N-type doped germanium single crystal and wafers obtained therefrom

Abstract

The present invention relates to n-type doped single crystalline uncoordinated Ge with a resistivity of less than 10 mOhm.cm, characterized in that phosphorus is the sole dopant. Such crystals can be obtained by using the Czochralski pulling method with GeP as the dopant.

Description

[Technical field]

[0001] The present invention relates to a method for producing dislocation-free monocrystalline Ge n-doped with phosphorus and having a resistivity of less than 10 mOhm.cm. It also relates to n-doped material in the form of large diameter bulk crystals, as well as wafers obtained from these crystals. [Background technology]

[0002] Electronic and optoelectronic device manufacturers require large, uniform, industrially grown single semiconductor crystals of germanium that, when sliced ​​and polished, provide substrates for the fabrication of microelectronic devices. The market for n-type Ge wafers is primarily targeted at optoelectronic devices such as vertical-cavity surface-emitting lasers (VCSELs) or mid-infrared plasmonic sensors. VCSELs are a type of semiconductor laser diode with a vertical laser beam emission from the top surface. VCSELs are used in a variety of laser products including computer mice, fiber optic communications, laser printers, face recognition, and smart glasses. Plasmonic sensors are based on the collective oscillation of free electrons and are suitable for a variety of applications, such as the detection of molecules.

[0003] The high electron density achieved in these highly doped wafers enables plasmonic effects in the germanium films, so n-type doping and low resistivity are desirable for these applications, but dislocations often degrade their performance.

[0004] On the other hand, p-doped germanium wafers are not suitable for infrared plasmons due to the large plasmonic losses. Frigerio et al., Physical Review B 94, 085202, 2016.

[0005] Dislocation-free semiconductor wafers with low resistivity are described in US Pat. No. 7,341,787. Very low resistivities are envisaged, such as less than 2 mOhm.cm. To achieve this goal, at least two electrically active dopants belonging to the same family of the periodic law of elements are introduced simultaneously. This is said to avoid the problem that above a certain concentration, some dopant atoms incorporated in the semiconductor material may become electrically inactive. The document mentions Si, Ge and Si-Ge alloys, but is apparently only concerned with doping of Si. No details regarding Ge are disclosed, and in particular the source of the dopants used is not disclosed.

[0006] Spitzer et al., J., Appl. Phys. 32, 1822, 1961, describes the preparation of Ge single crystals heavily doped with Sb, As, and P. Resistivities much lower than 2 mOhm.cm are reported. In this context, all phosphorus-doped samples are obtained by pulling single crystals from calcium orthophosphate sources. However, as shown in the comparative example below, the use of calcium orthophosphate as a dopant necessarily precludes the obtaining of dislocation-free crystals.

[0007] US Patent No. 8,574,363 teaches that high doping concentrations in silicon-based semiconductor crystals can also be obtained by using so-called dopant chambers, for example containing phosphorus. The chambers are placed in close proximity to the melt. When the temperature is raised to the melting point of phosphorus, phosphorus is released as a gas, some of which is incorporated into the melt, while others escape to the environment. Gas-phase operations therefore require additional care and calculations to predict the amount of phosphorus released into the melt. For doping silicon with phosphorus and germanium, US Patent No. 8,574,363 further teaches the use of two separate chambers, one for phosphorus provided by evaporation and the other for germanium provided by liquefaction. US Patent No. 7,132,091 suggests the use of a dopant chamber that partially dissolves when the cover is lowered into the melt. The use of such chambers can introduce unwanted contaminants into the melt. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 7,341,787 [Patent Document 2] U.S. Patent No. 8,574,363 [Patent Document 3] U.S. Patent No. 7,132,091 [Non-patent literature]

[0009] [Non-Patent Document 1] Frigerio et al., Physical Review B 94, 085202, 2016 [Non-Patent Document 2] Spitzer et al., J., Appl. Phys. 32, 1822, 1961 [Non-Patent Document 3] “Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials” P.Clapper, Ed., John Wiley and Sons Ltd, Chichester, England, 2005 Summary of the Invention [Problem to be solved by the invention]

[0010] To this end, the present invention provides a doped n-type germanium single crystal and wafers obtained therefrom. [Means for solving the problem]

[0011] In a first aspect, the present invention provides n-type doped Ge single crystals, with phosphorus as the sole dopant. This simplifies the process and allows for better process control as well as more accurate prediction of the resistivity of the formed crystal ingot. The combination of high n-type doping and dislocation-free wafers opens up the possibility of enhancing the behavior of the aforementioned optoelectronic devices.

[0012] In a second aspect, the present invention provides a wafer comprising an n-type doped Ge single crystal according to the first aspect of the invention. More specifically, said n-type doped single crystal Ge wafer comprises phosphorus as the sole dopant. Such single crystal is dislocation free and preferably has a resistivity of less than 10 mOhm.cm.

[0013] In a third aspect, the present invention provides a method for producing an n-type doped Ge single crystal according to the first aspect of the invention, comprising the steps of: - preparing the Czochralski furnace; - Germanium and phosphorus at least 1×10 18 / c m3 into the furnace in relative amounts to obtain a dopant level of - The process of pulling up the crystals The present invention provides a method comprising: DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Unless otherwise defined, all terms used in the disclosure of the invention, including technical and scientific terms, have the meanings commonly understood by those of ordinary skill in the art to which the invention belongs. With further indication, definitions of terms are included to provide a more thorough understanding of the teachings of the present invention.

[0015] As used in this disclosure, the following terms have the following meanings:

[0016] As used in this disclosure, "a," "an," and "the" refer to both singular and plural referents unless the context clearly dictates otherwise. For example, "a compartment" means one or more than one compartment.

[0017] As used in this disclosure, "about" in reference to a measurable value, e.g., a parameter, amount, temporal period, etc., is meant to encompass deviations from the particular numerical value by up to + / -20%, preferably up to + / -10%, more preferably up to + / -5%, even more preferably up to + / -1%, and even more preferably up to + / -0.1%, insofar as such deviations are appropriate for the practice of the disclosed invention. However, it is understood that the value to which "about" refers that modifies the value is itself expressly disclosed.

[0018] As used in this disclosure, "comprise," "comprising," "comprises," and "comprised of" are synonymous with "include," "including," "includes," or "contain," "containing," or "contains," and are inclusive or open-ended phrases that specify the presence of, for example, ingredients described below, but do not exclude or preclude the presence of additional, unspecified ingredients, features, elements, components, or steps that are known in the art or disclosed therein.

[0019] The specification of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the specified endpoints. All percentages are understood to be percent by weight, abbreviated as "wt.%", unless otherwise defined or unless a different meaning is apparent to one of ordinary skill in the art from its usage and in the context in which it is used.

[0020] The growth of semiconductor crystals according to the invention requires heating the source material to its melting point to create a crystalline source melt, contacting the melt with a high quality seed crystal, and crystallizing the melt upon contact with the seed crystal. A variety of processes are known to achieve this. These include the Czochralski (Cz) process and the related Liquid Encapsulated Czochralski (LEC) process, the Horizontal Bridgman process and the Bridgman-Stockbarger process (HB) and their vertical variants (VB), as well as the Gradient Freeze (GF) and the related Vertical Gradient Freeze (VGF) process. Such techniques are described in "Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials" P.Clapper, Ed., John Wiley and Sons Ltd, Chichester, England, 2005.

[0021] Crystallization of the melt causes the seed crystal at the bottom of the crystal feedstock to grow along its longitudinal axis, essentially forming a cylindrical crystal, called an ingot. The equipment required to form a semiconductor crystal includes a crystal growing furnace, a crucible, and sometimes a crucible support.

[0022] In a first aspect, the present invention provides n-type doped Ge single crystals, with phosphorus as the sole dopant. This simplifies the process and allows for better process control as well as more accurate prediction of the resistivity of the formed crystal ingot. The combination of high n-type doping and dislocation-free wafers opens up the possibility of enhancing the behavior of the aforementioned optoelectronic devices.

[0023] Preferably, the Ge single crystal is substantially free of dislocations. In the context of the present invention, the term "substantially free of dislocations" means a dislocation density of 1 cm 2 The number of dislocations is less than 0.025 per cm 2 More preferably, the number of dislocations is less than 0.005 per cm 2 This is interpreted as a number of dislocations per unit area of ​​less than 0.001. Most preferably, the Ge single crystal does not have dislocations and is therefore dislocation-free. Dislocations occurring in crystals grown by the Czochralski method can be measured by etching and / or copper decoration methods. Sources of dislocations include thermal shock or residual dislocations in the seed from surface damage, epitaxy failure at the seed, plastic formation in the bulk of the crystal, and impurity segregation effects. Those skilled in the art will naturally understand that it is possible to eliminate residual dislocations and grow dislocation-free crystals therefrom, for example by Dash necking. In a preferred embodiment, the Ge single crystal according to the invention is produced in a procedure in which a crystal growth furnace produces a crystal ingot that is free of dislocations or lines. Preferably, the ingot is grown by a vertical growth process.

[0024] In a preferred embodiment, the present invention relates to a method for producing the dopant, the dopant being at least 5×10 17 / cm 3 in an amount of, preferably, 5 x 10 17 / cm 3 From 2.5 × 10 19 / cm 3 More preferably, in an amount of 1×10 18 / cm 3 From 2.5 × 10 19 / cm 3 and more preferably in an amount of 1×10 18 / cm 3 From 6×10 18 / cm 3 or any value therebetween.

[0025] In a preferred embodiment, the present invention provides n-type doped Ge single crystals having a resistivity of less than 10 mOhm.cm, preferably between 1 and 10 mOhm.cm, more preferably between 1 and 7 mOhm.cm, most preferably between 2 and 6 mOhm.cm, such as 2.0, 3.0, 4.0, 5.0, 6.0 mOhm.cm, or any value therebetween.

[0026] In a preferred embodiment, the present invention provides an n-type doped Ge single crystal that is substantially cylindrical and has a diameter of 1 cm to 50 cm, more preferably 5 cm to 35 cm. Most preferably, said diameter is about 100 mm or 4 inches, about 150 mm or 6 inches, about 200 mm or 8 inches, or about 300 mm or 12 inches, or any diameter therebetween. Preferably, said Ge single crystal is in the form of an ingot, more preferably in the form of a Czochralski grown crystal ingot.

[0027] In a preferred embodiment, the present invention provides an n-doped Ge single crystal that is substantially cylindrical and has a length of 1 cm to 300 cm, preferably 5 cm to 200 cm, more preferably 10 cm to 150 cm, for example 30 cm, 45 cm, 60 cm, 75 cm, 90 cm, 105 cm, 120 cm, or 135 cm, or any length therebetween.

[0028] In a second aspect, the present invention provides a wafer comprising an n-type doped Ge single crystal, preferably according to the first aspect of the invention. More specifically, said n-type doped single crystal Ge wafer comprises phosphorus as the sole dopant. Such single crystal is dislocation free and preferably has a resistivity of less than 10 mOhm.cm. Preferably, said resistivity is between 1 mOhm.cm and 10 mOhm.cm, more preferably between 1 mOhm.cm and 7 mOhm.cm. Most preferably, said resistivity is between 2 mOhm.cm and 6 mOhm.cm, such as 2.0 mOhm.cm, 3.0 mOhm.cm, 4.0 mOhm.cm, 5.0 mOhm.cm, 6.0 mOhm.cm, or any value therebetween.

[0029] In a preferred embodiment, the present invention provides a wafer according to the second aspect of the invention, wherein the wafer is obtained by cutting from a single crystal ingot, preferably a Czochralski-grown single crystal, the ingot having a diameter of 1 cm to 50 cm, more preferably 5 cm to 35 cm. Most preferably, the diameter is about 100 mm or 4 inches, about 150 mm or 6 inches, about 200 mm or 8 inches, or about 300 mm or 12 inches, or any diameter therebetween. The ingot may have a length of 1 cm to 300 cm.

[0030] In a preferred embodiment, the present invention provides a wafer according to the second aspect of the invention having a thickness of 25 to 1000 μm, more preferably said wafer has a thickness of 100 μm to 750 μm, and even more preferably said wafer has a thickness of about 140 μm, 180 μm, 220 μm, 260 μm, 300 μm, 450 μm, 650 μm or any thickness therebetween.

[0031] In a third aspect, the present invention provides a method for producing an n-type doped Ge single crystal according to the first aspect of the invention, comprising the steps of: - preparing the Czochralski furnace; - Germanium and phosphorus at least 1×10 18 / cm 3 into the furnace in relative amounts to obtain a dopant level of - The process of pulling up the crystals The present invention provides a method comprising:

[0032] In a preferred embodiment, the present invention provides a method according to the third aspect of the invention, wherein phosphorus is provided into said furnace in the form of GeP.

[0033] In a preferred embodiment, the present invention comprises: - cutting the crystal into wafers; - grinding the wafer with coarse grains; - performing chemical mechanical polishing of the wafer; - A process for cleaning the surface of the wafer. There is provided a method according to a third aspect of the invention, further comprising:

[0034] In a further aspect, the present invention provides an electronic or optoelectronic device comprising an n-type doped Ge single crystal according to the first aspect of the invention, or a wafer according to the second aspect of the invention. Single crystal dislocation-free Ge according to the first aspect of the invention.

[0035] In a further aspect, the present invention provides a vertical cavity surface emitting laser or infrared plasmon sensor comprising an n-doped Ge single crystal according to the first aspect of the invention, either directly or after being cut to suitable dimensions for use in a vertical cavity surface emitting laser or infrared plasmon sensor, or a wafer according to the second aspect of the invention, either directly or after being cut to suitable dimensions for use in a vertical cavity surface emitting laser or infrared plasmon sensor.

[0036] In a further aspect, the present invention provides the use of single crystal dislocation-free Ge according to the first aspect of the invention for a vertical cavity surface emitting laser or an infrared plasmonic sensor.

[0037] In other words, the present invention aims at the preparation and provision of n-type doped, single crystal dislocation-free Ge with a resistivity of less than 10 mOhm.cm, characterized by phosphorus as the sole dopant. This simplifies the process and allows for better process control as well as more accurate prediction of the resistivity of the formed crystalline ingot. The combination of a high degree of n-type doping and the dislocation-free nature of the wafers opens up the possibility of enhancing the behavior of the aforementioned optoelectronic devices.

[0038] Another embodiment according to any of the above embodiments relates to said dislocation-free single crystalline Ge obtained by providing phosphorus in the form of GeP. This ensures that a phosphorus-doped product is obtained that is single crystalline and dislocation-free. The use of GeP as a dopant source is strongly preferred over, for example, red or white phosphorus, due to the need for safety considerations when working with the latter two. Furthermore, GeP is available in high purity (99.999%), minimizing the addition of unwanted impurities to the melt.

[0039] Another embodiment according to any of the above embodiments relates to dislocation-free single crystal Ge in the form of a Czochralski-grown crystal ingot.

[0040] Another embodiment according to any of the above embodiments relates to dislocation-free single crystal Ge in the form of wafers obtained from a Czochralski-grown crystal ingot. Such wafers preferably have a thickness of 140 to 1000 μm and may have a diameter of 5 to 35 cm.

[0041] Another embodiment according to any of the above embodiments relates to the use of dislocation-free single crystal Ge for a vertical cavity surface emitting laser or an infrared plasmonic sensor.

[0042] To achieve this goal, - preparing the Czochralski furnace; - Ge and GeP at least 1×10 18 / cm 3into the furnace in relative amounts such that a dopant level of - The process of pulling up the crystals A method was developed that includes:

[0043] The optional additional step is - cutting the crystal into wafers by a wire saw; - grinding the wafer with coarse grains; - performing a chemical mechanical polishing; - A process to clean the wafer surface It is.

[0044] This method is illustrated in the following examples, which are intended to further clarify the invention but are not intended to limit the scope of the invention.

[0045] [Example] A 100 kg load of high purity germanium is introduced into a graphite crucible Czochralski furnace, to which 62.3 g of GeP are added as dopant.

[0046] The dopant amount corresponds to the dopant level in the crystal, ranging from 1 to 6×10 18 / cm 3 , which corresponds to a resistivity variation of about 2 to 6 mOhm.cm. The variation is due to the known fact of impurity segregation at solid interfaces during crystal growth. As a result, the phosphorus concentration increases towards the tail of the crystal, where a drop in resistivity occurs.

[0047] The furnace is first heated to 1000° C. in a nitrogen environment to melt the germanium. At around 725° C., the germanium phosphide dissociates into solid Ge and liquid phosphorus. At 1000° C., the germanium also melts and phosphorus is incorporated into the melt. Once the germanium is completely melted, the temperature of the furnace is reduced to 950° C. After 6 hours, the temperature stabilizes and immediately afterwards, a germanium seed crystal is lowered through the shaft of the furnace until it touches the molten bath. A procedure called "Dash necking", known to those skilled in the art, is then performed to initiate the growth. More specifically, a thin crystal with a diameter of 5 mm is grown to a length of 150 mm. The crystal is then slowly pulled at a controlled rate of 10 mm / h to increase its diameter to 150 mm. The diameter of the crystal is then stabilized by controlling the heater temperature and / or the pulling speed. This phase is generally called bulk growth. The pulling speed reaches about 10 mm / h.

[0048] At the end of the growth, a tail forms on the crystal by gradually reducing its diameter, after which the crystal is immediately separated from the melt. This procedure is useful to minimize thermal shock as it helps to avoid dislocations. The crystal is pulled into the shaft of the furnace and slowly cooled to below 50°C over 28 hours. It is then removed from the furnace.

[0049] The crystals are cut perpendicular to the crystal axis into cylindrical pieces and the resistivity is measured at six different positions along the length of the crystal using a four-point probe, the results are shown in Table 1.

[0050] [Table 1]

[0051] Doping of germanium melts with GeP has been shown to efficiently produce low resistivity n-type germanium crystals with resistivities ranging between 2 and 6 mOhm.cm. This resistivity variability is entirely acceptable for the intended applications. Theoretical calculations further suggest that these amounts of dopant loading, nearly every phosphorus atom, are electrically active within the germanium lattice.

[0052] It is then confirmed that a dislocation-free crystal is obtained. This is done by etching a cross-section piece taken from the tail of the crystal with a dislocation revealing agent. In this case, a solution consisting of 75 g Cu(NO3)2·3H2O, 300 mL H2O, 300 mL HNO3 (69%), and 600 mL HF (49%) is prepared to etch the crystal piece. The surface is then analyzed under a microscope to confirm the absence of dislocations.

[0053] Dislocations generated in a crystal multiply and extend towards the tail of the crystal, so analyzing the tail of the crystal is sufficient to ensure that the crystal is entirely dislocation free.

[0054] The crystals can be further processed as described below to obtain wafers.

[0055] The crown and tail of the crystal are collected and then the crystal is ground to the desired diameter using a cylindrical grinder. A plane or notch is then machined onto the rounded crystal to mark the crystal orientation. The crystal is then cut into individual wafers using a wire saw. For tracking purposes, these wafers are laser marked with a unique identification code. The edges of the wafer are rounded to prevent them from breaking during further processing. The wafer surface is coarsely ground to eliminate thickness variations that appear after sawing. Any subsurfaces damaged by this process are removed by chemical etching. Chemical mechanical polishing is then performed until a mirror-like surface is obtained. A final cleanup ensures an epi-ready surface for the growth of the various epilayers.

[0056] (Comparative Example) A crucible is loaded with 2500 g of germanium and 5 g of calcium orthophosphate as dopant in a Czochralski furnace. The furnace is then heated to the normal operating temperature of 1100°C. However, it is observed that most of the dopant does not dissolve and particles formed float on the surface of the germanium melt. The same crystal growth and analysis procedures are carried out as in the previous examples. Analysis of the crystal shows multiple dislocations, probably due to absorption of the particles near the solid-liquid interface.

[0057] It must therefore be concluded that the use of calcium orthophosphate as a dopant necessarily precludes the obtaining of dislocation-free crystals.

Claims

1. A dislocation-free N-type doped Ge single crystal having a resistivity of less than 10 mOhm.cm, in the form of an ingot, characterized in that phosphorus is the sole dopant, A dislocation-free N-doped Ge single crystal with less than 0.025 dislocations per cm 2 .

2. The dopant is 5×10 １７ / cm ３ From 2.5 x 10 １９ / cm ３ 2. The N-type doped dislocation-free Ge single crystal of claim 1, wherein the N-type doped Ge single crystal is present in an amount of 0.1 to 0.5 wt.

3. 3. An N-type doped, dislocation-free Ge single crystal according to claim 1 or 2, having a resistivity of 2.0 to 6.0 mOhm.cm.

4. 4. An N-type doped dislocation-free Ge single crystal according to any one of claims 1 to 3, which is cylindrical and has a diameter of 1 cm to 50 cm.

5. 5. An N-type doped dislocation-free Ge single crystal according to any one of claims 1 to 4, which is cylindrical and has a length of 1 cm to 300 cm.

6. comprising a dislocation-free N-type doped Ge single crystal having a resistivity of less than 10 mOhm.cm, characterized in that phosphorus is the sole dopant, and having a thickness of 25 μm to 1000 μm; The N-type doped dislocation-free Ge single crystal wafer has less than 0.025 dislocations per cm 2 .

7. 7. The wafer of claim 6, wherein the Ge single crystal has a resistivity of 2.0 to 6.0 mOhm.cm.

8. 8. The wafer according to claim 6 or 7, having a thickness of 100 μm or more.

9. 1. A method for producing dislocation-free N-type doped Ge single crystals having a resistivity of less than 10 mOhm.cm, in which phosphorus is the sole dopant, comprising the steps of: - preparing a Czochralski pulling furnace, Germanium and phosphorus at least 1×10 １８ / cm ３ into the furnace in relative amounts to obtain a dopant level of - Crystal pulling process Including, The method of claim 1, wherein said N-type doped dislocation free Ge single crystal has less than 0.025 dislocations per cm 2 .

10. 10. The method of claim 9, wherein phosphorus is introduced into the furnace in the form of GeP.

11. - cutting the crystal into wafers; - grinding the wafer with coarse grains; - carrying out a chemical mechanical polishing of the wafer; - cleaning the surface of the wafer 11. The method of claim 9 or 10, further comprising:

12. 4. An electronic or optoelectronic device comprising an N-type doped Ge single crystal according to claim 1.

13. A vertical cavity surface emitting laser or an infrared plasmon sensor comprising the N-type doped Ge single crystal according to any one of claims 1 to 3.

14. 4. Use of the single crystal dislocation-free Ge according to any one of claims 1 to 3 for a vertical cavity surface emitting laser or an infrared plasmonic sensor.

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