Background technology
At present, in the method preparing chip of square thyristor, generally all comprise and formed logical isolated area with to logical diffusion method, pure boron, gallium aluminium or fine aluminium are mainly divided into the diffuse source that logical part adopts.Fine aluminium be to the advantage of logical diffuse source be diffusion time short, speed fast, the N-type silicon chip two face portion P type of more than 400 microns can be realized to leading to.Silicon chip completes after logical isolation, then carries out passivation in p type impurity diffusion, photoetching, N-type impurity diffusion, table top moulding, groove, two-sided metallization and chip separation successively, finally makes thyristor chip.
The aluminium of prior art comprises the following steps logical diffusion conventional method: (1) Wafer Cleaning; (2) the two-sided evaporation of aluminum of silicon chip; (3) photoengraving aluminium; (4) to logical diffusion, aluminium is formed to logical isolated area.Conventional simple to logical diffusion method technique, but because this is carry out logical diffusion to the aluminium of silicon chip surface to circulation method, its diffusion time is long, diffusion temperature is high, and particularly owing to anti-carving aluminium, its reticle overwhelming majority is black matrix, area is larger, be difficult to intact in the process of reprint, then in photoetching process, silicon chip contact with reticle and easily causes reticle to damage, and inevitably produces aluminium island thus at silicon chip surface.And because silicon dioxide can not shield aluminium, gallium, aluminium island will spread in logical diffusion process in wafer bulk, its degree of depth and suitable to logical position diffusion depth, can cause forward and reverse voltage low pressure, even break-through, have a strong impact on the qualification rate of thyristor chip.
Summary of the invention
The present invention mainly solves the aluminium island problem that silicon chip in thyristor chip preparation uses conventional method to exist logical diffusion, newly provides a kind of thyristor chip preparation method, improves thyristor chip qualification rate.
A kind of thyristor chip preparation method of the present invention, comprises the following steps:
(1) select in the region of doing logical diffusion at silicon chip, with the etching groove of the method two sides symmetry of photoetching and corrosion, the wide 60-300 micron of its grooving, dark 20-120 micron;
(2) at the two-sided evaporation of aluminum of the silicon chip of grooving, aluminum layer thickness 0.3-3 micron;
(3) will the silicon chip of aluminium lamination in grooving, be had to be placed on prediffusion in diffusion furnace, temperature 600-1200 DEG C, time 1-20 hour;
(4) by the silicon chip twin polishing after prediffusion, one side removes thickness 5-15 micron;
(5) polished silicon slice is carried out in diffusion furnace aluminium to spread again logical, temperature 1200-1250 DEG C, time 10-50 hour, form aluminium to logical isolated area.
The present invention is in conjunction with grooving and finishing method, make silicon chip form aluminium to logical isolated area, its grooving shortened logical diffusion time, more thoroughly removed aluminium lamination through polishing and anti-carve residual island, with the conventional aluminium of employing to compared with circulation method, thyristor chip rate of finished products improves more than 10%.
Embodiment
Accompanying drawing mark illustrate: after N-type silicon chip sectional view (1-1), the two-sided evaporation of aluminum of silicon chip after sectional view (1-2), silicon chip photoengraving aluminium sectional view (1-3), silicon chip aluminium to schematic cross-section (1-4) after logical diffusion; After N-type silicon chip schematic cross-section (2-1), silicon chip photoetching and etching groove after schematic cross-section (2-2), the two-sided evaporation of aluminum of silicon chip after schematic cross-section (2-3), silicon chip twin polishing schematic cross-section (2-4), silicon chip aluminium to schematic cross-section (2-5) after logical diffusion.And N-type silicon chip (10,20), grooving 21, aluminium lamination (12,22,23), aluminium is to logical isolated area (14,24).
As shown in (1-2) to (1-4) of Fig. 1, in conventional thyristor chip preparation method, its silicon chip aluminium to logical diffusing step is: the two-sided evaporation of aluminum of Wafer Cleaning, silicon chip, silicon chip photoengraving aluminium and silicon chip aluminium are to logical diffusion.
As shown in (1-2) to (1-5) of Fig. 2, a kind of thyristor chip preparation method of the present invention, comprises the following steps:
(1) in the selected region of doing logical diffusion isolation of silicon chip 20, with the etching groove 21 of the method two sides symmetry of photoetching and corrosion, the wide 60-300 micron of its grooving 21, dark 20-120 micron;
(2) at the two-sided evaporation of aluminum of the silicon chip of grooving 21, aluminium lamination (22,23) thickness 0.3-3 micron;
(3) will the silicon chip of aluminium lamination 23 in grooving 21, be had to be placed on prediffusion in diffusion furnace, temperature 600-1200 DEG C, time 1-20 hour;
(4) by the silicon chip twin polishing after prediffusion, one side removes thickness 5-15 micron;
(5) polished silicon slice is carried out in diffusion furnace aluminium to spread again logical, temperature 1200-1250 DEG C, time 10-50 hour, form aluminium to logical isolated area.
The present invention successively by Wafer Cleaning, photoetching corrosion grooving, evaporation of aluminum, prediffusion, polishing, spread logical, thus makes silicon chip complete aluminium to isolate logical diffusion again.Grooving and polishing combine by its method dexterously, shortened logical diffusion time, thoroughly remove aluminium lamination anti-carve residual island by polishing by grooving diffusion, and with conventional aluminium to compared with circulation method, thyristor chip rate of finished products of the present invention improves more than 10%.
In addition, polishing and aluminium are carried out passivation in p type impurity diffusion, photoetching, N-type impurity diffusion, table top moulding, groove, two-sided metallization and chip separation to the silicon chip after logical diffusion successively in rear operation, makes mesa thyristor chip.
Described p type impurity diffusion carries out the diffusion of gallium aluminium, temperature 1200-1260 DEG C under polishing and aluminium are placed on closed ampoule vacuum environment to the silicon chip after logical diffusion, time 10-30 hour, junction depth 30-120 micron, surface concentration 30-100 Europe nurse ∕ square, forms silicon chip base PN junction.
Described N-type impurity is diffused as phosphorus diffusion, diffusion temperature 1000-1200 DEG C, time 1-6 hour, junction depth 10-30 micron, surface concentration 0.08-1.5 Ou Mu ∕ square.
Described table top moulding, be adopt photoetching process to erode away etching tank, the component volume proportion of corrosive liquid is: fuming nitric aicd: nitric acid: hydrofluoric acid: glacial acetic acid=3:2:4:2, etching time: 5-8 minute; Groove depth 70-150 micron.
In described groove, passivation is glassivation.
Described two-sided metallization adopts evaporation aluminium, titanium, nickel, silver, alloy under vacuum and temperature 380-500 DEG C of condition.
Described chip separation is divided into single thyristor chip from aluminium to cutting in the middle of logical isolated area.
The present invention removes the deionized water solution that impurities on surface of silicon chip can use 5-20% concentration hydrogen potassium oxide or NaOH before photoetching corrosion grooving, heating 50-100 DEG C, etching time 5-30 minute, silicon chip surface glimmer.
The present invention carries out aluminium to logical diffusion in the bottom of grooving, and conventional aluminium carries out aluminium diffusion to logical method of diffusion at silicon chip surface, and with conventional method ratio, the present invention can shorten 20-50 hour to logical diffusion time.
At conventional aluminium in logical diffusion process, photo-mask process causes and remains island unavoidably at silicon face, makes the deliquescing of chip puncture voltage or break-through.And the inventive method carries out polishing after aluminium prediffusion, two-sidedly remove 5-15 micron respectively, by the aluminium lamination of silicon chip surface and anti-carve aluminium remain under aluminium island all remove totally, thus thyristor chip qualification rate is significantly improved.
The present invention adopts the method that grooving and polishing combine on silicon chip, enables silicon chip comparatively fast form aluminium to logical isolated area, and thoroughly solves the conventional aluminium of long-standing problem to the silicon chip surface residual aluminum island problem of logical diffusion technology.Polishing process removes silicon wafer thickness 5-15 micron, and rooved face width can be made to be reduced to width less than 1/2nd before polishing, but can not affect other operation and carry out.The present invention be also suitable for other semiconductor product to logical diffusion technology.
It is understood that above-described embodiment is just to explanation of the present invention, any innovation and creation do not exceeded in spirit of the present invention, all fall within protection scope of the present invention.