Device for insulating and sealing electrode holders in CVD reactors

Abstract

Improved sealing of Siemens reactor electrodes which results in improved reactor campaign times, is accomplished by use of an electrically insulating ring in combination with two seals, a first seal located in a groove in the insulating ring or in a groove in the reactor base plate adjacent the insulating ring, and a second seal not contained in a groove.

Claims

1. An apparatus for insulating and sealing electrode holders in CVD reactors having an electrode suitable for accommodating a filament rod disposed atop an electrode holder made of an electrically conductive material and mounted in a recess in a floor plate, comprising: an electrically insulating ring made of a material of construction having a specific thermal conductivity at room temperature of 0.2-50 W/mK, a minimum flexural strength of greater than 120 MPa, and a specific electrical resistance at room temperature of greater than 10.sup.9 cm, located between the electrode holder and the floor plate, wherein at least two ring-shaped sealing elements for sealing between the electrode holder and the floor plate are present, wherein the electrically insulating ring or the electrode holder or the floor plate comprises at least one groove in which a first sealing element is secured, wherein at least one second sealing element not secured in a groove is present between the electrically insulating ring and the floor plate or between the electrically insulating ring and the electrode holder, and wherein the at least two ring-shaped sealing elements are not located on the same side of the electrically insulating ring.

2. The apparatus of claim 1, wherein the material of construction of the electrically insulating ring is selected from the group consisting of aluminum oxide, silicon nitride, boron nitride, zirconium oxide, and yttrium-oxide-, magnesium-oxide- or calcium-oxide-stabilized zirconium oxide.

3. The apparatus of claim 2, wherein the first sealing element is a graphite foil ring.

4. The apparatus of claim 1, wherein the first sealing element is a graphite foil ring.

5. The apparatus of claim 1, wherein the first sealing element is a metallic O-ring or a metallic seal having an open profile having a spring action.

6. The apparatus of claim 5, wherein the metallic seal has a C-profile and is coated with silver.

7. The apparatus of claim 1, wherein the second sealing element is a gasket comprising graphite or PTFE.

8. The apparatus of claim 7, wherein the gasket is chambered on the reactor-side seal circumference as a result of metal or silver foil being flanged around the reactor-side sealing surface of the gasket.

9. A process for producing polycrystalline silicon, comprising introducing a reaction gas comprising a silicon-comprising component and hydrogen into a CVD reactor comprising at least one filament rod which is disposed atop an apparatus of claim 1, the filament rod supplied with current via the electrode and thus heated by direct passage of current to a temperature at which polycrystalline silicon deposits on the filament rod.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic representation of a fitted insulating ring having a groove in the insulating ring.

(2) FIG. 2 shows a schematic diagram of an insulating ring with a groove.

(3) FIG. 3 shows a schematic representation of an externally flanged gasket.

(4) FIG. 4a shows a schematic representation of a fitted insulating ring with a groove in the insulating ring and with a protrusion c of the top of the electrode holder and a sealing body in the groove before compression.

(5) FIG. 4b shows a schematic representation of a fitted insulating ring with a groove in the insulating ring and with a protrusion c of the top of the electrode holder and a sealing body in the groove after compression.

(6) FIG. 5 shows a schematic representation of a fitted insulating ring with a groove in the electrode holder.

(7) FIG. 6 shows a schematic diagram of an insulating ring without a groove.

(8) FIG. 7 shows a cross section through a metal C-ring.

(9) FIG. 8 shows cross sections through further implementations for sealing elements made of metal.

(10) FIG. 9 shows a cross section through a graphite foil ring consisting of a plurality of compressed individual foils

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) Preferred embodiments of the invention are discernible from the accompanying claims and the description which follows.

(12) The invention provides for separating the sealing body and the insulating body, i.e. dividing sealing and insulating functions over a plurality of components, an insulating ring being provided for electrical insulation and two sealing elements being provided for sealing with respect to the floor plate and the electrode holder.

(13) This makes it possible to choose for the insulating ring and the sealing part different materials of construction that are better suited for the respective functions of the two components.

(14) In a departure from the prior art only one of the sealing elements is located in a groove in the insulating ring or in a groove in the floor plate or electrode holder. Either the seal against the floor plate or the seal against the electrode holder is effected by a sealing element secured in a groove but not both the seal against the floor plate and against the electrode holder.

(15) On the opposite side of the insulating ring the seal against the floor plate or the electrode holder is effected by means of a sealing element not secured in a groove of the insulating ring, floor plate or electrode holder. In the simplest case this sealing element is a gasket.

(16) The insulating ring should be high temperature resistant and dimensionally stable but a sealing function is not necessary. The higher dimensional stability compared to elastomeric insulating bodies allows insulating rings of greater height to be employed. The greater distance between the electrode holder and the floor plate permits application of greater electrical voltage. The advantage of this is that a plurality of rod pairs may be connected in series thus allowing savings to be made on capital expenditure on the reactor current supply.

(17) In one embodiment the top of the electrode holder may have a protrusion c relative to the insulating ring. This affords further thermal and mechanical protection. The insulating ring is shaded from heat radiation and is subjected to lower levels of stress.

(18) The thermal stress on the sealing elements is also reduced.

(19) A protrusion is present when the external diameter of the electrode holder D_E is larger than the external diameter of the insulating ring D_R.

(20) The groove for accommodating the first sealing element may be disposed either in the insulating ring or in the floor plate and/or in the top of the electrode holder.

(21) In one embodiment the groove is located in the insulating ring and accommodates a sealing element to seal the insulating ring and the electrode holder. A second sealing element is located between the side of the insulating ring opposite the groove, and the floor plate.

(22) In another embodiment the groove is located in the electrode holder and accommodates a sealing element to seal the insulating ring and the electrode holder. A second sealing element is located between the side of the insulating ring facing the floor plate, and the floor plate.

(23) The groove is preferably located at a distance a of 10-40% of the total width b of the insulating ring to the electrode feedthrough (internal diameter of insulating ring). This ensures that the sealing element is sufficiently far removed from the side of the insulating ring facing the reactor. This is advantageous in relation to the thermal stress on the sealing elements.

(24) In a further embodiment the groove may also be at the same position (distance a of 10-40% of the total width b of the insulating ring to the electrode feedthrough) in the floor plate or in the top of the electrode holder. In this case the insulating ring does not have a groove.

(25) The sealing element secured in a groove is preferably cooled by the cooling medium in the floor plate and/or the cooling medium in the top of the electrode holder and the feedthrough of the electrode. As a result of the cooling, the sealing elements assume a considerably lower temperature than the insulating ring.

(26) Suitable sealing elements in the groove are in particular an O-ring made of FFKM (perfluoro rubber), a graphite foil ring, a graphite-filled spiral seal or a metal C-ring.

(27) A silver-coated metal C-ring with or without an internal coil spring is preferred.

(28) The use of a graphite foil ring is particularly preferred.

(29) A gasket is employed as the second sealing element not secured in a groove. This gasket may be fabricated from graphite or from PTFE, preferably from graphite. The gasket preferably has at its edges at least one metal flange, wherein a metal flange is preferably attached to the side facing the reactor space. Particular preference is given to a gasket made of graphite having a reactor-side metal flange. In one embodiment this gasket is located between the insulating ring and the floor plate.

(30) The side of the insulating ring facing the reactor interior has a surface temperature of up to 600 C. The sealing elements should therefore withstand sustained use temperatures of greater than 250 C.

(31) Low thermal conductivity of the insulating ring facilitates the low thermal stress on the sealing elements.

(32) The gasket serves to compensate for fabrication inaccuracies (unevennesses) in the mating sealing surface as are customary for large workpieces (floor plates) in apparatus manufacture with standard methods (e.g. turning, drilling, welding). Further precision machining (e.g. grinding, polishing) increases fabrication costs for the apparatuses.

(33) By contrast, small components (top of the electrode holder) can be precision machined without substantial additional costs and compensation of fabrication inaccuracies is therefore not necessary here.

(34) The top of the electrode holder typically receives poorer cooling than the floor plate. It is therefore advantageous when the sealing element between the insulating ring and the top of the electrode holder is better protected from thermal stress from the reactor space. In a preferred embodiment this may be achieved by placing the sealing element in a groove, wherein the groove is recessed in the insulating ring or in the top of the electrode holder.

(35) The groove is located at a distance a of 10-40% of the total width b of the insulating ring to the electrode feedthrough (internal diameter of insulating ring). Furthermore, the chambering of the sealing element by the groove minimizes diffusion of reaction gas through the sealing element since for diffusion only a very small maximum protrusion of the sealing element from the groove f of 0-1 mm, preferably of 0-0.3 mm, is permissible.

(36) Depending on the nature of the sealing body in the groove, two embodiments are possible. In a 1st embodiment, metal C-rings and O-rings have a protrusion f of 0 mm after compression. Force transmission occurs not through the sealing body but around the sealing body in a force bypass. Depending on the position of the groove, force transmission occurs between the electrode holder and a supporting ring or the supporting ring and the floor plate.

(37) In a 2nd embodiment, graphite foil rings or spiral seals have a greater thickness than the groove depth. The plastic deformation of the sealing bodies during compression causes the part of the seal protruding from the groove to begin to flow. The original protrusion of the sealing body F in the uncompressed state is flattened in the course of the compression to a smaller, remaining protrusion f>0 and 1 mm. Simultaneously, when the groove is located in the electrode holder or in the supporting ring on the side facing the electrode holder sealing material flows into the slot having a thickness f>0 mm and 1 mm between the electrode holder and the supporting ring.

(38) When the groove is positioned in the floor plate or in the supporting ring on the side facing the floor plate sealing material correspondingly flows into the slot having a thickness f>0 mm and 1 mm between the supporting ring and the floor plate during compression.

(39) As a result of the flowing of the sealing body the width of the sealing body increases to the value e in the sealing slot by 5-100%, preferably 5-70%, based on the width of the groove/width of the sealing body in the uncompressed state E. As a result of the flowing of the sealing body in the sealing slot during compression the sealing material fills very small unevennesses in the to-be-sealed surfaces of the supporting ring and/or floor plate. Furthermore, the flowing of the sealing material increases the sealing area. Both effects, compensating unevennesses and greater sealing area, achieve complete sealing of the interfaces between the sealing body and the supporting ring and also between the sealing body and the electrode holder or between the sealing body and the floor plate. Since at any point in time during compression the protrusion f of the sealing body is >0 mm and 1 mm, force transfer occurs through the sealing body in a direct force transmission.

(40) For further thermal and mechanical protection the top of the electrode holder may project beyond the external contour of the insulating ring. The protrusion c may be 0 to 30 mm.

(41) In one embodiment the protrusion is 0 to 15 mm.

(42) Compared to a one-part sealing and insulating ring the material properties in multi-part constructions may be better configured for the respective demands on the sealing function and insulating function.

(43) The insulating ring need not have any sealing material properties. There is therefore no compulsion to use PTFE and materials of construction having higher dimensional stability and thermal stability may be employed. The sustained use thermal stability of PTFE is 250 C. By contrast, the ceramic materials of construction have a sustained use thermal stability of >1000 C. and higher dimensional stability.

(44) The specific thermal conductivity at room temperature of the insulating ring is in the range from 0.2-50 W/mK, preferably 0.2-20 W/mK, and more preferably in the range of 0.2-5 W/mK.

(45) The specific electrical resistance of the insulating ring at room temperature is greater than 10.sup.9 cm, preferably greater than 10.sup.11 cm, and more preferably greater than 10.sup.13 cm.

(46) To compensate for unevennesses on the application surfaces of the floor plate and the top of the electrode holder, the insulating ring must have a minimum flexural strength.

(47) The flexural strength of the insulating ring must be greater than (determined as per DIN EN 843 for ceramics) 120 MPa, preferably greater than 300 MPa, and more preferably greater than 800 MPa. In addition, ceramics must have K1C values (fracture toughness as per DIN CEN/TS 14425) of greater than 3 MPa*m{circumflex over ()}0.5, preferably greater than 4 MPa*m{circumflex over ()}0.5.

(48) Suitable materials for the insulating ring therefore include: aluminum oxide (Al.sub.2O.sub.3); silicon nitride (Si.sub.3N.sub.4); boron nitride (BN); zirconium oxide (ZrO.sub.2), zirconium oxide stabilized with yttrium oxide (ZrO.sub.2Y.sub.2O.sub.3), with magnesium oxide (ZrO.sub.2MgO) or with calcium oxide (ZrO.sub.2CaO).

(49) Particular preference is given to yttrium-stabilized zirconium oxide produced by the HIP process (hot isostatic pressing) since this material of construction has a flexural strength of greater than 1200 MPa at 20 C. and a fracture toughness of >6 MPa*m{circumflex over ()}0.5.

(50) The sealing element present in the groove should withstand a sustained use temperature of 320 C. and be resistant to an HCl/chlorosilane atmosphere at up to 320 C.

(51) Possible materials of construction are FFKM (perfluoro rubber), graphite and metallic seals resistant to oxidative acids.

(52) Possible sealing elements made of graphite may be graphite cords made of braided graphite fibers and graphite foil rings. A graphite foil ring consists of a plurality of graphite plies pressed together. The sustained use temperature of these sealing elements made of graphite is up to 600C.

(53) Low compression forces suffice for the sealing elements made of graphite since the sealing area is very small. The sealing area is determined by the dimensions of the groove. The sealing area is preferably between 600 and 3000 mm.sup.2, more preferably between 600 and 2000 mm.sup.2 and most preferably between 600 and 1500 mm.sup.2. The contact pressure on the graphite sealing elements is between 20-70 N/mm.sup.2, preferably 25-50 N/mm.sup.2, and more preferably 30-40 N/mm.sup.2. This results in only a low level of mechanical stress on the insulating ring which prevents fracturing of the insulating rings.

(54) In a further embodiment seals made of metal are concerned.

(55) The sealing elements made of metal are preferably metallic annular spring seals. Due to the small sealing areas of the metallic sealing elements a low compression force suffices for sealing here too. For the metal sealing elements a low compression force is to be understood as meaning a compression force of 60-300 N/mm of seal circumference, preferably 60-200 N/mm of seal circumference, more preferably 60-160 N/mm of seal circumference.

(56) The metallic seals preferably have one of the following shapes: closed O-ring hollow on the inside (hollow metal O-ring); open metal profiles, for example C-shaped, U-shaped, E-shaped or any other desired profiles having a spring action, for example corrugated metal sealing rings; open metal profiles may be spring supported, for example a C-ring with an additional internal coil spring.

(57) A C-ring is a hollow O-ring having an open inside or outside.

(58) To increase chemical resistance and to increase the sealing action, the metallic sealing elements may be coated with ductile metals, for example with silver, gold, copper, nickel or with another ductile and HCl/chlorosilane atmosphere-stable metal. The flowability of these ductile coating materials markedly increases the sealing action of the metallic sealing elements. These sealing elements made of metal have a sustained use temperature of up to 850 C.

(59) The term ductile coating materials is to be understood as meaning metals where the grain boundaries and dislocations move/flow under mechanical stress even at an elongation less than the elongation at break. This flowing under the stress of an application of force, as is present during compression, compensates unevennesses in the sealing surfaces. This achieves improved sealing.

(60) The use of a silver-coated metal C-ring with or without internal coil spring is particularly preferred.

(61) Possible sealing elements made of FFKM are O-rings.

(62) The gaskets employed may be made of graphite or PTFE, in the case of PTFE with or without fillers such as fused quartz or iron oxide to increase strength and reduce flow propensity.

(63) Gaskets made of graphite may be encapsulated in a thin (less than 0.5 mm) elastomeric layer (PTFE) to improve sealing.

(64) To avoid a leakage stream through the sealing material by diffusion the gaskets are preferably chambered on the reactor-side seal circumference.

(65) To this end a thin metal foil, preferably made of a halosilane-resistant stainless steel, preferably 1.4571 or 316L, or silver, is flanged around the reactor-facing sealing surface.

(66) The foil thickness here is 0.05-0.3 mm.

(67) In addition, the gasket may also be chambered on the inner seal circumference, i.e. facing the shaft of the electrode holder.

(68) The features listed in connection with the abovedescribed embodiments of the process according to the invention may be correspondingly applied to the apparatus according to the invention. Conversely, the features listed in connection with the abovedescribed embodiments of the apparatus according to the invention may be correspondingly applied to the process according to the invention. These and other features of the embodiments according to the invention are elucidated in the description of the figures and in the claims. The individual features may be implemented either separately or in combination as embodiments of the invention. Said features may further describe advantageous implementations eligible for protection in their own right

(69) The invention is also elucidated hereinbelow with reference to FIGS. 1 to 9.

LIST OF REFERENCE NUMERALS USED

(70) 1 electrode holder 2 insulating ring 3 floor plate 4 sealing element 5 gasket 6 floor plate cooling means 7 electrode holder cooling feed 8 electrode holder cooling means 9 insulating sleeve 10 groove for sealing element 11 flange a groove distance from internal diameter b total width h insulating ring height c protrusion of the electrode holder f protrusion of sealing element after compression F protrusion of sealing element before compression e width of sealing element after compression E width of sealing element before compression D_E electrode holder external diameter D_R insulating ring external diameter

(71) FIG. 1 shows a schematic representation of a fitted insulating ring with a groove in the insulating ring. Located between electrode holder 1 and floor plate 3 are insulating ring 2 and sealing element 4 and also gasket 5.

(72) The floor plate 3 is provided with a hole which is lined with an insulating sleeve 9 and through which an electrode holder 1 has been passed and fitted.

(73) Floor plate 3 and electrode holder 1 are cooled by cooling means 6 and 8 respectively.

(74) 7 shows the feed for the cooling means 7 of electrode holder 1.

(75) Sealing is effected on the one hand via sealing element 4 and gasket 5.

(76) Sealing element 4 is located in a groove in insulating ring 2 toward the electrode holder 1

(77) Gasket 5 is located between insulating ring 2 and floor plate 3.

(78) The external diameter D_E of electrode holder 1 may be flush or protruding relative to the external diameter D_R of the insulating ring 2. The electrode holder is preferably protruding.

(79) FIG. 1 shows an embodiment without a protrusion.

(80) FIGS. 4a and b show an embodiment with a protrusion c

(81) For further thermal and mechanical protection the top of the electrode holder 1 may thus project beyond the external contour of the insulating ring 2. The protrusion c should be 0-8*h, wherein h is the height of the insulating ring 2. A protrusion of 0-4*h is particularly preferred.

(82) FIG. 2 shows an insulating ring 2 with a groove 10 for accommodating a sealing element. The groove is preferably located at a distance a of 10-40% of the total width b of the insulating ring to the electrode feedthrough (internal diameter of insulating ring). This ensures that the sealing element is sufficiently far removed from the side of the insulating ring facing the reactor. This is advantageous in relation to the thermal stress on the sealing elements.

(83) FIG. 3 shows an externally flanged gasket 5 with a flange 11.

(84) FIG. 4a shows a schematic representation of a fitted insulating ring 2 with a groove in which sealing element 4 is secured. The representation shows the state of the sealing element before compression with the width E of the sealing body and the protrusion F of the sealing body from the groove in the starting state. Sealing with respect to the floor plate 3 is effected by means of a gasket 5. An embodiment with a protrusion c is concerned.

(85) FIG. 4b shows a schematic representation of a fitted insulating ring 2 with a groove in which sealing element 4 is secured. In the following, the sealing body is a spiral seal compression a graphite foil ring. The representation shows the state of the sealing element after compression with the width e of the sealing body after compression and the protrusion f of the sealing body from the groove after compression. Sealing with respect to the floor plate 3 is effected by means of a gasket 5. An embodiment with a protrusion c is concerned. As a result of the increase in the sealing area on account of the greater width e of the sealing body leakage between the insulating ring and the sealing body and between the sealing body and the electrode holder is reduced by the factor of increase in the sealing area.

(86) At least 70%, preferably >85% of the height of the sealing body in the compressed state is encapsulated in the groove. Internal leakage by diffusion through the sealing material is thus possible only over not more than 30% of the circumferential area of the sealing body, preferably <15% of the circumferential area of the sealing body, in the compressed state. The greater sealing width a of the sealing body after compression further reduces leakage through the sealing material in the ratio of the sealing width e in the compressed state to the sealing width E in the uncompressed state.

(87) FIG. 5 shows an implementation where the sealing element 4 is located in a groove 10 in the electrode holder 1. Sealing on the opposite side, i.e. between the insulating ring 2 and the floor plate 3, is effected by means of a gasket 5.

(88) FIG. 6 shows a schematic representation of an insulating ring 2 without a groove. Such an insulating ring is employed in the implementation according to FIG. 5 where the groove for accommodating the sealing element 4 is located in the electrode holder 1.

(89) FIG. 7 shows a cross section through a metallic sealing element having a C-profile.

(90) FIG. 8 shows cross sections through further implementations for sealing elements made of metal, namely O-profile, U-profile. E-profile, spring-action profile.

(91) The E-ring is a twice-folded double U-ring.

(92) FIG. 9 shows a cross section through a graphite foil ring consisting of a plurality of compressed individual foils.

EXAMPLES

(93) Polycrystalline silicon rods having a diameter between 160 and 230 mm were deposited in a Siemens deposition reactor.

(94) Several implementations of insulating rings and sealing elements were tested. The results of these tests are hereinbelow elucidated on selected examples and comparative examples.

(95) The parameters of the deposition process were identical in each case for all experiments. The deposition temperature was between 1000 C. and 1100 C. in the batch run. During the deposition process a feed consisting of one or more chlorine-containing silane compounds of formula SiH.sub.nCl.sub.4-n (where n=0 to 4) and hydrogen was added as carrier gas.

(96) The experiments differed exclusively in the implementation of the insulating rings and the sealing elements.

(97) For comparison, a PTFE insulating ring which simultaneously assumes sealing and insulating functions was initially analyzed. This ring thus does not provide for division of functions via an insulating ring and additional sealing elements.

(98) Insulating rings made of zirconium oxide in conjunction with metallic sealing elements were also tested. Sealing elements made of graphite or of elastomeric materials of construction such as perfluoroelastomers yield comparable results.

(99) By way of comparison an implementation was investigated where the sealing elements are secured in grooves of the zirconium oxide ring.

(100) It was found that the advantageous implementations have at least one sealing element secured either in a groove in the floor plate or in a groove in the electrode holder. A protrusion of the electrode holder relative to the insulating ring can further reduce the thermal stress on the sealing elements.

Comparative Example

(101) CVD reactor with insulating ring made of PTFE:

(102) In this prior art embodiment the insulating ring made of PTFE assumes the sealing function and the insulating function. Owing to low dimensional stability the height of the insulating ring is limited to 7 mm when new.

(103) Because of the high thermal stress during operation and the necessary pressing force of 30 to 40 kN to ensure the sealing function of the insulating ring the height of the insulating ring was reduced to a minimum value of 4 mm within 3 months.

(104) The service life is thus limited to 3 months.

(105) Owing to the thermal stress brought about by the hot reaction gas both the sealing of the floor plate and the electrical insulation were no longer intact due to thermal cracking and settling of the sealing body. Thus after this period costly and inconvenient replacement of all insulating rings was required. Repair operations resulted in a considerable loss of capacity.

Example

(106) CVD reactor with insulating ring made of zirconium oxide (ZrO2):

(107) In this implementation the sealing function and the insulating function are divided over two components. The insulating ring made of ZrO.sub.2 is employed to achieve electrical insulation between the electrode holder and the floor plate. The insulating ring has a height of 8 mm when new.

(108) The insulating ring has a groove toward the top of the electrode holder. The sealing function is assumed by a graphite foil ring in the groove and a graphite gasket having a metal flange toward the floor plate, the flange being oriented toward the reaction space. Being a ceramic component ZrO.sub.2 does not exhibit settling behavior. After compression the graphite foil ring still had a protrusion f between the top of the electrode holder and the insulating ring of 0.3 mm. The graphite foil ring was compressed with a contact pressure of 35 N/mm.sup.2. After 12 months the insulating ring was replaced in the course of regular maintenance cycles. The width e of the graphite foil ring outside the groove was 1.6 times the width E of the graphite foil ring in the groove of the supporting ring. As a result of the very high thermal stability and the markedly higher specific heat conductivity compared to PTFE the side of the insulating ring facing the reactor and also the graphite foil ring and the gasket had not undergone thermal attack. No silica deposits were detected at the shaft of the electrode holders after exchange of the electrode holders. Service life was increased to 12 months. The sealing system, i.e. insulating ring and sealing elements, is thus no longer limiting of service life.

(109) The description hereinabove of illustrative embodiments is to be understood as being exemplary. The disclosure made thereby enables a person skilled in the art to under-stand the present invention and the advantages associated therewith and also encompasses alterations and modifications to the described structures and processes obvious to a person skilled in the art. All such alterations and modifications and also equivalents shall therefore be covered by the scope of protection of the claims.