Hide a shadow behind a transparent object

Hi,

I have a quad object with this shader :

Shader "Custom/InvisibleMask" { SubShader { Tags { "Queue" = "Transparent+1" } Pass { Blend Zero One } } }

And then I have a regular sphere with a normal shader with a Render Queue of Transparent+2. That way I can hide objects behind the quad. Problem is that the shadow of my sphere is not hidden. How can I hide it as well ?

As you can see in this image, the quad is hiding the sphere but not the shadow :