Method for cleaning a workpiece

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cleaning apparatus for cleaning workpieces, such as semiconductor wafers or glass substrate for LCDs.

2. Description of the Related Art

Generally, a cleaning apparatus is employed prevalently in a semiconductor device fabricating process. The cleaning apparatus carries workpieces, such as semiconductor wafers or glass substrate for LCDs, (hereinafter referred to as “wafers”) sequentially to cleaning tanks respectively containing chemical liquids and rinsing liquids for cleaning and the like. A known cleaning apparatus shown in

FIG. 13

has a cleaning tank c having an inner tank a containing a cleaning liquid L in which wafers W are immersed and an outer tank b surrounding an upper end part of the inner tank a. A circulation line f connecting cleaning liquid supply nozzles d disposed in a lower part of the inner tank a and a drain port e formed in a bottom wall of the outer tank b is provided, for example, with an air bellows circulating pump g, a damper h and a filter i. Wafers W held on a wafer boat j are immersed in the cleaning liquid L contained in the inner tank a of the cleaning apparatus, the cleaning liquid L is supplied from a cleaning liquid source into the inner tank a so that the cleaning liquid L overflows the inner tank a into the outer tank b. The cleaning liquid L overflowed into the outer tank b is filtered and circulated. The wafers W are thus cleaned.

As the cleaning liquid is used repeatedly, contaminative particles, such as particles removed from the wafers W, are accumulated in the cleaning liquid. The wafers subjected to cleaning in the cleaning liquid are contaminated, the yield of the cleaning process is reduced and the cleaning performance of the cleaning apparatus is reduced if the particle concentration of the cleaning liquid exceeds a predetermined level.

As shown in

FIG. 13

, a branch line k for quality testing is connected to a part of the circulation line f on the discharge side of the circulating pump g, a testing means, for example, a particle counter m, is connected to the branch line k, and the discharge side of the particle counter m is connected to the outer tank b. A portion of the cleaning liquid L contained in the inner tank a is sampled and the number of particles contained in the sample cleaning liquid is measured to monitor the number of particles contained in the predetermined quantity of cleaning liquid L. In

FIG. 13

, indicated at n is a shutoff valve placed in the circulation line f, at p is a drain pipe connected to a drain port q formed in the bottom wall of the inner tank a, and at r is a drain valve placed in the drain pipe q.

Since the circulating pump g is of an air bellows type, the flow rate of the sample cleaning liquid is unstable and, consequently, accurate measurement of particles cannot be achieved. Since the circulating pump g serves also as means for supplying the cleaning liquid to the particle counter m, the cleaning liquid is supplied at a flow rate exceeding the ability of the particle counter m. Furthermore, since the measurement of particles uses the sample cleaning liquid sampled at a part of the circulation line f on the discharge side of the circulating pump g, the particle counter m adds the number of particles produced by the circulating pump g to the number of particles originally contained in the cleaning liquid and, consequently, the number of particles originally contained in the cleaning liquid cannot accurately be measured.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide a cleaning apparatus capable of accurately measuring fine contaminative particles, such as particles contained in a cleaning liquid, of operating at an improved yield and of exercising improved cleaning performance, and to provide a cleaning method to be carried out by the cleaning apparatus.

The foregoing object can be achieved by the followings.

According to one aspect of the present invention, a cleaning apparatus comprises a cleaning tank for containing a cleaning liquid in which workpieces are immersed for processing, a circulation line connected to the cleaning tank and provided with a filtering device, and a measuring line separate from the circulation line, provided with a fixed-quantity delivery means and a measuring means for measuring fine contaminated particles, such as particles, contained in the cleaning liquid and having a suction end connected to the cleaning tank.

In the cleaning apparatus of the present invention, the measuring means may be connected to the suction side of the fixed-quantity delivery means.

In the cleaning apparatus of the present invention, the measuring means may be connected to the discharge side of the fixed-quantity delivery means.

The measuring means is able to measure fine contaminative particles, such as particles, contained in the cleaning liquid accurately because a fixed quantity of the cleaning liquid can be taken out from the cleaning tank.

The cleaning apparatus of the present invention may be provided with a control means for synchronously operating the fixed-quantity delivery means and the measuring means.

The control means makes the measuring means carry out a measuring operation while the fixed-quantity delivery means is in suction operation.

A fixed quantity of the cleaning liquid can be sampled from the cleaning tank and the measuring means is able to achieve the accurate measurement of the fine contaminative particles, such as particles, contained in the cleaning liquid. The synchronous operation of the fixed-quantity delivery means and the measuring means improves measuring accuracy.

In the cleaning apparatus, the discharge end of the measuring line may be connected to the cleaning tank.

When the discharge end of the measuring line is connected to the cleaning tank, the sample cleaning liquid can be returned to the cleaning tank for the effective use of the cleaning liquid.

In the cleaning apparatus of the present invention, the cleaning tank may have an inner tank in which workpieces are immersed in the cleaning liquid, and an outer tank for containing the cleaning liquid overflowed the inner tank, and the suction side of the measuring line may be connected to the inner tank.

When the cleaning apparatus is thus constructed, a fixed quantity of the cleaning liquid contained in the inner tank in which workpieces are immersed in the cleaning liquid can be sampled and fine contaminative particles, such as particles, contained in the cleaning liquid can accurately be measured by the measuring means.

In the cleaning apparatus of the present invention, the discharge side of the measuring line may be connected to the outer tank.

When the discharge side of the measuring line is connected to the outer tank, the sample cleaning liquid subjected to measurement can be discharged into the outer tank instead of directly returning the same into the inner tank in which the workpieces are immersed in the cleaning liquid. Accordingly, the cleaning ability of the cleaning liquid is not reduced and the cleaning liquid can be circulated for the effective use of the same.

In the cleaning apparatus the present invention, the fixed-quantity delivery means may be a motor-operated bellows pump comprising a corrosion-resistant and chemical-resistant bellows, and a ball screw mechanism for driving the bellows.

The use of the chemical-resistant, durable motor-operated bellows pump capable of pumping a fixed quantity of the cleaning liquid extends the life of the apparatus, and improves measuring accuracy and the reliability of the apparatus.

In the cleaning apparatus of the present invention, the fixed-quantity delivery means may comprise a plurality of motor-operated bellows pumps arranged in parallel, and the bellows pumps may be driven so that the bellows pumps operate in different phases, respectively.

When the motor-operated bellows pumps excellent in ability to pump a fixed quantity of fluid, chemical resistance and durability are employed the fixed-quantity delivery means, the life of the apparatus can be extended, measuring accuracy can be improved, the reliability of the apparatus can be enhanced, and fine contaminative particles, such as particles, contained in the cleaning liquid can accurately and continuously be measured.

In the cleaning apparatus of the present invention, the control means may provide a detection signal when the contaminated particle number of the cleaning liquid determined on the basis of measured data provided by the measuring means exceeds a predetermined upper limit value.

According to another aspect of the present invention, a cleaning method which immerses workpieces in a cleaning liquid contained in a cleaning tank and circulates the cleaning liquid contained in the cleaning tank through a circulation line provided with a filtering device for filtering the cleaning liquid comprises a step of sampling a fixed quantity of the cleaning liquid from the cleaning tank by a fixed-quantity delivery means, a step of measuring fine contaminative particles contained in the cleaning liquid sampled by the fixed-quantity delivery means by a measuring means, and a step of providing a detection signal representing the contaminative particle number of the cleaning liquid determined on the basis of measured data measured by the measuring means by a control means.

The control means of the present invention may provide a cleaning liquid change request signal when the contaminative particle number of the cleaning liquid on the basis of measured data provided by the measuring means exceeds a predetermined upper limit value.

The control means of the present invention may compare the contaminative particle number of the cleaning liquid sampled before a start of a first cleaning cycle and that of the cleaning liquid sampled after the completion of a cleaning cycle, and may provide the detection signal when a differential particle number between the respective contaminative particle numbers of the cleaning liquids, exceeds a predetermined upper limit value.

The control means of the present invention may provide an abnormal workpiece signal when the contaminative particle number on the basis of the measured data provided by the measuring means exceeds a predetermined upper limit value.

According to the present invention, a fixed quantity of the cleaning liquid can be sampled from the cleaning liquid contained in the cleaning tank at a sampling position other than the circulation line before starting a cleaning process or during a cleaning process, and the quantity of contaminative particles contained in the cleaning liquid is measured. Therefore, contaminative particles contained in the cleaning liquid can accurately be measured, and it is possible to inform the operator of an inappropriate condition of the cleaning liquid by a detection signal indicating the quantity of contaminative particles exceeding a predetermined upper limit value. It is also possible to inform the operator that the quantity of contaminative particles contained in the cleaning liquid is not greater than the predetermined upper limit value and the normal cleaning process can be achieved.

The cleaning method of the present invention may further comprise a step of cleaning workpieces by immersing the same in the cleaning liquid contained in the cleaning tank after it is decided on the basis of a detection signal provided by the control means that the cleaning liquid is appropriate to cleaning.

According to the present invention, the ability and the yield of the cleaning process can be improved by cleaning the workpiece after it is decided that the measured quantity of contaminative particles is not greater than the predetermined upper limit value indicating the upper limit of the quantity of contaminative particles for the cleaning liquid appropriate to cleaning.

The cleaning method of the present invention may further comprise a step of changing the cleaning liquid when the cleaning liquid change request signal is provided continuously by the control means for a time exceeding a predetermined time.

According to the present invention, the cleaning liquid is changed if the quantity of contaminative particles does not decrease below the predetermined upper limit value in the predetermined time. Therefore, the ability and the yield of the cleaning process can be improved.

The cleaning method of the present invention may further comprise a step of changing the cleaning liquid when a differential particle number between the measured contaminative particle number of the cleaning liquid sampled before a start of a first cleaning cycle and that of the cleaning liquid sampled after the completion of a cleaning cycle exceeds a predetermined upper limit value.

According to the present invention, the cleaning ability of the cleaning liquid is improved and the yield can be improved because the cleaning liquid is changed when the differential particle number, i.e., the difference between the measured contaminative particle number of the cleaning liquid sampled before the start of the first cleaning cycle and that of the cleaning liquid sampled after the completion of the cleaning cycle, exceeds the predetermined upper limit value.

The cleaning method of the present invention may further comprise a step of comparing the measured contaminative particle concentration of the cleaning liquid sampled before a start of a cleaning cycle and that of the cleaning liquid sampled after the completion of the cleaning cycle, and providing the detection signal when a differential particle number between the respective contaminative particle numbers of the cleaning liquid, exceeds a predetermined upper limit value by the control means, and changing the cleaning liquid when the detection signal is provided by the control means.

According to the present invention, the cleaning ability of the cleaning liquid is improved and the yield can be improved because the cleaning liquid is changed when the differential particle number, i.e., the difference between the measured contaminative particle number of the cleaning liquid sampled before the start of the cleaning cycle and that of the cleaning liquid sampled when the completion of a cleaning cycle, exceeds the predetermined upper limit value.

The cleaning method of the present invention may change the cleaning liquid after the cleaning liquid has been used for a predetermined number of cleaning cycles or for a predetermined time.

According to the present invention, the cleaning ability of the cleaning liquid is improved and the yield can be improved because the cleaning liquid is changed when the same has been used for the predetermined number of cleaning cycles on the basis of experimental data or for the predetermined time determined on the basis of experimental data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic plan view of a cleaning system to which a cleaning apparatus in a first embodiment according to the present invention is applied;

FIG. 2

is a schematic sectional view of the cleaning apparatus employed in the cleaning system shown in

FIG. 1

;

FIG. 3

is a schematic sectional view of a fixed-quantity delivery pump and a particle counter included in the cleaning apparatus shown in

FIG. 2

;

FIGS.

4

(

a

) and

4

(

b

) are diagrams of assistance in explaining the operating modes of the fixed-quantity delivery pump;

FIG. 5

is a fragmentary schematic view of a cleaning apparatus in a modification of the cleaning apparatus shown in

FIG. 2

, provided with two fixed-quantity delivery pumps;

FIG. 6

is a graph showing the variation of the number of particles contained in a unit volume of the sample cleaning liquid with time;

FIG. 7

is a schematic sectional view of a cleaning apparatus in a second embodiment according to the present invention;

FIG. 8

is a graph showing the variation of the number of particles contained in a unit volume of the sample cleaning liquid with time;

FIG. 9

is a diagram of assistance in explaining a method of timing the start of a cleaning cycle;

FIG. 10

is a diagram showing the occurrence of an abnormal state during a cleaning cycle;

FIG. 11

is a diagram showing the effect of filtering on the variation of differential particle quantity;

FIG. 12

is a flow chart of a cleaning process; and

FIG. 13

is a schematic sectional view of a conventional cleaning apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A cleaning apparatus in a first embodiment according to the present invention will be described as applied to a semiconductor wafer cleaning system. Referring to

FIG. 1

, a cleaning system comprises, as principal components, a conveying section

2

for conveying a carrier

1

holding semiconductor wafers (workpieces) (hereinafter referred to simply as “wafers”) in ahorizontal position, i.e., a wafer container, a wafer processing section

3

for processing the wafers W in a chemical liquid and a cleaning liquid and drying the same, and a wafer handling section

4

interposed between the conveying section

2

and the processing section

3

for transferring wafers W from the conveying section

2

to the processing section

3

and vice versa, adjusting the position of wafers W and changing the position of wafers W.

The conveying section

2

has a carrier receiving unit

5

a,

a carrier delivering unit

5

b

and a wafer transfer unit

6

, which are disposed at one end of the cleaning system. A conveying mechanism, not shown, is disposed between the carrier receiving unit

5

a

and the wafer transfer unit

6

to convey the carrier

1

from the carrier receiving unit

5

a

to the wafer transfer unit

6

.

Carrier lifters, not shown, are installed in the carrier receiving unit

5

a

and the wafer transfer unit

6

, respectively. The lifters deliver empty carriers

1

to and receive the same from a carrier storage unit, not shown, disposed above the conveying section

2

. A transfer robot, not shown, capable of moving in horizontal directions, i.e., directions along an X- and a Y-axis, and vertical directions, i.e., directions along a Z-axis is installed in the carrier storage unit. The transfer robot arranges empty carriers

1

received from the wafer transfer unit

6

and carries empty carriers

1

to the wafer transfer unit

6

. Loaded carriers

1

containing wafers W also can be stored in the carrier storage unit.

The wafer transfer unit

6

has an opening opening into the wafer handling section

4

, and a lid operating device

8

is disposed in the opening of the wafer transfer unit

6

. The lid operating device

8

removes a lid, not shown, from a carrier

1

and put the same on the carrier

1

. The lid of a loaded carrier

1

loaded with unprocessed wafers W can be removed by the lid operating device

8

to carry the wafers W out of the carrier

1

, and the lid can be put on the empty carrier

1

after all the wafers W have been carried out of the carrier

1

. The lid of an empty carrier

1

transferred from the carrier storage unit to the wafer transfer unit

6

can be removed by the lid operating device

8

, and the lid can be put on the carrier

1

after the carrier

1

has been loaded with wafers W. A mapping sensor

9

is disposed near the opening of the wafer transfer unit

6

to count the number of wafers W contained in a carrier

1

.

Installed in the wafer handling section

4

are a wafer transfer arm

10

, i.e., a horizontal conveying means, for receiving wafers W from the wafer transfer unit

6

and returning wafers W to the wafer transfer unit

6

, a pitch changing mechanism, not shown, for holding a plurality of wafers W, such as fifth wafers W, in a horizontal position at predetermined intervals, a position changing mechanism

11

(position changing means) disposed between the wafer transfer arm

10

and the pitch changing mechanism to change a plurality of wafers W, such as twenty-five wafers W, from a horizontal position to a vertical position and vice versa, and a notch aligner (notch detecting means), not shown, for detecting notches, not shown, formed in wafers W held in a vertical position. The wafer handling section

4

has a conveying path

12

extended along the processing section

3

. Wafer conveying devices

13

(wafer conveying means) travel along the conveying path

12

.

The processing section

3

comprises a first processing unit

14

for removing particles and, organic contaminants from wafers W, a second processing unit

15

for removing metallic contaminants from wafers W, a cleaning unit

16

for removing a chemical oxide film formed on wafers W and drying wafers W, and a cleaning unit

17

for cleaning the wafer conveying device

13

, which are arranged in a straight row. A cleaning apparatus in accordance with the present invention is applied to each of the first processing unit

14

, the second processing unit

15

and the cleaning unit

17

. The wafer conveying devices

13

are disposed in sections of the conveying path

12

corresponding to the units

14

,

15

,

16

and

17

, respectively. Each wafer conveying device

13

is capable of moving in capable of moving in horizontal directions, i.e., directions along an X- and a Y-axis, and vertical directions, i.e., directions along a Z-axis, and of turning about a θ-axis.

The cleaning apparatus in the first embodiment according to the present invention will be described hereinafter. Referring to

FIG. 2

, the cleaning apparatus comprises a cleaning tank

20

having an inner tank

21

containing a cleaning liquid, such as diluted hydrofluoric acid solution (DHF) prepared by diluting hydrofluoric acid (HF) or a rinsing liquid, such as pure water, and an outer tank

22

surrounding an upper open part of the inner tank

21

to contain the cleaning liquid L overllowing from the inner tank

21

, cleaning liquid supply nozzles

23

disposed in a lower part of the inner tank

21

, a circulation pipe

24

connecting the cleaning liquid supply nozzles

23

and a drain port

22

a

formed in the bottom wall of the outer tank

22

, and a shutoff valve

25

, an air bellows circulating pump

26

, a damper

27

and a filter

28

arranged in that order from the side of the drain port

22

a

toward the cleaning liquid supply nozzles

23

on the circulation pipe

24

. A wafer boat

29

capable of holding, for example, fifth wafers W is disposed in the inner tank

20

of the cleaning tank

20

. A drain pipe

21

c

provided with a drain valve

21

b

is connected to a drain port

21

a

formed in the bottom wall of the inner tank

21

. The circulation pipe

24

, and the shutoff valve

25

, the circulating pump

26

, the damper

27

and the filter

28

placed on the circulation pipe

24

constitute a circulation line.

The cleaning apparatus is provided with, in addition to the circulating pump

26

placed on the circulation pipe

24

, a motor-operated bellows pump (hereinafter referred to as “fixed-quantity delivery pump”)

30

. The fixed-quantity delivery pump

30

has a suction port

31

connected by a suction pipe

51

to the inner tank

21

, and a discharge port

32

connected by a discharge pipe

52

to the outer tank

22

. A particle counter (measuring means)

50

for measuring fine contaminative particle contained in the cleaning liquid L sucked from the inner tank

21

by the fixed-quantity delivery pump

30

is placed on the suction pipe

51

. A central processing unit (abbreviated to “CPU”) (control means)

60

controls the particle counter

50

so as to operate in synchronism with the sucking operation of the fixed-quantity delivery pump

30

. Upon the detection of the actuation of the fixed-quantity delivery pump

30

, the CPU

60

actuates the particle counter

50

to measure the quantity (particle number per milliliter) of particles contained in the cleaning liquid L while a sample cleaning liquid is being sampled from the cleaning liquid L contained in the inner tank

21

. The CPU

60

provides a detection signal on the basis of the output signal of the particle counter

50

. For example, the CPU

60

provides an alarm as a detection signal and displays an alarm or the like when the quantity (particle number) of the particles is greater than a predetermined thresh value.

The suction pipe

51

, the discharge pipe

52

, the fixed-quantity delivery pump

30

and the particle counter

50

form a measuring line.

As shown in

FIG. 3

, the fixed-quantity delivery pump

30

has a stationary end member

33

provided with a suction port

31

and a discharge port

32

, a movable end member

34

disposed opposite to the stationary end member

33

, a bellows

35

made of a corrosion-resistant, chemical-resistant synthetic rubber and extended between the stationary end member

33

and the movable end member

34

, and a ball screw mechanism

36

for moving the movable end member

34

toward and away from the stationary end member

33

. A threaded rod

38

is linked through a plurality of steel balls to a nut

39

, and the nut

39

is connected to the movable end member

34

by a connecting member

40

. The threaded rod

38

is driven for rotation by a reversible stepping motor

37

to suck a fixed quantity (for example, 40 ml) of the cleaning liquid L from the inner tank

21

by making the bellows

35

expand and to discharge the sucked cleaning liquid L into the outer tank

22

by making the bellows

35

contract. Check valves

41

and

42

are placed in an end part of the suction pipe

51

connected to the suction port and in an end part of the discharge pipe

52

connected to the discharge port, respectively.

As shown in

FIG. 3

, the particle counter

50

has a wholly or partly transparent measuring pipe

53

placed in the suction pipe

51

, a laser light source

54

capable of emitting a laser beam and disposed on one side of the measuring pipe

53

, and a photodetector

55

disposed on the other side of the measuring pipe

53

opposite to the laser light source

54

.

The fixed-quantity delivery pump

30

is driven to suck a quantity of the cleaning liquid L from the inner tank

21

and, at the same time, the particle counter

50

is operated. The laser light source

54

emits a laser beam to irradiate the cleaning liquid L flowing through the measuring pipe

53

at a flow rate of 40 ml/min at the maximum. Deflection and interception of the laser beam by fine contaminative particles contained in the cleaning liquid L are detected by the photodetector

55

to count the number of particles contained in a predetermined quantity of the cleaning liquid L to determine the number of particles per milliliter (particles/ml). If the output shaft of the stepping motor

37

is operated in the normal and the reverse direction at the same rotating speed, a suction period, i.e., a time necessary for a suction stroke, and a discharge period, i.e., a time necessary for a discharge stroke, are equal to each other and the measuring operation of the particle counter

50

is interrupted while the bellows

35

is in a discharge stroke as shown in FIG.

4

(

a

). However, since the suction period and the discharge period are only a few seconds, the measurement of the particles is not affected by the interruption of the measuring operation of the particle counter

50

. The time of the measuring operation of the particle counter

50

can be increased and the time of interruption of the measuring operation of the particle counter

50

can be reduced by driving the output shaft of the stepping motor

37

at a low rotating speed for the suction stroke of the bellows and at a high rotating speed for the discharge stroke of the bellows

35

as shown in FIG.

4

(

b

).

The particle counter

50

can continuously be operated by providing the cleaning apparatus with a measuring line comprising the particle counter

50

and two fixed-quantity delivery pumps

30

A and

30

B connected in a parallel to the particle counter

50

as shown in FIG.

5

. The two fixed-quantity delivery pumps

30

A and

30

B are connected in parallel to the suction pipe

51

and the discharge pipe

52

and are operated in different phases, respectively; that is, the fixed-quantity delivery pump

30

A is driven for a discharge stroke while the other fixed-quantity delivery pump

30

B is driven for a suction stroke, whereby the particle counter

50

is able to operate for the continuous measurement of particles contained in a predetermined quantity of the cleaning liquid L flowing through the measuring pipe

53

.

The configuration of the measuring line shown in

FIG. 5

is the same as that of the measuring line shown in

FIG. 3

, except that the fixed-quantity delivery pump

30

A is connected to the suction pipe

51

and the discharge pipe

52

, and the other fixed-quantity delivery pump

30

B is connected to a branch suction pipe

51

A connected to the suction pipe

51

, and a branch discharge pipe

52

A connected to the discharge pipe

52

in the measuring line shown in

FIG. 5

, and hence parts shown in FIG.

5

and like or corresponding to those shown in

FIG. 3

are designated by the same reference characters and the further description thereof will be omitted.

The cleaning apparatus according to the present invention thus constructed cleans wafers W by immersing the wafers W in the cleaning liquid L contained in the inner tank

21

of the cleaning tank

20

, supplying the cleaning liquid L from a cleaning liquid source, not shown, into the inner tank

21

so that the cleaning liquid L overflows the inner tank

21

into the outer tank

22

, and filtering and circulating the cleaning liquid L collected in the outer tank

22

. The fixed-quantity delivery pump

30

(or the fixed-quantity delivery pumps

30

A and

30

B) and the particle counter

50

are operated during or before starting a cleaning process to sample a fixed quantity of the cleaning liquid L from the inner tank

21

through the measuring line separate from the circulation line and to measure particles contained in the sample cleaning liquid L. The sample cleaning liquid L sucked through the particle counter

50

by the fixed-quantity delivery pump

30

is discharged through the discharge port

32

of the fixed-quantity delivery pump

30

and is returned into the outer tank

22

of the cleaning tank

20

. Since the sample cleaning liquid L is not discharged into the inner tank

21

and is discharged into the outer tank

22

, the cleaning ability of the cleaning liquid L contained in the inner tank

21

is not reduced and the cleaning liquid L can effectively used. The sample cleaning liquid may be discharged into a waste tank or the like instead of returning the same into the outer tank

22

.

The particle concentration (particle number) of the cleaning liquid L contained in the inner tank

21

is thus monitored. For example, the particle concentration of the cleaning liquid L is determined before starting a cleaning cycle, wafers W are carried into the inner tank

21

and are subjected to the cleaning process if a detection signal provided by the CPU

60

indicates a particle concentration not greater than a predetermined upper limit particle concentration, such as 10 particles/ml as shown in FIG.

6

. Thus, wafers W can efficiently be cleaned. If the detection signal provided by the CPU

60

indicates a particle concentration (particle number) exceeding the upper limit particle concentration of 20 particles/ml, the CPU

60

display an alarm to inform the operator of an inappropriate cleaning state.

Although the cleaning apparatus in the first embodiment has been described on an assumption that the cleaning liquid L is DHF, the particle concentration (particle number) of the cleaning liquid can be monitored even if the cleaning liquid L is a mixed liquid of ammonia and hydrogen peroxide (APM) or a mixed liquid of sulfuric acid and hydrogen peroxide (SPM).

Although the cleaning apparatus in the first embodiment has been described as applied to the semiconductor wafer cleaning system, needless to say, the cleaning apparatus is applicable to cleaning articles other than semiconductor wafers, such as glass substrates for forming LCDs and such.

As is apparent from the foregoing description, the cleaning apparatus in accordance with the present invention thus constructed has the following excellent effects.

A fixed quantity of the cleaning liquid can be sampled from the cleaning liquid contained in the cleaning tank, and particles contained in the sample cleaning liquid can accurately be counted by the measuring means. Therefore, the quality of the cleaning liquid can be monitored, the cleaning liquid of an optimum condition can be used for cleaning, so that the cleaning apparatus is able to operate at an improved yield and to exercise an improved cleaning ability.

A fixed quantity of the cleaning liquid can be sampled from the cleaning liquid contained in the cleaning tank, particles contained in the sample cleaning liquid can accurately be counted by the measuring means and measuring accuracy can be improved by synchronously operating the fixed-quantity delivering means and the measuring means.

A fixed quantity of the cleaning liquid can be sampled from the cleaning liquid contained in the inner tank in which workpieces are immersed in the cleaning liquid, and particles contained in the sample cleaning liquid can accurately be measured by the measuring means.

Since the sample cleaning liquid can be discharged into the outer tank instead of discharging the same into the inner tank in which workpieces are immersed in the cleaning liquid, the cleaning liquid can be circulated without deteriorating the cleaning ability of the cleaning liquid contained in the inner tank and the cleaning liquid can effectively used.

Since the durable, chemical-resistant motor-operated bellows pump capable of metering the cleaning liquid can be employed as the fixed-quantity delivering means, the life of the cleaning apparatus can be extended, and the measuring accuracy of the measuring means and the reliability of the cleaning apparatus can be improved.

Since the durable, chemical-resistant motor-operated bellows pump capable of metering the cleaning liquid can be employed as the fixed-quantity delivering means, the life of the cleaning apparatus can be extended, measuring accuracy of the measuring means and the reliability of the cleaning apparatus can be improved, and particles contained in a large quantity of the cleaning liquid can continuously and accurately be measured.

Second Embodiment

A cleaning apparatus in a second embodiment according to the present invention is substantially identical with the cleaning apparatus in the first embodiment shown in

FIGS. 1

to

6

, except that the former carries out a cleaning method different from that carried out by the latter. Parts of the second embodiment like or corresponding to those of the first embodiment shown in

FIGS. 1

to

6

are designated by the same reference characters and the description thereof will be omitted.

In

FIG. 2

, the particle counter

50

is connected to the suction port

31

of the fixed-quantity delivery pump

30

. However, the particle counter

50

need not necessarily be placed on the suction pipe

51

connected to the suction port

31

of the fixed-quantity delivery pump

30

, but may be placed on a discharge pipe

52

connected to the discharge port

32

of a fixed-quantity delivery pump

30

as shown in FIG.

7

. When the particle counter

50

is placed in the discharge pipe

52

connected to the discharge side of the fixed-quantity delivery pump

30

, the sample cleaning liquid L sampled from the cleaning liquid L contained in an inner tank

21

is prevented from bubbling.

The cleaning apparatus shown in

FIG. 7

is the same in construction and function as the cleaning apparatus shown in

FIG. 2

, except that the particle counter

50

is connected to discharge side of the fixed-quantity delivery pump

30

in the cleaning apparatus shown in FIG.

7

and hence the fumer description of the cleaning apparatus shown in

FIG. 7

will be omitted.

In either the cleaning apparatus shown in

FIG. 2

or the cleaning apparatus shown in

FIG. 7

, wafers W are immersed in the cleaning liquid contained in the inner tank

21

of the cleaning tank

20

, the cleaning liquid L is supplied from the cleaning liquid source, not shown, into the inner tank

21

so that the cleaning liquid L overflows the inner tank

21

into the outer tank

22

, and the cleaning liquid collected in the outer tank

22

can be filtered and circulated while the wafers W are being cleaned. The fixed-quantity delivery pump

30

and the particle counter

50

are operated during or before starting a cleaning process to sample a fixed quantity of the cleaning liquid L from the inner tank

21

through the measuring line separate from the circulation line and to measure particles contained in the sample cleaning liquid L. The sample cleaning liquid L sucked through the particle counter

50

and discharged through the discharge port

32

of the fixed-quantity delivery pump

30

or the sample cleaning liquid discharged through the discharge port

32

of the fixed-quantity delivery pump

30

into the particle counter

50

is returned into the outer tank

22

of the cleaning tank

20

to use the sample cleaning liquid again for cleaning. Thus, the cleaning liquid can effectively used. The sample cleaning liquid may be discharged into a waste tank or the like instead of returning the same into the outer tank

22

.

A cleaning method in accordance with the present invention will be described hereinafter with reference to

FIGS. 8

to

12

. In step A (FIG.

12

), the fixed-quantity delivery pump

30

and the particle counter

50

are operated during or before starting a cleaning process to sample a fixed quantity of the cleaning liquid L from the inner tank

21

through the measuring line separate from the circulation line and to measure particles contained in the sample cleaning liquid L. If a particle concentration (particles/ml) determined on the basis of the number of particles counted by the particle counter

50

is greater than the upper limit particle concentration of, for example, 20 particles/ml, as shown in

FIG. 8

, the CPU

60

provides an alarm signal to inform the operator of an inappropriate cleaning condition (steps B and C). When the CPU

60

provides an alarm signal, the operator replaces the old cleaning liquid L with the new cleaning liquid L by discharges the old cleaning liquid L from the cleaning tank

20

and supplying the new cleaning liquid L into the cleaning tank

20

before starting the next cleaning cycle. The cleaning liquid L may be changed when the alarm signal provided by the CPU continues longer than a predetermined time. The cleaning liquid L is changed if the particle concentration of the cleaning liquid L does not decrease below the upper limit particle concentration before starting a cleaning cycle.

The alarm signal provided by the CPU may be interpreted as a cleaning liquid change request signal or an abnormal wafer indication signal.

If the measured particle concentration (particle number) is not greater than the upper limit particle concentration (particle number) and is on an acceptable level as shown in

FIG. 8

, wafers W are carried into the cleaning tank

20

, more specifically, into the inner tank

21

, the cleaning liquid L is supplied from the cleaning liquid source, not shown, into the inner tank

21

so that the cleaning liquid L overflows the inner tank

21

, the cleaning liquid L overflowing from the inner tank

21

is filtered and circulated while the wafers W are subjected to a cleaning process for a predetermined cleaning time, such as 10 min (steps D and E). The wafers W are carried out of the cleaning tank

20

after the elapse of the cleaning time. After the wafers W have been taken out of the cleaning tank

20

, the cleaning liquid L contained in the cleaning tank

20

is circulated through the circulation line while particles contained in the cleaning liquid L are filtered out. A plurality of wafers W, such as fifty wafers W, are carried into the cleaning tank

20

for the next cleaning cycle after the particle concentration of the cleaning liquid L has been decreased to an acceptable level as shown in FIG.

9

. Then, the next cleaning cycle is executed. During the cleaning process, the cleaning liquid L contained in the inner tank

21

is sampled, and the number of particles contained in the sample cleaning liquid L is measured by the particle counter

50

. If the particle concentration increases extraordinarily beyond the upper limit particle concentration during the cleaning process, the CPU

60

provides an alarm signal as shown in

FIG. 6

to inform the operator of the abnormal condition, and the cleaning process is interrupted.

The CPU

60

may compare a particle concentration (particle number) measured before starting the first cleaning cycle and a particle concentration (particle number) measured after the completion of every cleaning cycle, and may provide an alarm signal if the difference between the particle concentration measured before starting the first cleaning cycle and the particle concentration measured after the completion of every cleaning cycle exceeds a predetermined upper limit value. The operator is able to perceive that the wafers W being cleaned are abnormal from the alarm signal provided by the CPU

60

, and the abnormal wafers W can be discriminated and separated from normal wafers.

A plurality of cycles of the cleaning process are carried out to clean a plurality of lots of wafers W. Particles contained in the cleaning liquid L are counted by the particle counter

50

during the plurality of cycles of the cleaning process, and the differences S

1

, S

2

and S

3

(

FIG. 11

) between the particle concentrations measured in the successive cleaning cycles may be calculated. If the difference is greater than a predetermined upper limit value, such as the difference S

3

(FIG.

11

), the cleaning liquid L is changed (steps F and G). The cleaning liquid L may be changed when the difference between a particle concentration of the cleaning liquid L at the start of the nth cleaning cycle and a minimum particle concentration of the cleaning liquid L reached after the completion of the nth cleaning cycle is greater than a predetermined upper limit value. A number of cleaning cycles to be carried out or a period for which the cleaning process can be carried out before changing the cleaning liquid L may be determined beforehand on the basis of experimental data, and it is possible to change the cleaning liquid L at optimum time by referring to the predetermined number of cleaning cycles or the predetermined time.

Although the cleaning method in accordance with the present invention has been described on an assumption that the cleaning liquid L is DHF, the particle concentration of the cleaning liquid can be determined and the quality of the cleaning liquid L can be monitored even if the cleaning liquid L is a mixed liquid of ammonia and hydrogen peroxide (APM) or a mixed liquid of sulfuric acid and hydrogen peroxide (SPM).

Although the cleaning method in accordance with the present invention has been described as applied to the semiconductor wafer cleaning system, needless to say, the cleaning method is applicable to cleaning articles other than semiconductor wafers, such as glass substrates for forming LCDs and such.

According to the present invention, a fixed quantity of the cleaning liquid contained in the cleaning tank is sampled from a part other than the circulation line before starting a cleaning process or during the cleaning process, and the quantity (particle number) of contaminative particles contained in the cleaning liquid is measured. Therefore, contaminative particles contained in the cleaning liquid can accurately be measured, and it is possible to inform the operator of an inappropriate condition of the cleaning liquid by a detection signal indicating a quantity of contaminative particles exceeding a predetermined upper limit value. Consequently, the cleaning liquid can be maintained in a quality suitable for cleaning, and cleaning ability and yield can be improved. It is also possible to inform the operator that the quantity of contaminative particles contained in the cleaning liquid is not greater than the predetermined upper limit value and the normal cleaning process can be achieved.

Since a fixed quantity of the cleaning liquid contained in the cleaning tank is sampled from a part other than the circulation line and the quantity of contaminative particles contained in the sample cleaning liquid is measured, the quantity of contaminative particles contained in the cleaning liquid can accurately be measured, and the cleaning liquid is changed if particle concentration of the cleaning liquid decreases below the predetermined upper limit value to improve the ability and the yield of the cleaning process.

Since a fixed quantity of the cleaning liquid contained in the cleaning tank is sampled from a part other than the circulation line and the quantity of contaminative particles contained in the sample cleaning liquid is measured, the quantity of contaminative particles contained in the cleaning liquid can accurately be measured, and the cleaning ability of the cleaning liquid and yield can be improved by changing the cleaning liquid if the difference between the particle concentration of the cleaning liquid before starting the first cleaning cycle and that of the cleaning liquid after the completion of a cleaning cycle is greater than a predetermined upper limit value.

Since a fixed quantity of the cleaning liquid contained in the cleaning tank is sampled from a part other than the circulation line and the quantity of contaminative particles contained in the sample cleaning liquid is measured, the quantity of contaminative particles contained in the cleaning liquid can accurately be measured, and the cleaning ability of the cleaning liquid and yield can be improved by changing the cleaning liquid if the difference between the particle concentration of the cleaning liquid before starting a cleaning cycle and that of the cleaning liquid after the completion of the same cleaning cycle is greater than a predetermined upper limit value.

The cleaning liquid can properly be changed and the cleaning ability of the cleaning liquid and yield can be improved by determining time for changing the cleaning liquid on the basis of a predetermined number of cleaning cycles to be carried out or a predetermined period for which the cleaning process may be carried out before changing the cleaning liquid, and the measured particle concentration of the cleaning liquid.

Number	Date	Country	Kind
10-051543	Feb 1998	JP
10-051544	Feb 1998	JP

Number	Name	Date
3964956	Snyder	Jun 1976
4033871	Wall	Jul 1977
5722441	Teramoto	Mar 1998

Number	Date	Country
62-32531	Feb 1987	JP
62-176585	Aug 1987	JP
63-137430	Jun 1988	JP
314835	Dec 1988	JP
02243784	Sep 1990	JP
04278529	Oct 1992	JP
08120462	May 1996	JP

Method for cleaning a workpiece

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (2)

US Referenced Citations (3)

Foreign Referenced Citations (7)