Carbon-doped silicon epitaxial layer-containing substrate and method for manufacturing the same

Abstract

The objective is to provide a carbon-doped silicon epitaxial layer-containing substrate that achieves both good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity, as well as a method for manufacturing the same. [Solution] A carbon-doped silicon epitaxial layer-containing substrate having a carbon-doped silicon epitaxial layer on a silicon substrate and a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer, wherein the carbon concentration of the carbon-doped silicon epitaxial layer decreases continuously or stepwise from the silicon substrate side to the non-carbon-doped silicon epitaxial layer side, and a method for manufacturing the same.

Description

[Technical Field]

[0001] The present invention relates to a carbon-doped silicon epitaxial layer-containing substrate and a method for producing the same. [Background technology]

[0002] Solid-state image sensors, such as CMOS image sensors, can be manufactured using existing CMOS production lines, thus requiring a rapid supply to meet demand (Non-Patent Literature 1). Recently, there has been a demand for sensors with a large number of pixels and high sensitivity. For this reason, substrate gettering is required.

[0003] This is because, while white scratches and other defects can occur due to the presence of impurities (especially heavy metals) that act as carrier generation centers, particularly in the photodiode portion, adding gettering capability can suppress this occurrence.

[0004] Regarding gettering, in addition to improvements in the device manufacturing process, many methods have been considered to add this capability to the substrate. Examples include a method of ion-implanting carbon and growing an epitaxial layer on top of it (Patent Document 1), a method of epitaxial growth on a carbon-doped layer (Patent Document 2), a method of doping carbon into the original silicon substrate (Patent Document 3), a method of implanting cluster carbon (Patent Document 4), and further, implantation of carbon and As (Patent Document 5), and a method containing silicon atoms, group 14 elements (C: carbon), and atoms that suppress the diffusion of said group 14 elements (Patent Document 6). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-338507 [Patent Document 2] Japanese Patent Publication No. 2006-216934 [Patent Document 3] International Publication No. 2008 / 029918 [Patent Document 4] International Publication No. 2012 / 157162 [Patent Document 5] Japanese Unexamined Patent Application Publication No. 06-163410 [Patent Document 6] Japanese Unexamined Patent Application Publication No. 2009-200231 [Non-Patent Document]

[0006] [Non-Patent Document 1] Albert J.P. Theuwissen, “There’s More to the Picture Than Meets the Eye (and in the future it will become only much more)” Abst. of ISSCC2021, Plenary Session - Invited Papers1-4 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] The method of doping carbon during silicon crystal growth in advance is a very effective method because it can be carried out during crystal growth. However, the amount of carbon that can be introduced depends on the solubility (thermal equilibrium concentration) during crystal growth, so the introduced carbon concentration will not be higher than the solubility, and high-concentration carbon cannot be introduced. Therefore, there is a method of introducing carbon by ion implantation, but since an ion implantation apparatus is used, there is concern about contamination from the apparatus. Therefore, if carbon can be introduced during epitaxial growth, it is considered an effective technique.

[0008] On the one hand, in the conventional ion implantation method and carbon-doped epitaxial growth, setting the carbon concentration is one of the important factors. In particular, in the case of carbon-doped epitaxial growth, it is considered that a higher carbon doping concentration results in higher gettering ability (such as an increase in solid solubility due to strain). Conversely, in order to grow an epitaxial layer on this carbon-doped layer, there is concern that the crystallinity of the epitaxial layer deteriorates due to strain caused by a high carbon doping concentration.

[0009] Therefore, there is a need to improve the crystallinity of the silicon epitaxial layer formed on the carbon-doped silicon epitaxial layer while having a high gettering ability.

[0010] The present invention has been made to solve the above problems, and an object thereof is to provide a carbon-doped silicon epitaxial layer-containing substrate in which good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity are compatible, and a method for manufacturing the same.

Means for Solving the Problems

[0011] The present invention has been made to achieve the above object, and provides a carbon-doped silicon epitaxial layer-containing substrate having a carbon-doped silicon epitaxial layer on a silicon substrate and a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer, wherein the carbon concentration of the carbon-doped silicon epitaxial layer decreases continuously or stepwise from the silicon substrate side toward the non-carbon-doped silicon epitaxial layer side.

[0012] [[ID=E18]] According to such a carbon-doped silicon epitaxial layer-containing substrate, good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity are compatible.

[0013] At this time, the carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 4×10 21 atoms / cm3 It can be assumed that the following applies:

[0014] This effectively suppresses the strain generated by high-concentration carbon doping.

[0015] At this time, the carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 1 × 10 19 atoms / cm 3 It can be considered as above.

[0016] This results in the carbon-doped silicon epitaxial layer having better gettering properties.

[0017] At this time, the carbon concentration on the side of the uncarbon-doped silicon epitaxial layer of the carbon-doped silicon epitaxial layer is 1 × 10⁻⁶ 19 atoms / cm 3 It can be assumed that the following applies:

[0018] This results in a higher quality, more crystalline non-carbon doped silicon epitaxial layer.

[0019] The present invention has also been made to achieve the above objectives and provides a method for manufacturing a carbon-doped silicon epitaxial layer containing a substrate, comprising the steps of forming a carbon-doped silicon epitaxial layer on a silicon substrate and forming a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer, wherein in the step of forming the carbon-doped silicon epitaxial layer, the carbon concentration of the carbon-doped silicon epitaxial layer is continuously or stepwise reduced from the silicon substrate side toward the non-carbon-doped silicon epitaxial layer side.

[0020] This method for manufacturing a carbon-doped silicon epitaxial layer substrate makes it possible to produce a carbon-doped silicon epitaxial layer substrate that exhibits both good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity.

[0021] At this time, in the step of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 4×10 21 atoms / cm 3 or less.

[0022] Thereby, the strain generated by high-concentration carbon doping can be effectively suppressed.

[0023] At this time, in the step of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 1×10 19 atoms / cm 3 or more.

[0024] Thereby, a carbon-doped silicon epitaxial layer having better gettering characteristics can be formed.

[0025] At this time, in the step of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the non-carbon-doped silicon epitaxial layer side of the carbon-doped silicon epitaxial layer is 1×10 19 atoms / cm 3 or less.

[0026] Thereby, a high-quality non-carbon-doped silicon epitaxial layer with better crystallinity can be formed.

Effect of the Invention

[0027] As described above, according to the carbon-doped silicon epitaxial layer-containing substrate of the present invention, good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity are compatible. Furthermore, the method for manufacturing a carbon-doped silicon epitaxial layer-containing substrate according to the present invention makes it possible to manufacture a carbon-doped silicon epitaxial layer-containing substrate that achieves both good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity. [Brief explanation of the drawing]

[0028] [Figure 1] This is a schematic diagram of a carbon-doped silicon epitaxial layer-containing substrate in an embodiment of the present invention. [Figure 2] This graph shows the relationship between the amount of carbon doping and the lattice spacing of silicon in a carbon-doped silicon epitaxial layer. [Figure 3] The carbon concentration of the carbon-doped silicon epitaxial layer-containing substrate in the example was measured using SIMS and the results are shown. [Figure 4] The SIMS analysis results of carbon-gettered metals when the carbon-doped silicon epitaxial layer substrate of the example was intentionally contaminated are shown. [Modes for carrying out the invention]

[0029] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0030] As described above, there was a need for a carbon-doped silicon epitaxial layer-containing substrate that achieved both good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity, as well as a method for manufacturing the same.

[0031] As a result of diligent research into the above-mentioned problems, the inventors have discovered that a carbon-doped silicon epitaxial layer containing a substrate having a carbon-doped silicon epitaxial layer on a silicon substrate and a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer, wherein the carbon concentration of the carbon-doped silicon epitaxial layer decreases continuously or stepwise from the silicon substrate side to the non-carbon-doped silicon epitaxial layer side, can achieve both good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity, and have completed the present invention.

[0032] The present inventors have also conducted extensive research on the above-mentioned problems and have found that a method for manufacturing a carbon-doped silicon epitaxial layer-containing substrate, comprising the steps of forming a carbon-doped silicon epitaxial layer on a silicon substrate and forming a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer, wherein in the step of forming the carbon-doped silicon epitaxial layer, the carbon concentration of the carbon-doped silicon epitaxial layer is continuously or stepwise reduced from the silicon substrate side to the non-carbon-doped silicon epitaxial layer side, makes it possible to manufacture a carbon-doped silicon epitaxial layer-containing substrate that achieves both good gettering characteristics and a high-quality silicon epitaxial layer with good crystallinity, thereby completing the present invention.

[0033] Embodiments of the present invention will be described below with reference to Figures 1 and 2.

[0034] [Substrate containing a carbon-doped silicon epitaxial layer] Figure 1 shows a schematic diagram of a carbon-doped silicon epitaxial layer-containing substrate according to an embodiment of the present invention. As shown in Figure 1, the carbon-doped silicon epitaxial layer-containing substrate 1 according to the present invention is a carbon-doped silicon epitaxial layer-containing substrate having a carbon-doped silicon epitaxial layer 3 on a silicon substrate 2 and a non-carbon-doped silicon epitaxial layer 4 on the carbon-doped silicon epitaxial layer 3.

[0035] The silicon substrate 2 is not particularly limited, but for example, it may have a diameter of 150 mm or more, may be p-type or n-type in conductivity, may have a low resistivity of 0.1 Ω·cm or less or a high resistivity of 1000 Ω·cm or more, and can be a silicon single crystal substrate manufactured using the same single crystal manufacturing equipment and procedures as in the past.

[0036] The carbon-doped silicon epitaxial layer 3 has a carbon concentration that decreases continuously or stepwise from the silicon substrate 2 side to the uncarbon-doped silicon epitaxial layer 4 side.

[0037] Due to this carbon concentration gradient, gettering occurs at the interface between the active layer, the uncarbon-doped silicon epitaxial layer 4, and the silicon substrate 2, which is far from the epitaxial layer 4. This suppresses diffusion current and results in good gettering characteristics. In addition, the non-carbon-doped silicon epitaxial layer 4 becomes a high-quality silicon epitaxial layer with good crystallinity.

[0038] The carbon concentration on the silicon substrate 2 side is 4 × 10 21 atoms / cm 3 The following is preferable: This effectively suppresses the strain generated by high-concentration carbon doping.

[0039] Furthermore, the carbon concentration on the silicon substrate 2 side is 1 × 10⁻⁶ 19 atoms / cm 3 It is preferable that the above conditions are met. This results in the carbon-doped silicon epitaxial layer 3 having better gettering properties.

[0040] Figure 2 shows a graph illustrating the relationship between the amount of carbon doping and the lattice spacing of silicon in a carbon-doped silicon epitaxial layer. As shown in Figure 2, 1 × 10 19 atoms / cm 3No significant difference in interstitial distance is observed at the following carbon concentrations. At least for this reason, the carbon concentration on the uncarbon-doped silicon epitaxial layer 4 side is 1 × 10⁻⁶. 19 atoms / cm 3 The following is preferable: This results in a higher quality, more crystalline non-carbon doped silicon epitaxial layer 4.

[0041] The thickness of the carbon-doped silicon epitaxial layer 3 is not particularly limited and can be changed as appropriate.

[0042] The non-carbon-doped silicon epitaxial layer 4 is not particularly limited and can be formed by an epitaxial growth process similar to that of the conventional method.

[0043] [Method for manufacturing a carbon-doped silicon epitaxial layer-containing substrate] Next, a method for manufacturing a carbon-doped silicon epitaxial layer-containing substrate according to the present invention will be described with reference to Figures 1 and 2. The method for manufacturing a carbon-doped silicon epitaxial layer-containing substrate 1 according to the present invention is a method for manufacturing a carbon-doped silicon epitaxial layer-containing substrate that includes the steps of forming a carbon-doped silicon epitaxial layer 3 on a silicon substrate 2 and forming a non-carbon-doped silicon epitaxial layer 4 on the carbon-doped silicon epitaxial layer 3.

[0044] (Process for forming a carbon-doped silicon epitaxial layer) On a silicon substrate 2, a carbon-doped Si layer is epitaxially grown under reduced pressure using a vacuum CVD apparatus, with trimethylsilane, monomethylsilane, or a gas mixture of a carbon source and monosilane gas as the raw material.

[0045] During epitaxial growth, the carbon concentration of the carbon-doped silicon epitaxial layer 3 is continuously or stepwise reduced from the silicon substrate 2 side towards the uncarbon-doped silicon epitaxial layer 4 side.

[0046] By creating such a carbon concentration gradient, gettering occurs at the interface with the silicon substrate 2, which is far from the active layer, the uncarbon-doped silicon epitaxial layer 4. This suppresses the diffusion current, allowing for the formation of a carbon-doped silicon epitaxial layer 3 with good gettering characteristics. In addition, a high-quality, non-carbon-doped silicon epitaxial layer 4 with good crystallinity can be formed on the carbon-doped silicon epitaxial layer 3.

[0047] In this case, by forming the film at a growth temperature preferably in the range of 700°C to 900°C, and more preferably in the range of 730°C to 750°C, it is possible to form a carbon-doped silicon epitaxial layer 3 with fewer defects.

[0048] The furnace pressure during growth is not particularly limited and can be, for example, 1 to 100 Torr.

[0049] At this time, the carbon concentration on the silicon substrate 2 side of the carbon-doped silicon epitaxial layer 3 is set to 4 × 10 21 atoms / cm 3 The following is preferable. This effectively suppresses the strain generated by high-concentration carbon doping.

[0050] Furthermore, the carbon concentration on the silicon substrate 2 side of the carbon-doped silicon epitaxial layer 3 is set to 1 × 10⁻⁶. 19 atoms / cm 3 It is preferable to keep the above in place. This makes it possible to form a carbon-doped silicon epitaxial layer 3 with better gettering properties.

[0051] Next, the carbon concentration is reduced by decreasing the flow rates of trimethylsilane, monomethylsilane, and other carbon-source gases. There are two main ways to change the carbon concentration: one is to continuously change the flow rates of trimethylsilane, monomethylsilane, and other carbon-source gases to continuously change the concentration, and the other is to fix the flow rate at a predetermined level for a certain period of time and change it in a stepwise manner. The method can be determined by considering the precision of the growth apparatus, etc.

[0052] At this time, the carbon concentration on the uncarbon-doped silicon epitaxial layer 4 side is set to 1 × 10⁻¹⁰, as shown in Figure 2, so that no change in interstitial distance is observed even when carbon is doped. 19 atoms / cm 3 It can be reduced to the following levels. This makes it possible to form a higher quality, non-carbon-doped silicon epitaxial layer 4 with better crystallinity.

[0053] The thickness of the carbon-doped silicon epitaxial layer 3 is not particularly limited and can be changed as appropriate.

[0054] (Process for forming a non-carbon-doped silicon epitaxial layer) Next, a non-carbon-doped silicon epitaxial layer 4 is formed on the carbon-doped silicon epitaxial layer 3. The growth conditions for the non-carbon-doped silicon epitaxial layer 4 are not particularly limited and can be formed by the same epitaxial growth treatment as in the past. [Examples]

[0055] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0056] A single-crystal silicon substrate with a diameter of 300 mm, a crystal orientation of (100), boron doping, and a resistivity of 10 Ω·cm was prepared.

[0057] On a silicon substrate, using a vacuum CVD apparatus, trimethylsilane is used as the raw material gas, the growth temperature is 700°C, and the furnace pressure is 10 Torr, resulting in 1 × 10¹⁶ carbon atoms. 20 atoms / cm 3 A doped Si epitaxial layer was grown to a thickness of 50 nm.

[0058] Subsequently, using the same method, 1 × 10 19 atoms / cm 3 A carbon-doped Si epitaxial layer was grown at a wavelength of 500 nm.

[0059] Subsequently, using SiH4 gas as the raw material, a Si layer (uncarbon-doped silicon epitaxial layer) of 1.5 μm was grown by epitaxial growth for 60 minutes at a growth temperature of 1080°C and a furnace pressure of 10 Torr, thereby producing a substrate containing a carbon-doped silicon epitaxial layer.

[0060] The carbon concentration profile of the obtained carbon-doped silicon epitaxial layer-containing substrate was evaluated using SIMS7f from Kameka Corporation. The evaluation results are shown in Figure 3.

[0061] As shown in Figure 3, it can be seen that the carbon concentration decreases in a stepwise manner from the interface between the silicon substrate and the carbon-doped silicon epitaxial layer to the uncarbon-doped silicon epitaxial layer.

[0062] Furthermore, the obtained carbon-doped silicon epitaxial layer containing substrate had a surface concentration of 1 × 10⁻⁶ 12 atoms / cm 2 The samples were intentionally contaminated with nitric acid solutions of Ni and Cu at the specified concentrations, and after diffusion treatment at 650°C / 15 min in a horizontal furnace, the metal concentration profiles were evaluated using a Kameka SIMS7f. The evaluation results are shown in Figure 4.

[0063] As a result, as shown in Figure 4, it was found that Ni and Cu were gettered at the interface between the silicon substrate and the carbon-doped silicon epitaxial layer (the high-concentration carbon layer).

[0064] Furthermore, XRD analysis of the non-carbon-doped silicon epitaxial layer revealed that it was a high-quality single-crystal silicon epitaxial layer.

[0065] As described above, according to the embodiments of the present invention, it was possible to manufacture a carbon-doped silicon epitaxial layer containing a high-quality silicon epitaxial layer that exhibits both good gettering characteristics and good crystallinity.

[0066] This specification includes the following embodiments: [1]: A carbon-doped silicon epitaxial layer containing substrate, having a carbon-doped silicon epitaxial layer on a silicon substrate and a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer, wherein the carbon concentration of the carbon-doped silicon epitaxial layer decreases continuously or stepwise from the silicon substrate side to the non-carbon-doped silicon epitaxial layer side. [2]: The carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 4 × 10 21 atoms / cm 3 A carbon-doped silicon epitaxial layer-containing substrate as described in [1] above, comprising the following: [3]: The carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 1 × 10 19 atoms / cm 3 A carbon-doped silicon epitaxial layer-containing substrate according to [1] or [2] above, including the above. [4]: The carbon concentration on the side of the carbon-doped silicon epitaxial layer that is not carbon-doped silicon epitaxial layer is 1 × 10 19 atoms / cm 3 A carbon-doped silicon epitaxial layer-containing substrate according to [1], [2], or [3] above, comprising the following: [5] A method for manufacturing a carbon-doped silicon epitaxial layer containing a silicon substrate, comprising the steps of forming a carbon-doped silicon epitaxial layer on a silicon substrate and forming a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer, wherein in the step of forming the carbon-doped silicon epitaxial layer, the carbon concentration of the carbon-doped silicon epitaxial layer is continuously or stepwise reduced from the silicon substrate side toward the non-carbon-doped silicon epitaxial layer side. [6]: In the process of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is set to 4 × 10 21 atoms / cm 3 A method for producing a carbon-doped silicon epitaxial layer-containing substrate according to [5] above, comprising the following: [7]: In the process of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is set to 1 × 10 19 atoms / cm 3 A method for manufacturing a carbon-doped silicon epitaxial layer-containing substrate according to the above [5] or [6], including the above. [8]: In the process of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the non-carbon-doped silicon epitaxial layer side of the carbon-doped silicon epitaxial layer is set to 1 × 10⁻¹⁰ 19 atoms / cm 3 A method for producing a carbon-doped silicon epitaxial layer-containing substrate according to [5], [6], or [7] above, comprising the following:

[0067] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0068] 1…Substrate containing a carbon-doped silicon epitaxial layer, 2…Silicon substrate, 3…Carbon-doped silicon epitaxial layer, 4…Non-carbon doped silicon epitaxial layer.

Claims

1. A carbon-doped silicon epitaxial layer-containing substrate having a carbon-doped silicon epitaxial layer on a silicon substrate and a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer, A carbon-doped silicon epitaxial layer containing substrate, characterized in that the carbon concentration of the carbon-doped silicon epitaxial layer decreases continuously or stepwise from the silicon substrate side to the uncarbon-doped silicon epitaxial layer side.

2. The carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 4 × 10 ２１ atoms / cm ３ The carbon-doped silicon epitaxial layer-containing substrate according to claim 1, characterized in that it is as follows.

3. The carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 1 × 10 １９ atoms / cm ３ The carbon-doped silicon epitaxial layer-containing substrate according to claim 1, characterized in that it is as described above.

4. The carbon concentration on the side of the carbon-doped silicon epitaxial layer to the uncarbon-doped silicon epitaxial layer is 1 × 10 １９ atoms / cm ３ A carbon-doped silicon epitaxial layer-containing substrate according to any one of claims 1 to 3, characterized in that it is as follows:

5. The process includes the steps of forming a carbon-doped silicon epitaxial layer on a silicon substrate and forming a non-carbon-doped silicon epitaxial layer on the carbon-doped silicon epitaxial layer. A method for manufacturing a carbon-doped silicon epitaxial layer containing a substrate, characterized in that, in the step of forming the carbon-doped silicon epitaxial layer, the carbon concentration of the carbon-doped silicon epitaxial layer is continuously or stepwise reduced from the silicon substrate side toward the uncarbon-doped silicon epitaxial layer side.

6. In the process of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is set to 4 × 10 ２１ atoms / cm ３ A method for producing a carbon-doped silicon epitaxial layer-containing substrate according to claim 5, characterized in that it is as follows.

7. In the step of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the silicon substrate side of the carbon-doped silicon epitaxial layer is 1×10 １９ atoms / cm ３ or more. The method for manufacturing a substrate containing a carbon-doped silicon epitaxial layer according to claim 5, characterized in that.

8. In the process of forming the carbon-doped silicon epitaxial layer, the carbon concentration on the non-carbon-doped silicon epitaxial layer side of the carbon-doped silicon epitaxial layer is set to 1 × 10⁻¹⁰ １９ atoms / cm ３ A method for manufacturing a carbon-doped silicon epitaxial layer-containing substrate according to any one of claims 5 to 7, characterized in that it is as follows:

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