WO2009092926A1

WO2009092926A1 - Method and related equipment for making thin poly- or mono-crystalline semiconductor substrates

Info

Publication number: WO2009092926A1
Application number: PCT/FR2008/050084
Authority: WO
Inventors: Michel Roche
Original assignee: Michel Roche
Priority date: 2008-01-21
Filing date: 2008-01-21
Publication date: 2009-07-30

Abstract

The invention relates to a method for making thin poly- or mono-crystalline semiconductor substrates that are deposited on an isolation layer (SOI) or on a metal layer (SOM). The method substantially comprises carrying out an ion implantation (protons, hellions, etc.) using a means (3) from the surface of a solid semiconductor ingot (1) having a parallelepiped shape, at an energy sufficient for penetrating to a depth (ε) equal to the thickness of the desired layer. At the end-of-travel, these ions remain trapped in a so-called separation layer (15) to the embrittlement of which they contribute. A so-called stiffening layer (9) is then glued, attached or welded to the surface of the ingot (1). A traction is applied on the dual layer (8, 9) in an unwinding movement using powered rollers (4) for separating the layer (8) from the ingot (1), either by stripping or tearing at the level of the separation layer (15). The invention can be used for making SOI or SOM substrates. The first ones are more particularly intended for making very high-density digital compounds, and the second ones for making photovoltaic diodes and discrete components (diodes, IGBT, MOSFET, etc.).

Description

METHOD AND APPARATUS FOR THE MANUFACTURE OF THIN SEMICONDUCTOR, POLY OR MONOCRYSTALLINE SUBSTRATES

The present invention relates to a method of manufacturing monocrystalline semiconductor or thin polycrystalline substrate and associated apparatus.

In known systems of this kind, there is essentially SOI technology (Silicon On Insulator) invented by Michel BRUEL and published on November 20, 1994 under US Patent No. 5374564. This method has the disadvantage of being expensive and of being applicable only to substrates of the SOI type.

Another method has been proposed in the US6.855.619.B2 patent of February 15, 2005 by Messrs. IWASAKI and GHYSELEN consisting in unrolling a layer, previously pre-cut by ion implantation from a cylindrical ingot. This method is difficult to implement and has the disadvantage of not keeping the constant crystalline orientation over the entire surface of the substrate. The process according to the invention avoids these disadvantages.

The invention will in any case be better understood from the following descriptions, referenced in the accompanying drawings in which: FIG. 1 very schematically represents the essential concept of the method: the detachment of the thin monocrystalline sheet (8) from the ingot (1).

Figure 2 shows the implantation profile of the ions. FIG. 3 represents the detachment mechanism of the layer (8) of its semiconductor ingot (1)

FIG. 4 schematically represents a production machine more particularly intended for the production of SOI by gluing showing the translation mechanism of the ingot (1).

FIG. 5 represents a production machine more particularly intended for the production of thin substrate on metal foil: SOM (Silicon On Metal).

Figure 6 shows in more detail the essential elements of Figure 5 with a grouping of the elements (24) and (5) on the one hand and (26) on the other hand into a single ion gun (29).

The invention relates to a method with associated apparatuses for the production of polycrystalline or thin monocrystalline semiconductor substrates comprising: a source of polycrystalline or monocrystalline semi-conductor material (1) of parallelepipedic shape driven by a translation movement. Means for implanting ions (3) of at least one type of ion into an energy suitable for implanting ions at a depth ε into the separation layer (15).

Means (5) suitable for securing, welding or gluing a stiffening sheet (9) to the surface of the ingot (D

Training means (4) for the layers

(8) and (9) at a controlled speed, making it possible to exert a traction T on these layers, thus ensuring the separation of (8) with respect to (1).

According to another feature, the system comprises means (2) for preparing the surface of the ingot (1) before implantation, including mechanical or ionic polishing and possible cancellation of surface stresses.

According to another characteristic, the means (5) for fixing a metal stiffener

(9) on the polycrystalline or monocrystalline sheet (8) are constituted by a cold weld on the ingot (1), previously oxidized or not, on which is deposited a layer of a metal advantageously identical to that constituting the stiffener (9 ), before pressing strongly, always under ultra-vacuum metal foil (9) on the cylinder (1) for example by means of a roller (21).

According to another characteristic, the means (5) for fixing a stiffener (9) made of metal or insulation, are constituted by a bonding system including at least one coater (20) and a rapid UV or thermal electron beam polymerization system (18).

According to another characteristic, the means for fixing an insulating stiffener (9) consists of making an intimate contact under ultra-vacuum between the adjacent faces of (8) and (9).

According to another feature, the method is included in a vacuum chamber (21) having a differential pump lock (13) from which the bilayer (8) and (9) can be extracted continuously at atmospheric pressure.

According to another feature, the system comprises means (10) for depositing an electrode on the free face of the layer (8) suitable for producing directly, including diodes and photovoltaic cells.

According to another feature, the device is used for the production of SOI substrate but also of substrate on metal (SOM) likely to improve certain manufacturing processes including IGBT and MOSFET and generally, all substrates for optics, electronics and optoelectronics. The invention is based on the principle of the implantation of a beam of ions of high energy (deθ.1 to 1 or 2 MeV for example when it is a proton beam) in a monocrystal semiconductor such as silicon. FIG. 2 represents the ion concentration curve obtained from a irradiation of protons for example as a function of depth x.

It can be seen that almost all the hydrogen ions, for example, will be housed in a layer (15) located at the average distance from the surface ε. This layer has a certain thickness Δε resulting from the ion - crystal interaction statistic over the distance ε, but also from the energetic dispersion of the incident ion beam as well as the angular aperture of the beam.

The detachment of the crystalline plate (8) of thickness ε will be substantially in the center of the layer (15) which will be called "separation layer". The fluence φ of the ion beam is related to the distribution C _(x) by the relation:

k = constant.

Cmax = concentration at the top of the curve. This value is imposed to obtain the separation, under the effect of a given tearing effort. It can be seen that Φ is smaller as the dispersion Δε is reduced, hence the importance of a good regulation of the accelerator voltage of the implanter (3).

For example, a proton beam of 150 keV will lift a blade thickness lμm.

In the "smart eut" process, the implanted ion is necessarily gaseous (H ₂ , N ₂ , He, rare gases) but according to the invention, it may be arbitrary. However, the defects created in the layer (8) by the passage of ions are all the more important that the atomic mass of the ion is high, hence the advantage of using light ions (protons, helions) . The accumulation of ions in the separation layer (15) creates stresses that weaken the crystal at the depth ε, which amounts to reducing the fracture energy in a cylindrical layer parallel to the free surface of the crystal (D

The layer (8), whose thickness is typically of the order of 1 .mu.m, can not be manipulated without having been previously fixed on a stiffener (9) by various methods which will be detailed later. Incidentally, this stiffener layer may act as an electrode when it is a metal layer intended for the manufacture of thin-crystal monocrystalline substrate of SOM (silicon on metal) type, whose interest in manufacturing Photovoltaic cells and also substrates for MOSFETs, IGBTs, diodes, etc. are considerable.

This stiffening layer (9) must have a sufficient thickness so that the substrate (8) + (9) can be easily handled in the various production processes of semiconductor components. It must also remain flexible enough to be able to wind on the various coils and rollers used in the process according to the invention as well as in future component production machines.

A thickness of 10 to 100 μm is a good compromise between these two requirements. It is in particular the flexibility of this blade that will be used to separate or tear the crystalline sheet (8) of the crystalline ingot (1). As can be seen in Figure 3, the tear is purely mechanical; it results from the traction T exerted on the ingot (1) by the sheet (9) There is accumulation of stresses along the generatrix Δ of the cylinder (21) over a width of a few atomic rows. The separation is therefore cold, without it being necessary to release a gas as in the "smart eut" process. This avoids the diffusion of hydrogen in the silicon and the maximum concentration Cm implanted, can be lowered due to the effectiveness of the tearing mechanism.

The attachment or attachment to the ingot (1) of the stiffening layer (9), which may be metallic or insulating (ceramic, silica, glass), may be carried out in many ways. Let's mention the main ones:

By cold welding, metal-metal, under ultra-vacuum pressure in order to obtain an intimate contact between a thin metal layer previously deposited on the ingot (1) and a metal strip (Al, Cu, Ni, Ag, Mo) (9), sufficiently plastic for the pressure roller

(21) make it adhere perfectly, thanks to a slight creep, to the ingot (1).

• By bonding with a suitable polymer such as epoxy resin or silicone or polyimide. The thickness of the film should be as thin as possible, just what is necessary to fill the imperfections of the surface of the ingot (1) and the stiffening band (9), which can be metallic or insulating. A glue thickness of 0.1 to 1 μm is sufficient. It can be deposited by means of a multiple roller coating system (20) outside the vacuum chamber (12) in which the strip (9) penetrates by differential pumping (13) to reduce the impact on the vacuum in the chamber (12), the generally high vapor pressure of these resins. The drying of the resins must be almost instantaneous. It can be used for this infra-red heating, a UV polymerization if the stiffening band

(9) is transparent to this radiation (silica for example) or even better, by electron beam, sufficient energy to pass through the strip (9). For example, if it is an aluminum sheet of 100 μm thick, the electrons must have an energy of at least 80 keV.

• By thermocompression with formation of Si-Al entectic. For this, depositing an aluminum layer on the cylinder (1) and the stiffener (9) is molybdenum, the latter is then heated for example by electron beam and compressed by the roller (21). • By intimate contact under ultra-vacuum as in the "smart eut" process.

The ion implantation is performed by means of an electrostatic accelerator (3) which must irradiate the surface of the ingot (1) with a monoenergetic and perfectly parallel ion beam. The linear density of current (dl / dz) required can be calculated as in the following example, concerning the implantation of protons in a silicon matrix in order to obtain a crystalline layer of thickness lμm. We have seen above that the proton energy must be equal to 150keV. The linear density of ion current dl / dz, in a system traveling at speed v satisfies the relation: dl _{= e} . _v φ dz e = charge of the electron, Φ = fluence of the ion beam. Either numerically, assuming a production speed of 36 meters per hour and irradiating at a fluence of 5 10 ¹⁶ p. cm ^"2

which is very easily achievable. The linear power is then 1.2 kW. cm ^"1. It is mainly dissipated in the sheet (8) but by thermal conduction, it diffuses into the ingot (1) to be cooled for example by a fluid flow on the opposite side of the ingot (1).

The acceleration can advantageously be carried out in mono-gap: a source of ions of radio-frequency type with multi-opening, linear, placed at one or two centimeters of the ingot (1), which is maintained at the potential of the earth while the source is raised to +15OkV.

The purpose of the surface preparation means (2) is to provide the implanter (3) with a smooth surface, free of asperities and also surface stresses. In all cases where contact is made by the metal foil (9), these means may also be used for doping the surface of the ingot (1) so that the metal electrode can contact a p-type or n-type semiconductor layer. Doping may advantageously be performed by implantation. The cancellation of the surface stresses can be carried out by a surface heating possibly pulsed, carried out for example by means of an electron beam. The polishing may be mechanical or, more advantageously, be performed by means of an ion beam under grazing incidence. Polishing, possibly controlled from a measurement of the asperities of the surface, is of great importance to avoid an accumulation of defects over the layers of sampling passes.

The invention will in any case be better understood from the preferred embodiments, given for information only and of course in no way limiting.

The first preferred embodiment concerns the production of thin monocrystalline substrate deposited on an insulating layer of SOI (silicon on insulator) type. FIG. 4 represents a production machine arranged in a vacuum chamber (12) pumped by a turbomolecular type pump (6) for example. This produces a vacuum of the order of 10 ^{~ 4} to 10 ^{~ 5} torr as required for the acceleration of the ion beam (3). This chamber comprises an atmospheric pressure lock chamber (13) having at least one differential pumping cell through which the substrate (8) +

(9) will be continuously extracted. The stiffening layer (9) 50 to 300mm wide and 50 to 100μm thick is wound on a coil placed outside the vacuum chamber (12) in which it enters via the lock (13). This layer can be made of polymer (kapton for example), ceramic (alumina for example) or glass (silica for example). The ingot (1) previously perfectly machined, of parallelepipedal shape It is fixed on a linear translation table (28), suitably robotized to effect the passage of the ingot (1) in front of the stations (3), (18) and ( 2) which are fixed. In order to compensate for the wear of the ingot as the thin layers (8) are taken out, the table (28) is animated with a downward movement. It makes it possible to position the ingot (1) at the position A at the beginning of the cycle and brings it, at a controlled speed, to position B at the end of the cycle with fast return to starting position A.

The cycle comprises the following operations: 1) Implantation of ions: the ingot, whose surface has been previously prepared, receives a flow of ions, for example protons of 0.1 to 1 or 2 MeV, delivered by an accelerator (3) which, at least for the low energies may advantageously be mono-gap type. In this case, the ingot (1) is maintained at the potential of the mass by suitable contacts and the ion source is brought to the accelerating potential, for example at +15OkV. 2) Plating on the surface of the ingot (1) of an insulating stiffening band (9) by means of two rollers (21) which, when introduced into the vacuum chamber (12), was coated with a layer of adhesive by means of a layer transfer or coating transfer system (20), (25). This glue is polymerized between the two rollers (21) for example by means of an electron beam (18). The crystalline layer (8) is then torn off by the traction exerted on the bilayer (8) and (9) by means of the motorized rollers (4). It is then extracted from the vacuum chamber (12) to be packaged outside.

3) Conditioning of the surface by the means (2) which can be mechanical (polishing) or, advantageously ionic. These means can also perform a surface heating in order to eliminate the surface stresses.

This device also makes it possible to produce an SOI substrate with a metal stiffener. For this, the preparation means (2) also provide oxidation of the surface of the ingot (1), for example by forming a layer of SiO ₂ .

According to a second preferred embodiment of the invention, the stiffening layer is made of a metal such as copper, aluminum, nickel, silver or molybdenum, chosen according to its good electrical and thermal conductivity and also its ability to adhere to the crystal (1). Under these conditions, the metal layer (9) will play the role not only of stiffener but also of metal electrode provided that we have taken care to implant beforehand on the surface of (1) a layer p or n on which the metal layer (9) comes to play the role of ohmic contact.

As shown diagrammatically in FIG. 5, the process is carried out in an ultrahigh vacuum chamber (12) pumped by a pump advantageously of the turbomolecular type.

(6). As before, the ingot (1) is transported by a robotic linear conveyor (28). Figure 5 shows the workstations performing the process:

The ingot (1), the surface of which has been suitably prepared, first passes an implanter (26) for doping its impurity surface with groups 3 and 5. This surface is then metallized for contacting by spraying. the target (5) under the effect of the bombardment by an ion source (24) or by magnetron cathode or by thermal evaporation. The metal thus deposited on the surface of the ingot (1) may be identical to that of the metal layer (9) or be selected to have excellent crystal bonding while allowing cold welding on the metal strip (9). There can also be two successive targets (5), one to deposit a bonding layer, the other to deposit the same metal as the strip (9) to optimize the cold weld. The band

(9) is introduced into the chamber by the lock (13) and is then etched by an ion beam (26) before being strongly pressed by the roller (21) on the surface of the ingot (1) so as to to achieve a cold weld. The bi-layer (8) + (9) is driven by means of the motorized rollers (4) which provide the traction T for the takeoff of the layer (8) of the ingot (1). The ingot then passes as before the station (2) for repackaging the surface.

In the case where the substrate is intended for the manufacture of photovoltaic cells, the process may advantageously include means (10) for making the doping of the second part of the pn junction on the mono or polycrystalline plate (8). this diode, the first having been achieved by the implantation (27). These means (10) therefore comprise an implanter advantageously PIII type (Plasma Immersed Ion Implantation) optionally followed by a metal deposition contact.

According to a third preferred embodiment of the invention, the ingot (1) is always animated with an alternating translational movement and is raised, in the manner of a plane which detaches a chip, a thin layer of crystal (8). ). The production is discontinuous but all the crystalline plates (8) are interconnected by the stiffening band (9) so that, at the outlet of the vacuum chamber (12), a continuous strip is extracted on which are juxtaposed, end-to-end, crystalline blades (8) whose length can reach 1 meter.

FIG. 6 shows in detail the different workstations in the case where a SOM is produced with a metallization carried out directly by sputtering, under the effect of a low energy ion bombardment of the stiffening band (9) by means of the ion source (29). Thus, with a single ion source of a few keV, stripping of the stiffener band (9) and the metallization of the surface of the ingot (1) are carried out.

The invention can be used to produce a very large variety of semiconductor components at greatly reduced prices. Some examples are: photovoltaic cells for the production of solar energy.

The invention makes it possible to automate the production and and to achieve a gain in terms of silicon consumption that can range from 500 to 1000.

SOI substrates for microelectronics with very high density. The cost of these substrates can be reduced considerably.

SOI substrates on metal allowing a better evacuation of the heat and having better performances in term of CEM.

The SOM substrates which are likely to simplify the manufacturing processes of certain discrete components (diodes, IGBTs, MOSFETs).

Flat screens LCD, DLP or others.

And in general, any monocrystalline or thin polycrystalline substrate for electronics, optics and optoelectronics.

Claims

1. Method and associated apparatus for the production of polycrystalline semiconducting substrates or monocrystalline thin, characterized in that it comprises: - a source of polycrystalline or monocrystalline semiconductor material (1) of parallelepipedic shape driven by a translational movement.

Means for implanting ions (3) of at least one type of ion at a suitable energy to implant the ions at a depth R in the separation layer (15).

Suitable means (5) for securing, welding, or gluing a stiffener sheet (9) to the surface of the ingot (D

Driving means (4) for the controlled velocity layers (8) and (9) for exerting a traction T on these layers ensuring the separation of (8) with respect to (1).

2. Method and devices according to claim 1 characterized in that means (2) allow a preparation of the surface of the ingot (1) before implantation including mechanical or ionic polishing and possible cancellation of surface stresses.

3. Device according to claims 1 or 2 characterized in that the means (5) for fixing a metal stiffener (9) on the monocrystalline sheet (8) consist of a cold weld on the ingot (1), previously oxidized or not, on which is deposited a layer of a metal, advantageously identical to that constituting the stiffener ( 9) before strongly pressing, still under ultra-vacuum, the metal foil (9) on the ingot (1), for example by means of a roller (21).

4. Device according to claims 1 or 2 characterized in that the fastening means (5) of a stiffener (9) metal or insulating, are constituted by a bonding system including at least one coating (20) and a system of rapid electron beam, UV or thermal polymerisation (18).

5. Device according to claims 1 or 2 characterized in that the means for fixing an insulating stiffener (9) consist in making an intimate contact under ultra-high vacuum between the adjacent faces of (8) and (9).

6. Device according to claims 1 to 5, taken separately, characterized in that the method is included in a vacuum chamber (21) having a differential pump lock (13) from which the bilayer (8) and (9) can be extracted continuously at atmospheric pressure.

7. Device according to claims 1, 2, 3 and 6 characterized in that the system comprises means (10) for depositing an electrode on the free face of the layer (8) suitable for direct realization, including diodes and photovoltaic cells.

8. Device according to any one of claims 1 to 7, characterized in that it is used for the production of SOI substrate but also of substrate on metal (SOM) likely to improve certain manufacturing processes including IGBT and of MOSFET and generally any substrate for optics, electronics and optoelectronics.