Apparatus and method for real-time measurement of thin film layer thickness and changes thereof

An apparatus for collecting information regarding the change in the thickness of a thin film being reduced in thickness on a substrate supported on a support in the presence of plasma emission radiation emitted throughout a volume of gas, the apparatus comprising:

• a. spaced away from said support, and on the opposite side of said volume of gas that emits said plasma emission, an array of means for sensing plasma emission radiation reflected from the thin film, the array providing an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film;
• b. filter means for transmitting plasma emission radiation of at least one selected range of wavelengths to said array of sensing means;
• c. means for focusing plasma emission radiation reflected from said film, said focusing means arranged between said thin film and said array such that an image of a region of said film is focused onto said array;
• and
• d. means for storing a time sequence of data signals corresponding to the signals generated by the array of sensing means over a period of time in response to plasma emission radiation transmitted through said filter means and in response to no other significant illumination, reflected from said film.

A method for determining when a layer of a thin film has been completely removed by a thickness reduction process in the presence of plasma emission radiation emitted throughout a volume of gas at a plurality of locations over the area of said thin film, comprising the steps of:

• a. reflecting said plasma emission radiation from said thin film, in the absence of any other significant illumination of said thin film, during the time said film is being reduced in thickness;
• b. focusing at least one selected range of wavelengths of said plasma emission radiation reflected from said film onto an array of means for sensing plasma emission radiation which provides an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film said array being located on the opposite side of said volume of gas that emits said plasma emission from said film;
• c. generating a time sequence of data signals corresponding to the signals generated by the array of sensing means over a period of time in response to plasma emission radiation focused on said array;
• d. correlating the amplitude of said data signals with the time during which said signals were generated;
• e. identifying a time periodic pattern in the amplitude of said data signals;
• f. at selected time intervals, comparing the rate of change of said amplitude of said data signals with said periodic pattern;
• and
• g. determining that said film has been removed if said rate of change of said amplitude of said signals departs from said periodic pattern.

A method for determining the rate of change of the thickness of a thin film to which is being applied a process of changing film thickness in the presence of plasma emission radiation emitted throughout a volume of gas at a plurality of locations over the area of said thin film, said method comprising the steps of:

• a. reflecting plasma emission radiation from said thin film, in the absence of any other significant illumination of said film, during the time said film is being changed in thickness;
• b. focusing at least one selected range of wavelengths of said plasma emission radiation reflected from said film onto an array of means for sensing electromagnetic radiation which provides an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film, said array being located on the opposite side of said volume of gas that emits said plasma emission from said film;
• c. generating a time sequence of data signals corresponding to the signals generated by the array of sensing means over a period of time in response to radiation focused on said array;
• d. correlating the amplitude of said data signals with the time during which said signals were generated;
• e. identifying a periodicity in the rate of change of the amplitude of said data signals;
• and
• f. determining the rate of change of the thickness of said film by relating said periodicity to said selected range of wavelengths.

A method for determining the thickness of a thin film at a plurality of locations over the area of said thin film, said method comprising the steps of:

• a. emitting plasma emission radiation throughout a volume of gas and reflecting said plasma emission radiation from said thin film, in the absence of any other significant illumination of said film, during the time said film is being changed in thickness;
• b. focusing at least two selected ranges of wavelengths of said plasma emission radiation reflected from said film onto an array of means for sensing plasma emission radiation which provides an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film said array being located on the opposite side of said volume of gas that emits said plasma emission from said film;
• c. generating a set of data signals corresponding to the signals generated by the array of sensing means in response to radiation of said selected at least two ranges of wavelengths focused on said array;
• d. correlating the amplitudes of said data signals with the wavelength of said plasma emission radiation from which said signals were generated;
• e. comparing said correlation of the amplitudes to a predetermined correlation between amplitudes and film thickness;
• and
• f. determining the thickness of said film by said comparison.