Formation of Cu Substrates with W Addition for Vertical Structure Light Emitting Diodes using Electroplating Method

Abstract

Pure Cu substrate has been previously electroplated on p-GaN side of vertical structure GaN-based light emitting diode (LED) to mechanically hold thin GaN-based multilayer after removal of a sapphire substrate by laser lift-off process. The ductile Cu substrate needs to be mechanically strengthened to prevent the GaN-based multilayer from being damaged during vertical LED chip fabrication. In this study, the formation of Cu substrate with W addition on Au-seeded LED wafer by electroplating is introduced. W presents as WO 3 in the Cu substrate. W content of W-added Cu deposits was dependent on constant reduction potential in an acidic citrate bath. The reduction potential also influenced directly the electrical resistivity, hardness, and residual stress of W-added Cu substrates. Applying moderate reduction potentials like −1.1 V resulted in 1.5 times larger hardness than that of pure Cu substrate by adding around 1.0 at % W to Cu. Nevertheless, the electrical resistivity of W-added Cu substrate was maintained as low as that of pure Cu substrate. At more positive reduction potentials than −1.1 V, very low residual stress between 4 and 42 MPa was measured. Wafer bowing induced by large residual stress of W-added Cu substrate can cause serious mechanical damage to LED structure.

Vertical Structure GaN-Based Light Emitting Diodes with Electrochemically Deposited Stress-Free Nickel Substrate

“…Our recent work showed that Cu substrate with a uniform distribution of WO 3 particles can be formed by electrodeposition method. 12 The residual stress of the WO 3 -added Cu substrate was managed to be almost zero, and moreover its electrical resistivity was not increased much from that of pure Cu substrate, in spite of adding WO 3 particles. The main benefit of using the WO 3 -added Cu substrate is to enhance the mechanical strength of Cu substrate by at least 1.5 times by adding less than 2.0 at% W as WO 3 .…”

“…Conditions for electrodepositing stress-free Cu and WO 3 -added Cu substrates can be found in our previous works. 7,12 A 248-nm KrF excimer laser was irradiated through the transparent sapphire substrate at an energy density of 0.3 J cm −2 to remove the sapphire substrate. An n-electrode of Ti (20 nm)/Al (20 nm)/Au (300 nm) was deposited on n-GaN surface exposed after etching the buffer GaN layer.…”

“…We have recently found that adding less than 2 at% W as WO 3 in Cu substrate by electrodeposition method can improve its hardness considerably. 12 However, a more simple and feasible alternative method to replace Cu substrate is to electrodeposit another pure metal substrate such as Ni. It was previously reported that vertical structure LEDs with electrodeposited Ni substrate could have better electrical and optical performances than conventional structure LEDs.…”

Characteristics of Electrodeposited Cu-Co Alloy Substrate for Vertical Structure GaN-Based LEDs

“…6 We also found that adding less than 2 at% W as WO 3 in pure Cu substrate by electrodeposition method could improve its hardness considerably. 7 It was also previously reported that the electrodeposition of pure Cu with higher mechanical strength and lower electrical resistivity can be achieved with high density of nanotwins. 8,9 In this study, we propose the electrodeposition of Cu-Co alloy substrate for vertical structure GaN-based LEDs.…”

Connecting plugs of high-powered GaN-based lighting-emitting diodes prepared by electroplating

“…The use of electroplating technology has improved the performance of GaN-based LEDs in solid-state lighting applications [1][2][3][4]. However, using electroplating technology adds an extra process to LED manufacturing because laser lift-off (LLO) technology must be used, causing LED manufacturers have low throughput, low yield, and high cost.…”