Device for one-side galvanic treatment of semiconductor plates

FIELD: electric engineering.

SUBSTANCE: invention relates to electric engineering equipment and may be used for application of coatings by electrochemical process. The device for one-side treatment of semiconductor plates comprises a galvanic bath with anode and a substrate holder with a set of electrode conducting contacts and support posts whereto a semiconductor plate is pressed. The device incorporates additionally a horizontal support frame with an angular flange and three needle-type stops with ring-like marks, the substrate holder being provided with a guiding angular recess and mounted on the support frame flange. Also, the device comprises the current source control unit and a system of forced mixing of electrolyte made up of a magnetic mixer with a shielding plate.

EFFECT: increased quality of galvanic treatment of semiconductor plates, simpler design of the device.

5 dwg

 

The device relates to the electrical equipment, in particular equipment for processing semiconductor wafers, and may be used for coating by electrolytic method.

A device for electrochemical treatment of a semiconductor washers (U.S. patent 6156167 from 05.12.2000,), in which the silicon wafer is installed in the receiving cassette horizontally, treated side down. Press the external current-carrying contacts to the peripheral areas of the plate, insulated from the electrolyte by means of dielectric pads. In the process of deposition plate rotate to remove the released gas bubbles and mixing of the electrolyte.

The disadvantage of this device is the low quality of deposited silver contacts of solar cells, due to the formation of dendrites is chaotic buildup of metal in the form of fringe around the perimeter of the contacts, due to turbulent flow occurring at the boundaries of the Windows photoresistive mask.

The signs above analog common with the proposed device, the following: galvanic bath with an anode, a source of electric current, the system of forced mixing of the electrolyte, the horizontal location of the processed wafer, the conductive contacts located on the perimeter deposited with the pile of plates.

The known method and device for electrochemical treatment of the surface of the plate (U.S. patent 6645356 from 11.11.2003,), in which electrical contact to the peripheral areas create through a set of discrete springs, the edge of which scratched the surface of the plate when it is crowded. The contacts are isolated from the electrolyte by a dielectric barrier and sealing gas. The flow of electrolyte is directed through the inlet of the pump.

The disadvantage of this device by the above method is the occurrence of mechanical loads on the plate, which lead to damage that is caused by uneven pressure and scratching of the thin fragile wafers of gallium arsenide in Germany (GaAs/Ge) spikes of current-carrying contacts.

The signs above analog common with the proposed device, the following: galvanic bath with an anode, a source of electric current, the system of forced mixing of the electrolyte, the horizontal location of the processed wafer, the current-carrying contacts on the perimeter of the deposited side of the plate.

Known connecting device for electrical power supply to the plate in the process of electrochemical machining (U.S. patent 6805778 from 19.10.2004,), in which the processed plate is pressed on the perimeter of the supporting columns of podarkticules electrode con who acts and is placed in the electroplating bath with an anode horizontally, deposited side down. Each electrode contact is made in an arc shape, is covered with an insulating film insulating the bell around the clamping area. The electrode is pressed against the conductive seed layer in the window photoresistive mask on the plate, and the insulating bell to the layer of photoresist, which avoids corrosion of the open area of the seed metal layer. The system of forced mixing of the electrolyte is that the plate is in the process of deposition is rotated around its axis, in addition, the fluid flow is forced upward through the perforated screen deposited to the side, shimmering in the follow-through the edge of the tub. Reverse side of the plate while not wetted. As a result of intensive mixing is suppressed gassing.

The disadvantage of the prototype is the complexity of construction, due to the simultaneous rotation of the plate with the current-carrying contacts and the discharge flow of the electrolyte from the bottom up to the besieged party. Turbulence of the electrolyte resulting from the perimeter Windows photoresistive mask, increase the fringe of the dendrites. The poor quality of the sludge is not allowed in the technology of solar cells, because the distorted geometry of the contacts increases the opacity of the plate. In the absence of forced mixing dendrites not prasouda, but as soon as the edge with the substrate layer of the electrolyte is depleted of metal ions, starts gassing. The gas bubbles accumulate under a horizontal plate, prevent deposition of metal. In addition, the device is a prototype and does not involve the deposition of metal in smooth, without stirring, the provisions of the electrolyte, as when you turn off the inlet of the pump, the liquid level will drop.

The characteristics of the prototype, shared with the proposed device, the following: galvanic bath with an anode, which is polictial with a set of current-carrying electrode contacts; polictial equipped with support bars to which is pinned a semiconductor wafer; an electrode current-carrying contacts are located on the perimeter of the semiconductor wafer; a system of forced mixing of the electrolyte; a source of electric current.

Technical result achieved in the proposed device for one-way galvanic processing of semiconductor wafers, is to improve the quality of the galvanic processing and simplify the design of the device.

This is achieved by the fact that in the device for one-way galvanic processing of semiconductor wafers containing electroplating bath and an anode, which is adaikalanathan with a set of current-carrying electrode contacts and the supporting bars, to which is pinned a semiconductor wafer, and an electrode current-carrying contacts are located on the perimeter of the semiconductor wafer, and in addition, contains a system of forced mixing and source of electric current, inputs of the reference frame with the angular ledge and three needle stops with design labels in the form of rings, providing horizontal support frame, and polictial made with angular guide groove. In addition, the device entered the control unit current source and mixing of the electrolyte, consisting of a magnetic stirrer with a shielding plate, the overwhelming Vorontsovskaya.

Distinguishing features of the proposed device for one-way galvanic processing of semiconductor wafers, ensuring compliance with a criterion of "novelty", the following:

- base frame with an angular projection;

three needle stops with design labels in the form of rings;

- execution of podarkticules guide with an angular recess and mounted on the protrusion of the support frame;

control unit electrical power source and mixing of the electrolyte, consisting of a magnetic stirrer with a shielding plate.

To substantiate the present invention, the criterion of "subretinally level" was the analysis of the known solutions according to literary sources, which is not found technical solutions containing a set of known and distinctive characteristics of the proposed device, giving the above technical result. Therefore, according to the authors, the proposed device for one-way galvanic processing semiconductor wafers meets the criterion of "inventive step".

The proposed device for one-way galvanic processing of semiconductor wafers is (1, 2) from galvanic baths 1 anode 2, podarkticules 3 with the supporting columns 4 and a set of current-carrying clamping pins 5, which are located on the perimeter of the semiconductor wafer 6, and polictial 3 is equipped with a guide angular recess 7. Polictial 3 with a semiconductor wafer 6 is mounted on the supporting frame 8, having an angular lug 9, moreover, the support frame 8 is laid on three needle stop 10, provided constructive labels in the form of rings 11 and has a top 12. To install the support frame 8 parallel to the surface of the electrolyte 13, filling electroplating bath 1, the needle stops 10 equipped with a screw connection 14. Polictial (3) determine its angular recess 7 on the ledge 9 of the base frame 8.

The device for one-way galvanic processing of semiconductor place is in is also equipped with a system of forced mixing of the electrolyte, which consists of a magnetic stirrer with 15 stirring rod 16 located at the bottom of the electroplating bath 1, above which is mounted on the supporting legs 17 of the shielding plate 18, the vast majority Vorontsovskaya electrolyte.

Figure 2 shows a fragment of the relative position of podarkticules 3 with a semiconductor plate 6 in contact with the electrolyte 13.

Galvanic processing of the semiconductor wafer 6 is performed using a source of electric current, consisting of a potentiostat P-50-1 and programmer PR-8 (figure 3).

The control unit current source and mixing of the electrolyte is made on the base of the time relay VL-64 and consists of three time-shifted initial launch channels with electric keys K1, K2, K3 (figure 4).

Time sequence circuit-breaking electric keys K1, K2 and K3 with the corresponding periods of mixing of the electrolyte - t1, the relaxation of electrolyte - t2 and pulse deposition - t3 depicted in figure 5.

A specific example of the device for one-way galvanic processing of semiconductor wafers.

To ensure one-sided wetting semiconductor plate 6 fixed to polictial 3, are placed on the surface of the electrolyte 13 gradually, starting from the end is th point of the N deposited side of the plate 6. Decreasing the angle of the contact area increases, due to the surface tension forces the air is squeezed out of the solution outside of the semiconductor wafer 6. The reverse side of the semiconductor wafer 6 is outside of the electrolyte 13, which excludes corrosive effect on her subsequent electrochemical deposition.

Polictial 3 with a semiconductor plate 6 moves along a set path. Originally polictial 3 mounted on the supporting frame 8 at an angle αstart=30° to the surface of the electrolyte 13, while the angular protrusion 9 of the base frame 8 is in the angular recess 7 of podarkticules 3 and the lower edge of the N deposited side of the semiconductor wafer 6 deals with the electrolyte 13.

Support frame 8 is laid on three needle stop 10, geometrically arranged at the vertices of an equilateral triangle.

Needle stops 10 provided constructive labels in the form of rings 11. The installation plane of the base frame 8 parallel to the surface of the electrolyte 13 is implemented by raising the needle stops 10 by means of a screw connection 14.

Equidistant position of the reference points 12 (vertices needle stops) from the surface of the electrolyte 13 is fixed at the time of rolling of the solution from the surface of the ring 11. The height of you who topusa above the electrolyte 13 plots the needle stops 10 corresponds to the height of the support bars 4 on polictial 3, the thickness of the semiconductor wafer 6 and the magnitude of the elevation h(0,3÷1.2 mm) plane deposited over the electrolyte surface (figure 2). When putting podarkticules 3 its trajectory is rigidly determined by the slip control points G and F angular protrusion of the base frame 8 on the surface of the angular undercut 7 of podarkticules 3. Clamped to the supporting frame 8 eliminates lateral tilt of podarkticules 3.

Angular recess 7 of podarkticules 3 necessary for the primary contact at the point N to the plane of deposition of the semiconductor wafer 6 with the surface of the electrolyte 13 and capture solution by surface tension, forming a meniscus. With decreasing angle α podarkticules 3 is simultaneously its rotational movement and the shift in the vertical (upward) and horizontal directions.

In the extreme point of N deposited side of the semiconductor wafer 6 by holding the solution, is removed from the surface of the electrolyte 13 for a specified distance, which eliminates wetting the backside of the processed semiconductor wafer 6.

In the absence of angular undercut 7 polictial 3 rotates down, the plane of the deposited side of the semiconductor wafer 6 is located below the plane of the electrolyte 13, and the solution wetted Tul the first party.

The projections of /AB/ and /BC/ on the vertical (figure 2), depending on the tilting angle of podarkticules 3, are determined by the expressions:

/AB/=[d1/sinβ-d2·sinx·(ctgβ+ctgx)]·cosx

where:

β - the angle of the undercut 7 polictial 3 (β=90° - αstart)

αstart- the initial angle of podarkticules 3;

d1- the thickness of the layer in polictial 3, in which is formed an angular recess 7;

d2- the thickness of the support frame 8;

d3the height of the support columns 4 podarkticules 3;

l - indents the edge of the semiconductor wafer 6 from the edge of podarkticules 3;

x - change angle of podarkticules 3.

Data to calculate the geometric distance h from the lowest point of the N semiconductor wafer 6 to the plane of the electrolyte 13 is presented in the table.

Table.

Lifting height region beset by a hand h above the level of the electrolyte depending on the angle of the semiconductor wafer α
α°

h, mm
4035302520151050
Options
design
(d1=12 mm;
d2=11 mm;00,40,711,21,41,5
d3=3 mm)
1) l=0 mm
αstart=30°
2)l=0.5 mm
αstart=30°00,40,70,91,11,21,2
3) l=1 mm
αstart=30°00,30,60,80,910,9
4) l=2 mm
αstart=30°00,20,40,50,60,60,5
5) l=3 mm
αstart=30° 00,20,30,30,30,1-0,1
6) l=4 mm
αstart=30°00,10,10,1-0,1-0,3and-0.6
7) l=2 mm
αstart=35°00,40,70,911,11,11
8) l=2 mm
αstart=40°00,50,91,21,51,71,81,81,7

When the angle initial setup p is docterate 3 equal α start=30° value uplift h deposited the plane of the semiconductor wafer 6 on the electrolyte layer 13 depends on its placement on polictial 3 (parameter l). The electrolyte solution 13 is held by surface tension in the range h=0÷1.5 mm, at the same time to prevent pulling air under the semiconductor wafer 6 or rolling of the electrolyte 13 on the back side with stirring, it is advisable to use h=0,3÷1,2 mm

When l=3 mm (see item 5 of the table) deposited side of the semiconductor wafer is below the level of the electrolyte 13 and possibly wetting the rear.

Increase αstartangle the initial installation of podarkticules 3 over 40° for l=(0÷2 mm) is impractical because it leads to a significant increase in h (more than 1.7 mm) and drawing air under the semiconductor wafer 6 with stirring.

The system of forced mixing of the proposed device consists of a magnetic stirrer 15 (MM-5) with a mixing rod 16 at the bottom of galvanic baths 1 on which is mounted a shielding plate 18, preventing the formation of a crater. Forced mixing is necessary for the enrichment of ions of the metal surface with a semiconductor plate 6 electrolyte layer 13. During the subsequent pause occurs relaxati the electrolyte 13, the solution settles down. The deposition of metal in conditions of forced mixing and turbulent flows arising on the border of the recesses in the photoresistive layer leads to the expansion of the chaotic structures of dendrites. In the absence of mixing at constant or pulsed current deposition surface of the semiconductor wafer 6 is covered with gas bubbles.

Galvanic treatment is performed by using a source of electric current (figure 3), consisting of a potentiostat PI-50-1 and programmer PR-8.

Pulse inversion mode of deposition to improve the quality of sediment, as in the anode period partially dissolve microfactory with high electric field intensity and convection occurs replenish the metal ions near-surface layer of the electrolyte 13. However, at the location of the semiconductor wafer 6 deposited face down convectional mixing is not enough, as in this case, the surface of the deposited metal layer heterogeneous bumpy, because microisolation in the formation of the depletion layer. To suppress gassing must alternating deposition of metal and forced mixing of the electrolyte 13.

Forced mixing is more intense than convection, enriches metal ions prepower the surface to the semiconductor wafer 6, the electrolyte layer 13, including in the recesses of the photoresistive mask.

The duration of deposition depends on the cathodic current density (ρto). The higher the current density, the shorter should be the period of deposition due to more rapid depletion of the surface layer of the electrolyte 13, for example ρto=60 mA/cm2not more than 1.5 min; for ρto=80 mA/cm2no more than 1 min; for ρto=120 mA/cm2not more than 30 seconds. When the Windows of the mask is formed of a dense fine-grained sediment with smooth edge geometry.

The cycle consisting of forced mixing of the electrolyte, the relaxation of the electrolyte, pulsed deposition, repeat several times before the formation of the metal layer of the required thickness.

The control unit (figure 4) sets the program cycle, indicating the duration of mixing (t1), relaxation (t2), pulsed deposition (t3), number of repetitions (n). Electric keys K1and K2the control unit (figure 4) is built into the circuit galvanic current (D-C-E)set the current source (figure 3). When open-loop electrical key K1the current source (figure 3) shunted closed key2, used galvanostatically mode of deposition of metal on the semiconductor wafer 6 is not happening. During mixing of the electrolyte 13 the key To3management IAHS is based mixer 15 is closed, during the relaxation of the electrolyte 13 is open. The sequential closure of a key K1and the break key To2proceeds galvanic current (during deposition of the metal). To stop the deposition closes the shunt To2and switches electric key K1.

The design of the proposed device allows full automation of the processing load, unload.

On both sides of the semiconductor wafer 6 sprayed contact layers of the metals chromium - palladium - silver(Cr/Pd/Ag) with a thickness of 400Å/500Å/1000Å, respectively. On the face of the epitaxial side of the semiconductor wafer 6 create a photoresistive mask with a pattern of contacts phototransducer. Using the photoresist OP-4-04-T.

The width of the contact Windows ˜10 μm. Length ˜40 mm, the thickness of the photoresistive layer ˜7 microns.

The semiconductor wafer 6 is placed back on the supporting bars 4 podarkticules 3 and pressed against the deposited side (in the Windows photoresistive mask) four current-carrying electrode contacts 5, located on the perimeter of the processed semiconductor wafer 6.

The surface electrode of the current-carrying contacts 5 are covered with an insulating layer except for the clamping end of the site.

Polictial 3 with a semiconductor plate 6 establish the business of the recess 7 to the corner ledge 9 of the base frame 8, moreover, the lower edge N plate 6 deals with the electrolyte 13 (figure 2). The initial angle of the plane of podarkticules 3 to the plane of the electrolyte 13 is αstart=30° (see item 4 of the table).

Gradually, reducing the angle of inclination, polictial 3 placed on the support frame 8, and the air is squeezed out from under the semiconductor wafer 6 by the surface tension forces and achieve complete wetting of deposited side. The movement of podarkticules 3 occurs along a certain trajectory, strictly due to the simultaneous sliding anchor points G and F angular protrusion of the base frame 8 on the surface of the sides of the angular undercut 7. As a result, the edge of the semiconductor wafer 6 by holding the solution by surface tension, is lifted above the plane of the electrolyte 13, and after the final placing of podarkticules 3 plane deposited side is higher than at h=0.5 mm electrolyte layer 13 outside the processed semiconductor wafer 6.

If during the initial installation of podarkticules 3 edge of the semiconductor wafer 6 is located below the level of the electrolyte 13, the value of raising the plane of deposition will decrease accordingly. For example, the location of the plate 6 according to l=1 mm (item 3 of the table) and the initial dive at point N at 0.2 mm, after the criminal code is edyvane of podarkticules 3, the height of raising the plane of deposition will be h=0,7 mm

Then with a magnetic stirrer 15 and its mixing rod 16, the electrolyte 13 is stirred for 20 sec for the enrichment of metal ions near-surface layer of a solution in Windows photoresistive mask. The shielding plate 18 prevents the formation of a crater during rotary movement of the electrolyte 13. Switch off the magnetic stirrer 15 is opened, the electric key3the control unit (figure 4). In the subsequent period pause 20 sec induces relaxation of the electrolyte 13, the solution settles down. The deposition of the metal in solution, continuing the movement of inertia, leads to the formation of irregular growths of dendrites. Perform the deposition in quiet without the forced mixing of the electrolyte 13 to until the surface layer of mortar will not be significantly depleted metal ions. Apply a pulse inversion mode of deposition. The duration of the cathodic and anodic pulses t=1·10-3s, current density ρto=80 mA/cm2and ρand=8 mA/cm2, respectively. The duration of deposition t=30 sec. Subsequent repetition of the cycle of forced mixing of the electrolyte 13 - relaxation of the electrolyte 13 pulsed deposition - increasing layer of metal of the required thickness. For example, the floor is placed a metal layer of a thickness of ˜ 7 μm when the selected mode of deposition of 7 cycles. Besieged contacts have a smooth edge geometry, fine-grained structure, trapezoidal configuration. On the back side of the semiconductor wafer 6 deposition does not occur. Further rotational movement relative angular undercut 7 polictial 3 is turned. Perform unloading semiconductor wafer 6. The semiconductor wafer 6 is washed with deionized water and dried. Then face with the besieged contacts the semiconductor wafer 6 is placed again on the supporting bars 4 podarkticules 3. Press the electrode current-carrying contacts 5 to the back, without photoresistive coating. Install polictial 3 with a semiconductor wafer 6 on the supporting frame 8, as described above. In the besieged side is located above the electrolyte level 13 on h=0.5 mm, keeping the solution by surface tension. Mix a solution mixing rod 16 of a magnetic stirrer 15 for t=15 sec. When this boundary with the semiconductor wafer 6, the electrolyte layer 13 is enriched with metal ions. During the subsequent pause t=20 sec solution relaxes, calms down, stops turbulent swirling of the fluid near the arc contact 5, is pressed against the semiconductor wafer 6.

In the beam deposition under conditions of forced mixing in the contact areas of the semiconductor wafer 6 are formed chaotic buildup of metal - dendrites.

If the duration of the relaxation of the electrolyte 13 is insufficient, less than 10 sec, when used speed solution ˜15 rpm, intensive movement of fluid inertia also results in the formation of dendritic structures that distort the morphology of the deposited layer, which is unacceptable in the technology of solar cells. In the subsequent period t=30 sec precipitated metal using pulse reverse mode: the density of the cathodic and anodic currents ρto=11 mA/cm2that ρa=1,1 mA/cm2, pulse duration t=1·10-3sec. When this surface layer of the electrolyte 13 is partially depleted of metal ions. If the duration of the deposition over 1.5 min, deteriorating the morphology of the deposited metal layer that is connected with emission. To build a layer of metal of the required thickness (˜7 μm) cycle forced mixing, relaxation, pulsed deposition is repeated using the control unit (figure 4) in the automatic mode 42 times. Generated sediment is fine-grained structure in the area of arcing contacts 5 dendritic lesions are absent.

In the proposed device as a main material is acrylic stamps top 12, GOST 17622-72.

The proposed device for one-way galvanic processing of semiconductor wafers is sluchae effect of the electrolyte 13 on the reverse side of the semiconductor wafer 6, that allows you to perform independently galvanic treatment of the two parties with different area of deposition.

Unlike devices with vertical semiconductor wafer 6, there is no need to isolate the back side by means of the sealing rings, which reduces the effective area of the processed plate 6, especially if you have a basic slice.

The proposed device provides a uniform deposition of the metal, as in effect on the horizontal position of the semiconductor wafer 6 besieged areas are equal.

Perform loop - forced mixing of the electrolyte 13, relaxation of the electrolyte 13, a pulse plating provides obtaining a dense fine-grained sediment without dendritic growths in the Windows photoresistive mask large thickness, which is necessary, for example, for formation of the contact grid PV with the small area of shading. Deposition in the electrolyte 13 without turbulent eddies provides a uniform build-up of metal in the area of the contacts 5 and in the absence of a photoresistive coating.

The processed semiconductor wafer 6 is not subjected to mechanical loads, which allows the use of thin fragile semiconductor structure.

Device for ednos is gonna galvanic processing of semiconductor wafers, containing electroplating bath and an anode, which is polictial with a set of current-carrying electrode contacts and the supporting bars to which is pinned a semiconductor wafer, and an electrode current-carrying contacts are located on the perimeter of the semiconductor wafer, and, in addition, the device contains a system of mixing of the electrolyte and the source of electric current, characterized in that it additionally introduced horizontally positioned base frame with corner ledge and three needle stops with design labels in the form of rings, with polictial made with angular guide groove and mounted on the corner ledge of the base frame, and in addition, the device introduced the control unit current source and mixing of the electrolyte, consisting of a magnetic stirrer with a shielding plate.



 

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