cleaning on a wafer with patterned structure by maintaining a stable bubble cavitation. The stable bubble cavitation is controlled by setting a sonic power supply with power P1 at a time interval shorter than τ1, and setting the sonic power supply with power P2 at a time interval longer than τ2, and repeat above steps till the wafer is cleaned, where power P2 is equal to zero or much smaller than power P1, τ1 is a time interval that the temperature inside bubble raises to a critical implosion temperature; and τ2 is a time interval that the temperature inside bubble falls down to a temperature much lower than the critical implosion temperature.
Another method of the present invention is to achieve a damage free ultra/mega sonic cleaning on a wafer with patterned structure by maintaining a stable bubble cavitation. The stable bubble cavitation is controlled by setting a sonic power supply with frequency f1 at a time interval shorter than τ1, and setting the sonic power supply with frequency f2 at a time interval longer than τ2, and repeat above steps till the wafer is cleaned, where f2 is much higher than f1, better to be 2 times or 4 times higher, T1 is a time interval that the temperature inside bubble raises to a critical implosion temperature; and τ2 is a time interval that the temperature inside bubble falls down to a temperature much lower than the critical implosion temperature.
Another method of the present invention is to achieve a damage free ultra/mega-sonic cleaning on a wafer with patterned structure by maintaining a stable bubble cavitation with bubble size less than space in patterned structure. The stable bubble cavitation with bubble size less than space in patterned structure is controlled by setting a sonic power supply at power P1 for a time interval shorter than τ1, and setting the sonic power supply at power P2 for a time interval longer than τ2, and repeat above steps till the wafer is cleaned, where P2 is equal to zero or much smaller than P1, T1 is a time interval that the bubble size increases to a critical size equal to or larger than the space in patterned structures; and τ2 is a time interval that the bubble size decreases to a value much smaller than the space in patterned structure.
Another method of the present invention is to achieve a damage free ultra/mega-sonic cleaning on a wafer with patterned structure by maintaining a stable bubble cavitation with bubble size less than space in patterned structure. The stable bubble cavitation with bubble size less than space in patterned structure is controlled by setting a sonic power supply with frequency f1 for a time interval shorter than T1, and setting the sonic power supply with frequency f2 for a time interval longer than τ2, and repeat above steps till the wafer is cleaned, where f2 is much higher than f1, better to be 2 times or 4 times higher, T1 is a time interval that the bubble size increases to a critical size equal to or larger than the space in patterned structures; and τ2 is a time interval that the bubble size decreases to a value much smaller than the space in patterned structure.
One method of the present invention is to achieve an effective ultra/mega-sonic cleaning on a substrate with features of deep holes by maintaining a non-saturated bubble cavitation. The non-saturated bubble cavitation is controlled by setting a sonic power supply with power P1 at a time interval shorter than τ1, and setting the sonic power supply with power P2 at a time interval longer than τ2, and repeating above steps till the substrate is cleaned, where power P2 is equal to zero or much smaller than power P1, T1 is a time interval that the cavitation or bubble density inside the deep hole raises to saturated status; and τ2 is a time interval that bubble density falls down to a level much lower than the saturated status.
Another method of the present invention is to achieve an effective ultra/mega-sonic cleaning on a substrate with features of deep holes by maintaining a non-saturated bubble cavitation. The non-saturated bubble cavitation is controlled by setting a sonic power supply with frequency f1 at a time interval shorter than τ1, and setting the sonic power supply with frequency f2 at a time interval longer than τ2, and repeating above steps till the substrate is cleaned, where f2 is much higher than f1, better to be 2 times or 4 times higher, τ1 is a time interval that the cavitation or bubble density inside the deep hole raises to saturated status; and τ2 is a time interval that bubble density falls down to a level much lower than the saturated status.
One method of the present invention is to achieve an effective ultra/mega-sonic cleaning on a substrate with features of deep holes by maintaining a certain size of bubble in cavitation status. The certain size of bubble in cavitation status is controlled by setting a sonic power supply with power P1 at a time interval shorter than τ1, and setting the sonic power supply with power P2 at a time interval longer than τ2, and repeating above steps till the substrate is cleaned, where power P2 is equal to zero or much smaller than power P1, T1 is a time interval that the cavitation or bubble density inside the deep hole raises to saturated status; and τ2 is a time interval that bubble size falls down to a level much smaller than the certain size.
Another method of the present invention is to achieve an effective ultra/mega-sonic cleaning on a substrate with features of deep holes by maintaining a certain size of bubble in cavitation status. The certain size of bubble in cavitation status is controlled by setting a sonic power supply with frequency f1 at a time interval shorter than τ1, and setting the sonic power supply with frequency f2 at a time interval longer than τ2, and repeating above steps till the substrate is cleaned, where f2 is much higher than f1, better to be 2 times or 4 times higher, τ1 is a time interval that the cavitation or bubble density inside the deep hole raises to saturated status; and τ2 is a time interval that bubble size falls down to a level much smaller than the certain size.
The idea gas equation can be expressed as follows:
p
0
v
0
/T
0
=pv/T (1),
where, p0 is pressure inside bubbler before compression, v0 initial volume of bubble before compression, T0 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.
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 wm did by sonic pressure PM during one time of bubbler compression (from volume N unit to volume 1 unit or compression ratio=N) can be expressed as follows:
Where, S is area of cross section of cylinder, x0 the length of the cylinder, p0 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).
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)=βwm/(mc)=βSx0p0 ln(x0)/(mc) (3)
where, Q is thermal energy converted from mechanical work, β ratio 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 m2, x0=1000 μm=1E-3 m (compression ratio N=1000), p0=1 kg/cm2=1E4 kg/m2, m=8.9E-17 kg for hydrogen gas, c=9.9E3 J/(kg ° k) into equation (3), then ΔT=50.9° k.
The temperature T1 of gas inside bubbler after first time compression can be calculated as
T
1
=T
0
+ΔT=20° C.+50.9° C.=70.9° C. (4)
When the bubble reaches the minimum size of 1 micron as shown in
T
2
=T1−δT=T0+ΔT−δT (5)
Where δT is temperature decrease after one time of expansion of the bubble, and δT is smaller than ΔT.
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=T0+ΔT−δT+ΔT=T0+2ΔT−δT (6)
When the second cycle of bubble cavitation finishes, the temperature T4 of gas and/or vapor inside bubbler will be
T4=T3−δT=T0+2ΔT−δT−δT=T0+2ΔT−2δT (7)
Similarly, when the nth cycle of bubble cavitation reaches the minimum bubble size, the temperature T2/1-1 of gas and or vapor inside bubbler will be
T
2n-1
=T
0
+nΔT−(n−1)δT (8)
When the nth cycle of bubble cavitation finishes, the temperature T2n of gas and/or vapor inside bubbler will be
T
2n
=T
0
+nΔT−nδT=T
0
+n(ΔT−δT) (9)
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
From equation (8), implosion cycle number ni can be written as following:
n
i=(Ti−T0−ΔT)/(ΔT−δT)+1 (10)
From equation (10), implosion time τi, can be written as following:
Where, t1 is cycle period, and f1 frequency of ultra/mega sonic wave.
According to formulas (10) and (11), implosion cycle number ni and implosion time τi, can be calculated. Table 1 shows calculated relationships among implosion cycle number ni, implosion time τi and (ΔT−δT), assuming Ti=3000° C., ΔT=50.9° C., T0=20° C., f1=500 KHz, f1=1 MHz, and f1=2 MHz.
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.
Step 1: Put ultra/mega sonic device adjacent to surface of wafer or substrate set on a chuck or tank;
Step 2: Fill chemical liquid or gas (hydrogen, nitrogen, oxygen, or CO2) doped water between wafer and the ultra/mega sonic device;
Step 3: Rotate chuck or oscillate wafer;
Step 4: Set power supply at frequency f1 and power P1;
Step 5: Before temperature of gas and vapor inside bubble reaches implosion temperature Ti, (or time reach τ1<τi 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.
Step 6: After temperature of gas inside bubble decreases to room temperature T0 or time (zero power time) reaches τ2, set power supply at frequency f1 and power P1 again.
Step 7: repeat Step 1 to Step 6 until wafer is cleaned.
In step 5, the time τ1 must be shorter than τi in order to avoid bubble implosion, and τi can be calculated by using equation (11).
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 Ti.
According to equations 8 and 9, if (ΔT−δT) can be known, the 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 τi experimentally.
Step 1: Based on Table 1, choosing 5 different time τ1 as design of experiment (DOE) conditions,
Step 2: choose time τ2 at least 10 times of τ1, better to be 100 times of τ1 at the first screen test
Step 3: fix certain power P0 to run above five conditions cleaning on specific patterned structure wafer separately. Here, P0 is the power at which the patterned structures on wafer will be surely damaged when running on continuous mode (non-pulse mode).
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 can be located in certain range.
Step 1 to 4 can be repeated again to narrow down the range of implosion time τi. After knowing the implosion time τi, the time τ1 can be set at a value smaller than 0.5τi for safety margin. One example of experimental data is described as following.
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:
It was clear that the τi=2 ms (or 2000 cycle number) introduced as many as 1216 damage sites to patterned structure with 55 nm feature size, but that the τi=0.1 ms (or 100 cycle number) introduced zero (0) damage sites to patterned structure with 55 nm feature size. So that the τi 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 wattsorcm2, 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 than 0.1 watts/cm2, it can be predicted that the cycle number will increase.
After knowing the time τ1, then the time T2 can be shorten based on similar DEO method described above, i.e. fix time τ1, gradually shorten the time τ2 to run DOE till damage on patterned structure being observed. As the time τ2 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 τc, the time τ2 can be set at value larger than 2τc for the same reason to gain safety margin.
Similar to method shown in
Again similar to method shown in
Again similar to method shown in
Again similar to method shown in
Again similar to method shown in
Again similar to method shown in
Step 1: Put ultra/mega sonic device adjacent to surface of wafer or substrate set on a chuck or tank;
Step 2: Fill chemical liquid or gas doped water between wafer and the ultra/mega sonic device;
Step 3: Rotate chuck or oscillate wafer;
Step 4: Set power supply at frequency f1 and power P1;
Step 5: Before temperature of gas and vapor inside bubble reaches implosion temperature Ti, (total time τ1 elapes), set power supply output at frequency f1 and power P2, and P2 is smaller than P1. Therefore the temperature of gas inside bubble start to cool down since the temperature of liquid or water is much lower than gas temperature.
Step 6: After temperature of gas inside bubble decreases to certain temperature close to room temperature T0 or time (zero power time) reach τ2, set power supply at frequency f1 and power P1 again.
Step 7: repeat Step 1 to Step 6 until wafer is cleaned.
In step 6, the temperature of gas inside bubble can not be cooled down to room temperature due to power P2, there should be a temperature difference 4T2 existing in later stage of τ2 time zone, as shown in
Step 1: Put ultra/mega sonic device adjacent to surface of wafer or substrate set on a chuck or tank;
Step 2: Fill chemical liquid or gas doped water between wafer and the ultra/mega sonic device;
Step 3: Rotate chuck or oscillate wafer;
Step 4: Set power supply at frequency f1 and power P1;
Step 5: Before size of bubble reaches the same dimension of space W in patterned structures (time τ1 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;
Step 6: After temperature of gas inside bubble continues to reduce (either it reaches room temperature T0 or time (zero power time) reach τ2, set power supply at frequency f1 power P1 again;
Step 7: repeat Step 1 to Step 6 until wafer is cleaned;
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 Ti. 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 τ1 can be determined experimentally by using the following method:
Step 1: Similar to Table 1, choosing 5 different time τ1 as design of experiment (DOE) conditions,
Step 2: choose time τ2 at least 10 times of τ1, better to be 100 times of τ1 at the first screen test
Step 3: fix certain power P0 to run above five conditions cleaning on specific patterned structure wafer separately. Here, P0 is the power at which the patterned structures on wafer will be surely damaged when running on continuous mode (non-pulse mode).
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 τi can be located in certain range.
Step 1 to 4 can be repeated again to narrow down the range of damage time Td. After knowing the damage time τd, the time τ1 can be set at a value smaller than 0.5 τd for safety margin.
All cleaning methods described from
As shown in
Below the saturation point, the ratio R of total bubbles volume VB to the volume of via or trench, or recessed space VVTR is:
R=V
B
/V
VTR
<R
s
And at or above the saturation point Rs, the ratio R of total bubbles volume VB to the volume of via or trench, or recessed space VVTR is:
R=V
B
/V
VTR
=R
s
The volume of the total bubbles in the features of vias, trenches or recessed space: VB=Nvb
Wherein N is the total bubble numbers in the features and vb is averaged single bubble volume.
As shown in
As shown in
Due to the total bubbles in the features is related to the bubble numbers and the bubble size in the features of vias and treches, the control of bubble size expanded by the cavitation is critical for the cleaning performance in the high aspect ratio features cleaning process.
As shown in
V
1
=V
0
−ΔV (12)
V
2
=V
1
+δV (13)
V
3
=V
2
−ΔV=V
1
+δV−ΔV=V
0
−ΔV+δV−ΔV=V
0
+δV−2ΔV (14)
Where ΔV is volume compression of bubble after one time of compression due to positive pressure generated by ultra/mega sonic wave, and δV is volume increase of the bubble after one time of expansion due to negative pressure generated by ultra/mega sonic wave, and δV−ΔV is volume increase due to temperature increment ΔT−δT as calculated in equation (5) after one time cycle.
After the second cycle of bubble cavitation, the size of bubble reaches to the larger bubble size during the temperature keeping increasing, the volume of V4 of gas and or vapor inside bubbler will be
V
4
=V
3
+δV=V
0
+δV−2ΔV+δV=V0+2(δV−ΔV) (15)
When the third cycle of bubble cavitation, the volume V5 of gas and/or vapor inside bubbler will be
V
5
=V
4
−ΔV=V
0+2(δV−ΔV)−ΔV=V0+2δV−3ΔV (16)
Similarly, when the nth cycle of bubble cavitation reaches the minimum bubble size, the volume V2n-1 of gas and or vapor inside bubbler will be
V
2n-1
=V
0+(n−1)δV−nΔV=V0+(n−1)δV−nΔV (17)
When the nth cycle of bubble cavitation finishes, the volume V2n of gas and/or vapor inside bubbler will be
V
2n
=V
0
+n(δV−ΔV) (18)
To restrict the volume of bubble into a desired volume Vi, which is a dimension with enough physical feasibility of movement or the bubbles status below the saturation point of cavitation or bubble density, rather than blocking the path of the chemical exchange in the features of vias, trenches or recessed areas, the cycle number ni can be written as following:
n
i=(Vi−V0−ΔV)/(δV−ΔV)+1 (19)
From equation (19), the desired time τi to achieve the Vi can be written as following:
Where, t1 is cycle period, and f1 frequency of ultra/mega sonic wave.
According to formulas (19) and (20), a desired cycle number ni and a time τi to restrict the bubble dimension can be calculated.
It should be pointed that when the cycle number n of bubble cavitation increases, the temperature of gas and liquid (water) vapor inside bubbler will increase, therefore more molecules on bubble surface will evaporate into inside of bubble, therefore the size of bubble 21082 will further increase and be bigger than value calculated by equation (18). In practical operation, since the bubble size will be determined by experimental method to be disclosed later, therefore bubble size impacted by the evaporation of liquid or water for bubble inner surface due to temperature increase will not be theoretically discussed in detail here. As the average single bubble volume keeping increasing, the ratio R of total bubbles volume VB to the volume of via, trench or recessed space VVTR increases from R0 continuously, as shown in
As the bubble volume increases, the diameter of bubble eventually will reach the same size or same order size of feature W1 such as via as shown in
In order to avoid the bubble growth up to a critical dimension to block the path of chemical exchanges in the features of vias or trenches,
R=V
B
/V
VTR
=Nv
b
/V
VTR,
the ratio R of total bubbles volume VB to the volume of via, trench or recessed space VVTR increases from R0 to Rn, where the average single bubble volume being expanded by the sonic cavitation after a certain cycle number n, in the time of τ1. And the Rn is controlled below the saturation point Rs,
R
n
=V
B
/V
VTR
−Nv
b
/V
VTR
<Rs.
And the ratio R of total bubbles volume VB to the volume of via, trench or recessed space VVTR decreases from Rn to R0, where the average single bubble volume return to original size in the cooling process in the time of τ2.
Operation process steps to avoid bubble size growth up according to the present invention are disclosed as follows:
Step 1: Put ultra/mega sonic device adjacent to surface of substrate or substrate set on a chuck or tank;
Step 2: Fill chemical liquid or gas (hydrogen, nitrogen, oxygen, or CO2) doped water between substrate and the ultra/mega sonic device;
Step 3: Rotate chuck or oscillate substrate;
Step 4: Set power supply at frequency f1 and power P1;
Step 5: After the volume of bubble expands to a certain volume Vn or diameter w, (or time reach τ1), set power supply output to zero watts, therefore the volume of gas inside bubble start to shrink down since the temperature of liquid or water cooling down the gas temperature;
Step 6: After the volume of bubble decreases to original volume while the gas temperature decreasing to room temperature T0 or time (zero power time) reaches τ2, set power supply at frequency f1 and power P1 again;
Step 7: repeat Step 1 to Step 6 until substrate is cleaned.
In step 5, the expanded bubble's volume of Vn or diameter w is not necessary to be restricted to be smaller than the dimension Vi or feature size w1 that blocking the features of vias or trenches. It can be certain volume above the Vi, but better to be smaller than the dimension Vi in order to obtain an effective cleaning with shortest process time. And the τ1 is also not necessary to be restricted to be smaller than τi, but better to be smaller than the τi as being defined in the equation (20).
In step 6, the volume of bubble is not necessary to shrink down to an original volume. It can be certain volume above original volume, but better to be significantly smaller than the Vi to restrict bubble size to get ultra/mega sonic power to be transmitted to the bottom of features such as via, trench, or recessed area.
The cooling state in the time τ2 plays a key role in this cleaning process. It should be defined precisely. And the τ1<τi time to restrict bubble size, is desired, and the definition of τi also is preferred. The following method can determine the time τ2 to shrink bubble size during a cooling down state and time τ1 to restrict the bubble expanded to the blockage size experimentally. The experiment is done by using an ultra/mega sonic device coupling with a chemical liquid to clean a pattern substrate with small features of vias and trenches, where the traceable residues exist to evaluate the cleaning performance.
Step 1: choose a τ1 which is big enough to block the features, which can be calculation as τi based on the equation (20).
Step 2: choose different time τ2 to run DOE. The selection of time τ2 is at least 10 times of τ1, better to be 100 times of τ1 at the first screen test.
Step 3: Fix time τ1 and fix certain power P0 to run at least five conditions cleaning on specific patterned structure substrate separately. Here, P0 is the power at which the features of vias or trenches on substrate will be surely not cleaned when running on continuous mode (non-pulse mode).
Step 4: Inspect the traceable residues status inside the features of vias or trenches of above five substrates by SEMS or element analyzer tool such as EDX.
The step 1 to step 4 can be repeated again to gradually shorten the time τ2 till the traceable residues inside the features of vias or trenches are observed. As the time τ2 is shorten, the volume of bubble cannot shrink down enough, which will gradually block the features and influence the cleaning performance. This time is called critical cooling time τc. After knowing critical cooling time τc, the time τ2 can be set at value larger than 2τc to gain safety margin.
A more detail example is shown as follows:
Step 1: choosing 10 different time τ1 as design of experiment (DOE) conditions, such as τ10, 2τ10, 4τ10, 8τ10, 16τ10, 32τ10, 64τ10, 128τ10, 256τ10, 512τ10, as shown in Table 3;
Step 2: choosing time τ2 at least 10 times of 512τ10, better to be 20 times of 512τ10 at the first screen test, as shown in Table 3;
Step 3: fixing certain power P0 to run above ten conditions cleaning on specific patterned structure substrate separately. Here, P0 is the power at which the features of vias or trenches on substrate will be surely not cleaned when running on continuous mode (non-pulse mode).
Step 4: Using above conditions as shown in Table 3 to process 10 substrates with features of vias or trenches post plasma etching. The reason to choose the post plasma etched substrate is that the polymers generated during etching process are formed on sidewall of trench and via. Those polymers formed on the bottom or side wall of via are difficulty to remove by a conventional method. Then inspect the cleaning status of features of vias or trenches on the ten substrates by SEMS with crossing section of substrates. The data are shown in Table 3. From the Table 3, the cleaning effect reaches the best point of 6 at τ1=32τ10, therefore the optimum time τ1 is 32τ10.
If there is no peak to be found, then the step 1 to step 4 with board time setting of τ1 can be repeated again to find the time τ1. After find the initial τ1, then step 1 to step 4 with time setting close to τ1 can be repeated again to narrow down the range of time After knowing the time τi, the time τ2 can be optimized by reducing the time τ2 from 512 τ2 to a value till the cleaning effect is reduced. A detail procedure is disclosed as follows Table 4:
From the Table 4, the cleaning effect reaches the best point of 7 at τ2=256τ10, therefore the optimum time τ2 is 256τ10.
Method and apparatus disclosed in
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.
As described above, the present invention discloses a method for effectively cleaning vias, trenches or recessed areas on a 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 f1 and power P1 to drive said ultra/mega sonic device; after the ratio of total bubbles volume to volume inside vias, trenches or recessed areas on the substrate increasing to a first set value, setting said ultra/mega sonic power supply at frequency f2 and power P2 to drive said ultra/mega sonic device; after the ratio of total bubbles volume to volume inside the vias, trenches or recessed areas reducing to a second set value, setting said ultra/mega sonic power supply at frequency f1 and power P1 again; repeating above steps till the substrate being cleaned.
The first set value is below the cavitation saturation point. The second set value is much lower than the cavitation saturate point. The temperature inside bubble cooling down results in the ratio of total bubbles volume to volume inside the vias, trenches or recessed areas reducing to the second set value. The temperature inside bubble cooling down to near temperature of said liquid.
At above embodiment, the first set value is a cavitation saturation point, and even after the ratio of total bubbles volume to volume inside vias, trenches or recessed areas on the substrate reaches to the cavitation saturation point, the ultra/mega sonic power supply is still kept at frequency f1 and power P1 for period of mτ1, here τ1 is the time to reach the cavitation saturation point, m is multiples of τ1, which is a number between 0.1 to 100, preferred 2.
According to an embodiment, the present invention discloses an apparatus for effectively cleaning vias, trenches or recessed areas on a substrate using an ultra/mega sonic device. The apparatus includes a chuck, an ultra/mega sonic device, at least one nozzle, an ultra/mega sonic power supply and a controller. The chuck holds a substrate. The ultra/mega sonic device is positioned adjacent to the substrate. The at least one nozzle injects chemical liquid on the substrate and a gap between the substrate and the ultra/mega sonic device. The controller sets the ultra/mega sonic power supply at frequency f1 and power P1 to drive the ultra/mega sonic device; after the ratio of total bubbles volume to volume inside vias, trenches or recessed areas on the substrate increasing to a first set value, the controller setting the ultra/mega sonic power supply at frequency f2 and power P2 to drive the ultra/mega sonic device; after the ratio of total bubbles volume to volume inside the vias, trenches or recessed areas reducing to a second set value, the controller setting the ultra/mega sonic power supply at frequency f1 and power P1 again; repeating above steps till the substrate being cleaned.
According to another embodiment, the present invention discloses an apparatus for effectively cleaning vias, trenches or recessed areas on a substrate using an ultra/mega sonic device. The apparatus includes a cassette, a tank, an ultra/mega sonic device, at least one inlet, an ultra/mega sonic power supply and a controller. The cassette holds at least one substrate. The tank holds the cassette. The ultra/mega sonic device is attached to outside wall of the tank. At least one inlet is used for filling chemical liquid into the tank to immerse the substrate. The controller sets the ultra/mega sonic power supply at frequency f1 and power P1 to drive the ultra/mega sonic device; after the ratio of total bubbles volume to volume inside vias, trenches or recessed areas on the substrate increasing to a first set value, the controller setting the ultra/mega sonic power supply at frequency f2 and power P2 to drive the ultra/mega sonic device; after the ratio of total bubbles volume to volume inside the vias, trenches or recessed areas reducing to a second set value, the controller setting the ultra/mega sonic power supply at frequency f1 and power P1 again; repeating above steps till the substrate being cleaned.
According to another embodiment, the present invention discloses an apparatus for effectively cleaning vias, trenches or recessed areas on a substrate using an ultra/mega sonic device. The apparatus includes a chuck, an ultra/mega sonic device, a nozzle, an ultra/mega sonic power supply and a controller. The chuck holds a substrate. The ultra/mega sonic device coupled with a nozzle is positioned adjacent to the substrate. The nozzle injects chemical liquid on the substrate. The controller sets the ultra/mega sonic power supply at frequency f1 and power P1 to drive the ultra/mega sonic device; after the ratio of total bubbles volume to volume inside vias, trenches or recessed areas on the substrate increasing to a first set value, the controller setting the ultra/mega sonic power supply at frequency f2 and power P2 to drive the ultra/mega sonic device; after the ratio of total bubbles volume to volume inside the vias, trenches or recessed areas reducing to a second set value, the controller setting the ultra/mega sonic power supply at frequency f1 and power P1 again; repeating above steps till the substrate being cleaned.
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.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16334703 | Mar 2019 | US |
| Child | 17378096 | US |
