Technology News
11/01/2003
E-manufacturing: Do you know where your fab stands?
Ensuring secure e-manufacturing access to data is "crucial when designing a collaborative work environment," say Stuart Perry and Bill Ramus at ILS Technology, Boca Raton, FL. Perry and Ramus have been stepping through the security requirements needed in their work to install ILS's e-Centre and ServiceNet at IBM's 300mm wafer fab in Fishkill, NY. They recently briefed Solid State Technology with a step-by-step look at what it takes to securely connect and retrieve data from fab tools.
Today, engineers and technicians want to collaborate real-time with each other, whether they are in the fab, the office, at home or in a hotel, or even when they're having a coffee at Starbucks. "They want to create sessions that include multiple participants, exchange files and data, access documentation and procedures, view a tool's monitor, and even operate a tool remotely," says Ramus. "These sessions must be secure, which is defined as keeping intellectual property in the hands of only those who need it and providing an audit of when data was accessed and distributed.
"Today, intellectual property is leaving the fab through 'sneaker nets' via equipment-maintenance personnel's laptops, rogue connections to tools, and file copying to CDs; there is no authentication, audit trail, or traceability," according to Ramus.
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For a table of attributes comparing secure vs. Internet collaboration, see the table.
"The key first step is creating virtual private networks [VPNs] and firewalls that separate the company's intranet from the public Internet and minimize the risks of targeted denial-of-service attacks or picking up a virus," says Perry. Then, the VPN requires security policies that use authentication and authorization controls to establish access. Further, the security measures must allow data filtering, control file transfers, and limit, monitor, or deny remote equipment operations. "Securing data is not just a concern for connections outside the fab, as many fabs are now placing isolation networks around the production floor and treating their own intranets as a possible security threat. Isolation networks can also be used around each tool to prevent users at one tool from telenet-hopping to another tool," he says.
Perry adds, "To ensure data security is not compromised, data originating from the tool should be secured from the source." ILS uses X509-certificate based strong authentication to ensure the e-diagnostics system is the application actually connecting to the tool.
"Encrypting data for transmission to the e-diagnostics system and digitally time-stamping data while it is being collected is crucial because it ensures system integrity by creating a legally binding audit trail of data being received from the tool," says Ramus. "In addition, the e-diagnostics system can guarantee data delivery and integrity to the end user." The encrypted time stamp is then returned along with the public key to the e-diagnostic system so it can be kept with the collected data.
Perry points out that "an e-diagnostic server must ensure that persisted data is logically separated by manufacturer, tool type, and tool so users have access only to tools that they are authorized to use. This is accomplished using different tables for each tool, or different physical locations may be specified for data persistence of the different tool types."
Perry says, "User authentication can range from single-factor authentication, such as user ID and password (for fab personnel), to full three-factor authentication (for OEMs). Fabs must be able to handle multiple forms of authentication within the same installation." By simply defining authentication servers and linking them to specific LDAP domains, the security administrator is able to support all the industry standard forms of authentication.
"While most people focus on what a user sees, it is also important to consider what types of external, programmatic interfaces are available," says Ramus. "For example, we use a secure Web services architecture to provide system access for data retrieval and system customization; this interface provides the most platform- and language-independent way to access a rich set of features. Applications must authenticate themselves to the server and must also have privileges to request specific tool data."
Perry and Ramus also believe that portability, features, and deployment are important aspects to consider when implementing e-manufacturing in a fab. "While ease-of-use is a rather subjective exercise, a rich feature set and portability are mission-critical in getting the job done," they say.
Start-up company pursues a nonporous low-k solution
Start-up Silecs has entered the low-k fray with an organosiloxane-based low-k dielectric material that is effectively nonporous (see table for materials properties). The company was founded in 2000 and is supported by organizations funded by the government of Finland and has access to the semiconductor-processing facilities at VTT Microelectronics Laboratories.
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While the industry has battled over CVD and SOD processes for low-k dielectrics, Silecs appears to straddle both worlds. The company's materials are developed using the SOD process, however, "Since [the materials] integration behavior has been shown thus far to be similar to that of TEOS, they are expected to facilitate the adoption of ULK dielectrics into standard IC manufacturing processes," explained Bob Donia, VP of business development at Silecs.
Key to the technology is a three-component precursor system comprising functional groups, bridging groups, and cross-linkers. "The material is constructed using a modular approach that enables tuning of the dielectric constant between 2.2 and 3.0 without specifically adding pores," said Donia.
 Figure 1. Gap fill on 0.25µm features. |
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The modular approach could work something like this: the organic functional group might be selected to optimize a specific property (e.g., tune polarizabilities, stabilize dipolarities/charges, allow photosensitivity), while the bridging group would be selected to optimize another capability (e.g., thermal/mechanical stability, CTE adjustment). The cross-linking group would be selected for yet another property (e.g., thermal/.mechanical stability, eliminating pore formation). The idea is to get the best balance of properties.
While the resulting materials are effectively nonporous, the total porosity is actually 8–12% with an average pore size ≤1.0nm. The glass transition temperature is >450°C, high enough to go through substrate processes without melting or changing properties. Figures 1 and 2 show examples of the SOD material being used for gap fill on 0.25µm features and filled tungsten vias.
 Figure 2. Filled tungsten vias. |
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Many of the precursors used in the process can be photosensitized. "A photosensitive dielectric allows for direct patterning of the dielectric, thus eliminating several lithographic steps," noted Donia.
The company's first alpha testing partner, Cypress Semiconductor, just completed its evaluation. A second alpha test partner — an unnamed IC manufacturer in Europe — has also agreed to work with Silecs. Meanwhile, the company expects to have a production-proven process ready by the end of 1Q04.
Putting the squeeze on probe technology
New low-k materials pose integration headaches not only for equipment suppliers and IC manufacturers, but also for those who test the die. With their threshold to cracking and structural failure an order-of-magnitude lower than traditional dielectrics, the fragile dielectric materials pose hazards during probing.
The European initiative to get the lead out of solder affects probe technology, since harder materials transfer more of the probe force to underlying circuitry. Also, increasing pin counts affect wafer level test. Finer-pitch bump layouts on the order of 200µm for high-density flip-chip devices are being used, but the industry is moving toward 175µm.
 Figure 1. Probe force results using MicroForce probing. (Courtesy Intel/TEL/FormFactor) |
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To address these concerns, FormFactor, Livermore, CA, recently introduced the BladeRunner175 (BR175) wafer probe, and currently is shipping it for production sort test. The probe can be scaled to meet the future 175µm pitch requirement.
According to Mark Brandemuehl, FormFactor VP of marketing, results presented jointly by TEL, Intel, and FormFactor at the Southwest Test Conference in June indicate a 10:1 reduction in probe force using the BR175 compared to previous generations of the company's probes as well as Cobra-.type vertical probe cards, made by others (Fig. 1).
Brandemuehl also noted that the results showed that scrub ratios — the ratio in movement in the x/y direction to movement in the z direction — ranged from 0–2.0. Contact resistance was in the range of 0.15–0.24W.
Figure 2 shows the differences in scrub marks and damage to flip-chip bumps between the MicroForce and standard probes. The company says a reduction in scrub marks and damage reduces the risk to package reliability, and smaller probe marks can eliminate the need for reflow.
 Figure 2. Probe mark comparison. (Courtesy FormFactor) |
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