How to position an object in 3d space according to a 2d screen position?

Question

There are several topics on how to get the 2d screen position of a 3d object in 3d space.

I was wondering how it works the other way around:

How can I get a position in 3d space according to a 2d position?

For example, how can I position a 3D object on the windows upper left corner?

So far I tried it like this:

https://github.com/cheesyeyes/19603.2d.screen.position/blob/master/src/index.js

https://cheesyeyes.github.io/19603.2d.screen.position/

function positionOnScreen(vector, object){

raycaster.setFromCamera( vector, camera );

var intersects = raycaster.intersectObject(plane);

if(intersects.length>0){
  object.position.copy(intersects[0].point);
 }
}

positionOnScreen(new Vector2(.8,.8), mesh1);

I am sending rays to a plane that is parallel to the screen, but I am pretty sure there must be a better way..