JP7293221B2 - Semiconductor wafer cleaning system - Google Patents

Description

The present invention relates to cleaning semiconductor wafers and, more particularly, to wet cleaning methods and apparatus using controlled sonic energy.

Semiconductor devices are manufactured or fabricated on semiconductor wafers using a series of processing steps that produce transistors and interconnect elements. These transistors are conventionally configured two-dimensionally, but recently, they are configured three-dimensionally, such as FinFET transistors. Interconnect elements include conductive (eg, metal) trenches, via holes, etc. formed in insulating material.

In forming these transistors and interconnect elements, the semiconductor wafer undergoes multiple masking, etching, and deposition processes to form the desired structures for the semiconductor device. In particular, multiple masking and plasma etching steps can be performed to form recessed regions in dielectric layers of semiconductor wafers that serve as trenches and via holes for fins and interconnect elements of finFET transistors. A wet cleaning step is required to remove particles and debris in the fin structures and/or trenches and vias by post etching or photoresist ashing. However, wet cleaning with chemicals can result in sidewall loss. Especially as device fabrication nodes shrink to 14 nm or 16 nm and beyond, sidewall losses in fins, trenches and via holes are critical to maintaining critical dimensions. To reduce or eliminate sidewall loss, it is important to use only moderate or dilute chemicals, or possibly deionized water. However, medium or dilute chemicals and deionized water typically cannot effectively remove particles in fin structures and/or trenches and via holes. Efficient removal of these particles therefore requires mechanical force generated, for example, by ultra sonic or mega sonic energy. Ultrasound or high frequency ultrasound produces bubble cavitation to apply mechanical forces to the wafer structure during cleaning.

However, cavitation is a chaotic phenomenon. The occurrence of cavitation bubble generation and its collapse is affected by many physical parameters. Severe cavitation such as transit cavitation or microjets can damage pattern structures (fins, trenches and via holes). In conventional ultrasonic or high-frequency ultrasonic cleaning processes, significant particle removal efficiency (PRE) is obtained only when the power is sufficiently high, eg, greater than 5-10 Watts. However, when the power exceeds about 2 watts, significant wafer damage begins to occur. Therefore, it is difficult to find a power window area that can effectively clean the wafer without causing significant damage. That is, maintaining stable or controlled cavitation plays an important role in controlling acoustic mechanical forces below damage limits while enabling efficient removal of foreign particles from patterned structures.

Accordingly, a system and method for controlling bubble cavitation generated by an ultrasonic or high frequency ultrasonic device during a wafer cleaning process effectively removes fine foreign particles without damaging pattern structures on the wafer. It would be desirable to provide a system and method that can be effectively removed.

A semiconductor wafer cleaning system disclosed herein includes a wafer holder for temporarily restraining a semiconductor wafer during a cleaning process, an inlet for supplying a cleaning solution to the surface of the semiconductor wafer, and a first predetermined set point. a sound wave generator configured to operate alternately between a first predetermined period of time and a second predetermined time period of a second predetermined set value; a controller programmed to determine a value, first and second predetermined time periods, and a number of alternations of the first and second predetermined setpoints. Bubble cavitation in the cleaning liquid increases during a first predetermined period of time and decreases during a second predetermined period of time. The first predetermined period and the second predetermined period are connected so as to be continuous with each other. Therefore, the air bubbles in the cleaning liquid can be sufficiently cooled after cleaning for each first predetermined period, and damage to the semiconductor wafer can be avoided.

Other aspects, features and techniques will become apparent to those of ordinary skill in the art upon consideration of the detailed description of the embodiments that follow.

The accompanying drawings, which form part of this specification, are included to illustrate certain aspects of the present disclosure. A clearer conception of the present disclosure, and of the components and operation of the system to which it is provided, may be had by reference to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings. will be readily apparent. Here, the same reference numbers (if in more than one drawing) indicate the same elements. The disclosure may be better understood by reference to one or more of these drawings in combination with the description presented below. It should be noted that features illustrated in the drawings are not necessarily drawn to scale.

1 illustrates a wafer cleaning apparatus using an ultrasonic or high frequency ultrasonic device according to one embodiment of the present invention; FIG. 1 illustrates a wafer cleaning apparatus using an ultrasonic or high frequency ultrasonic device according to one embodiment of the present invention; FIG. Fig. 2 shows various shapes of ultrasonic or high frequency ultrasonic transducers; Fig. 2 shows various shapes of ultrasonic or high frequency ultrasonic transducers; Fig. 2 shows various shapes of ultrasonic or high frequency ultrasonic transducers; Fig. 2 shows various shapes of ultrasonic or high frequency ultrasonic transducers; Fig. 2 shows various shapes of ultrasonic or high frequency ultrasonic transducers; Fig. 2 shows various shapes of ultrasonic or high frequency ultrasonic transducers; Fig. 2 shows various shapes of ultrasonic or high frequency ultrasonic transducers; FIG. 2 illustrates bubble implosion during a wafer cleaning process; FIG. 4 illustrates transit cavitation damaging pattern structures on a wafer in a wafer cleaning process; FIG. 4 illustrates transit cavitation damaging pattern structures on a wafer in a wafer cleaning process; FIG. 10 is a diagram showing changes in thermal energy inside a bubble in an sonic wafer cleaning process; FIG. 10 is a diagram showing changes in thermal energy inside a bubble in an sonic wafer cleaning process; FIG. 10 is a diagram showing changes in thermal energy inside a bubble in an sonic wafer cleaning process; FIG. 3 illustrates a sonic wafer cleaning process with microjets ultimately generated; FIG. 3 illustrates a sonic wafer cleaning process with microjets ultimately generated; FIG. 3 illustrates a sonic wafer cleaning process with microjets ultimately generated; FIG. 2 illustrates an sonic wafer cleaning process according to one embodiment of the present invention; FIG. 2 illustrates an sonic wafer cleaning process according to one embodiment of the present invention; FIG. 2 illustrates an sonic wafer cleaning process according to one embodiment of the present invention; FIG. 2 illustrates an sonic wafer cleaning process according to one embodiment of the present invention; FIG. 2 illustrates an sonic wafer cleaning process according to one embodiment of the present invention; FIG. 4 illustrates an sonic wafer cleaning process according to another embodiment of the present invention; FIG. 4 illustrates an sonic wafer cleaning process according to another embodiment of the present invention; FIG. 4 illustrates an sonic wafer cleaning process according to another embodiment of the present invention; FIG. 4 illustrates an sonic wafer cleaning process according to another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates an sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates an sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates an sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to still yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to still yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates a sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates an sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 5 illustrates an sonic wafer cleaning process according to yet another embodiment of the present invention; FIG. 4 illustrates stable cavitation damaging patterned structures on a wafer in an sonic wafer cleaning process; FIG. 4 illustrates stable cavitation damaging patterned structures on a wafer in an sonic wafer cleaning process; FIG. 4 illustrates stable cavitation damaging patterned structures on a wafer in an sonic wafer cleaning process; 4 is a flowchart illustrating an alternative wafer cleaning process according to one embodiment of the invention; FIG. 3 illustrates a wafer cleaning process according to one embodiment of the invention; FIG. 3 illustrates a wafer cleaning process according to one embodiment of the invention; FIG. 3 illustrates a wafer cleaning process according to one embodiment of the invention; FIG. 4 illustrates a wafer cleaning process according to another embodiment of the invention; FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 2 illustrates bubble cavitation control to improve circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 4 is a diagram showing changes in bubble volume in response to sonic energy; FIG. 4 is a diagram showing changes in bubble volume in response to sonic energy; FIG. 4 is a diagram showing changes in bubble volume in response to sonic energy; FIG. 4 is a diagram showing changes in bubble volume in response to sonic energy; FIG. 2 illustrates a sonic wafer cleaning process that effectively cleans pattern features such as high aspect ratio via holes and trenches according to one embodiment of the present invention. FIG. 2 illustrates a sonic wafer cleaning process that effectively cleans pattern features such as high aspect ratio via holes and trenches according to one embodiment of the present invention. FIG. 2 illustrates a sonic wafer cleaning process that effectively cleans pattern features such as high aspect ratio via holes and trenches according to one embodiment of the present invention. FIG. 2 illustrates a sonic wafer cleaning process that effectively cleans pattern features such as high aspect ratio via holes and trenches according to one embodiment of the present invention. FIG. 4 illustrates another cleaning process according to an embodiment of the invention; FIG. 4 illustrates another cleaning process according to an embodiment of the invention; FIG. 4 illustrates another cleaning process according to an embodiment of the invention; FIG. 4 illustrates a wafer cleaning process using sonic energy according to another embodiment of the present invention; FIG. 4 illustrates a wafer cleaning process using sonic energy according to another embodiment of the present invention; 23 illustrates an example wafer cleaning apparatus for performing the wafer cleaning process illustrated in FIGS. 7-22 according to one embodiment of the present invention; FIG. 23 is a cross-sectional view of another wafer cleaning apparatus for performing the wafer cleaning process shown in FIGS. 7-22 according to one embodiment of the present invention; FIG. 1 illustrates a control system for monitoring operating parameters of a wafer cleaning process employing sonic energy in accordance with one embodiment of the present invention; FIG. 26 is a block diagram of the detection system shown in FIG. 25 according to one embodiment of the present invention; FIG. Figure 26 is a block diagram of the detection system shown in Figure 25 according to another embodiment of the present invention; 27 illustrates an example of the voltage attenuator circuit shown in FIG. 26 according to one embodiment of the present invention; FIG. 27 illustrates an example of the voltage attenuator circuit shown in FIG. 26 according to one embodiment of the present invention; FIG. 27 illustrates an example of the voltage attenuator circuit shown in FIG. 26 according to one embodiment of the present invention; FIG. 27 shows an example of the shaping circuit shown in FIG. 26 according to one embodiment of the present invention; FIG. 27 shows an example of the shaping circuit shown in FIG. 26 according to one embodiment of the present invention; FIG. 27 shows an example of the shaping circuit shown in FIG. 26 according to one embodiment of the present invention; FIG. FIG. 28 illustrates an example of the main controller of FIGS. 26 and 27 in accordance with one embodiment of the present invention; FIG. 28 illustrates an example of the main controller of FIGS. 26 and 27 in accordance with one embodiment of the present invention; FIG. 28 illustrates an example of the main controller of FIGS. 26 and 27 in accordance with one embodiment of the present invention; FIG. 12 illustrates the sonic power supply vibrating several times after the host computer shuts down the sonic power supply; 28 shows an example of the amplitude detection circuit shown in FIG. 27 according to one embodiment of the present invention; FIG. 28 shows an example of the amplitude detection circuit shown in FIG. 27 according to one embodiment of the present invention; FIG. 28 shows an example of the amplitude detection circuit shown in FIG. 27 according to one embodiment of the present invention; FIG. 4 is a flowchart illustrating a wafer cleaning process according to one embodiment of the invention; 4 is a flowchart illustrating a wafer cleaning process according to another embodiment of the invention;

One aspect of the present disclosure relates to controlling bubble cavitation in semiconductor wafer cleaning using sonic energy. Preferred embodiments of the present invention will now be described in detail with reference to the drawings.

1A and 1B are diagrams illustrating a wafer cleaning apparatus using an ultrasonic or high frequency ultrasonic apparatus according to one embodiment of the present invention. FIG. 1A is a cross-sectional view of a wafer cleaning apparatus including a wafer chuck 1014 that holds a wafer 1010, a rotary drive module 1016 that drives the wafer chuck 1014, and a nozzle 1012 that supplies a cleaning solution 1032 to the surface of the wafer 1010. FIG. Cleaning fluid 1032 may be cleaning chemicals or deionized water. The wafer cleaning apparatus also includes an ultrasonic or high frequency ultrasonic device 1003 positioned above the wafer 1010 . Then, with the rotation of the wafer 1010 and the constant flow of the cleaning liquid 1032 from the nozzle 1012 , a film of the cleaning liquid 1032 of thickness d is maintained between the wafer 1010 and the acoustic wave device 1003 . The ultrasonic or high frequency ultrasonic device 1003 further includes a piezoelectric transducer 1004 acoustically coupled to a resonator 1008 in contact with the cleaning liquid. Piezoelectric transducer 1004 is electrically excited to vibrate, and resonator 1008 transmits high frequency sonic energy to cleaning liquid 1032 . The cavitation of the air bubbles generated by the high frequency acoustic energy vibrates and dislodges foreign particles or contaminants on the surface of the wafer 1010 .

Referring again to FIG. 1A, the wafer cleaning apparatus also includes arm 1007 . An arm 1007 is coupled to the sonic device 1003 to change the liquid film thickness d by moving the sonic device 1003 in the vertical direction Z. Vertical drive module 1006 moves arm 1007 vertically. Both vertical drive module 1006 and rotary drive module 1016 are controlled by controller 1088 .

As shown in FIG. 1B, which is a plan view of the wafer cleaning apparatus shown in FIG. 1A, sonic device 1003 covers only a small area of wafer 1010. FIG. Therefore, wafer 1010 must rotate to receive uniform acoustic energy across its entirety. Although only one sonic device 1003 is shown in FIGS. 1A and 1B, in other embodiments, multiple sonic devices may be used simultaneously and intermittently. Similarly, two or more nozzles 1012 may be used to more uniformly spray the cleaning liquid 1032 .

2A-2G are diagrams illustrating various shapes of ultrasonic or high frequency ultrasonic transducers. 2A shows a triangle or pie shape, FIG. 2B shows a rectangle, FIG. 2C shows an octagon, FIG. 2D shows an ellipse, FIG. 2E shows a semicircle shape, and FIG. 2F shows a quarter circle shape. , and FIG. 2G shows a perfect circular shape. Acoustic transducers in each of these shapes may be used in place of piezoelectric transducer 1004 in acoustic device 1003 shown in FIG.

FIG. 3 is a diagram illustrating implosion of bubbles during the wafer cleaning process. The shape of bubble 3012 is gradually compressed from spherical A to apple-shaped G as sonic energy is applied to bubble 3012 . Eventually, bubble 3012 reaches implosion state I and forms a microjet. As shown in FIGS. 4A and 4B, the microjets are very violent (sometimes reaching thousands of atmospheres and thousands of degrees Celsius), especially when the pattern structure element size t shrinks below 70 nm. may damage the micropatterned structure 4034.

4A and 4B illustrate transit cavitation damaging pattern structures on a wafer in a wafer cleaning process. As shown in FIG. 4A, bubbles 4040, 4042 and 4044 are formed by acoustic cavitation above patterned structures 4034 on semiconductor wafer 4010. As shown in FIG. The pattern structure 4034 includes multiple elements that need to be cleaned including, but not limited to, fins, via holes, trenches, and the like. Bubbles 4044 become very violent microjets reaching several thousand atmospheres and several thousand degrees Celsius. As shown in FIG. 4B, when the microjet is generated, part of the pattern structure 4034 is blown away. Such damage is more severe for wafers with device feature sizes of 70 nm and below.

5A-5C are diagrams showing changes in thermal energy inside bubble 5016 during the wafer cleaning process. When air bubble 5016 is subjected to positive sonic pressure, air bubble 5016 reduces its volume, as shown in FIG. 5A. In the process of this volume contraction, the sonic pressure P _M acts on the bubble 5016 and mechanical work is converted into thermal energy within the bubble 5016 . Accordingly, the temperature T of the gas and/or vapor inside bubble 5016 increases, as shown in FIG. 5B. The relationship between various parameters can be expressed by the following equations.

p ₀ v ₀ /T ₀ =pv/T (1)

where p ₀ is the pressure inside the bubble before compression, v ₀ is the initial volume of the bubble 5016 before compression, T ₀ is the temperature of the gas inside the bubble before compression, and p is the pressure inside the bubble during compression. , v is the volume of the bubble during compression, and T is the temperature of the gas inside the bubble during compression.

To simplify the calculations, we assume that the temperature of the gas does not change during compression, or that the compression is very slow and the temperature rise is offset by the liquid surrounding the bubbles. In this case, the mechanical work w _m due to the sonic pressure P _M in one bubble compression (from N unit volume to 1 unit volume, that is, compression ratio=N) can be expressed as follows.

Here, S is the cross-sectional area of the cylinder, _X0 is the length of the cylinder, and _p0 is the gas pressure inside the cylinder before compression. Equation (2) above does not take into account the temperature rise factor during compression, so the actual pressure inside the bubble will be higher due to the temperature rise. Therefore, the actual mechanical work due to sonic pressure will be greater than that calculated by equation (2).

Part of the mechanical work due to the sonic pressure is converted into thermal energy and partly mechanical energy of the high-pressure gas and/or vapor inside the bubble, which thermal energy contributes completely to the temperature rise inside the bubble (bubble ) and that the mass of the gas inside the bubble remains constant before and after compression, the temperature rise ΔT can be expressed by the following equation.

ΔT=Q/(mc)=βwm/(mc)=βSx ₀ p ₀ ln(x ₀ )/(mc) (3)

where Q is the thermal energy converted from mechanical work, β is the ratio of thermal energy to total mechanical work due to sonic pressure, m is the mass of the gas inside the bubble, and c is the gas is the specific heat coefficient. β=0.65, S=1E ⁻¹² m ² , x ₀ =1000 μm=1E ⁻³ m (compression ratio N=1000), p ₀ =1 kg/cm ² =1E ⁴ kg/m ² , m=8. Substituting 9E ⁻¹⁷ kg (for hydrogen gas) and c=9.9E ³ J/(kg ⁰ k) into the above equation (3), ΔT=50.9°C.

As shown in FIG. 5B, when the bubble reaches a minimum size of 1 micron, the gas temperature _T1 inside the bubble after the first compression is calculated as follows.

T ₁ =T ₀ +ΔT=20° C.+50.9° C.=70.9° C. (4)

At such high temperatures, some liquid molecules around the bubble evaporate. After that, the sonic pressure becomes negative and the bubble size begins to expand. In this reverse process, hot gas and/or vapor with pressure _PG will do work on the surrounding liquid surface. At the same time, as shown in FIG. 5C, the negative sonic pressure P _M also does some work on the surrounding liquid because the sonic pressure P _M pulls the bubble in the direction of expansion. As a result of these actions working together, the thermal energy inside the bubble cannot be completely released or converted into mechanical energy, so the temperature of the gas inside the bubble is reduced to the original gas temperature _T0 or the liquid temperature. cannot be cooled. After the first cycle of cavitation, the temperature _T2 of the gas and/or vapor inside the bubble will be somewhere between _T0 and _T1 , as shown in FIG. 6B. Here, _T2 can be expressed as follows.

T ₂ =T ₁ −δT=T ₀ +ΔT−δT (5)

Here, δT is the width of temperature decrease after the bubble expands once, and δT is smaller than ΔΔT.

When the second cycle of bubble cavitation reaches the minimum bubble size, the temperature _T3 of the gas and/or vapor inside the bubble is:

T ₃ =T ₂ +ΔT=T ₀ +ΔT−δT+ΔT=T ₀ +2ΔT−δT (6)

At the end of the second cycle of bubble cavitation, the temperature _T4 of the gas and/or vapor inside the bubble is:

T ₄ =T ₃ -δT=T ₀ +2ΔT-δT-δT=T ₀ +2ΔT-2δT (7)

Similarly, when the nth cycle of bubble cavitation reaches the minimum bubble size, the temperature T _2n−1 of the gas and/or vapor inside the bubble is:
T _2n−1 =T ₀ +nΔT−(n−1)δT (8)

At the end of the nth cycle of bubble cavitation, the temperature _T2n of the gas and/or vapor inside the bubble is:

T _2n =T ₀ +nΔT−nδT=T ₀ +n(ΔT−δT) (9)

From equation (8), the implosion cycle number _ni can be expressed as follows.

n _i =(T _i −T ₀ −ΔT)/(ΔT−δT)+1 (10)

From equation (10), implosion time τ _i can be expressed as follows.

τ _i =n _i t ₁ =t ₁ ((T _i −T ₀ −ΔT)/(ΔT−δT)+1)

=n _i /f ₁ =((T _i −T ₀ −ΔT)/(ΔT−δT)+1)/f ₁ (11)

where _t1 is the cycle period and _f1 is the frequency of the ultrasound/high-frequency ultrasound.

Equations (10) and (11) allow the number of implosion cycles n _i and implosion time τ _i to be calculated. Implosion cycle number n _i , implosion time _{τ i and ( ΔT} -δT) is shown in Table 1.

Figures 6A-6C illustrate the sonic wafer cleaning process when microjets are finally generated and the processing parameters follow equations (1)-(11). As shown in FIG. 6A, power (P) is continuously supplied to the sonic device to generate bubble cavitation in the cleaning liquid. As the number of bubble cavitation cycles n increases, the temperature of the gas and/or vapor increases as shown in FIG. 6B. As such, more molecules on the surface of the bubble evaporate toward the interior of the bubble 6082, resulting in its size increasing over time, as shown in FIG. 6C. Eventually, the temperature within the bubble 6082 during compression reaches the implosion temperature T _i (typically, T _i is as high as several thousand degrees Celsius) and violent microjets 6080 are generated, as shown in FIG. 6C. . Therefore, stable cavitation must be maintained and bubble implosion or microjets must be avoided in order to avoid damage to the patterned structures of the wafer during cleaning.

Figures 7A-7E illustrate an sonic wafer cleaning process according to one embodiment of the present invention. FIG. 7A shows the waveform of the power output intermittently applied to the sonic device to generate bubble cavitation in the cleaning liquid. FIG. 7B shows temperature curves corresponding to each cycle of cavitation. FIG. 7C shows that during each cycle of cavitation, the bubble size increases during period τ ₁ and decreases when power is turned off during period τ ₂ .

A detailed process multiple steps for avoiding bubble implosion according to the first embodiment of the present invention is shown in FIG. 7D. The process begins at step 7010 by placing an ultrasonic or high frequency ultrasonic device near the top surface of the wafer being cleaned. In step 7020, a cleaning solution, either chemical or gas doped water, is introduced over the wafer and fills the gap between the wafer and the sonic device with the cleaning solution. At step 7030, the rotation or oscillation of the wafer held by the chuck is initiated. At step 7040, a power source having frequency _f1 and power level P1 is applied to the acoustic wave device. In step 7050, the power supply output is reduced to 0 before the temperature of the gas and/or vapor inside the bubble reaches the implosion temperature T _i or the period τ ₁ reaches the time τ _i calculated by equation (11). do. The temperature of the gas and/or vapor inside the bubble then begins to drop since the temperature of the cleaning liquid is much lower than the temperature of the gas. In step 7060, after the temperature of the gas and/or vapor inside the bubble has decreased to room temperature _T0 , or after the duration has reached _τ2 (during period _τ2 , the power supply output is set to 0), the power supply The output is restored to frequency _f1 and power level P1. At step 7070, the wafer is inspected for cleanliness. Then, if the wafer is not yet cleaned to the desired degree, steps 7010 through 7060 are repeated. Alternatively, cleanliness checks may not be performed every cycle. The number of cycles to be used may be determined experimentally in advance using sample wafers.

Referring again to FIG. 7D, in step 7050, period τ ₁ must be shorter than τ _i calculated using equation (11) to avoid bubble implosion. At step 7060, the temperature of the gas and/or vapor inside the bubbles need not be cooled to room temperature or the cleaning liquid temperature. Rather, it can be at room temperature or at a temperature above the wash liquid temperature. Preferably, this temperature is well below the implosion temperature T _i .

According to equations (8) and (9), the implosion time τ _i can be calculated if (ΔT−δT) is known. However, usually (ΔT-δT) cannot be calculated and cannot be easily measured directly. On the one hand, τ _i can be determined experimentally.

FIG. 7E is a flowchart illustrating a process for empirically determining implosion times τ _i . First, at step 7210, five different time periods τ ₁ are illustratively selected as design of experiments (DOE) conditions based on Table 1. At step 7220, the period τ ₂ is set to be at least 10 times longer than the selected period τ ₁ , preferably 100 times longer for the first screening test. In step 7230, with the power level fixed at _P0 , five different wafers with the same specific pattern structure are separately cleaned under the above five DOE conditions. Here, P ₀ is the power level at which pattern structures are reliably damaged when performing continuous mode (non-pulsed mode) as shown in FIG. 6A. In step 7240, the five wafers are inspected for damage status by an electron microscope (SEM) or wafer pattern damage investigation tool such as AMAT SEM Vision or Hitachi IS3000. This allows the implosion time τ _i to be narrowed to a specific range. The percentage of damaged pattern structure elements can be calculated by dividing the total number of damaged pattern structure elements inspected by the SEM by the total number of pattern structure elements. There may be other methods of determining the percentage of pattern structure elements that are damaged. For example, final wafer yield may be used as an indicator of the percentage of pattern features that are damaged.

By repeating steps 7210-7240 above, the range of implosion times τ _i can be narrowed. After obtaining the implosion time τ _i , the period τ ₁ may be set to a value less than 0.5*τ _i for safety margin. The following paragraphs describe examples of such experiments.

Assuming that the pattern structure is formed by 55 nm polysilicon gate lines, the ultrasonic frequency is 1 MHz, and the ultrasonic wave is placed in the gaps to achieve uniform energy deposition within the wafer and from wafer to wafer. It is produced by an ultrasound/high frequency ultrasound device manufactured by Prosys, Inc. operating in an oscillating mode (disclosed in the specification of PCT Application No. PCT/CN2008/073471). Other experimental parameters and final pattern damage data are summarized in Table 2 below.

In experiments, for τ ₁ =2 ms (2000 cycles), the sonic cleaning process described above produces 1216 damage sites for a patterned structure with an element size of 55 nm. For τ ₁ =0.1 ms (100 cycles), the sonic cleaning process produces zero (0) damaged sites for the same pattern structure. The implosion time τ _i is therefore a value between 0.1 ms and 2 ms. An additional test with a narrower range of τ ₁ allows a narrower range of τ _i .

In the above experiments, the number of cycles depends on the power density and frequency of the ultrasound or high-frequency ultrasound, with higher power densities leading to fewer cycles and lower frequencies leading to fewer cycles. From the above experiments, when the power density of ultrasound or high-frequency ultrasound is greater than 0.1 Watt/cm ² and the frequency of ultrasound or high-frequency ultrasound is 1 MHz or less, the number of cycles without damage is greater than 2,000. can be expected to be small. It is expected that the number of cycles will increase as the frequency increases into the range greater than 1 MHz or the power density decreases below 0.1 watts/cm ² .

After obtaining the period τ ₁ , the period τ ₂ can be experimentally obtained based on the same DOE method as described above. In this case, τ ₁ is fixed at a given value and τ ₂ is gradually shortened with each DOE until damage is observed in the pattern structure. As the period _τ2 becomes shorter, the temperature of the gas and/or vapor inside the bubble cannot be sufficiently lowered, the average temperature of the gas and/or vapor inside the bubble gradually increases, and finally the bubble implodes. cause. The time that causes this implosion is called the critical cooling time _τc . Knowing the critical cooling time τ _c allows us to set the period τ ₂ to a value greater than 2*τ _c with a safety margin.

Thus, the parameters of the cleaning process may be determined such that the yield enhancement caused by the cleaning effect of applying sonic energy is greater than the yield loss caused by the damage of applying said sonic energy. A predetermined threshold for damage rate may be specified by the customer, for example. The parameters of the cleaning process may be determined such that the damage rate is less than a predetermined threshold, or substantially zero or exactly zero. The predetermined threshold may be, for example, 10%, 5%, 2% or 1%. The damage rate is substantially zero if the final yield of wafer fabrication is substantially free of any damage caused by the cleaning process. In other words, the damage caused by the cleaning process is acceptable from the point of view of the overall manufacturing process. Damage rates can be determined by examining sample wafers using an electron microscope, as described above.

Figures 8A-8D illustrate an sonic wafer cleaning process according to another embodiment of the present invention. In this sonic wafer cleaning process, the amplitude of the power supply P is varied over time rather than maintained at a constant level P1 as in step 7040 of FIGS. It remains the same as shown. In one embodiment, as shown in FIG. 8A, the amplitude P of the power supply increases during period _τ1 . In another embodiment, as shown in FIG. 8B, the power supply amplitude P decreases during the period _τ1 . In yet another embodiment, the power supply amplitude P decreases at the beginning of period τ ₁ and then increases, as shown in FIG. 8C. In the embodiment shown in FIG. 8D, the power supply amplitude P increases at the beginning of period _τ1 and then decreases.

Figures 9A-9D illustrate an sonic wafer cleaning process according to yet another embodiment of the present invention. In this sonic wafer cleaning process, the frequency of the power supply is varied over time rather than being held at a constant value f ₁ as in step 7040 of FIGS. 7A and 7D, but otherwise shown in FIGS. remains the same as before. In one embodiment, as shown in FIG. 9A, the frequency of the power supply is f ₁ at the beginning of period τ ₁ and then f ₃ . where _f1 is a higher frequency than _f3 . As shown in FIG. 9B, in one embodiment, the frequency of the power supply is increased to f ₃ at the beginning of period τ ₁ and then to f ₁ . As shown in FIG. 9C, in one embodiment, the frequency of the power supply changes from f ₃ to f ₁ for a period of time τ ₁ and then back to f ₃ . As shown in FIG. 9D, in one embodiment, the frequency of the power supply changes from f ₁ to f ₃ during a period of time τ ₁ and then back to f ₁ .

Similar to the cleaning process shown in FIG. 9C, in one embodiment, the power supply frequency is first set to _f1 , then to _f3 , and finally to _f4 during period _τ1 . where _f4 is smaller than _f3 and _f3 is smaller than _f1 .

Further, similar to the cleaning process shown in FIG. 9C, in one embodiment, the power supply frequency is first set to _f4 , then to _f3 , and finally to _f1 in time period _τ1 . where _f4 is smaller than _f3 and _f3 is smaller than _f1 .

Further, similar to the cleaning process shown in FIG. 9C, in one embodiment, the power supply frequency is first set to _f1 , then to _f4 , and finally to _f3 in time period _τ1 . where _f4 is smaller than _f3 and _f3 is smaller than _f1 .

Further, similar to the cleaning process shown in FIG. 9C, in one embodiment, the power supply frequency is first set to _f3 , then to _f4 , and finally to _f1 during period _τ1 . where _f4 is smaller than _f3 and _f3 is smaller than _f1 .

Further, similar to the cleaning process shown in FIG. 9C, in one embodiment, the power supply frequency is first set to _f3 , then to _f1 , and finally to _f4 during period _τ1 . where _f4 is smaller than _f3 and _f3 is smaller than _f1 .

_Further , similar to the cleaning process shown in FIG. 9C, in one embodiment, the power supply frequency is first set to _f4 , then to f1, and finally to _f3 during period _τ1 . where _f4 is smaller than _f3 and _f3 is smaller than _f1 .

Figures 10A-10C illustrate an sonic wafer cleaning process according to yet another embodiment of the present invention. Referring to FIG. 10A, similar to the cleaning process shown in FIG. 7A, a power source with power level P1 and frequency _f1 is applied to the sonic device at time period _τ1 . However, in period τ ₂ , the power is reduced to level P2 rather than dropping to 0 as shown in FIG. 7A. Therefore, the temperature of the gas and/or vapor inside the bubble drops to T ₀ +ΔT ₂ , as shown in FIG. 10B.

FIG. 10C is a flowchart illustrating operations of the wafer cleaning process shown in FIGS. 10A and 10B. Step 10010 places an ultrasonic or high frequency ultrasonic device near the top surface of the wafer being cleaned. In step 10020, a cleaning liquid, either chemical or gas doped water, is introduced over the wafer and fills the gap between the wafer and the sonic device with the cleaning liquid. At step 10030, the chuck holding the wafer begins to rotate for the cleaning process. At step 10040, a power source having frequency _f1 and power level P1 is applied to the acoustic wave device. In step 10050, before the temperature of the gas and/or vapor inside the bubble reaches the implosion temperature T _i or the period τ ₁ reaches the period τ _i calculated by equation (11), the frequency is reduced to f _{1 .} while maintaining the power level down to P2. In step 10060, the power level is returned to P1 after the temperature of the gas and/or vapor inside the bubble has decreased to near room temperature _T0 or after the duration has reached _τ2 . At step 10070, the wafer is inspected for cleanliness. Then, if the wafer is not yet cleaned to the desired degree, steps 10010 through 10060 are repeated. Alternatively, cleanliness checks may not be performed every cycle. The number of cycles to be used may be determined experimentally in advance using sample wafers.

11A-11B illustrate an sonic wafer cleaning process according to yet another embodiment of the present invention. This sonic wafer cleaning process is similar to that shown in FIGS. In the wafer cleaning process shown in FIGS. 11A and 11B, instead of maintaining the power supply frequency at f ₁ , the frequency is reduced to f ₂ for a period of time τ ₂ . The power level P2 should be sufficiently smaller than P1, preferably 1/5 or 1/10, so that the temperature of the gas and/or vapor inside the bubble can be lowered to near room temperature _T0 .

Figures 12A-12B illustrate an sonic wafer cleaning process according to yet another embodiment of the present invention. The only difference between this cleaning process and that shown in FIGS. 10A-10C is step 10050 . In this wafer cleaning process, the power frequency is increased to _f2 while the power level P2 in the period _τ2 is substantially the same as P1.

Figures 13A-13B illustrate an sonic wafer cleaning process according to yet another embodiment of the present invention. The only difference between this cleaning process and that shown in FIGS. 10A-10C is step 10050 . In this wafer cleaning step, the power frequency is increased to _f2 while the power level is decreased from P1 to P2 in period _τ2 .

Figures 14A-14B illustrate an sonic wafer cleaning process according to yet another embodiment of the present invention. The only difference between this cleaning process and that shown in FIGS. 10A-10C is step 10050 . In this wafer cleaning process, the power level is increased from P1 to P2 in period _τ2 while the power supply frequency is increased from _f1 to _f2 . The power level _P2 may be slightly higher than _P1 because the sonic energy does not heat the bubble as strongly since the frequency f2 is higher than f1, but the temperature of the gas and/or vapor inside the bubble increases to should not be too high to ensure that it decreases during the period τ ₂ as shown in .

15A-15C illustrate stable cavitation damaging patterned structures on a wafer in an sonic wafer cleaning process. As shown in FIG. 15A, pattern structures 15034 having a spacing W are formed on the wafer 15010 . Some bubbles 15046 formed by the cavitation process are in the interstices of the pattern structure 15034 . As bubble cavitation continues, the temperature of the gas and/or vapor within the bubble 15048 increases and the size of the bubble 15048 increases, as shown in FIG. 15B. When the bubble 15048 size is larger than the spacing W, the expansion force of bubble cavitation can damage the pattern structure 15034, as shown in FIG. 15C. Therefore, new wafer cleaning processes are needed.

The damage area caused by bubble expansion shown in FIG. 15C may be smaller than the damage area caused by bubble implosion shown in FIG. 4B. For example, expansion of a bubble can result in a damage site on the order of 100 nm, while implosion of a bubble may result in a larger damage site on the order of 1 μm.

Figure 15D is a flowchart illustrating an alternative wafer cleaning process according to one embodiment of the invention. An alternative wafer cleaning process begins at step 15210 by placing an ultrasonic or high frequency ultrasonic device near the top surface of the wafer being cleaned. In step 15020, a cleaning liquid, either chemical or gas doped water, is introduced over the wafer and fills the gap between the wafer and the sonic device with the cleaning liquid. At step 15230, the rotation or oscillation of the wafer held by the chuck is initiated. At step 15240, a power source having frequency _f1 and power level P1 is applied to the acoustic wave device. At step 15250, the power supply output is zeroed before the bubble size reaches the W spacing value. The temperature of the gas and/or vapor inside the bubble then begins to drop since the temperature of the cleaning liquid is much lower than the temperature of the gas. In step 15260, after the temperature of the gas and/or vapor inside the bubble has decreased to room temperature _T0 , or after the duration has reached _τ2 (during period _τ2 , the power supply output is set to 0), the power supply The output is restored to frequency _f1 and power level P1. At step 15270, the wafer is inspected for cleanliness. Then, if the wafer is not yet cleaned to the desired degree, steps 15210 through 15260 are repeated. Alternatively, cleanliness checks may not be performed every cycle. The number of cycles to be used may be determined experimentally in advance using sample wafers.

Referring again to FIG. 15D, the temperature of the gas and/or vapor inside the bubble does not need to be cooled to room temperature _T0 , but preferably should be well below the implosion temperature _T1 . be. At step 15250 , the bubble size can be made slightly larger than the spacing W of the pattern features 15034 as long as the expansion force of the bubbles does not break or damage the pattern features 15034 .

Referring again to FIG. 15D, the duration of step 15240 can be experimentally obtained as τ ₁ from the procedure shown in FIG. 7E. In some embodiments, the wafer cleaning process shown in FIGS. 7-14 can be combined with the wafer cleaning process shown in FIG.

Figures 16A-16C illustrate a wafer cleaning process according to one embodiment of the present invention. This wafer cleaning process is similar to that shown in Figures 7A-7E, except for step 7050 in Figure 7D. In _{this wafer} cleaning process, the power supply _output is set to the positive DC value shown in FIG. 16A or the negative DC value shown in FIGS. 16B and 16C. As a result, the temperature of the gas and/or vapor inside the bubble begins to drop, since the temperature of the cleaning liquid is much lower than the temperature of the gas and/or vapor. In some embodiments, the amplitude of the DC output, either positive or negative, is greater than the amplitude of the power level P1 applied during the period _τ1 to produce bubble cavitation in the cleaning liquid (not shown). ), equal (see FIGS. 16A and 16B), or smaller (see FIG. 16C).

FIG. 17 illustrates a wafer cleaning process according to another embodiment of the invention. This wafer cleaning process is also similar to that shown in Figures 7A-7E, except for step 7050 in Figure 7D. This wafer cleaning step inverts the phase of the power supply output while maintaining the same frequency f ₁ applied during period τ ₁ , so that bubble cavitation can be stopped quickly. As a result, the temperature of the gas and/or vapor inside the bubble begins to drop, since the temperature of the cleaning liquid is much lower than the temperature of the gas and/or vapor.

Referring again to FIG. 17, the power level in period _τ2 is P2, which in different embodiments is greater than, equal to, or less than P1, the power level in period _τ1 . can be In one embodiment, the power supply frequency in period τ ₂ may be different from f ₁ if the phase is reversed. In some embodiments, the frequency f ₁ of the ultrasonic or high frequency ultrasonic power source is between 0.1 MHz and 10 MHz.

Figures 18A-18J illustrate bubble cavitation control that enhances the circulation of fresh cleaning liquid in via holes or trenches of semiconductor wafers. FIG. 18A is a cross-sectional view of a plurality of via holes 18034 formed in wafer 18010. FIG. Here, the diameter of the via hole opening is indicated as W1. Bubbles 18012 created within via hole 18034 by sonic energy facilitate removal of impurities such as residue and particles therefrom. FIG. 18B is a plan view of the via hole shown in FIG. 18A.

FIG. 18C is a cross-sectional view of a plurality of trenches 18036 formed in wafer 18010. FIG. Similarly, bubbles 18012 generated within trenches 18036 by sonic energy facilitate removal of impurities such as residue and particles therefrom. FIG. 18D is a plan view of trench 18036 shown in FIG. 18C.

The maximum amount of bubbles that can be contained in a pattern feature such as via hole 18034, trench 18036, or another recessed area defines the saturation point R _s . If the amount of bubbles exceeds the saturation point R _s , the cleaning liquid will be blocked by the bubbles and will be less likely to reach the bottom of the sidewalls of via hole 18034 or trench 18036, adversely affecting cleaning performance. When the amount of bubbles is below the saturation point R _s , there is sufficient effectiveness of the cleaning liquid inside pattern features such as via holes 18034 or trenches 18036 to obtain good cleaning performance.

Below the saturation point, the ratio R of the total bubble volume _VB to the volume of the via hole or trench or recessed space _VVTR is:

R= _VB / _VVTR < _Rs

And the ratio R at the saturation point R _s is as follows.

R= _VB / _VVTR < _Rs

The total bubble volume in pattern features such as via holes 18034, trenches 18036 or other recessed spaces is:

V _B =N*V _B

where N is the number of bubbles in the pattern element and _VB is the average volume of a single bubble.

As shown in FIGS. 18E-18H, when ultrasonic or high-frequency ultrasonic energy is applied to the cleaning liquid, the size of the bubble 18012 gradually expands to a certain volume, thereby filling the via hole or trench or recessed space V. The ratio R of the total bubble volume _VB to the volume of _{the VTR} is near or above the saturation point _Rs . The expanded bubble 18012 blocks the replacement of the cleaning solution and the removal of impurities in the via hole or trench. In such cases, acoustic energy cannot efficiently transfer to the via holes or trenches to reach their bottoms and sidewalls, and particles, residue and other impurities 18048 become trapped within the via holes or trenches. This can easily occur in advanced semiconductor processes where the critical dimension W1 becomes smaller.

As shown in FIGS. 18I-18J, the size expansion of the bubble 18012 by ultrasound or high-frequency ultrasound energy is within limits, and the ratio R of the total bubble volume V _B to the volume of the via hole, trench or recessed space V _VTR is , much lower than the saturation point R _s . The fresh cleaning liquid 18047 circulates freely in the via holes or trenches due to small bubble cavitation inside the pattern structure elements, so that impurities 18048, e.g., residues and particles, are easily removed from the pattern structure elements. Extruded for good cleaning performance.

Since the total volume of bubbles in pattern features such as via holes or trenches is determined by the number and size of the bubbles, controlling the bubble size expansion due to cavitation is critical to the cleaning performance of wafers with high aspect ratio pattern features. is important.

19A-19D are diagrams showing changes in bubble volume in response to sonic energy. During the first cycle of cavitation, the bubble volume is compressed from V ₀ to V ₁ via a positive sonic power cycle and then expands to V ₂ via a negative sonic power cycle. However, the bubble temperature T ₂ corresponding to V ₂ is higher than the temperature T ₀ corresponding to V ₀ , so the volume V ₂ is greater than the volume V ₀ as shown in FIG. 19B. This volume increase is caused by the liquid molecules surrounding the bubble evaporating at higher temperatures. Similarly, the bubble volume _V3 after the second compression will be somewhere between _V1 and _V2 , as shown in FIG. 19B. V ₁ , V ₂ and V ₃ can be expressed as follows.

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 the amount of volumetric compression of the bubble through one compression by the positive pressure generated by the ultrasound/high frequency ultrasound, and δV is the negative pressure generated by the ultrasound/high frequency ultrasound. (δV-ΔV) is the volume increase due to the temperature rise (ΔT-δT) due to one cycle calculated by Equation (5). be.

After a second cycle of bubble cavitation, the temperature continues to rise and the bubbles expand to a larger size. The volume _V4 of gas and/or vapor inside the bubble is:

V ₄ =V ₃ +δV=V ₀ +δV−2ΔV+δV=V ₀ +2(δV−ΔV) (15)

After the third compression, the volume _V5 of gas and/or vapor inside the bubble is:

V ₅ =V ₄ -ΔV=V ₀ +2(δV-ΔV)-ΔV=V ₀ +2δV-3ΔV (16)

Similarly, when the n-th cycle of bubble cavitation reaches the minimum bubble size, the volume of gas and/or vapor inside the bubble V _2n−1 is:

V _2n−1 =V ₀ +(n−1)δV−nΔV=V ₀ +(n−1)δV−nΔV (17)

At the end of the nth cycle of bubble cavitation, the volume of gas and/or vapor within the bubble V _2n is:

V _2n =V ₀ +n(δV−ΔV) (18)

Limit the bubble volume to a desired volume V _i that is below a value or saturation point that has sufficient physical mobility to block cleaning fluid reshuffling at pattern structure elements such as via holes, trenches, or other recessed areas. , the number of cycles n _i can be expressed as follows.

n _i =(V _i −V ₀ −ΔV)/(δV−ΔV)+1 (19)

From equation (19), the desired time τ _i to achieve V _i can be expressed as:

τ _i =n _i t ₁ =t ₁ ((V _i −V ₀ −ΔV)/(δV−ΔV)+1)

=n _i /f ₁ =((V _i −V ₀ −ΔT)/(δV−ΔV)+1)/f ₁ (20)

where _t1 is the cycle period and _f1 is the frequency of the ultrasound/high-frequency ultrasound. Therefore, the desired number of cycles n _i and the desired time τ _i to prevent the cell size from reaching the blocking level of the pattern structure element can be calculated from equations (19) and (20).

Note that as the number of bubble cavitation cycles n increases, the temperature of the gas and/or vapor inside the bubble increases, so more molecules on the surface of the bubble evaporate into the bubble. Therefore, the size of bubble 19082 will increase further and become larger than the value calculated by equation (18). In operation, the bubble size is determined by the experimental method disclosed below, so the size of the bubble affected by the evaporation of liquid or water onto the inner surface of the bubble due to temperature rise is here theoretically do not discuss specific details. As the average single cell volume increases, the ratio R of the total cell volume _VB to the volume _VVTR of the via hole, trench, or other recessed space increases continuously from _R0 , as shown in FIG. 19D.

As the bubble volume increases, the diameter of the bubble eventually becomes the same size or the same order of size as the pattern structure element W1 of the via hole 18034 shown in FIGS. 18A and 18B or the trench 18036 shown in FIGS. 18C and 18D. will reach. And, especially if the aspect ratio (depth/width) is 3 or greater, the air bubbles inside the via holes 18034 and trenches 18036 will block further ultrasonic/high frequency ultrasonic energy from entering these bottoms. Therefore, contaminants or particles at the bottom of such deep via holes or trenches cannot be effectively removed or cleaned. Therefore, a new cleaning process is proposed to prevent bubbles from growing to critical dimensions that would block the replacement path of the cleaning solution in the pattern features of via holes or trenches.

20A-20D illustrate a sonic wafer cleaning process that effectively cleans pattern features such as high aspect ratio via holes and trenches according to one embodiment of the present invention. This wafer cleaning process limits the size of bubbles in cavitation due to sonic energy. FIG. 20A shows the waveform of the power supply output with power level P1 during period τ ₁ and turned off during period τ ₂ . FIG. 20B shows bubble volume curves corresponding to each cycle of cavitation. FIG. 20C shows how the bubble size expands with each cycle of cavitation. FIG. 20D shows a curve of the ratio _R of the total cell volume _VB to the volume VVTR of a via hole, trench, or other recessed space.

R= _VB / _VVTR = _Nvb / _VVTR

According to _the above equation, if the average single bubble volume expands by acoustic cavitation over a given number of cycles n in the period τ ₁ , then the total bubble volume V The ratio R of _B increases from R ₀ to R _n . R _n is then controlled below the saturation point R _s as follows.

_Rn = _VB / _VVTR = _Nvb / _VVTR < _Rs

And if the average single bubble volume returns to its original size in the cooling process in period _τ2 , the ratio _R of the total bubble volume VB to the volume of the via hole, trench or other recessed space _VVTR is from _Rn to _R0 to

Referring again to FIG. 20B, the bubble expands to a large volume Vn with ultrasonic/high frequency ultrasonic power applied to the cleaning liquid in period _τ1 . In this state, the path of mass transfer is partially blocked. And the fresh cleaning solution cannot sufficiently flow into the bottom and sidewalls of the via hole or trench. Meanwhile, particles, residue and other impurities trapped in via holes and trenches cannot be removed efficiently. However, this state transitions to the next state where the bubble contracts when the ultra-high/high frequency ultrasonic power is turned off to cool the bubble in period τ ₂ , as shown in FIG. 20A. In this cool state, fresh cleaning liquid can flow into the via holes and trenches to clean their bottoms and sidewalls. When the ultrasonic/high frequency ultrasonic power is turned on again in the next cycle, particles, residue, and other impurities can be dislodged from the via holes and trenches by the pulling force generated by the increased bubble volume. High aspect ratio pattern features in via holes, trenches, and other recessed areas on wafer substrates can be effectively cleaned when the two conditions are alternated in a cleaning process using ultrasonic waves/high frequency ultrasonic waves. can.

The cooling state in period τ ₂ plays an important role in this cleaning process. Also, the condition (τ ₁ <τ _i ) is desirable to limit the bubble size. In the following method, we can experimentally determine the period τ ₂ for contracting the bubble size during the cooling state and the period τ ₁ for limiting the bubble expansion to the path blockage size. This experiment was performed using an ultrasonic/high frequency ultrasonic device coupled with a chemical liquid to clean a patterned substrate having small pattern features such as via holes and trenches with traceable residues, Evaluate cleaning performance.

The first step is to choose τ ₁ long enough to block the pattern structure elements, which may be to calculate τ _i based on equation (20). The second step is to choose different time periods τ ₂ for performing the DOE. The choice of period τ ₂ is at least 10 times τ 1 and preferably 100 times τ ₁ for the first screen test. The third step is to fix period 1 and power P ₀ and perform individual cleaning of substrates with specific pattern structures under at least five conditions. Here, P ₀ is the power at which the pattern features of via holes or trenches on the substrate are not reliably cleaned when operating in continuous mode (non-pulsed mode). The fourth step is to inspect the status of traceable residues in the pattern structural elements of the via holes or trenches of the five substrates by device analysis tools such as SEM or EDX. By repeating the above steps 1 to 4 several times, the period τ ₂ can be gradually shortened until traceable residues in the pattern structural elements of via holes or trenches are observed. . As the period τ ₂ becomes shorter, the bubble volume cannot be reduced sufficiently, which gradually blocks the pattern structure elements and affects the cleaning performance. This period is referred to as the critical cooling period τ _c . After the critical cooling period τ _c is obtained, the period τ ₂ is set to a value greater than 2τ _c to ensure a safety margin.

A more detailed example is given below. In the first step, as shown in Table 3, as design of experiments (DOE) conditions, τ ₁₀ , 2τ ₁₀ , 4τ ₁₀ , 8τ ₁₀ , 16τ 10 , 32τ ₁₀ , 64τ ₁₀ , 128τ _{10 ,} 256τ ₁₀ , To choose 10 different periods τ ₁ , such as 512τ ₁₀ . The second step is to choose a period τ ₂ of at least 10 times, preferably 20 times 512τ ₁₀ in the initial screen test, as shown in Table 3. The third step is to fix the power _P0 and separately clean the substrates with specific pattern structures under the above ten conditions. Here, P ₀ is the power at which the pattern features of via holes or trenches on the substrate are not reliably cleaned when operating in continuous mode (non-pulsed mode). The fourth step is to process 10 substrates with pattern features of via holes or trenches after plasma etching using the conditions shown in Table 3. The reason for choosing the substrate after plasma etching is that the polymer produced during the etching process forms on the sidewalls of the trenches and via holes. These polymers formed on the bottom or sidewalls of via holes are difficult to remove by conventional methods. The next step is to inspect the cleaning condition of the pattern structure elements of via holes or trenches on ten substrates in cross section of the substrate by SEM. The data obtained are shown in Table 3 below. From Table 3 it can be seen that the cleaning effect is best on substrate #6 with τ ₁ =32τ ₁₀ . Thus, the optimal period τ ₁ is 32τ ₁₀ .

If no peak is found, the first through fourth steps above are repeated again with τ ₁ as a wider time range to find the period τ ₁ . After finding the initial τ ₁ , the first and fourth steps above are repeated again with a narrower time range τ ₁ to narrow the range of the period τ ₁ . After knowing the period _{τ i} , the period τ ₂ can be optimized by decreasing it from 512τ ₂ to a value where the cleaning effect begins to diminish. Detailed procedures are disclosed in Table 4 below. From Table 4, the optimal period τ ₂ is 256τ ₁₀ since the cleaning effect reaches the best point on substrate #5 where τ ₂ =256τ ₁₀ .

Figures 21A-21C illustrate another cleaning process according to one embodiment of the present invention. The present cleaning process is similar to that shown in FIGS. 20A-20D, where the current cleaning process power remains on for a period of mτ ₁ even after cavitation reaches the saturation point R _s . They differ only in respect. Here m is any number between 0.1 and 100, preferably 2, depending on the structure of the via holes and trenches and the cleaning solution used. The value of m then needs to be optimized by experiments similar to the embodiment shown in FIGS. 20A-20D.

Figures 22A and 22B illustrate a wafer cleaning process using sonic energy in accordance with another embodiment of the present invention. During the period τ ₁ in which the sonic power P1 is applied to the cleaning liquid, bubble implosion begins to occur when the temperature of the first bubble reaches the implosion temperature T _i , and then during the temperature rise from T _i to Tn ( During the period Δτ) some bubble implosion continues to occur. After turning off the sonic power for a period of time τ ₂ , the temperature of the bubble is cooled back from Tn to T ₀ by the surrounding liquid. T _i is determined as the temperature threshold for bubble implosion in pattern features of via holes and trenches, which causes the first bubble implosion.

Since heat transfer is not exactly uniform within the pattern structure elements, more bubbles may continue to form after the temperature reaches T _i . The implosion strength of the bubble becomes higher and higher as the bubble temperature T increases. However, bubble implosion must be controlled to be below the implosion strength that would cause damage to the pattern structure. Bubble implosion can be controlled by controlling the temperature Tn below the temperature Td by adjusting the time Δτ. where Tn is the maximum bubble temperature due to the sonic power applied to the cleaning liquid during n cycles, and Td is the amount of is the temperature of the bubble implosion buildup. In the present cleaning process, the bubble implosion strength is adjusted to an initial It is controlled by adjusting the time Δτ after bubble implosion starts.

In order to increase particle removal efficiency (PRE), it is desirable to have controlled transit cavitation in the ultrasonic or high frequency ultrasonic cleaning process, as shown in FIGS. 22A-22B. Controlled transit cavitation causes the sonic power source to have power P1 for time intervals shorter than _τ1 , then power _P2 for time intervals longer than _τ2 , and repeat the above steps until the wafer is cleaned. achieved by repetition. where power _P2 is equal to 0 or much less than power P1, _τ1 is the time interval during which the temperature inside the bubble rises above the critical implosion temperature, and _τ2 is the temperature inside the bubble is the time interval during which is lowered below the critical implosion temperature. Because controlled transit cavitation involves specific bubble implosion in the cleaning process, controlled transit cavitation minimizes pattern structure damage and provides higher PRE (particle removal efficiency). Become. The critical implosion temperature is the lowest temperature inside the bubble at which the first bubble implosion occurs. To increase PRE further, the temperature of the bubble needs to be increased further, thus requiring a longer period τ ₁ . Also, the bubble temperature can be increased by shortening the period τ ₂ .

Another parameter for controlling implosion level is the frequency of the ultrasound or high frequency ultrasound. The controlled transit cavitation is to subject _the sonic power source to frequency f1 for time intervals shorter than _τ1 , then to frequency _f2 for time intervals longer than _τ2 , and repeat the above steps until the wafer is cleaned. is achieved by repeating Here, _f2 is much higher than _f1 , preferably twice or four times. Generally, the higher the frequency, the lower the implosion level or intensity. Again, τ ₁ is the time interval during which the temperature inside the bubble rises above the critical implosion temperature, and τ ₂ is the time interval during which the temperature inside the bubble drops to a temperature well below the critical implosion temperature. be. Controlled transit cavitation provides higher PRE (particle removal efficiency) while minimizing damage to pattern structures. The critical implosion temperature is the lowest temperature inside the bubble at which the first bubble implosion occurs. To increase PRE further, the temperature of the bubble needs to be increased further, thus requiring a longer period τ ₁ . Also, the bubble temperature can be increased by shortening the period τ ₂ . Generally, in the methods disclosed in the present invention, ultrasonic waves with frequencies of 0.1 MHz to 10 MHz or high frequency ultrasonic waves may be applied to the wafer cleaning process.

FIG. 23 illustrates an example wafer cleaning apparatus for performing the wafer cleaning process illustrated in FIGS. 7-22 according to one embodiment of the present invention. This wafer cleaning apparatus includes a wafer chuck 23014 on which a wafer 23010 is placed. Wafer chuck 23014 rotates with wafer 23010 during the cleaning process driven by rotation drive mechanism 23016 . The wafer cleaning apparatus also includes nozzles 23064 for applying cleaning chemicals or cleaning fluids such as deionized water 23060 to the wafers 23010 . An ultrasonic or high frequency ultrasonic device 23062 is coupled to the nozzle 23064 for applying ultrasonic or high frequency ultrasonic energy to the cleaning liquid. The ultrasonic waves or high-frequency ultrasonic waves generated by the ultrasonic wave or high-frequency ultrasonic device 23062 propagate from the nozzle 23064 to the wafer 23010 via the cleaning liquid 23060 .

FIG. 24 is a cross-sectional view of another wafer cleaning apparatus for performing the wafer cleaning process illustrated in FIGS. 7-22 according to one embodiment of the present invention. This wafer cleaning apparatus includes a cleaning tank 24074 containing most of the cleaning liquid 24070 and a wafer cassette 24076 holding a plurality of wafers 24010 immersed in the cleaning liquid 24070 . The wafer cleaning apparatus also includes an ultrasonic or high frequency ultrasonic device 24072 mounted on the wall of the cleaning tank 24074 for imparting ultrasonic or high frequency ultrasonic energy to the cleaning liquid. At least one inlet (not shown) is provided for filling the cleaning tank 24074 with a cleaning solution 24070 such that the wafer 24010 is immersed in the cleaning solution 24070 during the cleaning process.

In the above embodiments, if all of the critical process parameters of the sonic power supply, such as power level, frequency, power on time (τ ₁ ) and power off time (τ ₂ ), are controlled by the power supply without real-time monitoring during the wafer cleaning process. Damage to the pattern structure can still occur due to some abnormal conditions during the wafer cleaning process if preset in the controller. Accordingly, there is a need for an apparatus and method for real-time monitoring of the operational status of sonic power sources. If the parameters are not within the normal range, the sonic power supply should be turned off and an alarm signal should be sent and reported.

FIG. 25 is a diagram illustrating a control system for monitoring operating parameters of a wafer cleaning process employing sonic energy in accordance with one embodiment of the present invention. The control system includes a host computer 25080, an acoustic wave generator 25082, an acoustic wave transducer 1003, a detection system 25086 and a communication cable 25088. The host computer 25080 sends sound wave parameter settings such as power setting P1, power on period setting τ ₁ , power setting P ₂ , power off period setting τ ₂ , frequency setting, and control commands such as power on command to sound wave generator 25082 . Send to After receiving these commands, the sonic generator 25082 generates sonic waveforms and transmits the sonic waveforms to the sonic transducer 1003 for cleaning the wafer 1010 . Meanwhile, the parameter settings from host computer 25080 and the actual output from sound wave generator 25082 are read by detection system 25086 . Detection system 25086 compares the actual output from sound wave generator 25082 with the parameter settings from host computer 25080 . The comparison result is transmitted to host computer 25080 via communication cable 25088 . The detection system 25086 sends an alarm signal to the host computer 25080 if the output of the sound wave generator 25082 differs from the parameter settings sent by the host computer 25080 . Upon receiving the alarm signal, the host computer 25080 stops the sound wave generator 25082 to prevent further damage to the pattern structure of the wafer 1010. FIG.

FIG. 26 is a block diagram of the detection system 25086 shown in FIG. 25, according to one embodiment of the invention. The detection system 25086 illustratively includes a voltage attenuation circuit 26090, a shaping circuit 26092, a main controller 26094, a communication circuit 26096, and a power circuit 26098. The main controller 26094 may be implemented with an FPGA. Communication circuitry 26096 is established as an interface with host computer 25080 . Communication circuit 26096 performs RS232/RS485 serial communication with host computer 25080 to read parameter settings from host computer 25080 and transmit comparison results to host computer 25080 . Power supply circuit 26098 is designed to convert 15V DC to target voltages of 1.2V DC, 3.3V DC, 5V DC for the entire system.

FIG. 27 is a block diagram of a detection system 25086 according to another embodiment of the invention. The detection system 25086 illustratively includes a voltage attenuation circuit 26090, an amplitude detection circuit 27092, a main controller 26094, a communication circuit 26096, and a power circuit 26098.

Figures 28A-28C show an exemplary implementation of a voltage attenuator circuit 26090 according to one embodiment of the invention. When the sonic signal output from sonic generator 25082 is first read, the amplitude value is relatively high as shown in FIG. 28B. Voltage attenuator circuit 26090 is designed to use two op amps 28102 and 28104 to reduce the amplitude value of the waveform as shown in Figure 28C. The attenuation factor of the voltage attenuation circuit 26090 is set in the range of 5-100, preferably 20. Voltage attenuation can be expressed by the following equation.

_Vout =(R2/R1)* _Vin

Assuming R1=200k and R2=R3=R4=10K, V _out =(R2/R1)*V _in =V _in /20.

Here, V _out is the amplitude value output by the voltage attenuation circuit 26090, V _in is the amplitude value input to the voltage attenuation circuit 26090, R1, R2, R3, R4 are the two operational amplifiers 28102, 28104 resistance.

29A-29C are diagrams illustrating an example of shaping circuit 26092 shown in FIG. 26, according to one embodiment of the present invention. Referring again to FIG. 26, the output of voltage attenuator circuit 26090 is connected to shaping circuit 26092 . The waveform output from voltage attenuator circuit 26090 is input to shaping circuit 26092 to convert the sine wave to a square wave for processing by main controller (FPGA) 26094 . Shaping circuit 26092 includes window comparator 29102 and OR gate 29104, as shown in FIG. 29A. If V _cal− <V _in <V _cal+ then V _out =0, otherwise V _out =1. where V _cal− and V _cal+ are two thresholds, V _in is the input value of the shaping circuit, and V _out is the output value of the shaping circuit. The waveform passing through voltage attenuator circuit 2190 is a sine wave as shown in FIG. 29B. Shaping circuit 26092 transforms the sine wave into a square wave as shown in FIG. 29C.

Figures 30A-30C show exemplary implementations of the main controller 26094 of Figures 26 and 27, according to one embodiment of the present invention. As shown in FIG. 30A, main controller 26094 includes pulse conversion module 30102 and period measurement module 30104 . The pulse conversion module 30102 converts the pulse signal of period _τ1 into a high level signal and keeps the low level signal intact for a period of time _τ2 , as shown in FIGS. 30B and 30C. The circuit symbol for the pulse conversion module 30102 shown in FIG. 30A is Clk_Sys is the 50 MHz clock signal, Pulse_In is the input signal, and Pulse_Out is the output signal. Period measurement module 30104 is used to measure the duration of high and low levels by means of counters using the following equations.

τ ₁ = Counter_H * 20ns, τ ₂ = Counter_L * 20ns

where Counter_H is the high level number and Counter_L is the low level number.

The main controller 26094 compares the calculated power-on time with the preset period _τ1 . If the calculated power-on time is longer than the preset period τ ₁ , main controller 26094 sends an alarm signal to host computer 25080 . Upon receiving the alarm signal, the host computer 25080 stops the sound wave generator 25082 . The main controller 26094 compares the calculated power-off time with a preset period _τ2 . If the calculated power-off time is shorter than the preset period τ ₂ , main controller 26094 sends an alarm signal to host computer 25080 . The host computer 25080 that received the alarm signal stops the sound wave generator 26082 . In one embodiment, the main controller 26094 may be implemented using an Altera Cyclone IV FPGA model number EP4CE22F17C6N.

FIG. 31 is a diagram showing how the sonic power supply oscillates several times due to the characteristics of the sonic device after the host computer turns off the sonic power supply. The period τ ₃ during which the sound wave generator 25082 oscillates several cycles after power down is measured by the main controller 26094 . The period τ ₃ can be determined experimentally. Therefore, if the time calculated by periodic measurement module 25104 is τ, the actual power-on time is equal to τ− _τ3 . The main controller 26094 compares the calculated power-on time with the preset period _τ1 . If the calculated power-on time is longer than the preset period τ ₁ , main controller 26094 sends an alarm signal to host computer 25080 .

32A-32C are diagrams illustrating examples of the amplitude detection circuit 27092 shown in FIG. 27 according to one embodiment of the present invention. Amplitude detection circuit 27092 includes a reference voltage generation circuit and a comparison circuit. As shown in FIG. 32B, the reference voltage generation circuit uses D/A converters 32118 that convert digital inputs from the main controller 26094 to analog DC reference voltages V _ref+ and V _ref− , as shown in FIG. 27C. is designed to The comparison circuit is designed to compare the attenuated amplitude V _in , which is the output from voltage attenuator circuit 26090, with reference voltages V _ref+ and V _ref− using window comparator 32114 and AND gate 32116. there is Amplitude detection circuit 27092 sends an alarm signal to host computer 25080 when decay amplitude V _in exceeds reference voltages V _ref+ and/or V _ref− . Upon receiving the alarm signal, the host computer 25080 stops the sound wave generator 25082 to prevent further damage to the pattern structure of the wafer 1010. FIG.

FIG. 33 is a flowchart illustrating a wafer cleaning process according to one embodiment of the invention. The wafer cleaning process begins with step 33010 of applying a cleaning liquid to the space between the wafer and the ultrasonic/high frequency ultrasonic device. At step 33020, the ultrasound/high frequency ultrasound power supply is set to frequency _f1 and power level P1 to drive the ultrasound/high frequency ultrasound device. At step 33030, the detected power-on time is compared with a preset period of time _τ1 . If the detected power-on time is longer than the period _τ1 , cut off the power and also send an alarm signal. At step 33040, the ultrasonic/high frequency ultrasonic power supply is set to 0 power before bubble cavitation in the cleaning solution damages pattern structures on the wafer. At step 33050, the sonic power source is returned to frequency _f1 and power level P1 after the temperature inside the bubble has decreased to a certain level. At step 33060, the detected power-off time is compared to a preset period of time _τ2 . If the detected power-off time is shorter than the period _τ2 , cut off the ultrasound/high-frequency ultrasound power supply and also send an alarm signal. At step 33070, the wafer is inspected for cleanliness. Then, if the wafer is not yet cleaned to the desired degree, steps 33010 through 33060 are repeated. Alternatively, cleanliness checks may not be performed every cycle. The number of cycles to be used may be determined experimentally in advance using sample wafers.

FIG. 34 is a flowchart illustrating a wafer cleaning process according to another embodiment of the invention. The wafer cleaning process begins with step 34010 of applying cleaning fluid to the space between the wafer and the ultrasonic/high frequency ultrasonic device. At step 34020, the ultrasound/high frequency ultrasound power supply is set to frequency _f1 and power level P1 to drive the ultrasound/high frequency ultrasound device. At step 34030, the amplitude of the sonic power is detected and compared to a specified value. If the detected amplitude is greater than the specified value, cut off the power supply and also send an alarm signal. At step 34040, the sonic supply is set to 0 power before air bubble cavitation in the cleaning solution damages pattern structures on the wafer. At step 31050, the sonic power source is returned to frequency _f1 and power level P1 after the temperature inside the bubble has decreased to a certain level. In step 34060, the wafer is inspected for cleanliness, and if the wafer is not yet as clean as desired, steps 34010 through 34050 are repeated. Alternatively, cleanliness checks may not be performed every cycle. The number of cycles to be used may be determined experimentally in advance using sample wafers.

In some examples, multiple wafer cleaning processes depicted in various figures throughout this disclosure can be combined to produce a desired cleaning result. As an example, the amplitude detection of step 34030 of FIG. 34 can be incorporated into the wafer cleaning process shown in FIG. As another example, voltage attenuation 26090 and shaping circuit 26092 of FIG. 26 and amplitude detection circuit 27092 of FIG. 27 can be applied to the wafer cleaning process shown in FIGS.

The present invention provides an apparatus for cleaning a semiconductor substrate using an ultrasonic/high frequency ultrasonic device, comprising: a chuck; an ultrasonic/high frequency ultrasonic device; at least one nozzle; It includes an acoustic power source, a host computer, and a detection system. A chuck holds a semiconductor substrate. An ultrasonic/high frequency ultrasonic device is positioned adjacent to the semiconductor substrate. At least one nozzle introduces a chemical solution onto the semiconductor substrate and into a gap between the semiconductor substrate and the ultrasound/high frequency ultrasound device. The host computer sets the ultrasonic/high-frequency ultrasonic power supply to frequency _f1 and power P1 to drive the ultrasonic/high-frequency ultrasonic device, before the bubble cavitation in the liquid destroys the pattern structure on the semiconductor substrate. , the ultrasonic/high-frequency ultrasonic power supply is set to output zero, and after the temperature inside the bubble is cooled to the set temperature, the ultrasonic/high-frequency ultrasonic power supply is set again to frequency _f1 and power P1. The detection system separately detects the power-on time and power-off time at power P1 and frequency _f1 and compares the detected power-on time at power P1 and frequency _f1 with a preset period of time _τ1 . If the detected power-on time is longer than a preset period _τ1 , the detection system sends an alarm signal to the host computer, and the host computer receives the alarm signal and turns on the ultrasonic/high-frequency ultrasonic power supply. Shut down. The detection system also compares the detected power-off time with a preset period of time _τ2 . If the detected power-off time is shorter than a preset period _τ2 , the detection system sends an alarm signal to the host computer, and the host computer receives the alarm signal and turns on the ultrasonic/high-frequency ultrasonic power supply. Shut down.

In one embodiment, the ultrasonic/high frequency ultrasonic device is further coupled to the nozzle and positioned adjacent to the semiconductor substrate, and the energy of the ultrasonic/high frequency ultrasonic device is directed from the nozzle through a liquid column. transmitted to the semiconductor substrate.

The present invention provides another apparatus for cleaning a semiconductor substrate using an ultrasonic/high frequency ultrasonic device, comprising a chuck, an ultrasonic/high frequency ultrasonic device, at least one nozzle, and an ultrasonic/high frequency ultrasonic device. It includes a high frequency ultrasound power source, a host computer and a detection system. A chuck holds a semiconductor substrate. An ultrasonic/high frequency ultrasonic device is positioned adjacent to the semiconductor substrate. At least one nozzle introduces a chemical solution onto the semiconductor substrate and into a gap between the semiconductor substrate and the ultrasound/high frequency ultrasound device. The host computer sets the ultrasonic/high-frequency ultrasonic power supply to frequency _f1 and power P1 to drive the ultrasonic/high-frequency ultrasonic device, before the bubble cavitation in the liquid destroys the pattern structure on the semiconductor substrate. , the ultrasonic/high-frequency ultrasonic power supply is set to output zero, and after the temperature inside the bubble is cooled to the set temperature, the ultrasonic/high-frequency ultrasonic power supply is set again to frequency _f1 and power P1. A detection system detects the amplitude of each waveform output from the ultrasound/high frequency ultrasound power source and compares the detected amplitude of each waveform to a specified value. If the detected amplitude of any waveform is greater than a specified value, the detection system outputs an alarm signal to the host computer, which receives the alarm signal and shuts down the ultrasound/high frequency ultrasound power supply. Here, the default value is a value larger than the waveform amplitude during normal operation.

In one embodiment, the ultrasonic/high frequency ultrasonic device is further coupled to the nozzle and positioned adjacent to the semiconductor substrate, and the energy of the ultrasonic/high frequency ultrasonic device is transmitted from the nozzle through the liquid column to the semiconductor substrate. be done.

The present invention provides another apparatus for cleaning semiconductor substrates using an ultrasonic/high frequency ultrasonic device, comprising a cassette, a tank, an ultrasonic/high frequency ultrasonic device, and at least one inlet. , an ultrasound/high-frequency ultrasound power source, a host computer, and a detection system. A cassette holds at least one semiconductor substrate. The tank holds the cassette. An ultrasonic/high-frequency ultrasonic device is attached to the outer wall of the tank. At least one inlet fills a tank for immersing the semiconductor substrate with a chemical solution. The host computer sets the ultrasonic/high-frequency ultrasonic power supply to frequency _f1 and power P1 to drive the ultrasonic/high-frequency ultrasonic device, before the bubble cavitation in the liquid destroys the pattern structure on the semiconductor substrate. , the ultrasonic/high-frequency ultrasonic power supply is set to output zero, and after the temperature inside the bubble is cooled to the set temperature, the ultrasonic/high-frequency ultrasonic power supply is set again to frequency _f1 and power P1. The detection system separately detects the power-on time and power-off time at power P1 and frequency _f1 and compares the detected power-on time at power P1 and frequency _f1 with a preset period of time _τ1 . If the detected power-on time is longer than a preset period _τ1 , the detection system sends an alarm signal to the host computer, and the host computer receives the alarm signal and turns on the ultrasonic/high-frequency ultrasonic power supply. Shut down. The detection system also compares the detected power-off time with a preset period of time _τ2 . If the detected power-off time is shorter than a preset period _τ2 , the detection system sends an alarm signal to the host computer, and the host computer receives the alarm signal and turns on the ultrasonic/high-frequency ultrasonic power supply. Shut down.

The present invention provides another apparatus for cleaning semiconductor substrates using an ultrasonic/high frequency ultrasonic device, comprising a cassette, a tank, an ultrasonic/high frequency ultrasonic device, and at least one inlet. , an ultrasound/high-frequency ultrasound power source, a host computer, and a detection system. A cassette holds at least one semiconductor substrate. The tank holds the cassette. An ultrasonic/high-frequency ultrasonic device is attached to the outer wall of the tank. At least one inlet fills a tank for immersing the semiconductor substrate with a chemical solution. The host computer sets the ultrasonic/high-frequency ultrasonic power supply to frequency _f1 and power P1 to drive the ultrasonic/high-frequency ultrasonic device, before the bubble cavitation in the liquid destroys the pattern structure on the semiconductor substrate. , the ultrasonic/high-frequency ultrasonic power supply is set to output zero, and after the temperature inside the bubble is cooled to the set temperature, the ultrasonic/high-frequency ultrasonic power supply is set again to frequency _f1 and power P1. A detection system detects the amplitude of each waveform output from the ultrasound/high frequency ultrasound power source and compares the detected amplitude of each waveform to a specified value. If the detected amplitude of any waveform is greater than the specified value, the detection system will output an alarm signal to the host computer, and the host computer will receive the alarm signal and shut down the ultrasound/high frequency ultrasound power supply. . Here, the default value is a value larger than the waveform amplitude during normal operation.

Although the present disclosure has been particularly shown and described with reference to exemplary embodiments thereof, workers skilled in the art will appreciate that various changes in form and detail may be made without departing from the spirit of the claims. will understand.

Claims (53)

A system for controlling damage during cleaning of a semiconductor wafer having a plurality of patterned features, comprising:
a wafer holder for temporarily restraining a semiconductor wafer during a cleaning process;
an injection port for supplying a cleaning liquid to the surface of the semiconductor wafer;
configured to operate alternately between a first frequency and a first power level for a first predetermined period of time and a second frequency and a second power level for a second predetermined period of time; A sonic generator for providing sonic energy, wherein the first predetermined time period and the second predetermined time period are contiguously linked to each other, and the bubble size in the cleaning liquid is increased during the first predetermined time period. a sonic generator that increases with sonic energy and decreases during the second predetermined time period;
said first and second frequencies; said first and second power levels; said first and second predetermined time periods; and a number of alternating said first and second predetermined time periods by said sound wave generator; and a controller programmed to provide
at least one of the first and second predetermined time periods, the first and second power levels, and the first and second frequencies being damaged in the pattern as a result of the application of the sonic energy; is determined such that the proportion of structuring elements is less than a predetermined threshold greater than zero;
Power is set to the second frequency and the second power level for the second predetermined period of time after the ratio of total bubble volume to volume of via holes, trenches or recessed spaces in the semiconductor wafer increases to a first predetermined value. and reducing power to said first frequency and said first power level for said first predetermined period of time after the ratio of total bubble volume to volume of via hole, trench or recessed space in the semiconductor wafer has decreased to a second predetermined value. system set to 3. The system of claim 1, wherein said wafer holder is a rotating chuck. 3. The system of claim 1, wherein said wafer holder is a cassette immersed in a cleaning tank. 3. The system of Claim 1, wherein the inlet comprises a nozzle. 3. The system of claim 1, further comprising an acoustic transducer coupled to said acoustic wave generator. 6. The system of claim 5, wherein the sonic transducers are positioned on the semiconductor wafer with gaps therebetween, the gaps being filled with the cleaning liquid during a cleaning process. 7. The system of claim 6, wherein said gap changes during said cleaning process. 6. The system of claim 5, wherein the sonic transducer is connected to the inlet and imparts sonic energy to the cleaning liquid flowing through the inlet. 2. The system of claim 1, wherein said cleaning liquid is selected from the group consisting of chemical solutions, deionized water, and combinations of said chemical solutions and said deionized water . 2. The system of claim 1, wherein the second power level is zero. the first frequency is equal to the second frequency, and the first power level is higher than the second power level while both frequencies remain constant for respective periods of time; and , the power levels of both remain constant in their respective periods. said first frequency being higher than said second frequency and said first power level being higher than said second power level while both said frequencies remain constant for respective periods of time; and wherein both said power levels remain constant in their respective time periods. said first power level being equal to said second power level while said first frequency is lower than said second frequency and both said frequencies remain constant for respective periods of time; and , the power levels of both remain constant in their respective periods. said first frequency being lower than said second frequency and said first power level being higher than said second power level while both said frequencies remain constant for respective periods of time; and wherein both said power levels remain constant in their respective time periods. said first power level being lower than said second power level while said first frequency is lower than said second frequency and both said frequencies remain constant for respective periods of time; and wherein both said power levels remain constant in their respective time periods. 2. The system of claim 1, wherein said first power level increases during said first predetermined time period. 2. The system of claim 1, wherein said first power level decreases during said first predetermined time period. 2. The system of claim 1, wherein said first power level both increases and decreases during said first predetermined time period. 2. The system of claim 1, wherein said second frequency is substantially near zero and said second power level is a constant positive value during said second predetermined time period. 2. The system of claim 1, wherein said second frequency is substantially near zero and said second power level is a constant negative value during said second predetermined time period. A system according to any one of claims 5 to 8 , wherein the sound waves from the sonic transducer during the first predetermined time period and the sound waves from the sonic transducer during the second predetermined time period are in anti-phase. . 2. The system of claim 1, wherein said first predetermined period of time is less than 2,000 times the cycle period of said first frequency. The implosion temperature is T _i , the cleaning liquid temperature is T ₀ , the temperature rise width due to one compression is ΔT, the temperature drop width due to one expansion is δT, and the first frequency is f _{1 .} 2. The system of claim 1, wherein said first predetermined period of time is less than ((T _i −T ₀ −ΔT)/(ΔT−δT)+1)/f ₁ , as. 2. The system of claim 1, wherein said first frequency varies from a higher value to a lower value during said first predetermined time period. 2. The system of claim 1, wherein said first frequency varies from a low value to a high value during said first predetermined time period. 2. The system of claim 1, wherein the first frequency changes from a low value to a high value and then returns to the low value during the first predetermined time period. 2. The system of claim 1, wherein the first frequency changes from a high value to a low value and then returns to the high value during the first predetermined time period. _4. The claim wherein said first frequency is first _f1 , then _{f3 and} finally _f4 in said first predetermined time period, where f4 is less than _f3 and _f3 is less than f1. 1. The system according to 1. _4. The claim wherein f4 is less than _f3 , and _f3 is less than _f1 , said first frequency being first _f4 , then _f3 , and finally _f1 in said first predetermined time period. 1. The system according to 1. _4. wherein f4 is less than _f3 and _f3 is less than _f1 , said first frequency being first _f1 , then _f4 and finally _f3 in said first predetermined time period. 1. The system according to 1. _4. The claim wherein said _first frequency _is first f3, then _f4 , and finally f1 in said first predetermined time period, where f4 is less than _f3 and _f3 is less than _f1 . 1. The system according to 1. _4. The claim wherein said _first frequency is first f3, then _f1 , and finally _f4 in said first predetermined time period, where f4 is less than _f3 and _f3 is less than _f1 . 1. The system according to 1. _4. The claim wherein f4 is less than _f3 , and _f3 is less than _f1 , and said first frequency is first _f4 , then _f1 , and finally _f3 in said first predetermined time period. 1. The system according to 1. 2. The system of claim 1, further comprising a detection circuit coupled to said sound wave generator for detecting an output of said sound wave generator. 35. The system of Claim 34, wherein said detection circuit includes a voltage attenuation circuit for attenuating an input signal. 35. The system of Claim 34, wherein the detection circuit includes a shaping circuit for transforming the signal from the first waveform to the second waveform. 37. The system of claim 36, wherein said first waveform is a sine wave and said second waveform is a square wave. The detection circuit includes an amplitude detection circuit for detecting an amplitude of an input signal and comparing it with a reference value, the detection circuit generating an alarm signal when the detected amplitude exceeds the reference value. 35. The system of claim 34, causing the sound wave generator to turn off. 39. The system of claim 38, wherein said reference value is generated by a digital-to-analog converter (DAC). The detection circuit detects the first predetermined period of time, compares it with a predetermined value, and generates an alarm signal to turn off the sound wave generator when the first predetermined period of time exceeds the predetermined value. 35. The system of claim 34, allowing The detection circuit detects the second predetermined period of time and compares it with a predetermined value, and generates an alarm signal to turn off the sound wave generator when the second predetermined period of time is less than the predetermined value. 35. The system of claim 34, allowing. 2. The system of claim 1, wherein the first predetermined period of time is experimentally determined to avoid implosion of air bubbles in the cleaning liquid by inspecting damage to the pattern structures in the semiconductor wafer. . The empirical determination maintains the first and second frequencies and the first and second power levels at constant values, and keeps the second predetermined period of time substantially longer than the first predetermined period of time. 43. The system of claim 42, comprising selecting different values for the first predetermined period of time in different cleaning processes while maintaining values. 2. The method of claim 1, wherein the first predetermined time period is experimentally determined to allow limited bubble implosion without causing damage to the pattern structures in the semiconductor wafer being cleaned. system. The empirical determination maintains the first and second frequencies and the first and second power levels at constant values, and keeps the second predetermined period of time substantially longer than the first predetermined period of time. 45. The system of claim 44, comprising selecting different values for the first predetermined period of time in different cleaning processes while maintaining values. 2. The system of claim 1, wherein the second predetermined period of time is empirically determined such that the temperature inside the bubbles in the cleaning liquid can be reduced to a predetermined temperature. 47. The system of claim 46, wherein said predetermined temperature is substantially near room temperature. wherein the first frequency and the first power level are experimentally determined to avoid implosion of bubbles in the cleaning liquid by inspecting damage to the pattern structures in the semiconductor wafer. Item 1. The system according to item 1. wherein the first frequency and the first power level were experimentally determined to allow limited bubble implosion without causing damage to the patterned structures in the semiconductor wafer being cleaned; The system of claim 1. 2. The system of claim 1, wherein the second frequency and the second power level were experimentally determined such that the temperature inside bubbles in the cleaning fluid can be reduced to a predetermined temperature. 51. The system of claim 50, wherein said predetermined temperature is substantially near room temperature. 2. The system of claim 1, wherein the number of alternations is empirically determined by inspecting damage to the semiconductor wafer. 2. The system of claim 1, wherein the yield enhancement caused by the cleaning effect of applying the sonic energy is greater than the yield loss caused by the damage of applying the sonic energy.

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