JPS5910960B2 - Continuous pulling single crystal production method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new method and apparatus for growing single crystals for semiconductors by pulling.

Semiconductor single crystals that are generally used in the electronics industry, taking silicon as an example, are industrially produced using the Czochralski set pulling method (hereinafter abbreviated as the CZ method) using high-purity silicon polycrystals as raw materials.
Alternatively, it is manufactured by a zone melting method (hereinafter abbreviated as FZ method).

In recent years, advances in large-scale integrated circuit manufacturing technology have resulted in the miniaturization of single electronic circuits, while increasing the area of single-crystal silicon wafers that serve as substrates, allowing the fabrication of BL into wafers in a single process. By increasing the number of circuits used, the cost per circuit is reduced.

For this reason, there is a constant demand for larger diameters in single crystal manufacturing technology, but at the same time, efforts are also being made to increase the length of each crystal in order to increase productivity per unit of time during single crystal manufacturing.

The CZ method is suitable for increasing the diameter of single crystals.
Not only has a 6-inch single crystal been obtained, but technological improvements such as automatic diameter control and semi-continuous processing using raw material polycrystalline glue charging have progressed, and the method surpasses the FZ method in terms of cost.

However, the conventional CZ method has the following problems (1) to (3), which remain unsolved.

(1) Resistivity, which is the most important factor in the design of electronic devices, is determined by the impurity (dopant) concentration doped into the single crystal, but in the current CZ method, the dopant concentration in the pulling direction is Since the increase is unavoidable, there is a limit to the pulling length in order to obtain a single crystal with a desired resistivity.

The proportion of dopants added to the melt that is incorporated into the single crystal is determined according to its unique segregation coefficient, but in the case of silicon, most impurities, except for oxygen, are incorporated into the melt with a segregation coefficient of less than 1. Because a large proportion of the dopant remains in the melt, as the pulling progresses, the dopant concentration in the melt increases, and as a result, the amount of dopant incorporated into the single crystal increases, and eventually the resistivity becomes so high that it deviates from the target resistivity. Even if the resistivity was within the desired range, it was inevitable that the resistivity of the cut wafers would be different for each wafer.

(2) Conventionally, as a means of making the CZ method semi-continuous, after pulling a single crystal of a predetermined size, the furnace was opened under the flow of inert gas, and new silicon polycrystals were loaded into the crucible. Generally, a so-called recharge method is used in which a new pulling process is performed, but this method cannot avoid the intrusion of oxygen into the pulling furnace during polycrystalline recharging. Carbon oxide is produced, which ultimately leads to an increase in the carbon concentration in the crystal.

(3) Generally, in order to obtain a high-quality single crystal with few crystal defects, it is desirable that the shape of the solid-liquid interface be flat, but in reality, in the CZ method, the melt surface sinks as the crystal growth progresses. Therefore, the positional relationship between the heating element and the molten liquid changes, causing the shape of the solid-liquid interface to change.

For this reason, the crucible is raised in response to the sinking of the melt surface so that the relative position does not change, but this time the heat shielding effect at the top of the crucible changes, changing the temperature distribution at the solid-liquid interface. I'll let you.

The present invention is a new C
This provides an improved method of the Z method.

In other words, by continuously supplying the silicon melt and dopant to the pulling crucible without opening the pulling furnace, the dopant distribution in the pulling direction can be made uniform, and the level of the melt surface can be made uniform. Since it is not necessary to open the pulling furnace during charging, it is possible to achieve even better crystallinity.

According to the present invention, in the Czochralski continuous pulling single crystal production method, a single crystal material melting vessel having a circular opening at the bottom is used, and the temperature distribution of the vessel is controlled to maintain a molten bath inside the vessel. The circular opening is maintained at a temperature at which the single-crystal material starts to solidify, and a rod-shaped single-crystal material having a cross section that corresponds to the cross-section of the circular opening is fed into the single crystal through the circular opening. A method is provided which is characterized in that it is introduced at a rate that compensates for the loss of bath due to pull production.

According to the present invention, there is further provided a crucible having a circular opening at the center of the bottom for melting the single crystal material, the edge of the opening extending downward in the axial direction of the crucible into a hollow cylindrical shape. A rotary shaft that is fixed to the cylinder and has an opening at the lower end of which the crucible is rotated by receiving the rod-shaped single crystal material to be inserted from the opening of the crucible, and rotates the rotary shaft. 1, driven by 1,000 stages; the temperature distribution is maintained so that the temperature of the cup-shaped body of the crucible is maintained at a temperature at which the single crystal material is melted, and the bottom opening is maintained at a temperature at which the material begins to solidify. means for storing each of the above-mentioned members and having an opening 1 in the upper part thereof through which a means for rotating and pulling up a single-crystal rod with a seed crystal from the molten bath of the single-crystal material in the crucible can be accessed and removed; a furnace body through which gas can flow; the lifting stage; and a single crystal capable of ten-dot movement and rotational movement for inserting the rod-shaped single crystal material into the molten bath through the rotating shaft and the opening of the crucible. A continuous pulling single crystal manufacturing apparatus is provided, including a material support for the invention.

Although the method and apparatus of the present invention can be used to manufacture single crystals of semiconductor materials in general, the following detailed description with reference to the drawings will be made for silicon, which is a typical semiconductor material.

The concept of the apparatus used in the method of the present invention is shown in FIG.

Crucible 2 with an opening [1] in the bottom forming the center of the device of the invention
is usually made of quartz, but other materials such as silicon nitride, quartz, boron nitride, graphite, etc. whose surfaces are coated with silicon nitride or silicon oxynitrite may also be used.

This support is usually supported by a susceptor 3 made of graphite, but the susceptor itself is not essential.

The crucible 2 has a cup-shaped part for melting the single crystal material, ie, silicon, and a hollow cylindrical part 2' extending downward in a cylindrical shape from the edge of the circular opening at the bottom.

A cylindrical rotating shaft 7 is fixed to this hollow cylindrical portion.

This rotary shaft 7 is provided with an opening 11 at the bottom, from which a rod-shaped single crystal material (polycrystalline silicon rod) is inserted.
20 is inserted into the bottom opening of the crucible 2 via the hollow cylinder 2'.

The space between the silicon rod and the bottom opening 11 of the rotating shaft 7 is sealed with a common sealing material such as silicone rubber or Teflon.

A main heater 4 and an auxiliary heater 5 are arranged outside the crucible 2 (and susceptor 3), and the temperature distribution inside the crucible is adjusted as shown in FIG. 3 in the case of silicon.

The heater is usually of an electric resistance heating type or a high frequency heating type, but is not limited thereto.

The members described above are stored in the furnace body 1, leaving the lower part of the rotary shaft 7 intact.

The furnace is usually made of stainless steel, and is divided into sections for convenient storage, removal, repair, and adjustment of the above-mentioned parts.The bottom opening 12 of the insertion part of the rotating shaft is made of silicone rubber or Teflon between the shaft and the shaft. sealed with a sealing material such as

Above the furnace body 1, there is an upper opening 121 through which the single crystal pulling shaft 9 passes, and this is opened and closed by a slide valve 13.

A bellows (usually made of stainless steel) 22 may be provided to protect the single crystal 18 being pulled.

The furnace may also be provided with a viewing window 16.

Further, a heat shielding body 6 may be provided in the furnace body.

Supply pipe 15, usually equipped with a valve for introducing inert gas
is provided.

Inert gas usually blows through the upper opening [-1.

Below the furnace body 1, there are a rotary drive means 10 for rotating a rotary shaft 7 protruding therefrom, a rod-shaped single crystal material support 8 that rotates and moves up and down to raise the polycrystalline silicon rod 20, and a polycrystalline silicon rod. Support arm 1 holding 20
4 etc. are provided.

These devices can be easily manufactured by those skilled in the art based on the above information.

To manufacture a silicon single crystal using this device, first, silicon is ground from the bottom opening 11 of the rotating shaft 7 into a cylinder with a diameter equal to that of the opening of a predetermined crucible held on the single crystal material support 8. The polycrystalline rod 20 is inserted by activating the lifting mechanism (not shown in the figure) of the support base 8, passes through the quartz hollow cylinder 2l, and reaches the bottom opening [1] of the quartz crucible 2.

At this time, the polycrystal supply port 11 and the shield portion 12 of the rotating shaft 7 are sufficiently airtightly sealed using a sealing material.

Next, the upper part of the furnace is opened and a predetermined amount of polycrystalline silicon is loaded into the crucible, and then the inside of the furnace is filled with inert gas in the same manner as in the conventional method, and the main heater 4 and auxiliary heater are heated using resistance heating or high frequency heating. 5 is operated to melt the silicon polycrystals loaded in the crucible.

At this time, the inside of the quartz crucible 2 and the quartz hollow cylinder 2' is
By controlling the temperature distribution as shown in the figure, polycrystalline silicon exists as a molten body in the area between the openings and openings in Figure 2, and solidifies in the area between the openings and c. Not only will it not spill to the bottom, but the polycrystalline support 8
The rise and rotation of the silicon polycrystalline rod 20 accompanying the movement of the silicon polycrystalline rod 20 is not hindered.

In this state, the rotary shaft 7 is rotated to transmit rotation to the quartz crystal 2, and the pull shaft 9 on which the seed crystal 17 is attached is lowered, and the single crystal 18 is grown in exactly the same manner as in the conventional method. Start lifting.

At the same time, melt 19 equal to the amount of the single crystal pulled up
In order to replenish the melt, the surface level of the melt 19 can be kept constant by raising the single crystal material support 8 and moving the silicon polycrystal 20 to the melting zone shown in Figure 2A. Therefore, not only can pulling be carried out under the same conditions as long as the pulling distance of the pulling device continues, but the concentration of impurities contained in the raw material will always be constant when melted, just as in the case of the FZ method. As a result, a uniform impurity concentration is achieved over the entire length of the raised single crystal, resulting in a single crystal with a uniform resistivity distribution.

Further, the supply of the silicon polycrystal 20 is carried out when the support stand 8 rises and approaches the silicon polycrystal supply 111, the support stand 8 is lowered while holding the silicon polycrystal with the extendable support arm 14, and a new polycrystal is supplied. Since it can be done by splicing sticks together, you can supply as much or as little as you need.

Moreover, since this operation does not require opening and closing the furnace or stopping heating, there is no contamination by undesirable external impurities, and the operating time is significantly reduced compared to the conventional glue charging method.

Regarding the doping method, there is not only the method of using pre-doped raw materials mentioned above, but also the method of making the dopant into a thin wire and placing it on the rod-shaped single crystal material (a vertical groove for this purpose may be provided in the rod-shaped material). It is also possible to add dopants using relatively short rod-shaped materials in the same way as when splicing them together, so the width of the resistivity distribution can be limited to an extremely narrow range. .

On the other hand, after the single crystal of a predetermined length was pulled, the single crystal was moved to the upper part of the slide valve shown by 13 in Figure 1, and the valve 13 was closed to seal the inside of the furnace. By opening the crystal extraction port (not shown), the single crystal can be taken out, replaced with a new seed crystal, and the next process can be repeated. Even in the supply of polycrystals, there is no external impurity contamination, and there is no need to interrupt the operation, making it possible to ideally continue supplying the polycrystal.

Although omitted from the description and drawings of the above-mentioned apparatus, the method and apparatus are typically automatically controlled.

The weight of the single crystal to be produced, that is, to be pulled, is constantly detected, and this information is fed back to the lifting mechanism of the single crystal material support to ensure that the supply rate of the single crystal material to the melting bath is just that of the bath. controlled to compensate for the decrease.

Such electronic circuits do not need to be described in detail since they can be easily constructed and manufactured by those skilled in the art.

Detection of molten bath loss may also be by monitoring changes in the bath level.

In this case, the level of the melt is monitored by optical or electrical detection means.

The present invention has great industrial value in that it solves all the problems of the current CZ method and makes it possible to continuously pull a large number of single crystals with uniform impurity concentrations.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a pulled single crystal manufacturing apparatus according to the present invention. In the figure, 1..., 2...crucible, 2'
...Hollow cylinder, 3...Graphite 1.
Sasepuku, 4... Main heater, 5...
・Auxiliary heater, 6...Heat shielding body, 7...
... Rotating shaft, 8 ... Rod-shaped single crystal material support stand, 9 ... Pulling shaft, 10 ...
...Rotating shaft 1 to 1 drive wheel, 11...Airtight seal type polycrystalline supply port, 12...Rotating shaft bottom open 1'', 13...Slide palf, 14...
...Support arm, 15...Inert gas supply port, 16...Peephole, 17...Seed crystal, 18...Pull-north Single crystal, 19...
Melt of material for single crystal, 20... Material for rod-shaped single crystal, 21... Upper opening of furnace body, 22... Bellows. FIG. 2 shows a diagram showing the temperature distribution of the portion corresponding to the extracted portion of the apparatus shown in FIG. 1 with the corresponding number.

Claims (1)

[Claims] 1. In the Czochralski continuous pulling single crystal production method, a single crystal material melting vessel having a circular opening at the bottom is used, and the temperature distribution of the vessel is adjusted to a temperature that maintains a molten bath inside the vessel. The temperature in the circular opening is maintained at a temperature at which the single crystal material begins to solidify, and a rod-shaped single crystal material having a cross section matching the cross section of the circular opening is pulled from the circular opening. A method characterized in that the introduction is carried out at a rate that compensates for the loss of bath due to production. 2. The method according to claim 1, which detects the weight of the continuously produced single crystal and automatically controls the introduction of rod-shaped single crystal material in accordance with the fluctuation thereof. A method characterized by: 3. The method according to claim 1, which detects fluctuations in the liquid level of the melt bath of the single crystal material and automatically adjusts the introduction of the rod-shaped single crystal material according to the fluctuation. A method characterized by controlling. 4 A crucible that has a circular opening in the center of the bottom for melting single crystal material, and the edge of the opening extends downward in the axial direction of the crucible into a hollow cylindrical shape; a rotary shaft having an opening at its lower end for receiving rod-shaped single crystal material to be inserted from the opening of the crucible, on which the crucible is rotated by being fixed to the crucible; Means: Heating the crucible so as to maintain a temperature distribution such that the temperature of the cup-shaped body is maintained at a temperature at which the single crystal material is melted, and the bottom opening is maintained at a temperature at which the material begins to solidify. Stage; storing each of the above-mentioned members and having an opening in the upper part through which a means for rotating and pulling up a single-crystal rod with a seed crystal from the molten bath of the single-crystal material in the crucible can enter and exit, and gas can be circulated inside. a continuous puller comprising a furnace body capable of vertical movement and rotational movement for inserting the rod-shaped single crystal material into the molten bath through the rotating shaft and the opening of the crucible; The above type single crystal manufacturing equipment. 5. The device according to claim 4, which includes an automatic control device that detects the weight of the continuously produced single crystal and adjusts or reduces the introduction of rod-shaped single crystal material in accordance with the fluctuation thereof. A device characterized by: 6. The device according to claim 5, which is an automatic control mechanism that detects fluctuations in the liquid level of the molten bath of single crystal material and adjusts or reduces the introduction of the rod-shaped single crystal material in accordance with the fluctuations. A device characterized by comprising: