WO2013092759A2

WO2013092759A2 - Method for etching of sio2 layers on thin wafers

Info

Publication number: WO2013092759A2
Application number: PCT/EP2012/076227
Authority: WO
Inventors: Marcello Riva; Reiner Fischer; Gerd Walther
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2011-12-21
Filing date: 2012-12-19
Publication date: 2013-06-27
Anticipated expiration: 2014-06-21
Also published as: WO2013092759A3

Abstract

A method for etching of SiO₂ layers with a thickness of equal to or less than 10 μm on a semiconductor item having a thickness of equal to or less than 10 μm, comprising a step of etching the SiO₂ layer wherein an etching gas is applied which contains NF₃, SF₆, or preferably, F₂ or COF₂, and wherein said etching gas further comprises O₂ and/or H₂.

Description

Method for etching of SiO? layers on thin wafers

The present invention claims priority to European patent

application 11195023.4 filed December 21, 2011 the whole content of which is incorporated herein for all purposes.

The present invention relates to a method for etching of Si0₂ layers from solid bodies, especially from thin wafers, especially from thin Si wafers.

Semiconductors, flat panel displays or photovoltaic elements ( also denoted as "solar panels") are manufactured in subsequent steps of applying inorganic or organic layers and etching them partially away to provide isolating layers or areas which are conductive or semi- conductive for electric current. The process for the formation of layers is often performed by operations which include chemical vapor deposition and plasma etching on a substrate which, during the process, is typically located on a support provided inside a plasma process chamber. Examples of substrates are semi-conducting inorganic materials ; preferred substrates in the frame of the present invention are silicon wafers. Etching agents are known. F₂ and COF₂ are preferred etching agents because they have no impact on the ozone layer and have a lower Global Warming Potential ("GWP") compared to other etching agents like SF₆,

hydro fluorocarbons or NF₃.

For certain uses, especially for solar panels (photovoltaic elements), very thin substrates or wafers are used. Often, wafers are applied having a thickness of equal to or lower than 500 μιη, often equal to or lower than 230 μιη down to a thickness of equal to or lower than 130 μιη and even equal to or lower than 100 μιη. During the manufacture of items based on thin wafers, Si0₂ (including phosphosilicate glass, "PSG") layers have to be removed. These layers may be very thin, for semiconductor items, they may be, for example, equal to or thinner than 10 nm, and in respect of solar panels, they maybe somewhat thicker, e.g. 10 μιη or thinner. It is known to etch them using aqueous hydrogen fluoride (hydrofluoric acid). An undesired percentage of the wafers breaks during the wet etching process due to mechanical impact.

F₂ or COF₂ may be used as etching gases to etch Si0₂ layers ; but they are very reactive towards Si, and after having etched the Si0₂ layer, the etching process would continue undesirably on the layer or layers coated by Si0₂. For example, p-n layers mainly consisting of Si (which is etched fast by F₂ or COF₂) are coated by the Si0₂ layer. Accordingly, it is difficult to etch thin Si0₂ layers reliably using these reactive etchants.

The present invention now makes available in particular an efficient process for the etching of Si0₂ layers, especially thin Si0₂ layers.

The invention concerns in consequence a method for the manufacture of a semiconductor item comprising a step of providing a semiconductor item having a coating of Si0₂ and etching a layer of Si0₂ from the surface of the

semiconductor item which comprises a step of treating the layer of Si0₂ in a plasma with a gas comprising NF₃, SF₆, molecular fluorine (F₂) or COF₂ which gas further comprises at least one additional gas selected from the group consisting of oxygen (0₂) or hydrogen (H₂), wherein the semiconductor item has a thickness of equal to or lower than 1000 μιη, and wherein the Si0₂ layer has a thickness of equal to or less than 10 μιη.

Detailed description of preferred embodiments

The term "Si0₂" includes PSG coatings.

While SF₆ and NF₃ appear as working etchant gases, they may provide technical or environmental disadvantages : formation of ammonium salts when NF₃ is applied, high GWP. Thus, the absolutely preferred embodiment of the invention is a method for the manufacture of a semiconductor item

comprising a step of providing a semiconductor item having a coating of Si0₂ and etching the Si0₂ layer wherein an etching gas is applied which contains F₂ or COF₂ wherein said etching gas further comprises at least one additional gas selected from the group consisting of 0₂ or H₂, and wherein the semiconductor item has a thickness of equal to or lower than 1000 μιη, and wherein the Si0₂ layer has a thickness of equal to or less than 10 μιη.

In one embodiment, the etching gas contains 0₂ or H₂. In another embodiment, the etching gas contains 0₂ and H₂. It is preferred that the etching gas contains H₂.

The semiconductor item is constituted from a material which reacts comparably faster with F₂ or COF₂ compared to Si0₂ but which reacts with F₂ or COF₂ and 0₂ and/or H₂ to form a compound with slower reactivity.

Alternatively, or at the same time, the semiconductor item is constituted from a material which has a slow reactivity with HF. The Si0₂ coating may extend over the whole surface of the item, or it may partially coat the surface of the item ; preferably, the semiconductor item is selected from the group consisting of a semiconductor, a flat panel display and a solar substrate, especially a solar panel. Preferably, the item is a flat panel display or a solar substrate, especially a solar panel. Preferably, it has the form of a wafer, especially preferably being a Si wafer having an Si0₂ coating or a PSG coating.

The invention will now be described in detail in view of a preferred embodiment where the semiconductor item is formed from silicon (Si).

Surprisingly, the step of etching the Si0₂ layer is performed in an improved manner by applying gases which, additionally to F₂ or COF₂, comprise 0₂ or H₂.

If the gas additionally contains 0₂, it is much easier to determine the moment when the etching process of the Si0₂ layer must be stopped to prevent Si in the semiconductor item to be etched. The etch rate of F₂ or COF₂ applied on Si0₂ is slow compared to the respective etch rate of Si. The presence of 0₂ in the etch gas leads to the formation of Si0₂ from the Si, and thus, the etch rate is reduced, with a reduced over-etching.

If the gas additionally contains H₂, HF is formed. HF assists in the etching of Si0₂, but is not reactive with Si. Thus, the etch reaction is preferential for Si0₂ etching.

The etching step is performed under the influence of a plasma. The plasma may be a remote plasma or an in-situ plasma. It may be capacitively or inductively coupled. A typical method to generate the plasma comprises exposing the gas to a high-frequency electrical field.

In a first aspect of the first particular embodiment, the frequency of the generated field is from 10 to 15 MHz. A typical frequency is 13.56 MHz.

In a second aspect of the first particular embodiment, the frequency of the generated field is from 40 to 100 MHz, preferably 40 to 100 MHz. A typical frequency is selected from 40 MHz and 60 MHz.

In a third aspect which is preferred, the frequency of the generated field is a microwave plasma with a frequency of equal to or greater than 500 MHz, preferably in the range of from 1 to 10 MHz with a typical frequency

of 2.45 GHz. Microwave frequency is preferred.

Plasma sources operating at the frequency ranges mentioned above, either in Remote Plasma Source configuration ("RPS"), or built in into the plasma chamber ("in-situ") are in use for the manufacture of Solar panel.

Solar panels or solar substrates in general, are often manufactured using the first-mentioned frequency range. In the first particular embodiment of the method according to the invention, the gas pressure is generally equal to or greater than 0.5 mbar, and often, it is equal to or greater than 0.5 Torr (0.67 mbar). Generally, the pressure is equal to or lower than 50 Torr (66.7 mbar). Preferably, the pressure is equal to or lower than 50 mbar.

Preferably, the pressure is equal to or greater than 1 Torr (0.67 mbar), and more preferably, it is equal to or greater than 1 mbar.

Preferably, the pressure is equal to or lower than 10 Torr (13.33 mbar), and more preferably, it is equal to or lower than 10 mbar. Especially preferably, the pressure is equal to or lower than 5 Torr (6.67 mbar).

A suitable pressure range according to one embodiment, is from 0.5 to 50 Torr (0.67 to 66.7 mbar). Another preferred range is from 0.5 mbar to 50 mbar. A more preferred range, according to one embodiment, often is from 1 Torr (1.33 mbar) to 10 Torr (13.33 mbar). According to another embodiment, the pressure is preferably in a range of from 1 to 10 mbar.

In the first particular embodiment of the method according to the invention, the life time of the radicals in the gas is generally from 1 to 1000 ms, more often from 400 to 700 ms.

In the first particular embodiment of the method according to the invention, the power applied to generate the plasma is generally from 1 to 100000 W, often from 5000 to 60000 W, especially preferably from 850 to 40000 W, and most preferably, from 1000 to 40000 W.

It is understood that these particular conditions also apply to the plasma according to the invention and the use according to the invention.

In one aspect of the first particular embodiment, the treatment is carried out by the remote plasma technology. In another aspect of this embodiment, in-situ plasma is generated, especially a microwave plasma. For example, such in-situ plasma is generated inside a process chamber comprising a device suitable for generating a plasma from the gases described above, in particular from purified molecular fluorine. Suitable devices include, for example, a pair of electrodes capable of generating a high frequency electrical field.

The semiconductor item has a thickness of equal to or lower than 1000 μιη, preferably equal to or less than 500 μιη, most preferably, equal to or less than 250 μιη.

The process of the invention is especially suitable to etch thin Si0₂ layers on thin bodies of Si. The term "thin Si0₂ layer" denotes preferably layers which, for solar panels, have a thickness of equal to or lower than several μηι, e.g. equal to or less than 10 μηι. Other semiconductor items may have thinner Si0₂ layers, especially layers of equal to or less than 1 μιη, preferably equal to or less than 500 nm, more preferably, equal to or less than 150 nm, e.g. layers of equal to or less than 100 nm and sometimes even layers of equal to or less than 10 nm.

The term "thin bodies of Si" preferably denotes Si bodies having a thickness of equal to or less than 1000 μιη as mentioned above, more preferably equal to or less than 500 μιη, most preferably, equal to or less than 250 μιη. These thin bodies can be, for example, part of a semiconductor, a solar panel or a thin film transistor. Preferred bodies are solar substrates, e.g. panels.

The dimension of the solar substrates is very flexible. Substrates of any geometrical form can be etched in the process of the present invention. The substrate may especially be a substrate in the form of a circle, it may be a square substrate, it may have a rectangular form or it may be an ellipse. Of course, it may have other geometrical forms. Often, the dimension of the substrate is equal to or larger than 150 mm. Preferably, the dimension is equal to or

greater 200 mm. The dimension may be equal to or lower than 500 mm, and is preferably equal to or lower than approximately 400 mm. It has to be noted that the technical trend in solar panels is directed towards larger panels, so in the future, the dimension may even be larger than 500 mm. The method of the invention is especially suitable for such large solar substrates.

The term "dimension" preferably denotes the diameter of substrates in the form of a circle, the longer diameter of an ellipse, the width of a rectangular form or the length of the side of a square form. Thus, the diameter of the solar panels is very flexible. Often, the diameter is equal to or larger than 150 mm.

Preferably, the diameter is equal to or greater 20 mm. The diameter may be equal to or lower than 500 mm, and is preferably equal to or lower than approximately 400 mm. It has to be noted that the technical trend in solar panels is directed towards larger panels, so in the future, the diameter may even be larger than 500mm. The same is true for elliptical, square or rectangular substrates. The method of the invention is also suitable for such large solar panels.

Especially preferred embodiments concern the etching of Si0₂ layers including PSG layers having a thickness of equal to or less than 250 nm on solar substrates having a thickness of equal to or less than 1000 μιη, preferably, equal to or less than 500 nm, and applying a microwave plasma in a range of from 1 to MHz. The etching gas consists preferably of COF₂ and H₂ ; more preferably, the etching gas consists of F₂ and H₂ which provided separately into the plasma apparatus. The pressure in this preferred embodiment is equal to or lower than 5 mbar, and more preferably, equal to or lower than 2 mbar. The F₂ may be provided in the form of a mixture with N₂ and argon.

The gas atmosphere in the Si0₂ layer etching step may preferably consist of F₂ and 0₂, F₂ and H₂, COF₂ and 0₂ or COF₂ and H₂. It has to be noted that F₂ and H₂ usually will form immediately HF in an exothermic reaction if F₂ and H₂ are introduced in the etching step. Thus, it may be advisable to supply H₂ and F₂ separately into the chamber under respective safety precautions.

If desired, one or more inert gases may be additionally present. Preferably, the inert gas is at least one gas selected from the group consisting of N₂, He, Ar and Ne. Preferably, N₂, Ar or N₂ and Ar are present as inert gas.

According to one embodiment, the etching gas comprises F₂ as etchant. In mixtures comprising F₂ and 0₂, the content of 0₂ is preferably equal to or lower than 20 % by volume. It may be higher but an undesired loss of etching activity may be observed.

The content of F₂ is preferably equal to or greater than 1 % by volume. In binary mixtures consisting of F₂ and 0₂, the content of 0₂ is preferably equal to or greater than 1 % by volume and equal to or lower than 20 % by volume, and F₂ is the balance to 100 % by volume.

In respect of mixtures comprising 0₂, F₂ and one or two further

constituents, a ternary mixture comprising F₂, 0₂ and an inert gas selected from Ar and N2, and a quaternary mixture comprising F₂, 0₂, Ar and N₂ are especially preferred. Often, the etching gas consists of 1 to 99 % by volume of F₂, 1 to 20 % by volume of 0₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar. In one embodiment, the content of at least one of N₂ and Ar is equal or greater than 1 % by volume.

In preferred embodiments, the content of F₂ is equal to or greater than 1 % by volume, and it is preferably equal to or lower than 30 % by volume, and especially preferably, it is equal to or lower than 20 % by volume. The content of 0₂ is preferably equal to or greater than 1 % by volume, and it is preferably equal to or lower than 20 % by volume. The content of Ar and/or N₂ is the balance to 100 % by volume. In quaternary mixtures, the content of Ar is preferably equal to or greater than 5 % by volume, and equal to or lower than 15 % by volume. According to another embodiment, the etching gas comprises COF₂.

In mixtures comprising COF₂ and 0₂, the content of 0₂ is preferably equal to or lower than 20 % by volume, and in mixtures comprising COF₂ and H₂, the content of H₂ is preferably equal to or lower than 20 % by volume.

An undesired loss of etching activity may be observed in mixtures containing COF₂ if the content of 0₂ or H₂ is too high. The content of COF₂ in mixtures containing it is preferably equal to or greater than 1 % by volume.

Often, the etching gas comprises or consists of 1 to 99 % by volume of COF₂, 1 to 20 % by volume of 0₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar, or wherein the etching gas comprises or consists of 1 to 99 % by volume of COF₂, 1 to 99 % by volume, preferably, 1 to 70 % by volume of H₂, e.g. l to 20 % by volume of H₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar. In one embodiment, the content of at least one of N₂ and Ar is equal or greater than 1 % by volume.

Preferably, the etching gas comprises or consists of 1 to 99 % by volume of COF₂, 1 to 99 % by volume of H₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.

In binary mixtures, the content of 0₂ or H₂ is equal to or greater than 1 % by volume and equal to or lower than 70 % by volume, e.g., the content of 0₂ or H₂ is equal to or greater than 1 % by volume and equal to or lower than 20 % by volume, and the content of COF₂ is the balance to 100 % by volume.

In respect of mixtures comprising 0₂, COF₂ and one or two further constituents, a ternary mixture comprising COF₂, 0₂ and an inert gas selected from Ar and N₂, and a quaternary mixture comprising COF₂, 0₂, Ar and N₂ are especially preferred. The content of COF₂ is equal to or greater than 1 % by volume, and it is preferably equal to or lower than 70 % by volume, preferably equal to or lower than 50 % by volume. It may be, for example, equal to or lower than 30 % by volume, and even equal to or lower than 20 % by volume. The content of 0₂ is preferably equal to or greater than 1 % by volume, and it is preferably equal to or lower than 20 % by volume. The content of Ar and/or N₂ is the balance to 100 % by volume. In quaternary mixtures, the content of Ar is preferably equal to or greater than 5 % by volume, and equal to or lower than 50 % by volume. The content of argon may even be equal to or lower than 15 % by volume.

In respect of mixtures comprising H₂, COF₂ and one or two further constituents, a ternary mixture comprising COF₂, 0₂ and an inert gas selected from Ar and N2, and a quaternary mixture comprising COF₂, 0₂, Ar and N₂ are especially preferred. The content of COF₂ is equal to or greater than 1 % by volume ; it is preferably equal to or lower than 70 % by volume, and it is more preferably equal to or lower than 50 % by volume. The content of COF₂ may be equal to or lower 30 % by volume ; and it may even be equal to or lower than 20 % by volume. The content of 0₂ is preferably equal to or greater than 1 % by volume, and it is preferably equal to or lower than 50 % by volume. The content of 0₂ may even be equal to or lower than 20 % by volume. The content of Ar and/or N₂ is the balance to 100 % by volume. In quaternary mixtures, the content of Ar is preferably equal to or greater than 5 % by volume, and equal to or lower than 50 % by volume. The content of Ar may even be equal to or lower than 15 % by volume. According to a specific embodiment of the invention, the invention concerns a gas mixture, consisting of 1 to 99 % by volume of COF₂, 1 to 99 % by volume of H₂ or 0₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar. The content of H₂ and 0₂ may be even equal to or lower than 20 % by volume.

The invention also concerns a gas mixture, consisting of 1 to 99 % by volume of SF₆ or NF₃, 1 to 99 % by volume of H₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.

Such gas mixtures as described above and as outlined in the claims are another aspect of the present invention. It has to be noted that for all gas mixtures given above the sum of constituents adds up to 100 % by volume.

The gas mixtures can be applied in a premixed form ; they may be stored in respective pressure resistant containers. If desired, the mixtures can be generated immediately before introduced into the chamber, or, often especially preferred because it allows a high flexibility to adapt the constitution of the mixtures, they may be introduced separately into the chamber. It is of course also possible to introduce a mixture of F₂ and N₂ (e.g. a 20/80 vol/vol mixture of F₂ and N₂), or a mixture of F₂/N₂/Ar (e.g. 20/70/10 vol/vol/vol) and to introduce 0₂ separately. The same is possible for mixtures containing COF₂.

Molecular fluorine for use in the present invention can be produced for example by heating suitable fluorometallates such as fluoronickelate or manganese tetrafluoride. Preferably, the molecular fluorine is produced by electrolysis of a molten salt electrolyte, in particular a potassium

fluoride/hydrogen fluoride electrolyte, most preferably KF.2HF. Preferably, purified molecular fluorine (F₂) is used in the present invention as etchant. Purification operations which are suitable to obtain purified molecular fluorine for use in the invention include removal of particles, for example by filtering or absorption and removal of starting materials, in particular HF, for example by absorption, and impurities such as in

particular CF₄ and 0₂. Typically, the HF content in molecular fluorine used in the present invention is lower than 10 ppm molar. The fluorine used in the present invention may contain at least 0.1 molar ppm of HF.

In a preferred embodiment, purified molecular fluorine for use in the present invention is obtained by a process comprising

(a) electrolysis of a molten salt, in particular as described above, to provide crude molecular fluorine containing HF, particles and optional impurities ;

(b) an operation to reduce the HF content relative to the HF content of crude molecular fluorine, comprising for example an adsorption on sodium fluoride and preferably reducing the HF content in the molecular fluorine to the values mentioned here before ;

(c) an operation to reduce the particle content relative to the particle content of crude molecular fluorine, comprising for example passing a fluorine stream containing particles through a solid absorbent such as for example sodium fluoride.

The molecular fluorine in particular produced and purified as described here before, can be supplied to the method according to the invention, for example, in a transportable container. This method of supply is preferred when mixtures of fluorine gas with an inert gas in particular as described above are used in the method according to the invention.

Alternatively, the molecular fluorine can be supplied directly from its manufacture and optional purification to the method according to the invention, for example through a gas delivery system connected both to the silicon hydride removal step and to the fluorine manufacture and/or purification. This embodiment is particularly advantageous, if the gas used in the method according to the invention consists or consists essentially of molecular fluorine.

The invention concerns also a process for the manufacture of a product wherein at least one treatment step for the manufacture of the product is carried out in a treatment chamber which process comprises etching an Si0₂ layer or a PSG layer by the method according to the invention. Typically, the manufacture of the product comprises at least one POCI₃ diffusion step or a chemical vapor deposition step of amorphous and/or microcrystalline Si0₂, as described above, onto a substrate. Typical products are selected from the group consisting of a semiconductor, a flat panel display and a photovoltaic element such as a solar substrate, e.g. a panel. Preferably, the product is a solar substrate, e.g. a panel.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

The examples here after are intended to illustrate the invention without however limiting it.

Examples

Example 1 : Etching of an Si0₂ layer using F₂/0₂ and a remote plasma

In the manufacture of a solar panel, a Si0₂ having a thickness of 500 nm on a Si wafer having a thickness of 128 μιη has to be etched. The Si wafer has a size of 200 mm.

The solar panel is located onto the chuck of a plasma chamber, a gas consisting essentially of molecular fluorine and oxygen in a molar ratio of 1 :4 (20 % by volume of F₂) is introduced at 35 slm, and separately thereof, oxygen at 7 slm. Thus, inside the chamber, a gas having a molar ratio of 1 :4 (20 % by volume of F₂) is contained. The gases are fed into the chamber through a remote plasma (RPS) system (10 kW, 13.56 Mhz) at a pressure of 100 mbar. After a 3 min treatment, the wafer is removed from the chamber.

Example 2 : Etching of an Si0₂ layer using F₂/0₂ and an in-situ plasma

In the manufacture of a solar panel, a Si0₂ having a thickness of 100 nm on a Si wafer having a thickness of 128 μιη has to be etched. The Si wafer has a size of 200 mm.

The solar panel is located onto the chuck of a plasma chamber, a gas consisting essentially of molecular fluorine is introduced at 35 slm into the chamber, and 0₂ is introduced at 3.5 slm separately. The in-situ plasma system (10 kW) is started at a pressure of 100 mbar ; after 3 min treatment, the wafer is removed from the chamber.

Example 3 : Etching of an Si0₂ layer using an F₂/Ar/N₂ mixture

Example 2 is repeated ; the F₂ is introduced into the plasma reactor in the form of a gas mixture consisting of F₂ (20 %), N₂ (70 %) and Ar (10 %) in a rate of 100 slm. 0₂ is introduced in a rate of 4 slm. Example 4 : Etching of an Si0₂ layer using COF₂ in combination with 0₂ as etchant in an in- situ plasma

A Si wafer with a thickness of approximately 250 μιη for a solar cell has a coating of Si0₂ with a thickness of 250 nm is brought into a plasma apparatus. A gas consisting essentially of COF₂ is introduced at 10 slm into the chamber ;

0₂ is introduced at 2 slm. The pressure in the plasma apparatus is pressure of 5 mbar. The in situ plasma is started and stable plasma is reached. After

5 min treatment, desired areas of the Si0₂ layer are etched away.

Example 5 : In situ plasma treatment with COF₂ and H₂

In the manufacture of a solar panel, a Si wafer having a thickness of 128 μιη with a coating of 100 nm Si0₂ is brought into a plasma chamber.

Neat COF₂ is fed into the chamber with a rate of 10 slm, and H₂ is fed in a rate of 2 slm. The in situ plasma source is activated and stable plasma is reached.

After 3 min plasma treatment, the desired area of the Si0₂ is substantially etched away, and the solar panel can be provided to the next treatment step.

Example 6 : Etching of an Si0₂ layer using F₂/H₂ and a remote plasma

In the manufacture of a solar substrate, a Si0₂ having a thickness of 500 nm on a Si wafer having a thickness of 128 μιη has to be etched. The Si wafer has a dimension of 200 mm.

The solar substrate is located onto the chuck of a plasma chamber, a gas consisting essentially of molecular fluorine and hydrogen in a molar ratio of 1 : 1

(50 % by volume of F₂) is created inside the chamber by introducing F₂ at 2 slm, and separately thereof H₂ at 2 slm. The gases are fed into the chamber through a remote plasma source (RPS) system (1.25 kW, 2.45 GHz) at a pressure of 1 mbar. After a 1 min treatment, the wafer is removed from the chamber.

Example 7 : Etching of an Si0₂ layer using F₂/H₂ and an in-situ plasma

In the manufacture of a solar substrate, a Si0₂ having a thickness of 100 nm on a Si wafer having a thickness of 128 μιη has to be etched. The Si wafer has a size of 200 mm.

The solar substrate is located onto the chuck of a plasma chamber, a gas consisting essentially of molecular fluorine is introduced at 2 slm into the chamber, and H₂ is introduced at 2 slm separately. The in-situ plasma system (2.5 kW) is started at a pressure of 1 mbar ; after 1 min treatment, the wafer is removed from the chamber. Example 8 : Etching of an Si0₂ layer using COF₂ in combination with H₂ as etchant in an in- situ plasma

A Si wafer with a thickness of approximately 250 μιη for a solar cell has a coating of Si0₂ with a thickness of 250 nm is brought into a plasma apparatus. A gas consisting essentially of COF₂ is introduced at 6 slm into the chamber ; H₂ is introduced at 2 slm. The pressure in the plasma apparatus is pressure of 1 mbar. The in situ plasma is started and stable plasma is reached. After 1 min treatment, desired areas of the Si0₂ layer are substantially etched away, and the solar substrate can be provided to the next treatment step.

Claims

C L A I M S

1. A method for the manufacture of a semiconductor item comprising a step of providing a semiconductor item having a coating of Si0₂ and etching the Si0₂ layer in a plasma wherein an etching gas is applied which contains SF₆, NF₃, F₂ or COF₂ wherein said etching gas further comprises 0₂ and/or H₂, wherein the semiconductor item has a thickness of equal to or lower

than 1000 μιη, and wherein the Si0₂ layer has a thickness of equal to or less than 10 μιη.

2. The method of claim 1 for the manufacture of a semiconductor item comprising a step of providing a semiconductor item having a coating of Si0₂ and etching the Si0₂ layer wherein an etching gas is applied which contains F₂ or COF₂ wherein said etching gas further comprises 0₂ and/or H₂.

3. The method of claim 1 or 2 wherein the semiconductor item has a dimension of equal to or greater than 150 mm.

4. The method according to anyone of claims 1, 2, or 3, wherein the semiconductor item is a solar substrate.

5. The method according to claim 1, wherein the Si0₂ layer has a thickness of equal to or less than 250 nm.

6. The method according to anyone of claims 1 to 5, wherein the etching gas consists essentially of F₂ and 0₂, of COF₂ and 0₂ or of COF₂ and H₂.

7. The method according to claim 1 wherein F₂ and H₂ are provided separately into a plasma apparatus.

8. The method according to anyone of claims 1 to 7, wherein the etching gas further comprises at least one inert gas selected from the group consisting of N₂ and Ar.

9. The method according to claim 1, wherein the etching gas consists of 1 to 99 % by volume of F₂, 1 to 20 % by volume of 0₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.

10. The method according to anyone of claims 1 to 9, wherein the etching gas comprises or consists of 1 to 99 % by volume of COF₂, 1 to 99 % by volume of H₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.

11. The method according to claim 7, wherein the etching gas in the plasma apparatus comprises or consists of HF formed from H₂ and F₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.

12. The method according to anyone of claims 1 to 11, wherein the gas pressure is from 0.5 to 50 Torr.

13. A process for the manufacture of a product wherein at least one treatment step for the manufacture of the product is carried out in a treatment chamber which process comprises etching an Si0₂ layer by the method according to anyone of claims 1 to 12.

14. A gas mixture, consisting of 1 to 99 % by volume of F₂, 1 to 20 % by volume of 0₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.

15. The gas mixture of claim 14, consisting of 1 to 99 % by volume of COF₂, 1 to 99 % by volume of H₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.

16. A gas mixture, consisting of 1 to 99 % by volume of SF₆ or NF₃,

1 to 99 % by volume of H₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.

17. A gas mixture, consisting of 1 to 99 % by volume of COF₂, 1 to 70 % by volume of H₂, 0 to 70 % by volume of N₂ and 0 to 20 % by volume of Ar.