Production of semiconductor device

A method of opposing and joining a surface of a solid device and a surf ace of a semiconductor chip. A metal electrode portion formed in a raised state on the surface of the solid device and a metal electrode portion formed in a raised state on the surface of the semiconductor chip are directly abutted and pressed against each other. In the state, ultrasonic vibration is transmitted to the metal electrode portions which are pressed against each other, to join the metal electrode portions to each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A, 1B and 1 C are illustrative cross-sectional views showing the steps of a method of producing a semiconductor device according to an embodiment of the present invention. The producing method shown in FIGS. 1A to 1 C is a method of producing a semiconductor device having a chip-on-chip structure by mounting a secondary chip (daughter chip) 20 on a surface 11 of a primary chip (mother chip) 10 serving as a solid device by a face-down method. The primary chip 10 and the secondary chip 20 are composed of silicon, for example. The surface 11 of the primary chip 10 is a surface, on the side of an active surface layer region on which functional devices such as a transistor forming an internal circuit are formed, of a semiconductor substrate forming a base body of the primary chip 10 . The uppermost surface is covered with a protective film composed of an insulating material. Similarly, a surface 21 of the secondary chip 20 is a surface, on the side of an active surface layer region on which functional devices forming an internal circuit are formed, of a semiconductor substrate forming a base body of the secondary chip 20 . The uppermost surface is covered with a protective film composed of an insulating material. A plurality of bumps 12 composed of gold, for example, are formed in a raised state on the surface 11 of the primary chip 10 . On the other hand, a plurality of bumps 22 composed of gold, for example, are formed in a raised state at positions, corresponding to the bumps 12 on the primary chip 10 , on the surface 21 of the secondary chip 20 . The bumps 12 and 22 can be formed by respectively forming openings in the protective films covering the uppermost surfaces of the primary chip 10 and the secondary chip 20 to expose internal wirings and then, gold-plating the exposed wirings. The secondary chip 20 is mounted on the primary chip 10 by a so-called face-down method with the surface 21 on which the bumps 22 are formed directed toward the surface 11 of the primary chip 10 . Specifically, the primary chip 10 and the secondary chip 20 are aligned with each other such that the bumps 22 on the secondary chip 20 can be respectively abutted against the bumps 12 on the primary chip 10 . Thereafter, the primary chip 10 and the secondary chip 20 are made to approach, to respectively abut the bumps 22 on the secondary chip 20 against the bumps 12 on the primary chip 10 , as shown in FIG. 1A . The approaching step of the primary chip 10 and the secondary chip 20 may be carried out after aligning the primary chip 10 and the secondary chip 20 , or may be carried out simultaneously with the alignment. As shown in FIG. 1 B, ultrasonic vibration at a predetermined energy is transmitted to the secondary chip 20 while pressing the secondary chip 20 against the primary chip 10 using a ultrasonic horn H. The ultrasonic vibration transmitted to the secondary chip 20 from the ultrasonic horn H propagates through the secondary chip 20 , to reach a joint surface between the bump 22 on the secondary chip 20 and the bump 12 on the primary chip 10 . Therefore, a shear force along the joint surface between the bump 22 on the secondary chip 20 and the bump 12 on the secondary chip 10 is exerted on the joint surface by the ultrasonic vibration in addition to a pressing force by pressing the secondary chip 20 . Even if an impurity layer adheres to surfaces of the bumps 12 and 22 , the impurity layer is torn by the shear force, exposing the surfaces of the bumps 12 and 22 . Consequently, the surface of the bump 12 and the surface of the bump 22 are directly brought into contact with each other, and gold which is a material composing the bumps 12 and 22 is satisfactorily diffused. Accordingly, the bump 12 and the bump 22 are bonded (ultrasonically welded). Time required for the bonding is relatively short, for example, approximately 0.2 seconds. When the joining between the bump 12 on the primary chip 10 and the bump 22 on the secondary chip 20 using ultrasonic waves is thus completed, mounting of the secondary chip 20 on the primary chip 10 is achieved, as shown in FIG. 1C . As described in the foregoing, according to the present embodiment, it is possible to bond the bump 12 on the primary chip 10 and the bump 22 on the secondary chip 20 to each other in a short time by transmitting the ultrasonic vibration to the joint surface between the bump 12 and the bump 22 while pressing the bump 22 against the bump 12 to directly bring the bumps into contact with each other. Accordingly, time required to produce the semiconductor device can be made shorter, as compared with that in the method of connecting the primary chip 10 and the secondary chip 20 with an anisotropic conductive film interposed therebetween. Even if the impurity layer adheres to the surfaces of the bumps 12 and 22 , the adhering impurity layer is torn by the transmission of the ultrasonic vibration. Consequently, gold composing the bumps 12 and 22 can be satisfactorily diffused between the bump 12 and the bump 22 , thereby making it possible to reliably bond the bump 12 and the bump 22 . Although description has been made of one embodiment of the present invention, the present invention can be also embodied in another embodiment. Although both the primary chip 10 and the secondary chip 20 are assumed to be composed of silicon, for example, they may be semiconductor chips using another arbitrary semiconductor material such as a compound semiconductor (for example, a gallium arsenide semiconductor) or a germanium semiconductor in addition to silicon. In this case, a semiconductor material for the primary chip 10 and a semiconductor material for the secondary chip 20 may be the same or different from each other. Although in the above-mentioned one embodiment, a case where the present invention is applied to a method of producing a semiconductor device having a chip-on-chip structure is taken as an example, the present invention is also applicable to a method of producing a semiconductor device having a flip-chip bonding structure for opposing and joining by a face-down method a surface of a semiconductor chip to a surface of a wiring board serving as a solid device. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. The application claims the conventional priority benefits of Japanese Patent Application Serial No. 11-184185 filed with the Japanese Patent Office on Jun. 29, 1999, the disclosure of which is incorporated herein by reference.