A method for detecting a leak in a valve-cell vacuum deposition apparatus, the vacuum deposition apparatus including at least one valve cell comprising: - an outer enclosure, - an inner tank (24; 224) located inside the outer enclosure, the inner tank (24; 224) containing a material to be evaporated, - an inner tank valve (28; 228) comprising a valve input port (28A; 228A) in fluidic communication with the inner tank (24; 224) and a valve output port (28B; 228B), - a vacuum deposition chamber, and - a leak detection device, said leak detection method being characterized in that it includes: - an initialization step in which: - vacuum is made inside the vacuum deposition chamber, then - an initial leak flow rate in the vacuum deposition chamber is measured by means of the leak detection device, and - a measurement step in which: - the inner tank valve (28; 228) is open to place the vacuum deposition chamber in fluidic communication with the inner tank (24; 224), then - a gaseous mixture is injected into the vacuum deposition chamber, then - a pressure P0 is measured inside the inner tank (24; 224), then - the inner tank valve (28; 228) is closed, then - vacuum is made inside the vacuum deposition chamber to a predetermined pressure in the vacuum deposition chamber, then - the vacuum deposition chamber is placed in fluidic communication with the leak detection device, then - a final leak flow rate in the vacuum deposition chamber is measured by means of the leak detection device, then - a leak rate of the inner tank valve (28; 228) is deducted therefrom. - an outer enclosure, - an inner tank (24; 224) located inside the outer enclosure, the inner tank (24; 224) containing a material to be evaporated, - an inner tank valve (28; 228) comprising a valve input port (28A; 228A) in fluidic communication with the inner tank (24; 224) and a valve output port (28B; 228B), - a vacuum deposition chamber, and - a leak detection device, - an initialization step in which: - vacuum is made inside the vacuum deposition chamber, then - an initial leak flow rate in the vacuum deposition chamber is measured by means of the leak detection device, and - vacuum is made inside the vacuum deposition chamber, then - an initial leak flow rate in the vacuum deposition chamber is measured by means of the leak detection device, and - a measurement step in which: - the inner tank valve (28; 228) is open to place the vacuum deposition chamber in fluidic communication with the inner tank (24; 224), then - a gaseous mixture is injected into the vacuum deposition chamber, then - a pressure P0 is measured inside the inner tank (24; 224), then - the inner tank valve (28; 228) is closed, then - vacuum is made inside the vacuum deposition chamber to a predetermined pressure in the vacuum deposition chamber, then - the vacuum deposition chamber is placed in fluidic communication with the leak detection device, then - a final leak flow rate in the vacuum deposition chamber is measured by means of the leak detection device, then - a leak rate of the inner tank valve (28; 228) is deducted therefrom. - the inner tank valve (28; 228) is open to place the vacuum deposition chamber in fluidic communication with the inner tank (24; 224), then - a gaseous mixture is injected into the vacuum deposition chamber, then - a pressure P0 is measured inside the inner tank (24; 224), then - the inner tank valve (28; 228) is closed, then - vacuum is made inside the vacuum deposition chamber to a predetermined pressure in the vacuum deposition chamber, then - the vacuum deposition chamber is placed in fluidic communication with the leak detection device, then - a final leak flow rate in the vacuum deposition chamber is measured by means of the leak detection device, then - a leak rate of the inner tank valve (28; 228) is deducted therefrom.