WO2012031417A1

WO2012031417A1 - Method for controlling defects in czochralski silicon single crystal rod

Info

Publication number: WO2012031417A1
Application number: PCT/CN2010/077860
Authority: WO
Inventors: 戴小林; 吴志强; 邓树军; 崔彬; 姜舰; 王雅南; 周旗钢; 张果虎; 屠海令; 肖清华
Original assignee: 有研半导体材料股份有限公司
Priority date: 2010-09-08
Filing date: 2010-10-19
Publication date: 2012-03-15
Also published as: CN102400210A

Abstract

Disclosed is a method for controlling the defects in Czochralski silicon single crystal rod, wherein the shape of crystal growth interface, temperature gradient of the interface and crystal growth speed can be regulated by controlling the number of heat insulation cylinders, each layer thickness, wall thickness of the cylinders and their combinations so as to control the defects in Czochralski silicon single crystal rod. The heat insulation cylinders are located at the upper heat insulation seat of the heat field in furnace chamber of Czochralski single crystal furnace. The control principle is as follows: the increase in the number or the thickness of heat insulation cylinders corresponds to the decrease in temperature gradient of molten silicon surface, which makes the crystal growth interface more even and the defects in single crystal distribute more uniformly, meanwhile, which may decrease the maximum speed of crystal growth. The decrease in the number of heat insulation cylinders corresponds to the increase in temperature gradient of molten silicon surface, which makes the crystal growth interface more uneven and is not convenient for the uniform distribution of the defects in single crystal, meanwhile, which may increase the maximum speed of crystal growth. The control method is advantageously simple and substantially efficient.

Description

Method for adjusting defects in Czochralski silicon single crystal rods

The invention relates to a method for adjusting defects in a Czochralski silicon single crystal rod. In particular, the shape of the crystal growth interface, the temperature gradient of the interface, and the crystal growth are adjusted by adjusting the number of the holding drums and the wall thickness of the drum provided on the heat-insulating cylinder seat in the furnace of the Czochralski furnace. The method of speed is achieved by adjusting the defects in the Czochralski silicon single crystal rod.

Background technique

Approximately 85% of the semiconductor silicon single crystals for integrated circuits are fabricated by the Czochralski method. In this method, polycrystalline silicon is packed into a quartz crucible, and after heating and melting, the molten silicon is slightly cooled, giving a certain degree of subcooling, and a specific crystal orientation of the silicon single crystal (called seed crystal) and the melt. Silicon contact, by adjusting the temperature of the melt and the upward lifting speed of the seed crystal, when the seed crystal grows to near the target diameter, the lifting speed is increased, and the single crystal is grown near the constant diameter. In the final stage of the growth process, the silicon melt in the crucible has not yet been fully proposed. By increasing the crystal lifting speed and adjusting the heating energy to the crucible, the crystal diameter is gradually reduced to form a tail cone, when the cone is When the tip is small enough, the crystal will detach from the melt, thereby completing the crystal growth process.

There are two types of point defects widely found in silicon single crystals: silicon interstitial atoms and vacancies. In a nutshell, if a silicon atom is trapped in a normal lattice region of a silicon, the silicon atom is called a silicon interstitial atom, see Figure 4b. The presence of silicon interstitial atoms causes the local silicon lattice to be stressed (outward pressure); if a silicon atom is removed in the normal silicon lattice region, the remaining gap is called "vacancy", see Figure 4c. The vacancy causes the crystal lattice around it to be subjected to inward pressure. If there is more vacancy defect in a silicon crystal, or "predominant", this crystal is called a vacancy crystal (V-rich); conversely, a crystal dominated by a silicon interstitial crystal is called a silicon-rich interstitial crystal (I- Rich). With As the crystal grows, the temperature of the crystal changes from the melting point of silicon to room temperature. These two point defects will be complicated with other surrounding atoms (including oxygen, carbon, nitrogen, silicon, etc.) by complexing, diffusing, and agglomerating. Form more complex defects.

After theoretical calculation and actual verification, there is a critical parameter in the silicon single crystal.

Here, V refers to the crystal growth rate at the crystal growth interface, and G refers to the longitudinal temperature gradient at the crystal growth interface. When the actual _{real is} greater than ξ. At the time, the instant grows into a V-rich crystal; when the actual _{real is} less than ξ. At the moment, a silicon-rich interstitial (I-rich) crystal is formed in an instant. It can be partially understood that the growth rate and the longitudinal temperature gradient of the growth interface crystal together determine the defect type and distribution at the initial stage of crystal growth. This theory was first proposed by VV Voronkov and is widely recognized by industry insiders.

Modern integrated circuits (IC processes) are mostly made of a polishing pad or an epitaxial wafer processed by cutting, grinding, polishing, and cleaning a silicon single crystal rod. Depending on the application, a different number of "test strips" (called "Test and Monitor Wafer" are used to monitor IC process parameters such as particle, focus, oxide or diffusion layer quality, etc.) "(called "Prime Wafer", used to make circuit chips), etc., they have different requirements for defects in silicon single wafers. For example: "Test strips" for monitoring particle levels in small environments are best for interstitial silicon-type (I-rich) wafers, while fast-drawing epitaxial V-rich sheets are commonly used. Positive film (Prime Wafer).

Now back to the point of the problem: How to control the longitudinal e _al in the vicinity of "=0.0013cm ² .min - K- ¹ in the process of crystal equal diameter growth. In engineering, there are many means to be used, many means are manufacturing The enthusiasm of the business is generally not open. For example: The thermal field consisting of graphite parts and insulation materials in the single crystal furnace chamber is very important; in addition, by adjusting the enthalpy, tumbling, and crystal transformation , crystal growth rate, etc. can also adjust G (temperature gradient at the solid-liquid interface) or V (longitudinal growth rate of crystal).

As we all know, the upper part of the thermal field of the single crystal furnace (referred to as "upper holding zone" in Figure 2) affects the temperature field distribution of the single crystal furnace (mainly the axial temperature gradient and radial temperature gradient near the growth interface). The largest, the following theoretical formula is proved: The maximum theoretical growth rate of the crystal: ^ is proportional to -~ or -~ ^G ;

(AH) p _c dz (AH) p _c is the thermal conductivity of the silicon crystal; AH is the entropy change upon crystallization; _A is the density of the silicon crystal; or G dz is the axial temperature gradient at the solid-liquid interface.

The expression of the initial vacancy concentration C _v of the crystal: C _v = (Cvo - Go)(l - (ξο / )), where: ^ is the vacancy concentration in the crystal near the growth interface; C _vQ is the melting point of silicon The vacancy equilibrium concentration at temperature; C _lQ is the equilibrium concentration of silicon interstitial atoms at the melting point of silicon; it is the critical number of V/G (V and G when the crystal hollow position at the solid-liquid interface is equivalent to the silicon self-interstitial atom concentration) G is the longitudinal growth rate and the longitudinal temperature gradient at the growth interface, respectively; For the actual growth interface, it can be seen from the above formula that the thermal field temperature gradient G has a great influence on the crystal growth, and the number of turns = V/G is determined. An important parameter for the growth rate and defects of silicon crystals. In order to control and change the V/G value, the traditional adjustment method is to change the shape of the heater, the structural charge of the heat shield, and the process parameters when changing the crystal growth: such as crystal rotation, twisting and clamping. Obviously, these adjustment methods are more complicated and the results are not satisfactory.

Thus, the present invention provides a method of adjusting the crystal growth rate and the growth interface temperature gradient and the shape of the interface, which can adjust the distribution of defects in the silicon single crystal rod.

Summary of the invention The object of the present invention is to provide a method for adjusting defects in a Czochralski silicon single crystal rod, which can adjust the shape of the growth interface, adjust the crystal growth rate and the temperature gradient of the interface, and the method can be applied to a Czochralski silicon single crystal furnace. Device.

In order to achieve the above object, the present invention adopts the following technical solutions:

The method for adjusting the defects in the Czochralski silicon single crystal rod is to adjust the number of the heat preservation drums, the thickness of each layer, and the wall of the drum by adjusting the heat preservation cylinder seat located in the heat chamber of the CZ furnace. Thickness or a combination thereof, thereby adjusting the shape of the crystal growth interface, the temperature gradient of the interface, and the crystal growth rate, achieves adjustment of the defects in the Czochralski silicon single crystal rod.

The upper heat preservation cylinder seat can be provided with a plurality of annular grooves, and the heat preservation drum is inserted in the annular groove, and the number of the heat preservation drums is one or more.

The annular groove has a cross-sectional shape of a square or a U shape. The cross-sections of the plurality of annular grooves opened in the upper heat-insulating cylinder base may be all square or all U-shaped or square-shaped alternately with U-shaped.

The width W of the cross section of the annular groove, the depth H, and the rounded corner R are 1.5-200 mm, 1.5-50 mm, and 1-50 mm, respectively.

The insulated drum has a wall thickness of 1.4-200 mm.

The material of the heat preservation drum is molybdenum, graphite, carbon-carbon composite material (commonly known as carbon fiber material), solidified carbon felt, graphite soft felt or a combination thereof.

The insulated drum is also referred to as "upper insulation".

The shape of the growth interface, the rate of crystal growth, and the temperature gradient of the interface were adjusted by adjusting the number and thickness of the increased holding drums. The principle of adjustment is as follows: Increasing the number or thickness of the holding cylinder is equivalent to lowering the temperature gradient of the surface of the molten silicon, making the crystal growth interface flatter; making the distribution of defects in the crystal more uniform and reducing the maximum speed of crystal growth. Reducing the number of holding drums is equivalent to increasing the temperature gradient of the surface of the molten silicon, making the crystal growth interface more uneven; it is not conducive to uniform distribution of defects in the crystal, but can increase the maximum speed of crystal growth.

The "maximum speed of crystal growth" here refers to the maximum allowable speed when the crystal diameter is not distorted when the crystal is grown in a specific thermal field, process parameters, and crystal growth.

The advantages of the invention are: The method is simple and effective.

DRAWINGS

Figure 1: Schematic diagram of the thermal field of a Czochralski silicon single crystal furnace.

Figure 2: Schematic diagram of the thermal field of a Czochralski silicon single crystal furnace.

Fig. 3 is a schematic view showing the thermal field adjustment of a Czochralski silicon single crystal furnace of the present invention.

Figure 4a: Intrinsic Schematic of a Czochralski Silicon Single Crystal (Perfect Silicon Lattice).

Figure 4b: Schematic diagram of intrinsic defects in a Czochralski silicon single crystal (silicon self-interstitial atoms).

Figure 4c: Schematic diagram of intrinsic defects in a Czochralski silicon single crystal (silicon vacancies).

Figure 5: Schematic diagram of the interface (solid-liquid interface) between a silicon single crystal rod and a silicon melt.

Figure 6a: Schematic diagram of the upper holding cylinder seat with square grooves.

Figure 6b: Schematic diagram of two upper insulation (heat preservation drums) on the square groove of Figure 6a. Figure 7a: Schematic diagram of the square groove and U-shaped groove on the upper insulation cylinder base.

Figure 7b: When a square groove is formed in the upper insulation cylinder seat, its height is indicated by H and the width is represented by W.

Figure 7c: When the U-shaped groove is opened on the upper holding cylinder base, its height is indicated by H, the width is represented by W, and the rounded corner is indicated by R.

Figure 8a: Schematic diagram of the effect of seed insulation on the shape of the interface. Figure 8b: Schematic diagram of the effect of another thermal insulation on the shape of the interface.

Figure 8c: A schematic diagram of the effect of upper insulation on the shape of the interface.

Figure 9: Maximum growth rate of the crystal under different conditions of insulation.

Figure 0 _: FPD density at different locations in a silicon single crystal rod under different conditions of thermal insulation. Figure 〖i: The shape of the streamline defect (called FPD defect) in a silicon single crystal observed under a microscope.

In Fig. 1, after entering the argon gas from the top, it flows along the periphery of the crystal from the furnace 21 and the intermediate heat preservation 6, and finally exits from the gas outlets 17 (2-4). The components in Figure 1 are as follows: upper furnace 1, furnace cover 2, guide tube 3, upper insulation 4, upper thermal insulation cylinder base 5, medium thermal insulation cylinder 7, heater 8, lower furnace 9, medium thermal insulation 10, lower insulation 11, lower insulation tube 12, bottom insulation 13, electrode 15, electrode plate 16, lower shaft 18, bottom 19, centering plate 20, graphite crucible 22, quartz crucible 23, silicon melt 24, thermal insulation The barrel 25 has a hole in its side for gas flow, a single crystal 26, and a seed crystal 27.

In Fig. 2, according to the general habit, the thermal field is divided into an upper heat preservation zone, a medium heat preservation zone and a lower heat retention zone. The upper heat preservation zone is located above the silicon melt, and is mainly composed of a draft tube 3, an upper heat preservation 4, an upper heat preservation cylinder 25, and an upper heat preservation cylinder base 5. The medium heat preservation zone is in the part of the heater, and the main components are composed of a heater 8, a medium heat preservation 6, a medium heat insulation tube 7, and a medium heat insulation tube holder 10. The lower holding zone is at the bottom of the temperature field, and the main components are composed of lower insulation 11, lower insulation cylinder 12 and bottom insulation 13.

In Fig. 3, compared with Fig. 1, the original flat-type upper thermal insulation cylinder base 5 is changed to an upper thermal insulation cylinder holder 5' having a plurality of grooves and a groove width changeable, and the original upper thermal insulation 4 is changed into There are more than 2 upper holding drums 4-1 or 4-2 whose thickness and material can be changed. The number, thickness and material of these upper holding drums can be adjusted according to the thickness. The material of the upper heat insulating tube may be graphite, graphite soft felt, graphite hard felt or molybdenum, or a combination thereof. In Figures 4a, 4b, and 4c, each small circle represents a silicon atom.

In Fig. 5, 24 is a silicon melt, 26 is a silicon single crystal rod, and 28 is a solid-liquid interface.

detailed description

Example 1

On the 24Z thermal field of MCZ CZ150, a polysilicon material of 130KG was loaded, and a 207 mm diameter silicon single crystal with a crystal orientation of 100 was grown. The shape of the solid-liquid interface after using different upper thermal insulation structures is shown in Fig. 8a, Fig. 8b, Fig. 8c. . The sample is taken from the equal-diameter 400 mm portion of the crystal, and after a specific heat treatment method, the shape of the solid-liquid interface can be displayed.

Fig. 8a, Fig. 8b, and Fig. 8c are the interface shapes when different insulation layers, thicknesses, and materials are used, respectively. The shape of the interface can be represented by its arc down or up and the height of the arc.

Figure 8a shows the addition of a 30 mm thick solidified carbon felt to the upper holding cylinder. The results of the interface shape measurement are: arc down, height 5 mm, not very flat;

Figure 8b shows a 2 mm thick molybdenum cylinder (made as an inner layer) and a 20 mm thick graphite barrel (made as an outer layer) on the upper holding cylinder base as the upper insulation. The measurement of the interface shape is : The arc is still down, but the height is reduced to 2.3 mm, which is flatter than the previous one;

Figure 8c shows the addition of three layers of 50 mm thick cured carbon felt to the upper holding sleeve, with a gap of 2-5 mm between each barrel. The total thickness of the upper insulation is 150 mm. The shape of the detected interface shape is: the arc is W-shaped and the height is only 1.5 mm, which is relatively flat; it can be seen that the shape of the solid-liquid interface is more controllable and flat after the number of layers and thickness of the upper insulation is increased. The units in the figure are all millimeters.

Example 2

On the MCZ CZ150 24 inch thermal field, the polysilicon material is loaded into 180KG, and the growth crystal orientation is 100. The 207 mm diameter crystal, the crystal begins to finish at 155 KG, and the weight of the remaining polysilicon is about 15-20 KG. The test compares the maximum pulling speed of the crystal in the case of the equal length of the crystal at 60 mm, 500 mm, and 1100 mm (the phenomenon that the ingot will be twisted beyond this speed).

• The curve is the highest speed curve of the crystal when it is insulated into a 40 mm thick cured carbon felt;

The curve of the country is the highest drawing speed curve of the crystal when the three layers of solidified carbon felt with a thickness of 40 mm are respectively insulated. At this time, the number of layers of the upper insulation layer is three, and the total thickness is 120 mm. The results show that reducing the thickness of the upper insulation can increase the crystal growth rate by 20-27%. The result is shown in Figure 9.

Example 3

On the MCZ CZ150 24 inch thermal field, a 150 KG polysilicon material was placed to grow a 207 mm diameter crystal with a crystal orientation of 100. Figure 10 is a graph showing the distribution of defects in crystals when using different thermal insulation layers and materials. The abscissa of the graph is the crystal isometric length (mm), and the ordinate is the density of the FPD defects (per/cm 2 ). FPD It is a vacancy type structural defect of a silicon single crystal, which is also called a streamline type defect. After the surface treatment of the single crystal sample, in the SC-1 solution, no agitation was carried out for 30 minutes, and then the density was counted under a microscope after rinsing. In Figure 10 (counting from top to bottom), the three curves are made of three layers of cured carbon felt each having a thickness of 30 mm, and a layer of 30 mm thick cured carbon felt for insulation. The 2 mm molybdenum cylinder is used as the upper insulation. The results show that the density distribution of FPD defects (a vacancy type defect, or D defect) in the crystal changes significantly after adjusting the thickness and material of the upper insulation layer, indicating that the patented invention can be used as a kind of adjustment of intra-crystal defects. The means of distribution. Figure 11 is a streamlined defect (referred to as FPD defect) in a silicon single crystal. The shape observed under the microscope has three inverted V words representing one FPD defect.

Claims

Rights request

1. A method for adjusting defects in a Czochralski silicon single crystal rod, characterized in that: it is a quantity of insulation drums arranged on the heat preservation cylinder seat of the furnace in the furnace of the CZO single furnace, The thickness, the wall thickness of the drum or a combination thereof, thereby adjusting the shape of the crystal growth interface, the temperature gradient of the interface, and the crystal growth rate, achieve the adjustment of defects in the Czochralski silicon single crystal rod.

2. The method for adjusting defects in a Czochralski silicon single crystal rod according to claim 1, wherein the upper heat insulating cylinder base is provided with a plurality of annular grooves, and the heat preservation drum is inserted in the annular groove. The number of holding drums is one or more.

3. The method for adjusting defects in a Czochralski silicon single crystal rod according to claim 1 or 2, wherein: the annular groove has a cross-sectional shape of a square shape or a U shape.

The method for adjusting defects in a Czochralski silicon single crystal rod according to claim 3, wherein the width W of the cross section of the annular groove, the depth H, and the radius R are 1.5-200 mm, respectively. , 1.5-50 mm, 1-50 mm.

5. A method of adjusting defects in a Czochralski silicon single crystal rod according to claim 4, wherein: said insulated drum has a wall thickness of 1.4 to 200 mm.

The method for adjusting defects in a Czochralski silicon single crystal rod according to claim 1, wherein the material of the heat preservation drum is molybdenum, graphite, carbon-carbon composite material, solidified carbon felt, Graphite soft felt or a combination thereof.