This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 72.37.248.4
`On: Tue, 27 Jan 2015 22:40:19
`
`SAMSUNG ET AL. EXHIBIT 1045
`Page 1 of 3
`
`

`
`GROWTH
`IEMPERHURE
`me” C
`new
`975
`
`BACK SIDE MASK
`SID?
`Si N
`254
`
`
`
`
`
`umwuvruCHANGFINCURVHURIno‘cm’):
`
`n~ICKNESSOFTN(RtMLSi()2
`
`(X;
`
`FIG. 2. Sample curvature induced by stresses in thermal SiO, grown in wet
`0, on (1 l I) and ( I00) samples versus SiO, thickness. The line represents
`the curvature introduction expected for an SiO, stress level of 7 X 10'’
`dyn/cm ’.
`
`temperature (time = O) is caused by the ditferences in ther-
`mal expansion between Si and Si02 . The Si,N,, back-mask
`sample in Fig. 1 has less curvature at room temperature and
`is curved in the opposite direction to that of the SiO, back-
`mask samples because the Si,N, on the back is thin and in
`tension while the Si0, on the back of the other two samples
`is thick and in compression. As seen in Fig. 1, after entry into
`the fumaoe, the samples straighten up as they equilibrate
`with the furnace (which takes approximately 5-8 min). If
`there is stress in the growing oxide, the samples continue to
`bend as seen in the 900 °C data, which shows continual bend-
`ing for times greater than 10 min. Note that the 1000 ‘C data
`shows no bending during Si02 growth (times greater than 10
`min, which leads to the conclusion that the SiO, is growing
`stress free at this temperature.
`Data such as that in Fig. 1 were obtained at several
`temperatures around the viscous flow point of 965 “C. Re-
`sults were analyzed as follows to obtain a best estimate for
`AKO , the value of curvature at growth temperature for zero
`Si0Z thickness, rsiol. A plot of raw data such as in Fig. 1
`versus 75“): exhibits an easily identified slope in the data for
`times after about 8 min. The intercept ofthis straight portion
`at zero 1-5.0} is taken as AK0 for that sample. The value of
`AK0 was generally different from zero (flat) because of a
`constant stress in the back mask. The value for AKO was
`subtracted from the data taken after 8 min and the resulting
`data replotted versus SiO2 thickness 1-5,02. Thickness 15,02 as
`a function of time was estimated by measuring the final oxide
`thickness and using published rsioz-vs-time plots for steam
`growth of $02 shifted to match the final thickness-time
`
`9
`
`Appl. Phys. Lett.. Vol. 35. No. 1, 1 July 1979
`
`data point (a typical run at 1000 °c grew 3200 A in 3 1:).
`Results are shown in Fig. 2 for various growth temperatures.
`Note first of all in Fig. 2 that there is a dramatic differ-
`ence in going from 950 to 975 or 1000 ‘C for both the (111)
`and (100) samples. Also note that the results for either back-
`mask choice are essentially the same for a given growth tem-
`perature, thus assuring that the major effects are due to
`stress (or lack of stress) in the growing Si02.
`The results for the Si3N‘ back-mask samples tended to
`level off as rsioz exceeded 600 K. This is not understood at
`present, but the quality of our Si,N,, films and their contin-
`ued masking ability is suspect because their etch rates in
`room-temperature HF are far too high (500 A/min) even
`though the index of refraction (1.97) is consistent with low-
`oxygen-content material. The SiO2 back-mask results at
`growth temperatures of 950 °C and below show that the sam-
`ples continue to curve as long as Si0, continues to grow.
`A line is included in Fig. 2 to indicate the level of stress-
`es seen in the SiO2 during growth. The curvature change AK
`is proportional to the integral of the stress through the oxide
`thickness. If we assume that the oxide stress is constant
`
`through rsio_, AK is proportional to -rsioz and is related to the
`stress in the SiO2 , $5.0, by
`
`AK =
`
`6$sao,7'sio,(1 " Vsi)
`
`.
`
`Est’;
`
`(2)
`
`where rsi is the sample thickness and E5,» and vsi are
`Young’s modulus and Poisson’s ratio, respectively. Letting ‘
`E5i(l — vsi) ‘ ' = 2.28 X 10" dny/cm 2, the line in Fig. 2 is
`plotted for Ssiol = 7 X 10° dyn/cm 2. This value of stress is
`large compared to the room-temperature stresses of 3 X 10 9
`dyn/cm 2 set up during cooldown 7 by the differences in ther-
`mal expansion for Si and SiO2 . Prediction of the existence of
`stress during growth by examination of the room-tempera-
`ture stresses in our samples after cooldown has been incon-
`clusive because there is apparently some occasional relief or
`compaction of the stressed films during cooldown. More
`work is needed here.
`
`Near discontinuities in the growing oxide, shear stress-
`es will exist in the SiO2 and Si near the Si/SiO2 interface.
`These shear stresses are ofthe order ofthe compressive stress
`in the oxide and are proportional to the integral over T5502 of
`the oxide stress. Since the recently measured 6 critical stress
`for shear flow in Si at 1000 °C is 3.4x 107 dyn/cm 2, it is
`entirely plausible to see plastic deformation of Si beneath
`discontinuities in growing SiO2 layers (near the edges of
`windows, etc.). In other words, the present results show that
`high stresses can exist in our SiO, at growth temperature
`where the Si is mechanically weak.
`The possibility of a tensile stress in the SiO, growing at
`1030 ‘C is seen in Fig. 2. This result is tentative because the
`effect is small and has not been checked yet at higher
`temperature.
`Several runs using dry 02 were attempted. The much
`reduced growth rate of thermal Si02 in dry 02 made the
`experiments more diflicult. Preliminary results suggest that
`the stress levels are much reduced over those seen in Figs. 1
`
`E.P. EerNIsse
`
`9
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`SAMSUNG ET AL. EXHIBIT 1045
`
`Page 2 of 3
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` This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 72.37.248.4
`On: Tue, 27 Jan 2015 22:40:19
`
`SAMSUNG ET AL. EXHIBIT 1045
`Page 3 of 3