WO2017054146A1 - Apparatus and methods for cleaning wafers - Google Patents

Apparatus and methods for cleaning wafers Download PDF

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Publication number
WO2017054146A1
WO2017054146A1 PCT/CN2015/091150 CN2015091150W WO2017054146A1 WO 2017054146 A1 WO2017054146 A1 WO 2017054146A1 CN 2015091150 W CN2015091150 W CN 2015091150W WO 2017054146 A1 WO2017054146 A1 WO 2017054146A1
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WO
WIPO (PCT)
Prior art keywords
wafers
chuck
rotation speed
fluid
cleaning
Prior art date
Application number
PCT/CN2015/091150
Other languages
French (fr)
Inventor
Xiaoyan Zhang
Jun Wu
Hui Wang
Fuping CHEN
Original Assignee
Acm Research (Shanghai) Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Acm Research (Shanghai) Inc. filed Critical Acm Research (Shanghai) Inc.
Priority to PCT/CN2015/091150 priority Critical patent/WO2017054146A1/en
Priority to CN201580083409.7A priority patent/CN108140595A/en
Publication of WO2017054146A1 publication Critical patent/WO2017054146A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L21/687—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches
    • H01L21/68714—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches the wafers being placed on a susceptor, stage or support
    • H01L21/68771—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches the wafers being placed on a susceptor, stage or support characterised by supporting more than one semiconductor substrate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67017—Apparatus for fluid treatment
    • H01L21/67028—Apparatus for fluid treatment for cleaning followed by drying, rinsing, stripping, blasting or the like
    • H01L21/6704—Apparatus for fluid treatment for cleaning followed by drying, rinsing, stripping, blasting or the like for wet cleaning or washing
    • H01L21/67051—Apparatus for fluid treatment for cleaning followed by drying, rinsing, stripping, blasting or the like for wet cleaning or washing using mainly spraying means, e.g. nozzles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L21/687—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches
    • H01L21/68714—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches the wafers being placed on a susceptor, stage or support
    • H01L21/68728—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches the wafers being placed on a susceptor, stage or support characterised by a plurality of separate clamping members, e.g. clamping fingers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L21/687—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches
    • H01L21/68714—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches the wafers being placed on a susceptor, stage or support
    • H01L21/68764—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using mechanical means, e.g. chucks, clamps or pinches the wafers being placed on a susceptor, stage or support characterised by a movable susceptor, stage or support, others than those only rotating on their own vertical axis, e.g. susceptors on a rotating caroussel

Definitions

  • the present invention generally relates to apparatus and methods for cleaning wafers. More particularly, relates to cleaning wafer-level packaged semiconductor structures by driving the chuck to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, which can remove flux residues more thoroughly and efficiently.
  • Wafer Level Package is applied to package wafer, which has a tendency to become one of the mainstream technology in the microelectronic packaging industry. And this WLP process is quite different from traditional chip package process. Because in the traditional chip package process, the process is divided into several steps. For instance, the chip units are diced into pieces from a wafer first, and then each chip units is packaged and tested one by one. While in the WLP process, almost all the subsequent steps can be finished in one time, which makes WLP process much more efficient.
  • the WLP process is superior and advantageous, but it is challenging for cleaning the wafers packaged by the WLP process. Because a wafer packaged by the WLP process has lots of chip units on its surface, and a plurality of tiny structures are formed between the adjacent chip units, such as beams, bridges, gaps or trenches, etc. As a result, cleaning this type of wafer is more complex than cleaning conventional surface of the wafer . Generally, there are two significant problems for thoroughly removing contaminates from the wafer packaged by the WLP process:
  • the packaged wafer before dicing is essentially a flip-chip assembly with an array pattern of bumps or solder balls.
  • the bump structure becomes more fragile and the tiny structure between the chip units becomes much smaller, the small and fragile bumps interconnect structure of packaged wafer only permits a very narrow space between the chip units to be cleaned, such narrow space makes thorough and consistent cleaning of packaged wafer a big challenge.
  • packaged wafers must be free of contamination, such as flux, finger soils, water, or other surface contaminants, otherwise such residue left will lead to ionic contamination and corrosion, and interfere with underfilling to create voids that promote moisture collection, overheating and part failure.
  • an apparatus for cleaning wafers comprises: a chuck configured to hold at least two wafers, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a surface of the wafer; a driving device configured to drive the chuck to rotate; and at least one nozzle configured to spray a fluid to the wafers for cleaning or drying the wafers.
  • the driving device drives the chuck to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed, wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  • a method for cleaning wafers comprises: loading at least two wafers on a chuck, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a a surface of the wafer; driving the chuck to rotate at a rotation speed; spraying a fluid to the wafers for cleaning or drying the wafers; wherein the chuck is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed, wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  • another method for cleaning wafers comprises: taking at least two wafers from a cassette and loading the at least two wafers on a chuck which is disposed in a process chamber, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a a surface of the wafer; driving the chuck to rotate at a rotation speed; spraying a fluid to the wafers for cleaning or drying the wafers; wherein the chuck is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed, wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and
  • FIGs. 1A-1B depict an exemplary wafer which is packaged by WLP process
  • FIG. 2 depicts an exemplary apparatus for cleaning wafers
  • FIGs. 3A-3B depict another exemplary apparatus for cleaning wafers
  • FIGs. 4A-4C depict an exemplary chuck for holding wafers
  • FIGs. 5A-5B depict another exemplary chuck for holding wafers
  • FIGs. 6A-6B depict an exemplary clamping element
  • FIG 7 depicts an exemplary locating pin for holding a piece of wafer
  • FIG 8 depicts another exemplary locating pin for holding a piece of wafer
  • FIGs. 9A-9C depict another exemplary apparatus for cleaning wafers
  • FIG. 10 is a flow chart illustrating an exemplary method for cleaning wafers
  • FIG. 11 depicts the method for cleaning wafers in FIG. 10 ;
  • FIG. 12 is a flow chart illustrating another exemplary method for cleaning wafers.
  • FIG. 13 depicts the method for cleaning wafers in FIG. 12.
  • FIG. 1A to 1B depict an exemplary wafer which is packaged by WLP process.
  • FIG. 1A shows a top view of the wafer 1000 which is packaged by WLP process.
  • FIG. 1B shows a cross-sectional view of the wafer 1000 in FIG. 1A.
  • the wafer 1000 so-called wafer-level packaged wafer, has a lot of chip units 1001 on its surface 1002, and a plurality of tiny structures 1003 are formed between the adjacent chip units 1001.
  • the tiny structures 100 include but not limit to beams, bridges, gaps or trenches, etc.
  • the chip units 1001 generally have a certain height, and the letter “h” in FIG. 1B is the height of the chip units 1001. Because of the complicated tiny structures 1003, the wafer 1000 which is packaged by WLP process is hard to clean.
  • an apparatus for cleaning the wafers 1000 is provided by the present invention.
  • FIG. 2 depicts an exemplary apparatus for cleaning wafers according to the present invention.
  • the apparatus 2000 comprises: a chuck 2001 holding at least two wafers 1000, each of the at least two wafers 1000 are disposed with a distance from the center of the chuck 2001, and each wafer has a plurality of tiny structures 1003 on the surface 1002 of the wafer.
  • a driving device 2002 is connected with the chuck 2001 and drives the chuck 2001 to rotate.
  • at least one top nozzle is provided for spraying a fluid for cleaning or drying the wafers 1000 held on the chuck 2001.
  • the fluid may be deionized water, cleaning solution, gas or vapor.
  • the driving device 2002 drives the chuck 2001 to rotate at a low rotation speed and a high rotation speed alternatively during the cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed.
  • the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  • the low rotation speed Nl is slower than the critical rotation speed
  • D is the diameter of the wafers 1000
  • r is the shortest distance between the wafers 1000 and the center of the chuck 2001
  • h is the height of the tiny structures 1003 on the wafers 1000
  • t is the rotation time of the chuck 2001
  • ⁇ is the fluid density (for example, the liquid density)
  • ⁇ is the fluid surface tension coefficient (for example, the liquid surface tension coefficient) .
  • the rotation speed of the chuck 2001 should be well controlled.
  • a low rotation speed and a high rotation speed are applied to the chuck alternatively during the cleaning process.
  • the deionized water or the cleaning solution sprayed by the nozzle 2003 can easily flow across the tiny structures 1003 and uniformly cover the surface 1002 of the wafer, the deionized water or the cleaning solution will stay on the surface 1002 of the wafer for a period of time before a high rotation speed is applied, which makes the deionized water or the cleaning solution dissolve the contaminants thoroughly during this period.
  • a high rotation speed is applied, a centrifugal force is generated and it is strong enough to overcome the liquid surface tension. The centrifugal force will pushes the deionized water or the cleaning solution away from the wafer 1000, so the contaminants will go out along with the deionized water or the cleaning solution. Therefore, the apparatus 2000 can provide a thorough and consistent cleaning of contaminants.
  • Figs. 3A to 3B depict another exemplary apparatus for cleaning wafers according to the present invention.
  • the apparatus 3000 comprises: a chuck 3001 holding at least two wafers 1000, the at least two wafers 1000 are disposed with a distance from the center of the chuck 3001, and each wafer has a plurality of tiny structures 1003 on the surface of the wafer 1002.
  • a driving device 3002 is connected with the chuck 3001 and drives the chuck 3001 to rotate.
  • at least one top nozzle is configured to spray a fluid to the wafers 1000 for cleaning or drying the wafers 1000.
  • the fluid may be deionized water, cleaning solution, gas or vapor.
  • the apparatus 3000 further comprises at least one ultrasonic or megasonic device 3005 disposed above the chuck 3001.
  • the ultrasonic or megasonic device 3005 can apply ultrasonic or megasonic energy to clean the wafer 1000 when the nozzle 3003 spraying deionized water , cleaning solution, gas or vapor for cleaning the wafers held on the chuck 3001.
  • the driving device 3002 drives the chuck 3001 to rotate at a low rotation speed and a high rotation speed alternatively during the cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed.
  • the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  • the low rotation speed Nl is slower than the critical rotation speed
  • D is the diameter of the wafers 1000
  • r is the shortest distance between the wafers 1000 and the center of the chuck 3001
  • h is the height of the tiny structures 1003 on the wafers 1000
  • t is the rotation time of the chuck 3001
  • ⁇ is the fluid density (for example, the liquid density)
  • ⁇ is the fluid surface tension coefficient (for example, the liquid surface tension coefficient) .
  • the chuck 3001 holds at least two wafers 1000 by vacuum suction.
  • FIG 4A shows a top view of the chuck 3001 which holds at least two wafers 1000 by vacuum suction.
  • FIG. 4B shows a top view of the chuck 3001 which has no wafers thereon.
  • FIG. 4C shows a cross-sectional view of the chuck 3001.
  • the chuck 3001 includes at least two independent gas pipelines 3006, every gas pipeline 3006 is used for holding a piece of wafer 1000 on the chuck 3001 by vacuum suction. Every single gas pipeline 3006 is controlled independently and all of them have no effect on each other.
  • FIGs. 5A-5B depicts another exemplary chuck for holding wafers.
  • the chuck 4001 in FIG. 5A has wafers 1000 on it, while the chuck 4001 in FIG. 5B has no wafers 1000.
  • the chuck 4001 includes at least two groups of holding assemblies 4002, every group of holding assemblies 4002 includes one locating pin 4003 and at least three clamping elements 4004 for holding a piece of wafer 1000 on the chuck 4001.
  • the one locating pin 4003 and the at least three clamping elements 4004 uniformly distribute around the wafer 1000, and the locating pins 4003 are positioned at positions closest to the center of the chuck 4001.
  • FIGs. 6A-6B depict an exemplary clamping element.
  • the clamping element 4004 comprises a base 4005 and a moving part 4006.
  • the moving part 4006 is movably mounted on the base 4005 and wiggling back and forth when an external force being applied.
  • a centrifugal force is generated and applied to the moving part 4006 as a external force.
  • the bottom side of the moving part 4006 goes up and the top side of the moving part 4006 goes down, which makes the top side of the moving part 4006 press the surface of the wafer 1000 and apply a down force to the wafer 1000. So the wafer 1000 is clamped by the clamping elements 4004 under the down force.
  • the moving part 4006 will remain upright under the force of gravity, which makes it easy to move the wafer 1000 by a robot.
  • FIG. 7 depicts an exemplary locating pin for holding a piece of wafer.
  • Said locating pin 4003 works with the clamping elements 4004 to keep the wafer 1000 from moving during the rotation of the chuck 4001.
  • the shape of the locating pin 4003 is optional. As shown in FIG. 7, in one embodiment of the present invention, the shape of the locating pin 4003a is a cuboid. In another embodiment , as shown in FIG. 8, the shape of the locating pin 4003b is a cylinder.
  • FIGs. 9A-9C depict another exemplary apparatus for cleaning wafers according to the present invention.
  • the apparatus 9000 comprises: a chuck 9001 holding at least two pieces of wafers 1000.
  • the apparatus 9000 comprises a chuck 9001 holding four or six pieces of the wafers 1000. Because if the chuck holds too many pieces of wafers 1000, the size of the chuck 9001 needs to enlarge, which makes the chuck 9001 hard to rotate.
  • the four or six pieces of wafers 1000 are disposed with a distance from the center of the chuck 9001.
  • Each wafer 1000 has a plurality of tiny structures 1003 on the surface 1002 of the wafer.
  • a driving device 9002 is connected with the chuck 9001 and drives the chuck 9001 to rotate.
  • top nozzle spraying deionized water, cleaning solution, gas or vapor for cleaning or drying the wafers 1000 held on the chuck 9001.
  • Nozzle 9003 and nozzle 9004 are disposed at the top of the chuck 9001, either of them is a scan nozzle or a swing nozzle which can rotate around a rotating axis and spray deionized water, cleaning solution, gas or vapor onto different points of the wafers 1000.
  • the apparatus 9000 further comprises at least one side nozzle 9006 disposed on a side of each wafer 1000, the side nozzle 9006 has a plurality of ejecting ports 9007 which are linearly disposed and parallel with each other for spraying a fluid for cleaning or drying the wafers 1000.
  • the apparatus 9000 further comprises at least one ultrasonic or megasonic device 9005 disposed above the chuck 9001.
  • the ultrasonic or megasonic device 9005 can apply ultrasonic or megasonic energy to clean the wafer 1000 when the nozzle 9003 spraying deionized water , cleaning solution, gas or vapor for cleaning the wafers held on the chuck 9001.
  • the driving device 9002 drives the chuck 9001 to rotate at a low rotation speed and a high rotation speed alternatively during the cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed.
  • the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  • the low rotation speed Nl is slower than the critical rotation speed
  • D is the diameter of the wafers 1000
  • r is the shortest distance between the wafers 1000 and the center of the chuck 9001
  • h is the height of the tiny structures 1003 on the wafers 1000
  • t is the rotation time of the chuck 9001
  • ⁇ is the fluid density (for example, the liquid density)
  • ⁇ is the fluid surface tension coefficient (for example, the liquid surface tension coefficient) .
  • a critical rotation speed N can be calculated and written as:
  • FIG. 10 is a flow chart illustrating an exemplary method for cleaning wafers.
  • FIG. 11 depicts the method for cleaning wafers in FIG. 10.
  • a method for cleaning wafers can be set as follows:
  • Step 1 load at least two wafers 1000 on a chuck 1101, the at least two wafers 1000 are disposed with a distance from the center of the chuck 1101, and each wafer 1000 has a plurality of tiny structures 1003 on a surface 1002 of the wafer;
  • Step 2 drive the chuck 1101 to rotate at a rotation speed
  • Step 3 spray a fluid to the wafers 1000 for cleaning or drying the wafers 1000.
  • the chuck 1101 is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed,
  • the critical rotation speed is determined based on the diameters of the wafers 1000, the shortest distance between the wafers 1000 and the center of the chuck 1101, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  • the critical rotation speed is determined by:
  • D is the diameters of the wafers
  • r is the shortest distance between the wafers and the center of the chuck
  • h is the height of tiny structures on the wafers
  • t is the rotation time of the chuck
  • ⁇ is fluid density
  • ⁇ is fluid surface tension coefficient
  • the method further comprises the following step:
  • the fluid sprayed by the at least one nozzle includes deionized water, cleaning solution, gas or vapor.
  • FIG. 12 is a flow chart illustrating another exemplary method for cleaning wafers.
  • FIG. 13 depicts the method for cleaning wafers in FIG. 12.
  • another method for cleaning wafers can be set as follows:
  • Step 1 take at least two wafers 1000 from a cassette 1302 and load the at least two wafers 1000 on a chuck 1301 which is disposed in a process chamber 1300, the at least two wafers 1000 are disposed with a distance from the center of the chuck 1301, and each wafer 1000 has a plurality of tiny structures 1003 on a surface 1002 of the wafer;
  • Step 2 drive the chuck 1301 to rotate at a rotation speed
  • Step 3 spray a fluid to the wafers 1000 for cleaning or drying the wafers 1000.
  • the chuck 1301 is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed,
  • the critical rotation speed is determined based on the diameters of the wafers 1000, the shortest distance between the wafers 1000 and the center of the chuck 1301, the height of tiny structures 1003 on the surface of the wafers 1002, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  • the critical rotation speed is determined by:
  • D is the diameters of the wafers 1000
  • r is the shortest distance between the wafers 1000 and the center of the chuck 1301
  • h is the height of tiny structures 1003 on the wafers 1000
  • t is the rotation time of the chuck 1301
  • ⁇ is fluid density
  • ⁇ is fluid surface tension coefficient
  • the method further comprises the following step:
  • the fluid sprayed by the at least one nozzle includes deionized water, cleaning solution, gas or vapor.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Cleaning Or Drying Semiconductors (AREA)

Abstract

An apparatus (2000,3000,9000) for cleaning packaged wafers (1000) is provided. The apparatus (2000,3000,9000) comprises: a chuck (2001,3001,9001) holding at least two wafers (1000), the at least two wafers (1000) are disposed with a distance from the center of the chuck (2001,3001,9001), and each wafer (1000) has a plurality of tiny structures (1003) on a surface of the wafer (1000); driving device (2002,3002,9002) drives the chuck (2001,3001,9001) to rotate; and at least one nozzle (2003,2004, 3003,3004, 9003,9004) sprays fluid to the wafers (1000) for cleaning or drying the wafers (1000). Apparatus (2000,3000,9000) further provides a method for cleaning wafers (1000). The method comprises: loading at least two wafers (1000) on the chuck (2001,3001,9001), the at least two wafers (1000) are disposed with a distance from the center of the chuck (2001,3001,9001), and each wafer (1000) has a plurality of tiny structures (1003) on a surface of the wafer (1000); driving the chuck (2001,3001,9001) to rotate at a rotation speed; and spraying fluid to the wafers (1000) for cleaning or drying the wafers (1000).

Description

APPARATUS AND METHODS FOR CLEANING WAFERS FIELD OF THE INVENTION
The present invention generally relates to apparatus and methods for cleaning wafers. More particularly, relates to cleaning wafer-level packaged semiconductor structures by driving the chuck to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, which can remove flux residues more thoroughly and efficiently.
BACKGROUND
As the sizes of semiconductor devices become smaller and smaller, the IC packaging technology has developed to a new stage. A method called Wafer Level Package (WLP) process is applied to package wafer, which has a tendency to become one of the mainstream technology in the microelectronic packaging industry. And this WLP process is quite different from traditional chip package process. Because in the traditional chip package process, the process is divided into several steps. For instance, the chip units are diced into pieces from a wafer first, and then each chip units is packaged and tested one by one. While in the WLP process, almost all the subsequent steps can be finished in one time, which makes WLP process much more efficient.
The WLP process is superior and advantageous, but it is challenging for cleaning the wafers packaged by the WLP process. Because a wafer packaged by the WLP process has lots of chip units on its surface, and a plurality of tiny structures are formed between the adjacent chip units, such as beams, bridges, gaps or trenches, etc. As a result, cleaning this type of wafer is more complex than cleaning conventional surface of the wafer . Generally, there are two significant problems for thoroughly removing contaminates from the wafer packaged by the WLP process:
(1) High-temperature during reflow soldering step will create charred and caramelized flux residues that are difficult to be removed；
(2) The packaged wafer before dicing is essentially a flip-chip assembly with an array pattern of bumps or solder balls. As shrinkage of the bump dimension and pitch continues, the bump structure becomes more fragile and the tiny structure between the chip units becomes much smaller, the small and fragile bumps interconnect structure of packaged wafer only permits a very narrow space between the chip units to be cleaned, such narrow space makes thorough and consistent cleaning of packaged wafer a big challenge.
To meet performance and dependability standards, packaged wafers must be free of contamination, such as flux, finger soils, water, or other surface contaminants, otherwise such residue left will lead to ionic contamination and corrosion, and interfere with underfilling to create voids that promote moisture collection, overheating and part failure.
Therefore, there remains a need for an improved cleaning system that can provide a thorough and consistent cleaning of contaminants.
SUMMARY
In one embodiment of the present invention, an apparatus for cleaning wafers is provided. The apparatus comprises: a chuck configured to hold at least two wafers, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a surface of the wafer； a driving device configured to drive the chuck to rotate； and at least one nozzle configured to spray a fluid to the wafers for cleaning or drying the wafers. Wherein the driving device drives the chuck to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed, wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
In one embodiment of the present invention, a method for cleaning wafers is provided. The method comprises: loading at least two wafers on a chuck, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a a surface of the wafer； driving the chuck to rotate at a rotation speed； spraying a fluid to the wafers for cleaning or drying the wafers； wherein the chuck is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed, wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
In one embodiment of the present invention, another method for cleaning wafers is provided. The method comprises: taking at least two wafers from a cassette and loading the at least two wafers on a chuck which is disposed in a process chamber, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a a surface of the wafer； driving the chuck to rotate at a rotation speed； spraying a fluid to the wafers for cleaning or drying the wafers； wherein the chuck is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed, wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGs. 1A-1B depict an exemplary wafer which is packaged by WLP process；
FIG. 2 depicts an exemplary apparatus for cleaning wafers；
FIGs. 3A-3B depict another exemplary apparatus for cleaning wafers；
FIGs. 4A-4C depict an exemplary chuck for holding wafers；
FIGs. 5A-5B depict another exemplary chuck for holding wafers；
FIGs. 6A-6B depict an exemplary clamping element；
FIG 7 depicts an exemplary locating pin for holding a piece of wafer；
FIG 8 depicts another exemplary locating pin for holding a piece of wafer；
FIGs. 9A-9C depict another exemplary apparatus for cleaning wafers；
FIG. 10 is a flow chart illustrating an exemplary method for cleaning wafers；
FIG. 11 depicts the method for cleaning wafers in FIG. 10 ；
FIG. 12 is a flow chart illustrating another exemplary method for cleaning wafers； and
FIG. 13 depicts the method for cleaning wafers in FIG. 12.
DETAILED DESCRIPTION
Figs. 1A to 1B depict an exemplary wafer which is packaged by WLP process. FIG. 1A shows a top view of the wafer 1000 which is packaged by WLP process. And FIG. 1B shows a cross-sectional view of the wafer 1000 in FIG. 1A. The wafer 1000, so-called wafer-level packaged wafer, has a lot of chip units 1001 on its surface 1002, and a plurality of tiny structures 1003 are formed between the adjacent chip units 1001. The tiny structures 100 include but not limit to beams, bridges, gaps or trenches, etc. The chip units 1001 generally have a certain height, and the letter “h” in FIG. 1B is the height of the chip units 1001. Because of the complicated tiny structures 1003, the wafer 1000 which is packaged by WLP process is hard to clean. However, in the following embodiments, an apparatus for cleaning the wafers 1000 is provided by the present invention.
FIG. 2 depicts an exemplary apparatus for cleaning wafers according to the present invention. The apparatus 2000 comprises: a chuck 2001 holding at least two wafers 1000, each of the at least two wafers 1000 are disposed with a distance from the center of the chuck 2001, and each wafer has a plurality of tiny structures 1003 on the surface 1002 of the wafer. A driving device 2002 is connected with the chuck  2001 and drives the chuck 2001 to rotate. And at least one top nozzle is provided for spraying a fluid for cleaning or drying the wafers 1000 held on the chuck 2001. In one embodiment, the fluid may be deionized water, cleaning solution, gas or vapor. In one embodiment, there two top nozzles in total according to the FIG. 2, one nozzle 2003 sprays deionized water, cleaning solution for cleaning the wafers 1000, and the other nozzle 2004 sprays gas or vapor for drying the wafers 1000.
The driving device 2002 drives the chuck 2001 to rotate at a low rotation speed and a high rotation speed alternatively during the cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed. The critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
According to one embodiment, the low rotation speed Nl is slower than the critical rotation speed
Figure PCTCN2015091150-appb-000001
and the high rotation speed Nh is higher than the critical rotation
Figure PCTCN2015091150-appb-000002
where D is the diameter of the wafers 1000, r is the shortest distance between the wafers 1000 and the center of the chuck 2001, h is the height of the tiny structures 1003 on the wafers 1000, t is the rotation time of the chuck 2001, ρ is the fluid density (for example, the liquid density) , and σ is the fluid surface tension coefficient (for example, the liquid surface tension coefficient) .
During the cleaning process, in order to clean the contaminants thoroughly and consistently, the rotation speed of the chuck 2001 should be well controlled. A low rotation speed and a high rotation speed are applied to the chuck alternatively during the cleaning process. When a low rotation speed is applied, the deionized water  or the cleaning solution sprayed by the nozzle 2003 can easily flow across the tiny structures 1003 and uniformly cover the surface 1002 of the wafer, the deionized water or the cleaning solution will stay on the surface 1002 of the wafer for a period of time before a high rotation speed is applied, which makes the deionized water or the cleaning solution dissolve the contaminants thoroughly during this period. Further, when a high rotation speed is applied, a centrifugal force is generated and it is strong enough to overcome the liquid surface tension. The centrifugal force will pushes the deionized water or the cleaning solution away from the wafer 1000, so the contaminants will go out along with the deionized water or the cleaning solution. Therefore, the apparatus 2000 can provide a thorough and consistent cleaning of contaminants.
Figs. 3A to 3B depict another exemplary apparatus for cleaning wafers according to the present invention. The apparatus 3000 comprises: a chuck 3001 holding at least two wafers 1000, the at least two wafers 1000 are disposed with a distance from the center of the chuck 3001, and each wafer has a plurality of tiny structures 1003 on the surface of the wafer 1002. A driving device 3002 is connected with the chuck 3001 and drives the chuck 3001 to rotate. And at least one top nozzle is configured to spray a fluid to the wafers 1000 for cleaning or drying the wafers 1000. In one embodiment, the fluid may be deionized water, cleaning solution, gas or vapor. In one embodiment, there are two top nozzles in total according to the FIG. 3, one nozzle 3003 sprays deionized water, cleaning solution for cleaning the wafers 1000, and the other nozzle 3004 sprays gas or vapor for drying the wafers 1000. The apparatus 3000 further comprises at least one ultrasonic or megasonic device 3005 disposed above the chuck 3001. The ultrasonic or megasonic device 3005 can apply ultrasonic or megasonic energy to clean the wafer 1000 when the nozzle 3003 spraying deionized water , cleaning solution, gas or vapor for cleaning the wafers held on the chuck 3001.
The driving device 3002 drives the chuck 3001 to rotate at a low rotation speed and a high rotation speed alternatively during the cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation  speed is faster than the critical rotation speed. The critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
According to one embodiment, the low rotation speed Nl is slower than the critical rotation speed
Figure PCTCN2015091150-appb-000003
and the high rotation speed Nh is higher than the critical rotation
Figure PCTCN2015091150-appb-000004
where D is the diameter of the wafers 1000, r is the shortest distance between the wafers 1000 and the center of the chuck 3001, h is the height of the tiny structures 1003 on the wafers 1000, t is the rotation time of the chuck 3001, ρ is the fluid density (for example, the liquid density) , and σ is the fluid surface tension coefficient (for example, the liquid surface tension coefficient) .
Accordingly, in one embodiment of the present invention, the chuck 3001 holds at least two wafers 1000 by vacuum suction. FIGs. 4A-4C depict an exemplary chuck 3001 for holding wafers 1000. FIG 4A shows a top view of the chuck 3001 which holds at least two wafers 1000 by vacuum suction. FIG. 4B shows a top view of the chuck 3001 which has no wafers thereon. And FIG. 4C shows a cross-sectional view of the chuck 3001. The chuck 3001 includes at least two independent gas pipelines 3006, every gas pipeline 3006 is used for holding a piece of wafer 1000 on the chuck 3001 by vacuum suction. Every single gas pipeline 3006 is controlled independently and all of them have no effect on each other.
Accordingly, in one embodiment of the present invention, another chuck is provided. FIGs. 5A-5B depicts another exemplary chuck for holding wafers. The chuck 4001 in FIG. 5A has wafers 1000 on it, while the chuck 4001 in FIG. 5B has no wafers 1000. The chuck 4001 includes at least two groups of holding assemblies  4002, every group of holding assemblies 4002 includes one locating pin 4003 and at least three clamping elements 4004 for holding a piece of wafer 1000 on the chuck 4001. The one locating pin 4003 and the at least three clamping elements 4004 uniformly distribute around the wafer 1000, and the locating pins 4003 are positioned at positions closest to the center of the chuck 4001.
FIGs. 6A-6B depict an exemplary clamping element. The clamping element 4004 comprises a base 4005 and a moving part 4006. The moving part 4006 is movably mounted on the base 4005 and wiggling back and forth when an external force being applied. When the chuck 4001 rotates, a centrifugal force is generated and applied to the moving part 4006 as a external force. Under the circumstance, the bottom side of the moving part 4006 goes up and the top side of the moving part 4006 goes down, which makes the top side of the moving part 4006 press the surface of the wafer 1000 and apply a down force to the wafer 1000. So the wafer 1000 is clamped by the clamping elements 4004 under the down force. On the contrary, if the chuck 4001 keeps still, the moving part 4006 will remain upright under the force of gravity, which makes it easy to move the wafer 1000 by a robot.
FIG. 7 depicts an exemplary locating pin for holding a piece of wafer. Said locating pin 4003 works with the clamping elements 4004 to keep the wafer 1000 from moving during the rotation of the chuck 4001. The shape of the locating pin 4003 is optional. As shown in FIG. 7, in one embodiment of the present invention, the shape of the locating pin 4003a is a cuboid. In another embodiment , as shown in FIG. 8, the shape of the locating pin 4003b is a cylinder.
FIGs. 9A-9C depict another exemplary apparatus for cleaning wafers according to the present invention. The apparatus 9000 comprises: a chuck 9001 holding at least two pieces of wafers 1000. Preferably, the apparatus 9000 comprises a chuck 9001 holding four or six pieces of the wafers 1000. Because if the chuck holds too many pieces of wafers 1000, the size of the chuck 9001 needs to enlarge, which makes the chuck 9001 hard to rotate. The four or six pieces of wafers 1000 are disposed with a distance from the center of the chuck 9001. Each wafer 1000 has a plurality of tiny structures 1003 on the surface 1002 of the wafer. A driving device  9002 is connected with the chuck 9001 and drives the chuck 9001 to rotate. And at least one top nozzle spraying deionized water, cleaning solution, gas or vapor for cleaning or drying the wafers 1000 held on the chuck 9001. In one embodiment, there are two top nozzles in total according to the FIG. 9A, one nozzle 9003 spraying deionized water, cleaning solution for cleaning the wafers 1000, and the other nozzle 9004 spraying gas or vapor for drying the wafers 1000. Nozzle 9003 and nozzle 9004 are disposed at the top of the chuck 9001, either of them is a scan nozzle or a swing nozzle which can rotate around a rotating axis and spray deionized water, cleaning solution, gas or vapor onto different points of the wafers 1000. In one embodiment, the apparatus 9000 further comprises at least one side nozzle 9006 disposed on a side of each wafer 1000, the side nozzle 9006 has a plurality of ejecting ports 9007 which are linearly disposed and parallel with each other for spraying a fluid for cleaning or drying the wafers 1000. The apparatus 9000 further comprises at least one ultrasonic or megasonic device 9005 disposed above the chuck 9001. The ultrasonic or megasonic device 9005 can apply ultrasonic or megasonic energy to clean the wafer 1000 when the nozzle 9003 spraying deionized water , cleaning solution, gas or vapor for cleaning the wafers held on the chuck 9001.
The driving device 9002 drives the chuck 9001 to rotate at a low rotation speed and a high rotation speed alternatively during the cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed. The critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
According to one embodiment, the low rotation speed Nl is slower than the critical rotation speed
Figure PCTCN2015091150-appb-000005
and the high rotation speed Nh is higher than the critical rotation
Figure PCTCN2015091150-appb-000006
where D is the diameter of the wafers 1000, r is the shortest distance between the wafers 1000 and the center of the chuck 9001, h is the height of the tiny structures 1003 on the wafers 1000, t is the rotation time of the chuck 9001, ρ is the fluid density (for example, the liquid density) , and σ is the fluid surface tension coefficient (for example, the liquid surface tension coefficient) .
During the cleaning process, a rotation speed must be high enough to generate a centrifugal force for overcoming the liquid surface tension, and this centrifugal force will cause a centripetal acceleration in the radial direction. According to Newton’s second law, the following formula can be obtained:
Fc-Fs＝mac   (1) ；
where Fc is centrifugal force, Fs is liquid surface tension, m is liquid mass, ac is centripetal acceleration. Referring to FIG. 9C, where D is the diameters of the wafers 1000, r is the shortest distance between the wafers 1000 and the center of the chuck 9001, h is the height of the tiny structures 1003 on the wafers 1000 . ω is the angular velocity of the chuck 9001. According to formula (1) , a critical rotation speed N can be calculated and written as:
Figure PCTCN2015091150-appb-000007
where t is the rotation time of the chuck 9001, ρ is liquid density, and σ is liquid surface tension coefficient.
In one embodiment, the rotation time t＝1s, the diameters of the wafers A＝B＝300mm, the height of the tiny structures 1003 h＝40um, the shortest distance between the wafers 1000 and the center of the chuck 9001 r＝100mm, the liquid is DIW and has a density of ρ＝1000kg/m3, and the DIW has a liquid surface tension coefficient of σ ＝0.0727N/m at 20℃， so the critical rotation speed N＝1181RPM.
FIG. 10 is a flow chart illustrating an exemplary method for cleaning wafers. And FIG. 11 depicts the method for cleaning wafers in FIG. 10. According to the embodiment mentioned above, a method for cleaning wafers can be set as follows:
Process sequence
Step 1: load at least two wafers 1000 on a chuck 1101, the at least two wafers 1000 are disposed with a distance from the center of the chuck 1101, and each wafer 1000 has a plurality of tiny structures 1003 on a surface 1002 of the wafer；
Step 2: drive the chuck 1101 to rotate at a rotation speed；
Step 3: spray a fluid to the wafers 1000 for cleaning or drying the wafers 1000.
Wherein the chuck 1101 is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed,
wherein the critical rotation speed is determined based on the diameters of the wafers 1000, the shortest distance between the wafers 1000 and the center of the chuck 1101, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
In one embodiment, the critical rotation speed is determined by:
Figure PCTCN2015091150-appb-000008
where D is the diameters of the wafers, r is the shortest distance between the wafers and the center of the chuck, h is the height of tiny structures on the wafers, t is the rotation time of the chuck, ρ is fluid density, and σ is fluid surface tension coefficient.
In one embodiment, the method further comprises the following step:
apply ultrasonic or megasonic energy to clean the wafers 1000 when spraying the fluid to the surface of the wafers 1002； . the fluid sprayed by the at least one nozzle includes deionized water, cleaning solution, gas or vapor.
FIG. 12 is a flow chart illustrating another exemplary method for cleaning wafers. And FIG. 13 depicts the method for cleaning wafers in FIG. 12. According to the embodiment mentioned above, another method for cleaning wafers can be set as follows:
Process sequence
Step 1: take at least two wafers 1000 from a cassette 1302 and load the at least two wafers 1000 on a chuck 1301 which is disposed in a process chamber 1300, the at least two wafers 1000 are disposed with a distance from the center of the chuck 1301, and each wafer 1000 has a plurality of tiny structures 1003 on a surface 1002 of the wafer；
Step 2: drive the chuck 1301 to rotate at a rotation speed；
Step 3: spray a fluid to the wafers 1000 for cleaning or drying the wafers 1000.
Wherein the chuck 1301 is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed,
wherein the critical rotation speed is determined based on the diameters of the wafers 1000, the shortest distance between the wafers 1000 and the center of the chuck 1301, the height of tiny structures 1003 on the surface of the wafers 1002, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
In one embodiment, the critical rotation speed is determined by:
Figure PCTCN2015091150-appb-000009
where D is the diameters of the wafers 1000, r is the shortest distance between the wafers 1000 and the center of the chuck 1301, h is the height of tiny structures 1003 on the wafers 1000, t is the rotation time of the chuck 1301, ρ is fluid density, and σ is fluid surface tension coefficient.
In one embodiment, the method further comprises the following step:
apply ultrasonic or megasonic energy to clean the wafers when spraying the fluid to the surface of the wafers； the fluid sprayed by the at least one nozzle includes deionized water, cleaning solution, gas or vapor.
Although the present invention has been described with respect to certain embodiments, examples, and applications, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the invention.

Claims (21)

  1. An apparatus for cleaning wafers, comprising:
    a chuck configured to hold at least two wafers, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a surface of the wafer；
    a driving device configured to drive the chuck to rotate； and
    at least one nozzle configured to spray a fluid to the wafers for cleaning or drying the wafers；
    wherein the driving device drives the chuck to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed,
    wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  2. The apparatus as claimed in claim 1, wherein the critical rotation speed is determined by:
    Figure PCTCN2015091150-appb-100001
    where D is the diameters of the wafers, r is the shortest distance between the wafers and the center of the chuck, h is the height of tiny structures on the wafers, t is the rotation time of the chuck, ρ is fluid density, and σ is fluid surface tension coefficient.
  3. The apparatus as claimed in claim 1, wherein the fluid sprayed by the at least one nozzle includes deionized water, cleaning solution, gas or vapor.
  4. The apparatus as claimed in claim 1, wherein the chuck includes at least two holding assemblies, each holding assembly includes one locating pin and at least three clamping elements for holding a piece of wafer.
  5. The apparatus as claimed in claim 4, wherein for each holding assembly, the one locating pin and the at least three clamping elements uniformly distribute around the wafer, and the locating pin is positioned at a position closest to the center of the chuck.
  6. The apparatus as claimed in claim 4, wherein the clamping element comprising a base and a moving part, the moving part is movably mounted on the base and wiggling back and forth when an external force being applied.
  7.  The apparatus as claimed in claim 1, wherein the chuck apparatus holds the at least two wafers by vacuum suction.
  8. The apparatus as claimed in claim 1, wherein the chuck includes at least two independent gas pipelines, each gas pipeline is used for holding one piece of wafer on the chuck by vacuum suction.
  9. The apparatus as claimed in claim 1, wherein the tiny structures include beams, bridges, gaps or trenches.
  10. The apparatus as claimed in claim 1, wherein the wafers are wafer-level packaged wafers.
  11. The apparatus as claimed in claim 1, wherein the chuck holds four or six pieces of wafers.
  12. The apparatus as claimed in claim 1, wherein the nozzle is fixed at the top of the chuck.
  13. The apparatus as claimed in claim 1, further comprising a top nozzle disposed on the top of the chuck, wherein the top nozzle is a scan nozzle or a swing nozzle.
  14. The apparatus as claimed in claim 1, further comprising at least one side nozzle disposed on a side of each wafer, the side nozzle has a plurality of ejecting ports which are linearly disposed and parallel with each other for spraying a fluid for cleaning or drying the wafers.
  15. The apparatus as claimed in claim 1, further comprising at least one ultrasonic or megasonic device disposed above the chuck for cleaning the wafers.
  16. A method for cleaning wafers, comprising:
    loading at least two wafers on a chuck, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a a surface of the wafer；
    driving the chuck to rotate at a rotation speed；
    spraying a fluid to the wafers for cleaning or drying the wafers；
    wherein the chuck is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed,
    wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  17. The method as claimed in claim 16 wherein the critical rotation speed is determined by:
    Figure PCTCN2015091150-appb-100002
    where D is the diameters of the wafers, r is the shortest distance between the wafers and the center of the chuck, h is the height of tiny structures on the wafers, t is the rotation time of the chuck, ρ is fluid density, and σ is fluid surface tension coefficient.
  18. The method as claimed in claim 16, further comprising the following step:
    applying ultrasonic or megasonic energy to clean the wafers when spraying the fluid to the surface of the wafers；
    the fluid sprayed by the at least one nozzle includes deionized water, cleaning solution, gas or vapor.
  19. A method for cleaning wafers, comprising:
    taking at least two wafers from a cassette and loading the at least two wafers on a chuck which is disposed in a process chamber, the at least two wafers being disposed with a distance from the center of the chuck, wherein each wafer has a plurality of tiny structures on a a surface of the wafer；
    driving the chuck to rotate at a rotation speed；
    spraying a fluid to the wafers for cleaning or drying the wafers；
    wherein the chuck is driven to rotate at a low rotation speed and a high rotation speed alternatively during a cleaning process, wherein the low rotation speed Nl is slower than a critical rotation speed and the high rotation speed is faster than the critical rotation speed,
    wherein the critical rotation speed is determined based on the diameters of the wafers, the shortest distance between the wafers and the center of the chuck, the  height of tiny structures on the surface of the wafers, the rotation time of the chuck, fluid density, and fluid surface tension coefficient.
  20. The method as claimed in claim 19, wherein the critical rotation speed is determined by:
    Figure PCTCN2015091150-appb-100003
    where D is the diameters of the wafers, r is the shortest distance between the wafers and the center of the chuck, h is the height of tiny structures on the wafers, t is the rotation time of the chuck, ρ is fluid density, and σ is fluid surface tension coefficient.
  21. The method as claimed in claim 19, further comprising the following step:
    applying ultrasonic or megasonic energy to clean the wafers when spraying the fluid to the surface of the wafers；
    the fluid sprayed by the at least one nozzle includes deionized water, cleaning solution, gas or vapor.
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