System for making a photoresist master for a hybrid optical recording disc

A laser beam recording system for making a hybrid optical master disc from which a stamper can be derived for forming a hybrid optical recording disc, the system comprising:

• a) a laser which emits a laser beam having a wavelength selected to provide activating radiation to a photoresist layer formed over a substrate of the master disc;
• b) a first optical modulator for modulating an intensity of the laser beam between a lower intensity for exposing a groove in the photoresist layer and a higher intensity for exposing a groove and a pattern of depressions in the groove in the photoresist layer, the pattern of depressions coincident with the groove, and the pattern of depressions exposed in response to an intensity-modulating signal;
• c) a second optical modulator for frequency-modulating the intensity-modulated laser beam with a wobble-frequency in response to a frequency-modulating signal, the first and the second optical modulators operative concurrently to expose a continuous frequency-modulated groove having portions corresponding to a ROM region of a hybrid optical recording disc in which the intensity-modulated pattern of depressions is exposed;
• d) means for rotating the photoresist master disc during exposure to the laser beam, and means for radially translating the master disc so that the laser beam incident on the photoresist layer will trace a continuous exposed spiral groove;
• and
• e) a laser beam modulation control system including
• (i) a clock;
• (ii) an ATIP generator connected to the clock and operative to generate a frequency-modulating ATIP signal and means for generating ATIP flag pulses;
• (iii) an EFM generator connected to the clock and operative to generate an intensity-modulating EFM signal in correspondence with digital data input signals and means for generating EFM flag pulses;
• (iv) logic circuits for providing logic control of temporal relationships between an intensity-modulating output signal of the EFM generator and a wobble-frequency-modulating output signal of the ATIP generator, the logic circuits receiving flag pulses from the EFM generator and directing such EFM flag pulses to the ATIP generator, and the logic circuits receiving flag pulses from the ATIP generator and directing such ATIP flag pulses to the EFM generator;
• (v) a function generator for generating a time-varying signal at an output thereof in response to input pulse signals received from a first output of the logic circuits;
• (vi) a waveform modifier receiving the intensity-modulating EFM signal from the EFM generator and providing a selectable bias level signal such that an output signal of the waveform generator will have a selected bias level signal and the EFM signal superimposed thereupon, whereby the selected bias level signal provides the lower intensity of the laser beam for exposing the groove in the photoresist layer, and the EFM signal superimposed upon the selected bias provides the higher intensity of the laser beam for exposing the groove and the pattern of the depressions in the groove in the photoresist layer;
• and
• (vii) a multiplexer operative to provide an intensity-modulating output signal to the first optical modulator in response to a multiplexer input control signal provided by a second output of the logic circuits, the intensity-modulating output signal of the multiplexer either being the EFM signal superimposed upon the bias level signal provided by the waveform modifier or being the time-varying signal provided by the function generator in correspondence with the presence or absence of the multiplexer input control signal.