JP2005200707A - Low stress electroless nickel plating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein it is impossible to convey a wafer by an air suction system and it is difficult to work the wafer in a succeeding process because of that when nickel plating is applied to a wafer, a nickel film shrinks, thus shrinkage stress is applied to an electrode part in a base material tightly stuck thereto to cause the warpage of the wafer. <P>SOLUTION: Molybdenum is added to an electroless nickel bath, and molybdenum is precipitated into a deposited nickel film, thus the generation of internal stress in the film is suppressed, and the warpage of a wafer can be stopped. The stress is large after heat treatment compared with that in plating, but, by incorporating molybdenum into the nickel film, it is effective also on heat treatment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor wafer and chip surface coating.

  In recent years, semiconductor mounting has shifted to surface mounting in which a chip is mounted on a lead frame or a package with leads and then mounted on a substrate.

  Conventionally, an IC or a transistor electrically connects a chip to a lead frame or a package with leads. The wire bonding method has been used as the conduction method.

  On the other hand, in surface mounting such as flip chip and wafer level package (WLP), mounting on a substrate has been performed by using gold bumps or solder bumps on which chip electrodes can be easily mounted.

  However, since gold bumps and solder bumps need to be sputtered in vacuum and require large-scale equipment, a wet film-forming method (hereinafter referred to as plating) has recently been used. Has been developed.

  Among the electroless plating methods using chemical reactions among electroplating, there is electroless nickel plating.

  Conventionally, when electroless nickel plating is performed, stress is generated at the time of film formation and after heat treatment. Therefore, the plated base material is deformed by the stress of the plating film.

JP2002-231970

JP 2003-96573 A JP2003-313669 Tetsuya Osaka, Masahiko Usuda, Ichiro Koiwa, Hideo Sawai; Metal Surface Technology, vol.39, NO11, 37-43p (1990) Tetsuya Osaka, Naganori Masume, Katsuya Arai, Yasuyuki Okuno; Surface Technology, vol.41, NO1, 49-52p (1990)

  In order to improve solderability, aluminum electrodes in flip chip and wafer level package (WLP) are subjected to electroless nickel plating and further gold plating.

  There are a lot of wafers to become chips, and the wafer is made into chips by dicing. Each chip is provided with a large number of pads serving as electrodes.

  When electroless nickel plating is performed on a large number of pads existing on a wafer, stress is generated during film formation and after heat treatment, which causes warping of a wafer that is an original of a flip chip or wafer level package (WLP). Further, after the electroless nickel plating, the temperature becomes 250 ° C. or higher during the soldering operation, so that the crystal in the deposited nickel is changed, and a compressive force is applied to the nickel film.

  On the other hand, the wafer has shifted from the conventional 650 μm to a thinner one, and 200 μm to 100 μm wafers are also produced. Therefore, if the nickel film contracts during plating, shrinkage stress is applied to the electrode part of the base material that is in close contact, and the wafer is It will warp. For this reason, problems such as the fact that the wafer cannot be transferred by the air suction method in the subsequent process and the processing of the wafer is difficult have occurred.

  The present invention is a nickel plating method in which a wafer does not warp, and an appropriate amount of molybdenum (hereinafter referred to as Mo) is added as an additive in an electroless nickel plating solution. It is characterized by relieving internal stress.

  When an appropriate amount of Mo is added to the electroless nickel plating, the stress inside the nickel film is reduced, so that the change in the shape of the wafer is eliminated and the wafer after the nickel film treatment is easily processed. In particular, since the thickness of the wafer has recently been reduced, the present invention makes it possible to significantly reduce the cost of sizing a wafer and manufacturing semiconductor components such as semiconductor integrated circuits, transistors, and diodes.

  Mo can be added to the electroless nickel plating solution, and Mo can be co-deposited in the nickel film, thereby relieving the stress of the nickel film.

  Table 1 shows the plating solution composition in which Mo is added to electroless nickel and electroless nickel plating solution.

  The size of the wafer used is 6 inches in diameter and the thickness is 120 μm. The plating solution was adjusted from PH8 to 10 and controlled at 60 ° C. During plating, air agitation was performed and experiments were performed at a thickness of 1 to 3 µm. Molybdic acid is replenished to the plating solution by a dropping method.

  In the electroless nickel plating process, the dirt on the wafer is removed by a degreasing process, and an activation process is performed with an acid. Next, after carrying out the catalyzing step, electroless nickel plating is performed, and finally the surface is covered with substitution gold. In addition, electroless nickel plating can be performed by zincate treatment.

  After plating the pads on the wafer with an electroless nickel plating solution and a plating solution in which Mo is added to the electroless nickel plating solution, a strip electrodeposition stress measuring instrument (manufactured by Electrochemical, USA; hereinafter referred to as a stress tester) The measurement was performed.

  As shown in Table 2, Mo in the nickel film is increased by the addition of molybdic acid. Further, the stress in the film is a compressive stress, and decreases with the addition of Mo as shown in Table 2 by a stress tester. However, if the amount of Mo is too large, the corrosion resistance of the film is deteriorated.

  Moreover, when the film is heat-treated, the value by the stress tester increases and the compressive stress increases. The test temperature was up to 400 ° C. as shown in Table 3, but increased up to 350 ° C. and slightly decreased at 400 ° C. However, in practical use, it cannot be used at 350 ° C. or higher because the polyimide on the wafer is altered.

  An appropriate amount of added Mo is determined from the warpage of the wafer, and it is necessary that the nickel film contains Mo in an amount of 0.90 at% or more. However, if Mo is contained at 5.5 at% or more, the corrosion resistance is deteriorated, which is a practical problem.

Currently, since a warp occurs when a nickel film is formed on a wafer, it is necessary to make the wafer to be plated thick, and unnecessary thickness is removed by back grinding. In the present invention, since the stress inside the nickel plating film is reduced, it is possible to cope with even a thin wafer, and the reduction of man-hours and the improvement of plating adhesion are ensured.

Claims (8)

Wafer with nickel coating containing 0.9at% to 5.5at% molybdenum Semiconductor component with nickel coating containing 0.9at% to 5.5at% molybdenum Semiconductor component having a film containing 0.9at% to 5.5at% molybdenum in a film formed by electroless nickel plating Wafer having a film containing 0.9 to 5.5 at% molybdenum in a film formed by electroless nickel plating to a thickness of 1 to 3 micrometers A semiconductor integrated circuit having a film containing 0.9 at% to 5.5 at% of molybdenum in a film formed by electroless nickel plating to a thickness of 1 to 3 micrometers. Transistors and diodes having a film containing 0.9 at% to 5.5 at% of molybdenum in a film formed by electroless nickel plating to a thickness of 1 to 3 micrometers A film in which electroless nickel plating is deposited on a wafer of 100 to 200 micrometers thickness to a thickness of 1 to 3 micrometers, and molybdenum is contained at 0.9 to 5.5 at% A film containing 0.9at% to 5.5at% of molybdenum in a film of 1 to 3micrometers thick by electroless nickel plating on a wafer of 100 to 200micrometer thickness is treated at 150 ℃ to 350 ℃ What