**2. Low-temperature bonding using ion beam etching**

For bonding at lower temperature, surface refresh is one of the effective methods, because contamination such as oxide scale and inclusion is formed at material surface exposed in the atmosphere. The contamination usually prevents from bonding of the materials. High-energy ion beam irradiation is useful for cleaning of the contaminated material surface. When the ion beam irradiation and the bonding of materials having the refreshed surface are done at same high-vacuum environment (without exposing atmosphere), bonding of both activated surfaces is achieved without suing a high temperature. This method is usually called "surface activation method" (**Figure 1**) [7].

Research group of Suga has studied several combination of similar- and dissimilarmaterial bonding (Si/Si [8, 9], Al/Al [10], Cu/Cu [8], Si/SiO2 [11]) using the surface activation method. Especially, aluminum always has strong oxide scale at the surface, but smooth and clear bonding interface without voids is formed by using this method (**Figure 2**) [10]. This indicates that ion beam irradiation is an effective

**49**

*Room-Temperature Formation of Intermixing Layer for Adhesion Improvement of Cu/Glass…*

*TEM images of (a) Al/Al [10] and (b) Cu/Cu [8] interfaces fabricated by surface activation bonding.*

method for removing the oxide scale. Also, achievement of bonding of Si and Si suggests that this method can be used for brittle materials. In addition, Takagi et al. reported the bonding of Si and SiO2 using the surface activation method [11]. This indicates that this method can be achieved by the dissimilar-material bonding. A report on Cu/glass (Cu/SiO2) bonding using the surface activation method also existed [12]. When the bonding temperature is increased to 423 K, good adhesion is obtained (**Figure 3**). The process temperature is very low than that of conventional diffusion bonding. This is considered to indicate that the surface cleaning by the ion

**3. Room-temperature formation of adhesion layer utilizing for adhesion** 

As mentioned in Section 1, formation of adhesion layer at Cu/glass interface is an effective method for improvement of adhesion. Recently, we demonstrate roomtemperature formation of Cu/glass stack with high adhesion strength [13, 14]. This adhesion improvement is due to effect of ZnO-based adhesion layer formed at room

beam irradiation is effective for the lower-temperature bonding.

**improvement of Cu/glass stacks**

*Cu/SiO2 interface fabricated by surface activation bonding [12].*

*DOI: http://dx.doi.org/10.5772/intechopen.84362*

**Figure 2.**

**Figure 3.**

**Figure 1.** *Surface activation bonding method [11].*

*Room-Temperature Formation of Intermixing Layer for Adhesion Improvement of Cu/Glass… DOI: http://dx.doi.org/10.5772/intechopen.84362*

#### **Figure 2.**

*Lead Free Solders*

these metals must be deposited with sequential high-vacuum deposition methods, which do not give a good step coverage. In addition, reactions between Cu and those metals can lead to a significant increase in resistance when the Cu film is thin.

Koike et al. have investigated the interfacial properties of the annealed Cu-Mn/ glass structure and reported that adhesion improvement was observed by formation of a several nm thick Mn oxide layer at the interface [1, 2]. Yi et al. reported the formation of interfacial layer by annealing in Cu-Mg/glass and showed that the adhesion strength improved by formation of a Mg oxide layer at the interface [3]. Other elements, such as Al, Ti, and Cr, added to Cu were studied previously, and they were reported to improve the adhesion strength between Cu and various substrates (not only glass) [4–6]. These studies mentioned above indicate that the effective adhesion layers contain elements that are easily oxidizable and miscible in Cu. However, it should be noted that these studies required heat treatment during/after deposition. For achieving the general trend of temperature reduction during microelectronic fabrication, room-temperature or lower-temperature adhesion improvement is required.

For bonding at lower temperature, surface refresh is one of the effective methods, because contamination such as oxide scale and inclusion is formed at material surface exposed in the atmosphere. The contamination usually prevents from bonding of the materials. High-energy ion beam irradiation is useful for cleaning of the contaminated material surface. When the ion beam irradiation and the bonding of materials having the refreshed surface are done at same high-vacuum environment (without exposing atmosphere), bonding of both activated surfaces is achieved without suing a high temperature. This method is usually called "surface activation method" (**Figure 1**) [7]. Research group of Suga has studied several combination of similar- and dissimilarmaterial bonding (Si/Si [8, 9], Al/Al [10], Cu/Cu [8], Si/SiO2 [11]) using the surface activation method. Especially, aluminum always has strong oxide scale at the surface, but smooth and clear bonding interface without voids is formed by using this method (**Figure 2**) [10]. This indicates that ion beam irradiation is an effective

**2. Low-temperature bonding using ion beam etching**

**48**

**Figure 1.**

*Surface activation bonding method [11].*

*TEM images of (a) Al/Al [10] and (b) Cu/Cu [8] interfaces fabricated by surface activation bonding.*

#### **Figure 3.**

*Cu/SiO2 interface fabricated by surface activation bonding [12].*

method for removing the oxide scale. Also, achievement of bonding of Si and Si suggests that this method can be used for brittle materials. In addition, Takagi et al. reported the bonding of Si and SiO2 using the surface activation method [11]. This indicates that this method can be achieved by the dissimilar-material bonding. A report on Cu/glass (Cu/SiO2) bonding using the surface activation method also existed [12]. When the bonding temperature is increased to 423 K, good adhesion is obtained (**Figure 3**). The process temperature is very low than that of conventional diffusion bonding. This is considered to indicate that the surface cleaning by the ion beam irradiation is effective for the lower-temperature bonding.
