RU2327249C1 - Device for one-side galvanic treatment of semiconductor plates - Google Patents

Abstract

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

Description

The device relates to electrical equipment, in particular to equipment for processing semiconductor wafers, and can be used for coating electrolytically.

A device is known for the electrochemical processing of semiconductor washers (US Pat. No. 6,156,167 of December 5, 2000), in which a silicon wafer is installed horizontally in the receiving cassette, processed side down. The external current-carrying contacts are pressed to the peripheral regions of the plate isolated from the electrolyte by means of a dielectric patch. During the deposition process, the plate is rotated to remove evolving gas bubbles and stir the electrolyte.

The disadvantage of this device is the low quality of the deposited silver contacts of the photoconverters, due to the formation of dendrites - chaotic metal growths in the form of a fringe around the perimeter of the contacts, due to turbulent flows arising at the borders of the windows of the photoresist mask.

Signs of the aforementioned analogue that are common with the proposed device are as follows: a galvanic bath with an anode, an electric current source, an electrolyte forced mixing system, a horizontal arrangement of the workpiece, conductive contacts located around the perimeter of the deposited side of the plate.

A known method and device for electrochemical processing of the surface of the plate (US patent 6645356 from 11.11.2003), in which the electrical contact to the peripheral regions is created by a plurality of discrete springs whose tips scratch the surface of the plate when it is pressed. The contacts are isolated from the electrolyte by a dielectric barrier and a sealing gas. The flow of electrolyte is directed by means of a discharge pump.

The disadvantage of the device according to the above method is the occurrence of mechanical loads on the plate, which lead to damage, due to the uneven pressing and scratching of a thin brittle plate of gallium arsenide on germanium (GaAs / Ge) by the points of current-carrying contacts.

Signs of the aforementioned analogue that are common with the proposed device are as follows: a galvanic bath with an anode, an electric current source, an electrolyte forced mixing system, a horizontal arrangement of the workpiece, current-carrying contacts along the perimeter of the deposited side of the plate.

A contact device for the current supply to the plate during electrochemical processing is known (U.S. Pat. No. 6,805,778 of 10/19/2004), in which the plate to be processed is pressed along the perimeter to the support columns of the substrate holder by electrode contacts and placed horizontally in the plating bath with the anode, deposited side down. Each electrode contact is made in the form of an arc, covered with an insulating film with an insulating bell around the clamping section. The electrode is pressed against the electrically conductive seed layer in the window of the photoresist mask on the plate, and the insulating bell is pressed against the photoresist layer, which avoids corrosion of the exposed portion of the seed metal layer. The forced electrolyte mixing system consists in the fact that the plate rotates around its axis during the deposition process, in addition, the fluid flow is pumped from bottom to top through the hole screen to the deposited side, subsequently overflowing over the edge of the bath. The reverse side of the plate is not wetted. As a result of intensive mixing, gas evolution is suppressed.

The disadvantage of the prototype is the complexity of the design, due to the simultaneous rotation of the plate with current-carrying contacts and forcing the flow of electrolyte from the bottom up to the deposited side. Electrolyte turbulence occurring around the perimeter of the windows of the photoresist mask leads to an increase in fringe from dendrites. Poor quality of the precipitate is unacceptable in the technology of photoconverters, since the geometry of the contacts is distorted, the shading of the plate increases. In the absence of forced mixing, dendrites are not formed, but as soon as the electrolyte layer bordering the substrate is depleted in metal ions, gas evolution begins. Bubbles of gas, accumulating under a horizontally located plate, prevent the deposition of metal. In addition, the device is a prototype and does not provide for the deposition of metal in a quiet, without stirring, position of the electrolyte, since when the pressure pump is turned off, the liquid level will decrease.

The features of the prototype, common with the proposed device, are as follows: a galvanic bath with an anode, in which a substrate holder with a set of electrode current-carrying contacts is located; the substrate holder is equipped with supporting posts to which the semiconductor wafer is pressed; electrode current-carrying contacts are located around the perimeter of the semiconductor wafer; forced electrolyte mixing system; source of electric current.

The technical result achieved in the proposed device for one-sided galvanic processing of semiconductor wafers is to improve the quality of galvanic processing and simplify the design of the device.

This is achieved by the fact that in a device for one-sided galvanic processing of semiconductor wafers, containing a galvanic bath with an anode, in which there is a substrate holder with a set of electrode current-carrying contacts and support columns, to which a semiconductor plate is pressed, and electrode current-conducting contacts are located around the perimeter of the semiconductor wafer, and in addition, containing a forced mixing system and an electric current source, an additional support frame with Glov protrusion and three needle stop design with marks in the form of rings, ensuring the horizontal position of the support frame, wherein the substrate holder is configured to guide the corner recess. In addition, a control unit for the current source and the electrolyte mixing system, consisting of a magnetic stirrer with a shielding plate that suppresses funnel formation, was introduced into the device.

Distinctive features of the proposed device for one-sided galvanic processing of semiconductor wafers, ensuring compliance with its criterion of "novelty", the following:

- supporting frame with an angled protrusion;

- three needle stops with structural marks in the form of rings;

- the implementation of the substrate holder with a guide angled recess and mounted on a protrusion of the support frame;

- a control unit for an electric current source and an electrolyte mixing system consisting of a magnetic stirrer with a shielding plate.

To justify the compliance of the proposed invention with the criterion of "inventive step", an analysis of known solutions based on literature was carried out, as a result of which no technical solutions were found containing a combination of known and distinctive features of the proposed device, giving the above technical result. Therefore, according to the authors, the proposed device for one-sided galvanic processing of semiconductor wafers meets the criterion of "inventive step".

The proposed device for one-sided galvanic processing of semiconductor wafers consists (Figs. 1, 2) of a galvanic bath 1 with an anode 2, a substrate holder 3 with support columns 4 and a set of current-conducting clamping contacts 5 located along the perimeter of the semiconductor plate 6, and the substrate holder 3 is provided with an angular guide Groove 7. Substrate holder 3 with semiconductor wafer 6 mounted on a support frame 8 having an angled protrusion 9, in addition, the support frame 8 is laid on three needle stops 10 provided with with structural marks in the form of rings 11 and having vertices 12. To install the support frame 8 parallel to the surface of the electrolyte 13 filling the plating bath 1, the needle stops 10 are provided with screw connections 14. The substrate holder 3 is mounted with its corner recess 7 on the protrusion 9 of the supporting frame 8.

The device for one-sided galvanic processing of semiconductor wafers is also equipped with a forced electrolyte mixing system, which consists of a magnetic stirrer 15 with a stirring rod 16 located at the bottom of the galvanic bath 1, above which a shield plate 18 is installed on the support legs 17, which suppresses the funnel formation of the electrolyte.

Figure 2 shows a fragment of the relative position of the substrate holder 3 with the semiconductor wafer 6 in contact with the electrolyte 13.

The galvanic processing of the semiconductor wafer 6 is performed using an electric current source consisting of a P-50-1 potentiostat and a PR-8 programmer (Fig. 3).

The control unit of the current source and the electrolyte mixing system is made on the element base of the VL-64 time relay and consists of three channels shifted by the time of the initial start-up with electric switches K1, K2, K3 (Fig. 4).

Temporary sequences of closing-opening of electric keys K1, K2 and K3 with the corresponding periods of mixing of the electrolyte - t1, relaxation of the electrolyte - t2 and pulse deposition - t3 are shown in Fig.5.

An example of a specific implementation of the proposed device for one-sided galvanic processing of semiconductor wafers.

To ensure one-sided wetting, the semiconductor wafer 6, mounted on the substrate holder 3, is laid on the surface of the electrolyte 13 gradually, starting from the extreme point N of the deposited side of the wafer 6. As the angle of inclination decreases, the contact area increases, due to surface tension forces, the air is squeezed out of the solution beyond the semiconductor wafer 6. The reverse side of the semiconductor wafer 6 is located outside the electrolyte 13, which eliminates the aggressive effect on it subsequently electrochemical deposition process.

The substrate holder 3 with a semiconductor wafer 6 moves along a rigidly set path. Initially, the substrate holder 3 is installed on the support frame 8 at an angle α _beg. = 30 ° to the surface of the electrolyte 13, while the angled protrusion 9 of the supporting frame 8 is included in the angled groove 7 of the substrate holder 3 and the lower edge N of the deposited side of the semiconductor wafer 6 is in contact with the electrolyte 13.

The supporting frame 8 is laid on three needle stops 10 geometrically located at the vertices of an equilateral triangle.

The needle stops 10 are provided with constructive marks in the form of rings 11. The installation of the plane of the support frame 8 parallel to the surface of the electrolyte 13 is carried out by raising the needle stops 10 using a screw connection 14.

The equidistant position of the support points 12 (the tips of the needle stops) from the surface of the electrolyte 13 is fixed at the time of the solution rolling off the surface of the rings 11. The height of the sections of the needle stops 10 protruding above the electrolyte 13 corresponds to the height of the support posts 4 on the substrate holder 3, the thickness of the semiconductor wafer 6 and the height h (0.3 ÷ 1.2 mm) of the plane of the deposited side above the surface of the electrolyte (figure 2). When laying the substrate holder 3, its path is rigidly determined by the sliding of the support points G and F of the angular protrusion of the support frame 8 on the surface of the corner recess 7 of the substrate holder 3. The pressing against the support frame 8 eliminates the lateral inclination of the substrate holder 3.

The angular undercut 7 of the substrate holder 3 is necessary for the initial contact of the extreme point N of the deposition plane of the semiconductor wafer 6 with the surface of the electrolyte 13 and capture of the solution by surface tension, the formation of the meniscus. With a decrease in the angle of inclination α of the substrate holder 3, both its rotational movement and shift in the vertical (up) and horizontal directions occur.

As a result, the extreme point N of the deposited side of the semiconductor wafer 6, while holding the solution, is removed from the surface of the electrolyte 13 by a predetermined distance, which eliminates the wetting of the back side of the treated semiconductor wafer 6.

In the absence of an angled groove 7, the substrate holder 3 rotates downward, while the plane of the deposited side of the semiconductor wafer 6 is located below the plane of the electrolyte 13, and the back side is wetted with the solution.

The magnitude of the projections / AB / and / BC / on the vertical (figure 2), depending on the change in the angle of inclination of the substrate holder 3, are determined by the expressions:

/ AB / = [d ₁ / sinβ-d ₂ · sinx · (ctgβ + ctgx)] · cosx

Where:

β is the angle of the groove 7 in the substrate holder 3 (β = 90 ° - α _beginning )

α _beg. - the initial installation angle of the substrate holder 3;

d ₁ is the thickness of the layer in the substrate holder 3, in which an angled undercut 7 is formed;

d ₂ - the thickness of the support frame 8;

d ₃ - the height of the supporting columns 4 of the substrate holder 3;

l is the amount of indentation of the edge of the semiconductor wafer 6 from the edge of the substrate holder 3;

x is the change in the angle of inclination of the substrate holder 3.

The calculation data of the geometric distance h from the extreme lower point N of the semiconductor wafer 6 to the plane of the electrolyte 13 are presented in the table.

Table.
The lifting height of the edge of the deposited side h above the electrolyte level depending on the angle of inclination of the semiconductor wafer α α °
h mm 40 35 thirty 25 twenty fifteen 10 5 0 Options constructions (d ₁ = 12 mm; d ₂ = 11 mm; 0 0.4 0.7 one 1,2 1.4 1,5 d ₃ = 3 mm) 1) l = 0 mm α _beg. = 30 ° 2) l = 0.5 mm α _beg. = 30 ° 0 0.4 0.7 0.9 1,1 1,2 1,2 3) l = 1 mm α _beg. = 30 ° 0 0.3 0.6 0.8 0.9 one 0.9 4) l = 2 mm α _beg. = 30 ° 0 0.2 0.4 0.5 0.6 0.6 0.5 5) l = 3 mm α _beg. = 30 ° 0 0.2 0.3 0.3 0.3 0.1 -0.1 6) l = 4 mm α _beg. = 30 ° 0 0.1 0.1 0.1 -0.1 -0.3 -0.6 7) l = 2 mm α _beg. = 35 ° 0 0.4 0.7 0.9 one 1,1 1,1 one 8) l = 2 mm α _beg. = 40 ° 0 0.5 0.9 1,2 1,5 1.7 1.8 1.8 1.7

When the angle of the initial installation of the substrate holder 3 is equal to α _beg. = 30 °, the magnitude of the rise h of the deposited plane of the semiconductor wafer 6 above the level of electrolyte 13 depends on its placement on the substrate holder 3 (parameter l). The electrolyte solution 13 is held by surface tension forces in the range h = 0–1.5 mm, while at the same time it is advisable to use h = 0.3–1.2 mm to prevent air from drawing under the semiconductor wafer 6 or rolling the electrolyte 13 on the back side with stirring .

At l = 3 mm (see clause 5 of the table), the deposited side of the semiconductor wafer is below the level of electrolyte 13 and rear wetting is possible.

The increase in α _beg. the angle of the initial installation of the substrate holder 3 above 40 ° at l = (0 ÷ 2 mm) is impractical, since this leads to a significant increase in h (over 1.7 mm) and drawing air under the semiconductor wafer 6 with stirring.

The forced mixing system of the proposed device consists of a magnetic stirrer 15 (MM-5) with a stirring rod 16 at the bottom of the galvanic bath 1, over which a shielding plate 18 is installed, which prevents the formation of a funnel. Forced mixing is necessary for the enrichment by metal ions of a surface layer of electrolyte 13 with a semiconductor wafer 6. During a subsequent pause, the electrolyte 13 relaxes, the solution calms down. The deposition of metal under conditions of forced mixing and the resulting turbulent flows at the boundary of the recesses in the photoresistive layer leads to the growth of chaotic dendrite structures. In the absence of mixing at a constant or pulsed deposition current, the surface of the semiconductor wafer 6 is covered with gas bubbles.

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

The pulsed inverse deposition mode contributes to an improvement in the quality of the precipitate, since during the anode period microprotrusions with increased electric field strength partially dissolve and metal ions convectively replenish the surface layer of electrolyte 13. However, when the semiconductor wafer 6 is deposited side down, convection mixing is not enough, since In this case, the surface of the deposited metal layer is inhomogeneous of the bump, which is associated with microgas evolution during the formation of ennogo layer. To suppress gas evolution, it is necessary to alternate the processes of metal deposition and forced mixing of the electrolyte 13.

Forced mixing more intensively than convection enriches with metal ions a layer of electrolyte 13 near the surface of the semiconductor wafer 6, including in the recesses of the photoresist mask.

The duration of deposition depends on the density of the cathode current (ρ _to ). The higher the current density, the shorter should be the period of deposition due to the more rapid depletion of the surface layer of electrolyte 13, for example, for ρ _k = 60 mA / cm ² not more than 1.5 min; for ρ _k = 80 mA / cm ² not more than 1 min; for ρ _k = 120 mA / cm ² not more than 30 seconds. At the same time, a dense fine-grained precipitate with an even edge geometry is formed in the mask windows.

The cycle, consisting of forced mixing of the electrolyte, relaxation of the electrolyte, pulse deposition, is repeated many times until the formation of a metal layer of the required thickness.

The control unit (figure 4) sets the program cycle indicating the duration of mixing (t ₁ ), relaxation (t ₂ ), pulse deposition (t ₃ ), the number of repetitions (n). Electric keys K ₁ and K ₂ of the control unit (figure 4) are built into the galvanic current circuit (DCE), specified by the current source (figure 3). When the electric key K _{1 is} open, the current source (Fig. 3) is shunted by the closed key K ₂ , while in the galvanostatic mode used, metal deposition on the semiconductor wafer 6 does not occur. During the mixing period of the electrolyte 13, the key K _{3 for} controlling the magnetic stirrer 15 is closed, during the relaxation period of the electrolyte 13 it is open. When the key K _{1 is} sequentially closed and the key K ₂ is opened, a galvanic current flows (metal deposition period). To stop the deposition, the shunt K ₂ closes and the electric switch K ₁ opens.

The design of the proposed device allows full automation of loading, processing, unloading.

Contact layers of chromium - palladium - silver (Cr / Pd / Ag) metals with a thickness of 400Å / 500Å / 1000Å, respectively, are sprayed on both sides of the semiconductor wafer 6. On the front epitaxial side of the semiconductor wafer 6 create a photoresistive mask with a pattern of contacts of the photoconverter. Use photoresist FP-4-04-T.

The width of the contact windows is ~ 10 μm. Length ~ 40 mm, photoresistive layer thickness ~ 7 μm.

The semiconductor wafer 6 is stacked with the back side on the supporting posts 4 of the substrate holder 3 and pressed against the deposited side (in the windows of the photoresistive mask) by four electrode current-carrying contacts 5 located around the perimeter of the semiconductor wafer 6 being processed.

The surface of the electrode current-carrying contacts 5 is covered with an insulating layer with the exception of the pressure end portion.

The substrate holder 3 with the semiconductor wafer 6 is mounted with an angled recess 7 on the angled protrusion 9 of the support frame 8, while the lower edge N of the wafer 6 is in contact with the electrolyte 13 (FIG. 2). The initial installation angle of the plane of the substrate holder 3 to the plane of the electrolyte 13 is α _beg. = 30 ° (see paragraph 4 of the table).

Gradually, decreasing the angle of inclination, the substrate holder 3 is placed on the support frame 8, while air is squeezed out from under the semiconductor wafer 6 due to surface tension forces and complete wetting of the deposited side is achieved. The motion of the substrate holder 3 occurs along a certain path, rigidly determined by the simultaneous sliding of the support points G and F of the angular protrusion of the support frame 8 along the surface of the sides of the corner recess 7. As a result, the edge of the semiconductor wafer 6, while holding the solution by surface tension, rises above the electrolyte plane 13, and after the final laying of the substrate holder 3, the plane of the deposited side is higher by h = 0.5 mm of the level of electrolyte 13 outside the processed semiconductor wafer 6.

If during the initial installation of the substrate holder 3 the edge of the semiconductor wafer 6 is below the level of the electrolyte 13, the amount of elevation of the deposition plane will decrease, respectively. For example, if the plate 6 is arranged according to l = 1 mm (table 3) and the initial immersion of the extreme point N by 0.2 mm, after laying the substrate holder 3, the height of the elevation of the deposition plane is h = 0.7 mm.

Then, using a magnetic stirrer 15 and the stirring rod 16 included in it, the electrolyte 13 is mixed for 20 seconds to enrich the metal with the surface layer of the solution in the windows of the photoresist mask. The shielding plate 18 prevents the formation of a funnel during the rotational movement of the electrolyte 13. Turn off the magnetic stirrer 15 by opening the electric key K ₃ of the control unit (figure 4). In the subsequent pause period of 20 sec, the electrolyte 13 relaxes, the solution calms down. The deposition of metal in a solution that continues to move by inertia leads to the formation of irregular growths - dendrites. The deposition is carried out in a calm electrolyte 13 without forced mixing until the surface layer of the solution is substantially depleted in metal ions. Apply pulsed inverse deposition mode. The duration of the cathodic and anodic pulses t = 1 · 10 ^-3 sec, current density ρ _to = 80 mA / cm ² and ρ _a = 8 mA / cm ² , respectively. The duration of the deposition period t = 30 sec. The subsequent repetition of the cycle of forced mixing of the electrolyte 13 - relaxation of the electrolyte 13 of the pulse deposition - build up a metal layer of the required thickness. For example, to obtain a metal layer ~ 7 μm thick with a selected deposition mode, 7 cycles are sufficient. Precipitated contacts have an even edge geometry, a fine-grained structure, a trapezoidal configuration. On the back of the semiconductor wafer 6, deposition does not occur. Then, by a rotational movement relative to the corner recess 7, the substrate holder 3 is inverted. The semiconductor wafer 6 is unloaded. The semiconductor wafer 6 is washed in deionized water and dried. Then, the face side with the deposited contacts, the semiconductor wafer 6 is laid again on the support posts 4 of the substrate holder 3. The electrode current-carrying contacts 5 are pressed to the back side, without a photoresistive coating. The substrate holder 3 with the semiconductor wafer 6 is mounted on the support frame 8, as described above. As a result, the deposited side is located above the level of electrolyte 13 by h = 0.5 mm, holding the solution by surface tension. Mix the solution with a stirring rod 16 of the magnetic stirrer 15 for t = 15 sec. In this case, the electrolyte layer 13 bordering on the semiconductor wafer 6 is enriched with metal ions. During a subsequent pause of t = 20 sec, the solution relaxes, calms down, and turbulent turbulence of the liquid near the arcs of contacts 5, pressed against the semiconductor wafer 6, stops.

In the case of deposition under conditions of forced mixing in the near-contact regions of the semiconductor wafer 6, chaotic metal growths — dendrites — are formed.

If the relaxation time of the electrolyte 13 is insufficient, less than 10 seconds, at the used solution rotation speed of ~ 15 rpm, the intensive inertia of the liquid also leads to the formation of dendritic structures that distort the morphology of the deposited layer, which is unacceptable in the technology of photoconverters. In a subsequent period of t = 30 sec, the metal is deposited using a pulsed reverse mode: cathodic and anodic current densities ρ _k = 11 mA / cm ² , ρ _a = 1.1 mA / cm ² , pulse durations t = 1 · 10 ^-3 sec . In this case, the surface layer of electrolyte 13 is partially depleted in metal ions. If the deposition time is more than 1.5 minutes, the morphology of the deposited metal layer is deteriorated, which is associated with gas evolution. To build up the metal layer of the required thickness (~ 7 μm), the cycle of forced mixing, relaxation, pulse deposition is repeated using the control unit (figure 4) in automatic mode 42 times. The formed precipitate has a fine-grained structure, in the area of arc contacts 5 dendritic rashes are absent.

In the proposed device, the main material used is Plexiglas brand TOSP 12, GOST 17622-72.

The proposed device for one-sided galvanic processing of semiconductor wafers eliminates the effect of electrolyte 13 on the reverse side of the semiconductor wafer 6, which allows independent galvanic processing of two sides with different deposition areas.

Unlike devices with a vertical arrangement of the semiconductor wafer 6, there is no need to insulate the reverse side by means of o-rings, which reduce the useful area of the wafer 6 being processed, especially in the presence of a base cut.

The proposed device provides uniform deposition of metal, since due to the horizontal arrangement of the semiconductor wafer 6, the deposited sections are in equal conditions.

Performing a cyclic treatment — forced mixing of the electrolyte 13, relaxation of the electrolyte 13, and pulsed metal deposition provides a dense fine-grained precipitate without dendritic growths in the windows of large-thickness photoresist masks, which is necessary, for example, to form a contact grid of a photoconverter with a small shading area. Precipitation in the electrolyte 13 without turbulent eddies ensures uniform metal buildup in the contact area 5 and in the absence of a photoresist coating.

The processed semiconductor wafer 6 does not experience mechanical stress, which allows the use of thin brittle semiconductor structures.

Claims (1)

A device for one-sided galvanic processing of semiconductor wafers, containing a galvanic bath with an anode, in which there is a substrate holder with a set of electrode current-carrying contacts and supporting columns, to which the semiconductor wafer is pressed, wherein the electrode current-conducting contacts are located around the perimeter of the semiconductor wafer, and, in addition, the device contains electrolyte mixing system and an electric current source, characterized in that it is additionally introduced into its design A horizontally located support frame with an angled protrusion and three needle stops with structural marks in the form of rings are provided, while the substrate holder is made with a guide angled recess and mounted on an angled protrusion of the support frame, and in addition, a control unit for a current source and an electrolyte mixing system is introduced into the device consisting of a magnetic stirrer with a shielding plate.

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