In the IC design and manufacturing process, products need to have their functionality verified after development and tape-out to confirm whether they meet testing standards. However, there are often differences in performance or even functional defects. When this happens, design debugging is necessary to determine the problem. Then the design must be revised and sent once again through production. This process forms a cycle. The faster problems are found, the shorter the time to market. As products become progressively more complex, the process from mask revision to production grows ever more time-consuming. As such, if one can save time on design debugging then one could shorten the time it takes for an engineering product to reach mass production. There are many methods for design debugging, from testing, simulation and failure analysis to circuit repair. A considerable amount of effort must be spent on the engineering end to identify problematic points and ensure that the next revision of a product can achieve the desired performance. Circuit repair is one method that almost all R&D engineers will employ. Circuit repair can save the costs of remaking the photo mask and undergoing the first trial production. This approach is absolutely effective in shortening the time from R&D to mass production while simultaneously reducing R&D costs, making customers’ products more competitive and timely in terms of research and development (Figure 1). This article illustrates the principles and important precautions for circuit repair to help R&D engineers communicate more effectively and efficiently with other engineers when proposing its use.
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Figure 1. Flowchart of the Process from Circuit Design and Product Manufacturing to Verification, Debugging and Revision; The faster you solve problems, the shorter the time to market and the greater your ability to seize market opportunities |
FIB circuit repair is also called circuit editing. The instrument commonly referred to as FIB was developed to help modify the layout on an IC. The FIB machine has many functions needed for structural or failure analysis, including local, cross-sectional observation and TEM sample preparation. Therefore, to avoid confusion, it is recommended to specify that circuit repair is to be performed when submitting a proposal rather than just mentioning the FIB. Circuit repair uses the single beam model. It operates as a circuit cutting tool by using an Ion Beam to remove surface materials via ion impacts. If circuit connections are to be made, a layer of metal, such as tungsten, must be used to connect more than two metal lines. This process requires decomposition of the W(CO)6 gas via a Ga+ ion beam to enable the completion of tungsten coating (Figure 2).
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Figure 2. Plan 1 line 1 cut calls for the cutting off of one metal line and the connecting of two metal lines; The connecting metal is tungsten |
The first step of the circuit repair process is for the client to conduct internal discussions to determine the locations that need to be modified then provide a plan and process. The plan should include the planer locations and metal layers that need to be cut and connected，Whether or not the client needs to provide a GDS file is determined by the specific situation. Typically, if the circuit lines cannot be clearly identified via the surface of the sample, the GDS will be required to enable automated location of the correct positions and reduce the execution failure rate (Figure 3). In consideration of information security risks, a partial GDS may be provided (Figure 4). After the sample is produced, if there is no subsequent need, the executing team will delete the file. After receiving a request, the executing team will have to discuss and evaluate the plan with the client, provide the required working hours and yield rate of the plan, and, if necessary, modify the plan to improve the success rate of implementation. Once both parties confirm that there are no problems, it will be added to the execution schedule. After completion, samples will be sent back to the customer so they can verify whether the solution was successful.
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Figure 3. Once the GDS layout is aligned with the sample surface, the correct position for circuit repair is found using the relevant coordinates
Figure 4. The GDS provided by the customer must include the four corners and GDS of the location and layers where circuit repair is to be conducted. Confidential information will not be revealed. |
The required time and yield for circuit repair will vary depending on the sample’s manufacturing process, the difficulty of the solution and the completeness of sample information. The methods and technology used must be adjusted in real time according to the situation. Therefore, we rely not only on advanced equipment but also on highly experienced engineers able to face and solve various unexpected challenges in order to achieve the results expected by our clients.
In view of the changes in current manufacturing processes and packaging technologies, in addition to typical circuit repair, which is conducted from the front-side of the IC, we also provide the following services:
- Backside CKT Analysis Services: Flip-chip packaging, for example, requires that circuit repair be performed from the IC’s backside. At present, most samples belong to the 5nm~28nm processes. For these samples, MA-tek is equipped with the latest Centrios machine as well as fully qualified engineers. The overall yield can exceed 90% (Figure 5).
Figure 5. Example of Backside Circuit Repair - N-wire External Lead: The signal lead that needs to be measured is routed to the surface of the IC via circuit editing, then ordinary bonding wires are used to connect the signal lead to the IC pin so that the machine can perform dynamic measurement. This method is more flexible than the traditional oscilloscope observation using a probe needle on a cross PAD (Figure 6).
Figure 6. The N-wire can extract internal signals from a chip for measurement
- CSP De-balling and Re-balling Services: If the location where circuit repair is required is beneath the solder balls, the solder balls can be removed then reinstalled once repairs are completed. This does not affect subsequent testing (Figure 7).
Figure 7. Photos of the various stages of the process of performing circuit repairs under the solder balls
As process technologies become more and more advanced, the difficulty of circuit repair also increases. So maintaining and improving yield is critical. It is also the key to retaining customers. Therefore, MA-tek spares no efforts when it comes to investing in equipment and training personnel. Our internal skill advancements, education and training are ongoing and proceed according to established processes and schedules. Progressing alongside the semiconductor industry, we ensure that we continue to be precise and accurate, efficient and effective! Just as MA-tek intended when it first set out, we are The Best R&D Partner！
