Positive- and negative-tone structuring of crystalline silicon by laser-assisted chemical etching

Pulse-duration dependence of laser-induced modifications inside silicon

“…5 must inevitably increase for longer pulses and reach unity level when the delivered fluence and LIDT curves cross each other. This picture is consistent with our previous studies and others [15,17,19] reporting modifications in Si with NA=0.45 for a pulse duration of about 5 ns. This proves that the ratio exceeds 1 in the nanosecond regime and a ratio reaching the unity level for minimum pulse duration between 20 ps and 5 ns.…”

“…Thanks to the ability to continuously tune the pulse duration, we have positioned very precisely a NA and pulse duration combination threshold in the picosecond regime. By reporting also on the same graph the extreme NA requirements with femtosecond pulses [2] and some successful conditions with relatively modest NA in the nanosecond regime [19], we can also show the typical dependence to these parameters of modification threshold by a dashed black line on this graph. This must represent an important guideline for the developments of ultrafast laser 3D writing technologies which remains challenging but holds great promises to the future electronic industry.…”

“…We report successful and unsuccessful attempts of this study by respectively hollow circle and cross symbols filled into respective pulse energy color scale value. The successful attempts obtained with more modest NA in the nanosecond regime (shown inside square box A) [19] and extremely high NA for the shortest pulses (illustrated under square box C) [2] are complemented by the current work (implemented under box B). In this way, we show with the dashed black line the probable threshold conditions which must be exceeded to achieve modification.…”

“…Future works should be based on the detailed response on these materials, but we observed that this 'Abnormal' response is not a specificity of Si but can be likely generalized to bulk interactions in narrow gap materials.Obviously, we are not the first to achieve bulk writing in Si, but it is striking to note that the data in the intermediate picosecond regime are scarce and somehow contradictory [5,23]. Over the last decades, important bulk Si modification technologies such as stealth dicing, laser assisted etching and some other photonics applications have been developed with nanosecond pulses that allow to readily induce internal damage in a Si wafer [15][16][17]19,32]. Also, it is only in the last few years that the possibility to achieve refractive index engineering in Si has been demonstrated with sub-picosecond pulses [2][3][4].…”

“…In particular, nanosecond pulses are today readily used for internal inscription in silicon leading to technologies as important as wafer stealth dicing [13] or internal marking [14]. It is also today used for more advanced processing with some optical and fluidic functionalities added to Si in this regime [15][16][17][18][19][20]. At the opposite, the shortest ultrashort pulses (sub-100 fs) usually fail in inducing permanent changes inside Si using conventional machining configurations [2,8,21,22].…”