行政院國家科學委員會專題研究計畫 成果報告
具有奈米尺寸孔隙極低介電常數薄膜之電性物理機制探討
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計畫類別： 個別型計畫 計畫編號： NSC92-2112-M-110-020- 執行期間： 92 年 08 月 01 日至 93 年 07 月 31 日 執行單位： 國立中山大學物理學系(所) 計畫主持人： 張鼎張 計畫參與人員： 吳興華、黃子軒、蔡美娜、施瓊詒 報告類型： 完整報告 報告附件： 出席國際會議研究心得報告及發表論文 處理方式： 本計畫可公開查詢中 華 民 國 93 年 11 月 22 日
一、中文摘要 多孔性的二氧化矽（PPSZ-M）薄膜由於具有多孔的結構，介電常數將有效的 降低，但是相對的機械強度一般來說都較緻密的材料差。由於在積體電路的製造 技術中，光阻的去除常是利用氧電漿處理的方式來將光阻中的碳氫成份分解，達 到光阻灰化的目地。本論文將探討兩種薄膜經氧電漿處理後對於銅導線之可靠性 分析，其中銅的擴散導致漏電流的上升和可靠性的下降較非多孔性薄膜來的嚴 重，但是若以 CMP(chemical-mechanical polish) 有效的去除被氧電漿破壞並 且吸水的薄層則其低介電常數的優勢又可再度展現出來。 關鍵詞：PPSZ、低介電常數、去光阻
Abstract
PPSZ (porous Methylsilsesquiazane) is the lower dielectric constant of porous low-k material due to porous structure. However, the mechanical strength of porous low-k materials is worse than that of dense materials. In the present IC manufacturing processes, photoresist stripping is commonly implemented with O2 plasma ashing. We
will investigate the reliability of these two low-k material with copper electrode after O2 plasma ashing. Copper diffusion in PPSZ is greater than other dense low-k film in
the same O2 plasma condition and the reliability of PPSZ film is not as good as other
dense low-k film. As a damaged layer formed on PPSZ surface can be effect removed by CMP (chemical-mechanical polish), the advantage of low dielectric constant will reappear.
二、緣由與目地
In device switching performance, the interconnection delay has become relatively major in comparison with the basic gate delay. This is caused by large interconnect parasitic capacitance. Therefore it is necessary to reduce this capacitance to realize
high performance VLSI. The low dielectric constant (low-k) materials are proposed to decrease the parasitical capacitor [1-6].
One of the low-k dielectrics, porous Methy- lsilsesquiazane ( PPSZ-M ) are commercially and available solution manufactured by Clariant Corp, exhibit good adhesion to silicon, CVD oxides, and aluminum whose dielectric constant is about 2.0~2.2. Compare to conventional siloxane-based spin-on glass, PPSZ-M materials with lower dielectric constant due to the presence of Si-CH3, C-H, S-N bonds instead of partial Si-O bonds. Therefore, the integration of the HOSP films as an interlayer dielectric into multilevel interconnects has received much attention in recent years. The low-k film provides good planarization, but an etchback process is needed to avoid an increase of via resistance. The cause is that the quality of PPSZ film will be degraded by damages from oxygen plasma for PR stripping process [7]. In this work, we have studied the post-CMP treatment to improve the quality of PPSZ film. Electrical measurement and material analyses have been used to evaluate the PPSZ film. In addition, O2-plasma ashing has been investigated to realize the impact of integrated processes on the dielectric film quality.
三、結果與討論
Figure 1 shows FTIR spectra of the as-cured PPSZ film before and after different O2 plasma treatment. The result lightly exhibits that PPSZ after O2 plasma treatment
will absorb moisture. The intensities of Si-OH bonds was increased after photoresist stripping. Furthermore, the intensities of Si-O, C-H and Si-CH3 peaks are decreased dramatically. During O2 plasma ashing, O radicals easily react with functional groups of PPSZ films, breaking Si-CH3 bonds and Si-O bonds. This will cause the PPSZ films to generate dangling bonds and to absorb moisture. The thickness of PPSZ with O2 plasma treatment are measured by n& k analysis, it shows that with the O2 plasma
time increasing the thickness goes to decrease and the dielectric constant goes to increase. The increase of dielectric constant is due to the damage of PPSZ surface and moisture absorption which is shown in Figure 2.
Figure 3 shows the leakage current density of PPSZ with different O2 plasma
treatment measured at room temperature. In accordance with this we know that with the O2 plasma time increasing, the leakage current density goes to increase. It is
because the long O2 plasma ashing time will result in more damage and moisture
absorption to PPSZ film. Figure 4 shows that leakage current density of standard, O2
plasma 60 sec and post-CMP PPSZ films. It wass very clearly that the damaged and moisture absorption of the PPSZ film which was treated by O2 plasma ashing could be
improved by post-CMP due to removing the damaged layer of PPSZ surface. The dielectric constant and leakage current would also effectively decrease after CMP process. The structure was shown in Figure 5 (a) and (b). Figure 6 (a) and (b) show leakage current density of Cu-electrode for standard PPSZ film and PPSZ film with O2 plasma 60 sec treatment on 2MV/cm 150oC 1000s BTS (Bias Temperature Stress).
With the BTS measurement, the reliability of PPSZ film could be realized clearly. And the reliability of low-k film is very important for IC process. Leakage current density of standard PPSZ film was measured at room temperature and 150℃ which
were almost the same like the sample after 2MV/cm 150oC 1000s BTS. Leakage
current density of the film after O2 plasma 60sec was measured at both room
temperature and 150℃ increase very obviously.
When Copper ion diffuses into PPSZ, the leakage current will increase greatly and the reliability will decrease. Figure 7 shows the leakage current density-time curve with different O2 plasma treatment for 2MV/cm, 150 oC 1000s BTS. It is shown in
Figure 7 that the tolerance of PPSZ film can achieve 30 sec O2 plasma treatment. But
plasma treatment and BTS treatment, the electrical property and reliability of PPSZ was investigated.
四、計劃成果自評
In this project, we have investigated the post-treatment with different O2 plasma
treatment and use the post-CMP technique to improve the quality of PPSZ after O2
plasma treatment on low-k PPSZ films. The existence of moisture will result in CuxOy
formation between Cu and PPSZ surface. It will be ionized into Cu+ ion and diffuses into PPSZ during high temperature and bias stress condition. When Copper ion diffuses into PPSZ, the leakage current will increase greatly and the reliability will decrease. But as the damaged layer could be effectively removed, moisture absorption and copper diffusing problems could be improved.
五、參考文獻
[1]M. G. Albrecht and C. Blanchette, J. Electrochem. Soc., 145 (1998) 4019
[2] M. J. Loboda, C. M. Grove, and R. F. Schneider, J. Electrochem. Soc., 145 (1998) 2861
[3] S.W. Lin, M. Miyata, T. Naito, Y. Shimogaki, Y. NaKano, K.Tada, and H. Komiyama Mat, Res. Soc. Symp., Vol.443, 1996, p. 143
[4] A. Grill, V. Patel, K.L. Saenger, C.Jahnes, S.A. Cohen, A.G. Schrott, D. C. Edelstein, and J.R.Paraszczak, Mat. Res. Soc. Symp., Vol. 443, 1996, p. 155 [5] S. M. Rossnagel, Proc of VLSI multilevel interconnection conference (VMIC),
1995, p. 576
[6] S. Okuda, Y. Shioya and H. Kashimada, Proc of VLSI multilevel interconnection conference (VMIC), 1995, p. 424
[7] P. T. Liu, T. C. Chang, Y. S. Mor, S. M. Sze, Japanese Journal of Applied Physics, 38 (1999) 3482
W a v e n u m b e r ( c m -1 ) 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 4 5 0 0 Ads o rbance ( A. U . ) - 6 0 - 4 0 - 2 0 0 2 0 4 0 6 0 8 0 1 0 0 1 2 0
D
ie
lect
ri
c
c
ons
tant
0 1 2 3 4S TD 15 sec 30 sec 60 sec
Figure.1 FTIR spectra of PPSZ with different O2plasmatreatment condition
Figure.2 Dielectric constant variation of different O2 plasma ashing
C-H Si-O network
Si-O cage-like Si-CH3
E ( M V / c m ) 0 1 2 J ( A /cm 2 ) 1 0- 1 1 1 0- 1 0 1 0- 9 1 0- 8 1 0- 7 1 0- 6 1 0- 5 S T D O2 p la s m a 3 0 s e c O2 p la s m a 6 0 s e c E ( M V /c m ) 0 .0 0 .5 1 .0 1 .5 2 .0 J ( A/c m 2 ) 1 0- 1 1 1 0- 1 0 1 0- 9 1 0- 8 1 0- 7 1 0- 6 1 0- 5 S T D O2 p la s m a 6 0 s e c p o s t- C M P
Figure.3 Leakage current of PPSZ with different O2plasma
ashing measured at R.T.
Figure.4 Leakage current of STD、O2 plasma 60 sec、post-CMP PPSZ
Figure.5 (a) The film of PPSZ before CMP
Figure.5 (b) The film of PPSZ after CMP
PPSZ
substrate
hydrophilic layer removal
PPSZ
substrate
Moisture absorption
E ( M V / c m ) 0 1 2 J ( A /c m 2 ) 1 0- 1 0 1 0- 9 1 0- 8 1 0- 7 1 0- 6 1 0- 5 1 0- 4 1 0- 3 1 0- 2 p r e - B T S a t R . T . p r e - B T S a t 1 5 0 o C p o s t - B T S a t 1 5 0 o C p o s t - B T S a t R . T . E ( M V /c m ) 0 1 2 J ( A/ c m 2 ) 1 0-1 0 1 0-9 1 0-8 1 0-7 1 0-6 1 0-5 1 0-4 1 0-3 1 0-2 p r e -B T S a t R .T . p r e -B T S a t 1 5 0oC p o s t-B T S a t 1 5 0oC p o s t-B T S a t R .T .
Figure.6(a) Leakage current density of Cu-electrode STD PPSZ after
2MV/cm, 150oC, 1000s BTS
Figure.6(b) Leakage current density of Cu-electrode、O2 plasma 60sec
T im e ( S E C ) 0 5 0 0 1 0 0 0 J ( A /cm 2 ) 1 0- 9 1 0- 8 1 0- 7 1 0- 6 1 0- 5
Figure.7 Leakage current density－Time curve of different O2 plasma
