Metallization of Polymers - ACS Publications - American Chemical

Chapter 6

Depth Profiles of Thin Films and Interfaces by the Elastic Recoil Detection Technique S. C. Gujrathi

Downloaded by UNIV LAVAL on July 11, 2014 | http://pubs.acs.org Publication Date: November 9, 1990 | doi: 10.1021/bk-1990-0440.ch006

Laboratoire de Physique Nucléaire and Groupe des Couches Minces, Université de Montréal, C.P. 6128, Succursale A, Montreal, Quebec H3C 3J7, Canada

An elastic recoil detection (ERD) technique, which also involves Rutherford forward scattering (RFS) and incorporates time-of-flight (TOF) principle for mass discrimination, is developed and successfully applied in the simultaneous "non-destructive" multielemental depth-profile studies of thin films and interfaces. In this technique, the light as well as medium mass elements are knocked out of the target by using energetic heavy ion beams obtained from the 6 MV Tandem accelerator. The mass separated energy spectra are deconvoluted into the depth profiles by using a newly developed computer analysis facility capable of yielding reliable atomic concentration ratios on routine basis without any a priori assumptions about the composition of an unknown target. The performance of the technique is illustrated through the results of some recent applications to a large number of targets such as Corning Glass 0211, silicon nitride and oxynitride films, borophosphoro silica glass, cobalt silicides and polyimide-metal interfaces. In several cases the quantitative results of ERD are compared with other material analysis methods, e.g. chemical analysis, energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), etc. and found to be in very good agreement. The effects of beam dose on radiation sensitive films of polymers and polyimides are briefly discussed and a few methods to minimize them are suggested. Typical performance characteristics of the system using 30 MeV Cl ions as beam probe are : 0.2 amu mass resolution in C region and ~ 0.7 amu in the Si-region, ~ 1 μm probing depth in Si, 80 - 100 Åsurface resolution and 0.01 at. % minimum detection limit. Rapidly growing applications of this technique makes it a valuable complementary tool to other conventional analysis methods such as A E S , E S C A and SIMS. 35

0097-6156/90/0440-0088$06.50/0 © 1990 American Chemical Society In Metallization of Polymers; Sacher, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


6. GUJRATHI

Depth Profiles of Thin Films and Interfaces

89

M o d e r n technological developments a n d m a n y fields of pure a n d applied research depend on the quantitative information about the spatial element distribution i n t h i n solid layers and thin-film systems. F o r example, without the use of thin films the experimental studies on the physics of semiconductor are very difficult. Similarly the diffusion processes i n solids, s a n d w i c h - l i k e t h i n f i l m s s t r u c t u r e s i n microelectronics, anti-reflecting or selectively t r a n s p a r e n t optical films, catalysts, coatings, composites - all rely on material properties on a n atomic scale. The development of these new materials as well as the understanding of the basic physical and chemical properties that determine t h e i r specific characters are not possible without the knowledge of t h e i r compositional structure, i n p a r t i c u l a r i n the interface regions. M o d e r n material technology could not have progressed without the simultaneous advent of analysis techniques which can examine the surface a n d interface regions of solids. Several such techniques have been developed, and some of the most commonly used are: secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS) which is also known as electron spectroscopy for chemical analysis ( E S C A ) , A u g e r electron spectroscopy ( A E S ) , particle induced X - r a y emission (PIXE), nuclear reaction analysis ( N R A ) , Rutherford backscattering spectrometry (RBS) and elastic recoil detection ( E R D ) . E a c h technique has its own sets of advantages and disadvantages, and none capable of providing itself complete information on structure as a function of depth. In practice it is essential to apply more than one technique to perform the desired analytical tasks. T h e energetic ion beam analysis techniques ( P I X E , N R A , R B S and E R D ) for accurate measurements of atomic composition and i m p u r i t y concentrations i n the near surface regions of solids have been now well established. T h e P I X E has an excellent sensitivity but has extremely poor depth resolution i n routine depth profile analysis of thin films. T h e most commonly used ion beam analysis techniques are R B S and N R A . T h e R B S , which has several merits, e.g. ability to give absolute results, profile several elements simultaneously without the use of any standards, moderately good depth resolution, non-destructive, etc., becomes difficult or i m p r a c t i c a l w h e n one want to profile light elements i n the present of medium to heavy elements i n the sample or substrate. One of the most difficult atomic species to profile but having enormous importance i n many technological fields and specifically the polymer science is the hydrogen, for example, A E S is insensitive to hydrogen while one can not use R B S because of its light mass. T h e commonly used technique is resonant nuclear reaction (15 N , ay) C at 6.4 M e V N energy or ( F , ay) 0 at either 6.4 M e V or 16.5 M e V 19F energy near the surface. However, this technique suffers from several disadvantages, e.g. long measuring times, large ion dose requirement to obtain detailed profile, etc. A very useful a n d powerful method to profile light elements including hydrogen i n presence of m e d i u m to heavy elements is the E R D technique originally developed at the U n i v e r s i t é de M o n t r é a l which has several advantages over R B S . T h e original E R D technique 1

2

1

5

1 9

1 6

In Metallization of Polymers; Sacher, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


90

METALLIZATION OF POLYMERS

(1) is based on the ejection of the recoiled particles out of the sample i n the forward direction by a n energetic heavy ion beam. T h e measured energy spectra of these recoiled atoms can be related to their concentration profiles. T h e use of range foil i n front of the energy detector to permit selective absorption of the various recoils introduces a few limitations i n the application of the technique, e.g. deterioration of the energy resolution and hence the depth resolution, the limitation on the accessible depth i n the depth profile information, etc. Indeed, the practical utility of the experimental set-up is enormously reduced i n the region where overlapping spectra of various atoms are difficult to separate. T h e drawbacks of the E R D u s i n g range foil for the mass discrimination have been removed by our group at the U n i v e r s i t é de M o n t r é a l i n a very efficient way by u s i n g a time-of-flight ( T O F ) detection system (2). Because R B S is now a relatively common and well established technique (3.), more emphasis is placed on the newly developed E R D - T O F facility. A brief description of our experimental facility as well as a newly developed versatile computer program (4) capable of converting mass separated energy spectra into the depth profiles are given i n the next section. Following that, some of the typical characteristics such as mass and depth resolution, sensitivity and quantitative reliability are illustrated through the applications of the technique to various thin films targets such as Corning Glass 0211, borophosphoro silica glass, silicon n i t r i d e a n d oxynitride, cobalt suicide and metal-polyimide interfaces. In the applications of E R D to the films of organic compounds one must be extra careful about the b e a m induced r a d i a t i o n effects. Some of these effects a n d a few possible solutions to minimize them have been pointed out. Experimental Procedures . Basic Principles i n N u c l e a r S c a t t e r i n g . T h e basic principles of R B S and E R D could be briefly described u s i n g the schematic shown i n Figure 1. T h e incident ion (Zi), of mass M l , and energy E penetrates 0

the target surface m a k i n g a n angle α and collides elastically with an atom (Z2) of M a s s M 2 situated at a depth X from the surface. After Coulomb scattering either the same mass M l , emerges with energy E l , or E ' i from the surface (RBS) or it recoils mass M 2 with energy E 2 i n the forward direction ( E R D ) m a k i n g a n angle β with the surface. B o t h the incident as well as outgoing ions suffer energy losses during their travel i n the film that are proportional to their stopping powers which are energy a n d target (the film) composition dependent. T h e detected energies E l or E ' i , and E 2 are related to the incident ion mass M i , a n d energy E t h r o u g h the k i n e m a t i c factors k i and k 2 , respectively a n d the above mentioned energy losses. T h e expressions for k i and k2 as well as Coulomb cross-sections σ ι and Ο2 for R B S and E R D , respectively are given below. 0


6. GUJRATIH

^ -sin e) 2

ki =

2

1/2

+ cos9

(1)

1+μ

4

k =

μ

2

0+μ)

„

COS3θ

(2)

2

(3)

σι = 4Ε


91


/

0

S

in4 0

(ΖιΖ θ2\ _^_ 2

σ

2

=

2

\ 4 Ε

0

/

2

μ(μ -5ίη2θ)

1 μ1

1 / 2

2

+

(4)

C0S4 θ

where μ = Μ 2 / Μ 1 , θ is the scattering angle i n the laboratory coordinate system a n d e is the electronic charge. Conventionally lighter ions such as protons and H e , and θ approaching 1 8 0 ° are used i n R B S i n routine applications. However, use of heavier ions such as l ^ C a n d l ^ O are also increasing i n selected applications because of their higher mass-resolution ability for heavier targets (5,6). F r o m the kinematics of Coulomb scattering it is evident that when M l > M 2 , there exists some critical angle 0 < π / 2 , where 0 = s i n " l ( M 2 / M i ) , above which there are no R B S events. In E R D the detector has to be in the forward direction while the incident b e a m choice depends on several other factors i n c l u d i n g the recoils under investigation. In general the use of heavier ion beam (30-40 M e V 3 5 c i r 40Ar) permits to study several light a n d m e d i u m mass recoils u s i n g conventional charge particle detectors. W h e n θ is less than 6 the scattering of the incident b e a m i n the direction of the detector is unavoidable, thus giving R B S (actually Rutherford forwarding scattering-RFS) events mixed with the recoils. T h e quantity of interest is the elemental concentration as a function of d e p t h . T h e detected n u m b e r of events are r e l a t e d to the concentration while their energies w i t h respect to the m a x i m u m energy (surface energy) gives the depth i n f o r m a t i o n . These are discussed further i n the depth profile analysis procedure described later. In E R D , from the consideration of various characteristics, e.g. m a x i m u m accessible depth, depth a n d mass resolution, detection sensitivity, etc, none of the experimental parameters, such as M i , E o , C

C

0

C

α , β , θ beam spot-size, and the detection solid angle Ω can be optimized without affecting the other. In our system, based on our needs as well as other anticipated applications, the overall choice of the E R D parameters are 30 M e V 3 5 c i as the probing beam with θ = 3 0 ° , α = β =


92

METALLIZATION OF POLYMERS 4


1 5 ° , a beam size of 0.25 m m (width) χ 2.0 m m (height), and Ω = 10" sr. We are also equipped with conventional R B S , heavy ion R B S , P I X E , N R A and R B S - c h a n n e l i n g facilities. E x p e r i m e n t a l A r r a n g e m e n t s i n E R D . T h e E R D technique and the extended E R D with the T O F method used at the U n i v e r s i t é de M o n t r é a l have already been described i n ref (1) and (2), respectively. Only a brief description is given below. The schematics of the system used are shown i n Figure 2. A well collimated incident ion beam strikes the target at glancing angle with the surface and the scattered incident ions as well as the recoils move i n the forward direction toward a silicon surface barrier detector ( S S B D ) . To profile hydrogen a range foil is used to stop all the ions except hydrogen as shown i n F i g u r e 2a. A n o t h e r S S B D without absorber serves the purpose of n o r m a l i z a t i o n . In the E R D - T O F experiments the particles first pass through a t h i n ( 5 - l ^ g . c m ~ ) carbon foil as shown i n Figure 2b. T h e secondary electrons emitted from the carbon foil are accelerated a n d t h e n collected by a microchannel ( M C P ) detector which generate the first signal for the time measurement. T h e second time signal a n d the energy are obtained from a low resistivity cooled S S B D situated ~ 70cm from the carbon foil. T h e mass M of the transiting ion is related to the particle energy Ε and the flight-time t through the relation 2

2

M = 2Et /L

(5)

2

where L is the flight-length. T h e accurate determination of the energy is a difficult problem because of the non-linearity of the detector to various ions, the pulse-height defect phenomenon and the relatively poor resolution. A s a first approximation the detector response is assumed to be linear and the mass is calculated event-by-event using the relation

(6)

2

M = 2 ( E + Ed) ( T - T d ) / L 2 a

a

where E is the apparent energy as given by the response curve for alpha particles; E d is the pulse-height defect; T is the apparent time as given by the time-to-amplitude converter (TAC); and T d represent various delays and walk corrections. T h e E d and T d parameters are k n o w n to be slowly v a r y i n g functions of energy a n d mass. Our knowledge of these parameters i n the regions encountered i n the present E R D technique is incomplete and therefore, with our software, we treat these parameters as constants and adjust them to maximize the mass resolution i n the chosen mass region. F r o m Equation 5 the mass resolution can be readily deduced as: a

a

2

2

2

ΔΜ/Μ = [(ΔΕ/Ε) + (2ΔΤ/Τ) + (2AL/L) ]

1 / 2


(7)


6.

GUJRATHI


93

F i g u r e 1 . Schematic diagram of E R D a n d R F S nuclear scattering processes.

35

C ^ ( 3 0 MeV)

(b)

mm

Absorber

Target

SSBD

Ε and T2 signols MCP detector T| signal Target F i g u r e 2. Schematics of the arrangements used i n (a) E R D with absorber and (b) E R D - T O F , experiments.


94



where Δ Ε , Δ Τ and AL are the variations i n energy, flight-time and flight-path, respectively. D e p t h Profile A n a l y s i s Procedure. B y gating the mass-spectra the i n d i v i d u a l energy spectra of each mass is generated from the stored information. T h e next step is the deconvolution of the energy spectra according to the k i n e m a t i c s , cross-section, stopping powers and experimental conditions to produce depth profile for each element without a n y a p r i o r i assumptions about the composition of an u n k n o w n target (4). T h e depth deconvolution procedure is briefly discussed i n the following. Assume a target of uniform composition of two elements A and Β as shown i n Figure 3. It can be considered as a series of layers of partial thickness Ax. T h e mass separated energy spectra of the recoils of the two compositional elements are also schematically sketched. The highest energy i n each spectrum corresponds to the scattering near the surface a n d the recoils from the i n n e r depth appear at lower energies. In nuclear scattering analysis the n a t u r a l and the most appropriate choice of the depth scale is i n units of mass per unit area (e.g. μ g c m • 2 ) because i n most practical applications the physical density of the target is unknown. It should also be remembered that even i n the layer structures or composites formed by the films of known densities, the interface region has unknown density which is changing as a function of depth. Consequently the stopping powers used i n the calculation must be i n density independent units (e.g. k e V c m ^ g " ) . 1

In depth profile the quantity of interest is the concentration η , expressed i n n a t u r a l units (e.g. atoms c m ^ g - l ) ;

it is related to the

number of counts Δ C i n a layer according to the relation

ΔΟ = σ(Ε) η Δ χ Ω Q where σ ( Ε ) is the Coulomb cross-section at energy Ε referred to the surface of the layer according to the Equations 3 and 4, Ω is the detector solid angle, and Q is the total number of incident probing ions. For very t h i n films w h e n the variations of the stopping powers are relatively very small, the total depth X can be calculated from the energy width ( E - E ) and the depth factor F using the equations s

E

s

(9)

-Ε = Fx

sina\dx/jn

d x

s

inB^ '

(10)

where k is the kinematic factor (see Equations 1 and 2) and ( d E / d x ) i and ( d E / d x ) u t are the stopping powers for the incident and outgoing ions, respectively. In general i n m a n y practical applications the n

0



6. GUJRATHI


DEPTH

0

DEPTH

95

0

Figure 3. Schematics of the depth profiling approach for a sample of a homogeneous mixture of two monoisotopic elements A and B .



96


variations i n the stopping powers are not negligible a n d therefore a complex computer program is required to evaluate the depth factors and the energies step by step at each layer. We have developed the required sophisticated computer software i n our laboratory. It is not a simulation program where some i n i t i a l i n f o r m a t i o n r e g a r d i n g the sample is needed for the successful analysis. T h e basic approach involves the deduction of the depth represented by the counts at a certain energy by tracking back the recoil a n d tracing forward the projectile, from the surface i n small fixed step sizes, a p p l y i n g stopping power formulas to change the energies until their ratio is the kinematic factor of the interaction: that the n u m b e r of steps determines the depth. T h e required stopping power for each ion/target element combination is taken from the recent p a r a m e t r i z a t i o n compilation given by Ziegler (7). In general these extrapolated values agree well with the available experimental energy loss measurements, the m a x i m u m deviation being less t h a n 10%. E a c h element is profiled relative to a normalization window i n the spectrum of a monitor element, which is usually the most abundant. T h u s , for a specific layer i n the target, the concentration of element A with respect to the concentration of element Β near the surface can be readily obtained by using the Equation 8, e.g.

ACA ACB(S)

=

σΑ Σ

Β

W)

Δ Ε Α FB

Ω

Α

Δ Ε

Ω

Β

Β

F

A

For an uniform composition of A and Β one expects T I B ^ B ^ ) l l to one as shown i n F i g u r e 3. T h e r e are several advantages of expressing the concentrations i n the ratio form. F i r s t l y , the need to know the incident ion dose Q is completely eliminated. In addition, i f the elements A and Β are detected i n the same measurement, the Ω factors are also removed. Another practical advantage of the ratio method is the fact that the depth factor ratio F ^ / F B is relatively less sensitive to the gradual changes i n the composition and the systematic errors i n the energy loss parameters used i n the calculation when a ratio is taken, the systematic changes i n the n u m e r a t o r a n d the denominator tend to cancel each other. e c

u a

The target material is generally of a more complex composition and i n a definite layer structure (hence the interest); therefore, an iteration procedure is executed using Bragg's L a w (&) which yields the stopping power of a complex target. T h e concentration of each element (from the i n i t i a l calculations), at each step i n depth, is used as weighting factor i n the Bragg's L a w calculation. T h e procedure is repeated with new profiles as weighting factors and generally converges after three iterations. Also since the calculation of the stopping power is done step by step, the iteration procedure automatically accounts for layer of different composition (such as t h i n layer of a l u m i n i u m on top of polyimide). T h e program, to our knowledge first of its kind, is capable of h a n d l i n g a large number of multielement layers and is equipped


6. GUJRATHI


w i t h a m e n u - d r i v e n database manipulation a n d storage of data.

package

which

facilitates

97 the

Applications of the E R D - T O F Technique C o r n i n g Glass 0211. T h e performance of the E R D - T O F system to simultaneously depth-profile several light a n d m e d i u m mass elements can be illustrated by using a Corning Glass 0211 (used as glass-slide cover i n optical microscopy) target. T h e chemical composition of this glass as specified by the manufacturer is given i n Table I.


Table I. Composition of the Corning Glass 0211 as given by the Manufacturer Component SiC-2 AI2O3 B2O3 Na20 K 0 ZnO T1O2 2

Wei£rht% 65 2 9 7 7 7 3

B y optimizing the E d and T d parameters i n E q u a t i o n 6 as well as neglecting the energy events below ~2.5 M e V a mass spectrum as shown i n Figure 4a is obtained. The mass identifications are based on the mass calibrations obtained by using known single element targets and also the glass composition given i n Table I. A n excellent mass resolution for the observed elements up to 2 3 N a is clearly evident. F o r heavier masses the resolution deteriorates m a i n l y because of the degradation of the S S B D energy resolution (see Equation 7). The weak 2 7 A l a n d 2 9 g i mass peaks are not resolved from the intense 2 8 s i . However, the strong 3 5 ç j l peak is completely separated from the adjacent 3 0 g i n d 3 9 χ peaks. T h e T i a n d Z n mass peaks have additional broadening of overlap effects because each of these elements has five stable isotopes with varying abundances. B y setting gates on v a r i o u s mass peaks the corresponding energy spectra could be deconvoluted from the total recoil energy spectrum as shown i n Figure 4b. T h e 3 5 Q energy spectrum results from the Rutherford forward scattering of the incident b e a m from the various target elements h a v i n g masses greater t h a n 18 mass units and has been subtracted from the total energy spectrum to get the total recoil spectrum. U s i n g the depth-profile p r o g r a m mentioned i n the previous section, the individual recoil spectra were converted into the depth profiles. Figure 4c shows a composite depth profile plot i n which the ordinate scale is expressed as weight percent for a n ease i n comparison. E a c h profile has been smoothed out using a special computer software routine i n a piece-wise fashion based on the user defined layer structure to retain the evident structure i n the transition regions. N e a r l y uniform depth a



98


CHANNEL

300

400

500 CHANNEL

NUMBER

600

700

NUMBER

F i g u r e 4. E R D - T O F results from a C o r n i n g Glass 0211 target: (a) mass spectrum, (b) mass separated energy spectra superimposed by total energy spectrum, and (c) composite depth profile of the observed elements.


6. GUJRATHI


99

distribution for nearly all the elements is consistent with the expected homogeneity of the material. In order to check the consistency of the results, the experiments were repeated after a period of two months u s i n g different targets of the same batch. A s can be seen from the T a b l e II, the reproducibility of the E R D results i n two separate experiments is excellent. In addition, the measured concentrations of elements of the target are i n very good agreement with the expected numbers deduced from the specified glass composition (see Table I). T h e e x p e r i m e n t a l n u m b e r s given i n S i c o l u m n includes the A l contribution.


Table II. E R D Results Compared with the Manufacturer's Specifications

Elements Β 0 Na Al Si Κ

Ti Zn

#1 2.67 47.20 4.39 31.27 5.90 2.04 6.05

Weight% ERD #2 Manuf. 2.74 2.83 47.37 47.33 4.72 5.19 1.06 31.22 30.33 5.82 5.40 2.09 1.80 6.44 5.62

#1 5.16 61.56 3.98 23.30 3.16 0.88 1.94

Atomic% ERD #2 Manuf. 5.22 61.02 4.25

5.21 61.94 4.60 0.79 23.05 21.95 3.02 2.86 0.76 0.90 2.21 1.73

It seems that i n E R D - T O F technique, the corning Glass 0211 can act as a suitable standard for not only the mass and energy calibrations but also for the relative concentrations of several elements. F u r t h e r work on different C o r n i n g Glass samples to explore the feasibility of establishing their use as calibration standards i n surface analysis techniques, such as E R D , S I M S , E S C A and A E S , are i n progress. Borophosphoro-silica G l a s s . T h i n films of borophosphoro silica glass films are extensively used i n integrated circuits i n silicon-based technology. O n e of the widely used methods to dope boron a n d phosphorous is achieved by adding their hydrides, phosphine (PH3) or diborane (B2H6), to the silane (S1H4) hydrogen gas mixture used i n various vapour deposition techniques. T h e knowledge of the film composition including other impurities is very important i n optimizing the fabrication conditions, such as gas flow rates, plasma frequency and power, a n d substrate temperature. T h e depth profiling by R B S technique has serious limitations as weak boron signal gets buried u n d e r the intense silicon b a c k g r o u n d while phosphorous is not resolved from silicon. O n the other h a n d the E R D - T O F technique not only readily and reliably gives depth profiles of boron and phosphorous


100


but can also quantify the presence of weak impurity elements such as hydrogen, carbon a n d nitrogen, i f present. Typical mass spectra i n the carbon a n d silicon region obtained from a 0.9 μτη thick borophosphoro silica glass are shown i n Figure 5a. A mass resolution (full width at half maximum-fwhm) of 0.2 a m u for B a n d -0.7 a m u (fwhm) for 8 S i is clearly evident. U s i n g the mass separated energy spectra and the deconvolution program the depth profiles of Β and Ρ can be deduced. In figure 5b the weight percent of Β and Ρ are plotted as a function of diborane flow rate keeping all other fabrication parameters constant. T h e concentrations of Β were also obtained by using chemical methods and by wave length dispersive X r a y analysis (WDX). S i m i l a r l y the Ρ concentrations were deduced from the chemical analysis as well as energy dispersive X-ray analysis ( E D X ) . These results are also shown i n Figure 5b for comparison. A close correlation of the E R D results with the other methods of analysis is clearly evident. However, it must be noted that the W D X and the E D X are incapable of providing the depth profile information. n


2

S i l i c o n N i t r i d e a n d O x v n i t r i d e F i l m s . A systematic study of the chemical composition and the associated physico-chemical properties of the films produced by plasma enhanced chemical vapour deposition ( P E C V D ) i n a large volume microwave plasma reactor ( L M P R ) has been a n ongoing activity of our group since the past three years (9, 10). T h i n dielectric layers of silicon compounds (P-SIN and S13N4: Η , PS1O2, P - S i O N , a-Si:H) are of great importance i n numerous S i and G a A s based microelectronics a n d macroelectronics applications. T h e r e are several critical fabrication parameters w h i c h affect the quality a n d the performance of the film. O f critical importance is the knowledge of correct chemical composition as a function of depth. T h e results to date have shown that the E R D method to be eminently applicable to study such films and the associated interfaces. Several of these films contain hydrogen as a n unavoidable intrinsic i m p u r i t y because of the basic conditions used i n film fabrication processes (11), l e a d i n g to the synthesis of new m a t e r i a l s such as amorphous polysilane polymers (12) a-(SiH2), or to the silane diimide (13) aSi(NH)2- Some times hydrogen is present due to deliberate preferential i n c o r p o r a t i o n e.g. i n P E C V D amorphous hydrogenated (or deteriorated) silicon nitrides (14) such induced hydrogen is known to play the specific roles i n film growth and structural properties. In m a n y applications hydrogen is also found to be responsible for the degradation of the chemical stability and thereby of dielectric and other physical properties (15). T h e application of E R D using range foil to profile hydrogen is now well established (16-18). A l t h o u g h modified E R D - T O F technique (2) has higher depth resolution and accessible depth, it has a lower detection efficiency for hydrogen due to the limitations on the response characteristics of the M C P detector to protons. A l l the hydrogen concentrations reported i n this article are based on the E R D technique using a range foil. Figure 6a displays a typical composite atomic percent depth profile plot of all the observed elements from a ~ 1 5 0 0 Â thick layer of nearly


6.

101


GUJRATIII

I6„

to

2430

-

1620

-

(a) FWHM«0.2amu io

810

—

R

E< 2.5 1_ 12

MeV

e


I ,

8

28, Si

1950

300

400

35

'ci

FWHM«0.7omu

1300 650

3L

0

600

700

800 NUMBER

CHANNEL

6

h

(b)

Metallization of Polymers - ACS Publications - American Chemical

Recommend Documents