CN113282878A

CN113282878A - Method for determining seeding temperature of single crystal furnace and method for preparing monocrystalline silicon by Czochralski method

Info

Publication number: CN113282878A
Application number: CN202110390415.4A
Authority: CN
Inventors: 魏星; 刘文凯; 薛忠营
Original assignee: Shanghai Institute of Microsystem and Information Technology of CAS; Zing Semiconductor Corp
Current assignee: Shanghai Institute of Microsystem and Information Technology of CAS; Zing Semiconductor Corp
Priority date: 2021-04-12
Filing date: 2021-04-12
Publication date: 2021-08-20

Abstract

The application discloses a method for determining the seeding temperature of a single crystal furnace and a method for preparing monocrystalline silicon by a Czochralski method. The method comprises the following steps: measuring the temperature of a melt for seeding in the single crystal furnace before seeding, and obtaining a temperature-time curve; carrying out Fourier analysis on the temperature-time curve to obtain a frequency-amplitude curve; and after judging that the temperature of the melt is not changed violently according to the temperature-time curve, taking a frequency-amplitude curve with stable seeding temperature as a standard reference curve, and comparing the obtained frequency-amplitude curve with the standard reference curve to judge whether the seeding temperature is stable. According to the method, the accuracy of the stability judgment of the seeding temperature is improved and the wire breakage rate caused by misjudgment of the seeding temperature is reduced through Fourier analysis assistance and a time-temperature curve.

Description

Method for determining seeding temperature of single crystal furnace and method for preparing monocrystalline silicon by Czochralski method

Technical Field

The application relates to the field of monocrystalline silicon preparation, in particular to a method for determining seeding temperature of a monocrystalline furnace and a method for preparing monocrystalline silicon by a Czochralski method.

Background

The czochralski method is commonly used industrially to produce large size semiconductor grade single crystal silicon. The preparation of the monocrystalline silicon by the Czochralski method comprises the following steps: melting, stabilizing temperature, seeding, shouldering, equalizing diameter, ending, cooling and taking a rod. Wherein the solution temperature needs to be stabilized at the seeding temperature before seeding. The seed crystal is generally immersed into the silicon melt and the brightness and shape of the aperture at the contact of the seed crystal and the melt are observed to see if the seeding temperature is proper. When the seeding temperature is not appropriate, the temperature needs to be adjusted manually.

However, in the production of large size semiconductor grade single crystal silicon using the Czochralski method, a magnetic field is typically used to control melt convection to control crystal defects, oxygen content, and impurity distribution. The added magnetic field inhibits the convection of the melt, the hot melt at the crucible wall is difficult to quickly reach the liquid level, and the change of the temperature from the manual adjustment of the temperature to the liquid level has the delay of several hours, so that a great amount of time is consumed in the process of searching for the seeding temperature, and the productivity is influenced.

Because the temperature fluctuation caused by the periodicity of melt flow and turbulence, the temperature of the seed crystal is not a constant but fluctuates in a certain range, and the measurement precision of an industrially adopted infrared thermometer is limited, so that whether the melt temperature is stable or not is difficult to determine by a conventional method of viewing the temperature curve. Temperature fluctuations are often treated by time averaging to obtain a smooth curve, but the method loses the periodic character of the fluid flow.

Therefore, improvements are required to solve the above problems.

Disclosure of Invention

In view of the problems in the prior art, the present application provides a method for determining a seeding temperature of a single crystal furnace, the method comprising:

measuring the temperature of a melt for seeding in the single crystal furnace before seeding, and obtaining a temperature-time curve;

carrying out Fourier analysis on the temperature-time curve to obtain a frequency-amplitude curve;

and after judging that the temperature of the melt is not changed violently according to the temperature-time curve, taking a frequency-amplitude curve with stable seeding temperature as a standard reference curve, and comparing the obtained frequency-amplitude curve with the standard reference curve to judge whether the seeding temperature is stable.

Optionally, the determining whether the seeding temperature is stable includes:

and comparing the position and amplitude value of the amplitude peak value appearing in the obtained frequency-amplitude curve with the position and amplitude value of the corresponding amplitude peak value in the standard reference curve, and if the position and amplitude value of the amplitude peak value in the frequency-amplitude curve and the standard reference curve correspond to each other, stabilizing the seeding temperature.

Optionally, the method comprises:

firstly, judging whether the position of the amplitude peak value in the frequency-amplitude curve corresponds to the position of the corresponding amplitude peak value in the standard reference curve;

if the amplitude peak values in the frequency-amplitude curve and the standard reference curve correspond to each other, further judging whether the difference value between the amplitude values of the specific amplitude peak values in the frequency-amplitude curve and the standard reference curve is within a preset threshold value, if so, stabilizing the seeding temperature, and if so, stabilizing the seeding temperature.

Optionally, the determining whether the amplitude peaks in the frequency-amplitude curve and the standard reference curve correspond to each other comprises:

if the difference value between the position of the amplitude peak value in the frequency-amplitude curve and the position of the amplitude peak value in the standard reference curve is within a set threshold value, the amplitude peak values in the frequency-amplitude curve and the standard reference curve are determined to correspond to each other;

and if the difference value between the position of the amplitude peak value in the frequency-amplitude curve and the position of the amplitude peak value in the standard reference curve exceeds a set threshold value, the amplitude peak values in the frequency-amplitude curve and the standard reference curve are not corresponding to each other.

Alternatively, the temperature of the melt for seeding in the single crystal furnace is measured at predetermined time intervals, and a temperature-time curve is obtained.

Optionally, the temperature of the melt is the temperature at the point in time of measurement or the average temperature over a set period of time.

Optionally, fourier analysis is performed on the obtained temperature-time curve at preset time intervals to obtain a frequency-amplitude curve.

Optionally, fourier analysis is performed on the temperature-time curve obtained at any previous time point at preset time intervals to obtain a frequency-amplitude curve.

Optionally, the melt temperature does not change drastically such that the difference in the change in the melt temperature is within a threshold range of error.

The present application also provides a method of producing single crystal silicon by the czochralski method, the method comprising determining a seeding temperature based on the method of determining a seeding temperature of a single crystal furnace as described above.

In order to solve the technical problems existing at present, the application provides a method for determining the seeding temperature of a single crystal furnace and a method for preparing single crystal silicon by a Czochralski method, wherein Fourier analysis is introduced to analyze the period of temperature fluctuation and assist in judging the stability of the solution temperature. Before seeding, parameters in the single crystal furnace are usually unchanged to keep the melt temperature stable, and the solution temperature fluctuation is caused by fluid instability. The instability presents a certain periodicity when various parameters in the single crystal furnace are unchanged, so that the temperature fluctuation also presents a certain periodicity. Therefore, the period of the melt temperature fluctuation at each stage can be observed by Fourier analysis, so as to judge the stability of the seeding temperature. According to the method, the accuracy of the stability judgment of the seeding temperature is improved and the wire breakage rate caused by misjudgment of the seeding temperature is reduced through Fourier analysis assistance and a time-temperature curve.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail embodiments of the present invention with reference to the attached drawings. The accompanying drawings are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings, like reference numbers generally represent like parts or steps. In the drawings, there is shown in the drawings,

FIG. 1 is a schematic flow chart illustrating a method for determining a seeding temperature of a single crystal furnace according to an embodiment of the present application;

FIG. 2 is a schematic illustration of a temperature-time curve as described in an embodiment of the present application;

FIG. 3 is a schematic diagram of a frequency-amplitude curve in an embodiment of the present application;

FIG. 4 is a schematic diagram of a frequency-amplitude curve as a standard reference curve in an embodiment of the present application.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present application. It will be apparent, however, to one skilled in the art, that the present application may be practiced without one or more of these specific details. In other instances, well-known features of the art have not been described in order to avoid obscuring the present application.

It is to be understood that the present application is capable of implementation in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like reference numerals refer to like elements throughout.

It will be understood that, although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application.

Spatial relational terms such as "under," "below," "under," "above," "over," and the like may be used herein for convenience in describing the relationship of one element or feature to another element or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term "and/or" includes any and all combinations of the associated listed items.

Embodiments of the invention are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the present application. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present application should not be limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the present application.

In order to solve the existing problems, the adopted solution is that the temperature is equal to the freezing point through the characteristic that the solid and liquid coexist, and the temperature is set as the seeding temperature when no change is detected for more than 5 minutes continuously in the material melting process. In the later stage of material melting, the temperature is stabilized at the seeding temperature for more than 20 minutes by utilizing automatic power control, and then seeding is started. However, the method does not describe how to determine whether the seeding temperature is stable in the case of a drastic fluctuation in temperature after suppressing the convection of the fluid by adding the magnetic field.

In the preparation of large size semiconductor grade single crystal silicon by the czochralski method, a magnetic field is generally used to control melt convection to control crystal defects, oxygen content and impurity distribution. The added magnetic field inhibits the convection of the melt, the hot melt at the crucible wall is difficult to quickly reach the liquid level, the temperature change from the manual temperature adjustment to the liquid level has the delay of several hours, so that a great deal of time is consumed in the process of searching for the seeding temperature, the productivity is influenced, and the temperature fluctuation degree of the melt is also enhanced by the introduction of the magnetic field.

In order to solve the problems of the present application, the present invention provides a method of determining a seeding temperature of a single crystal furnace, as shown in fig. 1, the method comprising:

step S1: measuring the temperature of a melt for seeding in the single crystal furnace before seeding, and obtaining a temperature-time curve;

step S2: carrying out Fourier analysis on the temperature-time curve to obtain a frequency-amplitude curve;

step S3: and after judging that the temperature of the melt is not changed violently according to the temperature-time curve, taking a frequency-amplitude curve with stable seeding temperature as a standard reference curve, and comparing the obtained frequency-amplitude curve with the standard reference curve to judge whether the seeding temperature is stable.

Fourier analysis is introduced into the method to analyze the period of temperature fluctuation and assist in judging the stability of the solution temperature. Before seeding, parameters in the single crystal furnace are usually unchanged to keep the melt temperature stable, and the solution temperature fluctuation is caused by fluid instability. The instability presents a certain periodicity when various parameters in the single crystal furnace are unchanged, so that the temperature fluctuation also presents a certain periodicity. Therefore, the period of the melt temperature fluctuation at each stage can be observed by Fourier analysis, so as to judge the stability of the seeding temperature. According to the method, the accuracy of the stability judgment of the seeding temperature is improved and the wire breakage rate caused by misjudgment of the seeding temperature is reduced through Fourier analysis assistance and a time-temperature curve.

The earphone of the present application is described in detail with reference to the accompanying drawings, wherein fig. 1 is a schematic flow chart of a method for determining a seeding temperature of a single crystal furnace according to an embodiment of the present application; FIG. 2 is a schematic illustration of a temperature-time curve as described in an embodiment of the present application; FIG. 3 is a schematic diagram of a frequency-amplitude curve in an embodiment of the present application; FIG. 4 is a schematic diagram of a frequency-amplitude curve as a standard reference curve in an embodiment of the present application.

The method for determining the seeding temperature of a single crystal furnace described in this application is applied to the Czochralski method for producing a single crystal in a single crystal furnace, but it should be noted that the method is also applied to other Czochralski methods.

In the step S1, the raw material silicon material is heated in a single crystal furnace to form a melt. Specifically, the single crystal furnace is provided with a main furnace chamber and a control system, a heating device for heating silicon materials in a crucible is arranged in the main furnace chamber, and a temperature measuring device is arranged on the outer surface of the main furnace chamber and can be an infrared thermometer.

When the temperature of the melt is measured in the step, the temperature of the melt can be continuously measured in real time to obtain a temperature-time curve;

further, the temperature of the melt for seeding in the single crystal furnace is measured at predetermined time intervals, which are fixed time periods, for example, in one embodiment, the temperature is measured once every 10 seconds.

Wherein after the temperature measurement of the melt, the temperature measurement results can be output in real time, for example, once every 10s, and the temperature at each temperature measurement time point is output in real time, and a temperature-time curve is established according to the time and the temperature.

In addition, the average temperature in the set time period may also be output, for example, in an embodiment, the temperature is measured once every 10s, but the temperature at each temperature measurement time point is not output in real time, but an average value of 12 temperatures collected within 2 minutes is calculated and the calculated average temperature is output, and a temperature-time curve is established according to the time and the average temperature.

In one example, shown in FIG. 2, which is a temperature-time plot of 2 hours prior to initiation of seeding, the data used is an average temperature of 2 minutes.

From the temperature-time curve shown in fig. 2, there was a significant drop in temperature in the previous hour, so the temperature was not stable in the previous hour and slightly fluctuated in the latter hour, but it was still difficult to determine whether the temperature had stabilized.

For this purpose, step S2 is performed to perform fourier analysis on the obtained temperature-time curve to obtain a frequency-amplitude curve.

In this step, fourier analysis is performed on the obtained temperature-time curve at preset time intervals to obtain a frequency-amplitude curve. The resulting temperature-time curve is fourier analyzed, for example, every 10 s.

Optionally, fourier analysis is performed on the temperature-time curve obtained at any previous time point at preset time intervals to obtain a frequency-amplitude curve. In one embodiment of the present application, fourier analysis of the previous hour melt temperature change at regular intervals yields an image of the frequency-amplitude curve. By observing the peak position from the frequency-amplitude curve, the period of the temperature fluctuation can be clearly known.

In the step S3, it is first determined that there is no drastic change in the melt temperature according to the temperature-time curve, and when it is determined that there is no drastic change in the melt temperature, it may be further determined whether the melt temperature is stable in combination with the frequency-amplitude curve.

The judgment method for the existence of the violent change of the melt temperature is to preset an acceptable temperature error threshold range, and the melt temperature is judged to have no violent change if the change difference value of the melt temperature is within the error threshold range.

Specifically, with the fluctuation period of the seeding temperature of a certain single crystal furnace as a reference, seeding can be started when the same periodicity occurs and the time average temperature is stable. In one embodiment, the frequency-amplitude curve with stable seeding temperature is used as a standard reference curve, and the obtained frequency-amplitude curve is compared with the standard reference curve to obtain a comparison result.

In the present application, a frequency-amplitude curve in which the seeding temperature is stable is detected and recorded as a reference for the fluctuation period of the seeding temperature, and the fluctuation period of the seeding temperature obtained in real time is compared with the reference to determine whether the temperature is stable.

Wherein comparing the obtained frequency-amplitude curve with a standard reference curve comprises:

and comparing the position and amplitude value of the amplitude peak value appearing in the obtained frequency-amplitude curve with the position and amplitude value of the corresponding amplitude peak value in the standard reference curve, wherein if the position and amplitude value of the amplitude peak value in the frequency-amplitude curve and the standard reference curve correspond to each other, the seeding temperature is stable, and if the position and amplitude value cannot correspond to each other, the seeding temperature is unstable.

In another embodiment, comparing the resulting frequency-amplitude curve to a standard reference curve comprises:

firstly, judging whether the position of the amplitude peak value in the frequency-amplitude curve corresponds to the position of the amplitude peak value in the standard reference curve, and then judging whether the amplitude peak value corresponds to the standard reference curve;

after the positions of the amplitude peak values in the frequency-amplitude curve and the standard reference curve correspond to each other, it may be determined whether all the amplitude values correspond to each other, and in order to simplify the steps, in an embodiment, the sizes of all the amplitude values may not be compared, and it is only necessary to determine whether an amplitude value difference of a specific amplitude peak value among the amplitude peak values of the frequency-amplitude curve and the standard reference curve is within a preset threshold, where the amplitude peak value at a position where the frequency is close to 0 is usually selected, when the amplitude value difference of the specific amplitude peak value among the amplitude peak values of the frequency-amplitude curve and the standard reference curve is within the preset threshold, the seeding temperature is stable, and if the amplitude value difference exceeds the preset threshold, the seeding temperature is unstable.

In the present application, the method and criteria for determining whether the amplitude peaks in the frequency-amplitude curve and the standard reference curve correspond to each other are:

presetting a set threshold value of a position difference value of an amplitude peak value, and if the difference value of the position of the amplitude peak value in a frequency-amplitude curve and the position of the amplitude peak value in a standard reference curve is within the set threshold value, determining that the amplitude peak values in the frequency-amplitude curve and the standard reference curve correspond to each other;

A specific embodiment of the present application will be described in detail with reference to fig. 2 and 3.

In this embodiment, the infrared thermometer may output a temperature that is 10 seconds apart and an average temperature of 2 minutes. FIG. 2 is a temperature-time curve 2 hours before seeding initiation, and the data used are 2 minute average temperatures. Fig. 3 is a graph of the frequency distribution over the time period, using data for temperatures at 10 second intervals.

And (3) from the temperature-time curve, the temperature is obviously reduced in the previous hour, and the temperature is considered to be unstable in the previous hour when the variation difference exceeds the error threshold range. There is a slight fluctuation beyond the latter hour, the difference in variation being within the error threshold, but it is difficult to determine whether the temperature has stabilized.

From the profile of the frequency-amplitude curve, where the frequencies (amplitude peaks) 1-3 represent the periodicity of the melt flow and the frequency (amplitude peak) 4 is close to a value of 0, the stronger the aperiodic the melt flow.

At 0-1h, the frequencies (peak amplitude values) 1 and 4 are strong, and the melt has certain periodicity but is unstable.

At 0.5-1.5h, frequencies (peak amplitude values) 2 and 3 appeared, frequency (peak amplitude value) 4 decreased, and the melt periodicity increased.

At 1-2h, the frequency (peak amplitude value) 4 is further reduced, and the frequencies (peak amplitude values) 2 and 3 are more significant.

Comparing the frequency-amplitude curve obtained in fig. 3 with the standard reference curve in fig. 4, it can be seen that the positions of the peak amplitude values 1-4 in the frequency-amplitude curve and the peak amplitude values 1' -4' in the standard reference curve correspond to each other, and the difference between the peak amplitude value 4 in the frequency-amplitude curve and the peak amplitude value 4' in the standard reference curve is within the preset threshold, at which time the melt tends to be stable and can be seeded.

Although the example embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the above-described example embodiments are merely illustrative and are not intended to limit the scope of the present application thereto. Various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the scope or spirit of the present application. All such changes and modifications are intended to be included within the scope of the present application as claimed in the appended claims.

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

In the several embodiments provided in the present application, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the above-described device embodiments are merely illustrative, and for example, the division of the units is only one logical functional division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another device, or some features may be omitted, or not executed.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the application may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the description of exemplary embodiments of the present application, various features of the present application are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the application and aiding in the understanding of one or more of the various inventive aspects. However, the method of the present application should not be construed to reflect the intent: this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this application.

It will be understood by those skilled in the art that all of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where such features are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Furthermore, those skilled in the art will appreciate that while some embodiments described herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the application and form different embodiments. For example, in the claims, any of the claimed embodiments may be used in any combination.

It should be noted that the above-mentioned embodiments illustrate rather than limit the application, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The application may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The usage of the words first, second and third, etcetera do not indicate any ordering. These words may be interpreted as names.

Claims

1. A method for determining a seeding temperature of a single crystal furnace, the method comprising:

2. The method of claim 1, wherein the determining whether the seeding temperature is stable comprises:

3. The method of claim 2, wherein the method comprises:

4. The method of claim 3, wherein determining whether amplitude peaks in the frequency-amplitude curve and the standard reference curve correspond to each other comprises:

5. The method according to claim 1, wherein the temperature of the melt for seeding in the single crystal furnace is measured at predetermined time intervals, and a temperature-time curve is obtained.

6. The method of claim 5, wherein the temperature of the melt is a temperature at a measurement time point or an average temperature over a set period of time.

7. The method of claim 1, wherein the temperature-time curve obtained is fourier analyzed at preset time intervals to obtain a frequency-amplitude curve.

8. The method of claim 7, wherein the temperature-time curve obtained at any previous time point is Fourier analyzed at preset time intervals to obtain a frequency-amplitude curve.

9. The method of claim 1, wherein the absence of a drastic change in the melt temperature is a difference in the change in the melt temperature within a threshold error value.

10. A method for producing single crystal silicon by the czochralski method, characterized in that the method comprises determining a seeding temperature based on the method for determining a seeding temperature of a single crystal furnace according to any one of claims 1 to 9.