Why do changes made to a cell propagate to other cells in this 2 dimensional array created using fill?

I have a problem with this 2-dimensional array in JS. When I change a[1][0], a[0][0] changes with it. Is there something wrong in the way I am initializing it? If yes, how can I initialize it properly?

>var a = Array(100).fill(Array(100).fill(false));
>a[0][0]
>false
>a[1][0]
>false
>a[1][0] = true
>true
>a[1][0]
>true
>a[0][0]
>true