CN100401537C

CN100401537C - Laser grinding, capable tech. for GaN base LED chip of reducing GaN layer burn

Info

Publication number: CN100401537C
Application number: CNB2004100774244A
Authority: CN
Inventors: 巫仕文
Original assignee: SHENZHEN FANGDA GUOKE OPTICAL ELECTRONIC TECHNOLOGY Co Ltd
Current assignee: Shenzhen Fangda Guoke Optoelectronic Technology Co., Ltd.
Priority date: 2004-12-07
Filing date: 2004-12-07
Publication date: 2008-07-09
Anticipated expiration: 2024-12-07
Also published as: CN1787238A

Abstract

The present invention relates to a laser scribing process of a GaN-base LED chip for reducing the GaN layer burn, which is characterized in that during laser scribing, an optical lens with a focal length which is from 18 to 22mm is used, so that lasers are densely radiated on a sapphire layer of the chip, and the preferred focal length is 20mm. During laser scribing, through the optical lens, lasers are focused within the range from the outer surface of the sapphire layer and 5 micrometer outer the outer surface of the sapphire layer, and the lasers are best focused on the outer surface of the sapphire layer. The present invention uses a long-focus optical lens with the focal length of 18 to 22mm. The divergence angle of the lasers is smaller, the power density is larger, and the absorption of laser energy by a sapphire is increased. Therefore, the present invention can better solve the burn of the GaN layer to the GaN-base LED chip by using a long-focus optical lens. In addition, lasers are strictly focused on the back surface of the chip or out of the back surface during scribing, and the generation of white points caused by the burn of lasers to the CaN layer can also be avoided effectively.

Description

Reduce the GaN base LED chip laser scribing technology that the GaN layer is burnt

Technical field

The present invention relates to a kind of GaN base LED chip laser scribing technology, be specifically related to the GaN base LED chip laser scribing technology that a kind of GaN of minimizing layer is burnt.

Background technology

The scribing process of the LED epitaxial wafer of present Sapphire Substrate, most of producers all adopt laser scribing technology, on the epitaxial wafer substrate sapphire, burn the Cutting Road of 1/4 chip thickness with laser scribing means, and then use the sliver machine chip to be split along Cutting Road, finish the scribing process of led chip.During laser scribing, the time regular meeting situation that laser burns the GaN layer takes place, examine under a microscope and be the continuous or discrete hot spot pattern of burning; through experimental identification, behind the laser burn GaN, the photoelectric parameter of chip can change; the parameter of particularly leaking electricity raises, and causes chip rejection.The power density of laser is most important parameter, because the absorptivity of different material for laser light depends on the size of its energy threshold, when the power density of laser during greater than the energy threshold of this material, material for laser light just can produce absorption very, when being lower than energy threshold, do not absorb basically.

Summary of the invention

The technical problem to be solved in the present invention is, at the above-mentioned defective that prior art exists, the GaN base LED chip laser scribing technology that provides a kind of GaN of minimizing layer to burn.

The technical solution used in the present invention is, the GaN base LED chip laser scribing technology that a kind of GaN of minimizing layer is burnt is characterized in that, when laser scribing, using focal length is the optical lens of 18～22mm, makes laser comparison concentrated area penetrate sapphire layer at described chip.

The GaN base LED chip laser scribing technology that above-mentioned minimizing GaN layer is burnt, described focal length is preferably 20mm.

The GaN base LED chip laser scribing technology that above-mentioned minimizing GaN layer is burnt when laser scribing, by described optical lens, gathers the sapphire layer outer surface to the sapphire layer outer surface in 5 micrometer ranges with laser.

The GaN base LED chip laser scribing technology that above-mentioned minimizing GaN layer is burnt when laser scribing, by described optical lens, gathers laser on the sapphire layer outer surface.

Compared with prior art, the present invention reduces the GaN base LED chip laser scribing technology that the GaN layer is burnt, using focal length is the long-focus optical lens of 18～22mm, and uses focal length to compare as 15mm or less than 15mm in the prior art to have outstanding substantive distinguishing features.Use long-focus, the dispersion angle of laser is smaller, place in skew focus same distance, the laser spots area A is smaller, when laser energy P is identical, power density D=P/A is just bigger, so sapphire is also just relatively abundant to laser energy absorption, and the leeway of laser focusing focus that can not produce white point is just bigger.Therefore using the optical lens of long-focus can solve laser preferably burns to the GaN layer of GaN base LED chip.Strictness focuses on beyond the chip back or the back side during scribing in addition, because focus helps sapphire layer at chip back laser energy is absorbed more fully, focus overleaf beyond, because the distance of GaN layer off-focal is bigger, the laser that arrives the GaN layer also just relatively disperses, can reduce of the absorption of GaN layer, thereby can avoid laser that the GaN layer is burnt effectively and produce white point laser energy.

Description of drawings

Fig. 1 is sapphire and GaN to the absorptivity of the laser situation of change figure with power density;

Fig. 2 is the absorbing state schematic diagram of laser when seeing through sapphire layer.

Embodiment

Embodiment one

The GaN base LED chip laser scribing technology that a kind of GaN of minimizing layer is burnt when laser scribing, is used the optical lens of focal length as 18mm, makes laser comparison concentrated area penetrate sapphire layer at described chip.

Above-mentioned optical lens focal length also can be 18,19,20,21 or 22mm.

Embodiment two

The GaN base LED chip laser scribing technology that a kind of GaN of minimizing layer is burnt when laser scribing, by optical lens, gathers sapphire layer outer surface 2.5 microns places to the sapphire layer outer surface with laser.All the other are identical with embodiment one.

The GaN base LED chip laser scribing technology that above-mentioned minimizing GaN layer is burnt, when laser scribing, by optical lens, also laser can be gathered sapphire layer outer surface 1,2,3,4 or 5 micron place to the sapphire layer outer surface, preferably laser is gathered on the sapphire layer outer surface.

In the present invention, power density D is most important parameter, because the absorptivity of different material for laser light depends on the size of its energy thresholding Et, as the power density D of laser during greater than the energy thresholding Et of this material, material for laser light just can produce absorption very, when being lower than energy thresholding Et, do not absorb basically.As shown in Figure 1, be sapphire and GaN to the absorptivity of laser situation of change, Et ' and Et with power density " represent GaN and sapphire energy thresholding respectively.

As shown in Figure 2, the absorbing state when seeing through sapphire layer for laser, E0 is the laser energy behind the object lens, and E1 is the energy that sapphire layer absorbs, and E2 is for seeing through the unnecessary laser energy of sapphire layer, E0=E1+E2.When E0 was constant, when E1 reduced, E2 increased, and the laser power density on the GaN just increases, and when it surpassed the energy thresholding of GaN, the GaN layer will produce hypersorption to remaining laser, and temperature raises, and burning produces white point; Otherwise when E1 increased, E2 reduced, and the laser power density on the GaN just reduces, and when it was lower than the energy thresholding of GaN, the GaN layer was will be to remaining laser absorption few or do not absorb, thereby avoids Yin Wendu to raise and the GaN layer of burning.

When the focus of laser is not during just on the sapphire layer surface, the laser energy of getting on the sapphire just relatively disperses, and it is just smaller that sapphire can produce the zone of hypersorption, and its E1 that sponges is also just smaller, the ENERGY E 2 that arrives the GaN layer so just increases, and white point has also just produced.

By above-mentioned analysis and research, want to avoid the generation of white point, the laser energy E2 that arrives the GaN layer will be reduced or the laser power density D that arrives the GaN layer is reduced, so following two kinds of methods are arranged to avoid the generation of white point.

(1) optical lens of use long-focus.

The optical lens of long-focus, the angle of laser is smaller, in the place of skew focus same distance, the laser spots area A is smaller, and when laser energy P was identical, power density D=P/A was just bigger, therefore sapphire is also just relatively abundant to laser energy absorption, and promptly E1 increases.The leeway of laser focusing focus that can not produce white point is just bigger.Therefore the generation of using the optical lens of long-focus can solve white point preferably.In one embodiment, with the optical lens of 18mm, the deviation range that the permission focus that can not produce white point through experiment and daily production testing departs from sapphire surface rises to 25um. from original 10um

(2) to avoid the generation of white point in theory, should focus on sapphire surface during laser focusing as far as possible, do not allow the focus of laser deflect away from sapphire the inside or above, make laser more concentrated, increase E1.But when owing to there not be the focusing that very accurate way can locating laser, and the also very perfection of the evenness of slice, thin piece, can deflect away from a little during focusing above the sapphire surface about 5 microns.Because focus is on the upper side the time, because the distance of off-focal is bigger, the laser that arrives the GaN layer also just relatively disperses, and power density reduces, and the possibility that produces white point is more much smaller when the sapphire the inside than focus.

Claims

1. one kind is reduced the GaN base LED chip laser scribing technology that the GaN layer is burnt, it is characterized in that, when laser scribing, using focal length is the optical lens of 18～19mm, make laser comparison concentrated area penetrate sapphire layer at described chip, when laser scribing,, laser is gathered the sapphire layer outer surface to the sapphire layer outer surface in 5 micrometer ranges by described optical lens.

2. the GaN base LED chip laser scribing technology that minimizing GaN layer according to claim 1 is burnt is characterized in that, when laser scribing, by described optical lens, laser is gathered on the sapphire layer outer surface.

3. the GaN base LED chip laser scribing technology that minimizing according to claim 1 GaN layer is burnt is characterized in that, when laser scribing, by described optical lens, laser is gathered sapphire layer outer surface 2.5 microns places to the sapphire outer surface.