JP2001228138A - Evaluation method of water quality, and retaining container for water quality evaluating semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate the quality of ultrapure water (water to be evaluated) used as cleaning water in the last of cleaning process in the manufacture of wafer. SOLUTION: The water to be evaluated is brought into contact with a semiconductor substrate (wafer), and fine particles adhered to the surface of the substrate are counted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ultrapure water for cleaning (water to be evaluated) which is used in a large amount in an LSI manufacturing process or the like.
Water quality that evaluates the quality of ultrapure water only for substances that may adhere to the surface of a semiconductor substrate (also referred to as a wafer) and affect the characteristics of the wafer, among the trace impurities present therein. And a container for holding a semiconductor substrate used in the method for evaluating water quality.

[0002]

2. Description of the Related Art Ultrapure water, which is used in a large amount in an LSI manufacturing process, is a substance that comes into contact with a wafer at the end of a cleaning process. Affects the cleanliness of the surface. For this reason, it is necessary to reduce the impurity concentration in the ultrapure water used in the manufacturing process together with the increase in the degree of integration of the LSI so far. Conventionally, all of the impurities contained in the ultrapure water have to be reduced. Efforts have been made to reduce it. For this reason, a technique has been developed which can analyze impurities in water to an extremely small amount using a highly sensitive analyzer.

[0003] Of the impurities in ultrapure water, fine particles, when adhered to the surface of a wafer, not only serve as a source of impurities but also interfere with the formation of a circuit by light exposure, and correct circuit formation. The adverse effect of not being able to do so. Therefore, it is necessary to keep the particulate impurities in the ultrapure water used at a very low concentration. To measure the number of particles in ultrapure water, irradiate the sample water with laser light,
Detects the light scattered when the laser hits the fine particles in the water, and determines the size of the fine particles from the intensity of the scattered light,
Measurement with a so-called water particle counter that measures the number of fine particles from the number of times of detection of scattered light, or a large amount of ultrapure water is filtered by a filter that can capture the fine particles to be measured on the surface, and the fine particles are filtered on the filter surface. A method of capturing and concentrating, observing with a microscope under magnification, counting, and calculating the number of fine particles in the original water has been performed.

[0004]

When ultrapure water is used for cleaning a wafer, it is not clear at all whether fine particles in the ultrapure water adhere to the wafer and have the above-mentioned adverse effects. . Since the number of particles measured by the above method covers all particles suspended in water, even if the concentration in ultrapure water is detected, they will all adhere when cleaning the wafer and adversely affect it. I do not know whether to exert. If it is possible to determine whether or not there are many fine particles that easily adhere to the wafer when the ultrapure water comes into contact with the wafer, it will be possible to evaluate whether or not the ultrapure water is ultrapure water that may have an adverse effect. The meaning is great.

[0005]

According to the water quality evaluation method of the present invention, ultrapure water for cleaning a wafer is used as the water to be evaluated, and when the water comes into contact with the wafer, the water to be evaluated tends to adhere to a large amount of fine particles which are likely to adhere to the wafer. The method for evaluating water quality according to claim 1, wherein the method includes contacting the surface of the semiconductor substrate with the water to be evaluated, and then counting the fine particles attached to the surface of the substrate. The water quality evaluation method according to claim 2 is characterized in that in the method for evaluating water quality according to claim 1, one semiconductor substrate is horizontally mounted inside with one surface facing upward, The water to be evaluated is supplied toward the center of the surface of the substrate, and after the water to be evaluated flows radially on the surface of the semiconductor substrate, the water to be evaluated is discharged from the peripheral portion of the substrate through the back surface of the semiconductor substrate, and the surface of the substrate and The distance on the inner surface of the container shifts radially outward from the center Runishitagatte with holding container of the semiconductor substrate is shorter, which comprises contacting the water to be evaluated on the surface of the semiconductor substrate. The container for holding a semiconductor substrate for evaluating water quality according to claim 3 is used when the water quality is evaluated according to claims 1 and 2, wherein one semiconductor substrate is placed inside with the surface facing upward. A water supply port for supplying water to be evaluated, comprising a holder for holding horizontally, and supplying water to be evaluated to a central portion of the surface of the semiconductor substrate, and flowing the surface radially outward toward the outer periphery; In a semiconductor substrate holding container having a drain port for discharging water to be evaluated from the outer periphery of the semiconductor substrate through the back surface thereof, a material to which voltage can be externally applied to the inlet of the water to be evaluated and the holder for the semiconductor substrate is used, It is characterized in that potential control between water and the semiconductor substrate is enabled. According to a fourth aspect of the present invention, there is provided a method for evaluating water quality, comprising: contacting water to be evaluated with a surface of a semiconductor substrate by using the semiconductor substrate holding container according to the third aspect, and then counting fine particles attached to the surface of the substrate. It is characterized by evaluating water quality by

[0006]

According to a first aspect of the present invention, there is provided a method for evaluating water quality, wherein ultrapure water is brought into contact with the surface of a wafer, and the number of fine particles adhering to the surface of the wafer is measured with a wafer particle counter. Evaluate water quality. Considering that fine particles contained in ultrapure water have an adverse effect on the wafer, the fine particles must first adhere to the wafer surface when water comes into contact with the wafer. The process by which fine particles in water adhere to the surface of the wafer can be performed when the fine particles are attracted to and adhere to the wafer surface by some force, such as electrostatic force, van der Waals force, or hydrophobic bonding. It is conceivable that the water contained evaporates and fine particles are left on the surface. However, since a drying method in which a large amount of water evaporates from the surface is not performed in the wafer manufacturing process, a process of adhering in water may be considered. That is, if impurities attached to the surface of the wafer when the ultrapure water comes into contact with the wafer are detected, the ultrapure water can be evaluated as water that may have a bad influence on the wafer.

[0007] In performing such an evaluation, it is necessary to efficiently attach fine particles in ultrapure water to the surface of the wafer.
To this end, as described in claim 2, one wafer is mounted horizontally with the surface facing upward, and the water to be evaluated is supplied toward the center of the surface of the wafer, and the water to be evaluated is supplied to the wafer. After flowing radially on the surface of the container, the wafer is discharged from the peripheral portion through the back surface of the wafer, and the distance between the surface of the wafer and the inner surface of the container decreases as the distance from the center portion to the radially outward direction decreases. The water to be evaluated is preferably brought into contact with the surface of the wafer by using a wafer holding container for evaluating the water quality.

[0008] The above-mentioned water holding evaluation wafer holding container is proposed by the present applicant in Japanese Patent Application No. 2000-015515. As shown in Fig. 1, the wafer holding container includes an upper lid 10 and a circular recess provided on the upper surface. 21 comprises a bottom plate 20 closed by the upper lid. The outer shapes of the top cover 10 and the bottom plate 20 are, for example, circular. A water supply port 11 is provided at the center of the top cover, and a drain port 22 is provided at the center of the bottom plate 20. Positioning protrusions 23 are provided at equal intervals in the circumferential direction on the peripheral edge of the upper surface of the bottom plate 20,
Correspondingly, a concave portion for receiving the positioning protrusion is provided in a peripheral portion of the lower surface of the upper lid. Therefore, when the upper lid is placed on the upper surface of the bottom plate and the concave portion of the upper cover is fitted to the positioning projection 23, the upper cover correctly overlaps the bottom plate and closes the upper surface of the circular recess 21 of the bottom plate.

The inner diameter of the circular recess 21 of the bottom plate is sufficiently larger than the diameter of the wafer W to be held, and the upper end of the drain port 22 is opened at the center of the bottom of the recess. Hollow 21
A plurality of, in the figure, three radial ridges 24 are ridged at equal intervals in the circumferential direction on the bottom surface of. The inner end of the radial ridge 24 is located around the drain port 22, and the outer end is spaced apart from the inner peripheral surface of the depression 21 inward.

Then, the wafer W is placed on the plurality of radial ridges 2.
Hold it horizontally on top of 4 above. For this purpose, a stair-shaped support 25 having a step 26 on which the peripheral portion of the wafer is placed is provided on the outer end of each ridge. The step of the step 26 corresponds to the thickness of the wafer (about 0.6 mm). If necessary, a support portion 27 for supporting the lower surface of the wafer in the radial direction is provided on the middle portion of each ridge 24.

On the lower surface of the upper lid 10, there is provided a mountain-shaped water-passing recess 12 connected to the lower end of the water supply port 11. The inner diameter of the water-passing recess 12 is equal to the inner diameter of the circular recess 21 of the bottom plate. The reason why the concave portion 12 for flowing water is referred to as Mt. Fuji shape is that, in the cross-sectional shape, the lower surface of the concave portion 12 faces outward in the radial direction.
The wafer W is gradually approached to the surface of the wafer W horizontally supported by the stepped support 25.

For example, when the radius of the wafer is 75 mm,
The distance of the water-passing recess 12 from the surface of the wafer supported horizontally with the surface facing upward is 15 mm radially outward from the center of the wafer at a position of 5 mm, 7.5 mm at a position of 10 mm, and also 15 mm. 5mm, 20mm at the position
3.75mm at the position, 2.5mm at the 30mm position,
It is 1.875 mm at a position of 40 mm, 1.25 mm at a position of 60 mm, and 1 mm at a position of 75 mm on the outer periphery.
This is because ultrapure water supplied into the inside from the water supply port 11 flows radially outward on the surface of the wafer W at a uniform flow rate and flow rate, and between the inner peripheral surface of the depression and the outer end of the radial ridge. To reach the peripheral edge 21 'of the bottom of the depression including the distance between the recesses. As a result, the amount of contact water can be controlled even during repeated tests, and evaluation with high reproducibility can be performed. Since the supplied water efficiently contacts the surface of the wafer, a large amount of water can be brought into contact with the surface of the wafer even in a short time, and the sensitivity is high. Since the flow velocity of the water stream flowing on the surface of the wafer is uniform, the adhesion of impurities to the surface of the wafer becomes uniform, and the reliability of the evaluation of the attached matter by surface analysis is high. Further, when water comes into contact with the wafer, the amount of impurities eluted from the wafer is extremely small, so that the amount of contamination from the supplied water to the wafer can be detected with high sensitivity. Has the effect.

The water that reaches the peripheral edge 21 'at the bottom of the depression flows toward the central drain port 22 through a gap between the bottom of the depression 21 and the back surface of the wafer lifted by the radial ridges. Spills out of outlet.

A valve is screwed into the water supply port 11 on the top lid and the drain port 22 on the bottom panel to shut off the outside air and the inside of the container. When carrying the container to a place other than the clean room, the valve is closed, and the valve is closed. Open only when making contact. The valve provided at the water supply port 11 is a three-way valve (raw water → inside the container, raw water →
(Switching to discharge) 13 is preferably used. Before the container is brought into contact with water, the valve 13 is set to “raw water → discharge”.
In this case, it is possible to wash the sampling flow path if water is allowed to flow without putting water in the container. Further, the valve 28 provided at the drain port 22 may be a two-way valve for opening and closing.

As materials for the upper cover 10 and the bottom plate 20, when metal components and ions in the test water are to be evaluated,
A durable synthetic resin or quartz which has a low content of impurities such as metals and ions and is relatively easy to process is used.
Further, in order to remove impurities adhering to the surface of the container, cleaning using heated ultrapure water or cleaning using ultrasonic waves is performed before using the container. On the other hand, when evaluating the organic impurities in the test water, the top cover and the bottom plate should be made of metal such as stainless steel or aluminum or quartz that does not elute organic substances, or the metal or quartz should be placed on the liquid contact part of the top cover or the bottom plate. Use

As described above, on the lower surface of the upper lid 10, a mountain-shaped water-passing recess 1 connected to the lower end of the central water supply port 11.
2, the distance h of the water-passing concave portion 12 from the surface of the horizontally supported wafer becomes shorter as the distance from the center to the radially outward direction increases, and the ultrapure water supplied from the water supply port to the inside of the wafer W Flows at a uniform flow rate and flow rate radially outward on the surface of the wafer to reach the outer periphery of the wafer. The distance h is expressed by a distance d from the center and the following equation. 2πdh = C where π is a circular constant and C is a constant determined by the flow rate of water. That is, the particles in the ultrapure water are attracted from the water to the surface of the wafer and adhere to the surface. For this reason, as described above, the ultrapure water flows at the same flow rate over the entire surface of the wafer, so that the conditions for adhering the fine particles are uniform on the surface of the wafer. Therefore, by mounting the wafer in the holding container of FIG. 1 and flowing ultrapure water, the measurement accuracy of the degree of adhesion of the fine particles is improved.

In addition, there is an electrostatic interaction as a part of the mechanism for attaching the fine particles in ultrapure water to the solid surface. In many cases, fine particles in water are known to have a negative surface potential. Therefore, by controlling the potential between the water and the surface of the wafer so that the wafer becomes positive with respect to the water, the adhesion of the fine particles in the water to the surface of the wafer can be promoted.

FIG. 2 shows an embodiment of the wafer holding container according to claim 3, wherein the potential between the ultrapure water and the wafer surface can be controlled. Since the holding container of this embodiment has almost the same configuration as the holding container of FIG. 1, the same components are denoted by the same reference numerals as in FIG. This holding container is different from that shown in FIG. 1 in that an upper electrode 31 for applying a potential to ultrapure water supplied into the vessel and a wafer W held in the container are applied to apply a potential to the wafer. Electrode 32 for
And that the potential between the ultrapure water and the wafer can be controlled during the supply of the ultrapure water.

Specifically, an upper electrode 31 for applying a potential to the supplied ultrapure water is provided in a cylindrical shape on the inner periphery of the water supply port 11 at the center of the upper lid 10. Then, the support portion 27 provided in the middle of each radial ridge 24 is omitted, and the bottom plate 20 is provided with a vertical hole 29 which opens from the upper surface of each ridge 24 to the lower surface of the bottom plate at the position of the support portion. A lower electrode 32 having a rectangular shape is attached through the hole. The height of each lower electrode 32 protruding from the upper surface of each ridge 24 is made the same as that of the support portion 27 so that the lower electrode 32 comes into contact with the back surface in the radial direction of the wafer held on the radial ridge. Further, the length of the downwardly protruding portion from the lower surface of the bottom plate of each electrode 32 may be any length as long as wiring can be connected.

The cathode of a DC power supply whose voltage can be adjusted by a transformer is electrically connected to the upper electrode 31, and the anodes are electrically connected to the three lower electrodes 32, respectively. If the applied voltage from the DC power supply is too weak, the effect of the voltage application is lost, and if it is too strong, the elution of the electrode is promoted and the life of the electrode is shortened.

By applying an electric potential between the ultrapure water supplied into the holding container and the wafer held in the holding container by using an appropriate power supply device, the ultrapure water on the surface of the wafer is provided. The adhesion of fine particles in water can be promoted, and the sensitivity of fine particle detection can be improved.

Example 1 Three n-type silicon wafers having a diameter of 6 inches were prepared, and normal RCA cleaning with ultrapure water was performed using a quartz tank to clean the surfaces of the wafers. Two of these were washed and dried, and the number of fine particles on the surface was measured with a wafer particle counter. As a result, the surface area of the wafer after cleaning is reduced to 0.
The average value of the number of fine particles of 2 μm or more was 2.3. With respect to this wafer, a silicon wafer was mounted on a polypropylene wafer holding container having the structure shown in FIG. 1, and ultrapure water was passed at a flow rate of 1 liter / min for 1 hour, that is, 60 liters.
Thereafter, the wafer was taken out of the container and dried so as not to contaminate the wafer, and the number of fine particles on the surface was measured with a wafer particle counter to obtain an average value. As a result, five fine particles were detected on the surface of the wafer. In other words, it could be evaluated as ultrapure water that caused contamination of only 5 wafers / wafer on average from 60 standing water.

Example 2 Three n-type silicon wafers having a diameter of 6 inches were prepared, and normal RCA cleaning with ultrapure water was performed using a quartz tank to clean the surfaces of the wafers. Two of them were washed and dried, and the number of fine particles on the surface was measured by a particle counter. As a result, 0.2 μm
The average value of the number of fine particles of m or more was 2.6. With respect to this wafer, a silicon wafer was mounted on a polypropylene wafer holding container having a structure shown in FIG.
Ultrapure water was passed through the electrode at a flow rate of 1 liter / minute for 1 hour, that is, 60 liters while applying a voltage of 2 volts to the electrode so that Thereafter, the wafer was taken out of the container and dried so as not to contaminate the wafer, and the number of fine particles on the surface was measured using a wafer particle counter to obtain an average value. As a result, seven fine particles were detected on the wafer surface. That is, 60
It could be evaluated as ultrapure water that caused contamination of only 7 wafers / wafer on average from standing water.

[0024]

By using the method for evaluating particulate contamination according to the present invention, the level of particulates in ultrapure water that actually contaminates the surface of a wafer can be evaluated, and the water can be evaluated closer to the actual effect. By using the wafer holding container of the present invention, the water quality during the pure water production process in the ultrapure water production apparatus outside the clean room can be evaluated using a method of contacting and analyzing the wafer, and the ultrapure water can be evaluated. It can be used for improving the quality of ultrapure water such as improving water quality and reducing costs.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view of an embodiment of a wafer holding container used in the method for evaluating water quality according to claim 2, and FIG. 1B is a perspective view of a bottom plate of the same.

FIG. 2A is a sectional view of an embodiment of a wafer holding container used in the method for evaluating water quality according to claim 3, and FIG. 2B is a perspective view of a bottom plate of the same.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 Upper lid of holding container 11 Water supply port of upper lid 12 Water passage recess of upper lid 20 Bottom plate of holding container 21 Circular depression of bottom plate 22 Drain port of bottom plate 24 Radial ridge of bottom plate 25 Stair-shaped support portion of radial ridge 31 Upper electrode 32 Lower electrode W Semiconductor substrate (wafer)

Claims (4)

[Claims] 1. A method for evaluating water quality, comprising: bringing water to be evaluated into contact with the surface of a semiconductor substrate, and counting the fine particles attached to the surface of the substrate to evaluate the water quality. 2. A semiconductor substrate is mounted horizontally with its surface facing upward, and water to be evaluated is supplied toward the center of the surface of the substrate. The semiconductor for water quality evaluation is discharged from the peripheral portion of the substrate through the back surface of the semiconductor substrate, and the distance between the substrate surface and the inner surface of the container is reduced as the distance from the central portion to the radially outward direction is reduced. The method for evaluating water quality according to claim 1, wherein the water to be evaluated is brought into contact with the surface of the semiconductor substrate using a substrate holding container. 3. A semiconductor device comprising: a holder for holding one semiconductor substrate horizontally with its surface facing upward; and supplying water to be evaluated to a central portion of the surface of the semiconductor substrate; Water supply port of the evaluated water for flowing the water radially outward,
In a semiconductor substrate holding container having a drain port for discharging water to be evaluated from the outer periphery of the substrate through the back surface thereof, using a material capable of externally applying a voltage to the inlet of the water to be evaluated and the holder of the semiconductor substrate, A semiconductor substrate holding container, wherein potential of water to be evaluated and a semiconductor substrate can be controlled. 4. After the water to be evaluated is brought into contact with the surface of the semiconductor substrate using the semiconductor substrate holding container according to claim 3,
A water quality evaluation method, wherein water quality is evaluated by counting fine particles attached to the surface of the substrate.