System and method for cleaning a sheet

Abstract

The invention discloses a system and a method for cleaning a sheet. The method includes applying ultrasonic work to a sheet, the sheet having an initial state, the initial state including particulate matter on a surface; the application of ultrasonic work that removes at least a portion of particulate matter from the surface is controlled to reach a total ultrasonic work to treat the sheet to a final state, where the surface of the sheet is at least partially free of particulate matter by optical detection at a light intensity of 5000 lux, and the surface of the sheet is at least partially free of particulate matter by optical detection at a light intensity of 5000 lux. The particle density of particles with the size larger than 5.0 microns on the surface of the sheet in the final state is smaller than 0.100 particles / cm < 2 >; the surface has an edge exclusion region of 1.0 cm and a B10 surface strength greater than 400 N. The method controls exposure of the sheet to ultrasonic waves to maintain good cleaning performance while minimizing surface damage.

Description

Technical Field

[0001] The present disclosure relates to a system and method for cleaning wafers. More particularly, the present disclosure relates to a system and method for reducing particle contamination on the wafer surface while minimizing subsurface damage that could weaken the wafer surface. Background Art

[0002] Thin sheets are typically produced by forming an ingot and slicing it to form thin sheets. The ingot is typically cylindrical, ranging in length from several hundred centimeters to a meter or more, and in diameter from tens to several hundred millimeters. The ingot is an inorganic material, such as glass or a semiconductor. By slicing the ingot, thin sheets with a thickness ranging from about one-tenth of a millimeter to several millimeters can be obtained from the ingot. The most common slicing method is a wire saw, in which the ingot is cut with a metal wire coated with diamond or other abrasive. Multiple thin sheets are formed by cutting the glass ingot at predetermined intervals along its length.

[0003] Thin wafers obtained by wire sawing typically have a high surface roughness and require polishing to produce the smooth surface required for many applications. Polishing is accomplished by applying a slurry containing fine abrasives to the surface. However, the polishing process can cause particulate matter to settle on the surface of the wafer. The wafer must then be cleaned to remove the particulate matter and provide a smooth, contamination-free surface. Ultrasonic cleaning is widely used to clean the surface of thin wafers. The wafer is placed in one or a series of ultrasonic tanks filled with detergent solution or water and then subjected to ultrasonic treatment. The energy of the ultrasonic waves acts on the surface of the wafer, dislodging contaminants. However, the ultrasonic energy required to effectively clean the surface is very high and can cause damage or defects, thereby reducing the surface strength. Low surface strength is undesirable for subsequent processing steps performed on the wafer, such as deposition of coatings or thin films, and patterning. Therefore, there is a need for a method for cleaning thin wafers that provides a surface with low particulate contamination and high strength. Summary of the Invention

[0004] This disclosure provides a system and method for cleaning wafer surfaces. This method incorporates the concept of ultrasonic work and controls the ultrasonic work applied to the wafer to balance the cleaning effect of the ultrasound with its tendency to damage the wafer surface or subsurface regions. By properly controlling the ultrasonic work, a wafer with minimal particle contamination and high surface strength can be achieved.

[0005] The wafer cleaning system includes a cleaning unit with one or more ultrasonic tanks. Each ultrasonic tank contains a liquid and an ultrasonic transducer that provides ultrasonic waves to the liquid. A wafer with particle contamination on its surface is immersed in the liquid and subjected to ultrasonic treatment to reduce the amount of particle contamination on the surface. The wafer preferably passes through multiple ultrasonic tanks to gradually clean the surface until the particle contamination level is below a predetermined threshold. Simultaneously, the total ultrasonic power applied to the wafer by the ultrasonic tank or a series of multiple ultrasonic tanks is controlled to minimize surface damage, thereby maintaining the surface intensity above a predetermined threshold.

[0006] This disclosure extends to: A method for cleaning a sheet, comprising: applying ultrasonic work to a sheet having an initial state comprising particulate matter on a surface thereof, controlling the application of ultrasonic power to achieve a total ultrasonic power to treat the sheet to a final state wherein the ultrasonic power removes at least a portion of the particulate matter from the surface, wherein the sheet in the final state has a particle density of less than 0.100 particles / cm2 on the surface of the sheet for particles larger than 5.0 microns as determined by optical inspection at a light intensity of 5000 lux. 2 ; The surface has an edge exclusion zone of 1.0 cm and a B10 surface strength greater than 400N.

[0007] This disclosure extends to: A system for cleaning a sheet, comprising: a first cleaning unit comprising a first spray cleaning tank, the first spray cleaning tank being configured to receive a wafer in an initial state, the wafer in the initial state comprising first particulate matter on a surface, the first spray cleaning tank being configured to clean the wafer by removing a first portion of the first particulate matter from the surface, the first spray cleaning tank cleaning the wafer to a first intermediate state; an intermediate processing unit configured to receive the sheet in the first intermediate state from the first cleaning unit, the intermediate processing unit processing the sheet in the first intermediate state to a second intermediate state, the processing forming a second particulate matter, a surface of the sheet in the second intermediate state including the second particulate matter; and a second cleaning unit configured to receive the wafer in a second intermediate state from the intermediate processing unit, and to clean the wafer to a final state by removing at least a portion of the second particulate matter from the surface of the wafer, wherein the particle density of particles larger than 5.0 μm on the surface of the wafer in the final state is less than 0.100 particles / cm by optical inspection under a light intensity of 5000 lux. 2 , the surface has an edge exclusion zone of 1.0 cm and a B10 surface strength greater than 400N.

[0008] Additional features and advantages are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art or may be learned by practice of the embodiments described in the written description and claims hereof as well as the accompanying drawings.

[0009] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework for understanding the nature and character of the claims.

[0010] The accompanying drawings are included to provide a further understanding and are incorporated into and constitute a part of this specification. The drawings illustrate selected aspects of the specification and, together with the description, explain the principles and operation of the methods, products, and compositions encompassed by the specification. The features shown in the drawings are illustrative of selected embodiments of the specification and are not necessarily drawn to scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] While the specification concludes with the claims which particularly point out and distinctly claim the subject matter of this written specification, it is believed that the specification will be better understood from the following written description when taken in conjunction with the accompanying drawings, in which:

[0012] Figure 1 A flake cleaning system is depicted.

[0013] Figure 2 A wafer cleaning system having two or more cleaning units is depicted.

[0014] Figure 3 A wafer cleaning system with two cleaning units is depicted.

[0015] Figure 4 A cleaning unit having multiple cleaning tanks is depicted.

[0016] Figure 5 A spray cleaning tank and an ultrasonic cleaning tank are depicted.

[0017] Figure 6 Depicted is the collapse of bubbles on a thin-film surface during ultrasonic cleaning.

[0018] Figure 7 The relationship between relative cavitation strength and ultrasonic frequency is depicted.

[0019] Figure 8 Depicted is a ring-on-ring testing instrument for determining surface strength.

[0020] Figure 9 Depicts the forces applied to a thin sheet during a ring-on-ring test of surface strength.

[0021] Figure 10 Weibull plots of the surface intensity of representative flakes are depicted.

[0022] Figure 11 The relationship between surface intensity and ultrasonic power is depicted for a wafer cleaning system according to one embodiment.

[0023] Figure 12 Depicted is a wafer cleaning system with a laser marking unit.

[0024] Figure 13-15 An embodiment of a first cleaning unit for a wafer cleaning system is depicted.

[0025] The embodiments shown in the drawings are exemplary in nature and are not intended to limit the scope of the detailed description or the claims. Wherever possible, the same reference numbers are used in the drawings to represent the same or similar features. DETAILED DESCRIPTION

[0026] The present disclosure provides a wafer cleaning system and method for cleaning wafers. The wafer cleaning system receives a wafer with particulate matter on its surface and cleans the wafer by reducing the particulate matter on the surface. The wafer cleaning system includes one or more cleaning units for the wafer to pass through. Each cleaning unit includes one or more cleaning tanks containing a cleaning liquid. Types of cleaning tanks include spray cleaning tanks and ultrasonic cleaning tanks. Spray cleaning tanks clean wafers by spraying cleaning liquid onto the wafer surface to remove particulate matter. Ultrasonic cleaning tanks are equipped with ultrasonic transducers that provide ultrasonic power to the cleaning liquid to clean the wafer surface. The total amount of ultrasonic power provided by the wafer cleaning system is controlled to achieve the desired degree of removal of particulate matter from the wafer surface while minimizing damage to the surface caused by the ultrasonic waves. The wafer cleaning system may optionally include a drying unit for removing residual cleaning liquid from the wafer surface, and a marking unit for marking identification information on the wafer.

[0027] The present disclosure is provided as an implementable teaching, and the present disclosure can be more easily understood with reference to the following description, drawings, examples, and claims. To this end, those skilled in the relevant art should be aware and understand that various changes can be made to the various aspects of the embodiments described herein while still being able to obtain beneficial effects. It is also apparent that some of the expected benefits of the present embodiment can be obtained by selecting some features without utilizing other features. Therefore, those skilled in the art will recognize that many modifications and adjustments are possible, even desirable in some cases, and are part of the present disclosure. Therefore, it should be understood that the present disclosure is not limited to the specific compositions, products, devices, and methods disclosed, unless otherwise stated. It should also be understood that the terms used herein are only used for the purpose of describing specific aspects and are not restrictive.

[0028] Disclosed are compositions (including materials, compounds, compositions, and method steps) that can be used, combined, used to prepare, or as embodiments of the disclosed systems and methods for cleaning glass sheets. It should be understood that when a combination or subset of compositions, or interactions, is disclosed, each composition individually and each combination of two or more compositions is contemplated and disclosed herein, even if not explicitly stated. For example, if a combination of compositions A, B, and C is disclosed, each of A, B, and C is disclosed individually, as well as each of the combinations AB, BC, AC, and ABC. This concept applies to all aspects of the present disclosure, including but not limited to compositions corresponding to materials, compounds, compositions, and method steps.

[0029] In this specification and the appended claims, a number of terms are referred to, which shall have the following meanings:

[0030] The terms "include", "comprising" or similar terms mean including but not limited to, that is, inclusive rather than exclusive.

[0031] As used herein, the term "and / or," when used in conjunction with a list of two or more items, means that any one of the listed items may be used alone, or any combination of two or more of the listed items may be used. For example, if a composition is described as containing components A, B, and / or C, the composition may contain only A; only B; only C; a combination of A and B; a combination of A and C; a combination of B and C; or a combination of A, B, and C.

[0032] In this document, relative terms such as first and second, top and bottom, etc. are used solely to distinguish one entity or action from another entity or action and do not necessarily require or imply any actual such relationship or order between these entities or actions.

[0033] The specific numerical values ​​and preferred numerical values ​​and ranges thereof disclosed with respect to compositions, components, ingredients, additives and the like are for illustration only and do not exclude other defined numerical values ​​or other numerical values ​​within the defined ranges. The compositions and methods of the present disclosure include compositions and methods having any numerical value or any combination of numerical values, specific numerical values, more specific numerical values ​​and preferred numerical values ​​described herein.

[0034] As shown in the exemplary embodiments, the construction and arrangement of the elements of the present disclosure are illustrative only. Although only some embodiments of the present invention are described in detail in the present disclosure, it is easy for those skilled in the art to understand that many modifications can be made (for example, to the size, dimensions, structure, shape and proportion of various elements; the value of parameters; installation arrangement; the use of materials; orientation, etc.) without substantially departing from the novel and non-obvious teachings and advantages of the subject matter. For example, an element shown as being integrally formed can be made up of multiple parts, or an element shown as multiple parts can be integrally formed, the length or width of other elements of the structure and / or member or system can vary, and the nature or quantity of the adjustment position provided between elements can vary. It should be noted that the elements and / or assemblies of the system can be made up of any one of a variety of materials that provide sufficient operability. Therefore, all of these modifications are intended to be included within the scope of the present invention.

[0035] As used herein, unless stated otherwise, the indefinite article "a" or "an" and the corresponding definite article "the" mean at least one, or one or more.

[0036] The following claims are incorporated into and constitute a part of the Detailed Description of the Invention.

[0037] Figure 1 A wafer cleaning system 100 is shown that receives an input wafer 10 and provides an output wafer 20. The input wafer 10 includes or consists of an amorphous or crystalline material. The input wafer 10 may also include or consist of a ceramic or glass-ceramic material. Representative materials include glass, semiconductors (e.g., Si, III-V, II-VI), and sapphire. Glass includes materials having a high refractive index n. d Glass with a high refractive index can be used as a substrate for many applications in augmented reality technology. The refractive index of such glass is n dThe high refractive index glass composition includes silicates, borates, tungstates and phosphates, and contains one or a combination of TiO2, Nb2O3, Bi2O3, WO3, Y2O3 and RE2O3 (wherein RE is a rare earth) in an amount greater than 10 mol%, greater than 20 mol%, greater than 30 mol%, greater than 40 mol%, greater than 50 mol%, or in the range of 10 mol% to 60 mol%, or 15 mol% to 55 mol%, or 20 mol% to 50 mol%.

[0038] In some embodiments, the input sheet 10 includes a coating on the surface, and particulate matter on the coating is removed by the cleaning system 100. The coating includes a reflective or anti-reflective layer, a protective layer, or a waveguide layer.

[0039] The input sheet 10 can have any shape or size that matches the dimensional requirements of the sheet cleaning system 100. The cross-section of the input sheet 10 is rounded, circular, square, rectangular, or polygonal. In embodiments, the input sheet 10 has an aspect ratio (defined as the ratio of the longest cross-sectional dimension through the center of the cross-section to the sheet thickness) greater than or equal to 10, or greater than or equal to 25, or greater than or equal to 50, or greater than or equal to 100, or greater than or equal to 200, or greater than or equal to 300, or from 10 to 500, or from 20 to 400, or from 50 to 300. In a representative embodiment, the input sheet 10 has a circular cross-section, with a longest cross-sectional dimension (diameter) greater than or equal to 25 mm, or greater than or equal to 50 mm, or greater than or equal to 100 mm, or greater than or equal to 200 mm, or greater than or equal to 300 mm, or from 25 mm to 400 mm, or from 50 mm to 350 mm, or from 100 mm to 300 mm, and a thickness greater than or equal to 0.1 mm, or greater than or equal to 0.3 mm, or greater than or equal to 0.5 mm, or greater than or equal to 0.7 mm, or greater than or equal to 1. 0mm, or greater than or equal to 1.5mm, or greater than or equal to 2.0mm, or greater than or equal to 2.5mm, or greater than or equal to 3.0mm, or 0.1mm to 5.0mm, or 0.2mm to 4.5mm, or 0.3mm to 4.0mm, or 0.4mm to 3.5mm, or 0.5mm to 3.0mm, or 0.7mm to 2.5mm, or 1.0mm to 2.0mm, or 0.1mm to 2.0mm, or 0.2mm to 1.5mm, or 0.3mm to 1.0mm.

[0040] The wafer cleaning system 100 removes particulate matter from the surface of an input wafer 10 to produce an output wafer 20. Input wafer 10 corresponds to the wafer in its initial state, and output wafer 20 corresponds to the wafer in its final state. The presence of particulate matter on the wafer surface may be a result of the wafer forming process or post-wafer processing. For example, wire saw cutting to form the wafer or polishing the wafer after cutting may generate particulate matter. For purposes of this disclosure, surface cleanliness refers to the number of particles larger than 5.0 microns (in their longest linear dimension) on the wafer surface as detected by optical inspection under a light intensity of 5000 lux. Optical inspection is performed manually on the wafer surface using an automated optical inspection system (KLA Zetascan ZS-800). An area 1.0 cm from the wafer edge is excluded from the measurement (1.0 cm edge exclusion zone). The number of particles larger than 5.0 microns is counted and normalized to the surface area (minus the 1.0 cm edge exclusion zone) to determine the particle density. The lower the particle density, the cleaner the surface. In the embodiments herein, the particle density is less than or equal to 0.100 particles / cm 2 , or less than or equal to 0.090 particles / mm 2 , or less than or equal to 0.080 particles / cm 2 , or less than or equal to 0.070 particles / cm 2 , or less than or equal to 0.060 particles / cm 2 , or less than or equal to 0.050 particles / cm 2 For example, a rounded wafer with a diameter of 30 cm and an edge exclusion zone of 1.0 cm has a measured surface diameter of 28 cm. If 45 particles larger than 5.0 microns are counted, the particle density of the wafer is 0.073 particles / cm 2 .

[0041] The wafer cleaning system comprises one or more cleaning units. For example, Figure 2 A sheet cleaning system 100 is shown having two or more cleaning units 210 (labeled 210a, 210b, etc.), and Figure 3 An embodiment of a wafer cleaning system comprising two cleaning units is shown. Figure 3 In the embodiment, the sheet cleaning system 100 includes cleaning units 210a and 210b. An input sheet 10 is supplied to the cleaning unit 210a and then transferred to the cleaning unit 210b to produce an output sheet 20. Each cleaning unit includes one or more cleaning tanks C. Figure 4 An embodiment of a cleaning unit 210 having a plurality of cleaning tanks C is shown.

[0042] Cleaning tank C includes a cleaning solution for cleaning or rinsing thin slices. The cleaning solution includes a detergent solution (dissolved in water or an organic solvent), a pure organic solvent (such as isopropyl alcohol) and pure (deionized) water. The cleaning tank containing the detergent solution is usually heated in a temperature range of 30°C to 70°C. The cleaning tank containing pure water is usually operated at room temperature. The cleaning solution can also include additives such as surfactants, emulsifiers, dispersants, solubilizers, wetting agents and stabilizers. Representative commercially available detergent solutions are given in Table 8 below. When used in the cleaning tank, the detergent solution is usually further diluted in water. In an embodiment, the cleaning solution does not contain detergent.

[0043] The types of cleaning tanks C include spray cleaning tanks S and ultrasonic cleaning tanks U ( Figure 5 The spray cleaning tank S operates by spraying a cleaning liquid onto the wafer surface. The direction and flow rate of the spray can be controlled to optimize the cleaning of the wafer surface. The spray can include multiple streams of cleaning liquid. The spray removes particulate matter from the wafer surface. Typical volumes for ultrasonic cleaning tanks and spray cleaning tanks are 120L and 60L, respectively.

[0044] The operation of the ultrasonic cleaning tank U is to apply ultrasonic waves to the cleaning liquid. The thin sheet is placed in a bath with the cleaning liquid and is subjected to ultrasonic treatment. The ultrasonic waves enhance the action of the cleaning liquid through the cavitation effect, in which the ultrasonic waves generate compression waves in the cleaning liquid, resulting in the formation of tiny bubbles within the cleaning liquid. The bubbles are unstable and then collapse. Once collapsed, the bubbles release energy, causing particulate matter to leave the surface. The ultrasonic waves are provided by a transducer integrated into the cleaning tank or immersed in the cleaning tank. The transducer is most commonly a piezoelectric transducer (e.g., lead zirconate titanate, barium titanate), which oscillates at ultrasonic frequencies, thereby introducing ultrasonic waves into the cleaning liquid. Figure 6 Ultrasonic cleaning of a wafer is schematically shown. Figure 6 From left to right, the approach of a bubble formed by cavitation to the sheet surface and its subsequent collapse are shown. Figure 6 The lower part shows an image of the bubble collapse.

[0045] In order to improve the cleaning of the thin slice, a study on the effect of bubble collapse on the thin slice surface was completed to support the disclosure of this article. Ultrasonic cleaning known in the prior art generally uses ultrasonic frequencies in the range of 10kHz to 40kHz to clean the surface. In cleaning studies within this frequency range that support the present disclosure, it was found that damage to the thin slice surface was accompanied by the movement of particulate matter caused by ultrasound. As described more fully below, surface damage (including subsurface damage near the surface) was assessed by measuring surface intensity using a ring-on-ring test. The higher the surface intensity, the less surface damage was indicated. Although not wishing to be bound by theory, it is believed that the surface damage and the reduction in surface intensity are caused by the energy released during bubble collapse during ultrasonic cavitation. Figure 7 The relative cavitation intensity (which is proportional to the energy released when the bubbles collapse) on an exemplary glass sheet is plotted as a function of the ultrasonic frequency of an ultrasonic cleaning tank using water as the cleaning fluid. The voltage, current, and duration of ultrasonic application were constant across the ultrasonic frequency range. For comparison, the relative cavitation intensity was normalized to the cavitation intensity at a frequency of 40 kHz. Figure 7 The results shown in show that the relative cavitation intensity decreases with increasing frequency. The relative cavitation intensities at 10kHz, 40kHz, 80kHz and 100kHz are greater than 10, 1.0, 0.1 and 0.07, respectively. Figure 7 , when ultrasonic cleaning is performed at high frequencies, it is expected that higher surface strength can be achieved. Similar results can be obtained regardless of the composition and size of the flakes.

[0046] To understand the effect of applied ultrasonic energy on surface strength and cleanliness, further testing was conducted. The tests showed that the ultrasonic work applied during the cleaning process affects surface strength and cleanliness. As used herein, ultrasonic work is defined in Equation (1): where the sum is the sum of all ultrasonic cleaning tanks in the wafer cleaning system and represents the total ultrasonic work of the wafer cleaning system, i represents an ultrasonic cleaning tank, n is the total number of ultrasonic cleaning tanks, and (voltage) i 、(current) i and (time) i are the transducer input voltage, transducer current, and ultrasonic application time of the i-th ultrasonic cleaning tank, respectively. The ultrasonic work is the sum of the ultrasonic energy of the cleaning fluid supplied by the transducer to each ultrasonic cleaning tank of the wafer cleaning system over all ultrasonic cleaning tanks.

[0047] The following example illustrates the trade-off between surface intensity and cleanliness (particle density) of a wafer surface as ultrasonic power is varied. In general, the greater the ultrasonic power, the cleaner the surface but the lower the surface intensity; the lower the ultrasonic power, the higher the surface intensity but the less effective it is in removing particulate matter from the surface. Based on the results described herein, it is recommended that (1) the particle density (or minimum particle density) required for the wafer's specific application be specified and the minimum amount of ultrasonic power be applied to achieve the specified particle density, or (2) the surface intensity (or minimum surface intensity) required for the wafer's specific application be specified and the maximum amount of ultrasonic power be applied to produce a surface with the specified surface intensity. Process (1) achieves the desired cleanliness (particle density) while maximizing surface intensity, and process (2) achieves the desired surface intensity while maximizing cleanliness (minimizing particle density).

[0048] For the purposes of this disclosure, surface strength is measured by a ring-on-ring test according to the standard specified in ASTM C1499-09 (2013). In the ring-on-ring test, the specimen is placed between a loading ring and a support ring ( Figure 8 The support ring is located on a fixed base and applies force to the loading ring. The force at which the specimen breaks is recorded.

[0049] Figure 9 A magnified cross-sectional view 400 of the contact area between the loading ring and support ring and the specimen is shown. Loading ring 430 contacts surface 4130 of specimen 410 at point 430a, forming a circle ("ring") whose diameter D1 is attributed to loading ring 430. Support ring 420 contacts surface 4230 of specimen 410 at point 420a, forming a circle ("ring") whose diameter D2 is attributed to support ring 420. Specimen 410 has a thickness h. In the tests described herein, diameter D1 of loading ring 430 was 15 mm, diameter D2 of support ring 420 was 30 mm, and thickness 2r of the ring formed by contact points 430a and 420a was 0.75 mm. An Instron 3345 testing instrument was used to apply force F to loading ring 430 at a loading rate of 10 mm / min. Multiple samples (30 or more) were tested for each specimen, and a Weibull plot was constructed showing the percentage of samples that failed as a function of the loading force. The surface strength (or B10 surface strength) as reported herein corresponds to the B10 value obtained from the Weibull plot. The B10 value corresponds to the load force at which 10% of the samples break (or, equivalently, the load force at which 90% of the samples do not break). A representative Weibull plot is shown in FIG. Figure 10 As shown, and a B10 value of surface strength of 861.332N is shown.

[0050] The surface strength of the sheets produced by the systems and methods disclosed herein is greater than or equal to 300N, or greater than or equal to 400N, or greater than or equal to 500N, or greater than or equal to 600N, or greater than or equal to 700N, or greater than or equal to 1000N, or greater than or equal to 1500N, or greater than or equal to 2000N, or greater than or equal to 2500N, or from 300N to 900N, or from 400N to 800N, or from 300N to 3000N, or from 400N to 2400N, or from 500N to 2000N, or from 600N to 1500N.

[0051] Example 1

[0052] A series of tests were performed on wafers with the following composition: 33.0 mol% B2O3, 20.0 mol% La2O3, 15.0 mol% Nb2O5, 9.0 mol% TiO2, 7.0 mol% ZrO2 and 16.0 mol% WO3. The refractive index of the wafer nd The wafer was 2.0 mm thick, 300 mm in diameter, and 0.6 mm thick. Equivalent samples of the wafer were cleaned under various conditions. Similar results were obtained on a wafer with the following composition: 15.5 mol% SiO2, 17.6 mol% B2O3, 25.7 mol% La2O3, 5.0 mol% Nb2O5, 25.7 mol% TiO2, 8.0 mol% ZrO2, and 2.5 mol% Y2O3.

[0053] The wafers were polished and then introduced into the cleaning unit. After polishing, the wafers had an average B10 surface strength of 910N and a surface roughness Rq of less than 0.5nm. The wafers were then placed in a box, with batches of five wafers, and introduced into the cleaning unit with a spacing of approximately 15mm between the wafers in the box. The cleaning unit included 15 ultrasonic cleaning tanks. Tables 1 to 6 give the operating configurations of the cleaning unit tested (herein referred to as configurations AF). In each configuration, the wafer entered cleaning tank 1 and passed through cleaning tank 2, cleaning tank 3, etc. (e.g., Figure 4 ) until leaving cleaning tank 15. Detergent, water and isopropyl alcohol (IPA) are used as cleaning liquids. Detergent solutions are commercially available, as shown in Table 8, which lists the ingredients by volume percentage. Sodium oleate is the sodium salt of cis-9-octadecanoic acid. EDTA is ethylenediaminetetraacetic acid. Detergent D1 is diluted to 6 volume % in water and then used in cleaning tanks 1 and 2. Detergent D2 is diluted to 7 volume % in water and then used in cleaning tank 4. Detergent D3 is diluted to 5 volume % in water and then used in cleaning tank 5. When water is used as the cleaning liquid, the water is deionized water. When isopropyl alcohol is used as the cleaning liquid, pure isopropyl alcohol is used. Some cleaning tanks of constructions A and B differ in ultrasonic frequency. In particular, construction B increases the ultrasonic frequency of cleaning tanks 2-7, 9, 12 and 13 relative to construction A. Construction CF retains the ultrasonic frequency of construction B and is operated to change the ultrasonic power. After leaving the cleaning tank 15, the average surface strength and particle performance of the wafers were measured and are shown in Table 7. A particle performance rating of "acceptable" means that the particle density on the wafer surface is less than or equal to 0.075 particles / cm 2 .

[0054] Table 1 - Cleaning unit structure A

[0055] Table 2 - Cleaning Unit Configuration B

[0056] Table 3 - Cleaning unit structure C

[0057] Table 4-Cleaning Unit Configuration D

[0058] Table 5-Cleaning Unit Structure E

[0059] Table 6-Cleaning Unit Structure F

[0060] Table 7

[0061] Table 8 - Detergent solution (volume %)

[0062] Comparison of Configurations A and F illustrates the improvement in surface strength achieved by increasing the ultrasonic frequency in the cleaning tanks selected for this embodiment. The improvement in surface strength is expected to be universal when increasing the ultrasonic frequency in one or more cleaning tanks of the wafer cleaning system. It is preferred to maintain an ultrasonic frequency greater than 40 kHz in one or more, two or more, three or more, or greater than 50%, or greater than 60%, or greater than 70%, or greater than 80%, or greater than 90% of the cleaning tanks in the wafer cleaning system, and / or maintain the number of cleaning tanks operating at an ultrasonic frequency of 40 kHz or less at less than 40%, or less than 30%, or less than 20%, or less than 10% of the cleaning tanks in the wafer cleaning system.

[0063] In further embodiments, less than 50%, or less than 40%, or less than 30%, or less than 20%, or less than 10% of the total ultrasonic power of the wafer cleaning system is provided at an ultrasonic frequency of 60 kHz or less, or 50 kHz or less, or 40 kHz or less, wherein the density of particles having a size (longest linear dimension) greater than 5.0 microns on the surface of a wafer produced by the wafer cleaning system is less than or equal to 0.100 particles / cm as detected by optical inspection at a luminous intensity of 5000 lux. 2 , or less than or equal to 0.090 particles / cm 2 , or less than or equal to 0.080 particles / cm 2 , or less than or equal to 0.070 particles / cm 2 , or less than or greater than 0.060 particles / cm2 , or less than or equal to 0.050 particles / cm 2 .

[0064] Configurations BF operated at the same ultrasonic frequency in each cleaning tank, but applied different amounts of ultrasonic work to the wafer. Configuration B's ultrasonic work was low, and the wafer failed the particle performance test. Configuration B's ultrasonic work was insufficient to adequately clean the surface, and unacceptable levels of particulate matter were observed to remain on the surface. Configurations CF employed higher levels of ultrasonic work. Each of Configurations CF passed the particle performance test. However, a decrease in surface strength was observed as the ultrasonic work increased.

[0065] Figure 11 The results shown in Table 7 are summarized and provide guidance for designing flake cleaning systems to provide flakes that meet surface strength and particle performance standards. Figure 11 The relationship between surface intensity (RoR B10) and total ultrasonic power is shown. Data points based on the results of the configurations CF shown in Table 7 are included. The initial surface intensity of the sheet (910N) was set to a total ultrasonic power value of 0 W-hr, and a best fit curve was drawn through the data points. Figure 11 Performance ranges 470, 480, and 490 are shown. Range 470 is a low total ultrasonic power region where high surface intensity is maintained ("ROR OK"), but the particle performance test fails ("Particle NG"). Range 490 is a high total ultrasonic power region where the particle performance test passes ("Particle OK"), but the surface intensity is low ("ROR NG"). Range 480 is an intermediate total ultrasonic power range where a specified minimum surface intensity is maintained and the particle performance test passes ("RoR and Particle OK"). Figure 11 In the example shown, the specified minimum surface intensity selected is 530N and is achieved at a total ultrasonic power of 342W-hr or less. However, the particle performance test can only be passed at a total ultrasonic power of 220W-hr or greater. The minimum ultrasonic power required to pass the particle performance test is 220W-hr, and the maximum ultrasonic power that can provide a surface intensity of 530N or greater is 342W-hr. Similar methods can be used to determine operating conditions for the sheet that provide passing other particle performance tests (e.g., tests with other acceptable levels of particulate matter and / or other levels of magnification) while maintaining the surface intensity at or above other specified minimum values.

[0066] In embodiments, the total ultrasonic power is less than 600 W-hr, or less than 550 W-hr, or less than 500 W-hr, or less than 450 W-hr, or less than 400 W-hr, or less than 350 W-hr, or less than 300 W-hr, or less than 250 W-hr, or greater than 100 W-hr, or greater than 150 W-hr, or greater than 200 W-hr, or greater than 250 W-hr, or greater than 300 W-hr, or from 100 W-hr to 600 W-hr, or from 150 W-hr to 500 W-hr, or from 200 W-hr to 400 W-hr.

[0067] Example 2

[0068] In other embodiments, the wafer cleaning system further includes a processing unit in addition to the polishing unit and the cleaning unit. Figure 12 A wafer cleaning system 500 with a laser marking unit 530 is depicted. The wafer cleaning system 500 is configured to clean one wafer at a time or multiple wafers simultaneously. The wafer surface is polished in the polishing unit 510. After polishing, the wafer is directed to a first cleaning unit 520 to remove particulate matter generated by polishing. After cleaning in the first cleaning unit 520, the wafer is directed to a laser marking unit 530. In the laser marking unit 530, identification information is marked on the wafer using a laser. This identification information may include, for example, a serial number, a batch number, the wafer manufacturing date, wafer characteristics, customer information, etc. Laser marking can cause ablation or wear of the wafer and introduce additional particulate matter onto the surface. To remove particulate matter caused by laser marking, the wafer is directed to a second cleaning unit 540 for additional cleaning. After additional cleaning, the wafer is directed to a drying unit 550. Additional units, such as those for packaging and shipping, may also be included. The laser marking unit 530 is one embodiment of an intermediate processing unit that produces particulate matter formed on the surface of the sheet. The laser marking unit 530 is located upstream of the sheet in its final state.

[0069] The terms "upstream" and "downstream" are used herein to refer to the relative positions of different units in the wafer cleaning system. The process flow starts at an upstream location and proceeds downstream. Figure 12 The process flow shown in is from left to right, and any process unit to the left of another process unit is upstream of the other process unit. Figure 12 In the embodiment, the polishing unit 510 is upstream of the first cleaning unit 520, the first cleaning unit 520 is upstream of the laser marking unit 530, and the laser marking unit 530 is upstream of the second cleaning unit 540, and the second cleaning unit 540 is upstream of the drying unit 550. The polishing unit 510 and the first cleaning unit 520 are upstream of the laser marking unit 530.

[0070] The reason why the wafer cleaning system 500 requires a first cleaning unit 520 and a second cleaning unit 540 is that, in addition to the particulate matter generated by polishing, intermediate process steps (such as laser marking) can also introduce particulate matter. The need for multiple cleaning units inevitably exposes the wafer to additional ultrasonic power, resulting in reduced surface strength. For example, using the above-mentioned Figure 11 The relevant standards mean that even if the first cleaning unit 520 and the second cleaning unit 540 are operated according to the above-mentioned configuration B (the configuration with the minimum ultrasonic power), Figure 12 The total ultrasonic power of the intermediate wafer cleaning system 500 will also reach 410 W-hr, exceeding the maximum ultrasonic power (342 W-hr) that can provide a wafer with a surface strength of at least 530 N. The wafer cleaning system requires a new design to accommodate intermediate processing units that generate particulate matter.

[0071] To minimize ultrasonic power to maintain high surface strength, embodiments of the wafer cleaning system 500 include a cleaning tank with no or low ultrasonic power. Figure 13 An embodiment is shown in which the first cleaning unit 520 includes a spray cleaning tank instead of an ultrasonic cleaning tank. Figure 14 One embodiment is shown in which the first cleaning unit 520 includes a spray cleaning tank upstream of the ultrasonic cleaning tank. In other embodiments, the first cleaning unit 520 includes one or more spray cleaning tanks and one or more ultrasonic cleaning tanks. It is contemplated that the second cleaning unit 540 is also configured accordingly and is located downstream of the laser marking unit 530.

[0072] Figure 15 An embodiment is described in which the first cleaning unit 520 includes two spray cleaning tanks upstream of two ultrasonic cleaning tanks. Figure 15 As the first cleaning unit 520, and using the cleaning unit having configuration C described in Table 3 as the second cleaning unit 540 to complete Figure 12Testing of the wafer cleaning system 500. In the test, five wafers of the type used in Embodiment 1 were cleaned simultaneously. Cleaning using the first cleaning unit 520 included cleaning with a detergent solution in an upstream spray cleaning tank and cleaning with deionized water in a downstream spray cleaning tank. The detergent solution used in the upstream spray cleaning tank was a mixture of D1, D2, and D3 given in Table 8, in a volume ratio of 1:1:2, further diluted in water to 6% by volume. Neither spray cleaning tank used ultrasonic waves. Cleaning using the first cleaning unit 520 was performed continuously, with cleaning using a detergent solution (D3 in Table 8 diluted in water to 4% by volume) in the upstream ultrasonic cleaning tank and deionized water in the downstream ultrasonic cleaning tank. Each ultrasonic cleaning tank of the first cleaning unit 520 was operated at an ultrasonic frequency of 40 kHz, a current of 0.8 A, and a voltage of 220 V for a period of time sufficient to provide 12 W-hr of ultrasonic power. Therefore, the ultrasonic power of the first cleaning unit 520 was 24 W-hr. Upon exiting the first cleaning unit 520, the wafer is directed to the laser marking unit 530. The laser marking unit 530 is an intermediate processing unit that receives the wafer in the first intermediate state. In the laser marking unit 530, the wafer is marked with a laser to encode an identification serial number. Upon exiting the laser marking unit 530, the wafer is in the second intermediate state, its surface containing particulate matter formed by the laser light in the laser marking unit 530. The wafer in the second intermediate state is directed to the second cleaning unit 540. The ultrasonic power applied in the second cleaning unit 540 is 220 W-hr (Table 3). The total ultrasonic power of the wafer cleaning system 500 of this embodiment is 244 W-hr. Of the applied ultrasonic power, 38.67 W-hr is at an ultrasonic frequency of 40 kHz or less, and 205.33 W-hr is at an ultrasonic frequency of 80 kHz or greater. The initial surface strength of the wafer is 910 N. After cleaning, the surface strength of the wafer is 660 N, and the wafer passes the particle performance test.

[0073] In an embodiment, less than 30%, or less than 25%, or less than 20%, or less than 15%, or less than 10%, or between 5% and 30%, or between 10% and 25% of the total ultrasonic power is applied upstream of a laser marking unit or other intermediate processing unit that generates particulate matter formed on the surface of the sheet. In other embodiments, less than 100 W-hr, or less than 80 W-hr, or less than 60 W-hr, or less than 40 W-hr, or less than 20 W-hr, or between 10 W-hr and 100 W-hr, or between 15 W-hr and 80 W-hr, or between 20 W-hr and 60 W-hr of ultrasonic power is applied upstream of a laser marking unit or other intermediate processing unit that generates particulate matter formed on the surface of the sheet.

[0074] In an embodiment, less than 30%, or less than 25%, or less than 20%, or less than 15%, or less than 10%, or 5% to 30%, or 10% to 25% of the total ultrasonic power is applied by the first cleaning unit 520. In other embodiments, less than 100 W-hr, or less than 80 W-hr, or less than 60 W-hr, or less than 40 W-hr, or less than 20 W-hr, or 10 W-hr to 100 W-hr, or 15 W-hr to 80 W-hr, or 20 W-hr to 60 W-hr of the ultrasonic power is applied by the first cleaning unit 520.

[0075] In an embodiment, the first cleaning unit 520 includes one or more ultrasonic cleaning tanks, each of which operates at an ultrasonic frequency of 40 kHz or less. In other embodiments, the first cleaning unit 520 does not include an ultrasonic cleaning tank that operates at an ultrasonic frequency greater than 40 kHz. In further embodiments, greater than 50%, greater than 60%, greater than 70%, greater than 80%, or greater than 90% of the ultrasonic power applied by the first cleaning unit 520 is applied at an ultrasonic frequency of 40 kHz or less.

[0076] In an embodiment, greater than 60%, or greater than 70%, or greater than 80%, or greater than 90%, or between 60% and 95%, or between 65% and 90%, or between 70% and 85% of the total ultrasonic power is applied downstream of the laser marking unit or other intermediate processing unit that produces particulate matter formed on the surface of the sheet. In other embodiments, greater than 150 W-hr, or greater than 175 W-hr, or greater than 200 W-hr, or greater than 225 W-hr, or greater than 250 W-hr, or greater than 275 W-hr, or greater than 300 W-hr, or between 150 W-hr and 350 W-hr, or between 175 W-hr and 325 W-hr, or between 200 W-hr and 300 W-hr of ultrasonic power is applied downstream of the laser marking unit or other intermediate processing unit that produces particulate matter formed on the surface of the sheet.

[0077] In an embodiment, greater than 60%, or greater than 70%, or greater than 80%, or greater than 90%, or between 60% and 95%, or between 65% and 90%, or between 70% and 85% of the total ultrasonic power is applied by the second cleaning unit 540. In other embodiments, the ultrasonic power applied by the second cleaning unit 540 is greater than 150 W-hr, or greater than 175 W-hr, or greater than 200 W-hr, or greater than 225 W-hr, or greater than 250 W-hr, or greater than 275 W-hr, or greater than 300 W-hr, or between 150 W-hr and 350 W-hr, or between 175 W-hr and 325 W-hr, or between 200 W-hr and 300 W-hr, or less than 450 W-hr, or less than 425 W-hr, or less than 400 W-hr, or less than 375 W-hr, or less than 350 W-hr.

[0078] In an embodiment, the second cleaning unit 540 includes one or more ultrasonic cleaning tanks, each of which operates at an ultrasonic frequency greater than 40 kHz. In other embodiments, the second cleaning unit 540 does not include an ultrasonic cleaning tank that operates at an ultrasonic frequency of 40 kHz or less. In further embodiments, greater than 50%, greater than 60%, greater than 70%, greater than 80%, or greater than 90% of the ultrasonic power applied by the second cleaning unit 540 is applied at an ultrasonic frequency greater than 40 kHz, greater than 50 kHz, greater than 60 kHz, or greater than 70 kHz.

[0079] Unless expressly stated otherwise, any method set forth herein should not be construed as requiring that its steps be performed in a specific order. Therefore, if a method claim does not actually state the order in which its steps are to be followed, or if it is not otherwise expressly stated in the claims or specification that the steps are to be limited to a specific order, no specific order is intended to be inferred.

[0080] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the illustrated embodiments. Since those skilled in the art may conceive of various modifications, combinations, sub-combinations, and variations of the disclosed embodiments in combination with the spirit and substance of the illustrated embodiments, the specification should be construed to include all of the contents within the scope of the appended claims and their equivalents.

Claims

1. A method for cleaning a sheet, comprising: applying ultrasonic work to a sheet having an initial state comprising particulate matter on a surface thereof, controlling the application of ultrasonic power to achieve a total ultrasonic power that removes at least a portion of the particulate matter from the surface to treat the sheet to a final state, The particle density of particles larger than 5.0 μm on the surface of the sheet in the final state is less than 0.100 particles / cm by optical detection under a light intensity of 5000 lux. 2 ; The surface has an edge exclusion zone of 1.0 cm and a B10 surface strength greater than 400N.

2. The method of claim 1, wherein the sheet comprises glass.

3. The method of claim 2, wherein the refractive index n of the glass is d Greater than 1.

8.

4. The method of claim 2, wherein the glass comprises one or a combination of TiO2, Nb2O3, Bi2O3, WO3, Y2O3 and RE2O3 in an amount greater than 30 mol%.

5. The method of claim 1, wherein the longest cross-sectional dimension of the sheet in the initial state is greater than 100 mm. The method of claim 1 , wherein the sheet has a thickness of 0.1 mm to 5.0 mm.

7. The method of claim 1, wherein: The ultrasonic power is applied by a plurality of ultrasonic cleaning tanks, each of which includes a cleaning fluid and is configured to provide ultrasonic waves to the cleaning fluid at an ultrasonic frequency greater than 40 kHz.

8. The method of claim 7, wherein: The cleaning solution includes detergent, deionized water or isopropyl alcohol.

9. The method of claim 7, wherein: The plurality of ultrasonic cleaning tanks include a first ultrasonic cleaning tank containing a first cleaning liquid and a second ultrasonic cleaning tank containing a second cleaning liquid that is different from the first cleaning liquid.

10. The method of claim 1, wherein: The surface strength of the sheet in the final state is greater than 600N.

11. The method of claim 1 , wherein the total ultrasonic power is greater than 100 W-hr and less than 600 W-hr.

12. The method of claim 1, wherein the total ultrasonic power is greater than 150 W-hr and less than 500 W-hr.

13. The method of claim 1, wherein the total ultrasonic power is greater than 200 W-hr and less than 400 W-hr.

14. The method of claim 1, wherein: Less than 40% of the total ultrasonic power is provided at ultrasonic frequencies of 40 kHz or lower.

15. The method of claim 1, wherein: Less than 20% of the total ultrasonic power is provided at ultrasonic frequencies of 40 kHz or lower.

16. The method of claim 1 further comprising applying a spray to the surface of the sheet, the spray comprising a cleaning fluid and applied upstream of the sheet in the final state.

17. The method of claim 16, wherein: The spray is applied to the sheet in the initial state.

18. The method of claim 1 further comprising polishing the wafer to form the wafer in the initial state, the polishing producing the particulate matter.

19. The method of claim 1, further comprising: pausing the application of the ultrasonic power to produce the sheet in a first intermediate state; treating the flake in the first intermediate state, the treating comprising adding a second particulate matter to a surface of the flake in the first intermediate state to provide a flake in a second intermediate state; and The application of the ultrasonic work is resumed, the resuming comprising removing at least a portion of the second particulate matter on the surface of the flake in the second intermediate state using the ultrasonic work to provide the flake in the final state.

20. The method of claim 19, wherein: The processing comprises marking the sheet in the first intermediate state with a laser.

21. The method of claim 19, wherein the ultrasonic power applied upstream of the sheet in the first intermediate state is less than 20% of the total ultrasonic power.

22. The method of claim 19, wherein the ultrasonic power applied upstream of the sheet in the first intermediate state is less than 10% of the total ultrasonic power.

23. The method of claim 1, wherein: The particle density is less than 0.090 particles / cm 2 .

24. The method of claim 1, wherein: The particle density is less than 0.080 particles / cm 2 .

25. The method of claim 1, wherein: The particle density is less than 0.070 particles / cm 2 .

26. The method of claim 1, wherein The surface strength is greater than or equal to 600N.

27. The method of claim 1, wherein: The surface strength is greater than or equal to 1000N.

28. The method of claim 1, wherein The surface strength is greater than or equal to 1500N.

29. A system configured to clean a wafer according to the method of claim 1.

30. A system for cleaning a sheet, comprising: a first cleaning unit comprising a first spray cleaning tank, the first spray cleaning tank being configured to receive a wafer in an initial state, the wafer in the initial state comprising first particulate matter on a surface thereof, the first spray cleaning tank being configured to clean the wafer by removing a first portion of the first particulate matter from the surface thereof, the first cleaning unit cleaning the wafer to a first intermediate state; an intermediate processing unit configured to receive the sheet in the first intermediate state from the first cleaning unit, the intermediate processing unit processing the sheet in the first intermediate state to a second intermediate state, the processing forming a second particulate matter, the surface of the sheet in the second intermediate state including the second particulate matter; as well as a second cleaning unit configured to receive the wafer in the second intermediate state from the intermediate processing unit, the second cleaning unit cleaning the wafer to a final state by removing at least a portion of the second particulate matter from a surface of the wafer, The particle density of particles larger than 5.0 μm on the surface of the sheet in the final state is less than 0.100 particles / cm by optical detection under a light intensity of 5000 lux. 2 ; The surface has an edge exclusion zone of 1.0 cm and a B10 surface strength greater than 400N.

31. The system of claim 30, wherein the first cleaning unit further comprises an ultrasonic cleaning tank downstream of the first spray cleaning tank, the ultrasonic cleaning tank being configured to apply ultrasonic waves to the wafer, the ultrasonic waves removing a second portion of the first particulate matter from the surface.

32. The system of claim 31, wherein the frequency of the ultrasonic waves is 40 kHz or less.

33. The system of claim 31 , wherein the first cleaning unit further comprises a second spray cleaning tank upstream of the ultrasonic cleaning tank, the second spray cleaning tank configured to clean the wafer by removing a third portion of the first particulate matter from the surface.

34. The system of claim 33, wherein the first spray cleaning tank comprises a first cleaning fluid and the second spray cleaning tank comprises a second cleaning fluid, the second cleaning fluid being different from the first cleaning fluid.

35. The system of claim 34, wherein the first spray cleaning unit is located upstream of the second spray cleaning unit, and wherein, The first cleaning solution contains detergent, while the second cleaning solution does not contain detergent.

36. The system of claim 31, wherein: When the wafer is cleaned to the first intermediate state, the first cleaning unit applies a first ultrasonic power to the wafer, wherein the first ultrasonic power is less than 100 W-hr.

37. The system of claim 36, wherein: The first ultrasonic power is less than 40 W-hr.

38. The system of claim 36, wherein: More than 80% of the first ultrasonic power is applied at an ultrasonic frequency of 40 kHz or less.

39. The system of claim 36, wherein: More than 90% of the first ultrasonic power is applied at an ultrasonic frequency of 40 kHz or less.

40. The system of claim 31, wherein: The first cleaning unit includes two or more ultrasonic cleaning tanks downstream of a first spray cleaning tank.

41. The method of claim 40, wherein: The two or more ultrasonic cleaning tanks include a first ultrasonic cleaning tank having a first cleaning liquid and a second ultrasonic cleaning tank having a second cleaning liquid that is different from the first cleaning liquid.

42. The system of claim 41, wherein: The first cleaning solution contains detergent, while the second cleaning solution does not contain detergent.

43. The system of claim 30, wherein the intermediate processing unit comprises a laser marking unit.

44. The system of claim 30, wherein: The second cleaning unit includes an ultrasonic cleaning tank configured to apply ultrasonic waves to the sheet, the ultrasonic waves removing a portion of the second particulate matter from the surface.

45. The system of claim 44, wherein the frequency of the ultrasonic waves is greater than 40 kHz.

46. ​​The system of claim 44, wherein: When the wafer is cleaned to a final state, the second cleaning unit applies a second ultrasonic power to the wafer, where the second ultrasonic power is greater than 150 W-hr.

47. The system of claim 46, wherein: The second ultrasonic power is greater than 200 W-hr.

48. The system of claim 46, wherein: The second ultrasonic power is greater than 250 W-hr.

49. The system of claim 46, wherein: The second ultrasonic power is less than 400 W-hr.

50. The system of claim 46, wherein: The second ultrasonic power is less than 300 W-hr.

51. The system of claim 46, wherein: More than 80% of the second ultrasonic power is applied at an ultrasonic frequency greater than 40 kHz.

52. The system of claim 46, wherein: More than 90% of the second ultrasonic power is applied at an ultrasonic frequency greater than 40 kHz.

53. The system of claim 46, wherein: More than 80% of the second ultrasonic power is applied at an ultrasonic frequency greater than 60 kHz.

54. The system of claim 46, wherein: More than 90% of the second ultrasonic power is applied at an ultrasonic frequency greater than 60 kHz.

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