Patent Application
20150343567
The present invention relates to laser-based drilling process methods, and more particularly, to a method and system for formation of vertical microvias in an opaque ceramic thin-plate by femtosecond laser pulses.
Femtosecond laser, so-called ultrafast laser, is characterized by femtoscale pulses (that is 10−15 second, fs). It is characterized with a central wavelength of 800 nm of infrared light. Due to its properties of instantaneously high energy power and insignificantly low accumulation of heat, femtosecond laser is widely applied to precise micro/nano processes. For a conventional method of femtosecond laser-drilling process (as shown in
With such taper microvias, each conductive pillar following the copper-filled vias process could cause an uneven electrical distribution of the impedance. This may further deteriorate the performance of the devices. This different phenomena of the vias formed by femtosecond laser drilling between an opaque and a transparent ceramic substrates may come from their different effective coverage angle of focus for a femtosecond laser pulse. For a transparent ceramic, the focus and the effective coverage angle of focus are stationary during the drilling process. On the contrary, it decreases in case of an opaque ceramic. This phenomenon may lead to two problems, one is the taper microvias, and the other is not easy to form through holes. Vertical microvias of a silicon wafer are conventionally formed by deep-reactive-ion-etch (DRIE) involved high cost and complicated processes such as lithography, vacuum, photomasks and so on. Although the DRIE process for vias formation is well-understood for silicon, it is inapplicable to the other materials, such as ceramic and glass. On the contrary, the advantages of laser-drilling are relative low costs and its process with polytropy, which draw lots of attentions. To increase the competitiveness of laser drilling, it is imperative to provide a method and system for formation of vertical microvias of an opaque ceramic substrate.
In view of the aforesaid drawbacks of the prior arts, the objective of this invention is to provide a method and system to form vertical microvias of an opaque ceramic thin-plate by femtosecond laser pulses. This system includes a titanium-sapphire laser generation, a thin-plate carrier, and a movable stage. It leads to fabricate vertical and high aspect ratio microvias of an opaque ceramic thin-plate.
To achieve the goals, this invention provides a method and a system, which comprising the following steps: (a) thin an opaque ceramic substrate to a thickness of 20-100 μm for a ceramic thin-plate; (B) place the ceramic thin-plate on a carrier; and (C) drill the ceramic thin-plate by femtosecond laser pulses. During the drilling process, the femtosecond laser pulses have the following parameters: a pulse width <100 fs, a pulse frequency of 1,000˜10,000 Hz, a central wavelength of laser of 800 nm, a movable stage with a speed of 20-200 μm/s and a laser power of 200-1000 mW.
The femtosecond laser pulses can be generated by a titanium-sapphire laser, but are not limited to it. The opaque ceramic thin-plate includes aluminum nitride, aluminum oxide, silicon carbide, but is not limited to above-mentioned materials.
To achieve the goals, this invention disclose another method for it, which comprises the following: (a) form blind microvias on the ceramic substrate by femtosecond laser pulses, which aspect ratio is smaller than 5; (b) at some position, further focus the laser to form a through vias on the ceramic thin-plate, the diameter of it is similar to the blind microvia and its aspect ratio is larger than 5; and (c) remove the portion of the lower aspect ratio vias by thinning and then obtain an opaque ceramic thin-plate with a higher aspect ratio vias. The thickness of it is within 20-100 μm.
The femtosecond laser pulses can be generated by a titanium-sapphire laser, but are not limited to it. During the drilling process, the femtosecond laser pulses have the following parameters: a pulse width <100 fs, a pulse frequency of 1,000˜10,000 Hz, a central wavelength of laser of 800 nm, a movable stage with a speed of 20-200 μm/s and a laser power of 200-1000 mW. The opaque ceramic thin-plate includes aluminum nitride, aluminum oxide, silicon carbide, but is not limited to above-mentioned materials.
To achieve the goals, this invention provides another method for formation of vertical microvias of a ceramic thin-plate by femtosecond laser pulses with the following parameters: a pulse width <100 fs, a pulse frequency of 1,000˜10,000 Hz, a central wavelength of laser of 800 nm, a movable stage with a speed of 20-200 μm/s and a laser power of 200-1000 mW.
The objectives, the features, and the advantages of the present invention are hereunder illustrated with specific embodiments in conjunction with the accompanying drawings, in which:
A detailed description of the further features and advantages of the present invention is given below. Therefore, a person skilled in the art can understand and implement the technical contents of the present invention and readily comprehend the objectives, features, and advantages thereof by reviewing the disclosure of the present specification.
A titanium-sapphire laser pulse is one of ultrafast pulses, which means its pulse width is extremely short. Therefore, the quality of the microvias would be significantly improved due to it provides well-defined annealing areas and few thermal budget effects. However, it would lead to form a seriously taper via of a substrate with a non-penetrable property for a central wavelength of 800 nm, such as aluminum nitride. Therefore, the present invention demonstrates, in this embodiment, a method and a system for formation of vertical microvias in an opaque or near-infrared light-absorbed ceramic thin-plate (such as aluminum nitride, aluminum oxide, silicon carbide and so on) by femtosecond laser pulses, which characterized a central wavelength of 800 nm, a pulse width <100 fs, a laser power of 200˜1,000 mW, and a frequency of 1,000˜10,000 Hz.
In another embodiment of the system, a laser head is either movable or stationary. In the situation where the laser head is movable, the movable stage and the laser head are coupled together, thus the motion of the movable stage drives the laser head to move. In the situation where the laser head is stationary, the movable stage and the thin-plate carrier 330 are coupled together, such that the motion of the movable stage drives the opaque ceramic thin-plate to move. The movable stage is a three-axis movable stage with a moving speed of 20-200 μm/s along the x or y axis, while its moving speed of the z-axis is approximately 10 μm/s.
This invention is disclosed above by preferred embodiments. However, persons skilled in the art should understand that the preferred embodiments are illustrative of the present invention only, but should not be interpreted as restrictive of the scope of the present invention. Hence, all equivalent modifications and replacements made to the aforesaid embodiments should fall within the scope of the present invention. Accordingly, the legal protection for the present invention should be defined by the appended claims.
