Title of Invention

A METHOD OF TREATING A LOW K DIELECTRIC MATERIAL LAYER COATED ON A SI SUBSTRATE

Abstract

A method of treating a low k porous dielectric material layer coated on a Si substrate. The method comprises exposing the dielectric material layer to hot wire generated atomic hydrogen (HWGAH) at a temperature of 200 to 300ºC and pressure of 400 mtorr to 600 mtorr. The atomic hydrogen is generated by heating tungsten wire at 1800 to 1900ºC. Also a low k dielectric material layer coated on a Si substrate treated by the method as stated above. Preferably the low k porous dielectric material layer is hydrogen silsesquioxane (HSQ) and the substrate is crystalline Si.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) As amended by the Patents (Amendment) Act, 2005 & The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2005 COMPLETE SPECIFICATION (See section 10 and rule 13) TITLE OF THE INVENTION A method of treating a low k dielectric material layer APPLICANTS Name Nationality Address INVENTORS Names Nationality Address Indian Institute of Technology, Bombay an autonomous research and educational institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961 Powai, Mumbai 400076, Maharashtra, India Dusane Onkar Rajiv, Kumbhar Anil Alka and Singh Kumar Sunil all Indian Nationals all of Indian Institute of Technology, Bombay Powai, Mumbai 400076, Maharashtra, India PREAMBLE TO THE DESCRIPTION The following specification particularly describes the nature of this invention and the manner in which it is to be performed : FIELD OF INVENTION This invention relates to a method of treating a low k dielectric material layer. This invention also relates to a low k dielectric material layer treated by the above method. BACKGROUND OF INVENTION During fabrication of integrated circuits, a Cu layer forming the contacts is deposited on a low k (dielectric constant) dielectric material layer on a semiconductor material substrate. In order to reduce the RC time constant associated with the integrated circuits and to improve the frequency or speed of operation of the integrated circuits, it is essential that the dielectric constant of the dielectric layer must be low. Si02 is traditionally used as a dielectric layer. Due to the dielectric constant of the SiC>2 layer being high (about 4), the speed of operation of the integrated circuits is reduced. Therefore, attempts are being made to develop dielectric materials of low k value for use in the manufacture of integrated circuits. Hydrogen silsesquioxane (HSQ) [chemical formula (Hsi03/2)2n, n = 3-8] with a dielectric constant k~2.9+0.05 is a recently developed low k dielectric material for use in the manufacture of integrated circuits. HSQ is, however, porous and like any other porous dielectric, HSQ is also susceptible to moisture attack, which degrades its properties with time thereby affecting the long-term reliability of integrated circuits comprising the same. During fabrication of an integrated circuit, a photo-resist layer is coated on the dielectric material layer already deposited on the semi-conductor material substrate. Removal of the photo-resist layer using oxygen plasma (plasma ashing) during patterning is an important step in the fabrication of integrated circuits and has to be carried out very precisely without damaging the other components or circuits on the semi conductor material substrate like 2 resistors or transistors. When the dielectric film is exposed to oxygen plasma, oxygen gets incorporated into the dielectric film in the form of (-OH) hydroxyl bonds. This increases the dielectric constant of the dielectric layer as the dielectric constant of water (moisture) is high thereby reducing the dielectric properties of the layer and resulting in reduced time constant and speed of operation or frequency of the integrated circuits comprising the same. US Patent 6423652 describes a method of implanting a dopant into the dielectric layer to form a compact layer on the surface of the dielectric layer and prevent the adverse effects of oxygen plasma treatment. There is, however, the possibility of the exposed layer being damaged by the presence of ions of boron during the implantation. US Patent 6583067 describes the use of hexamethyldisilazane (HMDS) treatment to repair the surface of the low k dielectric layer damaged during the photo-resist stripping. US Patent 6521547 describes the use of trimethylchlorosilane (TMCS) treatment to repair the damage of oxygen plasma treatment. As the above treatments are carried out after exposure of the dielectric layer to the oxygen plasma they are not very effective in controlling the adverse effects of the plasma treatment. US Patent Pub No 2005/666354 describes a method of lowering the dielectric constant of an organo-silicon low dielectric layer while improving its hardness and thermal stability by treating with He plasma followed by H2 plasma. Due to the H2 plasma treatments, some of the Si-0 and Si-CH3 bonds near the surface of the dielectric layer are converted to Si-H bonds thereby further lowering the dielectric constant and increasing the thermal stability and hence the breakdown resistance. Plasma deposition technique 3 requires RF generators and impedance matching circuits. Therefore, the process is expensive and difficult to carry out. Besides, the plasma deposition gives rise to increased surface roughness of the dielectric layer due to damages caused by ion and electron bombardment and induced charge. "The effects of plasma treatment for low dielectric constant hydrogen-silsesquioxane (HSQ)", Thin Solid Films 332 (1998) 345-350 and "Enhancing the resistance of low-k hydrogen silsesquioxane (HSQ) to wet stripper damage" Thin Solid Films 398-399(2001)523-526, report the use of H2 plasma treatment which provides hydrogen passivation of the HSQ films necessary to prevent HSQ from water uptake during photo-resist stripping. The undesirable effects of plasma treatment are well documented. OBJECTS OF INVENTION An object of the invention is to provide a method of treating a low k dielectric material layer, which method is simple and convenient to carryout and cost effective. Another object of the invention is to provide a method of treating a low k dielectric material layer, which method does not damage the dielectric layer. Another object of the invention is to provide a method of treating a low k dielectric material layer, which method renders the dielectric layer very effective against the adverse effects of oxygen plasma treatment and improves the hydrophobicity of the dielectric layer thereby reducing moisture absorption or uptake thereof and leakage current. Another object of the invention is to provide a method of treating a low k dielectric material layer, which method retains the dielectric properties of the dielectric layer. 4 Another object of the invention is to provide a low k dielectric material layer treated by the method described above and having the properties and attributes stated above. DETAILED DESCRIPTION OF INVENTION According to the invention there is provided a method of treating a low k porous dielectric material layer coated on a Si substrate, the method comprising exposing the dielectric material layer to hot wire generated atomic hydrogen (HWGAH) at a temperature of 200 to 300°C and pressure of 400 mtorr to 600 mtorr According to an embodiment of the invention, the method comprises treating a low k porous dielectric material layer comprising hydrogen silsesquioxane (HSQ) coated on the Si substrate. According to an embodiment of the invention, the method comprises exposing the low k porous dielectric material layer coated on the Si substrate to atomic hydrogen generated by heating tungsten wire at 1800 to 1900°C. According to an embodiment of the invention, the method comprises exposing the low k porous dielectric material layer comprising HSQ coated on the Si substrate to atomic hydrogen generated by heating tungsten wire at 1800 to 1900°C. According to the invention there is also provided a low k dielectric material layer coated on a Si substrate treated by the method as stated above. 5 The low k dielectric material layer is for example MSQ (Methyl silsesquioxane) or SiLk (porous HSQ) or SiOCH, preferably hydrogen silsesquioxane (HSQ). Preferably, the substrate is crystalline Si. According to the invention the dielectric layer on the substrate is treated with HWGAH which eliminates the use of RF generators and impedance matching circuits thereby rendering the process simple and convenient to carry out and cost effective. The method of the invention does not damage the dielectric layer as it does not generate ions and electrons or induced charge. It effectively prevents penetration of oxygen into the dielectric layer during the oxygen plasma treatment and the adverse effects thereof. It improves the hydrophobicity of the dielectric layer thereby reducing the moisture absorption or uptake thereof and leakage current. It also retains the dielectric properties of the dielectric layer. Therefore, integrated circuits fabricated using the dielectric layer will have reduced RC time constant and improved frequency or speed of operation. The following example is illustrative of the invention but not limitative of the scope thereof. Example 1 Flowable oxide (Fox-14) also called HSQ from Dow Corning was spin coated on c-Si substrates to a thickness of 200nm. The low dielectric constant films were baked sequentially on a hot plate at 150°C, 250°C and 350°C for 1 minute followed by furnace 6 curing at 400°C for one hour in nitrogen atmosphere. The HSQ films had a dielectric constant of 2.85 as measured at l00KHz using a C-V meter. Hotwire generated atomic hydrogen treatment was given to the HSQ coated substrates as follows: HSQ coated substrate was mounted on the substrate holder of a hot wire (tungsten) chemical vapour deposition (CVD) reactor and the reactor was evacuated to 10" Torr. H2 gas was allowed to flow into the reactor at a controlled flow rate of 10 seem (standard cubic centimeter per minute). The wire temperature was maintained at 1900°C, the substrate temperature was maintained at 250°C and pressure within the reactor was maintained at 500 mtorr. The substrate was allowed to cool down to room temperature and then removed from the reactor. HSQ coated substrates (test samples) were thus HWGAH treated for durations of 3, 6 and 9 minutes. The test samples were oxygen plasma treated as follows: HWGAH treated substrate was loaded in a plasma chamber and the chamber was evacuated to 10"6 Torr. Oxygen gas was passed into the chamber at a controlled flow rate of 10 seem and pressure of 500 mtorr. Oxygen plasma was generated with the help of an RF generator (RF Power 100W, 4 inch electrode area). After exposure to oxygen plasma for 9 minutes, the substrate was allowed to cool down to room temperature and then removed from the chamber. 7 The dielectric constant and leakage current of the HWGAH and oxygen plasma treated low dielectric constant layer were studied as follows : The substrate was loaded into a physical vapour deposition (PVD) chamber and the chamber was evacuated to 10"6 Torr. Al was evaporated on the uncoated side of the substrates as the bottom contact. Cu was evaporated on the coated side of the substrates in the form of dots (1mm diameter) through a physical mask to serve as the top contact. The substrate was sintered at 420°C in nitrogen ambient to have a good ohmic contact. The change in chemical bonding in the HSQ layer after the HWGAH treatment and after the oxygen plasma treatment was studied by FTIR spectroscopy. The dielectric constant of the test samples was measured at lOOKHz using a C-V meter. The leakage current of the test samples was measured using I-V setup. The HSQ layers in 50 test samples treated with HWGAH for 3, 6 and 9 minutes did not reveal any discernible change in the FTIR spectrum as compared to the test samples comprising HSQ layers untreated with HWGAH as seen in the Fig 1 of the accompanying drawings. The modifications to the chemical bonding by the HWGAH treatment were thus restricted only to the surface of the layer and the bulk material was not affected by the HWGAH treatment. The leakage current density in the 50 test samples treated with HWGAH was compared with the test samples without the HWGAH treatment. It was observed that the leakage current reduced in the case of the test samples treated with HWGAH as seen in Fig 2 of the accompanying drawings. Further there was more than one order of magnitude reduction in the leakage current and no indication of any electrical breakdown within the desired range of applied electric field for 8 the HWGAH treated test samples as seen Fig 2. In addition to the reduction in leakage current, a decrease in the dielectric constant from 2.85 to 2.8 was also observed in the case of test samples treated with HWGAH over test samples without HWGAH treatment as seen in Fig 3 of the accompanying drawings. Studies carried out to determine the effectiveness of HWGAH treatment in suppressing moisture absorption showed incorporation of (-OH) (hydroxyl) bonds in the broad Si-OH related band at around 3300 cm" in the FTIR spectra of the HSQ layer exposed to O2 plasma without HWGAH treatment as seen in Fig.4 of the accompanying drawings. Such an increase in the -OH bonds was not at all seen in FTIR of the layers which were treated with HWGAH prior to the exposure to oxygen plasma as seen in Fig 4. This shows that moisture absorption or uptake is completely avoided by the HWGAH treatment as is evident by the absence of the Si-OH bond at 3300 cm'1 in the FTIR spectra of the HSQ layer treated with HWGAH even after exposure to O2 plasma. The increase in leakage current density in case of the HWGAH treated HSQ layers is negligible as compared to that of the non-treated HSQ layers (more than two orders of magnitude) after exposure to O2 as seen in Fig.5 of the accompanying drawings. The dielectric constant shows little increase for the HWGAH treated layers (increases to 3 from 2.9) compared to an appreciable increase for the HWGAH non-treated layers (it increases up to 3.4 in this case) as seen in Fig.6 of the accompanying drawings. This suggests that the HWGAH treatment of the HSQ layer makes it very robust against O2 plasma and avoids its subsequent degradation. To evaluate the hydrophobicity (tendency to absorb less moisture) in the HSQ layers the water contact angle of HSQ layers treated and untreated with HWGAH after exposing to O2 plasma was studied. The HWGAH treated HSQ layers showed higher water contact angle as compared to HSQ layers untreated HWGAH with after O2 plasma exposure as seen in Fig. 7 of the accompanying drawings. Thus the water absorption in HWGAH treated layers was found to be significantly less than the non-treated HSQ layers. 10 We claim: 1. A method of treating a low k porous dielectric material layer coated on a Si substrate, the method comprising exposing the dielectric material layer to hot wire generated atomic hydrogen (HWGAH) at a temperature of 200 to 300°C and pressure of 400 mtorr to 600 mtorr. 2. A method as claimed in claim 1, which comprises treating a low k porous dielectric material layer comprising hydrogen silsesquioxane (HSQ) coated on the Si substrate. 3. A method as claimed in claim 1 or 2, wherein the substrate is crystalline Si. 4. A method as claimed in claim 1, which comprises exposing the low k porous dielectric material layer coated on the Si substrate to atomic hydrogen generated by heating tungsten wire at 1800 to 1900°C. 5. A method as claimed in claim 4, which comprises exposing the low k porous dielectric material layer comprising HSQ coated on the Si substrate to atomic hydrogen generated by heating tungsten wire at 1800 to 1900°C. 6. A method as claimed in claim 4 or 5, wherein the substrate is crystalline Si. 11 A low k dielectric material layer coated on a Si substrate treated by the method as claimed in claim 1 or 4. A low k dielectric material layer comprising hydrogen silsesquioxane (HSQ) coated on a Si substrate treated by the method as claimed in claim 2 or 5. A low k dielectric material layer coated on a crystalline Si substrate and treated by the method as claimed in claim 1 or 4. A low k dielectric material layer comprising hydrogen silsesquioxane (HSQ) coated on a crystalline Si substrate and treated by the method as claimed in claim 2 or 5. Dated this 2nd day of January 2006. (Jose M A) of Khaitan &Co Agent for the Applicants 12

Documents:

5-mum-2006-abstract(2-1-2006).pdf

5-MUM-2006-ABSTRACT(22-4-2008).pdf

5-mum-2006-abstract(granted)-(3-3-2009).pdf

5-mum-2006-cancelled pages(22-04-2008).pdf

5-MUM-2006-CLAIMS(22-4-2008).pdf

5-mum-2006-claims(complete)-(2-1-2006).pdf

5-mum-2006-claims(granted)-(22-04-2008).doc

5-mum-2006-claims(granted)-(22-04-2008).pdf

5-mum-2006-claims(granted)-(3-3-2009).pdf

5-mum-2006-claims.doc

5-mum-2006-claims.pdf

5-MUM-2006-CORRESPONDENCE(17-10-2008).pdf

5-mum-2006-correspondence(3-4-2009).pdf

5-mum-2006-correspondence(ipo)-(03-03-2009).pdf

5-mum-2006-correspondence(ipo)-(23-3-2009).pdf

5-mum-2006-correspondence-received-ver-020106.pdf

5-mum-2006-correspondence-received-ver-220206.pdf

5-mum-2006-description (complete).pdf

5-mum-2006-description(complete)-(2-1-2006).pdf

5-MUM-2006-DESCRIPTION(COMPLETE)-(22-4-2008).pdf

5-mum-2006-description(granted)-(3-3-2009).pdf

5-MUM-2006-DRAWING(17-10-2008).pdf

5-mum-2006-drawing(2-1-2006).pdf

5-mum-2006-drawing(22-04-2008).pdf

5-mum-2006-drawing(granted)-(3-3-2009).pdf

5-mum-2006-drawings.pdf

5-mum-2006-form 1(02-01-2006).pdf

5-MUM-2006-FORM 1(17-10-2008).pdf

5-mum-2006-form 1(22-02-2006).pdf

5-mum-2006-form 18(15-06-2006).pdf

5-mum-2006-form 2(complete)-(2-1-2006).pdf

5-mum-2006-form 2(granted)-(22-04-2008).doc

5-mum-2006-form 2(granted)-(22-04-2008).pdf

5-mum-2006-form 2(granted)-(3-3-2009).pdf

5-MUM-2006-FORM 2(TITLE PAGE)-(22-4-2008).pdf

5-mum-2006-form 2(title page)-(complete)-(2-1-2006).pdf

5-mum-2006-form 2(title page)-(granted)-(3-3-2009).pdf

5-mum-2006-form 26(12-01-2006).pdf

5-mum-2006-form 26(22-2-2006).pdf

5-mum-2006-form 3(02-01-2006).pdf

5-MUM-2006-FORM 8(29-5-2007).pdf

5-mum-2006-form-1.pdf

5-mum-2006-form-2.doc

5-mum-2006-form-2.pdf

5-mum-2006-form-26.pdf

5-mum-2006-form-3.pdf

5-mum-2006-specification(amended)-(22-4-2008).pdf

abstract1.jpg