A new diffusion method

Abstract

The present invention discloses a novel diffusion method. A flow homogenizing device is added at the gas inlet end of the furnace tube, so that the gas is evenly dispersed after entering the furnace tube, avoiding the direct impact of the gas flow on the silicon wafer, and improving the inter-wafer difference among the upper, middle and lower parts at the furnace tail. When the present invention is energized, nitrogen is supplemented near the gas outlet to dilute the doping source, mix and push the gas, improving the concentration difference of the local doping source, enhancing the uniformity of the sheet resistance of the silicon wafer, and can improve the inter-wafer uniformity at the inlet position of the exhaust pipe without changing the existing exhaust structure, and has no influence on the sheet resistance of other boats, and can realize the independent regulation of the sheet resistance of the region.

Description

Technical Field

[0001] The present invention relates to the fields of semiconductor manufacturing and solar photovoltaic cell manufacturing, and particularly to a novel diffusion method. Background Art

[0002] At present, most of the preparation equipment for photovoltaic cells, such as diffusion furnaces, annealing furnaces, oxidation furnaces, LPCVD, PECVD, etc., uses multi-tube equipment, and the multi-tube equipment shares a purification table and loading and unloading equipment. Diffusion is an important process for preparing PN junctions. The conventional diffusion method is as follows: Put the silicon wafers into a quartz boat, push the quartz boat with the silicon wafers into the tube of the tube-type diffusion furnace, heat the diffusion furnace to a first preset temperature, introduce process gas into the diffusion furnace, maintain the temperature for a certain period of time for source deposition, stop introducing the process gas, change to a second preset temperature, and perform source diffusion.

[0003] In the current diffusion process, whether it is the diffusion process of horizontal wafer placement or vertical wafer placement, whether it is furnace mouth intake and furnace tail exhaust or furnace tail intake and furnace mouth exhaust, the sheet resistance will be uneven at the outlet or inlet, and the difference is very large. There are two conventional methods: (1) Reduce the number of silicon wafers to avoid the defective ratio; (2) Adjust the sheet resistance unevenness through pressure, gas flow, etc. However, the effects are not obvious, and even the silicon wafers in the originally uniform sheet resistance area will be affected. Summary of the Invention

[0004] In view of the above situation, to overcome the defects of the prior art, the present invention provides a novel diffusion method.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A novel diffusion method, comprising the following steps:

[0007] (1) Send the boat carrying the silicon wafers into the furnace tube, place the flow equalizing barrel inside the furnace tube, and the flow equalizing barrel is close to the furnace tail.

[0008] (2) Vacuumize and leak check;

[0009] (3) After the furnace tube is heated to 770 - 790 °C, introduce oxygen and nitrogen, and the furnace tube pressure is 150 - 170 mbar;

[0010] (4) Keep the temperature constant at 770 - 790 °C, carry POCl 3 source with small nitrogen, mix oxygen and large nitrogen to enter from the furnace tail, and the furnace tube pressure is 150 - 170 mbar;

[0011] (5) Gradually heat up from 770 °C to 845 °C with a slope, for 10 minutes, introduce oxygen and nitrogen during the heating process, and the furnace tube pressure is 160 mbar;

[0012] Maintain a constant temperature of 845 °C for 10 min. During the constant temperature process, supplement nitrogen gas, and the furnace tube pressure is 160 mbar.

[0013] (7) Cool down, pass nitrogen gas to return to atmospheric pressure, and take out the product from the furnace.

[0014] Furthermore, in step (4), the gas supply pipe is inserted into the furnace tube from the furnace tail and extends towards the furnace mouth; the end of the gas supply pipe close to the furnace mouth is closed, and the other end is open for gas injection. There is a gas outlet on the gas supply pipe; the gas introduced into the gas supply pipe is an inert gas or / and nitrogen gas.

[0015] Furthermore, in step (4), the small nitrogen flow rate is 1.2 - 1.5 L / min, the oxygen flow rate is 0.8 - 1 L / min, the large nitrogen flow rate is 3 - 3.5 L / min, and the injection time is 12 - 15 min.

[0016] Furthermore, in step (4), the gas introduced into the gas supply pipe is nitrogen gas.

[0017] Furthermore, in step (4), the flow rate of the introduced nitrogen gas is 0.5 - 2 L / min.

[0018] Furthermore, in step (5), the oxygen flow rate is 1 - 1.5 L / min, and the nitrogen flow rate is 3 - 3.5 L / min.

[0019] Furthermore, in step (6), the nitrogen flow rate is 3 - 3.5 L / min.

[0020] Furthermore, in step (7), cool down to 800 °C.

[0021] Furthermore, in step (3), the oxygen flow rate is 1 - 1.5 L / min, the nitrogen flow rate is 3 - 3.5 L / min, and the injection time is 5 - 7 min.

[0022] Furthermore, the flow - equalizing device adopts a barrel - shaped structure, including a barrel body. One end of the barrel body is open, and the other end of the barrel body is connected to a closed surface, and there are openings on the closed surface.

[0023] Furthermore, there are support members provided at the lower part of the flow - equalizing device, and the support members are fixedly connected to the barrel body.

[0024] Furthermore, the support member is cylindrical.

[0025] Furthermore, the inside of the support member is hollow.

[0026] Furthermore, one end of the support member is open.

[0027] Furthermore, the flow - equalizing device further includes a connecting member, and the connecting member connects the support member.

[0028] Furthermore, the connecting member is located on the side where the barrel body is open.

[0029] Further, the gas supply pipe is configured to be capable of supplementing gas, and the gas may be nitrogen or / and inert gas.

[0030] Further, the gas supply pipe is in the form of a plug. One end of the gas supply pipe is closed and the other end is open for introducing gas, and a gas outlet is provided on the gas supply pipe.

[0031] Further, the gas supply pipe is inserted into the furnace tube from the furnace tail and extends towards the furnace mouth; the end of the gas supply pipe close to the furnace mouth is closed and the other end is open.

[0032] The beneficial effects of the present invention are as follows:

[0033] (1) A flow equalizing device is added at the gas inlet end of the furnace tube, so that the gas is evenly dispersed after entering the furnace tube, avoiding direct impact of the gas flow on the silicon wafer, and improving the inter-wafer difference in the upper, middle and lower parts of the furnace tail. When the present invention is energized, nitrogen is supplemented near the gas outlet to dilute the doping source, mix and push the gas, improving the concentration difference of the local doping source, improving the uniformity of the sheet resistance of the silicon wafer, and improving the inter-wafer uniformity at the inlet position of the exhaust pipe without changing the existing exhaust structure, and having no influence on the sheet resistance of other boats, and can realize independent regulation of the sheet resistance of the region.

[0034] (2) The present invention provides a diffusion method, which improves the uniformity of the diffusion sheet resistance, reduces the sheet resistance range, and can increase the production capacity of the equipment.

[0035] (3) The present invention adds a nitrogen pipeline to fill nitrogen at the bottom, which can dilute the high-concentration doping gas at the gas outlet, push the gas flow upward and mix it evenly, and reduce the pumping force of the tail exhaust pipe on this part. At the same time, by adjusting the thermal field temperature here (adjusting the sheet resistance of the boat by adjusting the temperature of the first temperature zone and the second temperature zone), silicon wafers with a small sheet resistance range can be obtained.

[0036] (4) By improving the uniformity at the furnace mouth, the present invention can improve both the production capacity and the uniformity of the silicon wafers, without increasing the length of the furnace tube, keeping the silicon wafers away from the unstable gas flow area, saving the machine space and the machine manufacturing cost.

[0037] (5) In the present invention, the flow equalizing device adopts a barrel-shaped structure, including a barrel body, and the other end of the barrel body is connected to a closed surface (i.e., the other end is closed), and an opening is provided on the closed surface; the setting of the barrel body can concentrate the gas entering the flow equalizing device, avoiding the diffusion of the gas to the surrounding. The gas flows out from the opening on the closed surface and is evenly dispersed, avoiding direct impact of the gas flow on the silicon wafer, and can improve the inter-wafer difference of the sheet resistance of the upper, middle and lower silicon wafers at the furnace tail.

[0038] (6) In the present invention, the closed surface of the flow homogenizing device is not provided with openings over the entire surface. The shape of the opening area corresponds to the shape of the boat (which can be set according to the shape of the boat), facilitating the more concentrated flow of gas towards the boat rather than flowing away from the side of the boat. This barrel-shaped flow homogenizing device has better stability inside the furnace tube, does not shake, and an additional connecting member is added, making it easier to put into and take out from the furnace tube.

[0039] (7) In the present invention, the connecting member of the flow homogenizing device is shaped like an arched handle. The two ends of the connecting member are respectively connected to one end of two cylindrical support members. The connecting member is convenient for the user to grasp, facilitating the taking and placing of the flow homogenizing device into and out of the furnace tube. At the same time, the connecting member is located on the side of the barrel opening, which can balance the weight distribution of the entire device, making the overall structure more stable.

[0040] (8) In the present invention, a gas supply pipe is adopted, which can be used to supplement nitrogen. It can improve the uniformity between the wafers at the exhaust port position without changing the existing exhaust structure, and has almost no impact on the sheet resistance inside other boats, enabling the individual regulation of the sheet resistance in the controlled area. By improving the uniformity between the wafers at the furnace opening, the production capacity and uniformity of the present invention can both be enhanced, without the need to increase the length of the furnace tube, saving the machine space and the manufacturing cost of the machine. The better uniformity of the sheet resistance after diffusion is beneficial for the matching of subsequent processes, and the overall electrical performance is also more stable. Description of the Drawings

[0041] Figure 1 is a schematic diagram of the conventional air intake method (showing the change of air flow in the figure).

[0042] Figure 2 is a schematic diagram of the air intake method of the present invention (showing the change of air flow in the figure).

[0043] Figure 3 is a schematic diagram of the structure of the flow homogenizing barrel.

[0044] Figure 4 is a schematic diagram of the structure of the flow homogenizing barrel viewed from another direction (showing the connection structure between the transverse connecting member and the cylinder).

[0045] Figure 5 is a schematic diagram of the flow homogenizing device installed inside the furnace tube (showing an installation example).

[0046] Figure 6 is a schematic diagram of the structure of the gas supply pipe inside the furnace tube (other components in the furnace tube are hidden). Detailed Embodiments

[0047] The following further elaborates on the technical invention of the present invention in conjunction with the drawings. It should be noted that the detailed embodiments are only a detailed description of the present invention and should not be regarded as a limitation of the present invention.

[0048] Example 1

[0049] Taking phosphorus diffusion as an example:

[0050] (1) Place the boat carrying the silicon wafer into the furnace tube;

[0051] (2) Evacuate and check for leaks;

[0052] (3) After the furnace tube is heated to 770 °C, introduce oxygen and nitrogen. The oxygen flow rate is 1 L / min, the nitrogen flow rate is 3 L / min, the furnace tube pressure is 160 mbar, and the time is 5 min;

[0053] (4) Keep the temperature constant at 770 °C. Small nitrogen carries POCl 3 source. Mix oxygen and large nitrogen and introduce them from the furnace tail. The small nitrogen flow rate is 1.2 L / min, the oxygen flow rate is 0.8 L / min, the large nitrogen flow rate is 3 L / min, the furnace tube pressure is 160 mbar, and the time is 12 min;

[0054] In this example, boats No. 1 and 2 correspond to the first temperature zone, and the temperature of the first temperature zone is adjusted to 795 °C. Boat No. 3 corresponds to the second temperature zone, and the temperature of the second temperature zone is adjusted to 780 °C.

[0055] The first temperature zone and the second temperature zone are the positions of the thermal fields corresponding to boats No. 1, 2, and 3.

[0056] (5) Heat up from 770 °C at a slope to 845 °C, time 10 min; oxygen flow rate 1 L / min, nitrogen flow rate 3 L / min, furnace tube pressure 160 mbar;

[0057] (6) Keep the temperature constant at 845 °C, time 10 min. During the constant temperature process, supplement nitrogen. The nitrogen flow rate is 3 L / min, and the furnace tube pressure is 160 mbar;

[0058] (7) Cool down to 800 degrees, introduce nitrogen to return to normal pressure, and take out of the furnace.

[0059] The schematic diagram of the gas inlet mode adopted in this example is as shown in Figure 2 shown. Among them, 1 represents the tail flow equalizing plate (the flow equalizing plate in the prior art, with small holes on the plate surface), 2 represents the furnace tube, 3 represents the thermal field, 4 represents the furnace mouth heat insulation plate, 5 represents the furnace door, 6 represents the paddle, 7 represents the tail exhaust pipe, 8 represents the inlet pipe, and 9 represents the supplementary gas pipe.

[0060] Take the silicon wafers in 8 boats in sequence from the furnace mouth to the furnace tail. For each boat, take 5 wafers at equal intervals from top to bottom. Measure the sheet resistance at 5 positions for each wafer, and calculate the range of 25 measurement points in 5 wafers. The silicon wafer size is 182 mm x 182 mm. The comparison sheet resistance and range values for the target sheet resistance of 160 Ω / □ are shown in Table 1 below.

[0061] Table 1

[0062]

[0063] Example 2

[0064] On the basis of Example 1, the original flow equalizing plate was removed, and a flow equalizing barrel was added at the furnace tail. Gases such as N 2 , O 2 , POCl 3 enter the furnace tube through the flow equalizing barrel; so that the gases are evenly dispersed after entering the furnace tube, avoiding the direct impact of the gas flow on the silicon wafer. Specifically, the flow equalizing barrel is placed inside the furnace tube, and the flow equalizing barrel is 10 - 15 cm away from the end of the intake pipe at the furnace tail.

[0065] In this embodiment, the flow equalizing barrel described in Example 1a is adopted. The flow equalizing barrel is 10 cm away from the end of the intake pipe at the furnace tail. The flow equalizing barrel is as Figure 3-4 shown and adopts a barrel-shaped design.

[0066] In this embodiment, during use, the gas first passes through the opening 3a on the closed surface and then flows out through the barrel body. In other embodiments, the gas can also first pass through the barrel body 1a and then flow out from the opening 3a. In other embodiments, flow equalizing devices with other structures can be adopted.

[0067] The remaining steps in this example are the same as those in Example 1.

[0068] With the same wafer taking method, the measured sheet resistance range is shown in Table 2.

[0069] Table 2

[0070]

[0071] Example 3

[0072] On the basis of Example 2, a supplementary gas pipe is added. The supplementary gas pipe is inserted from the furnace tail and extends towards the furnace mouth. In this embodiment, a quartz supplementary gas pipe is adopted. The end of the supplementary gas pipe close to the furnace mouth is closed, and the other end is open for ventilation. The specific structure of the supplementary gas pipe is as described in Example 2a, as Figure 6 shown.

[0073] In this embodiment, the No. 1 boat is close to the furnace mouth heat insulation board, and the No. 2, 3, 4... 8 boats are arranged in sequence towards the furnace tail direction.

[0074] On the supplementary gas pipe, 3 holes are respectively opened at the 1 / 4, 1 / 2, and 3 / 4 positions along the furnace tube length corresponding to the No. 1 boat; 2 holes are respectively opened at the 1 / 3 and 2 / 3 positions along the furnace tube length corresponding to the No. 2 boat; 1 hole is opened at the 1 / 2 position along the furnace tube length corresponding to the No. 3 boat; the hole diameter is 1.5 mm.

[0075] In this embodiment, the opening is a circular hole. In other embodiments, the shape of the opening can be set to other shapes, and the present invention does not specifically limit it.

[0076] On the basis of the process of Embodiment 1, step (4) is modified to:

[0077] (4) Keep the temperature constant at 770 degrees, with small nitrogen carrying POCl 3 source, mix oxygen and large nitrogen to enter from the furnace tail. The flow rate of small nitrogen is 1.2 L / min, the flow rate of oxygen is 0.8 L / min, the flow rate of large nitrogen is 3 L / min, the furnace tube pressure is 160 mbar, the time is 12 min, and nitrogen with a flow rate of 0.95 L / min is passed through the compensating pipe. The temperatures of the 1st, 2nd, and 3rd boats corresponding to the first temperature zone and the second temperature zone are increased by 5 degrees compared with Embodiment 1.

[0078] In this embodiment, nitrogen is introduced only when the source is passed (i.e., nitrogen compensation is turned on), and it is turned off at other times. The nitrogen introduction time is the same as the source passing time. In other embodiments, an inert gas, such as helium, is passed through the compensating pipe.

[0079] The remaining steps in this embodiment are the same as those in Embodiment 2.

[0080] With the same wafer taking method, the measured sheet resistance range is as shown in Table 3 below.

[0081] Table 3

[0082]

[0083] Embodiment 4

[0084] On the basis of the process of Embodiment 3, step (4) is modified to:

[0085] (4) Keep the temperature constant at 770 degrees, with small nitrogen carrying POCl 3 source, mix oxygen and large nitrogen to enter from the furnace tail. The flow rate of small nitrogen is 1.2 L / min, the flow rate of oxygen is 0.8 L / min, the flow rate of large nitrogen is 3 L / min, the furnace tube pressure is 160 mbar, the time is 12 min, and nitrogen with a flow rate of 0.5 L / min is passed through the compensating pipe. The temperatures of the 1st, 2nd, and 3rd boats corresponding to the first temperature zone and the second temperature zone are increased by 3 degrees compared with Embodiment 1.

[0086] The remaining steps in this embodiment are the same as those in Embodiment 1.

[0087] With the same wafer taking method, the measured sheet resistance range data is shown in Table 4.

[0088] Table 4

[0089]

[0090] Embodiment 5

[0091] Based on the process of Example 1, step (4) is modified as follows:

[0092] (4) Keep the temperature constant at 770 degrees, and small nitrogen carries POCl 3 source. Mix oxygen and large nitrogen to enter from the tail of the furnace. The flow rate of small nitrogen is 1.2 L / min, the flow rate of oxygen is 0.8 L / min, the flow rate of large nitrogen is 3 L / min, the pressure of the furnace tube is 160 mbar, the time is 12 min, and nitrogen with a flow rate of 2 L / min is passed through the compensating pipe. The temperatures of the first, second, and third boats corresponding to the first temperature zone and the second temperature zone are increased by 9 degrees compared with Example 1.

[0093] The remaining steps in this example are the same as those in Example 1.

[0094] The measured data of the sheet resistance range are shown in Table 5.

[0095] Table 5

[0096]

[0097] Example 1a

[0098] As Figure 3-4 shown, a flow equalizing device. The flow equalizing device adopts a barrel-shaped structure, including a barrel body 1a. One end of the barrel body 1a is open (this is the first opening 7a), and the other end of the barrel body 1a is connected to a closed surface (that is, the other end of the barrel body is closed). An opening 3a is provided on the closed surface 2a. The barrel body 1a can concentrate the gas entering the flow equalizing device and prevent the gas from diffusing around; the gas flows out from the opening 3a on the closed surface 2a and is evenly dispersed, avoiding the direct impact of the air flow on the silicon wafer.

[0099] In some preferred ways, the shape of the opening 3a can be circular, elliptical, square, triangular, etc. The present application does not limit the shape of the opening. The number of openings can also be set according to actual needs. In this example, the shape of the opening is circular.

[0100] In some preferred ways, as Figure 3-4 shown, a support member 4a is provided at the lower part of the flow equalizing device. The support member 4a is fixedly connected to the barrel body 1a. The support member 4a can support the entire flow equalizing device. At the same time, the support member 4a can be used to stably place the flow equalizing device at a certain position, such as placing the flow equalizing device inside the furnace tube. In some preferred ways, the shape of the support member 4a matches the shape of the placement area inside the furnace tube, which is beneficial to stably placing the flow equalizing device inside the furnace tube.

[0101] In some preferred ways, the support member 4a is cylindrical, and the contact part of the cylindrical support member 4a matches the circular furnace tube. In this example, as Figure 3-4As shown, the flow equalizing device includes two cylindrical supports 4a.

[0102] In some preferred embodiments, as Figure 3 shown, the interior of the support 4a is hollow, and one end of the support 4a is open (this is the second opening 8a). The support 4a can be sleeved on the corresponding fixing member 6a, as Figure 3-4 shown. The opening direction of the support 4a is opposite to the opening direction of the barrel 1a. The flow equalizing device is placed inside the furnace tube, and the support 4a is sleeved on the fixing member inside the furnace tube. Since the interior of the support 4a is hollow, the weight of the entire flow equalizing barrel can also be reduced. Figure 5 shows an installation method of a flow equalizing device. The support is sleeved on the fixing member 6a to realize the connection between the flow equalizing device and the furnace tube. In other embodiments, other installation methods can be adopted, such as an installation in a snap - fit form. There are card slots inside the furnace tube that can cooperate with the support to realize the connection between the flow equalizing device and the furnace tube.

[0103] For the flow equalizing device in this application, during use, the gas can first pass through the opening 3a on the closed surface and then flow out through the barrel; or the gas can first pass through the barrel 1a and then flow out from the opening 3a.

[0104] In some preferred embodiments, as Figure 4 shown, the flow equalizing device further includes a connecting member 5a. The connecting member 5a connects the support 4a. The connecting member 5a is configured to be used for the user to grip, and the connecting member 5a is connected to the support 4a, making the entire structure relatively stable. The connecting member 5a can be of various shapes, such as any one or a combination of several shapes like a square connecting member, an arched connecting member, a transverse connecting member, etc.

[0105] In this embodiment, the shape of the connecting member 5a is similar to an arched handle, as Figure 4 shown. The two ends of the connecting member 5a are respectively connected to one end of the two cylindrical supports 4a. The connecting member 5a is convenient for the user to grip, which is beneficial for taking or placing the flow equalizing device into the furnace tube. At the same time, the connecting member 5a is located on the side of the opening of the barrel 1a, which can balance the weight distribution of the entire device, making the entire structure relatively stable.

[0106] In some preferred embodiments, the flow equalizing device is placed at the gas inlet end of the furnace tube, and the flow equalizing device is 10 - 15 cm away from the inlet end. This can increase the contact area between the gas and the flow equalizing barrel and better disperse the gas flow.

[0107] In some preferred embodiments, as Figure 3As shown, the closed surface 2a does not have openings 3a over the entire surface. The shape of the area with the openings 3a corresponds to the shape of the boat (set according to the shape of the boat), which is conducive to the gas flowing more concentratedly towards the boat rather than flowing away from the side of the boat. This barrel-shaped flow homogenizing device has better stability in the furnace tube and will not shake. Moreover, the flow homogenizing device includes a connecting member 5a, which facilitates putting the flow homogenizing device into the furnace tube and taking it out of the furnace tube.

[0108] Embodiment 2a

[0109] In some preferred ways, such as Figure 6 As shown, the intake structure further includes a make-up gas pipe, which is configured to be able to supplement gas. The gas can be nitrogen or / and inert gas. In this embodiment, the make-up gas pipe is mainly used to supplement nitrogen.

[0110] In some preferred ways, the make-up gas pipe is in the form of a plug. The make-up gas pipe is inserted into the furnace tube from the furnace tail and extends towards the furnace mouth; the end of the make-up gas pipe close to the furnace mouth is closed, and the other end is open (this is the third opening 9a) for introducing gas. In some preferred ways, the make-up gas pipe is provided with a gas outlet 10a. By opening a gas outlet on the make-up gas pipe, the gas outlet position can be in an area with a lower sheet resistance, and by increasing the local nitrogen concentration to dilute the phosphorus source or boron source concentration, the effect of improving the sheet resistance can be achieved.

[0111] In this embodiment, such as Figure 6 As shown, the gas outlet is located directly above the make-up gas pipe. The shape of the gas outlet is a round hole with a diameter of 1.5 mm. In other embodiments, the gas outlet may not be located directly above the make-up gas pipe and may be located obliquely above the make-up gas pipe or in other positions. The specific position of the gas outlet can be set according to actual needs.

[0112] In this application, the shape of the gas outlet can be square, oval, etc. This application does not specifically limit the shape of the gas outlet.

[0113] In this embodiment, such as Figure 6 As shown, the gas outlet is located directly above the intake pipe. The shape of the gas outlet is a round hole with a diameter of 1.5 mm, and the number of gas outlets is 6, which is a combination of 3, 2, and 1. There are 3 holes below the first boat near the furnace mouth, 2 holes below the second boat, and 1 hole below the third boat. The make-up gas pipe passes through from below the flow homogenizing device and extends to below the boat at the furnace mouth.

[0114] In some preferred ways, the diameter of the make-up gas pipe is 12 mm. In other embodiments, the diameter of the make-up gas pipe can be other values and can be set according to specific requirements.

[0115] In some preferred embodiments, during the process gas supply step, a gas supply pipe is added and nitrogen gas is introduced. In some embodiments, a nitrogen compensation flow rate of 0.5 - 2 L / min is set during the process gas supply step.

[0116] The intake structure in the present invention can be used for phosphorus diffusion or boron diffusion.

[0117] As can be seen from the data in the table, the sheet resistance range of Example 3 is the smallest. Under the conditions of a silicon wafer size of 182 mm x 182 mm and a target sheet resistance of 160 Ω / sq, the present invention dilutes and reduces the doping source concentration near the air extraction port (the air extraction port is the intake port of the tail exhaust pipe) by supplementing nitrogen gas, mixes the air flow, and pushes it upward, reducing the influence of the air extraction port on this area, reducing the concentration difference, and thus reducing the sheet resistance range of the silicon wafer. By adding a flow equalizing barrel at the tail of the furnace, after fully dispersing the air flow, as much as possible flows into the boat interior, greatly improving the range of the several boats near the furnace tail. Under the premise of large-size silicon wafers, high sheet resistance, and high-efficiency battery processes, the requirement for the uniformity of the silicon wafer sheet resistance is getting higher and higher, and the problems of conventional diffusion processes are gradually emerging, and it is necessary for multiple parties to jointly improve and enhance the process quality.

[0118] The present invention solves the non-uniformity of the sheet resistance of the silicon wafers near the air extraction port and reduces the sheet resistance range by adding gas compensation at the silicon wafer position near the air extraction port (one end of the tail exhaust pipe in the furnace tube). In the conventional method, some silicon wafers near the air extraction port need to be discarded, and the loading amount of silicon wafers per tube is reduced to obtain the uniformity of the whole tube. The present invention can directly improve the sheet resistance range of the silicon wafers near the air extraction port, make the uniformity of the silicon wafers reach the qualified area, and improve the production capacity.

[0119] As Figure 1 shown, in the conventional intake method, the gas flow at the furnace mouth is biased towards the tail exhaust port, resulting in a large gas flow at the lower part of the furnace mouth. Since the density of the doping gas is generally large, it sinks in the mixed gas, resulting in a large gas concentration and flow rate at the lower part of the furnace mouth, thus causing the sheet resistance of the lower part of the silicon wafer to be small and the sheet resistance range of the silicon wafer to become larger. In the conventional method, the furnace tube pressure is adjusted, the gas flow ratio is improved, and the temperature at the silicon wafer position at the furnace mouth is changed to improve the abnormal sheet resistance at the furnace mouth. The method of inlet gas at the furnace mouth and exhaust gas at the furnace tail also has similar problems. Such conventional adjustments can slightly reduce the difference, but to maintain the stability of the silicon wafers at other positions, the improvement is limited. Usually, the number of silicon wafers at the outlet is reduced to achieve the consistency of the whole tube of silicon wafers.

[0120] The present invention adds a nitrogen gas pipeline at the furnace mouth and fills nitrogen gas at the bottom. As Figure 2 shown, it can not only dilute the high-concentration doping gas here, but also push the gas flow upward here to mix evenly, reducing the suction force of the tail exhaust pipe on this area. At the same time, in combination with the adjustment of the thermal field temperature here, silicon wafers with a small sheet resistance range can be obtained.

[0121] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A novel diffusion method, Characterized in that, It includes the following steps: (1) Place the boat carrying the silicon wafer into the furnace tube, and place the flow equalizing device inside the furnace tube. The flow equalizing device is close to the furnace tail. Among them, the flow equalizing device adopts a barrel structure, including a barrel body. One end of the barrel body is open, and the other end is connected to a closed surface. There are openings on the closed surface; (2) Evacuate and leak check; (3) After the furnace tube is heated to 770 - 790 °C, introduce oxygen and nitrogen, and the furnace tube pressure is 150 - 170 mbar; (4) Keep the temperature constant at 770 - 790 °C, with small nitrogen carrying POCl 3 source, mix oxygen and large nitrogen to enter from the tail of the furnace, and the pressure in the furnace tube is 150 - 170 mbar. Among them, the gas supply pipe is inserted into the furnace tube from the tail of the furnace and extends towards the furnace mouth. The end of the gas supply pipe close to the furnace mouth is closed, and the other end is open for introducing gas. There is a gas outlet on the gas supply pipe, and an inert gas or / and nitrogen is introduced into the gas supply pipe; (5) Heat up from 770 °C at a slope to 845 °C for 10 min. During the heating process, introduce oxygen and nitrogen, and the furnace tube pressure is 160 mbar; (6) Keep the temperature constant at 845 °C for 10 min. During the constant temperature process, supplement nitrogen, and the furnace tube pressure is 160 mbar; (7) Cool down, introduce nitrogen to return to normal pressure, and take out of the furnace.

2. A novel diffusion method according to claim 1, Characterized in that, In step (4), the small nitrogen flow rate is 1.2 - 1.5 L / min, the oxygen flow rate is 0.8 - 1 L / min, the large nitrogen flow rate is 3 - 3.5 L / min, and the introduction time is 12 - 15 min.

3. A novel diffusion method according to claim 1, Characterized in that, In step (3), the oxygen flow rate is 1 - 1.5 L / min, the nitrogen flow rate is 3 - 3.5 L / min, and the introduction time is 5 - 7 min.

4. A novel diffusion method according to claim 1, Characterized in that, In step (4), the nitrogen flow rate introduced into the compensating pipe is 0.5 - 2 L / min.

5. A novel diffusion method according to claim 1, Characterized in that, In step (5), the oxygen flow rate is 1 - 1.5 L / min, and the nitrogen flow rate is 3 - 3.5 L / min.

6. A novel diffusion method according to claim 1, Characterized in that, In step (6), the nitrogen flow rate is 3 - 3.5 L / min.

7. A novel diffusion method according to claim 1, Characterized in that, In step (7), cool down to 800 °C.

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