JPH11274123A - Method of cleaning wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method of cleaning wafer by which the amount of heavy metals adsorbed to a wafer is small, and particularly heavy metal contaminants are reduced to a wafer adsorbing amount of 5×10<8> atoms/cm<2> or less suitable to a finely processed 64 M DRAM device. SOLUTION: A method of cleaning a wafer, of a combination of a plurality of chemical cleaning steps and ultrapure water rinsing steps so as to removing the contaminant on a surface of a wafer, is characterized in that the temperature of ultrapure water is set at 0-20 deg.C. The ultrapure water is used in at least one of the ultrapure rinsing steps. Cooled ultrapure water of 0-20 deg.C, preferably 5-15 deg.C is used in at least one of the rinsing steps after an HCl/H2 O2 cleaning step of removing the metal contaminants.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer cleaning method using ultrapure water, and more particularly to a wafer cleaning method characterized by a device for wafer harness using ultrapure water.

[0002]

2. Description of the Related Art In LSI manufacturing, wafer surface contaminants degrade device characteristics and become a major cause of defects. Therefore, in order to manufacture an LSI with high yield and high reliability, it is important to clean the wafer in the wafer manufacturing process and not to contaminate the wafer. However,
Since an LSI is manufactured through several hundred unit processes, the wafer surface is subjected to various kinds of contamination from a clean room atmosphere, people, manufacturing equipment, and the like. For this reason, there are a wet cleaning process and a dry cleaning process as cleaning processes for cleaning the contaminated wafer surface.
I Wet cleaning is still the mainstream in the manufacturing industry,
Specifically, ammonia (NH ₄ OH), hydrogen peroxide (H
_In many cases, a cleaning process called so-called RCA cleaning is used in which ₂ O ₂ ), hydrogen chloride (HCl) and a pure water rinsing step are combined.

That is, in the wafer cleaning technology, a cleaning process such as RCA, which is a combination of conventional mechanical cleaning methods such as brushing and scrubber, and removal of foreign substances on the surface with chemicals and rinsing with pure water, is often used. I have.

[0004] A typical procedure of such an RCA cleaning process is shown below. 1) NH ₄ OH / H ₂ O ₂ / H ₂ O (1: 1: 5) 2) Pure water rinse 3) HF immersion 4) Pure water rinse 5) HCl / H ₂ O ₂ / H ₂ O (1: 1) 1: 6) 6) Rinse with pure water 7) Spin dry And the rinse step with pure water may be repeated a plurality of times.

[0005] Ultrapure water is used as the pure water used in the RCA cleaning step, for example, UV (ultraviolet sterilization step) → RO (reverse osmosis membrane transmission step) → UV (ultraviolet sterilization step). → CP (Ion exchange resin membrane permeation process) →
It is manufactured through a UF (ultrafilter permeation step), and the ultrapure water thus produced is introduced into a pure water rinse or the like to perform ultrapure water cleaning.

[0006]

As the contaminants on the wafer surface that degrade the device characteristics, there are fine particles, metal impurities such as heavy metals, organic substances, natural oxide films, and the like.
The purpose of the cleaning process is to remove these.However, as fine processing advances as devices become more highly integrated, the effects of these contaminants also increase. It needs to be purified.

Although it is not always clear how much the surface of the wafer should be cleaned, a 16 MDRAM
In manufacturing the device, the heavy metal is 10 ¹⁰ atoms / cm ² and the carrier life of the minority is reduced. Therefore, the heavy metal contaminants need to be lower, for example, 10 ⁹ atoms / cm ² (atoms / cm ² ) or less. Also, 64MDRA of even finer processing
For the M device, 5 × 10 ⁸ atoms / cm ² (atoms /
cm ² ).

For this reason, ultrapure water is used as the cleaning solution for the pure water rinse. However, even ultrapure water contains impurities (heavy metals) at a ppt level concentration. When a wafer is washed using such ultrapure water, the longer the wafer is immersed in the ultrapure water, the more the adsorption of impurities increases.

On the other hand, an electronic material 1993 issued by the Industrial Research Council
140 ~ in the section "Ultra pure water production equipment"
On page 141, "The necessity of submicron trench cleaning due to high integration and rapid cleaning of the cleaning process with a small amount of pure water, so-called steam or electric heater from conventional ordinary temperature ultrapure water cleaning (25 ° C) due to the need for cost reduction. High-temperature ultra-pure water cleaning is performed by heating, etc. However, in both of such high-temperature water ultra-pure water cleaning and room-temperature ultra-pure water cleaning, heavy metal contaminants are compatible with micromachined 64MDRAM devices. 5 × 10 ⁸ atoms / cm ² (atoms / cm
² ) It was not possible to reduce the amount of wafer adsorption below.

In view of the above technical problem, the present invention reduces heavy metal contaminants to a wafer adsorption amount of 5 × 10 ⁸ atoms / cm ² (atoms / cm ² ) or less, which corresponds to a micromachined 64M DRAM device. It is an object of the present invention to provide a wafer cleaning method capable of performing the following.

[0011]

The present inventors have found that the adsorption speed of heavy metals on a wafer tends to increase as the temperature increases. Metal impurities include Na, Al, C
Although there are r, Fe, Ni, Cu, Zn, Ca, etc., in particular, Fe, Al, and Zn are easily adsorbed due to the relationship of oxidation-reduction potential (other metals increase so much even after long-time rinsing (adsorption)). No tendency to do so). Therefore, by lowering the temperature, adsorption of these metals can be suppressed.

According to the present invention, contaminants on a wafer surface are removed by combining a plurality of chemical cleaning steps and an ultrapure water rinsing step.
In the wafer cleaning method for cleaning, ultrapure water used in at least one ultrapure water rinsing step of the plurality of ultrapure water rinsing steps is 0 ° C to 20 ° C, preferably 5 ° C to 15 ° C.
° C. According to such a cleaning process, heavy metal contaminants are reduced to 64MDRA of fine processing.
5 × 10 ⁸ atoms / cm ² (atoms
/ Cm ² ) or less. Further, the present invention is applicable to other wet cleaning processes other than the RCA cleaning process. In particular, it is preferably used in a chemical cleaning step for removing heavy metals.

In this case, the rinsing step of rinsing while maintaining the ultrapure water at 0 ° C. to 20 ° C., preferably 5 ° C. to 15 ° C., is performed after the HCl / H ₂ O ₂ cleaning step for removing metal contaminants. It is preferably used in at least one of the one or more ultrapure water rinsing steps. HCl / H ₂
O ₂ cleaning removes the metal on the wafer surface,
If rinsing is performed after this cleaning, there is a high possibility that the metal concentration remaining on the wafer in the rinsing tank will increase. In this rinsing bath (process), there is a problem that the heavy metal is easily adsorbed on the wafer again. By making the temperature of the ultrapure water 0 ° C. to 20 ° C., preferably 5 ° C. to 15 ° C., lower than room temperature, it becomes difficult to adsorb.

The reason why the lower limit is set to 0 ° C. or 5 ° C. is that the temperature at which ultrapure water does not freeze and the capacity of a heat exchanger (cooler) are taken into consideration. The reason why the upper limit is set to 20 ° C. is that the upper limit of the temperature at which heavy metal contaminants can be effectively reduced to a wafer adsorption amount of 5 × 10 ⁸ atoms / cm ² (atoms / cm ² ) or less corresponding to a micromachined 64M DRAM device. It is. However, if the temperature is set to 15 ° C. or less, 2 × 10 ⁸ atoms /
cm ² or less, and more stable cleaning can be performed.

The place where the ultrapure water is cooled may be cooled before rinsing, or may be cooled in a rinsing tank. Further, any cooling method such as heat exchange with chiller water (ice mixed water) or a refrigerant may be used, but a portion capable of preventing contamination during heat exchange is preferable. Therefore, according to the present invention, as described in claim 3, during the production of ultrapure water, a heat exchange step of ultrapure water is arranged before the permeation step of the ion exchange resin membrane for producing the ultrapure water. Is cooled to 0 ° C. to 20 ° C., preferably 5 ° C. to 15 ° C. in the heat exchange step.

Ultrapure water may be contaminated by troubles during heat exchange. Therefore, an ion-exchange resin permeation step is provided after the heat exchanger so that heavy metals can be removed by the ion-exchange resin even if the metal is contaminated. That is, 5 ° C in the rinsing process
Washing with ultrapure water at １５15 ° C. has little effect if the ultrapure water contains too much heavy metal. Therefore, as a countermeasure when ultrapure water is contaminated during heat exchange, a heat exchange step is arranged before the ion exchange resin permeation step or the like.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to an embodiment shown in the drawings. However, unless otherwise specified, dimensions, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the invention, but are merely illustrative examples. FIG. 1 shows a combined system configuration diagram of a multi-tank type wafer cleaning apparatus and an ultrapure water production apparatus according to an embodiment of the present invention.

The multi-tank type wafer cleaning apparatus A is, for example, an SC-1 cleaning tank (NH ₄ OH / H ₂₎ between a loader 2 at the most upstream side and an unloader 7 at the most downstream side of the wafer cassette transfer system 1. O ₂ ) 3 → Ultrapure water rinsing tank 11 →
HF cleaning tank 4 → ultrapure water rinse tank 12 → ultrapure water rinse tank 1
3 → SC-2 cleaning tank (HCl / H ₂ O ₂ ) 5 → ultra pure water rinsing tank 14 → ultra pure water rinsing tank 15 → ultra pure water rinsing tank 16 →
A process of drying 6 is arranged, and the transfer system 1
Wafer cleaning is performed while sequentially transporting the wafer cassette to the downstream tank by the robot arm. (Just an example)

In particular, for cleaning of metal impurities, the SC-1 cleaning tank (NH ₄ OH / H ₂ O ₂ ) 3 or the HF cleaning tank 4 and SC-2 are used.
It is repeatedly removed by the washing tank (HCl / H ₂ O ₂ ) 5, but here, since washing with water has an important meaning,
Two or three ultrapure water rinsing tanks are provided between the respective cleaning tanks as necessary, and the water washing is repeatedly performed. Ultrapure water production equipment B is UV21 (ultraviolet sterilization process) → RO22
(Reverse osmosis membrane permeation step) → pure water that has passed through UV23 (ultraviolet sterilization step) is passed through CP (ion exchange resin membrane permeation step) 24B
→ Room temperature (25 ° C.) ultrapure water production process B1 produced through UF (ultra filter transmission process) 25B, and UV23
The pure water that has passed through the (ultraviolet sterilization step) is heat-exchanged with chiller water (ice mixed water) introduced from the chiller 30 in the heat exchanger 31, and then the CP (ion exchange resin membrane transmission step) 24A → UF.
(Ultra-filter permeation step) A low-temperature (15 ° C.) ultrapure water production step B2 produced through 25A.

The heat exchanger 31 is constructed such that a chiller water pipe is disposed so as to cover a pipe around which ultrapure water flows, and heat is exchanged. The pipes are thinned or the pipes are thinned. At this time, there is a possibility of contamination due to trouble or the like. Therefore, an ion-exchange resin membrane permeation step 24A is provided after the heat exchanger 31 so that heavy metals can be removed by the ion-exchange resin even if contaminated.

In the present embodiment, the cooled ultrapure water at 15 ° C. is washed in the SC-2 cleaning tank (HCl / H ₂ O ₂ ) 5 and then placed in the three-stage ultrapure water rinsing tank. The water was introduced only into the one-stage ultrapure water rinsing tank 14, and the other ultrapure water rinsing tank used was room-temperature ultrapure water at 25 ° C. The time during which the wafer was immersed in ultrapure water in each of these rinsing tanks was as long as 45 minutes in order to easily confirm the effect.
This cleaning time is also a mere example, and the same tendency is observed even if the time is shortened. The cleaning time may be appropriately determined according to the process.

In this embodiment, ten 8-inch polishing wafers were washed by the washing flow, and after drying, heavy metals on the wafers, in this embodiment, Fe were detected by atomic absorption method. Was below the lower limit of detection. The lower limit of detection of Fe in this evaluation method is 2 × 10 ⁸ atoms / cm ² (atoms / cm ² ).

Therefore, according to the present embodiment, the heavy metal contaminants have a size of 5 × corresponding to a micromachined 64 MDRAM device.
It was confirmed that the wafer adsorption amount could be reduced to 10 ⁸ atoms / cm ² (atoms / cm ² ) or less. IPA Vapor (isopropyl alcohol vapor) drying was performed at a temperature of about 80 ° C. as drying D after rinsing.
It was also confirmed that when the thing washed at a low temperature of 15 ° C. was put into a high-temperature dryer, the drying time was shorter than that of the conventional (25 ° C.) washing due to the effect of the temperature difference. However, this is 15
This was confirmed by another example in which cooling ultrapure water at a temperature of ° C was introduced into ultrapure water rinsing tanks 14, 15, and 16.

Next, the cooled ultrapure water cooled to 5 ° C. in the heat exchanger 31 is supplied to the SC-2 cleaning tank (HC
1 / H ₂ O ₂ ) First-stage ultrapure water rinse tank 1 immediately after washing with 5
In another embodiment where only 10 wafers were introduced, 10 8-inch polishing wafers were washed and dried, and Fe evaluation was detected by an atomic absorption method.
Similarly to the above, it was below the lower limit of detection.

(Comparative Example 1) [Normal temperature] The same process as in the example was performed, except that heat exchange was not performed, and the ultrapure water (25 ° C.) produced in the process B1 was used in all the ultrapure water rinsing tanks. When the wafer was cleaned by the cleaning flow, the impurity concentration of Fe was 8 × 10 ⁸ atoms / cm ² (atom
s / cm ² ) and metal contaminants are 5 × 10 ⁸ atoms / cm ² (atoms / cm ² ) corresponding to a micromachined 64M DRAM device.
² ) It was confirmed that it exceeded.

(Comparative Example 2) [Hot water: 45 ° C.] Heating was not performed in the same process as in the example, and a heating means was provided after the UF (ultra filter) 25. When the wafer was cleaned using the same cleaning flow as above, the impurity concentration of Fe was 15 × 10 ⁸ atoms / cm ² (atoms / cm ² ), and the metal contaminants were 5 × 10 ⁸ corresponding to the 64MDRAM device of fine processing. It was confirmed that it exceeded atoms / cm ² (atoms / cm ² ). Thus at least 25 ° C to 45 ° C
It can be seen that in the range, the adsorption amount increases as the temperature increases.

From the results of these Examples and Comparative Examples,
FIG. 2 shows a plot of the relationship between the temperature of the ultrapure water and the impurity concentration. From this result, by using ultrapure water of 20 ° C. or less, 5 × 10
Cleaning at a level of ⁸ atoms / cm ² or less can be performed.
Further, the temperature is more preferably 15 ° C. or lower, and the impurity is at a level lower than the detection lower limit, so that more stable cleaning can be performed, and it is possible to cope with the cleaning of a lower impurity level required in the future.

[0028]

As described above, according to the present invention, the amount of heavy metal adsorbed on the wafer can be reduced,
In particular, it is possible to obtain a wafer cleaning method capable of reducing heavy metal contaminants to a wafer adsorption amount of 5 × 10 ⁸ atoms / cm ² (atoms / cm ² ) or less corresponding to a micromachined 64M DRAM device. Further, according to the present invention, the drying time of IPA Vapor after rinsing is shorter than that of the conventional (25 ° C.) washing due to the effect of the temperature difference. And so on.

[Brief description of the drawings]

FIG. 1 shows a combined system configuration diagram of a multi-tank type wafer cleaning apparatus and an ultrapure water production apparatus according to an embodiment of the present invention.

FIG. 2 shows the relationship between the temperature of ultrapure water and heavy metal impurities (Fe) adsorbed on a wafer.

[Explanation of symbols]

A Multi-wafer type wafer cleaning apparatus B Ultrapure water production apparatus 11-16 Ultrapure water rinsing tank 3 SC-1 cleaning tank (NH ₄ OH / H ₂ O ₂ ) 4 HF cleaning tank 5 SC-2 cleaning tank (HCl) / H ₂ O ₂ ) 24 CP (ion exchange resin membrane permeation step) 31 heat exchanger

Claims (3)

[Claims] 1. A wafer cleaning method for removing contaminants on a wafer surface by combining a plurality of chemical solution cleaning steps and an ultrapure water rinsing step, wherein at least one of the plurality of ultrapure water rinsing steps is a rinsing step. A wafer cleaning method, wherein rinsing is performed while maintaining ultrapure water to be used at 0 ° C to 20 ° C. 2. A wafer cleaning method for removing contaminants on a wafer surface by combining a plurality of chemical cleaning steps and an ultrapure water rinsing step, wherein the wafer is cleaned after a HCl / H ₂ O ₂ cleaning step for removing metal contaminants. A wafer cleaning method, wherein rinsing is performed while maintaining ultrapure water used in at least one of the one or more ultrapure water rinsing steps at 0 ° C to 20 ° C. 3. The wafer cleaning method according to claim 1, wherein ultrapure water produced through the ion exchange resin membrane permeating step is introduced into the rinsing step. A wafer cleaning method, wherein a water heat exchange step is provided, and ultrapure water before ion exchange is cooled to 0 ° C. to 20 ° C. in the heat exchange step.