F. Deng

Salicidation process using NiSi and its device application

Self-aligned silicidation is a well-known process to reduce source, drain, and gate resistances of submicron metal-oxide-semiconductor devices. This process is particularly useful for devices built on very thin Si layers (∼1000 A or less) on insulators because of the large source and drain resistances associated with the thin Si layer. NiSi is a good candidate for salicidation process due to its low resistivity, low formation temperature, little silicon consumption, and large stable processing temperature window. In this article, the formation of nickel mono-silicide (NiSi) using rapid thermal annealing, the thermal stability of NiSi on n+ poly-Si and the contact resistance of NiSi on n+ Si layers in a SIMOX structure were investigated. NiSi salicidation process was, then, incorporated into a NMOS/SIMOX device fabrication for partial and full consumption of the Si in the source and drain regions during the salicidation process. The effects of void formation and silicide encroachment on the device performa...

Study of contact formation in AlGaN/GaN heterostructures

The contact formation of Ti/Al and Ti metallization on AlGaN/GaN heterojunction field effect transistors (HFET) was investigated. It was found that ohmic contact formation is related to the low work function of the Ti contacting layer and the formation of a TiN phase at the Ti/nitride interface. Contact resistance as low as 1 Ω mm or less can be obtained on HFET samples with a nsμ product of ∼0.8×1016/V s and on n-GaN with a carrier concentration of 1.5×1018/cm3. Ti/Al bilayer contact scheme is superior to Ti-only contact due to a surface Al3Ti layer in the bilayer contact, which may reduce the oxidation problem when annealed in N2 at high temperatures. Preannealing the HFET samples at 850 °C for 1 h in N2 appears to improve the ohmic contact in general, but not always observed. Our results indicate that Ti/Al contact scheme yields sufficiently low contact resistance on HFET structures for microwave applications.

Ni and Ni silicide Schottky contacts on n-GaN

The electrical characteristics of Ni and NiSi Schottky diodes on n-GaN have been investigated as a function of annealing. Ni diodes were found to be stable up to 500 °C for 1 h in sequential annealing, with a barrier height φ (I–V) of 0.8–0.9 eV and an n factor of ∼1.1. The barrier height deduced from C–V measurements, φ (C–V), was typically 0.15 eV higher than φ (I–V). At 600 °C the diodes failed, and Ga was found to migrate into the Ni layer. NiSi diodes were stable up to 600 °C for 1 h, φ (I–V) was found to be about 0.8–1 eV with an n-factor of about 1.15. The value of φ (C–V) was between 0.3 to 0.6 eV higher than φ (I–V), consistent with the notion of the presence of a thin insulating layer at the NiSi/GaN interface. The electrical characteristics obtained in this study are also compared with those obtained for Pt and PtSi Schottky diodes on n-GaN.

Resistivity and thermal stability of nickel mono-silicide

Abstract Nickel monosilicide (NiSi) has been well recognized as a promising silicide for future ULSI devices. It can have low resistivity of 15 μΩ cm on deep submicron lines and after high temperature (>600°C) annealing. This work studies the resistivity and thermal stability of thin NiSi layer on B, As, P-doped and in situ boron doped deep submicron polycrystalline silicon (poly-Si) lines after 500–800°C/1 h of annealing. The stability of NiSi on crystalline silicon (c-Si), poly-Si and amorphous silicon (a-Si) film will also be studied.

TEXTURE AND STRESS OF AG FILMS IN AG/TI, AG/CR BILAYERS, AND SELF-ENCAPSULATED STRUCTURES

The texture of evaporated Ag films prepared on Ti or Cr underlayers before and after encapsulation process has been studied by x-ray diffraction. In addition, the stress state in self-encapsulated Ag/Ti structures has also been investigated using a “sin2 ψ” technique. Silver films deposited on Ti layers exhibit a strong 〈111〉 texture, which is in contrast to the nearly random orientation of Ag films on Cr underlayers. The minimization of interfacial energy with respect to lattice match can account for this underlayer dependence. After an encapsulation process involving Ti reactions in an ammonia ambient, the texture of Ag films in Ag/Ti bilayers is further enhanced. Highly textured Ag films may provide the basis for electromigration-resistant Ag metallization in integrated circuit devices. For the Ag/Ti bilayer structures, a low tensile stress of approximately 61 MPa arising from the nonequilibrium growth during the film deposition is present in the Ag films. This results in a lattice tension state in the...

Texture and microstructural evolution of thin silver films in Ag/Ti bilayers

The texture and microstructure of thin silver films in Ag/Ti bilayer structures have been characterized as a function of vacuum annealing temperature and time with the use of x-ray diffraction and transmission electron microscopy. A strong preexisting (111) texture in Ag films was further improved upon annealing as evidenced by an increased intensity and narrower distribution of the texture along the film normal. A new (200) texture component was generated after 600 °C annealing; it however had a relatively low intensity when compared to the dominant (111) texture. No abnormal grain growth was observed in annealed Ag films. The texture evolution in all films appeared to complete within the first 15 min annealing, while the microstructure continued to change with additional annealing time. The roles of both surface energy and strain energy in the grain growth were evaluated. A model of the grain growth and texture evolution has been proposed to explain these observations.

Photoelastic waveguides and the controlled introduction of strain in III‐V semiconductors by means of thin film technology

We have investigated the use of thin film technology to introduce controllable and thermally stable stress into semiconductor heterostructures. Two simple schemes are used. The first scheme is to use interfacial reactions between a metal and the substrate, such as Ni, Co, Pd, and Pt on GaAs/AlGaAs. The induced stress in the structure is reproducible and controllable because the volumetric change for a given reaction is fixed, as long as the deposited film is fully reacted to form a compound. The stability of the stress depends on the stability of the compound. In the case of Ni and Co on GaAs/AlGaAs, the induced stress is thermally stable up to 600 °C. Evaporated films and reacted films are usually under tension. The second scheme is to use rf sputtered W or WNi alloy films where W or WNi is sputtered onto a negative dc biased substrate. This scheme effectively provides highly compressed films. The thermal stability depends on the concentration of Ni in the WNi alloy. Using the two schemes above, we have ...

Formation of titanium nitride by annealing Ag/Ti structures in ammonia ambient

Titanium nitride thin films have been formed in the temperature range of 400–600 °C by annealing Ag/Ti bilayer films on oxidized Si substrates in an ammonia ambient. Rutherford backscattering spectrometry and Auger depth profiling have shown the segregation of Ti at the surface and at interface. Ti diffused out through the silver layer and reacted with ammonia to form a TiN layer that self-encapsulated the silver film. A near-bamboo structure in the encapsulated Ag films was observed using cross-sectional transmission electron microscopy. Such a structure is expected to improve the electromigration resistance of the silver metallization. The kinetics of the Ti-nitride growth was studied by investigating its dependence on time, temperature, and Ag/Ti bilayer thicknesses. We also found that two processes govern the nitridation reaction. A dominant nitridation process takes place initially at fast growth rates. After 15 min anneals the nitride growth can be described by x2=B t, where B is a parabolic rate co...

Kinetics of Cu3Ge formation and reaction with Al

Cu3Ge films have been found to have a low resistivity, good adhesion on SiO2, good thermal stability on Si, and good oxidation resistance. It has the potential as an ideal adhesion/barrier/passivation layer for Cu ultralarge scale integration metallization. The kinetics of Cu3Ge formation and the thermal stability of Cu3Ge against Al were studied by in situ resistivity measurement, Rutherford backscattering spectrometry, and transmission electron microscopy. We found that Cu reacted with Ge in the temperature range of 100–200 °C. The activation energy of the Cu–Ge compound formation was found to be 1.1±0.1 eV. The Cu–Ge compound was identified as e-Cu3Ge from transmission electron microscope diffraction patterns. Upon annealing the e-Cu3Ge became unstable on Al at the temperature range of 300–350 °C. In the reaction between Al and Cu3Ge, Cu preferentially reacted with Al to form an e-Al2Cu3 compound. The activation energy of formation of the Al–Cu compound was found to be 2.1±0.1 eV.

Ohmic contact formation mechanism of the Au/Ge/Pd/n‐GaAs system formed below 200 °C

We report the ohmic contact formation mechanism of the low resistance (∼1×10−6 Ω cm2) Au/Ge/Pd contact to n‐GaAs annealed at 175 °C. Cross‐sectional transmission electron microscopy and Rutherford backscattering spectrometry were utilized in this study. It is found that the solid phase regrowth process, interdiffusion between Au and Ge, and the enhancement of the conductivity of the excess Ge layer are responsible for the observed low contact resistivity.