DE1521794A1 - Apparatus for chemical polishing of semiconductor wafers - Google Patents

Description

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Böblingen, August 10, 1967 bg-hn

Official "" file number: J 23 638 Ib / 67a File number of the applicant: Docket 25 505; Ge 89/64 New introduction to the description Device for chemical polishing of semiconductor wafers DU invention relates to a · device «for chemical polishing of half ·

conductor material with the help of a tilting device known per se, with wel-

rather a drum-shaped carrier, on the underside of the shark material is glued, rotates on a polishing plate in the same direction as this, but at a higher peripheral speed.

For the fine treatment of metallic surfaces are for example by the magazine "technika", 1965 »No. 2, pages 12«, 121 »Flacblappmaechinen known» in which a small one on a rotating polishing wheel drum-shaped carrier rotates at a higher speed »on the underside of which the work pieces are glued.

In the magazine of 4 "MeUlI -reinigung + pretreatment ¹ *" issue January 1, 1965, pages 16, 17, such Llppsaatchinen are also described in which

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the workpieces, for example silicon putties, medium · a · wax ··· are glued to the underside of the drum-shaped door and the polishing pad has a fibrous surface.

Also disclosed in US Pat. No. 2,080,880 is a lapping device made known «which uses a cloth-covered polishing pad. A polishing liquid is fed from a container through a hose to the center of the polishing plate.

In these known devices, mechanically acting polishing agents such as s.B. Diamond pastes odor foingemsienes aluminum are used. However, mechanical polishing does not yet produce sufficiently smooth and flawless · surfaces. This is more important than the polishing time is great.

In various technological processes for the production of semiconductor components, for example when growing monocrystalline layers by epitaxy, it is of utmost importance that the monocrystalline substrate on which the epitaxial layer grows has the smoothest possible surface in the crystal plane concerned. The Kauhüofo of such a surface should not be more than 100 % . Such a level and flawless ritche can, however, be achieved with mechanically acting polishing agents!

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hardly achieve with diamond paste. Besides that * there * a long one Polishing time of around 20 hours is required to preserve usable substrate surfaces * and these surfaces always remain still afflicted with crata, which subsequently lead to disturbances in the crystal growth of the epitaxial layer.

Attempts to remedy this deficiency have become known polished Surfaces chemically through a purely chemical attack caustic. By means of the half-door surface. This a't * - medium on the one hand, but in general, have the disadvantage that they are selective work «i.e. * that * they individual crystal planes to varying degrees attack. The surfaces of dimples treated in this way, so-called pitting, are clumsy. prevent net growing up. Alkaline metal hypochlorite solutions are known as relatively cheap etchants for gallium arsenide and germanium. With these etchants it can be achieved that at least with certain When there are crystal orientations, there is no selective removal of the surface.

A polishing device, especially for Selgnettesalse, has also become known through German patent specification 664 780, in which a solvent such as water is approached to the center of the polishing disk soaked with a cloth. The workpiece to be polished is held on the edge of the polishing wheel by a fixed holding device. at

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This known device uses the etching effect of a liquid for polishing. The holding device for the workpieces however stands feet. So that the ventilation fluid is quickly discharged, It is recommended to provide a slot in the holding device through which the excess solvent can be sucked off.

In the case of the invented device around chemical foiling Semiconductor materials is the polishing effect of a caustic Liquid exploited.

The invention is characterized by the fact that the levels of the roller plate · and the drum-shaped support opposite a horizontal one Level la in the same direction are inclined by about 3, so that the drum-like support is arranged above the lowest point of the polishing plate, and that an alkali metal hypochlorite solution is in the center of the polishing plate is discharged.

Because the carrier for the semiconductor pods rotates as a result of the movement of the etchant, interspersed with the finest eddies, supported by the relatively rapid fly-off of the etchant as a result of the A tilted position of the device is achieved, since a much stronger concentration of the ataiimetallhypochlorite solution can be used as until now. A stronger removal at the edge than in the middle of the half

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Ladder slices are avoided and it arises regardless of the Crystal orientation, perfect within a surface roughness of about 100 Λ smooth and flawless surfaces. This also disappears so far occurred "disturbing coating completely, so that the polished plate surfaces can be put to their use without further reworking. The resulting substantial shortening of the bollard toi t is particularly great with regard to the mass production of semiconductor components Meaning.

In an advantageous manner, the drum-shaped carrier possesses in the middle its underside has an ice circular depression. This prevents » daJ! the polishing strength is squeezed against the edge of the drum, and it is on this "far" possible "" in ") grOfier" Ansah! of platelets Polish on the same side.

According to a further development of the invention, a control device is provided for the supply of the peeling liquid, through which the alkali metal pochlorite solution, which serves as a polishing liquid, is added drop by drop and in increasing quantities as the polishing process progresses. The filming liquid consists preferably of an aqueous potassium hypochlorite solution or a sodium pochlorite solution. It has also been shown to be particularly advantageous that the poUerüüsilgkeit from a NaOCl solution, the comaentratie "W in polishing w G * lUm ** - at least 0.45%, when polishing Oermaai" at least "

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The invention is explained using one of the drawings AusfÜhrungsbeispieles described. Show it:

Fig. 1: an adjustment of the polishing device, partly schematic

illustrated, and

Fig. 2: a section through the drum-shaped carrier of the su be

working platelets.

Continuation since 6 of the description rom July 20, 1965

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J; In Figure 1, 1 denotes the polishing plate, which is mounted on the 'Tieoh 2 and fastened on its axis jj

te roller4 is driven to a rotating movement. Of the Polishing plate is not exactly level, but is about

! ' wa 3 ° inclined to the horizontal plane. On the Polishing plate is the polishing wheel 5 raised, the whole or

■ - consists of a fibrous, felt-like material at least on its surface. Such discs are specially made for polishing purposes.

In the lowest region of the polishing plate, the drum-shaped carrier 6, on the underside of which the semiconductor wafers to be processed are attached in a manner to be described, is placed eccentrically on the polishing plate. The axis 7 of the carrier 6 _t, which is parallel to the axis J of the polishing plate, protrudes with its lower end formed into a spherical cap into the hub 8 of the carrier 6. It forms a joint with the ball socket 9 (FIG. 2), by means of which the carrier 6 can always adapt itself in its position to the plane of the polishing plate. The axle 7 is mounted in the block 10. With the help of the coil spring 11 located above the block 10, which seeks to compensate for the weight of the carrier 6 and its axis 7, and the adjusting screw 12, it is possible to reduce the

/ ο
cm amount of contact pressure of the carrier against the

Polishing plate still to be varied. The drum-shaped carrier β itself consists of titanium, which is corrosive against the used Polishing fluid is chemically insensitive. '

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The lateral surface 1jJ of the carrier 6 is convex and also serves as a roller that engages with the intermediate roller. The one made of elastic material Intermediate roller 14 is thereby through the. attached to its axis Pinion 15 driven by the ring gear 16 attached to the circumference of the polishing plate * The contact pressure of the running surface 13 of the carrier 6 and the intermediate roller 14 is with the help of on the guide 17 acting knurled screw 18 adjustable. The drum-shaped carrier β rotates by means of this drive in. the same direction of rotation as the polishing plate 1, as indicated by the arrows 19, 20, but at a higher speed. than this. In the embodiment on which this description is based, circumferential speeds of 45 m / min, for the polishing plate and 54 m / min. for the wearer best proven.

The carrier 6 is arranged on the polishing plate in such a way that it is now a small amount, about 5 over the edge of the fibrous Disc 5 protrudes, the edge 24 of the carrier is here above the drainage channel 22 provided with the drainage openings 21 on the periphery of the polishing plate.

The lower end of the carrier 6 serves to receive the i. ~ 2J5 oesrbeitenden plate of semiconductor material. It is completed by the upstanding edge 24 and has a circular recess 25 in the middle through which on

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A cavity is formed on the support placed on the polishing plate, which can absorb polishing liquid during the polishing process can. This ensures that the entire end face of the carrier is evenly covered by the etching liquid. is rinsed so that it is possible to have the end face of the carrier simultaneously with a number of platelets to be polished 23 to be fitted.

The semiconductor wafers 23 are with a wax 26 on the Carrier face glued and embedded in the wax up to the level of the surface to be polished. This measure serves to protect the edges of the die that are preferred by the etchant, especially at higher concentrations be attacked (cobblestone effect). In order to prevent wax from getting on the to be polished Semiconductor surface. Arrived, a wax is used, which only becomes plastic at higher temperatures. As particularly cheap glycol phthalate has proven to be suitable for the purpose described.

The polishing liquid 27 is located in the container 28 and is fed dropwise via the pipe 29 towards the center of the polishing plate. The amount of liquid supplied is regulated by the control device JO, which influences the valve 32 via the shaft 31. The control device 30 works in such a way that, as the polishing process progresses, the amount of the polishing liquid supplied is gradually increased.

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An aqueous NaOCl solution is used as the preparation liquid 27. The concentration of this solution to be selected is very critical with regard to the optimal effect of the polishing process and disruptive side effects. The crystal plane to be polished in each case as well as the amount of any doping substances present in the crystal also exert an influence. The measures listed enable the use of a relatively high concentration. The best results were obtained when polishing gallium arsenide at a concentration of about 0.45 % _t when polishing germanium at a concentration of about 0.62 % .

In the following, the sequence of a polishing process with the described device shown in context. The ground and lapped platelets made of monocrystalline Semiconductor material, e.g. made of gallium arsenide, is first glued to the end of the drum-shaped carrier in the manner described and completely inserted into the adhesive wax embedded, then lapped again briefly and cleaned with soap under the action of ultrasound. After that, the Carrier placed on the fibrous disk 5 of the polishing plate and brought into engagement with its drive. After starting the machine, the drum-shaped carrier rotates in the same direction as the polishing plate, but at a higher peripheral speed than this. At the same time, the polishing liquid, the concentration of which was determined by titration, is added drop by drop fed to the center of the polishing plate. The polishing liquid

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is absorbed by the fibrous material of the disc 5 and in a movement interspersed with the finest eddies past the surfaces of the semiconductor wafers to be polished. As already mentioned, the indentation in the putty of the support face prevents this the polishing liquid is pressed out to the edge of the carrier so that all the platelets glued to the carrier are uniform be washed around.

'The device described also has the effect that the polishing fluid quickly drains off after it has passed the semiconductor wafers. This measure is to avoid scratches on the polished surfaces tiny, detached particles are particularly important. This is achieved in particular by the inclined position of the axes, and by the sticking-out of the carrier over the edge of the polishing plate. The already mentioned supply of polishing liquid, which increases towards the end of the polishing process, also helps to avoid this from scratches.

After a polishing time of about 100-15Ο minutes, the Platelets at the concentration of the NaOCl solution mentioned reaches a roughness of its surface that is not more than 100 A. The removal rate is around 25 - 55 / The now completely polished platelets are completely bare and can be cleaned without additional cleaning and rinsing Support can be removed with the help of acetone and fed to their further processing into semiconductor components.

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Claims (3)

J 28 633 Ib / 67a Böblin bg-hn ii Böblingea, August 10, 1967 NEW PATENT CLAIMS 1 TO 3 1. device sum chemical foil ren of semiconductor material, with the help of a lapping device known to "I, in which a drum-shaped carrier, on the underside there" Semi-material glued on, on a polishing plate at the same • level as this, but at a higher peripheral speed rotates * characterized by »that the planes of the polishing plate · and the · drum-shaped carrier · are opposite one another horizontal plane la inclined by about 3 in the same direction, so that the drum-shaped carrier is arranged at the lowest point of the polishing plate and that an alkali metal hypochlorite solution is fed to the center of the polishing plate. 2. Device according to claim 1, characterized in that the drum-shaped carrier (6) has a circular recess (25) in the middle of a lower end face, 3. Device according to claims 1 or? ·. characterized) that a control unit (30) is provided through which the alkali metal hvpochlorlt- Solution drop by drop and as the polishing process progresses 909843/1538 in increasing quantities. SAD ORIGINAL Blank page