1

1. Introduction

As small and high-performance electronic devices, such

as smartphones and tablet PCs, continue to permeate the

market, the market demand for packaging semiconductor

chips with increasingly higher densities is growing. In or-

der to package micro-wired chips, interface substrates

that connect the chips to the main substrate are needed.

This interface substrate is referred to as an interposer

(package substrate), and there are various types for dif-

ferent applications. For example, the interposer called the

FC-CSP substrate is used for the application processor

and baseband processor in smartphones and tablet PCs.

Figure 1 shows an interposer structure and its fabrica-

tion process. An interposer has a core substrate (a glass

epoxy substrate with copper films), on both sides of which

are resin layers (build-up films) and Cu wiring layers al-

ternately laminated to form four to six layers in total. Up-

per and lower wiring layers are connected with Cu via

holes. Since the interposer substrate is made by laminat-

ing wiring layers, it is also known as the build-up sub-

strate. A method called the semi-additive process (SAP) is

used for micro-wiring. The SAP process uses electrolytic

plating for Cu wiring only. This process consists of the fol-

lowing steps: forming a seed layer (electroless plating or

sputtering), forming wiring patterns by using photoresist,

Cu wiring by electrolytic plating, resist stripping, and

etching unwanted seed layers.

2. Deposition of seed layers by sputtering

As technologies for micro-wiring chips and high-density

chip packaging advance today, the interposer wiring also

needs to be micro-fabricated. Figure 2 shows a roadmap

of interposer wire line widths and seed layer forming

methods. Electroless plating, which is a wet process, is

used to form interposer seed layers whose line width is 20

μm or larger. It does not work for smaller widths, so the

sputtering process is used instead. This is because the

electroless plating has the following problems when it

comes to micro-wiring:

ULVAC TECHNICAL JOURNAL No.77E 2013

Sputtering System SMV-500F for Manufacturing Printed Substrates

Eriko Mase*, Harunori Iwai*, Kouji Takahashi*, Tetsushi Fujinaga**, Masahiro Matsumoto**, Makoto Arai** and Atsuhito Ihori**

＊　 Advanced Electronics Equipment Division, ULVAC, Inc.＊＊ Institute for Super Materials, ULVAC, Inc.

Figure 1　Manufacturing process of an interposer (SAP)

2

(1) Line peeling (disconnection)In the electroless plating process, chemical solutions

are used to increase the surface roughness of a base sub-

strate to enhance the adhesion of plated films by the an-

chor effect. However, for a resin substrate with a large

roughness, when wet etching the seed Cu film, the etch-

ing solution seeps between the Cu wiring and the sub-

strate, etching the wired lines. This causes lines to peel

off, and micro-wiring lines are particularly vulnerable.

(2) Signal transmission lossAs semiconductor devices operate faster, interposers

are required to transmit more signals faster. The signal

frequency is expected to reach 45 GHz in 2018 1). The

higher the signal frequency is, the nearer to the conduc-

tor surface (approx. 0.3 μm for 45 GHz) signal currents

pass 2). Larger roughness means longer paths for signals

to travel along, which increases the transmission loss. To

reduce the transmission loss of Cu-plated lines, the line

surfaces have to be smooth.

(3) Flawed plating inside via holesPlating solutions often fail to enter into tiny via holes re-

sulting in non-plated areas.

In contrast, the sputtering method forms a tightly ad-

hered thin film on a low-roughness resin substrate by de-

positing an adhesion metal layer between the resin sub-

strate and the Cu seed layer. After the Cu electrolytic

plating, unwanted seed layer areas are wet-etched, so the

seed layer has to be a thin film. Since the wet-etching of

the seed layer is isotropic, a thick seed layer causes large

undercuts of wired lines. This requires finishing the wet-

etching in a short time in order to ensure small wiring

widths, which means the seed layer has to be a thin film.

The sputtering method has no problem forming films in

and around small via holes that electroless plating strug-

gles with.

3． ULVAC’s development of sputtering sys-tems for printed substrates

In 2007, our Advanced Electronics Equipment Division

released the SCV-500R sputtering system for manufactur-

ing glass-epoxy substrates. The SCV-500R is a pass-

through type sputtering system with a production capacity

of 36 sides/hr. We have recently released the SMV-500F

which has a capacity of 26 substrates/hr for double-sided

sputtering (52 sides/hr) as a result of improving the sub-

strate cooling method, the transport mechanism, and the

overall process.

Table 1 lists requirements for the seed layer deposition

system. The SMV-500F was developed to meet these re-

quirements.

4. Features of SMV-500F

This is a double-sided sputtering system for thin rectan-

gular substrates (650×550 mm max.). As shown in Fig-

ure 3, it has a transport chamber in the center that also

flips substrates over, three process chambers (etching,

adhesion metal sputtering, and Cu sputtering), and a buf-

fer chamber that heats substrates, that are all connected

together. Figure 4 shows the film deposition process. Af-

ter a substrate is heated to be degassed in a heating cham-

ber, it is transported to the etching chamber to be etched

on one side. Next, the substrate is flipped over in the cen-

Figure 2　Trend in interposer wiring width and seed layer forming methods

3

[Requirements for the seed layer]- Adhesiveness to the resin substrate- Good thin film thickness distribution- Good film formation in and around via holes

[Requirements for the manufacturing system]- High productivity- Compactness- High reliability

Table 1　Requirements for the seed layer deposition system

Figure 3　Appearance and overhead view of SMF-500F

Figure 4　Seed layer sputtering process in SMF-500F

4

tral reversing chamber before being carried into the etch-

ing chamber again for the other side to be etched. Then,

after passing through the reversing chamber, it is trans-

ferred into the adhesion metal sputtering chamber where

it is sputtered on both sides through steps similar to the

etching process. Finally, the substrate enters the Cu sput-

tering chamber to be processed on both sides. The SMV-

500F has the following five features:

(1) High adhesiveness; excellent film thickness distri-

bution

(2) Deposition at low temperatures

(3) High productivity

(4) Small footprint

(5) Substrate holding mechanism for thin substrates

(substrate holder)

Details on each item are described below:

(1) The SMV-500F achieves an adhesion strength of 0.8

kgf/cm or more for a Ti/Cu seed film deposited on a

build-up material for the SAP process by heating the

substrate before sputtering, the surface treatment,

and our original adhesion layer sputtering process.

Also it employs a multi-magnet cathode to ensure the

thickness distributions of the adhesion metal (Ti) and

Cu films are within±5% per 500-mm square area.

(2) The build-up material properties require a low-temper-

ature process, 150℃ or lower. The SMV-500F deposits

films at low temperatures by employing an electrostat-

ic chuck 3) for cooling substrates.

(3) The SMV-500F shows high performance in cooling

substrates with its electrostatic chuck, which enables

low-temperature deposition at high power, so its film

deposition time is about half that of the SCV-500R, a

conventional pass-through type sputtering system.

Also, since the SMV-500F has a substrate reversing-

cum-transport chamber at the center, it can flip and

transport a substrate at the same time in a vacuum to

perform double-sided film deposition in a short time.

(4) Employing an electrostatic chuck enables stationary

deposition for both the adhesion metal layer and the

Cu film. For this reason, one chamber is designed for

the adhesion metal layer, and another for Cu, and this

system has fewer chambers than conventional in-line

sputtering systems. Consequently, the equipment foot-

print is about half of a typical in-line system.

(5) The substrate holding method is important for thin

substrate vertical transport and double-sided film de-

position systems. The SMV-500F employs a substrate

holder that can set substrates without producing wrin-

kles or slack.

5. Conclusion

We have already accepted orders for SMV-500F sys-

tems from leading overseas manufacturers. Our demo

systems have provided a number of domestic and over-

seas customers with the experience of using the system.

Printed substrate manufacturers have changed their seed

layer deposition method from electroless plating to sput-

tering in their ongoing development and test production

of packaging for micro-wired chips. Since we have already

carried out many experiments for customers with this sys-

tem, we expect the SMV-500F to become the standard

model in the industry by 2014 when the mass-production

of interposers for micro-wired chips is supposed to start.

Among our future goals, the development of the best

process conditions for each base material is first priority.

Responding to the trend of micro-wiring, material manu-

facturers are launching new materials of various surface

roughness levels and thermal expansion coefficients one

after another. We need to develop processes for these ma-

terials.

Also, to promote the advantageous dry process, we

need to reduce its cost. For that reason, we are now devel-

oping new seed layer materials and cathodes that ensure

more efficient target consumption.

In addition, we are developing etching/ashing equip-

ment for rectangular thin substrates and PECVD systems

as well. We aim at providing total solutions for manufac-

turing printed substrates.

References and patents

1）ITRS2010 Update, Assembly and Packaging

2）Yoshihiro Konishi, “Microwave Technology,” Nikkan

Kogyo Shinbun, 2001

3）Japanese Patent Application No. 2013-019767 “Thin

Substrate Processing System”