Coated article with low-E coating having multilayer overcoat and method of making same

A coated article including a coating having a layer system supported by a glass substrate, the layer system comprising:

• a first dielectric layer on the glass substrate;
• an IR reflecting layer comprising silver on the glass substrate over at least the first dielectric layer;
• a contact layer on the glass substrate over and directly contacting the IR reflecting layer;
• a second dielectric layer comprising silicon nitride on the glass substrate over at least the contact layer;
• a layer comprising niobium zirconium on the glass substrate over and directly contacting the second dielectric layer comprising silicon nitride, wherein the layer comprising niobium zirconium comprises from about 2 to 15% Zr (atomic %);
• a third dielectric layer comprising silicon nitride on the glass substrate over and directly contacting the layer comprising niobium zirconium;
• a layer comprising zirconium oxide on the glass substrate over and directly contacting the third dielectric layer comprising silicon nitride, so that the layer comprising niobium zirconium is located between and directly contacting said second dielectric layer comprising silicon nitride and said third dielectric layer comprising silicon nitride;
• wherein the layer comprising niobium zirconium is from 1-3 nm thick;
• wherein the layer comprising zirconium oxide is from 3-8 nm thick;
• wherein the layer comprising niobium zirconium is substantially thinner than each of the second and third dielectric layers comprising silicon nitride and is also substantially thinner than the IR reflecting layer comprising silver;
• wherein the layer comprising zirconium oxide is substantially thinner than each of the second and third dielectric layers comprising silicon nitride;
• and
• wherein the coating contains only one silver-based IR reflecting layer.