High-Performance Metal Hard Mask Process Using Fiber-Textured TiN Film for Cu Interconnects

Abstract

One of the most challenging issues in the metal hard mask process for copper interconnects is controlling the residual stress in TiN mask. The relationship between the residual stress and the feature size of the trench was investigated using a mechanical simulation. It was found that the trench deformation at a specific pattern due to the residual compressive stress in TiN film resulted in void formation in Cu. To overcome this problem, the correlation between the residual stress and the film properties of TiN was investigated and a potential TiN mask in the metal hard mask process was studied. The residual stress in TiN film and the etching performance were correlated with the composition and the crystal structure of TiN. The grain growth was suppressed by reducing the energy of sputtered atoms during the deposition of TiN, resulting in low residual stress in TiN film with keeping the etching performance for TiN. By applying low stress TiN mask which had a fiber-textured structure, the trench deformation at a specific pattern could be suppressed and thus Cu filling was perfectly achieved. The metal hard mask process using TiN film which had a fiber-textured structure was demonstrated to be high performance. As the wiring pitches in copper (Cu) interconnect continue to become smaller, resistive-capacitive (RC) delay due to the increase in the capacitance between Cu lines becomes a critical problem. Therefore, the low k-value dielectric materials have been studied to reduce the capacitance between Cu lines.1-8 However, the low-k materials are known to be easily damaged by the post-processes such as the resist ashing process with oxygen (O 2 ) plasma 9-11 because of their low mechanical strength, and it results in k-value increasing.To suppress the damage of interlayer dielectric by the ashing process during the removal of the trench resist, the metal hard mask (MHM) process has been studied instead of the conventional resist mask process.12-24 As a hard mask in the MHM process, Titanium nitride (TiN) has been investigated. [20][21][22][23][24][25][26][27][28][29][30][31] This is because the alignment pattern for photolithography can be easily recognized through TiN film compared to other metal films such as Tantalum nitride (TaN) film. However, the serious problems occurred in the MHM process due to high residual stress in TiN mask. One of the problems is that the trench deformation after the etching process, which is known as the wiggling phenomenon.32 This is due to the stress relaxation of TiN film after the trench formation with the etching process, and it results in the buckled structure. Therefore, the approaches to reduce the residual stress in TiN film used as a hard mask have been also studied. One approach to reduce the residual stress is to reduce the thickness of TiN mask. However, thinner TiN mask tends to result in worse property of a hard mask in the self-aligned via process, and the shrink of the pitches between via and trench occurs. It results in degrading the device yield or the reliability per...

High-Performance Extremely Low-k Film Integration Technology with Metal Hard Mask Process for Cu Interconnects

“…In this test, TiN film which had a fiber-textured structure was used for a hard mask. 36 The residual compressive stress in the fiber-textured TiN film was about 600 MPa and it was enough low to suppress the wiggling phenomenon. 41 The ratio of Ti and N in TiN film was almost 1:1 and TiN contained O with the concentration of 8.0 at.%.…”

“…[33][34][35] We have studied the MHM process using the low stress TiN mask which had a fiber-textured structure for the perfect Cu filling and it has been demonstrated to be high performance. 36 However, the reports on the integration of lower k-value dielectric materials (k < 2.5) with the MHM self-aligned via process have been limited, and the complete process including reliability performance in chip packaging has not been reported.…”

“…[33][34][35] We have studied the MHM process using the low stress TiN mask which had a fiber-textured structure for the perfect Cu filling and it has been demonstrated to be high performance. 36 However, the reports on the integration of lower k-value dielectric materials (k < 2.5) with the MHM self-aligned via process have been limited, and the complete process including reliability performance in chip packaging has not been reported.In this paper, high performance Cu interconnects using extremely low-k (ELK) film (k = 2.4) for the interlayer dielectric with the MHM self-aligned via process and the interfacial surface oxygen treatment between extremely low-k film and the underlying liner layer was studied. The maximum performance for ELK dielectric film and complete reliability performance in chip packaging by enhancing the adhesion strength between ELK film and liner layer are discussed.…”

Review—Beyond the Highs and Lows: A Perspective on the Future of Dielectrics Research for Nanoelectronic Devices

“…225,226 This approach was adopted primarily to reduce patterning induced degradation of the low-k ILD dielectric constant and enable etching of high aspect ratio features. 227,228 The success of the approach was based primarily on the ability to selectively etch the overlying metal hard mask relative to the low-k ILD 227 and the metal hard mask to shield and protect the underlying low-k ILD from the various subsequent damaging plasmas used to perform the pattern transfer etch and cleans (see Fig. 10).…”

“…10). 228 Titanium nitride (TiN) was commonly selected for this application due to its acceptable transparency, 229 high etch selectivity relative to other dielectric hard mask materials such as C:H and SiC:H, 230 and the ability to be removed in subsequent post etch wet cleans. 226,227 However, traditional single pass dry optical lithography methods utilizing 193 nm wavelengths became incapable of printing the finer dimensions needed for < 45 nm technologies and the lack of EUV readiness forced the transition to both immersion lithography [231][232][233][234] and pitch division/double patterning methods.…”