Thermal Stresses in Passivated AlSiCu-Lines From Wafer Curvature Measurement
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50 passivated SiO2 -lines
all
0
U7
Ti/TiN
Si0 2 :0.5Am
/0 /i'//>'
OAA
w /Mrn d=2psm-1
'
7
K
SiNx :0.4Am
A1Si(1%)Cu(0,5%): 0.8pm
t-
lb
.JSjQOSO
* 50 SN.,tSiN. + ySio02-I"etSO 2 -,...: -fine-.. . !S'N- ++ yS'i02 -fin.SiO2 e
a I SiNx
wu.
-
0-0"100 26600 360 400 5o0 Temperature
Figure 2:
Figure 1: The geometry of passivated Allines and the three stress directions.
Measured
[°C]
stress variation,
aU"'i- &siOjimo2 , of passivated SiO 2 - lines
versus temperature (full lines) in comparison to FEM calculation (broken lines). Measurement Technique And Data Evaluation To detect the change of the in-plane mechanical stresses, Aao (N-direction) and Aa± (_l -direction), in the film-system SiO 2/A1-lines/SiN. we used a bending beam technique, described in [4,5]. The change of the substrate curvature, Ap, was detected capacitively. It was necessary to prepare two beams from each sample, because the stresses and therefore the bendings in the two in-plane directions are generally different. Additionally the transverse contraction of the stress in one direction influences the stress in the other direction. With the curvature technique it is not possible to detect the stress in the direction of the film normal, o,, which is non-zero in passivated lines. The total stress contains, aside from the Al-stress, aO'A,also the unknown intrinsic stress in the SiN.-passivation. For the separation of the Al-stresses we assumed OAl1to be zero along all directions at T = 3000C, because at this temperature data from X-ray diffraction of the same samples give stress free Al-lines. If the effective film thickness, t = Vfi/A, which is defined as the quotient of the film volume, Vf•, and the substrate surface area, A, is much smaller than the substrate thickness, tsi, the volume integral of the stress in the film system in line direction or perpendicular to the lines divided by A is given by (1) Vf
it.n
where Esi = 1.31 • 10"Pa is the Young modulus and vsi = 0.2783 the Poisson number of the substrat and al-'- the mean film stress, &"'- = (1/V) • fv,, 7 ou"'dV. If the change in the substrate bending is equal in both directions, p11 = p', like in blanket films (equibiaxial stress state), Eq. 1 reduces to the well-known Stoney-equation [6, 7]. The measured value (1/A). fv,,., 'o&-dV of the multilayer-system SiO 2 /Al - line/SiN. can be separated into the 424
sum of the integrals from each layer [4]:
(
+ o"1±dV S~O
o-I''dV = -A
A1 V1,1,
Vso
J
2
IO
' SN dV±
VsiNý
,
)N2 )
2
VAI
or in expressions of the mean stresses times effective thickness: -
o-, iSiO, +
"S, • N +Oj • iA tl
ttsio + iSiN. + !At. 0
(3)
To calculate the stress in the lines, &A1 we need the mean stresses in the SiO 2 -underlayer and the SiN.-passivation. The stress in the thermal SiO 2 were taken from a separate measurement of an uncovered blanket Si0 2 -film for which: Usio 2 = &si02 = &sio2T situation in the passivation is more complex because its stress depends strongly on the orientation to the Al-lines caused by the complicated wavy pa
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