Two-In-One With PECVD

• PECVD tools accomplishes complete passivation requirements on rear of PERC cell – deposition of aluminium oxide capped with silicon nitride – in one go
• Among 7 PECVD products, listed in TaiyangNews Market survey on PERC cell production equipment, 5 are based on direct plasma with parallel and vertical tube reactor designs from various companies
• Ability to process larger wafers and higher through are the common improvements among these tools

As part of our PERC Solar Cell Production 2022 report, we also looked into passivation tools. PECVD is one of the two mainstream methods employed to deposit aluminium oxide used as the rear passivation dielectric in PERC structure. Irrespective of the deposition method, be it PECVD or ALD,  aluminum oxide requires a capping with silicon nitride that is typically applied with PECVD. And PECVD scores high on this account. One inherent advantage of a PECVD system over ALD is its ability to deposit the silicon nitride capping layer on top of aluminum oxide in one system without breaking the vacuum. That means the whole rear passivation process is executed in one pass, something that holds true for all the listed products in this section.

A total of 7 products are listed in this part of the survey for aluminum oxide deposition system based on PECVD, and 5 of them are direct plasma based. Of these, 4 are typical parallel-plate tube reactors; and again, Semco is somewhat different here. It uses a vertical reactor design, while all the other direct plasma tools are horizontal. Actually, Semco has combined the vertical reactor with the traditional boat design and has been successfully selling this configuration for several years. The reactor can be loaded with more than 700 G12 wafers, and has integrated wafer loading automation system. The design also supports adding more reactors to the setup, while up to 6 is typical. Another important feature of Semco's design is that all the reactors are independent, with their own gas panels and pumps. "We still remain cost competitive as we have a larger wafer load in the reactor," said Raymond de Munnik, the CEO of Semco Smartech . The VICTOR 7000-Alox Series of the company supports a throughput of up to 7,000 wafers per hour with G12 wafers. However, as mentioned above, Semco is shifted its focus on to the ALD tools for aluminum oxide deposition (see: ALD Based Aluminum Oxide System In PERC Processing).

The latest c.Plasma XL AlOx is the name of the PECVD tool from Centrotherm for this application. It is a 10-tube configuration with shared automation. This configuration offers redundant processing, as each of the tubes in the stack can be operated independently and each tube can be loaded with 416 M6, 350 M10 and 288 M12 wafers with about a 40-minute processing time. Following this sequence, the tool supports a net throughput of 6,500 M6 wafers per hour.

S.C New Energy's direct plasma PECVD, based on parallel graphite plate, is offered in a 5-tube configuration. Each tube accommodates a boat with a capacity of either 558 pieces of M10 or 448 of G12 wafers and processes them in a cycle time of about 40 minutes. The 5-tube setup supports a throughput of 3,900 M10 and 3,200 G12 wafers per hour, respectively. At the end, the rear passivation stack deposited by its tools consists of 3 layers – aluminum oxide, silicon oxynitride and silicon nitride –, while the equipment is also capable of depositing the capping layer with a gradient refractive index, highlights the company.

Naura has provided the data for 2 tools, and the difference among the pair is hard to assess. The only obvious one is that HORIS P12571M handles a relatively larger batch of 576 pieces of M10 and 448 of G12. The HORIS P12622M, though an even more recent model launched in 2020, has a lower loading ability – 432 M10 and 336 G12. The throughput also varies correspondingly, for example, HORIS P12571M processes 2,868 of G12 wafers, while HORIS P12622M processes 2,746 slices of the same size.

Just as a reminder, the throughputs mentioned above – not just for the tools from Naura but all the tools discussed above – are with reference to the deposition of aluminum oxide and the silicon nitride stack put together.

The ZR5000X2 from Leadmicro also has a similar functionality, i.e., the tool fulfills all the rear passivation requirements; however, an ALD and a direct plasma PECVD are fused into one reactor shell to deposit both the aluminum oxide and the capping SiNx layer, respectively, in one tool. The reactor frame is integrated with 2 process chambers for aluminum oxide and 4 for SiNx capping, while the company is open to providing a higher number of chambers upon request. The tool ultimately supports a throughput of 5,000 wafers per hour, but is not clear for which wafer size as Leadmicro has not provided this information.

Singulus' offering is perhaps the most integrated configuration in this segment. Its 3-in-1 system fulfills all the passivation needs for the PERC cell, meaning the application of aluminum oxide and silicon nitride capping stack on the rear side and also the SiNx on the front side. The GENERIS PECVD 6000 PERC processes all commercial wafer sizes from M6 to G12 and has 5 process chambers and 10 plasma sources. Another important differentiation of this tool is its fairly different plasma technology called Inductively Coupled Plasma (ICP). The reactor is built on inline-batch philosophy where the wafers are processed in a carrier in a horizontal orientation. The GENERIS PECVD 6000 PERC processes 64 of M6 wafers at a time and, at this rate, the tool reaches its max throughput of 6,000 wafers per hour carrying out all 3 of its tasks.

The Text is an excerpt from TaiyangNews recent report on PERC Cell Production Equipment 2022, which can be downloaded for free here.