DE102011077455A1 - Method for determination of impurities in silicon, comprises separating polycrystalline silicon using electrode with stream, preparing rod from single crystal silicon from solitary polycrystallines silicon, and analyzing crystalline rod - Google Patents

Abstract

Method for determination of impurities in silicon, comprises: separating a polycrystalline silicon using electrode with stream supplied by direct electrical continuity of heat filament rod by introduction of reaction gas incorporating silicon containing component in a chemical vapor deposition (CVD) reactor, and a base plate (6) of the CVD reactor; preparing a rod from single crystal silicon from solitary polycrystallines of the silicon rod by zone pulling; and analyzing the single crystalline silicon rod on impurities by photo luminescence measurements. Method for determination of impurities in silicon, comprises: separating a polycrystalline silicon using electrode with stream supplied by direct electrical continuity of heat filament rod by introduction of reaction gas incorporating silicon containing component in a chemical vapor deposition (CVD) reactor, and a base plate (6) of the CVD reactor, on which those is located at at least one electrode (7) to the power source of the filament rod covered with a shroud from silicon; preparing a rod from single crystal silicon from solitary polycrystallines of the silicon rod by zone pulling; and analyzing the single crystalline silicon rod on impurities by photo luminescence measurements. An independent claim is included for a reactor for the deposition of polycrystalline silicon, comprising a bell from quartz, a base plate including at least one opening for the supply of reaction gas, and at least one opening for the removal of exhaust air, an electrode for receiving and supplying power to a filament rod, where the base plate comprises a covering of silicon.

Description

The invention relates to a method for the determination of impurities in silicon.

In particular, the invention relates to a method that allows conclusions about the impurities in the reaction gas in the deposition of polycrystalline silicon in a Siemens reactor.

In the Siemens process thin filament rods made of silicon are heated in a bell-shaped reactor by direct current passage and a reaction gas containing a silicon-containing component and hydrogen is introduced.

The silicon-containing component of the reaction gas is usually monosilane or a halosilane of the general composition SiH _n X _4-n (n = 0, 1, 2, 3, X = Cl, Br, I)

It is preferably a chlorosilane or chlorosilane mixture, more preferably trichlorosilane.

Mostly SiH ₄ or SiHCl ₃ (trichlorosilane, TCS) is used in admixture with hydrogen.

In EP 2 077 252 A2 The typical structure of a reactor used in the production of polysilicon will be described.

The bottom of the reactor is provided with electrodes which receive the thin rods on which silicon is deposited during the growth process, thus growing to the desired polysilicon rods. Typically, two thin rods are connected by a bridge to a pair of thin rods, which form a circuit via the electrodes and external devices, which serves to heat the rod pairs to a certain temperature.

The reactor bottom is usually additionally provided with nozzles which supply the reactor with fresh gas. The exhaust gas is passed through openings again from the reaction space.

The supplied amount of reaction gases is usually varied depending on the rod diameter, d. H. usually increased with increasing rod diameter.

High-purity polysilicon is ideally deposited on the heated rods and bridge, increasing rod diameter over time.

The degree of purity of the deposited Poylsilicums depends crucially on the purity of the reaction gas.

As already mentioned above, the reaction gas may be trichlorosilane (TSC).

• A) Si + 3HCl → SiHCl₃ + H₂ + Nebenprodukte
• B) Si + 3SiCl₄ + 2H₂ → 4SiHCl₃ + Nebenprodukte
• C) SiCl₄ + H₂ → SiHCl₃ + HCl + Nebenprodukte

This TCS is mainly generated by three different methods.

• A) Si + 3HCl → SiHCl ₃ + H ₂ + by-products
• B) Si + 3SiCl ₄ + 2H ₂ → 4SiHCl ₃ + by-products
• C) SiCl ₄ + H ₂ → SiHCl ₃ + HCl + by-products

Such produced TCS has impurities z. B. with boron and phosphorus and by-products such as dichlorosilane (DCS).

Therefore, the TCS must be purified by distillation, for example.

Various approaches are known for the separation of boron contaminants from TCS.

In addition to purely distillative processes, hydrolysis, complexing or adsorption steps are also described in the prior art.

In DE 10 2007 014 107 A1 describes a process for obtaining boron-depleted chlorosilanes from a boron-containing chlorosilane mixture by distillative separation of a boron-enriched distillation stream.

DE 10 2008 002 537 A1 discloses a method for reducing the content of boron in compositions comprising at least one silicon halide by adding water in a suitable form. Reaction of boron halide with water results in higher-boiling hydrolysates, which are easier to separate from chlorosilane by distillation.

In EP 2 036 858 A2 a process is claimed in which boron- and phosphorus-containing chlorosilanes are brought into contact with the complexing agent benzaldehyde and oxygen. By oxidation and complex formation, the boron compounds contained in the chlorosilane can be easily separated.

In DE 10 2008 054 537 describes a method in which the boron content is lowered in chlorosilanes by contacting with anhydrous adsorbent.

For process control, it is necessary to monitor the boron and phosphorus concentrations in the trichlorosilane or in the end product polysilicon.

For this purpose, preferably in a Siemens reactor produced polycrystalline silicon is examined for corresponding impurities.

For this purpose, it is customary to convert the polysilicon produced into monocrystalline material.

The monocrystalline material is investigated with respect to carbon and dopants such as aluminum, boron, phosphorus and arsenic.

Dopants are analyzed by photoluminescence according to SEMI MF 1398 on an FZ single crystal (SEMI MF 1723) produced from the polycrystalline material.

Bases of the FZ process are, for example, in DE-3007377 A described.

In the FZ process, a polycrystalline stock rod is gradually melted by means of a high-frequency coil and the molten material is converted into a monocrystal by seeding with a monocrystalline seed crystal and subsequent recrystallization. In the recrystallization, the diameter of the resulting single crystal is first conically enlarged (cone formation) until a desired final diameter is reached (rod formation). In the cone formation phase, the single crystal is also mechanically supported to relieve the thin seed crystal.

The problem, however, is that there is a risk that in the deposition of silicon, the reaction gases are contaminated by constituents of the reactor again with boron or phosphorus. These impurities are then also found in the polycrystalline silicon and in the FZ silicon produced for the measurements of the dopant concentrations.

The inventors have recognized that in conventional reactors, the boron and phosphorus components in the reaction gas and thus in the deposited polysilicon can rise again.

From this problem, the task of the present invention resulted.

The object of the invention is achieved by a method for determining the impurities of reaction gas in a CVD reactor, comprising depositing polycrystalline silicon on at least one supplied by an electrode and heated by direct current passage filament rod by introducing reaction gas containing a silicon-containing component in the CVD reactor, wherein a bottom of the CVD reactor, on which the at least one electrode for powering the at least one filament rod is arranged, is covered with silicon, generating a rod of monocrystalline silicon from the deposited polycrystalline silicon rod by means of zone pulling and examination of the monocrystalline silicon rod on impurities by means of photoluminescence measurements.

The object is also achieved by a reactor for the deposition of polycrystalline silicon, comprising a bell made of quartz, a bottom plate containing at least one opening for the supply of reaction gas and at least one opening for the discharge of exhaust air, an electrode for receiving and supplying power to a filament rod wherein the bottom plate has a silicon cover.

By examining the impurities in the monocrystalline silicon rod produced by FZ, it is possible to conclude the impurities in the reaction gas during the deposition process,

The silicon-containing component of the reaction gas is preferably monosilane or a halosilane of the general composition SiH _n X _4-n (n = 0, 1, 2, 3, X = Cl, Br, I)

It is preferably a chlorosilane or a chlorosilane mixture, more preferably trichlorosilane.

Very particular preference is given to using SiHCl ₃ (trichlorosilane, TCS) in admixture with hydrogen.

Essential to the invention is that the bottom of the reactor or the bottom plate is covered with silicon.

Preferably, this is silicon with a defined and the lowest possible dopant content.

Preferably, it is silicon with the following dopant concentrations:
Boron max. 10 ppta and phosphorus max. 20 ppt.

In addition, the silicon preferably contains max. 20 ppta aluminum and max. 20 ppt arsenic.

The bottom plate itself is usually made of steel, stainless steel or silver or quartz. DE 1 292 640 discloses that all walls of the reaction space consist of quartz.

Deposition produces high-boiling compounds that condense on the steel bottom plate and negatively impact safety and quality.

To avoid condensing high boilers, quartz covers can be used on the bottom plate. In this case, with the quartz bell and quartz plate on the bottom plate, about 90% of the product contacting parts of the reactor are made of quartz.

The inventor has recognized that not only metallic bottom plates without cover, but also any quartz covers are disadvantageous. This is related to the fact that quartz deposits are often contaminated with dopants. In addition, quartz deposits are fragile, which can not be ruled out that metallic impurities from the bottom plate negatively affect the purity of the reaction gases.

Although the possible contamination of the reaction gas by dopants from the quartz cover can be counteracted by the so-called. Clean the reactor. However, this process of reactor purification usually takes several days, which is detrimental to the availability of the test deposit equipment.

Covering the bottom plate with silicon reduces the possibly contaminating surface of the reactor space by about 25 to 30%.

At the same time, the duration of the cleaning process is reduced by approx. 45%, which offers clear economic benefits.

Also, scattering and detection limits with respect to contamination improve.

In the following the invention will be explained with reference to two figures.

1 schematically shows the structure of a CVD reactor.

2 shows schematically the construction of a reactor bottom plate.

LIST OF REFERENCE NUMBERS

1

Hood

2

quartz bell

3

cover

4

exhaust pipe

5

Zugasleitung

6

baseplate

7

electrodes

8th

silicon rod

1 shows a reactor with hood 1 , Quartz bell 2 , an exhaust pipe 4 and a supply line 5 ,

Hood 1 usually consists of aluminum.

Zugasleitung 5 serves to pass reaction gas into the interior of the reactor.

exhaust pipe 4 serves to discharge unreacted reaction gas as well as resulting in the reaction of exhaust gas from the reactor.

Reactor comprises a bottom plate 6 , z. B. steel, preferably stainless steel.

On the bottom plate are electrodes 7 arranged, which serve to power the filaments.

8th shows a silicon rod bridge comprising two silicon rods, which has the typical U-shape for Siemens processes.

baseplate 6 has a cover 3 on.

Essential to the invention is that cover 3 consists of silicon.

2 shows a plan view and a cross section of the bottom plate 6 with cover 3 ,

Shown are two openings for receiving electrodes 7 , an opening for exhaust pipe 4 , an opening for access pipe 5 that are in the center of the bottom plate 3 located.

Example and Comparative Example

In a CVD reactor polycrystalline silicon was deposited in several series of experiments.

For this purpose, in principle, a device, as in DE 1 155 759 is described. Deviating from DE 1 155 759 the bottom plate is covered with quartz (comparative example) or with silicon (example).

From the polycrystalline silicon produced, a monocrystalline rod was subsequently produced by means of FZ, which was examined by means of photoluminescence measurements.

Two series of tests were carried out under the same, usual process conditions.

The reaction gases used (trichlorosilane and hydrogen) had the same purity in both series of experiments.

Comparative example

In the test series according to the comparative example, the reactor bottom was covered during the deposition with a quartz plate.

The free measurement (cleaning) took 117 hours.

Free measurement is the qualification / clean-up of the system with reference media until specified specification limits for dopant measurements are undershot and the system can be released for quality inspection trips (eg B 10 ppta maximum, P 20 ppta max, 20 ppta aluminum max As much as 20 ppta).

The detection limits for boron were 3.02 ppta, those for phosphorus were 1.21 ppta.

The average relative standard deviation was 45% for boron and 28% for phosphorus.

example

In the test series according to Example, the reactor bottom was covered during the deposition with a silicon plate.

The free measurement (cleaning) took only 63 hours.

The detection limits for boron were 2.21 ppta, those for phosphorus were 0.77 ppta, ie significantly lower than in the comparative example.

The average relative standard deviation was 26% for boron and 35% for phosphorus.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2077252 A2 [0007]
• DE 102007014107 A1 [0019]
• DE 102008002537 A1 [0020]
• EP 2036858 A2 [0021]
• DE 102008054537 [0022]
• DE 3007377A [0028]
• DE 1292640 [0043]
• DE 1155759 [0066, 0066]

Claims (9)

Method for the determination of impurities in silicon, comprising the steps Depositing polycrystalline silicon on at least one filament rod powered by an electrode and heated by direct current passage by introducing reaction gas containing a silicon-containing component into a CVD reactor, a bottom plate of the CVD reactor on which the at least one electrode for Power supply of the at least one filament rod is arranged, covered with a cover made of silicon; - Producing a rod of single-crystal silicon from the deposited polycrystalline silicon rod by means of zone pulling; - Investigation of the monocrystalline silicon rod on impurities by means of photoluminescence measurements. The method of claim 1, wherein said single crystal silicon rod is analyzed for concentration of dopants selected from the group consisting of aluminum, boron, phosphorus and arsenic. A method according to claim 1 or claim 2 wherein the rod of single crystal silicon is analyzed for carbon concentration. The method of any of claims 1 to 3, wherein the cover of the bottom of the reactor is silicon of defined dopant content, the content of boron being less than or equal to 10 ppta and the content of phosphorus being less than or equal to 20 ppta. The method of claim 4 wherein the content of aluminum is less than or equal to 20 ppta and the content of arsenic is less than or equal to 20 ppta. A process according to any one of claims 1 to 5, wherein the reaction gas is a mixture of trichlorosilane and hydrogen. A reactor for depositing polycrystalline silicon, comprising a bell ( 2 ) made of quartz, a base plate ( 6 ) including at least one opening ( 5 ) for the supply of reaction gas and at least one opening ( 4 ) for the removal of exhaust air, an electrode ( 7 ) for receiving and supplying power to a filament rod ( 8th ), the bottom plate ( 6 ) a cover ( 3 ) of silicon. Reactor according to claim 7, wherein the cover ( 3 ) of the bottom plate ( 6 ) of the reactor of silicon having a defined dopant content, wherein the content of boron is less than or equal to 10 ppta and the content of phosphorus is less than or equal to 20 ppta. Reactor according to claim 8, wherein the content of aluminum is less than or equal to 20 ppta and the content of arsenic is less than or equal to 20 ppta.

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