Silicon Nitride Membranes

We would like to buy some low-stress SiN on Si wafer. We want to use the wafer to develop some etching and coating process that will be transferred to a SiN TEM grid that we purchased from elsewhere. Therefore, we want to find product with similar SiN properties, such as stress, Si:N stoichiometry etc., to that of the SiN TEM grid. A thick coating is preferred since we are going to use it to study the etching rate and the surface properties after etching.

Please find the specifications of the SiN TEM grid in the attached PDF. Could you please suggest some options in stock? Please let me know if you need other or more detailed information about the SiN membrane on the TEM grid.