Method And Apparatus For Subdividing A Crystal Wafer

Abstract

A body, such as a crystalline semiconductor body for the production of diodes, transistors, thyristors or other electronic components, is severed from a crystal wafer by placing the wafer face-to-face onto the surface of a griddle which has a slit along each cutting line. A sandblast is directed from a jet nozzle upon the top face of the wafer above the slit, and relative movement is imparted between griddle and jet nozzle in a direction lengthwise of the slit, simultaneously exhausting the sand out of the slit. In this manner, the crystal body is separated from the rest of the wafer along the slit. Preferably, the device for performing the method is provided with a griddle whose top surface has a group of parallel slits extending crosswise to another group of parallel slits, a comb structure, also with intersecting slits, being mounted above the griddle surface proper. Such apparatus is capable of simultaneously severing a multiplicity of individual bodies from a crystal wafer.

Description

My invention relates to a method of severing crystalline bodies from a crystal slice or wafer.

In electrical appliances for industrial, kitchen and other purposes, it has become increasingly desirable to employ semiconductor circuit components whose power demand is relatively low and whose external dimensions, therefore, may be relatively small.

The use of such small-area semiconductor components in electrical appliances on the one hand, and the large number of these components required for such uses, are predicated upon the availability of particularly economical mass production methods. These must be of such character, however, as to avoid appreciable deleterious effect upon the properties, particularly the electrical qualities, of the semiconductor components produced. The electrical properties of a semiconductor component are particularly liable to be impaired when the crystalline body of this component is cut from a large-area crystalline slice or wafer that incorporates a sequence of parallel zones having alternate different types of conductivity parallel to the wafer main faces. When severing the semiconductor components by sawing or breaking, the separating edge and surface portion of the resulting bodies is subjected to deeply penetrating damage and destruction of the crystalline lattice structure which may virtually form short-circuits across the p-n junctions where these emerge at the surface so that the junctions no longer possess a sufficient if any blocking ability. Although the damaged crystal layers at the surface of the severed semiconductor components can be eliminated by etching, this method requires the use of acidic etchants, for example a mixture of hydrofluoric acid and nitric acid, as well as long periods of etching time so that any contact electrodes of metal on the semiconductor component are attacked by the etchant.

It is an object of my invention to devise a different method which, on the one hand, secures an improved economy of manufacture and, on the other hand, avoids or minimizes the occurrence of crystalline damage at the severing edges that require subsequent treatment by acidic etchant.

To this end, and in accordance with a feature of my invention, I sever a crystal body from a crystal slice or wafer by placing the wafer face-to-face onto a surface area of a griddle which is slitted in that area. I further direct from a nozzle a jet of sandblast upon the other face of the wafer above each slit and impart a relative motion between the griddle and the jet in a direction lengthwise of the slit. Simultaneously, I exhaust the sand out of the slit. As a result, the crystal body is severed from the wafer along the slit.

With such a method, the damages to the crystal lattice structure at the cutting edge of the bodies separated from the crystal wafer are extremely slight and can be removed within a minimum of time with the aid of alkaline etchants which do not attack any metal electrodes attached to the crystal bodies. Consequently, the blocking ability of any p-n junctions that may emerge at the severing faces remains fully effective or does not exhibit appreciable deterioration. Furthermore, cuts of a sharp contour are produced in the crystal wafers, and the edges of the separated bodies are free of broken-away localities.

According to further features of my invention, I perform the above-described method with the aid of a device which has a griddle whose supporting surface for the crystalline wafer is provided with crosswise arrays of parallel slits, the device further comprising a group of metal combs which form a crosswise design matching that of the slitted griddle and which are stationarily fixed in a frame.

According to another feature of the invention, a griddle arrangement particularly simple to manufacture is made of a metal block which has crosswise parallel incisions at the supporting surface for the crystalline wafer and whose bottom is traversed by exhaust bores communicating with the incisions.

The above-mentioned and further objects, advantages and features of my invention will be apparent from the following description of embodiments of processing equipment according to the invention illustrated by way of example on the accompanying drawings in which:

FIG. 1 is a lateral view of apparatus for severing crystal bodies from a crystal wafer.

FIG. 2 is a perspective view of the griddle structure in apparatus according to FIG. 1.

FIG. 3 shows on a larger scale a portion of the wafer-supporting griddle surface corresponding to FIG. 2.

FIG. 4 is a vertical section through FIG. 3, the left-hand portion of FIG. 4 being sectioned along the line A--B, and the right-hand portion of FIG. 4 being sectioned along the line B--C of FIG. 2.

FIG. 5 is a schematic and perspective view of another embodiment of a griddle applicable in apparatus otherwise corresponding to FIG. 1.

FIG. 6 is a lateral view, partly in section, of a device according to FIG. 5, the section being taken along the line D--D of FIG. 5.

The apparatus according to FIG. 1 comprises a support 2 with an opening 3 to which a downwardly extending exhaust pipe 4 is connected by means of a duct flange. Mounted on the support 2 above the exhaust opening 3 is a griddle 5. The griddle is fastened on the support 2 by two angle pieces 7 located opposite each other and entering into recesses 6 at correspondingly opposite lateral faces of the griddle 5. The angle pieces 7 are secured to the support 2 by mounting screws such as those visible in FIG. 2. The recesses 6 permit an adjustable fastening of the griddle 5 to the support 2.

The supporting surface 8 on top of the griddle 5 is preferably lapped to planar shape. Four crystal slices or wafers 9 which, for simplicity, are shown only by dot-and-dash lines, are placed face-to-face on top of the griddle. The wafers 9 are preferably cemented by cellulose varnish to the supporting surface 8 which is only slightly roughened by the lapping treatment. The crystal wafers 9, for example, may consist of silicon and may have metal coatings on their main faces so as to contain a sequence of zones having alternately different conductivity types and extending parallel to the main faces. It is the purpose of the apparatus shown in FIG. 1 to separate the silicon wafers 9 into a multiplicity of small silicon components for electronic semiconductor purposes.

Mounted above the support 2 is a sandblasting device 10 with a jet nozzle 11 directed vertically toward the supporting surface 8 of the griddle 5. Preferably the nozzle 11 has a slot-shaped orifice. The sandblasting device is adjustably mounted on a horizontal holder rod 12 and is connected at the top with a sandblast supply hose 14. The rod 12 is adjustably mounted on a holder structure 13 which can be displaced in the direction of the arrow 18 within the plane of illustration, and which can also be displaced in a direction perpendicular to the plane of illustration, each time in parallel relation to the supporting surface 8 of the griddle 5. As is shown in FIGS. 2 and 3, the griddle 5 comprises a frame structure 5a in which a packet of identical metal combs are firmly clamped. The tips of the teeth on these metal combs 15, in totality, constitute the above-mentioned supporting surface 8 of the griddle for accommodating the crystal wafers 9.

The support 2 is rotatable in a plane parallel to the supporting surface 8. The support 2 has a lug projecting from the periphery. The angular movement of the lug is limited by two fixed stops 18 so that the support 2 can be turned a maximum angular amount of 90.degree..

As will be seen from the section A-B in FIG. 4, a strip-shaped spacer 16 is arranged on both sides of the griddle 5. Each spacer is located between two combs 15. The spacer strips thus provide for slits 21 which are parallel to the combs and interrupt the supporting surface 8. The section B--C shown in FIG. 4 indicates that the interspaces between the individual teeth of the combs 15 form further slits 24 perpendicular to the combs 15.

After the crystal wafers 9 are cemented to the supporting surface 8 of the griddle 5, the sandblasting device is so set that the orifice of the blast nozzle 11 is located above one of the slits 21. When the holder 13 is shifted in the direction of the arrow 18 along the slit 21, starting from the frame 5a of the griddle 5 and moving at uniform speed, the sandblast cuts through two wafers 9 located above the slit 21. The sand of the blast is exhausted from beneath the griddle 5 through the slit 21 and the exhaust duct 4. This prevents the sand from backing up and collecting in the slit.

After thus producing the severing cut above the slit 21, the holder 13 is shifted perpendicularly to the plane of illustration (FIG. 1), i.e. in the direction of the arrow 25 in FIG. 2, so that the orifice of the jet nozzle 11 is located above slit 21. Now the cutting operation is repeated, again starting from the frame 5a of the griddle 5 by shifting the holder 13 together with the sandblasting device 10 in the direction of the arrow 18 along the other slit 21 at uniform speed. This produces another severing cut through two crystal wafers 9.

After the cuts are completed along all of the parallel slits 21, the support 2 is turned 90.degree.. Thereafter, the crystal wafers 9 are cut in the same manner as described above, but now along the slits 24 perpendicular to the slits 21. Subsequently, the small silicon bodies cut from the wafers 9 are removed from the griddle 8, for example, with the aid of acetone.

A cutting rate of 3 to 5 cm per minute has been found well suitable for severing crystal wafers 9 or 0.3 mm thick silicon having a nickel layer of 3 to 5 micron thickness on each of the two main faces. The width of the severing cut is preferably 0.2 mm. This cutting width is obtained with a jet nozzle 11 whose slotted orifice has a width of about 0.15 mm. The width of the slits 21 and 24 in the griddle is preferably twice to three times the width of the slit-shaped nozzle orifice. The sand employed preferably has a grain size of 10 to 30 microns, preferably about 20 microns.

After severing the crystal bodies from the silicon wafers 9, the small silicon bodies already provided with area electrodes, are etched for 1 to 2 minutes in an aqueous solution of KOH or NaOH The crystal damages caused by the sandblasting at the surface of these silicon bodies are so slight that all of the damaged lattice structure is removed by this treatment, and the full blocking ability of the p-n junctions emerging at the cutting faces is preserved without damage to the metal electrodes.

The sandblasting device 10 may also be provided with several jet nozzles 11' located beside one another, as shown in FIG. 6, so that simultaneously several parallel cuts can be passed through the crystal wafers 9.

The further embodiment of the griddle shown in FIG. 5 and applicable in apparatus otherwise corresponding to FIG. 1, comprises essentially a prismatic block 31 which is provided at the supporting surface for the semiconductor wafers 9 with a number of crosswise and parallel incisions 32 and 33. The other components of the griddle device according to FIG. 5 are denoted by the same reference numerals as those used in FIGS. 1 and 2 for corresponding items respectively.

As will be seen from the cross section illustrated in FIG. 6, the crosswise parallel incisions 32 and 33 extend downward to approximately one-half the height of the metal block 31. The bottom portion of the block 31 is provided with suction bores 34 which preferably are arranged precisely beneath the intersection points of the crosswise parallel incisions 32, 33.

The griddle according to FIGS. 5 and 6 can be fastened, in the same manner as the griddle 5 of FIG. 2, above the suction opening 3 on the support 2.

To those skilled in the art it will be obvious upon a study of this disclosure that my invention permits of various modifications and hence may be given embodiments other than particularly illustrated and described herein, without departing from the essential features of my invention and within the scope of the claims annexed hereto.

Claims

I claim:

1. The method of subdividing a thin semiconductive crystal wafer into individual semiconductor members by forming cuts in the wafer perpendicularly to the faces thereof which comprises cementing a face of the wafer onto a planar support formed with an array of slits extending in direction in which the cuts are to be formed in the wafer, disposing a sandblast nozzle having an elongated outlet opening, that is narrower than the width of the slits formed in the support directly above the opposite face of the wafer and in alignment with one of the slits, blasting a jet of sand having a grain size of substantially 10 to 30 .mu. from the nozzle onto the opposite face of the wafer along the respective slit, and then passing the nozzle along the respective slit and parallel to the faces of the wafer so as to form a severing cut in the wafer, and simultaneously removing sand by suction from the respective slit wherein sand from the nozzle has accumulated.

2. The method of claim 1 wherein the slits are arranged in parallel criss-cross relationship, and which comprises disposing a plurality of the sandblast nozzles in alignment with a corresponding plurality of the slits, blasting a corresponding plurality of jets of the sand from the nozzles onto the wafer along the respective plurality of slits, and then passing the plurality of the nozzles along the respective slits to form severing cuts in the wafer, and simultaneously sucking the sand accumulating in the respective slits out of the same.