CN113840943A

CN113840943A - Chemical vapor deposition apparatus with resettable deposition zones

Info

Publication number: CN113840943A
Application number: CN202080035790.0A
Authority: CN
Inventors: R·蒙纳; T·德斯鲁
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2019-05-15
Filing date: 2020-05-13
Publication date: 2021-12-24
Also published as: FR3096058B1; FR3096058A1; EP3947771A1; WO2020229529A1

Abstract

The invention relates to an apparatus for plasma-assisted chemical vapor deposition on a plurality of substrates, comprising: a chamber (2) configured to perform plasma-assisted chemical vapor deposition, a carriage (4) comprising n stacked plates (P1, P2), each plate supporting at least one substrate, the plates (P1, P2) are made of conductive material and electrically insulated from each other, - connected to the gas supply and exhaust means (6) of the chamber, ‑ generator (8), ‑ electrical connection circuit (10) between the generator and the panels, comprising switching means (C1, C2) so that, at least in one switching state, two adjacent panels have the same polarity and two adjacent plates have opposite polarities.

Description

Chemical vapor deposition apparatus with resettable deposition zones

Technical field and background

The invention relates to a plasma enhanced chemical vapor deposition apparatus having a resettable deposition area.

Plasma enhanced chemical vapor deposition or PECVD is a process for depositing thin layers on a substrate from a gaseous state.

Such deposition is for example implemented in the field of manufacturing photovoltaic cells, for depositing a dielectric layer on a substrate (for example made of silicon).

The plasma enhanced chemical vapor deposition process proceeds as follows. The chemical reaction occurs after the gas forms a plasma. For example, a plasma is generated from one or more gases by applying a discharge excitation generated by a radio frequency source (40kHz to 440kHz) to the gas or gases.

For example, capacitive discharge excitation is performed by applying an alternating or radio frequency current between two electrodes. The injection of gas at the top of the tube, the extinguishing and ignition of the plasma over time allow to obtain a good uniformity of the deposition along the tube. Low frequency excitation (40kHz to 440kHz) requires hundreds of volts to sustain the discharge. These high voltages result in energetic ion bombardment of the surface. The operating pressure is between 100mTorrs (millitorr) and 2000 mTorrs.

In the fabrication of silicon photovoltaic cells, plasma deposition is used to perform passivation of the front and back surfaces and the antireflective layer. Silicon nitride (SiNx) is widely used to utilize Silane (SiH)₄) And ammonia (NH)₃) The mixture of gases causes the antireflective layer to deposit on the front side of the cell. Silane and dinitrogen monoxide (N)₂O) can deposit silicon oxide (SiOx), typically at pressures ranging from a few hundred millitorr to a few torr.

PECVD deposition is also widely used to deposit an aluminum oxide (AlOx) layer to passivate the back of a photovoltaic cell with PERC structure (passivate the emitter and back cell).

For example, in the case of industrial manufacturing, a tray (nanocell) comprising a plurality of plates stacked on top of each other is used to form the electrodes, the plates being electrically isolated from each other. Each plate forms a support for one or more substrates on which deposition needs to be performed.

To perform the deposition, opposite polarities are applied to two adjacent plates by a high frequency generator. An electric field is then generated between two adjacent electrodes, causing the plasma to form and deposit on a substrate supported by the plate.

Operation of the deposition apparatus results in deposition on all substrates occurring simultaneously. However, it is considered that deposition can be performed only on a part of the substrates arranged in the carrier.

Furthermore, as mentioned above, in the case of photovoltaic cells, a plurality of different types of layers may be deposited on both sides of the substrate. It is then desirable to provide an apparatus that allows differential deposition to be performed on both sides of the substrate.

Disclosure of Invention

It is therefore an object of the present invention to provide a PECVD deposition apparatus which allows greater freedom in accomplishing deposition on substrates arranged in a carrier.

The above-mentioned object is achieved by a PECVD deposition apparatus comprising a chamber configured for PECVD deposition, at least one carrier, at least one generator for supplying power to the plates, and electrical connection means between the generator and the plates, the at least one carrier comprising a plurality of electrically conductive plates superimposed on each other and electrically isolated from each other, the connection means comprising switching means allowing in a switched state at least one plate to have the same polarity as an immediately adjacent plate. The region located between the two plates having the same polarity is not where the electric field is located, and no plasma is generated in this region. No deposition then occurs on the substrate in this region.

The deposition apparatus comprises at least three 3 plates, so two adjacent plates may have the same polarity and two adjacent plates may have opposite polarities.

Thanks to the invention, it is thus possible to at least partially personalise the polarisation of the plates and thus the deposition. The deposition area may then be at least partially configured as desired.

Advantageously, the connection means are configured to allow modifying the polarity of one of the two plates, and each plate is pierced by at least one through hole. Thus, both sides of the substrate are exposed to the environment in the chamber and may be covered by deposition. By separately managing the polarity of at least some of the plates, deposition can be performed on only one side of the substrate during the deposition phase. This is of particular interest in the manufacture of photovoltaic cells, and in particular silicon photovoltaic cells, which comprise a final antireflective layer on the front side and a final passivation layer on the rear side.

Furthermore, an advantage of a plate with holes is that there is no need to process the substrate between two deposition stages on two different sides of the substrate.

In one mode of operation, it may be considered to polarize only one set of plates, so that deposition is only performed on the substrate accommodated between the plates.

Then, one object of the present invention is an apparatus for plasma enhanced chemical vapor deposition on a plurality of substrates, comprising a chamber configured to carry out plasma enhanced chemical vapor deposition, at least one carrier comprising n superimposed plates intended to support at least one substrate, a gas supply and exhaust connected to the chamber, a generator and an electrical connection circuit between the plates, the plates being made of electrically conductive material and being electrically isolated from each other. The connection circuit comprises a switching device such that, at least in one switching state, two adjacent plates have the same polarity and two adjacent plates have opposite polarities.

In one embodiment, the switching device has a switching state in which adjacent plates have opposite polarities.

The connection circuit may comprise a direct electrical connection between the generator and at least m (0 ≦ m) boards, and an electrical connection with switching means between the generator and n-m boards.

It is quite advantageous that at least part of the plate comprises at least one hole forming a space for the substrate, the hole comprising means for supporting the outer edge of the substrate. For example, the support means comprises a lug.

The connection circuit may comprise means for controlling the switching means in relation to the deposition to be performed.

For example, the plates are oriented such that the substrate is horizontal within the carrier.

Another object of the invention is a plate for a plasma enhanced chemical vapor deposition apparatus, the plate being made of an electrically conductive material and comprising at least one through hole forming a space for a substrate, the hole comprising means for supporting an outer edge of the substrate. For example, the support means comprises a lug.

Another object of the invention is a plasma enhanced chemical vapor deposition method implementing a deposition apparatus according to the invention, comprising:

a) a substrate is disposed on the plate.

b) The switching state of the switching means is selected in dependence on the deposition to be performed.

c) Gas is supplied.

d) The plate is polarized.

e) A plasma is formed between the plates of opposite polarity and a layer of material is deposited over all or a portion of the substrate.

f) The polarization is stopped.

The deposition method may include, after stopping poling:

a') purging the chamber to remove residual gases from a previous deposition phase,

b') the switching state of the switching means is selected in accordance with the deposition to be performed.

c') supplying a gas.

d') polarize the plate.

e') forming a plasma between the plates having opposite polarities and depositing a layer of material on all or part of the substrate.

f') the polarization is stopped.

Steps a ') to f') may be repeated for each additional layer deposited.

When the plates comprise at least one hole forming a space for a substrate and the substrate comprises a first face and a second face, the substrates may be loaded during stage a) such that the first faces of the substrates supported by two adjacent plates face each other, or their first surfaces face each other.

Drawings

The invention will be better understood from the following description in conjunction with the accompanying drawings:

figure 1 is a schematic view of a PECVD deposition apparatus according to one embodiment,

figure 2 is a schematic view of an example of a carrier and an example of a connection circuit implemented in a deposition apparatus in a first connected state,

figures 3A and 3B are perspective views of examples of plates containing holes with and without substrates,

figure 4 is a graphical representation of an example of the polarization of two adjacent plates capable of forming a plasma,

figure 5 is a diagram of an example of the polarization of two adjacent plates that are not capable of forming a plasma,

fig. 6 shows the bracket and the connection circuit of fig. 2 in a second connected state.

Detailed Description

More particularly, the following description relates to a PECVD deposition apparatus in which the substrate is horizontally arranged. The invention is also applicable to PECVD devices in which the substrate is vertically arranged.

In fig. 1, a schematic view of a PECVD deposition apparatus can be seen, comprising a closed chamber 2 with an access door, a carriage 4 intended to be housed inside the chamber 2 during a deposition phase and to be able to come out of the chamber to load/unload at least the substrates.

The carriage 4 comprises plates P1, P2, P3, …, Pn. In the example shown, n is 8. N is at least equal to 3. Generally, n ranges between 70 and 100. The plates are superimposed on each other so as to form spaces E1, E2, …, En-1 between each pair of plates.

The plates are made of an electrically conductive material and are intended to form electrodes between which an electric field can occur. The plates are made of graphite, for example.

The plates are electrically isolated from each other. For example, electrically insulating spacers (for example made of alumina) are interposed between each pair of plates. The spacers also ensure the spacing between the plates to form spaces E1, E2, …, En-1.

For example, the distance between the plates is comprised between 8mm and 12 mm.

The apparatus also comprises a fluid supply connection 6.1 for the input of gases for forming the plasma and performing the deposition, and a fluid connection 6.2 for the exhaust of gases after the deposition phase. Preferably, the gas is supplied from the top and discharged from the bottom, allowing the gas to pass through the carrier.

The device also comprises at least one generator 8 for powering the plates of the carriage 4. The generator 8 is, for example, a radio frequency voltage generator or an alternating current generator. The deposition apparatus also includes electrical connection circuitry 10 between the positive ("+") and negative ("-") terminals of the generator and the plates of the carriage.

For example, the frequency of the radio frequency generator is between 40kHz and 440kHz and the voltage between the two electrodes is between 50 volts and 500 volts.

In fig. 2, a detailed example of the electrical connection circuit 10 can be seen.

In this example, the connection circuit 10 includes an electrical connector 12 that directly connects a positive ("+") terminal to the boards P2, P6, and an electrical connector 14 that directly connects a negative ("-") terminal to the boards P4, P8.

The connection circuit also includes an electrical connector 16 connecting the positive ("+") terminal to the boards P1, P3, P5, P7 through switching devices C1, C2 and an electrical connector 18 connecting the positive ("+") terminal to the boards P1, P3, P5, P6 through switching devices C1, C2.

Depending on the position of the switching device, the plates P1, P3, P5, P7 may be connected all to the positive ("+") terminal, or all to the negative ("-") terminal, or partially to the positive ("+") terminal and partially to the negative ("-") terminal.

In this example and very advantageously, the plate P2 … Pn-1 (P2 in fig. 3A and 3B) comprises a through hole 20 passing through the thickness of the plate and intended to accommodate the substrate S on whose surface deposition should take place. The plates P1 and PN (P8 in fig. 2) are solid to avoid having a substrate with a face that cannot perform deposition. In this example, plate P1 is solid and does not support any substrate, while plate P8 is solid and supports a substrate.

Alternatively, all plates are identical. The substrates of plates P1 and P8 were then specially treated.

The opening 20 includes a support for the substrate. In the example shown, the support is formed by lugs 22 protruding from the edges of the opening 20. The implementation of the ledge reduces the surface not exposed to the plasma. In the example shown, the openings and the substrate are square. Alternatively, the substrate is square with four corners cut, referred to as a "pseudo-square".

Still alternatively, the substrate has a disk shape and the opening has a circular shape.

Preferably, the openings are shaped such that the substrate substantially completely seals them.

In fig. 2, the substrate can be seen mounted in a plate. Due to these plates, both faces F1, F2 or front and rear faces of each substrate are therefore available for deposition. Furthermore, due to these openings 20 the impedance of each plate is reduced, which allows to increase the deposition rate, in fact the voltage at the electrode terminals will be higher at the same radio frequency power. The thermal mass of each plate is also reduced, which allows for a reduction in the time to set the temperature of the carrier.

The operation of the deposition apparatus according to the present invention will now be described.

Consider switches C1 and C2 in the switch state in fig. 2.

The plates P2 to P8 have been loaded with the substrate S. Preferably, the substrates are loaded so that the same faces of the substrates carried by two adjacent plates face the same space En. For example, the front face of a substrate supported by a plate faces the same space as the front face of a substrate carried by an adjacent plate. Thus, thanks to the invention and to this particular orientation, layers made of the same material can be deposited simultaneously on the same face of both substrates of two adjacent plates.

Face F1 of the substrate faces upward on plates P3, P5 and P7 and downward on plates P2, P4, P6 and P8.

The chamber being supplied with a gas, e.g. Silane (SiH)₄) And ammonia (NH)₃) To form a silicon nitride layer.

The polarization state of each plate at time point t is shown in fig. 2.

The adjacent panels P1 and P2 are of positive polarity.

The adjacent panels P5 and P6 are of positive polarity.

The adjacent plates P3 and P4 have a negative polarity.

The adjacent plates P5 and P6 have a negative polarity.

In fig. 4, it can be seen that the graphically represented variation of the voltage V applied to two adjacent plates (for example P2 and P3) as a function of time t allows the polarization state of the plates between which the plasma can be generated. At any time, both plates are at opposite polarities. This state corresponds to the pairs of plates P2-P3, P4-P5, P6-P7.

In fig. 5, the graphically represented variation of the voltage V applied to two adjacent plates (for example P2 and P3) whose polarization states do not allow the formation of a plasma, as a function of time t, can be seen. At any time, both plates are at the same polarity. This state corresponds to the pairs of plates P1-P2, P3-P4, P5-P6, P7-P8.

A plasma can only be generated when an electric field is present between two adjacent plates. In view of the above polarization, plasma is generated only in the spaces E2, E4, E6. Deposition then takes place on face F1 of the substrate of plates P2, P3, P4, P5, P6 and P7.

No deposition occurs on the other side of the other substrate.

In fig. 6, the switches C1 and C2 can be seen in another connection state, which means that the plates P1, P3, P5, P7 are in another polarization state.

The adjacent panels P2 and P3 are of positive polarity.

The adjacent panels P6 and P7 are of positive polarity.

The adjacent plates P4 and P5 have a negative polarity.

The adjacent plates P1 and P8 have a negative polarity.

In this switching state, plasma will be generated in the spaces E1, E3, E5, and E7.

Deposition then takes place on face F2 of the substrate of plates P2, P3 and P4, P5 and P6, P7 and P8.

It should be understood that the same material or different materials may be deposited on the faces F1 and F2 of the substrate when switching from the switching state of fig. 2 to the switching state of fig. 6.

Thanks to the invention, in the case of photovoltaic cells, it is possible to deposit on both faces F1, F2 of each substrate a passivation layer (for example made of a material derived from silane and nitrous oxide (N)₂O) silicon oxide (SiOx), typically at a pressure of a few hundred millitorr to a few torr, in two steps (switching state of fig. 2 and then of fig. 6), then only on the front face F2 is deposited from Silane (SiH)₄) And ammonia (NH)₃) An anti-reflection layer made of silicon nitride of the mixture of (1).

Advantageously, the connection circuit comprises means for programmatically controlling the switching of the switches C1 and C2 according to the deposition cycle on both faces of the substrate. Thus, the operator does not need to intervene in the deposition device during the entire deposition cycle.

The perforated plate and the connecting circuit according to the invention have the advantage of allowing all the depositions on both faces of the substrate to be carried out without the need to flip the substrate, which represents a considerable saving in time and energy. In fact, in the PECVD apparatus of the prior art, all plates are solid, the deposition on each face implies flipping the substrate. However, flipping means cleaning the chamber, opening the chamber and cooling the carrier prior to processing. This time is very long compared to the deposition time. Thanks to the invention, the deposition can be carried out continuously without opening the chamber. Furthermore, energy savings may be realized because the chamber may be maintained at a high temperature.

In the example shown, the holes are made so that they are aligned in the vertical direction when the plates are stacked, but this configuration is not limiting. In fact, the substrates of two adjacent plates may not face each other.

This connection circuit configuration allows only two switches to be implemented. But does not allow the polarity of all plates to be modified.

In another embodiment (not shown), the connection circuit comprises a switch associated with each plate, which allows to modify the polarity of each plate individually and thus to manage each deposition space individually. The connecting circuit may then be configured to enable simultaneous deposition on all sides, which facilitates deposition of the dielectric layer on the front and back sides of the photovoltaic cell.

It should be understood that any configuration of the connection circuit that allows for modifying the polarity of at least one board of the tray to have the same polarity or an opposite polarity as an adjacent board is within the scope of the present invention.

The operation of the apparatus is described as allowing deposition to be performed on either side of the substrate during the deposition phase.

It should be noted that the switching state of the switch may remain unchanged between two successive depositions.

In the case of solid plates, preferably the plates include protrusions (e.g., spikes) on their larger surfaces to support the substrate.

As described above, the present invention is also applicable to a PECVD apparatus in which substrates are vertically arranged. In this case, the plate is vertical and comprises means for vertically holding the substrate. The connection circuit is similar to one of the above.

The apparatus may also be operable to deposit on both faces of a substrate carried by plates located in one or more regions of the carrier, for example, the substrate of a plate located in the top portion of the carrier, the plates then having alternating polarities, and all plates in the bottom portion having the same polarity.

The device according to the invention is therefore characterized by great flexibility in the deposition, in particular the continuity of the deposition. Furthermore, the apparatus allows for multiple depositions on different sides of the substrate in succession without the need to process the substrate, which represents a considerable time and energy saving.

Claims

1. An apparatus for plasma enhanced chemical vapor deposition on a plurality of substrates, comprising:

- a chamber (2) configured for plasma enhanced chemical vapor deposition,

- at least one carrier (4) comprising n superimposed plates (P1, P2), n greater than or equal to 3, each plate intended to support at least one substrate, said plates (P1, P2) made of conductive material into and electrically isolated from each other,

- a gas supply (6.1) and a discharge (6.2) connected to the chamber,

- generator (8),

- an electrical connection circuit (10) between said generator and said panels,

Wherein, the connection circuit (10) comprises switching means (C1, C2), so that in at least one switching state, two adjacent plates have the same polarity and two adjacent plates have opposite polarities.

2. The deposition apparatus according to claim 1, wherein the switching means (C1, C2) have a switching state, wherein adjacent plates have opposite polarities.

3. The deposition apparatus according to claim 1 or 2, wherein the connection circuit comprises a direct electrical connection between the generator (8) and at least m plates, and between the generator and n-m plates There is an electrical connection between the boards with a switching device, 0≤m.

4. Deposition apparatus according to any one of claims 1 to 3, wherein at least part of the plate (P2) comprises at least one hole (20) forming a space for the substrate (S), the hole ( 20) Including means for supporting the outer edge of the substrate.

5. The deposition apparatus according to claim 4, wherein the support means comprise lugs (22).

6. Deposition apparatus according to any one of claims 1 to 5, wherein the connection circuit (10) comprises means for controlling switching means related to the deposition to be performed.

7. The deposition apparatus of any preceding claim, wherein the plate is oriented such that the substrate is horizontal within the carrier.

8. A plate for a plasma-enhanced chemical vapor deposition apparatus, the plate being made of a conductive material and comprising at least one hole (20) forming a space for a substrate (S), the hole (20) Means are included for supporting the outer edge of the substrate.

9. A panel according to claim 8, wherein the support means comprise lugs (22).

10. A plasma-enhanced chemical vapor deposition method implementing the deposition apparatus according to any one of claims 1 to 7, comprising:

a) Disposing the substrate on the plate.

b) Selecting the switching state of the switching device according to the deposition to be performed.

c) Supply gas.

d) Polarizing the plate.

e) A plasma is formed between the plates of opposite polarity and a layer of material is deposited on all or part of the substrate.

f) Stop polarization.

11. The deposition method according to the preceding claim, comprising after stopping the polarization:

a') purging the chamber to remove residual gases from previous deposition stages,

b') Selecting the switching state of the switching device according to the deposition to be performed.

c') Supply gas.

d') Polarizing the plate.

e') A plasma is formed between the plates of opposite polarity and a layer of material is deposited on all or part of the substrate.

f') stop polarization.

12. The deposition method according to the preceding claim, wherein steps a') to f') are repeated for each additional layer deposited.

13. The deposition method according to any one of claims 10 to 12, wherein when the plate includes at least one hole forming a space for a substrate and the substrate includes a first side and a second side , loading the substrates during stage a) such that the substrates supported by two adjacent plates have their first faces facing each other, or their second faces facing each other.