A method and device for direct thermosonic flip-chip bonding of copper and copper between micro-copper pillars

Abstract

The invention discloses an inter-micro-copper-cylinder copper-copper direct thermosonic flip-chip bonding method and apparatus. The method comprises the steps of aligning micro-copper cylinders between an upper chip and a lower chip, and heating the upper chip and the lower chip to the temperature of 60-220 DEG C required for flip-chip bonding; pressing the upper chip on the lower chip, and when a pressure applied to the chip reaches an expected pressure of 10-30MPa, turning on an ultrasonic power supply and outputting high power of 1-6W for 10-200ms; and then increasing the pressure to 20-80MPa and reducing the ultrasonic output power to 1-3W for 100-200ms, thereby finishing inter-micro-copper-cylinder copper-copper direct thermosonic flip-chip bonding of the upper and lower chips. According to the inter-micro-copper-cylinder copper-copper direct thermosonic flip-chip bonding method and apparatus, the formation of a bonding interface microstructure and the strength and reliability after bonding can be ensured.

Description

technical field [0001] The invention relates to a method for direct flip-chip bonding of copper and copper between micro-copper pillars, in particular to a method for direct thermosonic flip-chip bonding of copper and copper between micro-copper pillars. The invention also relates to a device for realizing the direct thermosonic flip-chip bonding method of copper and copper between micro-copper pillars. Background technique [0002] The integrated circuit (IC) industry is the core of modern high-tech and information industries, as well as the foundation of various industries such as finance, national defense, aviation, aerospace, and the Internet. A complete integrated circuit is composed of a bare chip (wafer) and a package (packaging substrate, sealing material, interconnection leads / solder balls, etc.). As an important part of integrated circuit manufacturing, packaging provides signal and power interconnection, mechanical support and heat dissipation channels, and envir...

AI Technical Summary

Problems solved by technology

On the one hand, it is to protect the surface of the copper pillars from being oxidized; on the other hand, because the existing reflow flip-chip or hot-press flip-chip interconnection technology cannot directly bond the copper pillars to the copper pillars, it is necessary to add transition metals to Forming Cu-Sn-Cu "sandwich" interconnection structure

However, the introduction of the Sn cap has brought many problems: ① During the reflow flip-chip interconnection, during the process of melting Sn by heating at high temperature (over 250°C), due to the limited content of Sn, the final formation is basically brittle The intermetallic compound (IMC) Cu 3 Sn, rather than Cu as expected from conventional reflow 6 sn 5 , which greatly reduces the reliability of the interconnect

②In the case of hot-pressed flip-chip, although the bonding temperature can be lowered to below 230°C, the time can be shortened, and the intermetallic compound (IMC) Cu can be reduced. 3 The content of Sn, but it brings the phenomenon of Sn extrusion at the interconnection interface under pressure, and the risk of bonding short circuit is greatly increased due to the overflow of Sn extrusion, especially in high-density, fine-pitch three-dimensional integrated packaging; at the same time, too large The pressure is also easy to crush the chip thinned to 100μm or even 50μm

[0010] 1) Most of the materials used in traditional thermosonic flip-chip bonding are Au or SnAg alloy bumps, which are not easy to oxidize, and the oxidation pollution layer on the surface of the bumps is only tens of nanometers, which has limited influence on the atomic diffusion and strength formation process of the bonding interface; However, the micro-copper pillars in the three-dimensional integrated package are generally electroplated copper, which is very easy to oxidize, and the thickness can reach several microns, while the diameter of the micro-copper pillars is only 5-10 microns, and the cross-section of the micro-copper pillars has only a few grains, and the oxide layer is If the proportion of micro-copper pillars exceeds 20%, it will seriously affect the formation of the bonding interface microstructure and the strength and reliability after bonding

[0011] 2) The bumps of traditional thermosonic flip-chip bonding are generally gold / copper bumps (Stud bump) or spherical solder bumps (Solder bump), with a diameter of more than 50 microns, and the diameter is generally greater than the height; the height of the amplitude is several microns The propagation of high-frequency ultrasonic vibration in the bump will not bring macroscopic fatigue damage to the bump; however, for vertically grown micro-copper pillars with a diameter of only 5-10 microns and a height greater than the diameter, the ultrasonic vibration with an amplitude of several microns will The stress concentration generated by the propagation in the point can be as high as hundreds of MPa, which will easily cause the damage of the root of the bump and the interconnection position of the pad.

The bumps of traditional thermosonic flip-chip bonding are generally gold / copper bumps (Stud bumps) or spherical solder bumps (Solder bumps), with a diameter of more than 50 microns, and the diameter is generally larger than the height; high-frequency ultrasonic waves with an amplitude of several microns The propagation of vibration in the bumps will not cause macroscopic fatigue damage to the bumps; however, for the vertically grown micro-copper pillars with a diameter of only 5-10 microns and a height greater than the diameter, the ultrasonic vibration with an amplitude of several microns in the bumps The stress concentration generated by the propagation can be as high as hundreds of MPa, which can easily cause damage to the root of the bump and the interconnection position of the pad.

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