TechNews
09/01/1999
In September TechNews:
New underfill material attacks flip-chip challenges
300mm etch-toolsnapshot given
New concept in long throw sputtering
Matrix test process control reduces costs
New underfill material attacks flip-chip challenges
A new underfill material, moisture-resistant cyanate ester (MRCE), may provide flip-chip developers with an alternative to conventional epoxy-anhydride ("epoxy") underfills, according to researchers at Johnson Matthey Electronics.
Research data show MRCE also meets increasing requirements for high adhesion retention, post environmental stress mechanical stability, and robust adhesion to various interfaces. For the latter, as the industry moves from ceramic to organic substrates, performance is expected to be maintained in a variety of new interfaces, including solder mask on laminate packages and new die passivations.
Because flip-chip packaging is increasing in standard JEDEC applications, underfill materials specifications will have to meet a broader range of moisture resistant requirements. Also, increased emphasis is being placed on key properties such as dielectric constant and volume resistivity of underfills. Bernard Ho, marketing and technical services manager at Johnson Matthey, says, "For any new material, all these requirements must be met while retaining ease of use in the manufacturing environment."
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Most epoxy-based underfill materials use acid anhydride curatives that, although they improve cure time, are moisture sensitive. "The anhydride hydrolizes rapidly, even at ambient conditions with resulting low molecular weight, low adhesion performance, low glass transition temperature (Tg), and high coefficient of thermal expansion (CTE) products," explains Ho. The polyesters formed by the epoxy decompose under autoclave conditions to yield polyols and polyacids. Common solder flux is rosin-based and can react with epoxy resins to form moisture sensitive beta-hydroxy esters that depolymerize to form low molecular weight and low performance products.
On the other hand, MRCE materials, polymerize via cyclotrimerization to form triazine rings. The resulting three-dimensional structures give excellent adhesive strength and mechanical stability. "The catalyst system employed in the MRCE results in a material that is chemically inert and resistant to moisture attack," says Ho.
At Johnson Matthey, Ho, Michael Chau, and Carl Edwards have gathered empirical data that shows the advantages of MRCE compared to epoxy underfill:
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- After just 8 hrs at 30°C/60% RH, they noted a significant depression in glass transition temperature (Tg) of epoxy while the MRCE material remained relatively stable.
- Under the same conditions, they noted an increase in the coefficient of thermal expansion (CTE) in epoxy material while MRCE remained relatively stable (see figure).
- For three tested substrates, MRCE exhibited superior adhesion performance.
Ho notes that these property changes are important for establishing material reliability in a specific application. "A stable Tg is a requirement because subsequent processing may include numerous temperature excursions. And, during thermal cycling, high CTE materials can create expansion mismatches with interface materials; this can cause excessive mechanical stresses to be placed on the die and package."
In turn, mechanical property shifts can cause changes in adhesion performance, where the performance indices include adhesion as a function of humidity exposure and performance on a variety of interface materials. -- Pete Burggraaf
300mm etch-toolsnapshot given
Development of 300mm tools is rapidly moving toward production readiness, says Dieter Pecher, department manager at the Semiconductor300 (SC300) fab, an Infineon-Motorola joint venture in Germany. Without identifying specific systems, Pecher's report - given at a Semi West conference sponsored by Lam Re search - summarized the characterization of the facility's etch tools from major suppliers. These tools are being used for silicon, polysilicon, oxide, metal etch, and ash. SC300 is now in its main phase of manufacturing technology de velopment, integrating lot processing for 64Mb DRAMs with 0.25µm processing.
 Figure 1. Relatively high 300mm etch tool pricing, compared to 200mm. (Source: SC300) |
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 Figure 2. Material and consumables for 300mm etch tools are still high. (Source: SC300) |
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Half of the etch tools at SC300 are alpha versions, 30% betas, and 20% production tools:
- All 300mm etch tools show an uptime equivalent to or better than 200mm tools. The favorable numbers are tempered by the fact that SC300 is still in its development stage and tool utilization is around 30%. The facility is currently ramping wafer starts.
- 40% of the 300mm etch tools at SC300 are "on track with throughput, being equivalent or better than 200mm capability," said Pecher. The best currently is only 1.1x200mm throughput. He characterized the throughput short fall as "limited mostly by software issues on what are predominantly pre-beta tools with just scaled-up 200mm software."
- Tool pricing (Fig. 1) is not competitive for a move to 300mm mass production. SC300 is looking for the same technology at the same price as 200mm. The industry in general is asking for 300mm tools at 1.3x200mm, including so-called bridge tools.
Putting tool pricing perspective, Sanjay Tandon, new products manager at Lam Research tells Solid State Technology, "Today, pricing is somewhat meaningless because tools, like those at SC300, are still 'one-off' systems. However, it is uncertain how far down tool prices will drop, given 300mm tool suppliers will have to maintain an economy of scale that justifies development costs and sale of fewer 300mm tools overall compared to 200mm sales."
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- None of the 300mm etch tools at SC300 meet the industry's target for a footprint <1.3x200mm. The analysis is that component and subsystems must be re-designed for better packaging efficiency.
- Material and consumable costs (Fig. 2) represent a major area for improvement where, once again, "costs are not competitive for a move to 300mm mass production," said Pecher. At SC300, running costs for etch systems fall between 1.4 and 2.4 that of 200mm, with 70% of the systems having higher consumable cost compared to an equivalent 200mm tool.
- "Automation needs to be more sophisti cated," said Pecher. Evaluating 300mm etch tools with a CIM index that rates SECS II, GEM, FOUP ID, overhead transport and guided vehicle compliance, etc., most SC300 tools received a 40% rating. Pecher concludes, "300mm tool development is rapidly moving tow ard production readiness, as is process development at SC 300. The move to 300mm is no longer a vision."
New concept in long throw sputtering
Ulvac has developed a new type of PVD system for long throw sputtering (LTS), using multiple small, rotating targets rather than the single large target in conventional systems. The long throw approach eliminates the aperture plate in which the small holes used to collimate the beam tend to clog as sputtering proceeds. Uniformity is a problem with long throw sputtering, however, especially toward the wafer edges and it is hard to fill high-aspect holes. By using 7 rotating targets, each 60mm dia. vs. 300mm for a 200mm wafer, and varying current to the cathodes, deep holes can be filled uniformly, says Nobuhiro Motegi, product manager. The needed current distribution was determined by experiment for the multicathode approach, he said.
An electrostatic chuck is used to control wafer temperature precisely using direct contact with a hot plate to get higher heat conduction than with gas. The system is being tailored for introduction with 0.13µm processing of 300mm wafers, which will be cost-effective be cause otherwise 400mm targets would be needed, according to Motegi. It should be useful for copper, he suggested, and experiments have shown good fill of 0.1µm dia. holes that were 10µm deep using this approach. -- Bob Haavind
Matrix test process control reduces costs
At Semicon West 99 Amkor Technology unveiled its success with matrix test handling in semiconductor manufacturing's backend. The technology enables simultaneous testing of 10 and 25 "mature product" ICs in strip form and can be integrated into the assembly process flow.
 Improved manufacturing through matrix test process control. (Source: Amkor Technology Inc.) |
Miles Prim, VP of worldwide test at Amkor, claimed, "This is a significant industry development that has the potential to reduce test cost/IC by 15%-30%." Amkor's success has come by combining its packaging format expertise with equipment suppliers ESH/Everet Charles (load boards, contactors and fixturing), FICO (matrix handling and integration), and Credence (testers and software support). - Pete Burggraaf