[email protected] memscontents.kocw.or.kr/document/wcu/2012/JunNam/LeeDongWeon... · 2013-03-15 · • Don’t: – touch your face or skin with gloves – touch building hardware,

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Clean room

Originally developed by NASA and the aerospace industry for satellite manufacturing. Clean rooms now in use for all MEMS and semiconductor manufacturing.

http://altair.chonnam.ac.kr/~mems/�


Clean room for microfabrication



Clean room for microfabrication



Clean room classification



DI water

• Water is the most prevalently used material in microfabrication processes, and is used mainly for rinsing and cleaning of wafers • Approximately 6000 gallons of de-ionized(DI) water are required for each 6” CMOS wafer • DI water must be manufactured on site to achieve the quality and purity levels required by modern microfabrication • Each gallon of DI water may require as much as 4-6 gallons of raw city grade water to manufacture. • DI water must be continuously recirculated in order to achieve the quality and purity levels

Clean water: de-ionized water



HEPA filter

How Big of a Particle is Tolerable? – Example: 0.5 µm CMOS technology • Lateral Features: – pattern size = 0.5 µm – pattern tolerance = 0.15 µm – level-level registration = 0.15 µm • Vertical Features: – gate oxide thickness = 10 nm – film thicknesses = 250-500 nm – junction depths = 50-150 nm

Clean Room Air Filters • High Efficiency Particulate Air (HEPA) Filters – most common type of clean room air filter – high efficiency, low pressure drop, good loading characteristics – uses glass fibers in a paper-like medium – are rated by their particle retention: • A true HEPA-rated filter will retain 99.97 % of incident particles of 0.3 µm.



Characteristics of cleanroom

– Air is recirculated through HEPA filters with about 20 % make up • Vapors are entrained, so contamination potential is very high • Extensive gas detection and alarm systems are installed – Temperature is controlled to 68 - 72 °F (20 ~ 22 °C) – Humidity is controlled to 40 - 46 % RH – Room is held at positive pressure • Typically 0.1 in H2O for Class 100, Class 1000, and Class 10,000 • Positive pressure constantly blows dust OUT (Biohazard rooms operate at negative pressure to keep bugs IN) • Doors open inward, so room pressure closes them shut • 0.1 in H2O = 3.6 x 10-3 psi = 0.52 lb/ft2

• This produces 9.1 lbs.(4.13kg) force on a 7’ x 30” door



Types of cleanroom

Laminar Flow Cleanroom Turbulent Cleanroom


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http://upload.wikimedia.org/wikipedia/commons/b/b2/Laminar_Flow_Reinraum.png�


Dos and don’t in cleanroom

• Don’t: – touch your face or skin with gloves – touch building hardware, oily machinery, or wafer loading areas – lean on equipment – wear cosmetics, powders, or colognes – wear anything on fingers-- remove all rings and bracelets – use paper, pencils or markers that leave dust or lint • Do: – change gloves whenever they get dirty or torn – use a fresh pair of gloves whenever handling wafers – wipe down wafer handling areas with isopropanol – use clean room paper and dust-free ball point pens



Clean benches

Vertical and Horizontal Laminar Benches



Steps in photolithography

1. Wafer cleaning

2. Apply adhesion promoter (HMDS)

3. Spin coat photoresist at 1000 – 10,000 rpm

4. “Soft bake” (90 – 120°C for 60 –120 sec) to remove solvent

5. Alignment

6. Exposure

7. Development

8. “Post bake” (100 – 180°C) to increase adhesion

9. Etch exposed regions

10. Strip resist



Key steps in photolithography

Photolithography: transfer patterns from a mask into photoresist



Cleaning process

Common contaminant sources 1. Wafer transfer box, cassette 2. Wafer handling 3. Process equipment 4. Residual photoresist or organic coating 5. Metal corrosion 6. Solvents, chemicals 7. Clothing, unclean room furniture, operator

Silicon wafer cleaning 관련 중요 사항 ∗ Surface을 contamination시키지 않는 일 (much more important) ∗ Surface의 contamination을 제거하는 일

궁극적으로는 반도체 공정 중에 발생하는 오염을 물리적 & 화학적인 방법으로 제거하는 일



Wafer : 1970년 RCA사의 W. Kern이 발표한 RCA를 기본으로 세척함

세척 대상 내용

Silicon Wafer

기판 웨이퍼의 초기세척 각 프로세스의 단계마다 세척 (각 전처리 공정)

Chip Scribe 후의 세척

Quartz

Tube 확산공정, CVD 공정, 에피택셜 공정 등에서의 정기적인 세척 (내벽의 침착물의 제거)

Boat 위와 같음

Beaker 세정용 각종 치구 세척

기타 치구류

Graphite Susceptor Epitaxial process, CVD process 등에서의 서셉터 세척

금속수지

증착용 벨져 부착 금속 (Al, Cr, Au등) 제거

증착장치 내부 기구 위와 같음

캐리어, 홀더 Teflon 치구 등의 세척

Common methods for wafer cleaning Wet treatment, RCA 1 and RCA 2 cleaning, Plasma or glow discharge techniques Ultrasonic agitation, Supercritical cleaning

Cleaning process



기본적인 Cleaning 개념

유기물 제거 산화막 제거 금속불순물 제거

이온성 불순물 제거 입자성 불순물 제거

산화막 제거 DI water Dry

RCA 1 (Organic dirt)

DI water(5):NH4OH(1), in a Pyrex beaker, and then heat to 70±5°C on hot plate. Remove from hot plate and add a part of H2O2. Solution will bubble vigorously after 1–2 minutes, indicating that it is ready for use.

RCA 2 (metal ions: Au, Cu, Cr, Na etc.)

DI water(6):HCl(1) in a Pyrex beaker, and then heat to 70±5°C on hot plate. Remove from hot plate and add 1 part of H2O2. Solution will bubble vigorously after 1–2 minutes, indicating that it is ready for use.

Cleaning process : wafer

RCA 1

RCA 2



Cleaning process : wafer A. Preliminary Cleaning 1. Remove bulk of photoresist film (if present) by oxygen plasma or immersion in organic photoresist stripper; then boil in hot H2SO4 - H2O2 mixture (2:1) at 120°C for 1

0 minutes with adequate safety precautions exercised. (800 cc of H2SO4 + 400 cc of H2O2). 2. Rinse with deionized (DI) water in overflow tank for > 5 minutes. Use of US is recommended. B. Removal of residual organic contaminants and certain metals (SC – 1, RCA 1) 1. Prepare fresh mixture of H2O - H2O2 - NH4OH (5:1:1) by measuring the following reagents into a beaker of fused silica: a. 5 volumes of water (1000 cc) b. 1 volume of hydrogen peroxide (30% unstabilized electronic grade) (200 cc) c. 1 volume of ammonium hydroxide (30% electronic grade) (200 cc) 2. Submerge holder with wafers in cold solution and place the beaker on hot plate. 3. Heat to 75 to 80°C. Then reduce heating to maintain the solution at 80°C for an additional 10 minutes (vigorous bubbling is due to oxygen evolution; make sure not t

o boil the solution so as to prevent rapid decomposition of H2O2 and volatilization of ammonia). 4. Remove holder with wafers and place it immediately in overflow water tank and rinse with DI water for > 5 minutes. C. Stripping of thin hydrous oxide film 1. Submerge wafer assembly from step B.4 directly in mixture of 1 volume hydrofluoric (HF) acid (49%, electronic grade) and 50 volumes of water. 2. Allow to remain in the solution for only 15 seconds. Exposed silicon (but not SiO2) should repel HF solution. Use a polypropylene beaker for this step. 3. Rinse in DI water for only 20 to 30 seconds with agitation to remove HF solution (this minimizes re-growth of a hydrous oxide film). 4. Transfer wafer assembly immediately, without drying, into hot SC - 2 solution of step D. D. Desorption of remaining atomic and ionic contaminants (SC -2, RCA 2) 1. Prepare fresh mixture of H2O - H2O2 - HCl (6:1:1) by measuring the following reagents into a beaker a. 6 volumes of water (1200 cc) b. 1 volume of hydrogen peroxide(30% unstabilized electronic grade) (200 cc) c. 1 volume of hydrochloric acid (37% electronic grade) (200 cc) 2. Place beaker on a hot plate and heat to 75 to 80°C. 3. Submerge still wet wafers (after step B.4 or C.3) in hot solution. 4. Maintain the solution at 80°C for 10 to 15 minute 5. Remove holder with wafers and place it immediately in DI water overflow tank and rinse for 10 minutes. E. Drying: 1. Transfer holder with wet wafers into rinser & dryer. 2. Keep rinsing until water resistivity meter indicates at least 12 Mohm - cm. 3. Use a nitrogen gun or spin dryer.

F. Storage: 1. Avoid storage of cleaned wafers, preferably by immediate continuation of processing. If storage is unavoidable store wafers in closed glass containers cleaned with ho

t SC - l solution, followed by water rinsing and drying. 2. Note concerning processing water and reagents: 3. All water used for preparing reagent mixtures or for rinsing should be thoroughly deionized and ultra filtered with resistivity in 10 to 20 Mohm range. All reagents sh

ould be electronic grade, preferably ultra filtered for freedom from particulate impurities.



Optical lithography: Types



Photolithography: Mask aligner



Mercury bulbs (Hg Arc Lamp) High pressure Hg Arc lamp spectrum



Photolithography Positive: gets more soluble after exposure

Negative: gets less soluble after exposure.



Photoresist

- Photoresist is an organic polymer which becomes soluble when exposed or non-exposed to ultraviolet light (UV)



Photoresist: Positive & Negative



Positive PR

DQ: PAC는 developer에서 용해 비율을 10배 혹은 그 이상의 차이를 만듦. N2의 약 결합이 원인 (UV light를 가지고 exposure Energy를 받아 N2의 연결 고리를 끊음)

N: 방향족 고리의 단위체로 된 polymer (2개의 메틸기 + 1개의 OH기)

cf. Novolak: 페놀을 산성 촉매 하에서 포름알데히드와 반응시킬 때 생성되는 열가소성이 있고 용제에 녹는 황색의 투명한 수지



Phenolic resins which contain ICA instead of DQ are readily dissolved by aqueous alkaline developers.

Photonic Active Compound (PAC)

Wolff arrangement

탄소고리로부터 질소는 자유로워지고 이 반응이 안정화 되기 위해 고리 바깥쪽으로 하나의 탄소원자가 이동

Positive PR



Negative PR

N3의 활성화 N2 gas 배출

다른 고분자 연결체와 결합으로 분자량 증가 녹지 않게 됨

현상 도중에 현상액을 흡수하여 패턴의 팽창이 발생: swelling effect Resolution을 제한



Comparison of PRs (Important)



Several PRs



SU-8 photoresist



General PR과의 차이점

SU-8 photoresist



Spin coating process

- Thickness of the photoresist depends on Concentration, Viscosity, Spin speed, Spin time

Spin speed

PR

thic

knes

s

Spin time P

R th

ickn

ess

- Photolithography steps Photoresist spinning, 1 to 50 mm spin coat Optical exposure through a photomask Developing to dissolve exposed or unexposed resist Bake to drive off solvents



Spin coating process



Photolithography 1: make a check list

Piranha, RCA 1 and RCA 2 cleaning

Ex. AZ 1512 1.2 µm at 4000 rpm



Check run-out

8.5s at 12mW

Photolithography 2



Soft bake 목적: 용제(solvent)를 증발시켜 감광막을 건조시키고, 웨이퍼와의 접착력을 향상시키며, 열에 의한 annealing effect로 응력을 완화 장비 Convection oven: 10 ~ 30분, 모든 웨이퍼에 동일 온도 유지 가능 Infra-red oven: 3 ~ 4분, 웨이퍼에 종류에 따른 반사 및 흡수의 차이로 동일 온도 유지가 어려움 Hot-plate: 0.5 ~ 1분, 가장 단시간에 가능, 진공흡착 등의 장비가 필요 적정온도 유지 필요: 과소 Orange peel (Nega), mask 접착 (Posi, Nega) 과대 열 다중화에 의한 Scum 현상

Pattern size가 줄어들수록 soft bake의 온도와 시간은 매우 중요한 변수가 됨

Photolithography 3



AZ 400K:DI(1:4) or AZ 300 MIF Inspection

AZ remover or Piranha cleaning

Inspection

Photolithography 4



Hard bake 목적: 잔여용제(solvent)를 제거하여 감광막을 건조시키며 용액에서의 공정에서 기판에 대한 감광막의 접착도 증가 장비 Convection oven: 30분, 모든 웨이퍼에 동일 온도 유지 가능 Infra-red oven: 3 ~ 4분, 웨이퍼에 종류에 따른 반사 및 흡수의 차이로 동일 온도 유지가 어려움 Hot-plate: 1 ~ 3분, 가장 단시간에 가능, 진공흡착 등의 장비가 필요 적정온도 유지 필요: 과대 Puddling: 감광막이 오므라드는 현상(Nega) 다음 공정 후 감광막의 제거가 힘이 듬 (Posi)

Photolithography 5



Importance of a bake process



How to remove PRs

Photoresist Removal (Stripping) • Want to remove the photoresist and any of its residues. • Simple solvents are generally sufficient for non-postbaked photoresists: – Positive photoresists: • acetone • trichloroethylene (TCE) • phenol-based strippers (Indus-Ri-Chem J-100) – Negative photoresists: • methyl ethyl ketone (MEK), CH3COC2H5 • methyl isobutyl ketone (MIBK), CH3COC4H9 • Plasma etching with O2 (ashing) is also effective for removing organic polymer debris. – Also: Shipley 1165 stripper (contains n-methyl-2-pyrrolidone), which is effective on hard, postbaked resist.


Documents

[email protected] memscontents.kocw.or.kr/document/wcu/2012/JunNam/LeeDongWeon... · 2013-03-15 · • Don’t: – touch your face or skin with gloves – touch building hardware,