Ion implantation in China

672

Nuclear

ION IMPLANTATION

IN CHINA

ZOU

Xianghuai

Shichang

and LIU

Instruments

and Methods

in Physics

Research B37/38 (1989) 672-675 North-Holland, Amsterdam

IORBeam Laboraiov, Shanghai Institute of Metallurgy, Academia Sinica, 865 Chang Ning Road, Shanghai 200050, China

Ion implantation in silicon has been widely used in the production of semiconductor devices and integrated circuits in China. Research of low energy ion implantation, high energy ion implantation and the SOI technology is in progress. Fully Si-implanted planar GaAs dual-gate MESFETs, high linear GaAs Hall effect sensors, light emitting diodes, laser devices, and infrared detectors made of HgCdTe have been fabricated by ion implantation and have been applied in telecommunication, transportation, medicine, and in a ground satellite station, The research of ion implantation in metals began in 1978 in China. Ion implantation for improving wear, corrosion, oxidation, fatigue-resistance and secondary electron emission characteristics has progressed. The artificial joints treated by ion implantation have been used in trial medical treatment. Thin films of high T, superconductors of Y,BazCu,O, with a zero resistance temperature of 86 K have been worked out with reactive ion beam coating. Recently, ion beam enhanced deposition has been used to synthesize Si,N, and other compound films. The process of ion beam enhanced deposition has been studied by a dynamic ion implantation model and Monte Carlocomputer simulation. It was at the end of the 1960s that China began to work on ion implantation. China now has more than 80 units involved in the field of research and application of ion implantation, including scientific research institutes, universities and factories.

1. Ion implantation in silicon Ion implantation in silicon has been widely used in the manufacturing of semiconductor devices and integrated circuits. In correspondence with the development of LSI, low energy ion implantation to produce shallow junctions, high energy ion implantation for the formation of buried insulating layers and n-p-n layered structures are being researched. The SO1 technology, which is based on the recrystallization of polycrystalline silicon by laser irradiation and high energy oxygen or nitrogen implantation in silicon, has been applied to the fabrication of high speed CMOS and radiation resistant devices. 1.1. Low energy ion implantation for formation junctions

Shallow junctions in silicon have also been formed by As: implantation at energies from 10 to 30 keV with doses from 1 X lOi to 5 X lOI /cm2 in combination with rapid thermal annealing. The results indicated that abrupt n+-p junctions as shallow as 700-1500 A with a sheet resistance of 60 Q/O can be obtained. Fig. 1 shows the depth profiles of the carrier concentration obtained by automatic spreading resistance measurements (ASR).

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*\

(a)

.

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of shallow

BF,f implanted Si wafers have been rapid thermally annealed by using a graphite heater at 1200 ’ C for 5-30 s to form p+-n shallow junctions. It is found that the electrical characteristics of p+-n junctions produced by BF; implantation is superior to that of B+ implantation after rapid thermal annealing. The double peak of the concentration profiles of fluorine is explained by the outdiffusion of F during recrystallization of the implanted layer. n+-p shallow junctions have been fabricated by As+-implantation (30 keV, lOi /cm2) and infrared transient annealing. The junction depth is 0.185 pm, the leakage current is less than lo-i5 A/pm2, and the breakdown voltage is above 25 V. 0168-583X/89/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

Depth

(2,

Fig. 1. Carrier concentration vs depth obtained by ASR for As; implanted Si after RTA and furnace annealing. (a) 20 keV, 1200°C, 30 s. (b) 20 keV, 900°C, 30 min. A: 1 X1014 /cm2; + : 5 X 1014/cm2; 0: 1 X 10’5/cm2; X : 5 X 10’5/cm2.

673

Zou Shichang, Liu Xianghuai / Ion implantation in China Hl ions have been implanted into a polysilicon solar cell at low energy to passivate intrinsic disorder and grain boundary defects. The improvement of photovoltaic properties of cells is stable. The spectral response of cells shows a significant improvement in the long wavelength region. 1.2. High energy ion implantation High energy (0.8-1.2 MeV) P2+ implantations were performed on a 600 keV ion implanter with doses of 5 X lo’*-75 X 10’4/cm2; the carrier concentration profiles and the damage annealing behavior were studied. Experiments were also conducted to obtain a more detailed knowledge of range, straggling and carrier concentration profiles of 0.5-6 MeV p+ implantation in silicon. An n-p-n layered structure was formed by boron ion implantation in n-type Si at energies of l-3 MeV with doses of 1 X 10i3-5 X lOI5 /cm2 followed by annealing at 900” C for 30 min (fig. 2). The double implantation of Bt and Sit is interesting for enhanced annealing, which is helpful in some cases for new applications of high energy ion implantation in IC processing. 1.3. SOI The cw Ar+ laser was used to recrystallize polysilicon films deposited on oxidized Si substrates. After recrystallization, a significant increase in grain size and improvement of electrical properties are obtained. Nchannel and P-channel MOSFETs, 6-stage CMOS in-

LOG N

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Fig. 2. ASR depth profiles for Si implanted with 3.0 MeV, 1 x lOI B+/cm* after 900 o C annealing.

a-Si 102 0

1 3000

SiOg I 6000

Metal I 9000

, 12000

Depth (2,

Fig. 3. ASR depth profile for SOM samples implanted As+ ions (180 keV, 5 ~10’~ /cm’) and after cw Arf recrystallization (5.0 W).

with laser

verters and 9-stage CMOS ring oscillators were successfully fabricated on the laser recrystallized polysilicon. The speed of CMOS/SO1 devices is higher than those fabricated on bulk silicon. A 9-stage three-dimensional CMOS ring oscillator was fabricated by cw Ar+ laser recrystallization and rapid thermal annealing. The propagation delay is 2.7 ns per stage at Vo, = 5 V. After zone melting recrystallization of MBE GaAs films deposited on oxidized Si by using a graphite strip heater, the grain size of GaAs SO1 films increases to 1 pm, the carrier concentration and electron mobility increase to 3 X 10” /cm3 and 1.1 x lo3 cm’/(V s), respectively. InP films deposited on oxidized Si substrates by sputtering were irradiated by Ar+ laser irradiation to obtain SO1 with mobility and carrier concentrations amounting to 1000 cm’/(V s) and 1 x 10” /cm3, respectively. The compositions of GaAs and InP SO1 are both stoichiometrical. A novel silicon on metal (SOM) material which has a large grain size (10 x 40 pm), uniform resistivity (60 Q/O) and good electrical insulation (fig. 3) has been used for the fabrication of a strain gauge with a pressure sensitivity of 6 mV/V for a pressure range up to 1 bar. The behavior of hydrogen during laser recrystallization, ion implantation and RTA of a-Si: H SO1 were investigated. The results show that about 96.4% of hydrogen was lost during the process of recrystallization. After RTA at 1150 o C, 35 s, there still remains about 1.1% of hydrogen in the a-Si : H films, which is favorable for passivation of defects at grain boundaries. The SO1 structure has been prepared by oxygen VI. APPLICATIONS

614

Zou Shichang,

Liu Xianghuai

implantation into silicon. After annealing, a high quality SO1 structure with a single crystalline silicon overlayer and an abrupt interface between silicon and buried SiO, has been formed. The SO1 material has been obtained also by high energy nitrogen ion implantation into silicon, and P-MOS transistors have been made on the SOI structure. In order to increase the thickness and to improve the quality of the top single crystalline silicon layer to meet the requirement of device fabrication, high temperature (1200 o C) vapor phase epitaxial growth was performed. The results show that the thickness of the top silicon layer can be increased to 0.8 ym, and the buried Si,N, is 2800 A.

2. Ion implantation in compound semiconductors Fully Si-implanted planar GaAs dual-gate MESFETs have been fabricated by using Si+ ion implantation at 110 keV with a dose of 3.5 x 10” /cm’. All the samples were capless annealed at 800 o C for 30 min. It is shown that the devices with Al gates of 1.5 X 300 pm and Au-Ge-Ni ohmic contact have an optimum NF,,

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Ion implantation

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(minimum noise factor) of 0.8 dB and an associated gain of 11.5 dB at a frequency of 1 GHz and bias of l& = 4 V, I’agls= - 2 V, Vazs = 0 V. These results were similar to those obtained with VPE materials. A highly linear GaAs Hall device fabricated with Si+-implantation and capless annealing has a linearity error of the Hall voltage better than 0.2% and 0.5% in the magnetic flux density range from 0 to 1 T and from 0 to 2.5 T, respectively, at room temperature. The sensitivity is 5-20 mV/(mA kg). A very thin n-type conducting layer has been fabricated by Si+ ion implantation into a semi-insulating InP substrate followed by capless annealing. The carrier concentration and the Hall mobility are 3 X 10” /cm3 and 2100 cm’/(V s), respectively. A higher activation efficiency has been achieved by ion implantation of p-type impurities into n-type InP substrate. After Mg+ ion implantation with doses from 1 x 10’2 to 5 X 1013 /cm2 and capless annealing, the activity is 60-70%, which is lo-20% higher than the published data, and the hole mobility is about 100 cm2/(V s). No apparent broadening of the carrier distribution was observed. Besides, GaAs and InP light emitting diodes, laser

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Fig. 4. Resistivity

138

transition

172.5

207

T (K) curve of YBaCuO

241.5

276

thin film.

310.5

345

Zou Shichang, Liu Xianghuai

devices and HgCdTe infrared detectors fabricated ion implantation have also been developed.

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3. Ion implantation in metals and other materials The research on ion implantation in metals and other materials began in 1978 in China. Investigations on ion implantation for improving wear, corrosion, fatigue-resistance and secondary electron oxidation, emission characteristics are in progress. Ion beam mixing and ion implantation were adopted to modify surface properties of aero-bearings which were made of GCrl5 or Cr4Mo4V. Artificial joints, such as titanium hip joints and femoral heads were implanted with N+ ions to improve the wear resistance and have been used in trial medical operation. Ion mixing of multiple metal layers has been employed to study alloy phases and pattern formation in binary metal systems. Ion beam mixing was used to increase the oxidation resistance of heat-resistant steel dies for forming glass covers of bus lamps. Oxidation resistance of steel was improved also by Al+ ion implantation. In order to obtain clear image pictures, a low secondary electron emission coefficient is required for the field grid located in front of the target of a TV camera. The secondary electron emission characteristics of copper grids were improved by Cr+ ion implantation. In comparison with copper grids coated with carbon, ion implantation is a more prospective method. Good quality thin films of high K superconductors of Y,Ba,Cu,O, with a zero resistance temperature of 86 K have been successfully prepared by the reactive ion beam coating technique. The interaction between YBaCuO thin films and YSZ and SrTiO, substrates has also been investigated. Reactive ion beam coating has

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Fig. 6. AES depth profiles of silicon nitride films obtained IBED. - - - Calculated Si; Calculated N.

by

proved to be an attractive technique for preparation of high c superconducting films because of its high purity, controllable composition and excellent reproducibility. Fig. 4 shows the temperature dependence of the electrical resistance for YBaCuO films prepared by reactive ion beam coating. Reactive ion beam etching has been applied successfully for microfabrication of acoustic surface wave devices on LiNbO,. Polymers have been doped by ion implantation for modification of electrical conductivity. The results show that two competing processes are involved in the implantation process: material degradation and chemical doping. From the point of view of electrical properties, the doping effect is dominating. It has been observed that the electrical conductivity of polymers could be increased by 20 orders of magnitude with ion implantation. 4. Ion beam enhanced deposition

I -.-

-0

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0.8

1.0

Atomic arrival ratio (N/Si)

Fig. 5. Composition ratio N/(N + Si) in the film as a function of N/Si

arrival

rate ratio. Monte AW Experimental.

Carlo

simulation;

Recently, ion beam enhanced deposition has been used to synthesize Si,N, and TiN films. The process of ion beam enhanced deposition has been studied by a dynamic ion implantation model and Monte Carlo computer simulation. The results show that the component ratio of nitrogen to silicon in silicon nitride films can be controlled by the arrival rate ratio of nitrogen to silicon (fig. 5). TEM analysis shows that the IBED film is composed of a silicon enriched layer on the surface, a silicon nitride layer with uniform composition and an intermixed layer at the interface between the silicon nitride layer and the substrate. Fig. 6 shows the composition depth profiles of the IBED silicon nitride film. The results of low cycle fatigue and corrosion testing indicated that the IBED Si,N, film can be used to suppress the initiation and propagation of cracks on the surface of stainless steel substrates. VI. APPLICATIONS