Direct bonding energy relates to the well-known “strength” or “toughness” of direct bonding interface. It is the energy needed to separate two bonded surfaces. In contrast, adhesion energy is the energy available to bring the two surfaces together. Due to hysteretic effects, the two energies may be different and, while the first energy has been largely measured, the second one is the subject of very few papers only [1, 2, 3].

In this study, a new phenomenon will be shown in the adhesion energy behaviour using two silicon wafers. As shown in figure 1b, several partial debondings and rebondings of the same silicon direct bonding structure result in an increase of the bonding wave speed. After reaching a maximum bonding wave speed, a full debonding brings the speed back to its initial value. As it has already been shown theoretically by Rieutord et al. [4] and verified experimentally by Larrey et al. [3], the bonding wave speed is linked to the adhesion energy of the system. Therefore, an increase of the bonding wave speed consequently indicates an increase of the adhesion energy. As shown in figure 1b, multiple partial debondings increase the bonding wave speed by more than 50%, which increases the adhesion energy by more than 40%. The relationship between adhesion energy and bonding wave speed is not linearly dependent, as defined in the equation of figure1a [4] and shown in figure1c.

Different experiments have been done to find the cause of this peculiar behavior. A model will be proposed and discussed.

REFERENCES

[1] D. Grierson and K.T. Turner, ECS Trans. 33, 573 (2010).

[2] D. Radisson, Direct Bonding of Patterned Surfaces, phdthesis, Université Grenoble Alpes, 2014.

[3] V. Larrey, G. Mauguen, F. Fournel, D. Radisson, F. Rieutord, C. Morales, C. Bridoux, and H. Moriceau, ECS Trans. 75, 145 (2016).

[4] F. Rieutord, B. Bataillou, and H. Moriceau, Physical Review Letters 94, (2005).