JP2000051796A - Method for evaluating washing of substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for evaluating washing of substrates capable of evaluating higher washing capability. SOLUTION: Plural sheets of the substrates for evaluating washing sprayed with a latex are formed by drying the substrates after coating of an aq. latex soln. prepd. by mixing the latex with pure water (S1). The substrates for evaluating washing are heated by heating every different temp., to fix the latex to the substrates for evaluating washing with fixing power varying at every heating temp. (S2). The substrates for evaluating washing under prescribed washing conditions (S4). The number of the particles of the latex sprayed onto the substrates for evaluating washing are respectively measured before and after the washing (S3, 5). The heating temp., of the substrate, with which the number of the particles of the latex on the substrate changes largely before and after the washing, are set as the indices for the washing capability of these washing conditions. The evaluation of the washing conditions, etc., having the high washing capability is made possible by deciding the respective heating temps. of the plural washing conditions as the indices (S6, 7).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the cleaning performance of a substrate, such as a semiconductor substrate or a glass substrate for a liquid crystal display, for cleaning the substrate.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of circuit elements, a brush type cleaning, a high pressure jet type, and the like have been used to remove finer particles adhering to a substrate such as a semiconductor substrate or a glass substrate for a liquid crystal display. Various types of substrate cleaning having relatively high cleaning ability, such as cleaning or ultrasonic cleaning, are performed. In this substrate cleaning, cleaning performance is regularly evaluated in order to maintain a predetermined substrate cleaning effect. Further, in order to find a cleaning condition with a higher cleaning effect or to manufacture a cleaning device with a higher cleaning effect, the cleaning performance is evaluated for each cleaning condition or for each cleaning device.

Conventionally, the evaluation of the cleaning ability is performed, for example, as follows. First, a substrate on which silicon powder has been sprayed is generated, and the number of silicon powders sprayed on the substrate is measured before cleaning. Next, the substrate on which the silicon powder has been sprayed is cleaned under predetermined cleaning conditions or a cleaning apparatus. Finally, the number of silicon powders remaining on the cleaned substrate is measured. Thus, the change in the number of silicon powders before and after the cleaning, that is, the removal rate calculated from the number of silicon powders before and after the substrate cleaning is indicated as the cleaning conditions or the cleaning capability of the cleaning apparatus. As a method other than using silicon powder, a method in which particles are adhered to the cleaning surface of the substrate by transporting the substrate so that the cleaning surface of the substrate touches the transport mechanism (hereinafter, simply referred to as “back surface transportation”). However, also in this case, the particle removal rate is indicated as the cleaning ability by the same method as in the case of silicon powder.

[0004]

However, the prior art having such a structure has the following problems. That is, in recent years, a cleaning apparatus and a cleaning condition with a higher cleaning performance are required, but the conventional method has a relatively sufficient cleaning performance with respect to silicon powder and particles adhered by conveying the back surface, and so on. Even if the cleaning equipment and cleaning conditions are changed, there is a phenomenon in which the particle removal rate does not significantly change, and by using the removal rate as an index, it is possible to evaluate cleaning equipment and cleaning conditions with higher cleaning performance. There is a problem that can not be.

[0005] In the case of backside transport, the particles adhering to the cleaning surface of the substrate are not constant between the substrates, so that many particles adhere in the initial state and cases where only a small amount of particles adhere. Therefore, there is a problem that the particle removal rate greatly changes depending on the initial state, and it is not possible to accurately evaluate the cleaning ability by using the particle removal rate before and after cleaning as an index.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a substrate cleaning evaluation method capable of evaluating higher cleaning performance.

[0007]

The present invention has the following configuration in order to achieve the above object. In other words, the invention according to claim 1 is a substrate cleaning evaluation method for evaluating a cleaning ability based on a change in the number of objects to be removed on the substrate before and after cleaning, when the substrate on which the objects to be removed are sprayed is cleaned. A step of spraying each of the latexes to be removed on the plurality of substrates, a step of heating each of the substrates at a different heating temperature, and a step of cleaning the number of latex particles sprayed on each of the substrates. Measuring before, washing each heated substrate, measuring the number of latex particles remaining on each substrate after the washing, and from each of the substrates, the latex on the substrate, A step of indicating the substrate heating temperature at which the number of particles has changed relatively significantly before and after the cleaning as a substrate cleaning ability.

According to a second aspect of the present invention, when cleaning a substrate on which the object to be removed has been sprayed, the cleaning performance is evaluated based on a change in the number of the object to be removed on the substrate before and after the cleaning. A method, wherein each step of spraying latex, which is an object to be removed, on a plurality of substrates, a step of heating each substrate at a constant temperature and a different heating time, and a step of heating latex sprayed on each substrate. A step of measuring the number of particles before washing, and a step of washing each heated substrate,
The process of measuring the number of latex particles remaining on each substrate after the washing and the heating time of the substrate, in which the number of latex particles on the substrate changed significantly before and after washing from among the substrates, And a step of indicating as a cleaning ability.

According to a third aspect of the present invention, in the method for evaluating cleaning of a substrate according to the first or second aspect, the latex is a polystyrene latex.

[0010]

The operation of the present invention is as follows. According to the first aspect of the present invention, latex is sprayed on each of the plurality of substrates. Each substrate on which the latex has been sprayed is heated at a different heating temperature. Washing the heated substrate removes the sparged latex on the substrate. By measuring the number of latex particles sprayed on the substrate before and after washing the substrate, the change in the number of latex particles removed by washing is determined. At this time, a change in the number of particles of the latex occurs at a certain heating temperature as a boundary and relatively large compared to other heating temperatures. This is presumably because the difference in the fixing power of the latex onto the substrate appears due to the difference in the heating temperature of the substrate. The heating temperature of the substrate where the number of particles of the latex greatly changed before and after the washing is indicated as the washing ability. For example, the cleaning ability under each cleaning condition is evaluated by comparing the heating temperature of the substrate where the number of particles of the latex changes greatly under various cleaning conditions.

According to the second aspect of the present invention, latex is sprayed on each of the plurality of substrates. Each substrate on which the latex has been sprayed is heated at a constant temperature for a different heating time. By washing the substrates having different heating times, latex sprayed on each substrate is removed. By measuring the number of latex particles sprayed on each substrate before and after washing the substrate, the change in the number of latex particles removed by washing is determined. At this time, a phenomenon occurs in which the number of particles of the latex changes relatively greatly after a certain heating time as compared with other heating times. This is presumed to be due to the difference in the fixing power of the latex onto the substrate due to the difference in the heating time of the substrate. The heating time of the substrate where the number of particles of this latex has changed greatly,
Index as cleaning ability. For example, the cleaning ability under each cleaning condition is evaluated by comparing the heating time of the substrate in which the number of latex particles changes greatly under various cleaning conditions.

According to the third aspect of the present invention, after the polystyrene latex is sprayed on a plurality of substrates, each of the substrates is subjected to the above-described substrate cleaning evaluation method of the first or second aspect.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. The substrate cleaning evaluation method according to the present invention includes, for example, a substrate rotating unit for spraying polystyrene latex on a substrate, a particle checker unit for measuring the number of particles of polystyrene latex sprayed on the substrate, and heating the substrate. This is performed by a unit such as a substrate heating unit that performs cleaning conditions and a substrate cleaning unit that performs cleaning conditions and the like for which cleaning performance is to be evaluated. In addition,
Latex refers to a colloidal aqueous dispersion of a polymeric material. The polystyrene latex refers to a latex mainly containing polystyrene colloid particles as a polymer material.

The substrate cleaning evaluation method according to the present invention is described below.
A description will be given with reference to the flowchart shown in FIG. 1 and specific processing performed by each unit (not shown) will be described.

Step S1 (spraying latex onto substrate) A predetermined amount of, for example, 0.196 μm diameter polystyrene latex is mixed with pure water to produce a predetermined concentration of polystyrene latex aqueous solution. A plurality of substrates to be cleaned are set in a substrate rotating unit. It is preferable that these substrates have a clean state in which particles are not attached to the surface.

The substrate rotation unit transports each substrate onto a spin chuck provided in the substrate rotation unit, holds the substrate on the spin chuck, and rotates the substrate. An aqueous solution of polystyrene latex is dropped onto the rotating substrate. The aqueous solution of polystyrene latex dropped on the substrate spreads over the entire surface of the substrate, that is, the aqueous solution of polystyrene latex is applied on the substrate. Furthermore, the substrate rotation unit evaporates a solution component such as pure water of a polystyrene latex aqueous solution applied on the substrate by rotating the substrate (spin drying).

As a result, the polystyrene latex is substantially uniformly dispersed on the substrate. Polystyrene latex is sprayed on a plurality of substrates in the same manner. In this embodiment, since a predetermined concentration of polystyrene latex aqueous solution is applied to each substrate by the substrate rotation method, the polystyrene latex sprayed on each substrate has relatively little variation between the substrates and the entire surface of the substrate. The polystyrene latex can be sprayed almost uniformly. Incidentally, the polystyrene latex is not limited to the one having the diameter shown in the present embodiment, but any one having an arbitrary diameter can be appropriately used. Further, in this embodiment, the polystyrene latex was sprayed on the substrate by applying an aqueous solution of polystyrene latex on the substrate by the substrate rotation method, but the present invention is not limited to this, and the polystyrene latex is not limited to this. Can be sprayed, and can be appropriately replaced with another spraying method.

Step S2 (heating each substrate at each heating temperature) The substrate heating unit is composed of, for example, a hot plate or an oven, and can heat the substrate at an arbitrary temperature for an arbitrary time. The substrate heating unit heats the substrate on which the polystyrene latex is sprayed, for example, at a heating temperature of 90, 100, 110, 120, 130, 140 ° C.
Then, separate substrates are heated at the respective heating temperatures to generate cleaning evaluation substrates at the respective heating temperatures. At this time, it is thought that the polystyrene latex sprayed on the substrate is fixed on the substrate by a different fixing force for each heating temperature. Note that the above heating temperature is merely an example, and the present invention is not limited to this.

Step S3 (Measure the number of particles before cleaning) The number of particles of polystyrene latex on the substrate for cleaning evaluation is measured by a particle checker unit.
By this measurement, the number of particles of the polystyrene latex sprayed on the substrate before washing is determined. The number of particles of the polystyrene latex dispersed on the substrate can be set substantially arbitrarily depending on the concentration of the above-mentioned aqueous solution of polystyrene latex. This particle checker unit irradiates a substrate with, for example, a laser beam,
The size and the number of particles attached to the substrate are measured based on the laser light reflected on the substrate. In the present example, after heating the substrate, the number of particles of the polystyrene latex was measured.However, the present invention is not limited to this, and it is sufficient that the number of particles is before cleaning.For example, the number of particles may be measured before heating the substrate. Can also.

Step S4 (Cleaning each substrate for cleaning evaluation) In the substrate cleaning unit, each substrate for cleaning evaluation after measuring the number of particles of polystyrene latex is cleaned, for example, under the same cleaning conditions. In other words, by cleaning each cleaning evaluation substrate according to the cleaning ability determined by the cleaning conditions, a cleaning effect corresponding to the cleaning ability can be obtained. As will be described later, this cleaning effect appears as a removal rate obtained by comparing the number of particles of the polystyrene latex before and after cleaning. In addition,
The substrate cleaning unit includes, for example, a high-pressure jet cleaning unit that performs cleaning with a cleaning liquid to which a relatively high pressure is applied, an ultrasonic cleaning unit that performs cleaning with a cleaning liquid to which ultrasonic waves are applied, and a brush-type cleaning unit that performs cleaning with a cleaning brush. It is configured to include any type of cleaning unit such as a cleaning unit.

Step S5 (Measurement of Number of Particles after Washing) The number of particles of polystyrene latex remaining on each cleaning evaluation substrate washed under the same washing conditions by the substrate washing unit is measured by the particle checker unit. By this measurement, the number of particles of the polystyrene latex remaining without being washed off on each substrate, that is, the number of particles after washing is determined.

Step S6 (Indicating Cleaning Ability) Based on the number of polystyrene latex particles before and after cleaning, the removal rate of polystyrene latex particles for each substrate for cleaning evaluation is determined. For example, the number of particles before washing is represented by A
If the number of particles after washing is B, the removal rate (%) =
(1−B ÷ A) × 100. The cleaning evaluation substrate having the increased removal rate is specified, and the heating temperature of the cleaning evaluation substrate is indexed as the cleaning ability under the cleaning conditions.

Here, the polystyrene latex on the cleaning evaluation substrate is fixed with a different fixing force for each heating temperature, and in the same cleaning evaluation substrate, each particle of the polystyrene latex is substantially the same fixing force. It seems that it has taken root. Therefore, the fixing power of the polystyrene latex that can be washed away under predetermined washing conditions is determined by the washing ability under the washing conditions. If the fixing power is not higher than the cleaning ability, the cleaning will wash out the majority of polystyrene latex particles fixed on the cleaning evaluation substrate, while if the fixing power is higher than the cleaning power, A phenomenon occurs in which the majority of polystyrene latex particles fixed on the cleaning evaluation substrate are not washed away. In other words, depending on the cleaning ability, it is considered that a relatively high removal rate of polystyrene latex and a relatively low removal rate of polystyrene latex appear.

As a result, the removal rate of polystyrene latex from the cleaning evaluation substrate heated at a certain range of heating temperature is low, while the removal rate of polystyrene latex from the cleaning evaluation substrate heated at another range of heating temperature is low. The phenomenon of becoming high occurs. Therefore, by specifying the heating temperature at which the removal rate of the polystyrene latex of the cleaning evaluation substrate increases, the heating temperature is indexed as the cleaning ability. That is, the heating temperature is used as an index for the cleaning ability under the cleaning conditions for cleaning the cleaning evaluation substrate.

Step S7 (Repeat?) The above-described cleaning conditions or cleaning method (substrate cleaning unit)
Is changed, and by repeating steps S1 to S6,
The cleaning ability in each cleaning condition or each cleaning method can be indicated by the heating temperature. In other words, by comparing the heating temperature indicated for each cleaning condition or each cleaning method,
It is possible to select optimum cleaning conditions and each cleaning method, that is, evaluate cleaning conditions and the like. For example, at the highest heating temperature, the fixing power of the polystyrene latex on the substrate is considered to be high. Therefore, it is considered that the cleaning condition and the like in which the heating temperature is indicated can be judged to be high in the cleaning ability.

In the above-described substrate cleaning evaluation method, the heating temperature at which polystyrene latex is heated on the substrate is used as an index for the cleaning performance when comparing the cleaning performance such as cleaning conditions and cleaning method (substrate cleaning unit). Thus, it is possible to solve the problem that the cleaning ability at a high level cannot be compared with the conventional case. In other words, conventionally, the removal rate was used to indicate the cleaning capacity, but the cleaning capacity is indicated by indicating the heating temperature according to the present invention, so that it is possible to make an absolute comparison of the cleaning capacity. Become.

The present invention can be modified as follows. (1) In the above-described embodiment, a plurality of substrates on which polystyrene lalex is sprayed are heated at different heating temperatures, but in the present invention, the substrates are heated at a constant heating temperature instead of this heating temperature. Heating time can also be used. Specifically, by changing the heating time at a constant heating temperature, it is possible to change the fixing power of the polystyrene lalex sprayed on the substrate for each substrate. In this case, this heating time is indexed as the cleaning ability. In the above-described embodiment, the cleaning evaluation substrate is generated for each different heating temperature. In this modification, each cleaning evaluation substrate is generated for each heating time at a constant heating temperature, and the heating time is reduced. Index as cleaning ability. Except for these points, all are the same as in the above-described embodiment, and a description thereof will be omitted.

(2) In the above-described embodiment, the case where the polystyrene larex is sprayed on the substrate has been described.
The present invention is not limited to this. For example, a polymer material can be used instead of polystyrene lalex.

<Experiment Result 1> Hereinafter, in the above-described embodiment, when the cleaning evaluation substrate was cleaned by ultrasonic cleaning, brush cleaning and high-pressure jet cleaning, the experimental result 1 obtained by each cleaning method was as follows. This will be described with reference to the graph shown in FIG.

FIG. 2A shows a heating temperature of 90 to 140 ° C.
Is a graph showing the relationship between the heating temperature and the removal rate of polystyrene larex before and after cleaning when ultrasonic cleaning is performed on each cleaning evaluation substrate heated at a heating temperature at intervals of 10 ° C. It is. As shown in FIG. 2A, it can be observed that the removal rate changes significantly between the heating temperatures of 100 to 110 ° C. For example, the heating temperature of 110 ° C. at which the removal rate has changed significantly is indexed as the cleaning capability of the ultrasonic cleaning. In addition, heating temperature 100-110
The heating temperature of 105 ° C., which is the average value of ° C., can also be used as an index for the cleaning capability of this ultrasonic cleaning.

FIG. 2B shows a heating temperature of 90 to 140 ° C.
Is a graph showing the relationship between the heating temperature and the removal rate of polystyrene larex before and after cleaning when each of the cleaning evaluation substrates heated at the heating temperature at intervals of 10 ° C. is subjected to brush-type cleaning in the range of FIG. It is. As shown in FIG. 2 (b), it can be observed that the removal rate changes greatly between the heating temperatures of 130 to 140 ° C. For example, a heating temperature of 140 ° C. at which the removal rate has changed greatly is indexed as the cleaning ability of this brush type cleaning. In addition, heating temperature 130-1
A heating temperature of 135 ° C., which is an average value of 40 ° C., can be used as an index for the cleaning ability of this brush type cleaning.

FIG. 2C shows a heating temperature of 90 to 140 ° C.
The relationship between the heating temperature and the removal rate of polystyrene larex before and after cleaning is shown when high-pressure jet cleaning is performed on each cleaning evaluation substrate heated at a heating temperature at intervals of 10 ° C. It is a graph. As shown in FIG. 2 (c), it can be observed that the removal rate changes greatly between the heating temperatures of 90 to 110 ° C. For example, the heating temperature of 110 ° C. at which the removal rate has changed significantly is indexed as the cleaning capability of the high-pressure jet cleaning. It should be noted that a heating temperature of 100 ° C., which is an average value of the heating temperatures of 90 to 110 ° C., can also be indexed as the cleaning ability of this brush-type cleaning.

By comparing the heating temperature, which is indicated as the cleaning ability in each of the above-described cleaning methods, for example, the heating temperature is the highest in the case of the brush type cleaning, and the cleaning ability is higher than those of the other cleaning methods. I understand. In this experimental result 1, the cleaning ability between the cleaning methods was evaluated, but the cleaning ability between the cleaning conditions in the same cleaning method can also be evaluated.

<Experimental Result 2> An experimental result 2 in the case where the cleaning ability is indicated by the heating time instead of the heating temperature described in the modification of the above embodiment will be described below. In this experiment, when the cleaning evaluation substrate was cleaned by ultrasonic cleaning and brush cleaning, the cleaning performance obtained by each cleaning method was compared with the experimental result 2.
This will be described with reference to the graph shown in FIG.

FIG. 3A shows a case where ultrasonic cleaning was performed on each cleaning evaluation substrate heated at a heating temperature of 110 ° C. and a heating time of 60 to 180 seconds at a heating time of every 20 seconds. 4 is a graph showing the relationship between the heating time and the removal rate of polystyrene larex before and after washing. FIG.
As shown in (a), it can be observed that the removal rate changes greatly between the heating times of 60 to 100 seconds. For example, the heating time 80S at which the removal rate has changed is indexed as the cleaning capability of the ultrasonic cleaning. In addition, heating time 60-1
The heating time 80S, which is an average value of 00 seconds, can also be indexed as the cleaning ability of this ultrasonic cleaning.

FIG. 3B shows a case where each cleaning evaluation substrate heated at a heating temperature of 140 ° C. and a heating time of 30 to 60 seconds at heating intervals of 5 seconds is subjected to brush cleaning. 4 is a graph showing the relationship between the heating time and the removal rate of polystyrene larex before and after washing. FIG.
As shown in (b), it can be observed that the removal rate greatly changes between the heating times of 30 to 40 seconds. For example, the heating time 35S at which the removal rate has changed is indexed as the cleaning ability of this brush-type cleaning. In addition, heating time 30 to 4
The heating time 35S, which is an average value of 0 seconds, can also be indexed as the cleaning ability of this brush-type cleaning.

In this experiment, since the heating temperature was changed between the ultrasonic cleaning and the brush cleaning, it was difficult to compare the two. However, by changing the heating time, the removal rate of polystyrene latex was compared. It can be understood that the heating time that significantly changes can be grasped. That is, it is possible to evaluate the cleaning ability by indexing the heating time during which the removal rate changes relatively largely as the cleaning ability.

[0038]

As is apparent from the above description, according to the first aspect of the present invention, a plurality of substrates on which latex has been sprayed are heated at different heating temperatures, respectively. , The heating temperature of the substrate at which the number of latex particles changes greatly before and after cleaning the substrate can be determined. In other words, a difference in the heating temperature at which the number of particles of the latex before and after the cleaning greatly changes occurs due to a difference in the cleaning conditions or the cleaning capability of the cleaning apparatus. By utilizing the phenomenon, the heating capacity of the substrate, in which the number of latex particles changes greatly before and after cleaning the substrate, under various cleaning conditions or cleaning devices, can be used to improve the cleaning performance of each cleaning condition or cleaning device. Can be evaluated. Also,
Since the cleaning ability is evaluated based on the heating temperature of the substrate, it is difficult to compare the cleaning ability with the removal rate that changes depending on the adhesion state of the particles as in the past, or the cleaning efficiency is too high to compare with the particle removal rate. It is also possible to more accurately grasp the cleaning ability as compared to other cases.

According to the second aspect of the present invention, a plurality of substrates on which latex has been sprayed are heated at a constant temperature for different heating times, and each substrate after the heating is washed. The heating time of the substrate at which the number of latex particles changes greatly before and after washing the substrate can be determined. In other words, a difference in the heating time during which the number of particles of the latex before and after the cleaning greatly changes depends on the cleaning conditions or the cleaning capability of the cleaning apparatus. By utilizing this phenomenon, the same effect as in the first aspect can be obtained by evaluating the cleaning ability based on the heating time.

According to the third aspect of the present invention, the substrate cleaning evaluation method of the first or second aspect is performed using polystyrene latex, so that the substrate cleaning evaluation method can be more suitably executed. . In addition, by using polystyrene latex, the method for evaluating and cleaning a substrate can be implemented at low cost.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a flow of a substrate cleaning evaluation method according to an embodiment.

FIG. 2 is a graph showing an experimental result when a heating temperature is indicated as a cleaning ability.

FIG. 3 is a graph showing an experimental result in a case where a heating time is indicated as a cleaning ability.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) H01L 21/66 H01L 21/66 J F term (reference) 2G051 AA51 AA73 AA90 AB20 BA10 CA02 CA20 CB01 DA08 3B116 AA03 BA11 BB21 BB83 BB90 CC05 3B201 AA03 BA11 BB21 BB83 BB90 BB94 CB01 CC21 4M106 AA01 BA10 CA29 CA41 DH01 DH11 DH32

Claims (3)

[Claims] 1. A substrate cleaning evaluation method for evaluating a cleaning ability by changing a number of objects to be removed on a substrate before and after cleaning when cleaning a substrate on which the objects to be removed are sprayed, comprising: A process of spraying each of the latexes to be removed on the substrate, a process of heating each of the substrates at a different heating temperature, and a process of measuring the number of particles of the latex sprayed on each of the substrates before washing. Washing the heated substrates, measuring the number of latex particles remaining on each substrate after the washing, and from among the substrates, the number of latex particles on the substrate before and after washing. Indexing the heating temperature of the substrate, which has changed relatively largely, as the cleaning ability of the substrate. 2. A substrate cleaning evaluation method for evaluating a cleaning ability by changing the number of objects to be removed on a substrate before and after cleaning when cleaning the substrate on which the objects to be removed are sprayed, comprising: A step of spraying each of the latexes to be removed on the substrates of the above, a step of heating the respective substrates at different heating times at a constant temperature, and measuring the number of particles of the latex sprayed on the respective substrates before washing A step of washing each heated substrate; a step of measuring the number of latex particles remaining on each substrate after the washing; and a step of measuring the number of latex particles on the substrate from among the substrates. Indexing the heating time of the substrate, which has changed relatively significantly before and after the cleaning, as the cleaning capability of the substrate. 3. The substrate cleaning evaluation method according to claim 1, wherein the latex is a polystyrene latex.