WO2018016979A1

WO2018016979A1 - Method for applying doping compositions and device for implementing same

Info

Publication number: WO2018016979A1
Application number: PCT/RU2016/000447
Authority: WO
Inventors: Георгий Сергеевич ДОГАДИН; Алексей Владимирович ПАНЮШКИН; Владимир Валерьевич ПАНЮШКИН; Надежда Сергеевна САВЦОВА; Сергей Иванович ХРЕНОВ; Александр Ильич ХУДЫШ; Виктор Николаевич ЩЕЛУШКИН
Original assignee: Общество С Ограниченной Ответственностью "Солэкс-С"
Priority date: 2016-07-18
Filing date: 2016-07-18
Publication date: 2018-01-25

Abstract

The invention relates to technology for manufacturing semiconductor devices, including solar photovoltaic cells (SPC). The essence of the invention consists in a method and a device for applying doping compositions for the manufacture of solar photovoltaic cells. The method includes placing a silicon wafer on a heated electrode in a precipitation chamber, turning on an exhaust pump to create negative pressure in the precipitation chamber, using a dosing syringe to feed a sol-gel doping reagent composition into an aerosol-forming chamber, transforming the sol-gel composition into an aerosol by means of an ultrasonic generator, transferring the aerosol from the aerosol-forming chamber to the precipitation chamber, creating cyclonic air flows in the precipitation chamber by means of a fan, and creating a high-intensity electric field such that the aerosol particles and the silicon wafer become positively charged. The device comprises a precipitation chamber, an electrode, an ultrasonic generator, an aerosol-forming chamber having an ultrasonic generator and a conduit, exhaust ventilation, a high-voltage source, a high-voltage breaker, and a fan. The technical result of the invention is that of enabling the conformal and even application, even on a textured surface, of a film coating based on a boric or phosphoric composition made from acidic alcoholic sol-gel solutions, and making it possible to regulate the thickness of the layer being applied.

Description

METHOD FOR APPLICATION OF LAYING COMPOSITIONS AND

DEVICE FOR ITS IMPLEMENTATION

The invention relates to the manufacturing technology of semiconductor devices, including solar photovoltaic cells (SFE).

State of the art

To create pn junctions, especially in the production of SFE, the diffusion of phosphorus and boron impurities into a semiconductor wafer from a film source is widely used. The main task in this case is the creation of such a source of impurities on the surface of the plate.

There is a method of applying a thin layer of diffusant on SFE semiconductor wafers, including dispersing a diffusant solution in an aerosol chamber of an ultrasonic generator, transporting an aerosol cloud into the volume of a precipitation chamber, into which a semiconductor layer is placed under aerosol sedimentation (Patent JP4037918 B2, publication date-January 23, 2008, name - Lioquid chemical atomizing device and lioquid chemical atomizing metod). The method does not provide the necessary performance due to the low sedimentation rate of the aerosol part with a size of the order of units of micrometers. In addition, large losses of diffusant occur, since aerosol deposition occurs not only on semiconductor elements, but also on the walls of the aerosol chamber. Also, due to the sufficiently long lifetime of the aerosol consisting of tetraethoxysilane, additives, and a hydroalcoholic liquid, alcohol begins to evaporate faster than water, and by the time of aerosol particle deposition on the surface of the semiconductor element, the specific concentration of water in the drop increases, which leads to a sharp reduce the quality of the applied diffusant.

A known method of applying alloying compositions by ultrasonic deposition (patent US5527389A publication date-18.

06.1996, name Apparatus for forming diffusion junctions in solar cell substrates).

In this method, an aqueous solution of phosphoric acid is sprayed using an ultrasonic head to obtain a fine mist (spray). Then, using the distribution-guide multi-chamber system, the spray is fed to continuously moving plates, where it condenses. The disadvantage of this solution is that the method provides for the application of only aqueous compositions, alcohol sol-gel compositions are not sprayed with an ultrasonic head. In addition, the presence of the plates in the air before diffusion in this method is limited to 2-3 seconds, since the films thus obtained on the surface of the plates are actively degraded in air.

The task of increasing productivity, reducing diffusant losses is solved in the method of applying a layer of sol-gel compositions to semiconductor wafers of solar cells (Patent RU 2444810 publication date - 03/10/2012 name Method for applying boron and phosphorus alloying compositions for the manufacture of solar photovoltaic cells (SFE)., including dispersing an alcohol-containing diffusant solution to an aerosol, transporting an aerosol cloud into the volume of the precipitation chamber into which place a semiconductor wafer for the duration of the exposure, act on the aerosol cloud and wafer with a corona discharge electric field or electrostatic field with tension, and the dispersion operation is carried out by centrifugal high-speed spraying of the diffusant However, the real spray pattern is 40-60 cm and requires continuous transportation of semiconductor wafers (square 156 x156 mm) in three rows.The exposure time in this case is different for the middle and extreme rows, t. E. The thickness of the layer on the middle row plates will be greater than on the extreme ones. Losses exist due to the deposition of aerosol on the walls of the precipitation chamber. In addition, the rapid surface overgrowth of the rotating cup of the atomizer with tetraethoxysilane, which leads to a change in the parameters of the aerosol cloud, an involuntary change in productivity, and, as a result, to the marriage of the deposited diffusant layer. Eliminating tetraethoxysilane deposits on the spray cup with hydrofluoric acid unnecessarily increases equipment maintenance costs.

Technical challenge

The technical problem is to create a high-performance method for producing a film of uniform thickness on the surface of a textured silicon wafer or other semiconductor material up to 200 mm in size from complex alcohol-acid sol-gel diffuser solutions, with the possibility of controlling the thickness of the resulting films from 70 nm to 1000 nm.

The technical result coincides with the task and consists in applying a conformal and uniform film coating based on boron or phosphorus composition on a textured surface from alcohol-acid sol-gel solutions with the ability to adjust the thickness of the applied layer

Decision

To solve this problem, a method for applying alloying compositions for the manufacture of solar photovoltaic cells is proposed, which includes the following steps:

a. - place the silicon plate on a heated electrode in the precipitation chamber,

b. - turn on the exhaust pump to create a vacuum in the precipitation chamber, c. - feed the sol-gel diffusant composition with a syringe dispenser into the aerosol forming chamber,

d. - translate the sol-gel composition into aerosol using an ultrasonic generator, while

e. - move the aerosol from the aerosol forming chamber to the precipitation chamber 1,

f. - create centrifugal air flows in the precipitation chamber using the impeller,

g. - create a high electric field so that the aerosol particles and the silicon wafer acquire the opposite charge,

h. - to complete the application of the diffusant layer, the electric field will be turned off.

When implementing the method, the frequency of operation of the ultrasonic generator is selected in the range from 0.9 to 1.5 MHz with a flow rate of sol-gel composition 5 - 10 ³ ml / s.

When implementing the method, a paper sheet is placed between the silicon wafer and the electrode and the electrode is heated to a temperature lying in the range from 40-50 ° C.

When implementing the method, the impeller is rotated with a linear speed of the outer sections of the impeller, lying in the range from 0.7 to 2.0 m / s.

When implementing the method, an electric field with a voltage of about 5 kV / cm is applied for a time of about 1 second.

When implementing the method to increase the thickness of the diffusant layer, the electric field is re-fed after 5 to 10 seconds. Moreover, the number of repetitions lies in the range from 1 to 15 times to obtain a diffusant layer with a thickness of 70 to 1000 nm.

To implement the above method, a device for applying alloying compositions for the manufacture of solar photovoltaic cells is proposed.

a. a precipitation chamber in which the alloying composition is applied to the silicon wafer,

b. an electrode made in the form of a substrate for silicon wafers with the possibility of heating,

c. an ultrasound generator for forming aerosols from the alloying composition in the liquid phase,

d. an aerosol forming chamber with an ultrasound generator and a conduit for transporting the aerosol to a precipitation chamber,

e. exhaust ventilation to create a vacuum in the precipitation chamber,

f. a high voltage source for creating high voltage between the electrodes, g. high voltage switch for creating and turning off an electric field between,

h. an impeller for forming a centrifugal air flow in the precipitation chamber, made with a metal and needle electrode for forming an electric field between the silicon wafer and the impeller, as well as for charging aerosol particles.

In the device, the precipitation chamber can be made in the form of a removable cap. It is recommended to choose a generator with the ability to adjust the frequency in the range from 0.9 to 1.5 MHz to form a maximum aerosol density with an aerosol flow rate of 5 · 10 ^"3 ml / s.

The device can be configured to accommodate silicon wafers measuring 156 mm by 156 mm.

To protect the substrate from aerosol, it is covered with a thin dielectric, which ensures the charge of the silicon wafer due to micro breakdowns. Moreover, as a thin dielectric, you can use a paper strip.

The device can be made in such a way that the needle electrode is displaced relative to the axis of rotation of the impeller, and the electrode on the impeller blades is turned towards the silicon wafer

Blueprints

In FIG. 1 shows a diagram of the process of applying diffusion compositions. The following notation is introduced:

1 deposition chamber;

2 - conductive electrode;

3 - rubber gasket;

4 - pipeline for aerosol;

5-camera;

6 - element of generation of ultrasound;

7 - frequency adjustment regulator;

8-dispenser;

9 - dielectric table for dispenser;

10 - pipeline for solution;

1 1 - a source of high voltage;

12 -. High voltage switch;

13 -. Metal electrode;

14-needle electrode;

15-impeller;

16 - silicon plate;

17 - paper gasket; 18 - power supply unit;

19- heater.

Detailed description

The solution to the technical problem is achieved by the fact that the proposed method of applying a diffusant layer on the SFE semiconductor wafers involves continuously dispersing the alcohol-containing solution of the diffusant to an aerosol in the aerosol chamber of the ultrasonic generator, transporting the aerosol cloud into the sedimentation chamber into which the semiconductor wafer is placed for the duration of the Te exposure, ensure a large area of uniform application of a diffusant layer in the precipitation chamber are created using multi-path impeller or other mixing device, centrifugal aerosol flows, impact on the aerosol cloud and semiconductor wafer during Te with a corona discharge electric field or electrostatic field with an intensity of 1- ^ 8 kV / cm for a short single pulse or a packet of them, and to obtain uniformity of the electric field one needle electrode is placed on a rotating impeller with a shift relative to the axis of rotation, and the remaining electrodes are located on the impeller blades. To prevent aerosol particles from entering the electrode supplying the grounding potential to the semiconductor wafer, a thin dielectric film can be placed between the electrode and the semiconductor wafer, while the zero potential is applied to the semiconductor wafer due to the formation of micro-breakdowns in the dielectric film.

The dispersion of the alcohol-containing solution is carried out continuously in the aerosol chamber of the ultrasonic aerosol generator with the adjustment of its operating frequency, and when the aerosol cloud is filled with a predetermined fraction of the chamber volume, the corona discharge electric field and / or electrostatic field are activated with a short-time single pulse or a packet thereof. The inclusion of the electric field of the corona discharge with single pulses allows the deposition of particles in the volume without the formation of vortex air movement in the chamber. For a time of the order of 1 sec. these vortices do not have time to develop. Bursts of pulses, especially in the presence of an additional electrostatic field, contribute to cleaning the volume of the precipitation chamber during the deposition of aerosol particles on silicon wafers. For uniform deposition of aerosol onto silicon wafers, forced mixing is applied using a multi-vane impeller or other mixing device.

The device operates as follows. The sol-gel diffusant composition is supplied by a syringe dispenser into chamber 5. An ultrasonic generator (ultrasonic generator) operating at a frequency F from 0.9 to 1.5 MHz with a flow rate of 5-10 ^"3 ml / s converts the liquid composition into aerosol. For about 4 sec The precipitation chamber is filled with aerosol. By adjusting the frequency of ultrasonic scanning, the maximum density of the aerosol cloud is achieved. A textured silicon plate 156x156 mm 16 in size is laid on a conductive electrode 2 heated by a heater 19 to 40-50 ° C through a paper pad 17, covered with a cap of the precipitation chamber 1 and include exhaust ventilation Due to the discharge that has arisen in the aerosol application unit, and therefore in the amount of precipitation the chamber begins filling the chamber 1 with a dispersed diffusant To obtain uniform aerosol throughout the chamber volume, the impeller 15 is rotated with a linear speed of rotation of the outer sections of the wing chatki 0,7-2,0 m / sec. Upon filling in a predetermined fraction of the volume of the chamber with an aerosol cloud, switch 12 supplies a high voltage from the output of the source 11 to the electrode 13 and 14 with an electric field of 5 kV / cm for a time of about 1 second. Then, the operation of turning on the electric field is repeated in 5-10 seconds. Under these conditions, comfortable diffuser layers were obtained that did not contain alcohols with a thickness of δ ~ 70 ± 20 nm. An increase in the thickness of the applied layer of diffusers can be achieved by repeating these operations. In addition, each cycle increases the thickness of the applied diffusant by 50–70 nm. Compared with the known application method, the consumption of the original diffusant is reduced by about 10 times. The quality of the deposited layer is satisfactory.

The proposed set of features of the method allows you to apply complex alcohol-acid sol-gel solutions, reduce diffusant losses, increase the stability of the characteristics of the deposited films and obtain comfortable layers of diffusers of the required thickness ranging from 70 to 1000 nm on textured plate sizes up to 200 mm.

The essence of the invention is illustrated by graphic materials, where the drawing shows a structural diagram of a device that allows to implement the proposed method.

A dielectric aerosol sedimentation chamber 1 is installed on an electrically conductive electrode 2. through a rubber gasket 3. A pipe for aerosol 4 is installed in the upper part of chamber 1, which connects the volume of chamber 1 with the exit of a transparent aerosol chamber 5. The ultrasonic oscillation generator 6 acts on the column of sprayed liquid and produces an aerosol. The frequency of ultrasonic vibrations can be changed by the regulator 7. The dispenser solution dispenser 8 is mounted on the dielectric table 9 and connected by a pipe 10 to the chamber 5. The isolated output of the high-voltage direct current source 11 through the switch 12 is connected to the electrodes 13-14, which are placed on the rotor blades of the impeller 15. The impeller is used for continuous mixing of the aerosol in order to equalize the particle density in the aerosol cloud. The semiconductor element 16 is installed on the electrode 2 through a paper pad 17. To remove the alcohols contained in the composition, the plate is heated.

As diffusants, for example, compositions of the following compositions can be used:

Phosphorus composition

- butanol 30-80%

- phosphoric acid 3-50%

- tetraethoxysilane 10-19%

- deionized water 5-30%

Boron composition

- boric acid 5-35%

- tetraethoxysilane 40-80%

- butanol 30-80%

- deionized water 5-30%

A possible implementation of the solution may be a method in which the spraying of an alcohol-containing solution is carried out continuously in the aerosol chamber of an ultrasonic aerosol generator with the adjustment of its operating frequency for each solution.

A possible implementation of the solution may be a method in which a sol-gel composition of the compositions of the phosphorus composition is used as a solution

- isopril alcohol 850 ml,

phosphoric acid 29 ml,

hydrochloric acid 1 ml,

Tetraethoxysilane 100 ml,

- water deionized 20 ml,

boron composition

- boric acid 5-35%,

- tetraethoxysilane 40-80%),

- hydrochloric acid 0, 1 -0.5%,

- isopropyl alcohol 30-80%),

- deionized water 5-30%.

A possible implementation of the solution may be a method in which, after filling in a predetermined fraction with an aerosol cloud, a corona discharge electric field and / or electrostatic field are switched on with a short-time single pulse or a packet of them that deposits the aerosol on the plate.

Claims

CLAIM

1. The method of applying alloying compositions for the manufacture of solar photovoltaic cells comprising the following steps:

b. - turn on the exhaust pump to create a vacuum in the precipitation chamber,

c. - feed the sol-gel diffusant composition with a syringe dispenser into the aerosol forming chamber,

e. - move the aerosol from the aerosol forming chamber to the precipitation chamber,

2. The method according to p. 1, characterized in that they select the frequency of the ultrasonic generator in the range from 0.9 to 1.5 MHz with a flow rate of sol-gel composition 5 10 ^" ml / s

3. The method according to p. 2, characterized in that a paper sheet is placed between the silicon plate and the electrode and the electrode is heated to a temperature lying in the range from 40-50 ° C.

4. The method according to p. 3, characterized in that the impeller is rotated with a linear speed of the outer sections of the impeller, lying in the range from 0.7 to 2.0 m / s.

5. The method according to p. 3, characterized in that an electric field with a voltage of 5 kV / cm is supplied for a time of about 1 second.

6. The method according to p. 4, characterized in that in order to increase the thickness of the diffusant layer, the electric field is re-fed after 5 to 10 seconds.

7. The method according to p. 5, characterized in that the number of repetitions lies in the range from 1 to 15 times to obtain a diffusant layer with a thickness of 70 to 1000 nm.

8. The device for applying alloying compositions for the manufacture of solar photovoltaic cells including

c. an ultrasound generator for forming aerosols from the alloying composition in the liquid phase, d. an aerosol forming chamber with an ultrasound generator and a conduit for transporting the aerosol to a precipitation chamber,

e. exhaust ventilation to create a vacuum in the precipitation chamber,

f. a high voltage source for creating high voltage between the electrodes,

g. high voltage switch for creating and turning off an electric field between,

9. The device according to p. 8, characterized in that the precipitation chamber is made in the form of a removable cap.

10. The device according to p. 9, characterized in that the generator is configured to adjust the frequency in the range from 0.9 to 1.5 MHz to form a maximum aerosol density with an aerosol flow rate of 5 10 ^'3 ml / s.

1 1. The device according to p. 10, characterized in that it accommodates silicon wafers with a size of 156 mm by 156 mm.

12. The device according to p. 11, characterized in that to protect the substrate from aerosol it is covered with a thin dielectric, which ensures due to micro-breakdowns the charge of the silicon wafer.

13. The device according to p. 12, characterized in that the dielectric is a paper gasket.

14. The device according to p. 13, characterized in that the needle electrode is displaced relative to the axis of rotation of the impeller, and the electrode on the impeller blades is turned towards the silicon wafer.