US 5,841,099 AGranted

Method employing UV laser pulses of varied energy density to form depthwise self-limiting blind vias in multilayered targets

AssigneeElectro Scientific Industries, Inc.

InventorsMark D. Owen, Bonnie A. Larson, Jozef Van Puymbroeck

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Abstract

The output of a continuously pumped, Q-switched, Nd:YAG laser (10) is frequency converted to provide ultraviolet light (62) for forming vias (72, 74) in targets (40) having metallic layers (64,68) and a dielectric layer (66). The invention employs a first laser output of high power density to ablate the metallic layer and a second laser output of a lower power density to ablate the dielectric layer. The parameters of the output pulses (62) are selected to facilitate substantially clean, sequential drilling or via formation. These parameters typically include at least two of the following criteria: power density first above and then below the ablation threshold of the conductor, wavelength less than 400 nm, a temporal pulse width shorter than about 100 nanoseconds, and a repetition rate of greater than about one kilohertz. The ability to generate ultraviolet light output pulses at two power densities facilitates the formation of depthwise self-limiting blind vias in multilayer targets, such as a target composed of a layer dielectric material covered on either surface by a layer of metal.

Claims43

Dependent claims

A method for laser machining a depthwise self-limiting blind via in a multilayered target including at least first and second conductor layers having respective first and second conductor ablation energy thresholds and a dielectric layer having surfaces and a dielectric ablation energy threshold, the first and second conductor layers positioned above and below, respectively, the surfaces of the dielectric layer and the first and second conductor ablation energy thresholds exceeding the dielectric ablation energy threshold, comprising:

generating, from a nonexcimer laser at a first repetition rate of greater than about 200 Hz. a first laser output having a wavelength of less than 400 nm and containing at least one first laser pulse having a first energy density over a first spatial spot size, the first energy density being greater than the first conductor ablation energy threshold;
applying the first laser output to the target to remove the first conductor layer within a spot area of the target;
changing the first repetition rate of the nonexcimer laser to a second repetition rate greater than the first repetition rate to decrease the first energy density to a second energy density over a second spatial spot size, the second energy density being less than the first and second conductor ablation energy thresholds;
generating. from the nonexcimer laser at the second repetition rate, a second laser output having a wavelength of less than 400 nm and containing at least one second laser pulse having the second energy density, the second energy density being greater than the dielectric ablation energy threshold;
and
applying the second laser output to the target to remove the dielectric layer within the spot area of the target and, as a consequence of the second energy density being less than the second conductor ablation energy threshold, to leave the second conductor layer substantially unvaporized and thereby form a depthwise self-limiting blind via.

3 more elements

A method for laser machining a blind via in a multilayered target including at least first and second conductor layers having respective first and second conductor ablation energy thresholds and a dielectric layer having surfaces and a dielectric ablation energy threshold, the first and second conductor layers positioned above and below, respectively, the surfaces of the dielectric layer, comprising:

generating, from a nonexcimer laser at a repetition rate of greater than about 200 Hz, a first laser output having a wavelength of less than 400 nm and containing at least one first laser pulse having a first energy density over a first spatial spot size and a temporal pulse width shorter than about 100 ns, the first energy density including an average output power of greater than about 100 mW measured over the first spatial spot size and being greater than the first conductor ablation energy threshold;
applying the first laser output to the target to remove the first conductor layer within a spot area of the target;
generating from a nonexcimer laser at a repetition rate greater than about 200 Hz, a second laser output having a wavelength of less than 400 nm and containing at least one second laser pulse having a second energy density over a second spatial spot size and a temporal pulse width shorter than about 100 ns, the second energy density including an average output power of greater than 100 mW, being greater than the dielectric ablation energy threshold, and being different from the first energy density;
and
applying the second laser output to the target to remove the dielectric layer within the spot area of the target to form a blind via.

2 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/651,036Filed 17 May 1996 · continuation in part
Priority: 18 Jul 1994
Granted: 24 Nov 1998
Term ends: Not estimatedThe source records don’t support an estimate.

Classification25 codes

C23C 14/046
Coating on selected surface areas, e.g. using masks: coating cavities or hollow spaces, e.g. interior of tubes; Infiltration of porous substrates
B23K 26/384
By boring: of specially shaped holes
B23K 26/389
By boring: of fluid openings, e.g. nozzles, jets
B23K 26/40
Removing material: taking account of the properties of the material involved