Thermal budget is becoming a serious issue for today’s semiconductor industry due to the use of diversified temperature-sensitive materials, especially for MEMS, TSV and OLED fabs, which use polymer materials for device fabrication. Samco meets these process challenges with low-temperature SiO2 and SiNx PECVD technologies that have unique process features and provide excellent film properties.
The SiO2 and SiNx films processed using our low-temperature PECVD technologies are suitable for passivation and barrier coating of the devices and will expand the potential applications of the new-generation devices in markets.
Why Low-temperature PECVD Technologies are in High Demand
The semiconductor industry has evolved along with the process development of materials. Process temperature (also known as thermal budget) is one of the most crucial requirements for the deposition of SiO2 and SiNx thin films, which are used for passivation, insulation or hard masks in device fabrication. Rapid thermal CVD (RTCVD) is a common technique used to deposit oxide layers on silicon substrates, but this technology requires high temperatures of over 800°C. Plasma Enhanced CVD (PECVD) technology, when compared to thermal CVD technology, offers relatively low-temperature deposition at around 300°C, and it has provided the industry with reliable and reproducible deposition process solutions for decades. Today a wide variety of materials are used for device fabrication in several markets to achieve superior device performance.
SiO2 film is used as a sacrificial layer for releasing free-standing structure such as cantilevers in wet etching, and SiNx film is used as a membrane and hard mask in device fabrication. On the other hand, polymers such as Polyimide and Parylene are some of the most common materials for membranes and device packaging. These materials enable low-cost and flexible MEMS devices, but they require severely limited process and operating temperatures due to their native glass transition temperature.
PECVD SiO2 film deposition is an important step in both Via Middle and Via Last. Thermal budget is critical for the oxide deposition process due to thermoplastic adhesives, which are used for temporary bonding and handling of thinned wafers.
SiNx film is a good candidate for barrier coating of flexible transparent substrates due to its hardness and moisture resistivity. Also, SiO2 film can be used as an etch-stop-layer during plasma etching processes. Since polymer substrates have low glass transition temperatures, a low-temperature PECVD process is required.
Breaking Thermal Budget Limits
As a pioneer of material processing technologies for device labs and fabs, Samco offers low-temperature PECVD process solutions. SiO2 and SiNx films can be deposited at low temperatures (including under 80°C). Sample temperature can be managed depending on customer’s thermal budget limitations and request.
Here are our process capabilities of low-temperature plasma CVD technologies.
High-speed SiO2 & SiNx Plasma Deposition
Samco offers two types of PECVD systems and process solutions (Anode PECVD and Cathode PECVD). While the RF power is applied to the upper electrode (Anode) and the substrate electrode (Cathode) is grounded in anode PECVD, Cathode PECVD utilizes ions which are accelerated by the negative electric field of the cathode. An RF-driven cathode makes maximum use of a self bias voltage by placing the sample on the cathode electrode. Samco’s Cathode PECVD enables high-speed deposition even in low temperature process. SiO2 deposition rate of 400 nm/min is achieved at stage temperature of 80°C.
Superior Stress Control over Wafers
SiO2 film deposited at 120°C or 150°C showed minimum stress shift even 30 days after the deposition processing. This PECVD process with stable film stress can be applied for TSV passivation which has a critical challenge in bow compensation of thinned wafers.
Low Current Leakage as Passivation
SiO2 film deposited at 120°C or 150°C showed low leakage (~ nA) between silicon substrate and passivation with 100 μm deep via. The SiO2 film deposited at low temperature is useful for passivation of TSV due to good electrical properties and the stable film stress for long period mentioned above.
More Material Options in Device Fabrication
Low-temperature processes eliminate concern for heat-sensitive materials.
High deposition rate over 400 nm/min is available for throughput improvement.
Excellent Film Properties
The films with superior stress, electrical and optical properties can be applied for various applications.