Investigation on Characteristics of W-B-C-N Diffusion Barrier according to Nitrogen Concentration through Applications of Various Thickness Measurement Techniques

Researchers : Hyoun Ju Sohna (skooblechemist@hanmail.net), Won Jun Choia (wonjun415@hanmail.net),Dajin Kima (dajin1202@hanmail.net), Minsuk Parka (school-pms@hanmail.net)

Guidance Professor : Chang Woo Leeb (cwlee@kookmin.ac.kr) Assistant Supervisor: Soo In Kimb (kksooin@kookmin.ac.kr)aNano Electro-Physics, KSA(Korea Science Academy), 614-100 Busan, South Korea

bNano Electro-Physics, Kookmin University, 136-702 Seoul, South Korea

1. IntroductionAs devices become more integrated, the width of the metal wires is reduced and the length is elongated and therefore, exhibits an increase in RC time. This causes the device to experience fallacy

due to the deceleration of device operation. Therefore the employment of low resistive materials is crucial. Also due to the diffusion between the wires and the silicon wafer, the search for an effective diffusion barrierplaced between the Si and the SiO2 layer is brisk. The main inquiry and research in the present day is the search for the appropriate diffusion barrier that are less resistive, less slackening and reliable. The W and Ta diffusionbarriers that are recently achieving attention are still defective in temperatures of 600°C to 700°C where these metals interact with Si and produce silicide causing variation in electronic characteristics. An idealistic diffusionbarrier should have low resistivity, be non-reactant with Si in high temperatures (over 800°C) and able to prevent the diffusion of Cu. In our studies and experimentations, we have proposed a relatively proficient diffusionbarrier that is composed of W-B-C-N.

This paper includes analysis of experimentation on finding the relationship between the Nitrogen concentration and the newly proposed proficient W-B-C-N diffusion barrier characteristicsaccompanied by preparatory experiments of various thickness measuring techniques. The first part shows preparatory experiments of using different thickness measuring techniques in order to be acquainted with thethickness measurement equipment and its errors. The thicknesses were measured by using four different types of equipments; α-step(Tencor), β-ray Backscattering Spectroscopy(Veeco), SpectraThick(KMAC ST-2000 DLX)and the SEM(FEI Nova 200) and also the information achieved here was applied to the actual experiment.

On the basis on the familiarity of various thickness measuring techniques, we have carried out the main purpose of this experiment of finding the optimized diffusion barrier. This paper proposesW-B-C-N diffusion barriers for a proficient diffusion barrier and includes experimentation on the relationship between the Nitrogen concentration and the diffusion barrier characteristics. The diffusion barriers were annexedwith B, C, N via RF Magnetron Sputtering with variation in sputter time, annealing rate, Nitrogen proportion inside of the sputtering equipment. The resistivity, deposition rate, heat stabilizations were measured andobserved and finally the XRD diffraction equipment was used to analyze the composition of the diffusion barriers.

3. Results

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W thin layer thicknesses according to sputter time (a) α-step average

value of center and side (b) SpectraThick

Thickness according to spinning rpm of PR on wafer (a) SpectraThick (b) α-step (c) β-ray

Thickness according to spinning rpm of PR on glass (a)

SpectraThick (b) α-step (c) β-ray

The center and side thickness measurement values of the α-step

according to sputter time (a) center (b) side

alpha step : Tencor, alpha step-500

SEM : FEI company, Nova 200

beta-ray : Veeco, MP-900

2. Experimental TechniquesA. Thickness Measurement

For thickness measurements, sputtered tungsten on silicon wafer, PR(photo resist) on siliconwafer and PF on glass was used as the samples. Sputter equipments were used to coat with tungsten.Variation for thickness was done by varying the sputter time with 96, 193, 289 seconds. For variationin thickness for the PR, the spinner rpm was varied as 2500, 3000, 3800 rpm. When making the PR,soft and hard baking was done 2 minutes and one minute respectively in 95℃. The spinner wasoperated so that the first 5 seconds was rotated in 500 rpm and afterwards at the varied rpm.Thickness measurements were done by α-step(Tencor), β-ray backscattering(Veeco), spectraThick(KMAC ST-2000 DLX), SEM(FEI Nova 200). Coating necessary for the SEM was done by theMOCVD process with Os.

B. Diffusion barrier productionFor W-B-C-N diffusion barrier sample preparation, 10:1 concentrated hydrofluoric acid was used

for a 30 second cleaning accompanied by DI water cleansing and Nitrogen gas-gun drying. The airpressure inside the sputter chamber was maintained to near vacuum (1ⅹ10-6 torr). The amount of Arand N2 was controlled accurately by the mass flow controller. The (N2+Ar) pressure was maintained to5 torrs and the N2/(N2+Ar) ratio was varied from 0% to 5%. For the W-B-C-N sputtering procedure, theco-sputtering conditions were W(100W), W2B(40W), WC(4W) and Si p-type(100) wafer was used for adiffusion barrier of 1000 Å. The 4-point probe was used for the area resistance and afterwards theresistivity was calculated using the β-ray. The annealing temperature was also varied with 700°C,800°C, 900°C and the electrical properties and stabilities were investigated.

Spectra Thick: K-MAC, ST- 2000LXn

A. Thickness Data

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The center and side thickness measurement values of the α-step according to spinning rpm (a) PR on Wafer, center (b) PR on Wafer, side (c) PR on Glass, center (d) PR on Glass, side

Thickness measurements of the PR on wafer according to equipment (spinning

rpm :2500 rpm) (a) Glass (b) Wafer

Sputter Equipment (left : exterior, right : interior

mailto:skooblechemist@hanmail.netmailto:wonjun415@hanmail.netmailto:dajin1202@hanmail.netmailto:school-pms@hanmail.netmailto:school-pms@hanmail.netmailto:school-pms@hanmail.netmailto:cwlee@kookmin.ac.krmailto:kksooin@naver.com

4. ConclusionA. Thickness measurements

1. When using the Alpha-Step , the sample needed a height difference.2. When using the Spectra Thick, the samples needed to be transparent3. When using the SEM, because the thickness needed to be over 500Å, thin membranes that were in our experiments could not be measured.4. The SEM was inconvenient in financial, periodic matters and procedures such as coating, cutting .5. Measuring the thickness was considered to be difficult due to the various requirements that was needed for each measurement method.6. Understanding the characteristics of the samples and the selection of the appropriate equipment was important for the thickness measurements.

B. Characteristics of the diffusion barriers according to the Nitrogen concentration1. The W-B-C diffusion barrier that was fabricated when the N2 partial pressure ratio was 0%, the barrier was not formed in temperatures over 850℃. However, in temperatures under 800℃, a electrically proficient di

ffusion barrier was formed with a resistivity of under 200. 2. The W-B-C-N diffusion barrier that was fabricated when the N2 partial pressure ratio was over 2.5%, the resistivity was lowered in temperatures over 1000℃ while when the N2 partial pressure ratio was 0%, the res

istivity increased rapidly in temperatures over 900℃ and showed an interaction between the silicon wafer and the diffusion barrier. Therefore, by annexing N, the C, B, N compete against the W bonding and eventually prevents reaction in the interface. In other words the for the diffusion barrier made in N2 partial pressure ratio of over 2.5% to have an electrical transition, a heat treatment of over 900℃ is necessary. The increase in resistivity due to the interaction between the diffusion barrier and the silicon wafer was not observed regardless of the N2 partial pressure ratio.

3. For N2 partial pressure ratios of over 2.5% and under 5%, due to the bonding competition between B,C,N and W, the B,C,N takes their place in the grain boundary of W and prevents the diffusion through the Cu grain boundary and exhibited great heat-stabilization. (When the N2 partial pressure ratio exceeds a certain value, the N wins the competition with B, C of bonding with W. This situation is shown in Figure 4 when the N

2 partial pressure ratio is 5.0%).

5. Future Work

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C. Various Characteristics of the W-B-C-N Thin Film

Resistivity according to Nitrogen partial ratio of the W-B-C-N thin film

Deposition rate according to Nitrogen pressure ratio for W-B-C-N thin film

Resistivity according to various nitrogen pressure ratio and annealing temperature of the W-B-C-N thin film

(a) 0%, (b) 2% and (c) 5%

XRD graph of various annealing temperatures at nitrogen pressure 0% (a) as-depo.

(b) 700˚C and (c) 800˚C

> XRD graph of various annealing temperatures at nitrogen pressure 2% (a) as-depo.

(b) 700˚C and (c) 800˚C (d) 900˚C

XRD graph of various annealing temperatures at nitrogen pressure 5% (a) as-depo.

(b) 700˚C and (c) 800˚C (d) 900 ˚C

Section photograph of PR/glass 2500rpm(R5) taken by SEM

Section photograph of PR/glass 3000rpm(R6) taken by SEM

Section photograph of PR/glass 3800rpm (R7) taken by SEM

Korea Science AcademyKorea Science Academy http://www.ksa.hs.krhttp://www.ksa.hs.krKookmin University http://www.kmu.ac.kr Kookmin University http://www.kmu.ac.kr

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3. Results (Cont’d) B. SEM images

1. Further investigations are going to made in order to minimize the errors in the thickness measurement process.2. More investigations on the electrical characteristics of the W-B-C-N diffusion barrier are going to be made by the employment of different equipment such as the XPS, TEM.3. The efficiency and application of lithography towards our diffusion barriers are going to be investigated.

N2 partial pressure ratio (%)Diffraction Angle 2θ (deg.)

N2 partial pressure ratio (%)Diffraction Angle 2θ (deg.) Diffraction Angle 2θ (deg.)