Apparatus and Method for Silicon Carbide Crystal Expansion Growth

Abstract

This invention provides a silicon carbide crystal diameter expansion growth apparatus and method, relating to the field of crystal growth. The diameter expansion growth apparatus and method arranges a powder chamber and a seed crystal horizontally and sets up a horizontally extending gas phase channel. The crystal growth gas phase formed in the powder chamber can flow horizontally to the uniformly rotating seed crystal in the gas phase channel. In this way, the crystal can grow rapidly and uniformly at various parts of the seed crystal peripheral wall, thereby improving the efficiency and growth quality of crystal diameter expansion growth.

Description

Technical Field

[0001] This invention relates to the field of crystal growth, and more specifically, to a silicon carbide crystal diameter expansion growth apparatus and method. Background Technology

[0002] The growth of silicon carbide crystals based on the PVT method generally has two modes: thickening growth (i.e., axial growth, increasing crystal thickness) and diameter expansion growth (i.e., radial growth, increasing crystal diameter). These two crystal growth modes can be selected or carried out simultaneously.

[0003] However, silicon carbide crystal growth devices in related technologies generally suffer from slow radial growth rate and uneven circumferential growth rate when performing diameter expansion growth (i.e., crystal diameter expansion growth), resulting in low crystal growth diameter expansion efficiency and poor diameter expansion quality. Summary of the Invention

[0004] The present invention aims to provide a silicon carbide crystal diameter expansion growth apparatus and method, which can improve the crystal diameter expansion growth efficiency and circumferential uniformity, and improve the crystal diameter expansion growth quality.

[0005] The embodiments of the present invention can be implemented as follows:

[0006] In a first aspect, the present invention provides a silicon carbide crystal diameter expansion growth apparatus, comprising:

[0007] A crucible, wherein a porous graphite plate is disposed inside the crucible, and the porous graphite plate and the side wall of the crucible together form a powder cavity for holding silicon carbide powder. The crucible has a gas phase channel extending in a horizontal direction inside, the gas phase channel being located on the side of the porous graphite plate away from the powder cavity, and the width of the gas phase channel gradually increases in the direction away from the powder cavity.

[0008] A movable rod is inserted vertically through the top wall of the crucible. A seed crystal is coaxially disposed at the bottom end of the movable rod. The seed crystal is located in the gas phase channel. The seed crystal can rotate at a constant speed in the gas phase channel under the drive of the movable rod, and at the same time move horizontally away from the powder cavity.

[0009] A heater, arranged around the crucible, is used to create a thermal field inside the crucible, so that the crystal growth vapor formed by the sublimation of silicon carbide powder can pass through the porous graphite plate and enter the vapor channel, and grow crystals on the peripheral wall of the seed crystal.

[0010] In an optional embodiment, the gas phase channel has opposing first and second sidewalls in the width direction, and during the horizontal movement of the seed crystal, the distance between the axis of the seed crystal and the first sidewall and the distance between the axis of the seed crystal and the second sidewall are always equal.

[0011] In an optional embodiment, the top and bottom walls of the crucible are respectively provided with L-shaped flow guide blocks, and the horizontal portions of the two flow guide blocks are parallel to each other and respectively constitute the upper and lower walls of the gas phase channel.

[0012] In an optional embodiment, a polycrystalline chamber is provided inside the crucible, the polycrystalline chamber is located below the gas phase channel, and the inlet of the polycrystalline chamber is connected to the outlet of the gas phase channel to guide the growing crystal gas phase passing through the gas phase channel into and crystallize.

[0013] In an optional embodiment, a weighing rod is connected to the bottom of the polycrystalline chamber, the weighing rod passing vertically through the bottom wall of the crucible and connected to a weighing device outside the crucible.

[0014] In an optional embodiment, the top wall of the crucible is provided with a strip-shaped hole and a sealing plate for sealing the strip-shaped hole. The movable rod passes through the sealing plate and can rotate relative to the sealing plate. During the process of the movable rod driving the sealing plate to slide horizontally on the top wall of the crucible, the sealing plate always completely seals the strip-shaped hole.

[0015] In an optional embodiment, the crucible is further provided with a transition cavity, which is located on the side of the porous graphite plate away from the powder cavity, and the side of the transition cavity away from the porous graphite plate is connected to the inlet of the gas phase channel.

[0016] Secondly, the present invention provides a method for expanding the diameter of a silicon carbide crystal, based on the silicon carbide crystal expansion growth apparatus described in the foregoing embodiments, comprising:

[0017] After the silicon carbide powder is filled, the heater is started so that the crystal growth gas phase formed by the sublimation of the silicon carbide powder passes through the porous graphite plate and enters the gas phase channel;

[0018] The movable rod is controlled to drive the seed crystal to rotate at a constant speed, and at the same time, the movable rod is controlled to drive the seed crystal to move horizontally in a direction away from the powder cavity.

[0019] In an optional embodiment, the horizontal movement rate of the seed crystal is determined according to the weight change rate of the polycrystalline chamber, wherein the polycrystalline chamber is located inside the crucible and the inlet of the polycrystalline chamber is connected to the outlet of the gas phase channel to guide the growing crystal gas phase passing through the gas phase channel into and crystallize.

[0020] In an alternative embodiment, the heater is configured to create a thermal field in which the temperature gradually decreases in the region containing the powder chamber, the region containing the gas phase channel, and the region containing the polycrystalline chamber.

[0021] The beneficial effects of the silicon carbide crystal diameter expansion growth apparatus and method provided in the embodiments of the present invention include:

[0022] This diameter expansion growth apparatus and method uses a horizontally arranged powder chamber and seed crystal, and a horizontally extending gas phase channel. The crystal growth gas phase formed in the powder chamber can flow horizontally to the uniformly rotating seed crystal in the gas phase channel. This enables rapid and uniform crystal growth at various parts of the seed crystal's peripheral wall, thereby improving the efficiency and quality of crystal diameter expansion growth. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 A schematic diagram of the structure of the silicon carbide crystal diameter expansion growth apparatus provided in this embodiment of the invention when resistance heating is used;

[0025] Figure 2 This is a schematic diagram of the structure of the silicon carbide crystal diameter expansion growth apparatus provided in an embodiment of the present invention when inductive heating is used;

[0026] Figure 3 This is a top view of the seed crystal moving horizontally within the gas phase channel, as provided in an embodiment of the present invention.

[0027] Icons: 100-Crucible; 102-Strip hole; 110-Porous graphite plate; 112-Powder chamber; 114-Transition chamber; 120-Sealing plate; 130-Moving rod; 140-Seed crystal; 150-Vacuum phase channel; 152-First sidewall; 154-Second sidewall; 156-Flow guide block; 160-Polycrystalline chamber; 170-Weighing rod; 172-Weigher; 180-Heater; 190-Insulation chamber; 200-Silicon carbide powder. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0032] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0033] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0034] In related technologies, crystal diameter expansion growth generally suffers from low growth efficiency and circumferential inhomogeneity. Regarding growth efficiency, in conventional PVT growth schemes, the growth vapor phase propagates axially from bottom to top, resulting in a much higher axial growth rate than diameter expansion, thus leading to slower diameter expansion growth. As for growth uniformity, due to differences in thermal field uniformity and the corrosion of the graphite structure, conventional diameter expansion growth results in uneven crystal growth rates in the circumferential direction, making crystal edges prone to defects.

[0035] To address the above issues, this invention provides a silicon carbide crystal diameter expansion growth apparatus and method that can simultaneously improve growth rate and circumferential uniformity. Through a horizontally arranged thermal field structure and vapor phase channel, the crystal growth vapor phase primarily deposits and grows radially, significantly improving diameter expansion growth efficiency (the seed crystal shape can be plate-like or rod-like; controlling the gap below the seed crystal allows for diameter expansion growth while also increasing thickness to some extent; when the seed crystal is rod-like, diameter expansion growth is the primary process). Furthermore, by setting the seed crystal to rotate at a uniform speed, the difference in growth rate between the side of the crystal closer to the silicon carbide powder and the side farther from the powder can be mitigated, ensuring a consistent growth rate in the circumferential direction, thus improving the circumferential growth uniformity of the crystal.

[0036] The silicon carbide crystal diameter expansion growth apparatus and method provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0037] Please refer to Figure 1 and Figure 2 This silicon carbide crystal diameter expansion growth apparatus includes a crucible 100, a movable rod 130, and a heater 180. A porous graphite plate 110 is disposed inside the crucible 100, and the porous graphite plate 110 and the sidewall of the crucible 100 together form a powder cavity 112 for holding silicon carbide powder 200. The crucible 100 has a horizontally extending gas phase channel 150 located on the side of the porous graphite plate 110 away from the powder cavity 112, and the width of the gas phase channel 150 gradually increases in the direction away from the powder cavity 112. The movable rod 130 passes vertically through the top wall of the crucible 100, and a seed crystal 140 is coaxially disposed at the bottom end of the movable rod 130. The seed crystal 140 is located within the gas phase channel 150 and can rotate uniformly within the gas phase channel 150 under the drive of the movable rod 130, while simultaneously moving horizontally in the direction away from the powder cavity 112. The heater 180 is arranged around the crucible 100 to create a thermal field inside the crucible 100, so that the crystal growth vapor formed by the sublimation of silicon carbide powder 200 can pass through the porous graphite plate 110 and enter the vapor channel 150, and grow crystals on the peripheral wall of the seed crystal 140.

[0038] This crystal expansion growth apparatus and method uses a horizontally arranged powder chamber 112 and seed crystal 140, and a horizontally extending gas phase channel 150. The crystal growth gas phase formed in the powder chamber 112 can flow horizontally to the uniformly rotating seed crystal in the gas phase channel 150. This enables rapid and uniform crystal growth at various parts of the seed crystal 140 periphery, thereby improving the efficiency and quality of crystal expansion growth.

[0039] The crucible 100 has a strip-shaped hole 102 on its top wall and a sealing plate 120 for sealing the strip-shaped hole 102. A movable rod 130 passes through the sealing plate 120 and can rotate relative to the sealing plate 120. During the horizontal sliding of the sealing plate 120 on the top wall of the crucible 100 driven by the movable rod 130, the sealing plate 120 always completely seals the strip-shaped hole 102 to achieve a sliding seal. In this way, the movable rod 130 can move horizontally along the extension direction of the strip-shaped hole 102 and rotate at a constant speed without affecting the airtightness of the crucible 100. This causes the seed crystal 140 to rotate at a constant speed in the gas phase channel 150 while moving horizontally away from the powder cavity 112.

[0040] Furthermore, please refer to... Figure 1 and Figure 2 The crucible 100 also includes a transition cavity 114, located on the side of the porous graphite plate 110 away from the powder cavity 112. This transition cavity 114 connects to the inlet of the gas phase channel 150 on the side away from the porous graphite plate 110. The transition cavity 114 increases the area from which the crystal growth gas flows out of the porous graphite plate 110. After filling the transition cavity 114, this crystal growth gas enters the gas phase channel 150 through its inlet.

[0041] The top and bottom walls of the crucible 100 are respectively provided with L-shaped flow guide blocks 156. The horizontal parts of the two flow guide blocks 156 are parallel to each other and respectively form the upper and lower walls of the gas phase channel 150, so as to guide the crystal growth gas phase to flow as horizontally as possible to the peripheral wall of the seed crystal 140.

[0042] Further, please refer to Figure 3 The vapor channel 150 has opposing first sidewalls 152 and second sidewalls 154 in the width direction. The inlet of the vapor channel 150 is formed between the ends of the first sidewalls 152 and the second sidewalls 154 that are closer to the powder cavity 112, and the outlet of the vapor channel 150 is formed between the ends that are farther away from the powder cavity 112. From the inlet to the outlet, the distance between the first sidewalls 152 and the second sidewalls 154 gradually increases, thus forming a vapor channel 150 whose width gradually increases in the direction away from the powder cavity 112. This arrangement ensures that during the radial horizontal movement of the seed crystal 140, there are always gaps between the crystal peripheral wall and the first sidewall, and between the crystal peripheral wall and the second sidewall, and the width of the two gaps is basically constant (generally 0.5-3 mm), so as to maintain the radial growth space of the crystal while improving the growth quality of the crystal edge.

[0043] The first sidewall 152 and the second sidewall 154 are symmetrically arranged with respect to a central plane, and the axis of the seed crystal 140 lies within this central plane. Thus, during the horizontal movement of the seed crystal 140, the distance between the axis of the seed crystal 140 and the first sidewall 152, and the distance between the axis of the seed crystal 140 and the second sidewall 154, remain constant. This ensures that during crystal expansion growth, the distances between the peripheral walls and the first and second sidewalls 152 remain substantially equal, resulting in approximately the same flow rates of the crystal growth gas phases passing between the peripheral walls and the first sidewall 152 and between the peripheral walls and the second sidewall 154, further improving the uniformity of crystal expansion growth.

[0044] Alternatively, please refer to Figure 1 and Figure 2 A polycrystalline chamber 160 is provided inside the crucible 100, located below the gas phase channel 150. The inlet of the polycrystalline chamber 160 is connected to the outlet of the gas phase channel 150, and is used to guide the long crystal vapor phase passing through the gas phase channel 150 into and crystallize. The polycrystalline chamber 160 can prevent the backflow of long crystal vapor phase that has not crystallized on the seed crystal 140, which would cause turbulence in the gas phase channel 150 and affect crystal growth, and can also prevent this part of the long crystal vapor phase from escaping from the crucible 100.

[0045] Furthermore, in order to monitor the weight change rate of the polycrystalline chamber 160, determine the deposition rate of the polycrystalline material, and thus determine the distance between the crystal periphery and the sidewall of the gas phase channel 150, so as to adjust the horizontal movement rate of the seed crystal 140, in this embodiment, a weighing rod 170 is connected to the bottom of the polycrystalline chamber 160. The weighing rod 170 passes through the bottom wall of the crucible 100 in a vertical direction and is connected to a weighing device 172 outside the crucible 100 to achieve real-time weighing and calculate the weight change rate of the polycrystalline chamber 160.

[0046] The type of heater 180 can be selected as a resistance heater as needed (see...). Figure 1 ) or inductive heaters (see Figure 2 In this embodiment, by adjusting the position layout of the heater 180 and the overall structure of the insulation chamber 190, the heater 180 is configured to create a thermal field in which the temperature of the powder chamber 112, the gas phase channel 150, and the polycrystalline chamber 160 gradually decreases (i.e., the temperature of the powder chamber 112 is greater than the temperature of the gas phase channel 150, and the temperature of the gas phase channel 150 is greater than the temperature of the polycrystalline chamber 160).

[0047] Furthermore, the relative position of the heater 180 and the heat preservation chamber 190 can also be set as needed. If the heater 180 is resistive, the heater 180 is located inside the heat preservation chamber 190. If the heater 180 is inductive, the heater 180 is located outside the heat preservation chamber 190. It should be noted that in order to achieve the horizontal movement of the seed crystal 140, a structure similar to the sealing plate 120 on the top wall of the crucible 100 also needs to be set at the position where the top wall of the heat preservation chamber 190 is penetrated by the movable rod 130 to achieve sliding sealing.

[0048] The silicon carbide crystal diameter expansion growth method supporting the silicon carbide crystal diameter expansion growth device is as follows:

[0049] After loading the silicon carbide powder 200, start the heater 180 to construct a thermal field, so that the long crystal gas phase formed by the sublimation of the silicon carbide powder 200 passes through the porous graphite plate 110 and then enters the transition chamber 114, and then enters the gas phase channel 150 from the inlet of the gas phase channel 150 and flows to the peripheral wall of the seed crystal 140 in the gas phase channel 150 to increase the crystal diameter expansion growth rate.

[0050] In the above process, control the movable rod 130 to drive the seed crystal 140 to rotate uniformly, and at the same time control the movable rod 130 to drive the seed crystal 140 to move horizontally in the direction away from the powder chamber 112. The uniform rotation of the seed crystal 140 can make the long crystal gas phase in the gas phase channel 150 crystallize uniformly at different positions on the peripheral wall of the seed crystal 140, thereby improving the uniformity of the crystal diameter expansion growth. When the seed crystal 140 rotates uniformly and moves horizontally in the direction away from the powder chamber 112, there is always a certain gap between the peripheral wall of the crystal and the side wall of the gas phase channel 150 and the size of this gap is basically unchanged. On the one hand, it leaves space for the continuous diameter expansion growth of the crystal, and on the other hand, it can make the flow rate of the long crystal gas phase basically unchanged, ensuring the stability of crystal growth.

[0051] It should be noted that if the seed crystal 140 remains stationary in the horizontal direction, as the crystal expands in diameter, the outer wall of the crystal will quickly touch the side wall of the gas phase channel 150, so that it cannot continue to grow and polycrystals are likely to appear. Although setting the width of the gas phase channel 150 larger and leaving enough gaps between the peripheral wall of the crystal and the side wall of the gas phase channel 150 can also improve this problem, it will cause a large waste of the long crystal gas phase, the cost of the silicon carbide powder 200 is too high, and it will also cause the gap between the peripheral wall of the crystal and the gas phase channel 150 to gradually decrease and the flow rate of the long crystal gas phase to gradually decrease, affecting the stable growth of the crystal.

[0052] Furthermore, the horizontal movement rate of the seed crystal 140 can be determined either experimentally or based on the weight change rate of the polycrystalline chamber 160. The weight change rate of the polycrystalline chamber 160 characterizes the change in the size of the gap between the crystal periphery and the sidewall of the gas phase channel 150. If the weight change rate of the polycrystalline chamber 160 increases, it indicates that the gap is larger because more long crystal gas phase has passed through the crystal but not crystallized. In this case, the movable rod 130 can be controlled to slow down the horizontal movement rate of the seed crystal 140, so that the gap between the crystal periphery and the sidewall of the gas phase channel 150 gradually decreases. Conversely, if the weight change rate of the polycrystalline chamber 160 decreases, it indicates that the gap is smaller because less long crystal gas phase has passed through the crystal but not crystallized. In this case, the movable rod 130 can be controlled to increase the horizontal movement rate of the seed crystal 140, so that the gap between the crystal periphery and the sidewall of the gas phase channel 150 gradually increases.

[0053] This adjustment ensures that the gap between the crystal periphery and the sidewall of the gas phase channel 150 remains essentially unchanged during crystal growth, providing space for crystal diameter expansion while maintaining the stability of crystal growth and thus guaranteeing the quality of crystal diameter expansion.

[0054] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A silicon carbide crystal up-drawing growth apparatus characterized by comprising: The application relates to a crucible (100) internally provided with a porous graphite plate (110), the porous graphite plate (110) and the side wall of the crucible (100) jointly forming a powder cavity (112) for containing silicon carbide powder (200), the crucible (100) internally has a gas phase channel (150) extending in the horizontal direction, the gas phase channel (150) is located on the side of the porous graphite plate (110) far away from the powder cavity (112), and the width of the gas phase channel (150) gradually increases in the direction far away from the powder cavity (112). A movable rod (130) penetrates the top wall of the crucible (100) in the vertical direction, the bottom end of the movable rod (130) is coaxially provided with a seed crystal (140), the seed crystal (140) is located in the gas phase channel (150), and the seed crystal (140) can uniformly rotate in the gas phase channel (150) under the drive of the movable rod (130) and horizontally move in the direction far away from the powder cavity (112). A heater (180) is arranged around the crucible (100) and is used for building a heat field in the crucible (100), so that the crystal growth gas phase formed by sublimation of the silicon carbide powder (200) can enter the gas phase channel (150) after passing through the porous graphite plate (110) and grow crystals on the peripheral wall of the seed crystal (140). The gas phase channel (150) has opposite first and second side walls (152) and (154) in the width direction, and the distance between the axis of the seed crystal (140) and the first side wall (152) and the distance between the axis of the seed crystal (140) and the second side wall (154) are always equal during the horizontal movement of the seed crystal (140). The crucible (100) is internally provided with a polycrystal chamber (160), the polycrystal chamber (160) is located below the gas phase channel (150), the inlet of the polycrystal chamber (160) is connected with the outlet of the gas phase channel (150), and the crystal growth gas phase passing through the gas phase channel (150) is guided to enter and crystallize. The top wall and the bottom wall of the crucible (100) are respectively provided with L-shaped flow guide blocks (156), the horizontal parts of the two flow guide blocks (156) are parallel to each other and respectively form the upper wall and the lower wall of the gas phase channel (150).

2. The apparatus of claim 1, wherein, The bottom of the polycrystal chamber (160) is connected with a weighing rod (170), the weighing rod (170) penetrates the bottom wall of the crucible (100) in the vertical direction and is connected with a weighing device (172) outside the crucible (100).

3. The apparatus of claim 1, wherein the carbon monoxide gas is supplied to the growth chamber through a plurality of gas supply lines. ​ 4. The apparatus of claim 1, wherein, The top wall of the crucible (100) is provided with a strip-shaped hole (102) and a sealing plate (120) for sealing the strip-shaped hole (102), the movable rod (130) penetrates the sealing plate (120) and can rotate relative to the sealing plate (120), during the process that the movable rod (130) drives the sealing plate (120) to slide horizontally on the top wall of the crucible (100), the sealing plate (120) always completely seals the strip-shaped hole (102).

5. The apparatus of claim 1, wherein, The crucible (100) is further provided with a transition cavity (114) inside, the transition cavity (114) is located on the side of the porous graphite plate (110) away from the powder cavity (112), and the side of the transition cavity (114) away from the porous graphite plate (110) is in communication with the inlet of the gas phase channel (150).

6. A method for the diameter-enlargement growth of a silicon carbide crystal, based on the silicon carbide crystal diameter-enlargement growth apparatus according to claim 1, characterized by, The method comprises the following steps: After the silicon carbide powder (200) is filled, the heater (180) is started to build a thermal field, so that the crystal growth gas phase formed by sublimation of the silicon carbide powder (200) enters the gas phase channel (150) after passing through the porous graphite plate (110); The movable rod (130) drives the seed crystal (140) to rotate at a constant speed, and at the same time, the movable rod (130) drives the seed crystal (140) to move horizontally away from the powder cavity (112).

7. The method of claim 6, wherein the diameter of the silicon carbide crystal is increased by a factor of at least 2.

5. The horizontal moving speed of the seed crystal (140) is determined according to the weight change rate of the polycrystal chamber (160), wherein the polycrystal chamber (160) is located in the crucible (100) and the inlet of the polycrystal chamber (160) is connected with the outlet of the gas phase channel (150) to guide the crystal growth gas phase passing through the gas phase channel (150) to enter and crystallize.

8. The method of claim 7, wherein the diameter of the silicon carbide crystal is increased by a factor of at least 2.

5. The heater (180) is configured to build a thermal field with gradually decreasing temperature in the area where the powder cavity (112) is located, the area where the gas phase channel (150) is located, and the area where the polycrystal chamber (160) is located.

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