static charge removal with ipa solution · 2) ipa condensation on pic4 surface and charge removal:...

Static Charge Removal with IPA Solution

著者大見忠弘journal orpublication title

IEEE Transactions on SemiconductorManufacturing

volume 7number 4page range 440-446year 1994URL http://hdl.handle.net/10097/48009

doi: 10.1109/66.330281

440 lEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING, VOL. I, NO. 4. NOVEMBER 1994

Static Charge Removal with IPA Solution Tadahiro Ohmi, Seiji Sudoh, and Hiroyuki Mishima

Abstract-Due to the an increase in pattern densities and wafer diameters, it is extremely difficult for wet chemical processing to perform complete cleaning, rinsing and drying for highly rugged surface of very fine pattern ULSI devices. IPA Vapor Drying is a widely used drying method in semiconductor manufacturing. As IPA has low surface tension and very high solubility to water, it is suitable for IPA vapor process to perfectly eliminate contamination of the wafer surface. This drying system also has an ability to eliminate static charge and can essentially achieve the high quality of the surface cleanliness.

Therefore, the mechanism of static charge removal was studied using a quantitative method for the direct measurement of static charge.

I. INTRODUCTION

CCOMPANYING an increase in pattern densities and A wafer diameters, the need to realize perfectly controlled semiconductor manufacturing environments is necessary to insure device reliability. Achieving a clean manufacturing environment involves several controllable factors, one of the most important of which is static charge.

Electrostatic discharge causes device destruction through insulation failure and circuit disconnection. This electrostatic discharge occurs when a charged object comes into contact with or into close proximity ta a device surface. In addition, static charge causes the problem of floating particle adhesion [I], [2]. Polymeric materials commonly used to make wafer carriers are natural insulators and easily develop high static charges due to the triboelectric phenomena. This causes floating particles, which are attracted by the static charge of a charged substance, and adhere and accumulate on its surface. In the age of submicron devices,, the particles which need to be controlled will become even smaller. Correspondingly, these finer particles are more sensitive to electrostatic force, and the problem of adhesion becomes more important.

To solve the problem of material charging in air, Nz or Ar inert gas ambience, the use of ionizer and UV (Ultraviolet) light irradiation are effective. In air, ionizers are excellent for the neutralization of static charge. In this method the ions are usually generated by corona discharge, and these ions then neutralize static charge. On the other hand, in inert gas ambience such as N2 or Ar, the static neutralization system employed is UV light which ionizes the N2 and Ar molecules. This method is superior to the static charge neutralization method employing corona discharge for neutralization in inert

Manuscript received August 20, 19Y3; revised December 23, 1993. T. Ohmi and S. Sudoh are with the Department o f Electronics, Faculty

of Engineering, Tohoku University, Aobaku Sendai City Miyagi Prefecture, Japan 022-263-9395.

H. Mishima is with Tokuyama Soda Co., Ltd., Mikage-cho Tokuyama City Yamaguchi Prefecture, Japan 0834-32-22 19.

IEEE Log Number 940523Y.

gas ambience. Additionally this method can be applied to reduced pressure ambience down to - lop3 Torr, demonstrating better neutralization capability than under at- mospheric pressure [3], [4].

In order to eliminate static charge build-up in wet chemical processes, the IPA (isopropyl alcohol) vapor drying method is the most effective [ 5 ] , [6]. The electrostatic charge built up after IPA rinsing can be completely neutralized by IPA vapor drying. It has been shown that the IPA vapor drying technology is excellent in the elimination of particulate contamination caused by electrostatic charge. As IPA has low surface tension and very large solubility in water, the water in deep trenches can be completely removed by IPA. Due to the excellent physical and chemical properties of IPA, along with the fact that high punty IPA is commercially available, IPA vapor drying method has become a key technology. IPA vapor drying method is characterized as follows 171-1 141:

1) Completely Particle Free Si Wafer after Drying 2) No Residual Water Mark or Haze on Si Wafer 3) Complete Elimination of Water in Deep Trenches 4) Complete Prevention of Static Charge build up. Although the IPA vapor drying method is considered to

be a very important technology for preventing static charge build up in wet chemical processes, the mechanism by which it works has not been studied sufficiently. There are only a few studies on the discharge mechanism and liquid charge phenomenon; one such study was based on electric double layer by Helmholts and another study was based on the donicity concept related to the charge of solid polymers and liquids [15].

In this study, in addition to the surface potential which was measured in place of static charge, a quantitative method for the direct measurement of static charge was adopted. We also observed that IPA and IPA-H2O solutions are excellent in the complete removal of static charge from charged substances. Furthermore, using a constant charging system with a parallel plate capacitor, the mechanism of static charge removal by IPA was studied.

11. MECHANISM OF STATIC CHARGE REMOVAL FROM THE POLYMER

A . Experiment

This experiment was carried out in a Clean Room at a temperature of 20 N 21"C, and a relative humidity of 50 - 60%. Teflon-PFA (4-fluor0 ethylene-perfluoroalkoxy copolymer) and glass were used as charged materials. For the investigation of the static charge removal phenomenon qualitatively, the wafer carrier, container, disk of PFA, and

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OHM1 et al.: STATIC CHARGE REMOVAL WITH IPA SOLUTION 441

I I _L

FARADAY CAGE

Fig. 1. Static charge measurement principle using a Faraday cage.

glass plate were rubbed with cotton cloth while wearing insulating gloves (Asahi Chemical Co. Ltd.: Bencot) to charge their surface.

The IPA used in this study was Ultra Clean grade IPA for semiconductor manufacturing. To obtain various H20 concentration IPA-H20 solutions UPW was added to IPA, and the concentration of H2O in the IPA-H20 solution was determined by Karl Fischer titration.

The static charge detector used in this study applied the theory of the Faraday cage. When a charged sample is placed in an isolated conductor, its real static charge appears on the external surface of the conductor. By measuring this static charge, the charge on the sample can be detected indirectly. The schematic diagram and equivalent circuit are described in Fig. 1 . The amount of static charge of the sample in the Faraday cage appears across the external capacitor Cm, by then measuring the voltage, V, across the capacitor with an electrometer, the static charge of the sample is obtained using the following expression.

Q = C m . V (1)

where Q = The amount of static charge [Cl [Fl Cm = Capacitance of capacitor

V = Potential drop across capacitor [VI. This detector assumes that the material (conductor, insu-

lator) of the sample, contact condition of the sample on the internal surface of the Faraday cage and sample phase (gas, liquid or solid) do not affect charge measurement. A grounded external metal container is used as a shield to isolate the Faraday cage.

Calibration of the static charge detector was done by the following method. After applying a dc voltage across capacitor Cm once, we measured the transition time of voltage across the capacitor and compared it with the calculated value. In general the voltage across the capacitor is calculated by ( 2 ) as shown below.

40 C

V ( t ) = --

where V = Potential drop t = Elapsed time yo = Initial Charge C = Capacitance R = Resistance

across the capacitor [VI [SI

[Cl tF1 Wl.

DISK SIZE : 125* x 2' W W

c L I

W 50 100 150 ELAPSED TIME [ Hr ]

Fig. 2. Surface static charge of PFA disk.

We calculated the theoretical time using the following values, qO/C = 1500 [mV], C = 0.367 [ p F ] , R = 1 x 10l2 [Q]. The result of a 24 h continuous experiment agrees well with calculated values. This result shows that calibration of the detector was carried out correctly.

The surface potential detector used in this experiment was either a vibrating reed electrometer (Japan Static Co. Ltd.: SV- 73A) or a rotational sector electrometer (Shishido Static Co. Ltd.: Statiron TL).

B. The Amount of Static Charge on PFA Surface

Next the amount of triboelectric charge is discussed. Both surfaces of a PFA disk (125 "4, 2 mm thick) were charged up by rubbing with a cotton cloth and the amount of static charge built up was measured using a closed type Faraday cage (see Fig. 2). The number of disks in the Faraday cage was either one or two. In the case of two disks, the amount of initial charge was approximately twice as much as one disk, indicating that the surface area was in proportion to the amount of charge. The amount of charge on the disk reduced gradually, following the attenuation characteristic of potential on the polymer as discussed above.

The charge, Q , per unit area is calculated in this experimental system as shown below.

(3) Q = 0.14pC/(.rr/4 x (0.1251n)~ x 2) = 5.7 pc/m2.

Generally surface charge density, U , of an isolated charged substance in air is shown in (4).

a = E x ~ (4)

where E = Surface electric field W/mI [c/m21 F/mI

Once the surface voltage increases up to the dielectric breakdown value, discharge occurs. Therefore, the maximum value of U can be calculated as follows.

(T = Surface charge density E = Dielectric constant of air

The surface charge density observed due to triboelectric phenomena was below ablAX. however, it was revealed that


442 IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING, VOL. 7, NO. 4, NOVEMBER 1994

-30

I

SPRAYING IPA-LIQUID

-10 t

1 2 3 4

IMMERSED TIME IN IPA VAPOR [ min ]

Relat~mhip between immersion time in IPA vapor and camer Fig 3 surface voltage

teflon PFA can be easily charged up to high voltages by only slight rubbing. Theoretical calculations carried out using material properties indicated that further charge attenuation are very slow after charging.

C. Static Charge Removal from Polymer with IPA

1 ) Drying Principle in IPA Vapor Drying System: When a rinsed wafer carrier is immersed into IPA vapor (boiling point = 82.4OC), IPA condenses into droplets on the carrier surface due to its cooler temperature. These droplets grow into bigger droplets by mixing with water on the wafer carrier; finally the droplet falls from the surface due to gravity. Condensation stops when the surface temperature of the carrier rises to the temperature of the IPA vapor; at this point the carrier surface is “dry.” Additionally it has been demonstrated that carrier surface chargc is almost 0 V after the above treatment [16].

2) IPA Condensation on PIC4 Surface and Charge Removal: First, we investigated at which stage the static charge was removed by IPA vapor during the drying process.

Fig. 3 shows the relationship between immersed time in IPA vapor and charge potential of PFA carrier. The open circles (0) represent the case where the PFA carrier surface temperature is at room temperature and thte filled circles ( 0 ) represent when the surface temperature is above 100°C. In order to raise the carrier temperature the camer was heated in an electric oven for 30 min at 100°C above the boiling point of IPA. In both cases, when the surface was rubbed with cotton cloth the static charge rose up to around -26 kV. These results indicate that the surface temperature does not affect charge potential build up itself. These charged carriers were then immediately immersed into IPA vapor and the drop in surface potential over time was measured in both cases.

In the case of the room temperature carrier, 10 s after immersion of carrier, the carrier surface potential reduced to around 0 V and remained level after that. It was observed that about 2 s after immersion of the room temperature carrier into IPA vapor, condensed IPA drops on carrier surface joined together and started to drip from the carrier. We have shown that charge removal speed is very high with IPA liquid and that charged potential decreaised rapidly just after an IPA drop falls from the surface.

When the pre-heated carrier was immersed into IPA vapor under these conditions phase change of IPA vapor to IPA

drops never occurred. Indeed no condensation of IPA was observed over the length of this experiment. As opposed to the room temperature case where the charge was removed in about 10 s after immersion into IPA vapor, the potential of the heated carrier remained at the initial level of -26 kV even after immersion into IPA vapor. This clearly indicates that IPA vapor has no ability to remove static charge.

Furthermore, A represents the results obtained when several ml IPA liquid were sprayed on the pre-heated charged carrier in IPA vapor. After this treatment, the carrier potential was dramatically reduced to -2 kV. The above result indicates that IPA liquid is very important in removing static charge from a charged camer.

The residual charge left after spraying with IPA liquid is because the area contacted with IPA liquid is not the same as with vapor immersion. In other words, the IPA spray method results in only partial contact between IPA liquid and carrier surface, whereas in the IPA vapor method IPA condensation occurs on the whole surface of the carrier uniformly. Refer to the following section for further details; only on the surface which contacts with IPA liquid does charge transfers occur; therefore, in noncontact area there is no removal of charge.

The above mentioned PFA materials were negatively charged, Next we will discuss positively charged materials. A pyrex glass plate (200 mm x 200 mm x 10 mm thick) was rubbed to charge up to +2.1 N f4.5 kV. After 10 min of immersion in IPA vapor, the surface potential of the pyrex glass became around 0 V. Therefore we have demonstrated that IPA liquid has the ability to eliminate both negative and positive static charge.

From the above results, we can draw the following four qualitative observations.

1) Static charge is not removed from charged polymer by contact with IPA vapor only.

2) After concentration of IPA vapor on polymer surface and continuous separation of IPA drop from polymer, static charge can be eliminated. That is to say, IPA liquid plays an important role in static charge removal.

3 ) Removal time of charge from polymer is relatively short using IPA vapor drying method. Charge removal speed appears to be very high.

4) IPA vapor drying has excellent properties for the removal of both negative and positive charges.

111. STATIC CHARGE REMOVAL MECHANISM FROM GENERAL MATERIAL

A. Constant Charging System Generally speaking the constant charging of a liquid is

difficult, conventionally an easily charged substance is rubbed with leather and resultant charge is transferred to the liquid by contact. Using this method, it is difficult to control the amount of charge transferred and its polarity reproducibly. Therefore we have developed a new constant charging system. The schematic diagram for this constant charging system is shown in Fig. 4. The charging system is basically composed of two 150 mm x 200 mm aluminum electrodes fixed at a


OHM1 er al.: STATIC CHARGE REMOVAL WITH IPA SOLUTION

240

220

200

0 PE

J . U

443

- IC -

PARALLEL PLA CAPACITOR

FARADAY C A ~ @

ELECTRO BALANCE lower electrode

IN NITROGEN GAS AMBIENCE e Fig. 4. Schematic diagram of constant charging system.

distance of 1.8 mm, thus making a parallel plate capacitor. This apparatus is mounted on an insulator and a dc supply is applied between the two electrodes. By dripping discharged IPA liquid onto the lower electrode, it is possible to charge the IPA liquid. The amount of charge is adjusted by varying the dc voltage and charge polarization is controlled by polarization (+. -) of the dc supply. The complete apparatus, therefore is comprised of an IPA supply system, constant charging system, and a charge measurement system. All parts of this system which come into contact with IPA liquid are under an inert gas (Nz) atmosphere.

Using this system, the amount of charge and charge polarization were able to be controlled easily and reproducibly. Additionally it was confirmed that, in the case of the changing dc supply polarization, the absolute value of charge generated was same (IPA can be charged the same amount both negatively and positively simply by switching the polarity).

B. Charge Remota1 Characteristics of IPA

I ) Charge Removal Capability of IPA Vapor: Although it was demonstrated qualitatively that IPA vapor itself is not able to eliminate static charge while condensed IPA has excellent charge removal capability, in this section we attempt to reassess this fact quantitatively.

The experimental procedure used is as follows. About 10 ml of charged IPA liquid was poured into the Faraday cage, after the IPA liquid was vaporized using an IR lamp and the transition of charge was recorded as function of time. If the total charge decreases as the IPA liquid vaporizes then IPA vapor has charge removal capability. On the other hand, if the charge in the Faraday cage remains constant in spite of vaporization, then IPA vapor has no ability of charge removal.

In Fig. 5 the experimental results are shown. The experiment was carried out three times under various lamp locations and various amounts of charge in the IPA. The horizontal axis represents elapsed time of lamp irradiation, while the vertical axis represents the potential drop across the capacitor which is equivalent to the amount of charge in the Faraday cage. Although the line is terminated past 10 min, these points represent complete vaporization time. Fig. 5 shows that initial charge does not decrease, thus we can say that IPA vapor has no capability to remove static charge.

TRANSITION OF ELECTRIC CHARGE IN VAPORIZATION

c 1

REMOVED CHARGE vs. VOLTAGE ACROSS THE CAPACITOR

VOLTAGE M

Fig. 6. IPA liquid (in Nz gas).

Voltage of charged substance and static charge removal capability of

2 ) Voltage of Charged Substance and Static Charge Removal Capability of IPA Liquid (in N2 Gas): We researched the relationship between charged voltage and charge removal capability of IPA liquid. It is generally believed that with an increase in charged voltage, the charge removal capability also rises for a constant volume of IPA. This belief was investigated experimentally by applying various voltage across the capacitor.

In this study the apparatus shown in Fig. 4 was used. By applying a dc supply from 0 V to 3000 V the amount of charge removal per gram of IPA was measured. Dimensions of the capacitor were 150 mm x 200 mm x 1.8 mm distance.

The results of this study are shown in Fig. 6. From 0 V to 3000 V voltage the applied voltage across the capacitor was in directly proportional to the amount of charge removed per gram of IPA as shown below.

Q = 5.67 x [pC/yV]. ( 5 )

C. Static Charge Removal and Resistivity in IPA-HzO Binary System

1 ) Static Charge Removal in IPA-HzO Binary System: In the IPA vapor drying process, there is some possibility of water carry-over from previous processes by the wafer carrier and even the wafer itself. Therefore charge removal characteristics


444 IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING. VOL. 7. NO. 4. NOVEMBER 1994

- ; Ql . 0

g 2 - .- E w (3 L T .

I

E l - o 2

- - . . _ - .- 1 . . 0

in B o Ld t; 1 0 0 10' id io3 104 105 io6

CONCENTRATION OF WATER IN IPA [ppm] U1

w

Fig. 7. Static charge removal in IPA-HzO binary system.

'.3 t I

0 10 20 30 WATER CONTENT [ wt% ]

Fig. 8. binary system.

Relationship between H 2 0 concentration and resistivity in IPA-HzO

of IPA solutions containing water and only water, should be investigated.

The static charge removal characteristics of the binary IPA- H20 system were examined using the apparatus shown in Fig. 4. The H20 concentration in IPA was measured using Karl Fischer titration for low H2O concentration (under O.l%), and gas chromatography was used in the case of high H2O level. These experiments were carried out under a N2 gas ambience.

In the low H20 concentration area (horizontal axis represents H2O concentration [ppmi]), charge removal characteristics results are shown in Fig. 7. This graph shows that from 0%) to 80% H2O concentration, IPA solutions have excellent static charge removal characteristics.

2) H20 Concentration and Resistivity in IPA-H20 Binary System: In the case of UPW addition into high purity IPA for semiconductor industry, the relationship between moisture concentration and resistivity of IPA solution is described in Fig. 8. Resistivity of IPA was measured after addition of UPW with a resistivity of 18.2 MR . c;m. Fig. 8 shows the results obtained in both the open and closed systems. The closed system experiment was carried out in a N2 gas ambient. In both systems, the resistivity decreased rapidly with the increase in H20 concentration.

Comparing the two results we can see that the resistivity value in the closed system was one order of magnitude higher than that in the open system. The resistivity of IPA itself was measured at 5 . 4 ~ 10"' R a n in the closed system. This value is much smaller than that for hydrocarbons N It "1)

I PARALLEL PLATE CAPACITOR I SUPPLY

DRAIN VALVE

Fig. 9. Schematic diagram of constant charging system for IPA liquid.

[ 171, therefore charge leak speed is slow through IPA liquid indicating that IPA is hard to charge up.

Finally, in this study it was demonstrated that the resistivity of IPA-H20 solution did not affect charge removal capability.

D. Charge Transfer Characteristic to IPA

1 ) E.xperimenta1 Apparatus: In a N2 gas ambient, there are always uncontrollable factors in the measurement system such as the contact condition of the IPA liquid with the electrode, contact time and so on. Therefore, a one electrode insulated capacitor (coated by epoxy resin) was employed, additionally the whole apparatus was immersed into IPA liquid and the charge transfer characteristics were studied. A5 the insulator used in this system was made of a polymer resin, the system applied voltage was controlled under 30 V in order to prevent leak current (see Fig. 9).

2) Charge Transfer Characteristic in IPA Liquid: As well as charge removal characteristics in a N2 gas ambient, charge transfer characteristics from a charged capacitor to the IPA liquid were examined at various applied voltages.

Using the apparatus displayed in Fig. 9, after charging up the capacitor, IPA liquid was drained through bottom valve and introduced into a Faraday cage below and its charge was measured. Before starting the experiment the IPA liquid in the tray was discharged by grounding. A voltage in the range from 0 V to 30 V was then applied, and so as to stabilize the amount of charge in the tray an auxiliary capacitor of 0.47 pF was installed.

Charge transfer characteristic for IPA liquid is shown in Fig. IO. The horizontal axis represents applied voltage and the vertical axis represents the amount of charge transfer to IPA liquid. As we found in the N2 gas phase experiment, applied voltage was directly proportional to the amount of charge transfer. However. at the same voltage the amount of charge transfer in IPA liquid was 40 times as large as in a Nz gas ambience. This may be due to the fact that the space between the two electrodes is now filled with IPA liquid which has a high dielectric constant, therefore charge density on the electrode becomes larger.

3) Surface Charge Density and Charge Transfer to IPA Liquid: Surface charge density and charge transfer to IPA


OHM1 er al.: STATIC CHARGE REMOVAL WITH IPA SOLUTION

8 0 Q

Q

8 g

345

IPA IPA ) MOLECULES DROP

g 1 ’ * * REMOVAL OF IPA DROP HAVING ELECTRON

VAPOR

CHARGE TRANSFER IN IPA LIQUID n WITH VARIOUS VOLTAGES e l o 1 I

VOLTAGE [VI

Fig. IO. of IPA liquid (in IPA liquid).

Voltage of charged substance and static charge removal capability

CHARGE TRANSFER in NZ GAS and in IPA liquid

- 51 J

CHARGE DENSITY [ C/m2 ] X lo-’

Fig. 11 . Surface charge density and charge transfer to IPA liquid.

liquid is discussed. In the two cases, where the capacitor was fixed in a N2 gas ambience, and where there was IPA liquid, the relationship between surface charge density on capacitor’s electrode and the amount of charge transfer to IPA was measured. The result is shown in Fig. 11. The amount of charge transfer to IPA seems to be in proportion to charge density on charged substance.

Iv. RESULT AND DISCUSSION 1 ) A Faraday cage was constructed and the development

of a constant charging system has been accomplished. Using this apparatus, quantitative measurement of static charge has been successfully carried out.

2) It was revealed that IPA vapor does not have the ability to remove static charge ‘from a charged substance.

3) IPA liquid was able to remove both positive and negative static charges equally well.

4) The amount of charge transfer from a parallel plate capacitor in both N2 gas and in IPA liquid, to the IPA liquid was proportional to the surface charge density.

5) In IPA-HpO binary system, charge removal capability was maintained over a wide range of moisture concentration. However, when the water concentration was over 80%, its capability decreased rapidly.

6) Static charge transferred from the charged substance to the IPA liquid quickly. Taking the above experimental results into consideration,

CHARGED SURFACE

DISCHARGED SURFACE

REFERENCES

[ 1 ] H. Inaba and T. Ohmi, “Influence of static charge,” Technology of high performance process in LSI manufacturing IV, Ultra Clean Society. pp. 197-217, Feb. 1990, (in Japanese).

121 -, “Super clean room technology,” Report of Takasago Thermal Engineering R&D Center, No. 4, pp. 43-63, 1990 (in Japanese).

[3] -, “Super clean room technology-Prevention of static charge and impurities in air-,” Nikkei Micro Device, no. 66. pp. 141-158, Dec. 1990 (in Japanese).

[4] H. Inaba, T. Yoshida, T. Okada, T. Ohmi, M. Morita, and M. Nakamura, “Neutralization of wafer charging in nitrogen-gas,” in 14th Ultra Clem Technology Work Shoi~ Proc., Ultra Clean Society. Oct. 1991, pp. 37-52 (in Japanese).

[SI S. Koyata, Matsuba, and T. Hattori, “Cleaning technology of Auoro- resin wafer carrier,” Semicon N e w . November issue, pp. 55-59, Nov. 1989 (in Japanese).

[6] T. Hattori, S . Koyata, M. Funada, and H. Miahima. “New IPA wafer carrier cleaning technology,” in Proc,. Mic,ror.ontrrmirfcrriorl ‘ Y l , San Jose, Oct. 1991, pp. .552-S61.

[7] H. Mishima and T. Ohmi, “Wafer cleaning and drying technology,” Supervised by T. Ohmi and T. Nitta, Edited by Ultra Clean Society, “UPW and High Pure chemicals delivery system,“ pp. 135-163, Feb. 1989 (in Japanese).

[XI T. Yasui, T. Mizuniwa, H. Mishima, M. Ahe, and T. Ohmi. “Particle- free cleaning and drying technology,” Supervised by T. Ohmi and T.


446 tEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING. VOL. I. NO. 4. NOVEMBER 1994

Nitta. Technology of High Performance Process in t S t Manufacturing It-Wet Process Technology-, pp. 135-163, Feb. 1989. (in Japanese).

191 T. Ohmi, H. Mishima, T. Mizuniwa, and M. Abe, “Wet cleaning technology reducing particles under 1/10,” Nikkei Micro Device, pp. 98-103, May 1988 (in Japanese).

[ I O ] H. Matsuzaki, “IPA vapor drying method in ultra clean cleaning technology.” Cleaning Technology, Autumn 1987 (in Japanese).

[ I I ] H. Matsuzaki. “IPA vapor drying system,” Semicon News, pp. 5 8 4 3 , Feb. 1989 (in Japanese).

[ 121 H. Mishima, T. Yasui. T. Mizuniwa, M. Abe, and T. Ohmi, “Particle- free wafer cleaning and drying technology,” IEEE Trans. Semicond. Manufact., vol. 2, No. 3. pp. 69-75. Aug. 1989.

1131 H. Mishima, “Wafer cleaning and drying technology,” in Proc. 2nd Symp. U L S I Ultra Clean Technology, Tokyo, Mar. 1986, pp. 397419 (in Japanese).

141 H. Mishima, T. Ohmi, T. Mizuniwa, and M. Abe, “Deposition characteristics of isopropanol (IPA) and moisture from IPA vapor dried silicon wafers,” IEEE Truns. Semicond. Manufact., vol. 2, no. 4, pp. 121-129. Nov. 1989.

{ 151 R. Williams and J. Colloid, Interface Sci., vol. 88, p. 530, 1982. [ 161 H. Mishima. “Particle-free IPA vapor drying technology.” in Proc.. Clean

Technology Symp. ‘88, Tokyo, pp. 2-2-1-2-2-15, 1988 (in Japanese). [ 171 E. 0. Foster, . I . Chem.. Phys., vol. 40: p. 86. 1964.

Tadahiro Ohmi (M’X I ) was bom in Tokyo, Japan, on January IO, 1939. He received the B.S., M.S., and Ph.D. degrees in electrical engineering from Tokyo Institute of Technology, Tokyo. Japan. in 1961, 1963 and 1966, respectively.

Prior to 1972, he served as a research Associate in the Department of Electronics of Tokyo Institute of Technology. where he worked on Gunn diodes such as velocity overshoot phenomena, multivalley diffusion and frequency limitation of negative differential mobility due to an electron transfer in the

multivalleys, high field transport in semiconductor such as unified theory of space-charge dynamics in negative differential mobility and block oscillators, and dynamics in injection lavers. He is presently a Professor in the Department of Electronics. Faculty of Engineering, Tohoku University. He is currently engaged in researches on high performance ULSI such as ultra high speed ULSI: Current Overshoot Transistor LSI, HBT LSI and SO1 on metal substrate, Base Store Image Sensor (BASIS) and high speed flat panel display, and advanced semiconductor process technologies, i.e., ultra clean technologies such as high quality oxidation, high quality metalization due to low kinetic energy particle bombardment. very low temperature Si epitaxy having simultaneous doping capability due to low kinetic energy particle bombardment, crystalinity control film growth technologies from single crystal, grain size conlrolled polysilicon and amorphous due to low kinetic energy particle bombardment, irr sitir wafcr surface cleaning technologies due to low kinetic energy particle bombardment, highly selective CVD, highly selective RIE, high quality ion implantations having low temperature annealing capability and etc., based on the new concept supported by newly developed ultra clean gas supply system. ultra high vacuum compatible reaction chamber having self-cleaning function. ultra clean wafer surface cleaning technology and etc. His research activities are as follows: 260 original papers and 190 patent applications.

Dr. Ohmi received Ichimura Award in 1979, Teshima Award in 1987, Inoue Harushige Award in 1989. The lchimura Prizes in Industry-Meritorious Achievement Prize in 1990, and The Okochi Memorial Technology PriLe in IY9l. He serves as the president of Ultra Clean Society. He is a member of Institute of Electronics, Information and Communication Engineers of Japan, the Institute of Electrical Engineers of Japan, the Japan Society of Applied Physics, and the ECS.

Seiji Sudoh received the B.S. degree in mechanical engineering from Tohoku University, Sendai, Japan, in 1985.

He joined Mitsubishi Kasei Corporation, Tokyo, Japan, in 1985. He worked on the chemical process development. He is a visiting researcher on the Faculty of Engineering of Tohoku University, where he is engaged in research of wet chemical precess.

Hiroyuki Mishima was born on February 6, 1952. He received the B.S. and the M.S. degrees in industrial chemistry from Okayama University, Okayama, Japan, in 1974 and 1976, respectively.

In 1976, he joined Tokuyama Soda Co., Ltd., where he has engaged in development of ion- exchange membrane system and water treatment system. From 1985 to 1988, he was a visiting researcher at Tohoku Ilniversity, where he has engaged in R&D on wafer-ioleaning and wafer- drvine svstems. In 1988. he came hack to Tokuvama

Soda, where he a chief engineer corporation.

has in

2 L ,

~ active in the same field at the corporation. Now he is the Special Equipment & Chcmicalls Department of the


static charge removal with ipa solution · 2) ipa condensation on pic4 surface and charge removal:...

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