Handbook of Sputter Deposition Technology (eBook)

Fundamentals and Applications for Functional Thin Films, Nano-Materials and MEMS

Kiyotaka Wasa (Autor)

eBook Download: PDF | EPUB

2012 | 2. Auflage
660 Seiten
Elsevier Science (Verlag)
978-1-4377-3484-3 (ISBN)

Infos

This thoroughly updated new edition includes an entirely new team of contributing authors with backgrounds specializing in the various new applications of sputtering technology. It forms a bridge between fundamental theory and practical application, giving an insight into innovative new materials, devices and systems.

Organized into three parts for ease of use, this Handbook introduces the fundamentals of thin films and sputtering deposition, explores the theory and practices of this field, and also covers new technology such as nano-functional materials and MEMS.

Wide varieties of functional thin film materials and processing are described, and experimental data is provided with detailed examples and theoretical descriptions.

1. A strong applications focus, covering current and emerging technologies, including nano-materials and MEMS (microelectrolmechanical systems) for energy, environments, communications, and/or bio-medical field. New chapters on computer simulation of sputtering and MEMS completes the update and insures that the new edition includes the most current and forward-looking coverage available.
2. All applications discussed are supported by theoretical discussions, offering readers both the 'how' and the 'why' of each technique.

40% revision: the new edition includes an entirely new team of contributing authors with backgrounds specializing in the various new applications that are covered in the book and providing the most up-to-date coverage available anywhere.

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This thoroughly updated new edition includes an entirely new team of contributing authors with backgrounds specializing in the various new applications of sputtering technology. It forms a bridge between fundamental theory and practical application, giving an insight into innovative new materials, devices and systems. Organized into three parts for ease of use, this Handbook introduces the fundamentals of thin films and sputtering deposition, explores the theory and practices of this field, and also covers new technology such as nano-functional materials and MEMS. Wide varieties of functional thin film materials and processing are described, and experimental data is provided with detailed examples and theoretical descriptions. A strong applications focus, covering current and emerging technologies, including nano-materials and MEMS (microelectrolmechanical systems) for energy, environments, communications, and/or bio-medical field. New chapters on computer simulation of sputtering and MEMS completes the update and insures that the new edition includes the most current and forward-looking coverage available All applications discussed are supported by theoretical discussions, offering readers both the "e;how"e; and the "e;why"e; of each technique 40% revision: the new edition includes an entirely new team of contributing authors with backgrounds specializing in the various new applications that are covered in the book and providing the most up-to-date coverage available anywhere

Textauszug

2

Sputtering Phenomena

Kiyotaka Wasa

Chapter Outline

2.1 Sputter Yield

2.1.1 Ion Energy

2.1.2 Incident Ions, Target Materials

2.1.3 Effects of Incidence Angle

2.1.4 Crystal Structure of Target

2.1.5 Sputter Yields of Alloys

2.2 Sputtered Atoms

2.2.1 Features of Sputtered Atoms

2.2.2 Velocity and Mean Free Path

Velocity of Sputtered Atoms

Mean Free Path

2.3 Mechanism of Sputtering

2.3.1 Sputtering Collisions

2.3.2 Sputtering Model

Classical Empirical Formula of Sputtering Yield

Linear Cascade Collision Theory

Simplified Model and Modern Yield Formula

Computer Simulation

References

Sputtering was first observed in a DC gas discharge tube by Grove in 1852. He discovered the cathode surface of the discharge tube was sputtered by energetic ions in the gas discharge, and cathode materials were deposited on the inner wall of the discharge tube.

At that time sputtering was regarded as undesired phenomena since the cathode and grid in the gas discharge tube were destroyed. Today, however, sputtering is widely used for surface cleaning and etching, thin film deposition, surface and surface layer analysis, and sputter ion sources.

In this chapter, the fundamental concepts of the various sputtering technologies are described. The energetic particles in sputtering are ions, neutral atoms, neutrons, electrons, and/or photons. Since most relevant sputtering applications are performed under bombardment with ions, this text deals with that particular process.

2.1 Sputter Yield

The sputter yield S, which is the removal rate of surface atoms due to ion bombardment, is defined as the mean number of atoms removed from the surface of a solid per incident ion and is given by

(2.1)

Sputtering is caused by the interactions of incident ions with target surface atoms. The sputter yield will be influenced by the following factors:

1. Energy of incident ions

2. Target materials

3. Incident angles of ions

4. Crystal structure of the target surface.

The sputter yield S can be measured by the following methods:

1. Weight loss of target

2. Decrease of target thickness

3. Collection of the sputtered materials

4. Detection of sputtered particles in flight.

The sputter yield is commonly measured by weight loss experiments using a quartz crystal oscillator microbalance (QCOM) technique. Surface analysis techniques including RBS are available for measuring the change in thickness or composition of targets on an atomic scale during sputtering. RBS is essentially nondestructive and the dynamic sputter yield is determined with a priori accuracy of some 10%. SEM and stylus techniques are used for the measurement of minute change in target thickness. These techniques need an ion erosion depth in excess of around 0.1 µm. The QCOM technique is sensitive probing method with submonolayer resolution.1

Both electron and proton probe beam techniques are also used successfully in situ dynamic and absolute yield determinations. AES could also be used for the determination of monolayer thickness. Particle-induced X-ray emission (PIXE) with proton energy of 100–200 keV2 and electron-induced X-ray emission with electron energy of around 10 keV are also used for the sputter yield measurement.3 The PIXE technique can quantify both initial surface impurities and the pure sputter yield of the target.

2.1.1 Ion Energy

Figure 2.1 shows a typical variation of the sputtering yield with incident ion energy. The figure suggests:

1. In a low-energy region, threshold energy exists for the sputtering.

2. The sputter yield shows maximum value in a high-energy region.

Figure 2.1 Variations of sputter yield with incident ion energy.

Hull first observed the existence of the sputtering threshold in 1923. He found that the Th–W thermionic cathode in gas rectifier tubes was damaged by bombardment with ions when the bombarding ion energy exceeded a critical value, which was in the order of 20–30 eV.4 The sputtering threshold has been studied by many workers because it is probably related to the mechanism of sputtering. Threshold values obtained by these workers ranged from 50 to 300 eV.5,6 Their results were somewhat doubtful because the threshold energy was mainly determined by measurements of small weight loss from the cathode in the range of 10−4 atoms/ion. The threshold energy is very sensitive to contamination of the cathode surface. In addition, the incident angle of ions and the crystal orientation of cathode materials also change the threshold values.

In 1962, Stuart and Wehner7 skillfully measured reliable threshold values by the spectroscopic method. They observed that threshold values are in the order 15–30 eV, similar to the observations of Hull, and are roughly 4 times the heat of sublimation of cathode materials.

A gas discharge tube used by Stuart and Wehner7 is shown in Fig. 2.2. The target is immersed in plasma generated by a low-pressure mercury discharge. In a noble gas discharge, the mercury background pressure is about 10−5 Torr (1.33×10−3 Pa) or less. The temperature of the target is kept at about 300°C so as to reduce condensation of the mercury vapor. The sputtered target atoms are excited in the plasma and emit the specific spectrum. The sputter yields at low energy are determined by the intensity of the spectral line. This technique eliminates the need for very sensitive weight measurements.

Figure 2.2 Experimental apparatus for the measurements of the threshold energy.7

Typical sputter yields in a low-energy region measured by Stuart and Wehner are shown in Fig. 2.3. The threshold values determined in the sputter yields are in the order of 10−4–10−5 atoms/ion. Table 2.1 summarizes the sputtering threshold energy measured by the spectroscopic method for various target materials.7,8

Figure 2.3 Sputter yield in a low-energy region.7

Table 2.1 Sputtering Threshold Data7,8

H, heat of sublimation.

The table suggests that there is not much difference in threshold values. The lowest value, which is nearly equal to 4 times the heat of sublimation, is observed for the best mass fit between target atom and incident ion. The higher threshold energy is observed for poor mass fits.

The threshold energy also strongly depends on the particular sputtering collision sequence involved. High threshold energy (i.e., Eth/U0>10 for Ar+→Cu, where Eth denotes the threshold energy; U0, the heat of sublimation) will be expected in the collision sequence where primary recoil produced in the first collision is ejected directly. Lower values will be observed for the multiple sputtering collisions. An incident angle of around 40–60° offers the minimum threshold energy (i.e., Eth/U02 for Ar+→Cu) under the multiple sputtering collisions.9

The sputter yield varies with the incident ion energy E. In the low-energy region near the threshold, S obeys the relation S∝E2 as seen in Fig. 2.1. This occurs at the energy region in the order of 100 eV, S∝E.6,10 In this energy region, the incident ions collide with the surface atoms of the target, and the number of displaced atoms due to the collision will be proportional to the incident energy.

At higher ion energies of 10–100 keV, the incident ions travel beneath the surface and the sputter yields are not governed by the surface scattering but by the scattering inside of the target. Above 10 keV, the sputter yields will decrease due to energy dissipation of the incident ions deep in the target.

Maximum sputter yields are seen in the ion energy region of about 10 keV. Figure 2.4 summarizes the energy dependence of the yield, i.e., the sputter rate, as reported by Sigmund.11

Figure 2.4 Sputter yield as a function of incident ion energy.11

2.1.2 Incident Ions, Target Materials

Sputter yield data have been extensively accumulated in relation to gas discharges, sputter deposition, etching, surface analysis, and radiation damage. At first, sputter yields were measured in the cold cathode discharge tube.12,13 But these measurements did not offer reliable data because the incident ions and sputtered atoms frequently collide with discharge gas molecules in the cold cathode discharge tube.

Laegreid and Wehner,14 in 1959, accumulated the first reliable data of sputter yields in a low gas pressure discharge tube. At present, this yield data is still widely used for sputtering applications. Figure 2.5...

Produkt-Details

• Erscheint lt. Verlag: 31.12.2012
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie ► Physikalische Chemie
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 1-4377-3484-7 / 1437734847
• ISBN-13: 978-1-4377-3484-3 / 9781437734843