Non-mass Separated Ion Beam Deposition Research Articles

Influence of substrate bias voltage on properties of Pt thin films deposited by non-mass separated ion beam deposition method

Pt thin films were deposited on Si substrates by applying a negative substrate bias voltage using a non-mass separated ion beam deposition method. The effect of the substrate bias voltage on the properties of the deposited films was investigated. In the case of Pt thin films deposited without the substrate bias voltage, a columnar structure and small grains were observed. The electrical resistivity of the deposited Pt films was very high (49.3 ± 0.65 µΩ cm). By increasing the substrate bias voltage, no clear columnar structure was observed. At the substrate bias voltage of − 75 V, the resistivity of the Pt film showed a minimum value of 16.9 ± 0.2 µΩ cm closed to the value of bulk (10.6 µΩ cm).

Improvement of Zr film purity by using a purified sputtering target and negative substrate bias voltage

We report an improvement of the purity of Zr films using a purified sputtering target and a negative substrate bias voltage. The Zr films were deposited on Si (100) substrates using a non-mass separated ion beam deposition system. Glow discharge mass spectrometry (GDMS) was used for trace impurity analysis in the Zr films deposited on a low-purity or a high-purity target and with or without a negative substrate bias voltage. Results showed that the sputtering target purity noticeably affects impurity concentrations in deposited films, which suggests that purer films are obtainable by increasing the sputtering target purity. This study further established that by applying a negative substrate bias voltage, much purer films are obtainable through prevention of an influx of impurities into the films during deposition.

Influence of Substrate Bias Voltage on the Impurity Concentrations in Hf Films Deposited by Ion Beam Deposition Method

Hf films have been deposited on Si(100) substrate with or without a substrate bias voltage using a non-mass separated ion beam deposition (IBD) method. Secondary ion mass spectrometry (SIMS) and glow discharge mass spectrometry (GDMS) have been used to determine impurity concentrations of Hf films and a Hf target. By the SIMS results with Cs + and O 2 + ion beams, the Hf film deposited at V s = 0 V contains more impurities than the Hf film deposited at V s = -50 V. In addition, from GDMS results for the Hf target and the Hf films deposited at V s = 0 and -50 V, almost all the impurities have reduced by applying a negative substrate bias voltage. It means that applying a negative bias voltage to the substrate can decrease the impurity concentrations in Hf films.

Influence of negative substrate bias voltage on the impurity concentrations in Zr films

Zr films were deposited on Si(1 0 0) substrates without a substrate bias voltage and with substrate bias voltages of −50 V and −100 V using a non-mass separated ion beam deposition system. Secondary ion mass spectrometry and glow discharge mass spectrometry were used to determine the impurity concentrations in a Zr target and Zr films. It was found that the total amount of impurities in the Zr film deposited at the substrate bias voltage of −50 V was much lower than that in the Zr film deposited without the substrate bias voltage. It means that applying a negative bias voltage to the substrate can suppress the increase in impurities of Zr films. Furthermore, it was confirmed that dominant impurity elements such as C, N and O have a considerable effect on the purity of Zr films and these impurities can be remarkably reduced by applying the negative substrate bias voltage.

Precise analysis of H, C, N, and O as dominant impurities in Cu films: complementary use of SIMS and GDMS

Secondary ion mass spectrometry (SIMS) and glow discharge mass spectrometry (GDMS) were used to determine the impurity concentrations of hydrogen, carbon, nitrogen, and oxygen elements in Cu films, and the results of SIMS and GDMS were carefully interpreted. The Cu films were deposited on Si (100) substrates at substrate bias voltages ranging from 0 V to −150 V using a non-mass separated ion beam deposition method. From the results of SIMS using a Cs− ion beam, as a whole, many high intensity peaks were observed in the Cu films deposited without substrate bias voltage. From the quantitative GDMS results, these peaks were determined to be signals detected as a cluster state such as CxHx, OxHx, CxOxHx. Therefore, using a combination of these dominant impurities, all the unknown peaks observed in the SIMS results could be interpreted. Moreover, it was found that the dominant impurities having a great influence on the film purity were hydrogen, carbon, nitrogen, and oxygen.

Interpretation of Dominant Impurities in Cu Films by Secondary Ion Mass Spectrometry and Glow Discharge Mass Spectrometry

Cu films were deposited on Si (100) substrates at substrate bias voltages of 0 V and -50 V by non-mass separated ion beam deposition. SIMS and GDMS were used to determine the impurity concentrations of a Cu target and Cu films. According to the quantitative GDMS results, many unknown peaks observed in the SIMS spectra of the Cu films were assigned to cluster states such as CxHx, OxHx, and CxOxHx. Moreover, it was found that the dominant impurities in the films were H, C, N, and O elements.

Trace Impurity Analysis in Ta Films Using Glow Discharge Mass Spectrometry: Concentration Change of Impurities by Applying Negative Substrate Bias Voltage

Glow discharge mass spectrometry (GDMS) was used to analyze a Ta target and Ta films for trace impurities. The Ta films were deposited on Si (100) substrate at substrate bias voltages of 0 V and -125 V using a non-mass separated ion beam deposition system. Although both Ta films were contaminated by impurities during the deposition, the Ta film deposited at a substrate bias voltage of -125 V showed lower impurity content than the Ta film deposited without the substrate bias voltage, which means that applying a negative bias voltage to the substrate decreased the total concentration of impurities. Furthermore, the concentration change of individual impurities in the Ta film is related to their ionization ratio in the argon discharge plasma. Considering the effect of the ionization potential of an individual impurity on the ionization ratio, purification by applying a negative bias voltage to the substrate results from Penning ionization and an ionization mechanism proposed in this study, as well as from the difference between the kinetic energies of Ta neutral atoms and Ta+ ions accelerated toward the substrate with/without a negative substrate bias voltage.

Effect of substrate bias voltage on the purity of Cu films deposited by non-mass separated ion beam deposition

Cu films were deposited on Si (1 0 0) substrates at room temperature by a non-mass separated ion beam deposition method. The effect of the negative substrate bias voltage on the property of the Cu films was investigated by using field emission scanning electron microscopy and secondary ion mass spectroscopy. The Cu film deposited at the negative bias voltage of −50 V showed an extremely fine and homogeneous morphology without a columnar structure. The purity of the Cu film deposited at the bias voltage of −50 V was much improved in comparison with the 6N Cu target, while the Cu film deposited without applying substrate bias voltage contained more impurities than the 6N Cu target.

Characteristics of ion beam deposited copper thin films as a seed layer: effect of negative substrate bias voltage

Cu thin films as a seed layer were deposited on Si (1 0 0) substrates by applying a negative substrate bias voltage using a non-mass separated ion beam deposition method. Using resistivity measurement, X-ray diffraction analysis, atomic force microscopy, secondary ion mass spectroscopy, and scanning electron microscopy, the Cu films were characterized. The Cu films deposited at the substrate bias voltage of −50 V showed higher purity, strong (1 1 1) preferred orientation, smoother surface and better step coverage in comparison with the Cu films deposited without the substrate bias voltage. The thickness dependence of the resistivity showed clear size effects with decreasing the film thickness. In the case of Cu (100 nm)/Ta (50 nm)/Si structures, the Cu films deposited on Ta/Si substrates by applied the substrate bias voltage maintained a completely (1 1 1) preferred orientation without (2 0 0) texture even after thermal annealing at 450 °C for 60 min.

Effect of Substrate Bias Voltage on the Thermal Stability of Cu/Ta/Si Structures Deposited by Ion Beam Deposition

The interfacial reactions of the Cu (100 nm)/Ta (50 nm)/Si structures and their relationship with the microstructure of Ta diffusion barrier are investigated. Ta films were deposited on Si (100) substrates using a non-mass separated ion beam deposition system at various bias voltages ranging from 0 to -200 V. An optimum applied substrate bias voltage of -125 V was found to yield a dominant α-Ta film with a noncolumnar structure, low electrical resistivity (about 40 µΩcm) and smooth surface. A Ta diffusion barrier which was deposited at the optimum bias voltage prevented Cu–Si interaction up to 600°C for 60 min in flowing purified H2, whereas a Ta layer with a columnar structure, deposited at zero bias voltage, degraded at 300°C. Two different reactions of the Cu/Ta (0 V)/Si and the Cu/Ta (-125 V)/Si structures concerning the thermal stability were investigated and discussed on the basis of the experimental results.

Effect of substrate bias voltage on the texture and microstructure of Cu thin films deposited by ion beam deposition

Cu thin films deposited by non-mass separated ion beam deposition under various substrate bias voltages were investigated. The film textures and microstructure were analyzed by X-ray diffraction and field emission scanning electron microscopy, and the resistivity of the film was measured with the Van der Pauw method. It was found that the optimum negative substrate bias voltage for Cu films was −50 V. The Cu films deposited without substrate bias voltage showed a columnar grain structure with small grains and random orientation. However, when a substrate bias voltage of −50 V was applied, the Cu films had a non-columnar structure with a strong (111) texture and large grains. The electrical resistivity of the Cu films decreased remarkably with increasing negative substrate bias voltage, and reaching a minimum value of 1.8±0.13 μΩ cm at the substrate bias voltage of −50V.

Preparation of high-purity Cu films by non-mass separated ion beam deposition

Cu films were deposited on Si(1 0 0) substrates by applying a negative substrate bias voltage using non-mass separated ion beam deposition (IBD) method. By the SIMS results with Cs + ion beam, the Cu film deposited at V S=0 V was found to contain more impurities than the Cu film deposited at V S=−50 V. On the other hand, from the SIMS results with O 2 + ion beam, it was found that elements which are easy to be positive ions such as B, Mg, Na, Al, K, Ca and Fe seem to be increased slightly as compared to the those of the Cu film deposited at V S=0 V. As a result, higher-purity Cu film deposited at V S=−50 V could be obtained in comparison with the film deposited at V S=0 V. The purification effect of the Cu film deposited at V S=−50 V was described in details.

Suppression of Cu agglomeration in the Cu/Ta/Si structure by capping layer

Cu/Ta/Si (100) structures deposited by the non-mass separated ion beam deposition system showed a slight resistivity increase at 650 °C due to a Cu agglomeration. To suppress the Cu agglomeration on the Ta layer, a capping layer was deposited on the Cu/Ta/Si structure using Ta or SiO2 as a suppressor. In the case of the Ta suppressor, the agglomeration of Cu was observed between two distorted Ta films due to the difference in thermal expansion between the Cu filmand the Ta film at high temperature. On the other hand, the SiO2 layer was found to be suitable as a suppressor, and the Cu agglomeration did not occur even after annealing at 650 °C by the suppression of the Cu diffusion.

Improvement of Ta Barrier Film Properties in Cu Interconnection by Using a Non-mass Separated Ion Beam Deposition Method

Ta/Si (100) and Cu/Ta/Si (100) film structures were fabricated by using ion beam deposition with a modified RF sputter-type ion source, in which a strong RF discharge was introduced in order to enhance the plasma density. For Ta/Si structures, Ta films were deposited at various bias voltages. When the substrate bias voltage was not applied, the Ta film showed a columnar structure and had a high resistivity of 2600 nΩm. On the other hand, when the substrate bias voltage of -50- - 200 V was applied, the cross-sectional observation did not show columnar structure at all. In this case, film deposition was considered to be sufficient migration energy by the accelerated Ta + ions. In particular, Ta films deposited at a bias voltage of -125 V had a very small resistivity of 360 nΩm. Thermal stability of Cu(100 nm)/Ta(50 nm)/Si films, where Ta plays a role of diffusion barrier, was evaluated after annealing in H 2 atmosphere for 60 min at various temperatures. Non-columnar structure Ta films deposited at substrate bias voltages of -50 V and -125 V were found to be stable up to 600°C, while columnar structure Ta films deposited at zero bias voltage degraded at 300°C. This result indicates that the thermal stability of the Ta films is mainly governed by the film microstructure of the deposited layer.

Ion bombardment-type high frequency metal ion source for compact ion beam deposition apparatus

A novel metal ion source has been developed for a compact nonmass-separated ion beam deposition apparatus. To produce a dense plasma, a high frequency (hf) antenna coil made of Cu was mounted inside the metallic ionization chamber and a hf power of 300 W (13.56 MHz) was applied to this coil. A Cr rod target 10 mm in diameter was fitted at the center of the hf coil and a dc bias voltage of −600 V was applied to it. The temperature of a tip of the Cr rod target increased locally by means of ion bombardment; the Cr target material vaporized vigorously by sublimation and effectively ionized in the high density plasma. A pure Cr ion current of 400 μA was obtained at an energy of 100 eV without mass separation. Circular Cr thin films of 10 mm in diameter and 500 nm in thickness were deposited on Si substrates at a deposition rate of 30 nm/min at an ion energy of 100 eV. No contamination due to a sputtering of Cu antenna coil was detected by X-ray fluorescence analysis.