JPH07235531A - Heat-treating apparatus - Google Patents

Abstract

PURPOSE:To provide a heat-treating device, which is capable of forming evenly a treatment film on the surface of a body to be treated. CONSTITUTION:A heat-treating apparatus is provided with a treating furnace 1, which is heated at a high temperature and at the same time, is made process gas G introduce, a support 17 for supporting a single body W to be treated in this furnace 1 and a gas flow buffer body 18 provided on this support 17 so as to prevent the body W from being exposed directly to the gas flow of the process gas G. Thereby, as the body W is prevented from being exposed directly to the gas flow of the process gas G by the body 18 provided on the support 17 for supporting the body W, a treatment film results in being formed quietly on the surface of the body W by diffusion of a process gas component and it becomes possible to form evenly the treatment film on the surface of the body W.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a heat treatment apparatus.

[0002]

2. Description of the Related Art In manufacturing a semiconductor wafer, which is an object to be processed, oxidation, diffusion, CVD (Chemical Vapor D
Various heat treatment apparatuses are used to perform processing such as eposition). The typical heat treatment apparatus carries a large number of wafers, for example, about 150 wafers, which are vertically supported at a predetermined interval from a lower furnace opening through a wafer boat into a vertical processing furnace and processes the wafers. Heat treatment is performed at a high temperature in a gas atmosphere.

In this batch processing type heat treatment apparatus, a large number of wafers can be heat treated at one time, which is sufficient for a certain degree of heat treatment, but the upper wafer and the lower wafer supported by the wafer boat are used. Since there is a distance between them, there is a time lag with respect to the thermal environment when loading and unloading into the processing furnace, and it takes some time to load and unload, so all heat treatments that require rapid temperature rise and fall are carried out. There is a limit to the uniform application to the wafer.

Therefore, a single-wafer processing type heat treatment apparatus is being developed which is capable of performing a heat treatment which requires a rapid temperature increase / decrease suitable for miniaturization of semiconductor elements by processing wafers one by one.

[0005]

However, in the above-mentioned single-wafer processing type heat treatment apparatus, when a processing film such as an oxide film is formed on the surface of a wafer by using a processing gas, the film thickness of the processing film is There is a problem that the film becomes thicker at the peripheral portion of the film and the film is nonuniformly formed. Initially, since the film formation rate depends on the processing temperature, the nonuniformity of the film formation is caused by the nonuniformity of the in-plane temperature that the in-plane temperature of the wafer is low in the central part and high in the peripheral part. Was thought to exist. Therefore, an experiment was conducted by making the in-plane temperature of the wafer higher in the central part than in the peripheral part, but the film thickness in the central part was slightly thicker, but the film thickness in the peripheral part was also thicker and the film formation was uneven. The conversion was not resolved.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a heat treatment apparatus capable of uniformly forming a treatment film on the surface of an object to be treated.

[0007]

As a result of intensive studies to achieve the above object, the present inventor has found that nonuniformity of film formation is not directly brought about by nonuniformity of the in-plane temperature of the object to be treated, The present invention has found that the gas flow of the processing gas is caused by dynamic behavior on the surface of the object to be processed, and that the film to be processed can be made uniform by preventing the object to be processed from being directly exposed to this gas flow. Has been completed.

That is, the heat treatment apparatus according to claim 1 is
A processing furnace which is heated to a high temperature and into which a processing gas is introduced, a support for supporting a single object to be processed in the processing furnace, and the object to be processed directly supplies a gas flow of the processing gas to the support. And a gas flow buffer provided so as not to receive the gas flow buffer.

The gas flow buffer may be provided integrally with the support or may be detachably provided. Further, the flow direction of the gas flow of the processing gas may be any direction in the processing furnace. Further, the support may be configured to carry in and carry out the object to be processed from a furnace opening formed in any of the processing furnaces,
Alternatively, the object may be permanently installed in the processing furnace and transferred from the furnace port by the transfer means.

As the heating means, a lamp, a heating resistor or the like can be applied, and it is preferable that the heating means is formed in a surface shape facing the object to be processed. As the object to be processed, for example, a semiconductor wafer, LCD or the like can be applied. As a material for the gas flow buffer, a material having heat resistance and radiant heat permeability, such as quartz or silicon carbide (SiC), can be applied.

A heat treatment apparatus according to a second aspect is the heat treatment apparatus according to the first aspect, wherein the processing furnace is formed so as to flow the processing gas from above to below in the furnace.
Further, the flat plate-shaped object to be processed is horizontally placed on the upper part of the support body, and the flat plate-shaped object having a size larger than the object to be processed is provided above the object to be processed with a predetermined gap. It is characterized in that the gas flow buffer is mounted horizontally.

Further, the heat treatment apparatus according to a third aspect is the heat treatment apparatus according to the first or second aspect, wherein the support is carried in and carried out from a furnace opening formed in a lower portion of the processing furnace. Therefore, it is possible to move up and down, and a holding portion for holding the gas flow buffer separately from the support is provided in the processing furnace.

[0013]

According to the heat treatment apparatus of the present invention, since the object to be processed is not directly exposed to the gas flow of the processing gas by the gas flow buffer provided on the support of the object to be processed, the diffusion of the processing gas components. By the action, the treatment film is gently formed on the surface of the object to be treated, and the treatment film can be uniformly formed on the surface of the object to be treated.

According to the second aspect of the present invention, there is provided a flat plate-shaped object to be processed on the support, and a size larger than the object to be processed with a predetermined gap above the object. Since the film formation can be made uniform with a simple configuration in which the flat plate-shaped gas flow buffer body is mounted, the manufacturing cost can be reduced and the processing efficiency can be improved by simplifying the structure.

Further, according to the heat treatment apparatus of the third aspect, the gas flow buffer can be preheated by holding the gas flow buffer separately from the support in the processing furnace. Therefore, when the object to be processed is carried into the processing furnace and heat-treated, the object to be processed can be quickly heated to the target processing temperature without heat loss, and the object to be processed after the processing can be processed in the processing furnace. Since the heated gas flow buffer is separated when it is carried out to the normal temperature, the temperature can be quickly lowered.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1 showing the vertical cross-sectional structure of the heat treatment apparatus, reference numeral 1 denotes a processing furnace (process tube) formed to be suitable for performing, for example, an oxidation process on an object to be processed, for example, a semiconductor wafer W. The processing furnace 1 is formed of a vertical cylindrical heat-resistant material, such as quartz, with an upper part closed and a lower part opened as a furnace opening 2. The process gas G or an inert gas such as nitrogen (N ₂ ) gas for purging the inside of the furnace is introduced into the lower side wall of the processing furnace 1 so that the outlet side rises along the inner wall of the furnace so as to be introduced into the upper part of the furnace. Pipe 3
Further, the lead-out pipe part 4 for discharging the treated exhaust gas or the inert gas to the outside of the furnace is integrally provided, and the processing gas G is configured to flow from the upper side to the lower side in the furnace. A supply pipe for processing gas or the like is connected to the introduction pipe part 3, and an exhaust pipe connected to a factory exhaust system is connected to the discharge pipe part 4 (not shown).

Above the processing furnace 1, as a heating means for heating the wafer W to a high temperature, for example, about 800 to 1200 ° C., a planar heating section 5 is horizontally arranged so as to face the wafer W. The heating unit 5 spirally or meanders a heating resistor such as a Kanthal wire made of an alloy of iron (Fe), chromium (Cr) and aluminum (Al) or a heating wire made of molybdenum disilicide (MoSi ₂ ). It is formed in a flat shape by arranging in a shape. The heating unit 5 is formed sufficiently larger (for example, twice or more) than the size (diameter) of the wafer W so that the radiant heat can be uniformly applied to the wafer W in the vertical direction. In addition, in order to eliminate the temperature difference in the surface of the wafer W caused by the finite size of the heating unit 5, the peripheral portion of the heating unit 5 may be formed in a stepped shape or curved downward.

Further, between the heating part 5 and the processing furnace 1, a heavy metal contamination preventive property made of, for example, alumina (Al ₂ O ₃ ) or silicon carbide (SiC) is provided so as to cover the upper part and the periphery of the processing furnace 1. Further, a soaking material 6 having soaking properties is arranged. The outside of the soaking material 6 and the heating portion 5 is covered with a heat resistant heat insulating material 7 such as quartz wool, and the outside of the heat insulating material 7 is covered with a double structure casing 8 made of stainless steel, for example. ing. In addition, this casing 8
In order to prevent thermal influence on the outside, a cooling pipe such as water cooling may be built in. Further, the casing 8 is installed on the base plate 9.

A lower casing 11 made of a heat-resistant material, such as quartz or stainless steel, for partitioning and forming a vertical transfer space 10 communicating with the furnace port 2 in the lower part of the processing furnace 1 is not shown, such as an O-ring. The lower casing 11 is connected via an airtight member, and a vertical elevating shaft 12 made of, for example, quartz is vertically pierced through the airtight member 13 at the center of the bottom portion of the lower casing 11. The lower end of the lifting shaft 12 has a lifting arm 1 of a lifting mechanism 14 formed of, for example, a ball screw.
5, the lifting arm 15 has a lifting shaft 1
A rotary drive unit 16 for rotating the 2 is provided.

A support 17 made of, for example, quartz for horizontally supporting a single wafer W, that is, one wafer W is integrally provided on the upper end of the elevating shaft 12, and the support 17 is shown in FIG. As shown, a gas flow buffer 18 for preventing the wafer W from directly receiving the gas flow of the processing gas G is detachably provided above the wafer W with a predetermined gap S therebetween. The gas flow buffer 18 is formed of a material having heat resistance and radiant heat permeability, such as quartz or silicon carbide (SiC), into a circular flat plate shape similar to the wafer W. The size of the gas flow buffer 18, that is, the outer diameter D is preferably equal to or larger than the size of the wafer W, for example, about 1 to 1.5 times the outer diameter of the wafer W. If the size of the gas flow buffer 18 is smaller than that of the wafer W, the peripheral portion of the wafer W is directly exposed to the gas flow G. Conversely, if it exceeds 1.5 times the outer diameter of the wafer W, the gas flow is reduced. This is because the buffering effect of (1) does not change, but the heat treatment apparatus becomes large.

The thickness t of the gas flow buffer 18 is
It is preferable that the thickness is, for example, about 2 mm so that the heat treatment of the wafer W is not hindered and the rigidity is maintained. Further, the gap S between the gas flow buffer 18 and the wafer W is preferably a gap such that a gas flow does not enter and a process gas component can diffuse as shown by a dotted arrow A, for example, about 3 to 10 mm. 4.76 mm for a wafer W with a diameter of 6 inches and 6.3 m for a wafer W with an diameter of 8 inches
It has been confirmed by experiments that m is suitable.

As shown in FIG. 4, the support 17 is composed of a plurality of support arms 19 opened upward, for example, three support arms 19.
At the upper ends of the support arms 19, first rod-shaped first support portions 20 of the same height are formed at equal intervals in the circumferential direction for horizontally mounting the wafer W and supporting, for example, three points. Further, the processing gas buffer 18 is horizontally mounted on the support arm 19 above the wafer W to support, for example, a second point for supporting at three points.
The first support part 2 so that the support part 21 does not interfere with the wafer W.
It is formed in the same way as the first support portion 20 apart from 0 to the outside. When the gas flow buffer 18 has substantially the same size as the wafer W, the upper end of the second support portion 21 is radially inward so that the upper end of the second support 21 can support the peripheral edge of the lower surface of the gas flow buffer 18. It is preferably formed by extension.

In order to separate the gas flow buffer 18 from the support 17 and hold it in the processing furnace 1 when the wafer W is carried out, as shown in FIG. A holding portion 22 made of, for example, quartz that holds the lower edge portion of the gas flow buffer body 18 horizontally is integrally provided. As shown in FIG. 3, the holding portion 22 includes a plurality of L-shaped locking pieces 23, for example, three L-shaped locking pieces 23 arranged so as to lock the peripheral edge of the lower surface of the gas flow buffer 18 at equal intervals in the circumferential direction. The gas flow buffer 18 is provided with a locking piece 23 on the periphery thereof so that the gas flow buffer 18 can be separated from the locking piece 23.
The cutout portions 24 through which the holes can pass are formed at the same intervals as the locking pieces 23. Thus, the support 17 allows the gas flow buffer 1 to
The support 17 can easily transfer the gas flow buffer 18 to and from the holding portion 22 by rotating and moving up and down 8.

The lower casing 11 is provided with a plurality of stages, for example, two stages of shutters 25 and 26 for thermally shielding the internal transfer space 10 from the inside of the processing furnace 1. These upper and lower shutters 25 and 26 are provided. Thus, the transfer space 10 has an upper intermediate chamber 27 of a size capable of accommodating the support 17.
And the lower wafer transfer chamber 28. These upper and lower shutters 25, 26 are horizontally driven in a direction in which they approach or separate from each other, for example, a pair of left and right shutter plates 25a, 25b and 26a, 26b that are linearly driven.
And each pair of shutter plates 25a, 25b and 26a, 2
The shutter drive unit 29 is mainly composed of, for example, a shutter drive unit 29 configured to open and close 6b.

Shutter plates 25a, 25b and 26a,
26b is formed of a heat resistant material such as quartz or stainless steel, and preferably has a heat insulating space or a heat resistant heat insulating material inside. Each pair of shutter plates 25a, 25b and 26a, 26b are configured to overlap vertically when closed, and a semi-circular cutout portion is formed at the tip end thereof to allow rotation and up-and-down movement of the elevating shaft 12 in the closed state. (Not shown). Also, the shutter plate 2
5a, 25b and 26a, 26b are configured to be closed in two stages, a first closed position that allows rotation and vertical movement of the lifting shaft 12 and a second closed position that is completely closed.

The intermediate chamber 27 and the wafer transfer chamber 28, which are defined by the upper and lower shutters 25 and 26, have a structure in which an inert gas is supplied and discharged to prevent the process gas and heat from being trapped. Is preferred. A loading side and a loading side for replacing the atmosphere and the inert gas when the wafer W is carried into the wafer transfer chamber 28 from the outside and when the wafer W is carried out from the wafer transfer chamber 28 to the outside. Side load lock chambers 30 and 31 are connected to each other via inner gate valves 32 and 33, and the load lock chambers 30 and 31 are connected to the outside gate valves 34 and
35 are provided. In addition, load-side load lock chamber 3
A wafer transfer device 36 for loading, which receives an unprocessed wafer W from the outside and transfers it to the support 17 which stands by in the wafer transfer chamber 28, is provided in 0, and in the unload-side load lock chamber 31. A wafer transfer device 37 for unloading is provided which receives the processed wafer W from the support 17 and transfers it to the outside.

Next, the operation of the embodiment will be described. First, the gas flow buffer 18 is held by the holder 22 in the processing furnace 1, the support 17 is lowered into the wafer transfer chamber 28, and the shutter plates 25a, 25b and 26 of the upper and lower shutters 25 and 26 are provided.
a and 26b are completely closed to the second closed position, and the processing furnace 1
The inside is replaced with an inert gas and is heated to a predetermined processing temperature by the heating unit 5. In this state, first, the wafer W before being processed by the carry-in wafer transfer device 36.
Is the first of the support 17 through the load-side load lock chamber 30.
When the support 17 is transferred onto the support 20, the support 17 is moved up by the elevating mechanism 14 to the upper part of the processing furnace 1. At that time, the shutter plates 26a and 26b of the lower shutter 26 and the shutter plates 25a and 25b of the upper shutter 25 are sequentially opened and closed (first closed position) to allow the support body to move upward.

When the support 17 reaches a position right below the gas flow buffer 18 held in the upper portion of the processing furnace 1, the second support 21 is gas-operated by a series of operations of raising, rotating at a predetermined angle and lowering. The flow buffer 18 is placed, and the cutout portion 24 is attached to the holding portion 22.
The gas flow buffer 18 is received from the holding part 22 in alignment with the locking piece 23 and is positioned in a predetermined temperature region in the processing furnace 1. At this stage, the processing gas G is introduced into the processing furnace 1 through the introduction pipe portion 3 and the heat treatment of the wafer W is performed. When the heat treatment is completed, the inside of the processing furnace 1 is replaced with an inert gas.

On the other hand, the support body 17 transfers the gas flow buffer body 18 on the second support portion 21 to the holding portion 22 in the reverse order of the above procedure, and then moves down to the wafer transfer portion 28. At that time, the shutter plates 25a and 25b of the upper shutter 25
And shutter plates 26a and 26b of the lower shutter 26
Are sequentially opened and closed (second closed position) to shield the inside of the processing furnace 1 while allowing the support 17 to move downward. When the support 17 reaches the wafer transfer chamber 28, the processed wafer W is transferred from the support 17 to the transfer-side load lock chamber 31 by the transfer wafer transfer device 37, and after the wafer W is returned to room temperature, it is exposed to the outside. Be delivered to. Then, the next wafer W is transferred to the support 17 standing by in the wafer transfer chamber 28, and the above-mentioned cycle is repeated, so that the wafers W are continuously heat-treated one by one.

In this way, the unprocessed wafer W can be quickly loaded into the processing furnace 1, and after the heat treatment for a predetermined time, the processed wafer W can be quickly carried out of the processing furnace 1. As a result, the thermal history of the wafer W can be minimized by rapidly increasing and decreasing the temperature, so that the semiconductor element can be miniaturized.
Further, during the heat treatment, the processing gas G flows from the upper side to the lower side in the processing furnace 1. However, as shown in FIG. 2, the processing gas G is provided above the wafer W on the support 17 with a predetermined gap S therebetween. Since the flow buffer 18 is arranged, the wafer W is not directly exposed to the gas flow of the processing gas G, and the wafer W is diffused by the process gas component passing through the gap S between the wafer W and the gas flow buffer 18. It is possible to form a treated film gently on the surface of the film with a uniform film thickness.

In addition, the structure is such that the wafer W is mounted on the upper part of the support 17, and the flat gas flow buffer 18 having a size larger than the wafer W is mounted above the wafer W with a predetermined gap S therebetween. Since the structure is simple, the manufacturing cost can be reduced and the processing efficiency can be improved by simplifying the structure. Further, a holding portion 22 for holding the gas flow buffer 18 is provided in the upper portion of the processing furnace 1, and the gas flow buffer 18 is held in the processing furnace 1 separately from the support 17. As a result, the gas flow buffer 18 can be preheated, so that when the wafer W is loaded into the processing furnace 1 and subjected to heat treatment, the wafer W is quickly heated to the target processing temperature without heat loss. be able to. Further, since the heated gas flow buffer 18 is separated from the support 17 when the processed wafer W is carried out of the processing furnace 1, the temperature of the wafer W can be rapidly lowered.

The present invention is not limited to the above embodiment, but various modifications can be made within the scope of the gist of the present invention. For example, in the above embodiment, the holding portion 22 of the gas flow buffer 18 is arranged in the upper portion of the processing furnace 1, but the holding portion 22 is arranged in the lower portion of the processing furnace 1 or in the intermediate chamber 27 of the lower casing 11. May be. FIG. 6 shows an example in which the holding portion 22 is arranged in the intermediate chamber 27 of the lower casing 11. The holding portion 22 has a plurality of locking pieces 38, which penetrate the side wall of the intermediate chamber 27 and advance and retreat horizontally toward the inside of the intermediate chamber 27 at equal intervals in the circumferential direction, and are arranged outside the side wall. A drive section 39 such as an air cylinder for driving the 38 forward and backward is provided.

According to this, the gas flow buffer 18 is mounted on the support 17 in the process of the ascending movement for loading the wafer W transferred onto the support 17 in the wafer transfer chamber 28 into the processing furnace 1. In addition, the gas flow buffer 18 can be separated from the support 17 during the descending movement of carrying out the processed wafer W. The separated gas flow buffer 18 is held in the intermediate chamber 27 and is thermally shielded by the shutter plates 26a and 26b of the lower shutter 26.
It is possible to lower the temperature in the transfer process. It should be noted that the holding portions 22 are arranged both in the processing furnace 1 and in the intermediate chamber 27, and, for example, after the wafer W after the processing is transferred, the gas flow buffer 18 is moved from the intermediate chamber 27 to the processing chamber by the empty support 17. You may make it move into 1 and preheat.

Further, in the above embodiment, in order to solve the thermal problem of the gas flow buffer 18, the gas flow buffer 18 is used as the support 1.
However, if the heat capacity is small, the gas flow buffer 18 does not necessarily have to be detachably provided on the support 17, and may be integrally provided on the support 17. Furthermore, the processing furnace 1 does not necessarily have to be vertical, and may be horizontal, and the support 17
The wafer W may be configured to be loaded and unloaded through a furnace opening formed in any of the processing furnaces 1. The flow direction of the gas flow of the processing gas G may be any direction in the processing furnace 1, and the gas flow buffer 18 is provided on the support 17 so as to face the flow direction of the gas flow G. Good.

Further, the support 17 does not necessarily have to be movable out of the processing furnace 1 in order to carry the wafer W.
It may be always arranged inside. In this case, for example, a furnace port may be formed on the side of the processing furnace 1, and the wafer W may be transferred to the support 17 by the wafer transfer means via the furnace port. As the heating means, for example, a lamp or the like can be applied in addition to the heating resistor, and as the object to be processed, for example, an LCD or the like can be applied in addition to the semiconductor wafer W. Further, as the heat treatment, besides the oxidation, for example, CVD using a processing gas, diffusion, annealing, etc. can be applied.

[0037]

In summary, according to the present invention, the following excellent effects can be obtained.

(1) According to the heat treatment apparatus of the first aspect, since the object to be processed is not directly exposed to the gas flow of the processing gas by the gas flow buffer provided on the support of the object to be processed, the processing gas is treated. Due to the action of diffusing the components, the treatment film is gently formed on the surface of the object to be treated, and the treatment film can be uniformly formed on the surface of the object to be treated.

(2) According to the heat treatment apparatus of the second aspect, a flat plate-shaped object to be processed is provided above the support, and a size larger than the object to be processed with a predetermined gap above the object to be processed. Since the film formation can be made uniform by a simple configuration in which a flat plate-shaped gas flow buffer having the above is mounted, the manufacturing cost of the heat treatment apparatus can be reduced and the processing efficiency can be improved by simplifying the structure.

(3) According to the heat treatment apparatus of the third aspect, the gas flow buffer can be preheated by holding the gas flow buffer separately from the support in the processing furnace. Therefore, it becomes possible to quickly raise the temperature of the object to be processed to a target processing temperature without heat loss when the object is carried into the processing furnace and heat-treated, and the processed object is treated. Since the heated gas flow buffer is cut off even when it is carried out of the furnace and returned to room temperature, the temperature can be quickly lowered.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the overall configuration of a heat treatment apparatus that is an embodiment of the present invention.

FIG. 2 is an enlarged side view showing a supporting structure of a semiconductor wafer and a gas flow buffer on a support.

FIG. 3 is a perspective view showing a supporting structure of a gas flow buffer body by a holding portion.

FIG. 4 is a perspective view of a support.

FIG. 5 is a cross-sectional view showing a state in which the support body faces the gas flow buffer body held by the holding portion.

FIG. 6 is a cross-sectional view showing a lower casing configured to hold a gas flow buffer in the middle of a semiconductor wafer transfer space.

[Explanation of symbols]

 1 Processing Furnace 2 Furnace Mouth 17 Support 18 Gas Flow Buffer 22 Holding Part G Processing Gas W Semiconductor Wafer (Processing Object)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Okada 1-24-1 Machiya, Shiroyama Town, Tsukui Group, Kanagawa Prefecture Tokyo Electron Tohoku Co., Ltd. Sagami Business Office

Claims (3)

[Claims] 1. A processing furnace that is heated to a high temperature and into which a processing gas is introduced, a support that supports a single object to be processed in the processing furnace, and the processing gas is used as the processing gas on the support. And a gas flow buffer provided so as not to directly receive the gas flow of the heat treatment apparatus. 2. The processing furnace is formed so that the processing gas flows from the upper side to the lower side in the furnace, and the flat plate-shaped object is horizontally mounted on the upper portion of the support. 2. The flat plate-shaped gas flow buffering body having a size larger than that of the object to be processed is horizontally placed above the object to be processed with a predetermined gap therebetween. Heat treatment equipment. 3. The support is configured to be movable up and down for loading and unloading the object to be processed from a furnace opening formed in a lower part of the processing furnace, and the gas flow buffer is provided in the processing furnace. The heat treatment apparatus according to claim 1 or 2, further comprising: a holding unit for holding the unit separately from the support.