Investigation of lateral straggling of Hg ions in Si3N4 by normal and glancingangle Rutherford backscatteringKeMing Wang, QingTai Zao, BoRong Shi, ZhongLie Wang, XiangDong Liu, and JiTian Liu Citation: Applied Physics Letters 58, 1401 (1991); doi: 10.1063/1.105205 View online: http://dx.doi.org/10.1063/1.105205 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/58/13?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Oxidation of SiC investigated by ellipsometry and Rutherford backscattering spectrometry J. Appl. Phys. 104, 014903 (2008); 10.1063/1.2949268 Determination of the lateral spread of Xe ions in silicon nitride and hydrated silicon nitride films by obliqueincidence Rutherford backscattering J. Vac. Sci. Technol. A 14, 240 (1996); 10.1116/1.579933 Investigation of lateral straggling of Xe ions in potassium titanyl phosphate J. Appl. Phys. 73, 7222 (1993); 10.1063/1.352396 Lateral straggle of Si and Be focusedion beam implanted in GaAs J. Vac. Sci. Technol. B 11, 581 (1993); 10.1116/1.586804 Lateral straggling of B and P ions implanted in channeling and random directions of Si single crystals Appl. Phys. Lett. 61, 1190 (1992); 10.1063/1.107643

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Investigation of lateral straggling of Hg ions in Si3N4 by normal and glancing angle Rutherford backscattering

Ke-Ming Wang, Qing-Tai Zao, Bo-Rong Shi, Zhong-Lie Wang, Xiang-Dong Liu, and Ji-Tian Liu Department of Physics, Shandong University, Jinan 250 100, Shandong, China

(Received 3 August 1990; accepted for publication 2 January 1991)

200 keV Hg ions were implanted in Si,N, at different angles of 0”, 45”, and 75”. The lateral straggling of Hg ions in Si,N4 was studied by glancing angle and normal Rutherford backscattering of 2.1 MeV He ions. The obtained result is compared with the Monte Carlo code TRIM ‘8% The lateral straggling is found to be in good agreement with the prediction.

With the development of ion-implanted devices to- wards smaller dimensions, the information concerning the lateral straggling of implanted ions is important in semi- conductor device technologies, especially in high- frequency devices.

It is well known that many papers, both theoretically and experimentally, have been published since the 1960’s to predict depth profiles (i.e., profiles along the surface normal) of implanted ions in solid.lA However, the situa- tion of study on “horizontal” ion distribution (i.e., distri- butions parallel to the samples surface) is quite different from the depth profiles along the surface normal.5 Very few experimental studies are reported which essentially cover the order of magnitude of the lateral straggling of the im- planted ions in the solids. In order to get the information of lateral straggling of implanted ions in solids, methods such as normal Rutherford backscattering, junction-stain method, or scanning electron microscope (SEM) in- duced current collection have been used.6 Some theories, for example TRIM '89, are capable of yielding predictions for this case, but have never been tested extensively.’

In the light of this situation, it seems worthwhile to perform some new measurements with improved experi- mental techniques. To our knowledge, there is no report on lateral straggling of Hg ions in solids. In order to improve measurement precision, we have presented a new method (glancing angle Rutherford backscattering) to study lat- eral straggling of implanted ions in solids. In this letter, the lateral straggling of Hg ions at an energy of 200 keV im- planted in Si,N4 was investigated by means of ion implan- tation into a tilted target and glancing angle Rutherford backscattering. The obtained result was compared with TRIM '89 simulation.

The Si3N4 target used in this work was provided by the Shanghai Institute of Metallurgy, Academy of Sciences of China. The Si3N4 film was deposited on a Si substrate. The thickness was about 2000 A. This layer was thick enough to stop 200 keV Hg ions implanted at different angles into Si,N.,. The following angles were used: O”, 45”, and 75”. The implantation was performed at room temperature. The current density was less than 0.2 PA/cm2 in order to de- crease excessive heating of the sample. To minimize the sputtering effect on the implanted ion distribution and to have sufficient sensitivity of the backscattering in determin-

ing impurities, the implantation dose of 1 x 1015 ions/cm2 was chosen. Accumulation of electric charge on Si,N, was prevented by placing a metal mask in direct contact in front of the sample. To ensure uniformity over the im- planted area, a two-directional electrostatic scanning sys- tem was used. The system for parallel scanning of the beam consisted of four sets of deflection plates. A neutral trap was also employed. The depth distribution of ions im- planted at a large tilted angle was measured by Rutherford backscattering (RBS) of 2.1 MeV He ions at normal inci- dence and with a scattering angle of 165”. In order to en- hance the depth resolution, glancing angle measurement was performed at an angle of 50” between the direction of He ion beam and the surface normal. With this arrange- ment the depth resolution was markedly improved.* For determining the Hg surface position, we have used Au film for calibration in RBS measurements. The ion implanta- tion was performed at a 400 keV ion implanter designed by Shandong University. The RBS measurement was carried out at 2 X 1.7 MV tandem accelerator of the Shandong University. The accuracy of the mean projected range was primarily determined by uncertainties in the assignment of the peak position with f two channels. Each channel cor-

0

Channel

FIG. 1. Glancing angle and normal Rutherford backscattering spectra of 2.1 MeV He ions for 200 keV Hg ions implanted in Si,N, at 0”. The signal for Si,N, substrate was obtained by glancing angle Rutherford back- scattering. (a) normal Rutherford backscattering, (b) glancing angle Ru- therford backscattering.

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TABLE I. Comparison of calculated values with extracted experimental data on mean projected range R, and range straggling AR, at different tilted angle implantation. The experimental data for 0” implantation are average values. The calculated values are obtained by TRIM '89. The ion numbers are more than 1000 for all TRIM '89 simulation.

Measurement R, (A) angle (Exp) (Calc)

0” 619 522 45 510 369 75” 161 143

AR, CA) (Expf (Calc)

146 105 126 96 64 72

responds to 27 A for normal Rutherford backscattering. In the case of ion implantation into a tilted target, the

depth distribution of the ions contains the information on the lateral straggling of the implanted ions. Let us assume that the spatial probability distribution of the deposited ions is a three-dimensional Gaussian, the standard devia- tions of lateral and longitudinal straggling being denoted by AXI and AR,, respectively. Then the depth distribution in a target tilted at an angle 8 to the incident ion beam also becomes Gaussian, the standard deviation AD being given by Ref. 9.

(AD)*= (AR,)*cos28+ (AXL)‘sin20.

The lateral straggling AX, can be estimated from two mea- surements of AD for two different implantation angles 13.

Figure 1 depicts normal and glancing angle Rutherford backscattering spectra for 200 keV Hg implanted in Si,N, at 0” implantation. Signal for Si,N4 substrate was obtained by glancing angle Rutherford backscattering. Figure 2 shows glancing angle Rutherford backscattering spectra of 2.1 MeV He ions for 200 keV Hg ions implanted in Si,N4 at 0” and 45”, respectively. It is found that the depth dis- tribution is well described by Gaussian distribution, as it is expected for heavy ions implanted into light matrix. The

200

d !z

s

0

3.O . %Oo

. ..$ 0

l * a .* 0

. 00 0

. B 00

. . 2

.O .*

. 00 0

l 0 . .O 0 E0

l *cP” 0

.*e to

.O 90

I ‘.“reo ,

850 Channel

950

FIG. 2. Glancing angle Rutherford backscattering spectra of 2.1 MeV He ions for 200 keV Hg ions implanted at 0” and 45” in Si3N,. Full and open circles represent the data of 0” and 45” implantation, respectively. Each channel equals to about 14 A in this case.

TABLE II, Comparisor of extracted experimental values with TRIM'89 prediction on mean projected range R,, range straggling ARp, and lateral straggling AX1 for 200 keV Hg ions implanted in Si;N,. (A) extracted by glancing an& Rutherford backscattering for the case of 0” and 45” implantation, (B) extracted by normal Rutherford backscattering for the case of 0’ and 75” implantation, (C) calculated by TRIM '8'1. Ion number is 3533.

Rp (A, AR, (A) AX, (A,

A 620 1.57 84 I3 618 134 56 c 522 105 77

true value of AD can be derived from the measured range straggling, after taking into account the energy resolution of the measuring sysr:em and the energy stragghng of He ions in the target, It is seen that the peak position of dis- tribution of implanted ions shifts towards the surface with increasing angle 0. The main step in data analysis is the conversion of the Rut herford backscattering energy spectra to depth profiles, This is done using the data of Chu et al.” The purpose of this letter is to compare the experimental lateral straggling with theoretical values. In this work, we have used a Monte C’arlo simulation (TRIM ‘89) to calcu- late the mean project :d range R,, range straggling (longi- tudinal spread) AR,, and lateral straggling AX,. To have sufficient statistical accuracy, we stimulated more than 1000 ions. Table I gives the comparison of experimental values with the TRIM ‘89 prediction on the mean projected range and range straggling at different tilted angle implan- tation. From our experiment, it is observed that the mean projected range shifts towards the surface with increasing implantation angle. The profile shapes closely resemble each other except for different full width at half maximum (FWHM). The FWH:M becomes narrower with increasing angle. Table II lists the comparison of experimental value with the TRIM’89 prediction on the mean projected range, range straggling, and lateral straggling for 200 keV Hg ions implanted in Si3N4. The experimental data were extracted by glancing angle and normal Rutherford backscattering for different tilted angle implantation.

In summary, 200 keV Hg ions were implanted into Si,N, at o”, 45”, and ‘75”. We have used the glancing angle and normal Rutherford backscattering to measure the lat- eral straggling of Hg ions implanted in Si3N,. The obtained lateral straggling is not negligible. The average values on mean projected range, range straggling, and lateral strag- gling for;00 keV Hg ions implanted in Si3N, are 619, 146, and 70 A, respectively. The ratio of lateral straggling to longitudinal straggling is 0.48. For comparison with theo- reticaI prediction, we have used the TRLM ‘89 simulation. The result shows that the experimental lateral straggling and mean projected range are in good agreement with the TRIM ‘89 prediction within experimental error, but the range straggling as measured by glancing angle Rutherford backscattering is higher than the value calculated by TRIM ‘89.

‘J. Lindhard, M. Scharff and H. E. &hi&t. K. Dan. Vidensk. Selsk. Mat. Medd. 33, 1 (1963).

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‘J. P. Biersack. Nucl. Instrum. Methods 182/183, 199 (1981). ‘Wang Ke-Ming, Liu Xi-Ju, Wang Yi-Hua, Shi Bo-Rong, and Liu Ji- Tian, J. Appl. Phys. 64, 3341 (1988).

‘H. H. Andersen and J. F. Ziegler, The Stopping Powers and Ranges of Ions in Matter (Pergamon, New York, 1977), Vols. 3 and 4.

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*J. S. Williams, Nucl. Instrum Methods 126, 205 ( 1975). 9S. Furukawa and H. Matsumura, Appl. Phys. Lett. 22, 97 (1973).

“W. K. Chu, J. W. Mayer, and M. A. Nicolet, Backscattering Spectrom- eter (Academic, New York, 1978).

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