• PDF / 822,894 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 2 Downloads / 280 Views

DOWNLOAD

REPORT

---

Direct Bonding of Silicon Wafers with Simultaneous Dopant Diffusion Igor V. Grekhov, Tatiana S. Agrunova, Lioudmila S. Kostina, Natalia M. Shmidt, Helmut Föll1, and Konstantin B. Kostin1 Solid State Electronics Division, Ioffe Physico-Technical Institute RAS, Polytekhnicheskaya ul. 26, 194021, St. Petersburg, RUSSIA 1

Materials Science Department, Christian-Albrechts-University of Kiel, Kaiserstr. 2, Kiel 24143, GERMANY ABSTRACT Bonding of silicon surfaces in aqueous solution of compounds containing III and IV impurities was performed for the first time. It was observed that the presence of aluminum at the bonding interface improved structural quality of the interface. This phenomenon is explained by the increase of the contact area due to Al-OH group sandwiched between the water molecules adsorbed at hydrophilic wafer surfaces at the first bonding stage. The incorporation of Al produces a p-type layer and the I/V characteristics of the resultant np+n diodes is shown not to be influenced by the presence of the bonding interface. The technique developed could be advantageous for the design of multi-layer large area semiconductor devices. INTRODUCTION Direct bonding technology can be used to bond partially or fully processed wafers to desired substrates [1,2]. However, doping selected areas or heavy doping of the whole wafer as required for device manufacturing before bonding often results in a deterioration of the wafer surface quality as well as in elastic strain. Bonding than may be difficult and imperfect or impossible. Large area bonding with an oxide free interface under those conditions remains a challenge up to now. In a monograph [1] and two reviews [2,3] different aspects of this problem– bonding conditions, reasons of bubble appearance, real surface structure influence–are discussed in detail. To decrease the detrimental influence of elastic strain and an imperfect surface morphology on bonding and the structural quality of the bonding interface, a grooved-surface direct bonding technology was suggested [4,5]. In this paper, the formation of p- or n-type layers in silicon wafers is proposed to be performed directly in the course of the direct bonding procedure by supplying a diffusion source placed between the wafers to be bonded. The structural and electronic quality of the resulting structural and electronic junctions was investigated and found to be very good for Al-based diffusion source. A model is suggested to explain the high interface continuity in the structures with interfacial aluminum. EXPERIMENTAL DETAILS Commercially available mirror-polished float-zone (FZ) n- and p- type silicon wafers of ~20 Ω·cm as well as p-type Czochralski (CZ) wafers of 0.005 Ω·cm, both 40-60 mm in diameter and (111) orientation, were used. An orthogonal net of grooves with a depth 0.2-0.3 µm, a width 50 µm and spaced at 200 µm, was made by photolithography on the surface of one wafer from each pair before bonding. The bonding procedure included the following steps: 1) the wafer I5.7.1

RCA cleaning; 2) the wafer atta