the dc power source 20 and the electrode 5 for the target 6 in the first embodiment but includes a grid 40 in place of the grid 10 in the first embodiment the grid 40 being capable of adjusting the potential distribution in the plane of the grid the remaining components of the seventh embodiment are identical to those of the first embodiment shown in fig1 the grid 40 shown in fig9 is constructed such that the grid surface is divided into four regions and potentials in these divided four regions can separately be changed using respective variable resistors 41 in order to avoid a detrimental influence upon the formation of a thin film it is preferable that wirings to connect between the variable resistors 41 are attached to the peripheral edge of the grid 40 or formed of thinner wires in the apparatus 107 thus constructed a stable plasma state can be created through adjustment of the power source 19 for heating the filament and the dc power source 18 for the grid also by imparting the potential distribution to the grid ions which pass through the grid can be so controlled in their directions as to stably provide a uniform thin film over a large area substrate a method of forming a thin film using the apparatus 107 of the seventh embodiment will be explained below in more detail as with the first embodiment the evaporated substance from the source of evaporation 4 and the introduced gas hit on the thermions generated from the filament 8 for being ionized to positive ions here these.