JP2893493B2 - Silicon wafer cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning semiconductor silicon wafers, which simplifies the cleaning process and facilitates waste liquid treatment.

[0002]

2. Description of the Related Art When manufacturing a semiconductor silicon wafer, the silicon wafer is cleaned in various steps, and final polishing is performed after polishing. The general washing process is (a)
Fine particles and organic substances that are the source of particle contamination are cleaned and removed using a cleaning solution composed of aqueous ammonia hydrogen peroxide, (b) rinsed with pure water, (c) washed with hydrofluoric acid, and iron, zinc, aluminum, etc. (D)
After rinsing with pure water, (e) heavy metal contaminants such as copper are removed using a cleaning solution comprising hydrochloric acid and hydrogen peroxide solution. The reason for performing a combination of alkali-based cleaning and acid-based cleaning in the conventional cleaning process is that ammonia-based cleaning can clean and remove the fine particles of the contamination source, but metal impurities easily adhere to the wafer surface and the metal contamination source cannot be removed. On the other hand, acid-based cleaning can remove metal contamination sources, but is less effective for particulate contamination.

[0003] As described above, in the conventional cleaning process, an alkali-based cleaning and an acid-based cleaning are performed in combination. However, since both processes use cleaning liquids having contradictory qualities, it is necessary to completely separate both processes. There is a problem that equipment becomes large and process management is difficult. Further, disposal of waste liquid discharged from each washing step is also a problem. On the other hand, regarding the removal of impurities in the cleaning liquid, a method of contacting a hydrofluoric acid cleaning liquid with silicon powder, adsorbing metal ions such as copper in the liquid to the silicon powder, purifying the silicon ions, and then cleaning the silicon wafer has been known ( Japanese Unexamined Patent Publication (Kokai) No. 3-102827) cannot remove particulate contamination only by cleaning a silicon wafer with hydrofluoric acid.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cleaning method which solves the above-mentioned problems in the conventional silicon wafer cleaning. In the present invention, the state of metal contamination of the silicon wafer was examined. In the cleaning with the ammonia hydrogen peroxide solution, the metal impurity concentration in the cleaning solution was 1 ppb.
When the level is on the order of magnitude, metal contamination cannot be removed, and in some cases the concentration of metal impurities on the wafer surface will be high.However, when the concentration of metal impurities in the cleaning solution is below 10 ppt, acid-based cleaning It has been found that the concentration of metal impurities on the wafer surface does not increase but rather tends to decrease even if the aqueous ammonia peroxide solution alone is washed without performing the above. Conventionally, it has been considered that metal impurities are likely to be adsorbed on the wafer surface and the impurity concentration is increased only by alkali-based cleaning using aqueous ammonia hydrogen peroxide, and the above findings are unexpected against such conventional wisdom. Was something. The present invention is based on the above findings, by cleaning with an aqueous solution of ammonia hydrogen peroxide having a metal impurity concentration of 10 ppt or less, preferably 1 ppt or less,
This eliminates the need for conventional acid-based cleaning, simplifies the cleaning process, and facilitates waste liquid treatment.

[0005]

According to the present invention, according to the present invention, there is provided a silicon wafer in which an acid-based cleaning is omitted by using a cleaning solution comprising an aqueous solution of ammonium hydrogen peroxide having a metal impurity concentration of 10 ppt or less, preferably 1 ppt or less. Is provided. Further, according to the present invention, the silicon wafer cleaning system is provided with a purification circulation unit for purifying the cleaning liquid and returning the cleaning liquid to the cleaning system, and the purification circulation unit is provided with a getter silicon for absorbing metal impurities. And a purifying unit provided with a filter for adsorbing fine particles, a cleaning liquid is introduced from the cleaning system into the purifying and circulating unit, and metal impurities and fine particles in the liquid are adsorbed and removed by the silicon or filter for getter, thereby removing metal. A method for cleaning a silicon wafer by purifying an impurity concentration to 1 ppt or less and returning to a cleaning system again is provided. Further, according to the present invention, when the cleaning liquid is supplied to the cleaning tank, a purification circulation unit is provided in the supply path of the cleaning liquid, and the purification unit provided with getter silicon for adsorbing metal impurities is provided in the purification circulation unit. A purifying section provided with a filter for cleaning, a cleaning liquid is introduced into the purifying and circulating unit in advance before the cleaning liquid is supplied to the cleaning tank, and metal impurities and fine particles in the liquid are adsorbed and removed by the getter silicon or the filter, respectively. This provides a cleaning method in which the metal impurity concentration is purified to 1 ppt or less and then supplied to the cleaning tank.

Ammonia hydrogen peroxide solution [H ₂ O: H ₂ O ₂ : NH ₄ OH
= 5: 1: 0.25, liquid temperature of 80 ° C], the silicon wafer was immersed in a cleaning solution containing 1 ppt, 10 ppt, and 1 ppb of Fe ions as metal impurities for 10 minutes to clean the wafer, and the Fe adhering to the wafer surface was removed. When the ion concentration was measured, the result of FIG. 1 was obtained. As shown in the figure, when the Fe ion concentration of the cleaning solution is 1 ppb (Sample No. 1), the Fe concentration on the wafer surface after cleaning is increased, and the effect of cleaning and removing metal impurities is not recognized. On the other hand, when the Fe ion concentration of the cleaning solution was 1 ppt or 10 ppt (Sample Nos. 2 and 3), the Fe concentration on the wafer surface after cleaning was reduced to 10 ⁹ (atoms / cm ² ).
Below, it is 10 ¹⁰ (atoms / cm ² ) or less, and the cleaning effect is clearly recognized. Therefore, when a cleaning effect of a metal impurity concentration on the wafer surface of 10 ⁹ (atoms / cm ² ) or less is required, it is not necessary to perform acid cleaning. Looking at the particle contamination, the number of particles adhering to the wafer surface (6 inch diameter) of Sample Nos. 2 and 3 was 0.1 μm or more and 10 particles or less on the entire surface. Are better.

Recently, a silicon wafer for high integration of 64 mechanisms or more has been demanded. In this case, the metal impurity concentration on the wafer surface is about 10 ⁹ (atoms / cm ² ). According to the cleaning method of the present invention, the cleaning liquid having a metal impurity concentration of 1
The desired cleaning effect can be obtained by single cleaning using an aqueous solution of ammonia hydrogen peroxide of ppt or less, and there is no need to further perform acid-based cleaning using hydrofluoric acid, hydrochloric acid, or hydrogen peroxide as in the related art.

The hydrogen peroxide solution and the ammonia water used in the cleaning method of the present invention have a concentration of 30 vol% which is commercially available, and the composition of the ammonia and the hydrogen peroxide is H ₂ O ₂ : NH ₄ OH = 1:
The concentration of hydrogen peroxide with respect to water may be adjusted within a range of 5 to 0.05% based on 0.25 to 1: 0.5. Cleaning solution temperature is 5
0-90 ° C is preferred. If the liquid temperature is lower than 50 ° C., the washing time becomes longer. On the other hand, when the liquid temperature is higher than 90 ° C., it is not preferable because the decomposition of the chemical liquid is quick and it becomes difficult to maintain a required liquid composition. The washing time may be about 1 to 20 minutes.

Next, an example of the cleaning step according to the present invention is shown in FIG.
Shown in In the washing step, a supply unit 20 for supplying a washing liquid, a washing tank 1, a washing tank 9, and a drying unit 10 are provided. The supply unit 20 includes a purification / circulation unit A for removing contaminant metals and fine particles from the cleaning liquid obtained by mixing the aqueous ammonia and the aqueous hydrogen peroxide.
Is attached. Further, the cleaning tank 1 is provided with a similar purification circulation unit B for purifying the cleaning liquid overflowing from the cleaning tank. These purification circulation units A and B include:
Cartridge-type metal impurity purifying units 4 and 6 having getter silicon for adsorbing and removing metal impurities and fine particle purifying units 5 and 7 including filters for adsorbing and removing fine particles are provided. The aqueous ammonia and the aqueous hydrogen peroxide are mixed at a predetermined concentration ratio (for example, H ₂ O ₂ : NH ₄ OH = 1: 0.5) and are introduced into the buffer tank 2 in advance as a cleaning liquid. Pure water is supplied to the buffer tank 2 through a water supply pipe (not shown). Next, the cleaning liquid is introduced into the purification circulation unit A to remove metal impurities and fine particles. That is, the cleaning liquid passes through a purifying section 4 of a cartridge type having silicon for getter and a purifying section 5 provided with a filter for adsorbing fine particles, and a valve 1 is provided.
It is circulated again to the buffer tank 2 via 1. The circulation of this cleaning solution is performed at a set value of the metal impurity concentration and the number of fine particles (e.g., one metal fine particle of 1 ppt or less, fine particles of 0.1 μm or more /
cc) It is repeated until it becomes below. The cleaning liquid whose metal impurity concentration and the number of fine particles have fallen below the set values is supplied to the cleaning tank 1 by opening the valve 12, and the silicon wafer is cleaned. In the cleaning tank 1, the cleaning liquid is guided to the purification circulation unit B and purified so that the metal impurities and fine particles removed from the wafer do not adhere to the wafer surface again. That is, the cleaning liquid overflowing from the cleaning tank 1 is guided to a cartridge-type purification unit 6 having getter silicon, and is introduced into a purification unit 7 having a fine particle adsorption filter after metal impurities are adsorbed and removed by the getter silicon. Here, after the fine particles are removed, the fine particles are circulated again to the cleaning tank 1. The washed silicon wafer is washed in a washing tank 9 using pure water, and then sent to a drying unit 10. Although it is possible to remove metal impurities and fine particles below the set value by using the purification unit B alone without providing the purification unit A, the purification unit A
, The purification time is longer than that in the case where. It is preferable that the getter silicon of the purification circulation units A and B be provided detachably. The shape may be any of a plate, a particle, and a block. As the getter silicon, one whose surface has an impurity concentration of 10 ⁹ / cm ² or less by hydrofluoric acid treatment is used.
By bringing the collected cleaning liquid into contact with the getter silicon, impurity metal ions such as iron, zinc, and aluminum in the cleaning liquid are adsorbed on the surface of the getter silicon and removed.

[0010]

EXAMPLE An aqueous solution of ammonia hydrogen peroxide having a metal impurity concentration of 1 ppt [H ₂ O: H ₂ O ₂ : NH ₄ OH = 5: 1: 0.25, liquid temperature 70 ° C.] and a metal impurity concentration on the surface of Al = 10 ¹¹ , a silicon wafer of Fe = 10 ¹¹ atoms / cm ₂ was immersed for 10 minutes and the wafer surface was cleaned, and the impurity concentration of Al and Fe was 10 ⁹ (atoms / cm 2).
² ) and an excellent cleaning effect was obtained (Sample No. 10). On the other hand, for comparison, silicon wafers having the same metal impurity concentration were subjected to conventional alkaline cleaning and acid cleaning. First, the silicon wafer was immersed in a conventional alkaline cleaning solution (H ₂ O: H ₂ O ₂ : NH ₄ OH = 5: 1: 1) for 10 minutes to be cleaned (sample No. 11). Further, after the above alkaline cleaning, the substrate was immersed in hydrofluoric acid (H ₂ O: HF = 100: 1) for 1 minute, rinsed with pure water, and then treated with a hydrogen peroxide solution [H ² O: H ² O ² : HCl = 5. : 1: 1] for 10 minutes, and then rinsed with pure water (Sample No. 12). The result is shown in FIG. As shown in the figure, the Fe and Al concentrations on the wafer surface after cleaning were both higher than those obtained by the cleaning method of the present invention, and did not reach the cleaning effect of the present invention.

[0011]

According to the cleaning method of the present invention, metal contamination and fine particle contamination can be effectively removed only by single cleaning with ammonia hydrogen peroxide solution without performing acid cleaning. Since it is greatly simplified and no acid cleaning is performed, waste liquid treatment is easy.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Fe ion concentration in a cleaning liquid and the Fe concentration on a wafer surface after cleaning.

FIG. 2 is a schematic process diagram showing a cleaning process of the present invention.

FIG. 3 is a graph showing the cleaning effect of an example of the present invention and a comparative example.

[Explanation of symbols]

1-washing tank, 2-buffer tank, 4,6-metal impurity purification section, 5,7-fine particle purification section, 9-water washing tank, 10-drying section, 11,12-valve, 20-supply section, A, B-Purification circulation unit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mari Sakurai 1-297 Kitabukurocho, Omiya City, Saitama Prefecture, Central Research Laboratory, Mitsubishi Materials Corporation (72) Inventor, Yasushi Shimanuki 3-8-16 Iwamotocho, Chiyoda-ku, Tokyo (56) References JP-A-3-102827 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/304

Claims (3)

(57) [Claims] 1. A method for cleaning a silicon wafer in which an acid-based cleaning is omitted by using a cleaning solution containing an aqueous solution of ammonium hydrogen peroxide having a metal impurity concentration of 10 ppt or less, preferably 1 ppt or less. 2. A purifying unit for purifying a cleaning liquid and returning the cleaning liquid to the cleaning system, wherein the purifying unit includes getter silicon for adsorbing metal impurities and fine particles. A purification unit provided with an adsorption filter is provided, a cleaning liquid is introduced from the cleaning system into the purification circulation unit, and metal impurities and fine particles in the liquid are adsorbed and removed by the getter silicon or the filter to remove the metal impurity concentration. 2. The cleaning method according to claim 1, wherein the silicon wafer is purified by purifying the silicon wafer to 1 ppt or less and returning to the cleaning system again. 3. A purifying unit provided with a purifying and circulating unit in a supply path of the cleaning liquid when supplying the cleaning liquid to the cleaning tank, wherein the purifying and circulating unit is provided with a getter silicon for adsorbing metal impurities and a filter for adsorbing fine particles. A purifying section provided with a cleaning liquid is introduced into the purifying and circulating unit before supplying the cleaning liquid to the cleaning tank, and metal impurities and fine particles in the liquid are respectively adsorbed to the getter silicon or the filter to remove them. The cleaning method according to claim 1, wherein the metal impurity is purified to a concentration of 1 ppt or less and then supplied to a cleaning tank.