A novel boron diffusion wet oxygen process

Abstract

The application discloses a novel boron diffusion wet oxygen process, and adopts H2+O2 to perform a wet oxidation process, water vapor is generated under certain pressure and temperature, the water vapor can dissolve B2O3 on a pipe wall, and is discharged outside the pipe through an exhaust pump evacuation system, and the excess water vapor can pass through an exhaust pipeline, and residual B2O3 in the exhaust pipeline and the pump is also cleaned, so that the maintenance time of the equipment is further prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to a novel boron diffusion wet oxygen process. BACKGROUND

[0002] In the whole process of N-type battery, the quality of PN junction preparation is the key step to determine the efficiency of the battery. At present, there are four kinds of N-type PN junction preparation technologies, namely boron doping technology: tubular BBr3 or BCl3 diffusion, spin-on boron source + diffusion, APCVD boron source + diffusion, ion implantation + annealing. Among them, tubular BBr3 / BCl3 diffusion has become the mainstream boron doping technology due to its low process difficulty, high cost performance, effective avoidance of metal ion pollution, and long minority carrier lifetime. However, there are still many problems in the process production of the diffusion furnace that need to be solved.

[0003] During the boron diffusion pre-deposition process, the boiling point of the reaction product B2O3 is above 1600℃, and the diffusion process is always in a liquid state. Therefore, it can only be diluted and dispersed to the surface of the silicon wafer by a large amount of nitrogen, and the diffusion uniformity is difficult to control. The reaction products B and B2O3 seriously corrode the quartz device, and quickly cool and solidify outside the constant temperature zone, which easily causes the tail pipe to be blocked, causing the diffusion quartz furnace door and the quartz furnace tube to be adhered, and the maintenance cost is high. The back-end process matching problem requires a certain thickness and uniformity of the oxide layer, so a long time of high-temperature oxidation is required, which undoubtedly increases the process time and indirectly increases the cost of the battery. SUMMARY

[0004] In view of the above situation, in order to overcome the defects of the prior art, the present application provides a novel boron diffusion wet oxygen process.

[0005] In order to achieve the above purpose, the present application provides the following technical scheme:

[0006] A novel boron diffusion wet oxygen process, comprising the following steps:

[0007] (1) Put the boat carrying the silicon wafer into the furnace tube;

[0008] (2) Vacuumize and leak test;

[0009] (3) Heat to 800-810℃, and introduce N2, and the furnace tube pressure is 150-180mbar;

[0010] (4) At 800-810℃, introduce N2 and O2 to perform oxidation;

[0011] (5) After heating to 800-810℃, introduce N2, O2 and boron source, and the furnace tube pressure is 150-180mbar;

[0012] (6) After heating to 830-840℃, introduce N2, O2 and boron source, and the furnace tube pressure is 150-180mbar;

[0013] (7) After heating to 850-860℃, N2, O2, boron source are introduced, and the pressure in the furnace tube is 150-180mbar;

[0014] (8) Heating to 950-960℃, N2 is introduced during the heating process, and the pressure in the furnace tube is 400-450mbar;

[0015] (9) Constant temperature at 950-960℃ for 20-23min, N2 is introduced during the heating process, and the pressure in the furnace tube is 400-450mbar;

[0016] (10) Heating to 1040-1050℃, N2, O2 are introduced during the heating process, and the pressure in the furnace tube is 600-650mbar;

[0017] (11) Oxidation at 1040-1050℃ for 20-22min, N2, O2 are introduced during the heating process, and the pressure in the furnace tube is 600-650mbar;

[0018] (12) Oxidation at 1040-1050℃ for 40-42min, H2, O2 are introduced during the heating process, and the pressure in the furnace tube is 250-300mbar;

[0019] (13) Cooling from 1040-1050℃ to 800℃, N2, O2 are introduced during the cooling process, and the pressure is 600-650mbar;

[0020] (14) Breaking vacuum to normal pressure.

[0021] (15) Taking out the boat.

[0022] Further, in step (3), the temperature is ramped from 700-710℃ to 800-810℃, and the time is 12-15min. In the present application, the above-mentioned heating rate is selected to improve the uniformity of heat, which is conducive to the subsequent oxidation step. If the heating rate is too fast, it will cause the difference in the heat radiation received by the silicon wafer in the furnace tube, which is not conducive to the uniformity of heat of the silicon wafer in the furnace tube; if the heating rate is too slow, it will prolong the process time and reduce the production capacity.

[0023] Further, in step (4), the flow rates of N2 and O2 introduced are 1000-1100sccm and 2000-2100sccm, respectively, and the introduction time is 10-12min.

[0024] Further, in step (5), the boron source is BCl3 or / and BBr3.

[0025] Further, in step (5), the flow rates of N2, O2 and boron source are respectively 1500-1600 sccm, 540-560 sccm and 200-250 sccm, and the time of inputting is 2-3 min.

[0026] Further, in step (6), the flow rates of N2, O2 and boron source are respectively 1500-1600 sccm, 540-560 sccm and 200-250 sccm, and the time of inputting is 4-6 min.

[0027] Further, in step (7), the flow rates of N2, O2 and boron source are respectively 1500-1600 sccm, 540-560 sccm and 200-250 sccm, and the time of inputting is 4-6 min.

[0028] Further, in step (8), the flow rate of N2 is 2000-2100 sccm, and the time of inputting is 20-23 min.

[0029] Further, in step (9), the flow rate of N2 is 2000-2100 sccm, and the time of inputting is 20-23 min.

[0030] Further, in step (10), the temperature is raised from 950-960 ℃ to 1040-1050 ℃ at a slope, and the time is 10-12 min. In the present application, the above-mentioned temperature rising rate is helpful to improve the uniformity of heat, and is conducive to the subsequent oxidation step. If the temperature rising rate is too fast, it will cause the difference of heat radiation received by the silicon wafer in the furnace tube, which is not conducive to the uniformity of heat of the silicon wafer in the furnace tube; if the temperature rising rate is too slow, it will prolong the process time and reduce the production capacity.

[0031] Further, in step (10), the flow rates of N2 and O2 are respectively 1000-1100 sccm and 10000-11000 sccm, and the time of inputting is 10-13 min.

[0032] Further, in step (11), the flow rates of N2 and O2 are respectively 1000-1100 sccm and 10000-11000 sccm.

[0033] Further, in step (12), the flow rates of H2 and O2 are respectively 1500-1700 sccm and 3500-3700 sccm.

[0034] Further, in step (13), the flow rates of nitrogen and oxygen are respectively 100-500 sccm and 10000-11000 sccm, and the time of inputting is 30-35 min.

[0035] The beneficial effects of the present application are:

[0036] (1) The present application adopts H2+O2 for wet oxidation process, and water vapor is generated under certain pressure and temperature, which can dissolve B2O3 on the pipe wall, and then is discharged outside the pipe through the evacuation system of the tail discharge pump. The excess water vapor can pass through the tail discharge pipeline, and the residual B2O3 in the tail discharge pipeline and pump is also cleaned. In this way, the pipeline and furnace tube are cleaned while the process is performed, further extending the maintenance time of the equipment.

[0037] (2) In the present application, H2 and O2 can quickly and uniformly diffuse in the furnace tube under low pressure, which greatly improves the uniformity of silicon growth, and the growth rate of the oxidation layer in the wet oxygen process is fast, which can greatly reduce the process time of boron diffusion.

[0038] (3) In the present application, H2 and O2 are gases, which can be accurately controlled in flow compared with water bottle bubbling wet oxygen, which is conducive to the stability of the process. Water bottle bubbling is easy to cause difference in water vapor concentration in the pipe, which leads to increased non-uniformity of the oxidation layer of the whole pipe.

[0039] (4) In the present application, the temperature range of H2 and O2 wet oxygen process is wide, which can be adjusted from 800-1100℃. In the conventional water bottle bubbling wet oxygen method, the temperature is generally controlled at about 900-950℃ to ensure uniformity.

[0040] (5) The wet oxygen process of the present application can be used for boron diffusion process of solar cells, for fast and uniform growth of the oxidation layer. The uniform oxidation layer plays a good protective role for the subsequent acid and alkali etching process. At the same time, with the rapid growth of the oxidation layer, the precipitation of B on the surface of the silicon wafer is accelerated, which reduces the surface concentration, so that the surface concentration of dry oxidation can be reached in a relatively short time, saving cost. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is the ECV detection result schematic diagram of the process in Comparative Example 1 and the wet oxygen process in Example 1. DETAILED DESCRIPTION

[0042] The technical solutions of the present application will be further described in detail below with reference to the accompanying drawings. It should be pointed out that the specific embodiments are only a detailed description of the present application, and should not be regarded as a limitation of the present application.

[0043] Example 1

[0044] A new type of boron diffusion wet oxygen process, comprising the following steps:

[0045] (1) The boat carrying the silicon wafer is sent into the furnace tube;

[0046] (2) Vacuumizing and leak detection;

[0047] (3) Ramp up: Ramp up from 700 °C to 800 °C in 15 min, N2 flow, furnace pressure 150 mbar;

[0048] (4) Pre-oxidation: Oxidation at 800 °C, 1000 seem N2, 2000 seem O2, both for 10 min;

[0049] (5) DEP1: After furnace tube is heated to 800 °C, 1500 seem N2, 540 seem O2, 200 seem BCl3, all for 2 min, furnace pressure 150 mbar;

[0050] (6) DEP2: After furnace tube is heated to 830 °C, 1500 seem N2, 540 seem O2, 200 seem BCl3, all for 4 min, furnace pressure 150 mbar;

[0051] (7) DEP3: After furnace tube is heated to 850 °C, 1500 seem N2, 540 seem O2, 200 seem BCl3, all for 4 min, furnace pressure 150 mbar;

[0052] (8) Ramp up: Ramp up from 850 °C to 950 °C in 20 min, 2000 seem N2 flow for 20 min, furnace pressure 400 mbar;

[0053] (9) Isothermal push: 950 °C isothermal push for 20 min, 2000 seem N2 flow for 20 min, furnace pressure 400 mbar;

[0054] (10) Ramp up: Ramp up from 950 °C to 1050 °C in 10 min, 1000 seem N2, 10000 seem O2, both for 10 min, furnace pressure 600 mbar;

[0055] (11) Oxidation: Oxidation at 1050 °C for 20 min, 1000 seem N2, 10000 seem O2, both for 20 min, furnace pressure 600 mbar;

[0056] (12) Wet oxidation: Wet oxidation at 1050 °C for 40 min, 1500 seem H2, 3500 seem O2, both for 40 min, furnace pressure 250 mbar;

[0057] In the present application, before wet oxidation, oxidation (i.e. step 11) is carried out first, so that oxygen uniformly fills the furnace tube, an oxygen-rich environment in the furnace tube is created in advance, and H2 is prepared for reaction with O2 to generate water vapor, thereby reducing the concentration of H2 and reducing the risk of explosion due to too high concentration of H2.

[0058] The high-temperature oxidation process has the effect of pushing boron atoms into the interior of silicon, and the slow growth rate of dry oxygen in step (11) can slow down the pushing speed, which is beneficial to the uniformity of sheet resistance.

[0059] (13) Cooling oxidation: from 1050℃ to 800℃, 100sccm N2 and 10000sccm O2 are introduced during the process, each for 30min, and the pressure is 600mbar;

[0060] In the present embodiment, wet oxidation is not used in step (13) cooling oxidation, mainly because the BSG layer has reached the required thickness. In the present application, wet oxidation or dry oxygen oxidation can be selected in step (13) according to the required thickness of the BSG layer in the process;

[0061] (14) Breaking vacuum: N2 is introduced to break the vacuum to normal pressure;

[0062] (15) Out of boat.

[0063] Example 2

[0064] A new type of boron diffusion wet oxidation process, comprising the following steps:

[0065] (1) The boat carrying the silicon wafer is sent into the furnace tube;

[0066] (2) Vacuum pumping and leak detection;

[0067] (3) Heating: from 700℃ to 800℃ at a slope of 12min, N2 is introduced, and the furnace tube pressure is 150mbar;

[0068] (4) Pre-oxidation: at 800℃, 1100sccm N2 and 2000sccm O2 are introduced, each for 10min, for oxidation;

[0069] (5) DEP1: After the furnace tube is heated to 800℃, 1500sccm N2, 540sccm O2 and 200sccm BCl3 are introduced, each for 2min, and the furnace tube pressure is 150mbar;

[0070] (6) DEP2: After the furnace tube is heated to 830℃, 1500sccm N2, 540sccm O2 and 200sccm BCl3 are introduced, each for 4min, and the furnace tube pressure is 150mbar;

[0071] (7) DEP3: After the furnace tube is heated to 850°C, 1500 seem of N2, 540 seem of O2, and 200 seem of BCl3 are introduced for 4 min each; the furnace tube pressure is 150 mbar;

[0072] (8) Heating: from 850°C to 960°C at a slope for 22 min, 2100 seem of N2 is introduced during the heating process for 20 min, and the furnace tube pressure is 440 mbar;

[0073] (9) Constant temperature promotion: constant temperature promotion at 960°C for 22 min, 2000 seem of N2 is introduced during the promotion process for 20 min; the furnace tube pressure is 400 mbar;

[0074] (10) Heating: from 960°C to 1050°C at a slope for 12 min, 1000 seem of N2 and 10000 seem of O2 are introduced during the heating process for 10 min each, and the furnace tube pressure is 600 mbar;

[0075] (11) Oxidation: oxidation at 1050°C for 20 min, 1000 seem of N2 and 10000 seem of O2 are introduced during the process for 20 min each; the furnace tube pressure is 600 mbar;

[0076] (12) Wet oxidation: wet oxidation at 1050°C for 40 min, 1500 seem of H2 and 3500 seem of O2 are introduced during the process for 40 min each, and the furnace tube pressure is 250 mbar;

[0077] (13) Cooling oxidation: from 1050°C to 800°C, 100 seem of N2 and 10000 seem of O2 are introduced during the process for 30 min each, and the pressure is 600 mbar;

[0078] (14) Breaking vacuum: breaking vacuum to normal pressure by introducing N2;

[0079] (15) Boat output.

[0080] Comparative Example 1

[0081] A new type of boron diffusion wet oxygen process, comprising the following steps:

[0082] (1) The boat loaded with silicon wafer is sent into the furnace tube;

[0083] (2) Vacuum pumping and leak detection;

[0084] (3) Heating: from 700°C to 800°C at a slope for 15 min, N2 is introduced, and the furnace tube pressure is 150 mbar;

[0085] (4) Pre-oxidation: at 800°C, 1000 seem N2, 2000 seem O2, both for 10 min, oxidation;

[0086] (5) DEP1 : after the furnace tube was heated to 800°C, 1500 seem N2, 540 seem O2, 200 seem BCl3, all for 2 min, the furnace tube pressure was 150 mbar;

[0087] (6) DEP2: after the furnace tube was heated to 830°C, 1500 seem N2, 540 seem O2, 200 seem BCl3, all for 4 min, the furnace tube pressure was 150 mbar;

[0088] (7) DEP3: after the furnace tube was heated to 850°C, 1500 seem N2, 540 seem O2, 200 seem BCl3, all for 4 min, the furnace tube pressure was 150 mbar;

[0089] (8) Heating: from 850°C to 950°C at a slope for 20 min, 2000 seem N2 was introduced during the heating process, all for 20 min, the furnace tube pressure was 400 mbar;

[0090] (9) Constant temperature promotion: 950°C constant temperature promotion for 20 min, 2000 seem N2 was introduced during the promotion process, all for 20 min, the furnace tube pressure was 400 mbar;

[0091] (10) Heating: from 950°C to 1050°C at a slope for 10 min, 1000 seem N2, 10000 seem O2, both for 10 min, the furnace tube pressure was 600 mbar;

[0092] (11) Oxidation: dry oxidation at 1050°C for 120 min, 1000 seem N2, 10000 seem O2, both for 120 min, the furnace tube pressure was 600 mbar;

[0093] (12) Cooling oxidation: from 1050°C to 800°C, 100 seem N2, 10000 seem O2, both for 30 min, the pressure was 600 mbar;

[0094] (13) Breaking vacuum: N2 was introduced to break the vacuum to normal pressure;

[0095] (14) Boat removal. 1.

[0097] Table 1

[0098]

[0099] The advancing pressure in Table 1 is the pressure in the wet oxygen oxidation step (12) of Example 1 and the pressure in the dry oxygen oxidation step (11) of Comparative Example 1, respectively. The tail maintenance period refers to the maintenance of the tail-related components, mainly the maintenance of the vacuum pump.

[0100] Compared with the O2 dry oxidation process in Comparative Example 1, the oxidation layer growth rate in Example 1 is 2.5 times that of the O2 dry oxidation process, and the process pressure of the present application is lower, which is conducive to increasing the service life of the quartz piece and the sealing piece; the whole process time is shortened by 60 min, greatly reducing the production cost; due to the cleaning of water vapor to the tail and the furnace tube, the maintenance period is also greatly extended, and the maintenance frequency is reduced.

[0101] 2. ECV & electrical performance data comparison:

[0102] The ECV doping concentration detection data is as shown in Table 1, and the boron diffusion is carried out by the process of Example 1 and the process of Comparative Example 1. The electrical performance data of the finally prepared battery is as shown in Table 2. Figure 1

[0103] Table 2 Electrical performance data

[0104]

[0105] Note: ETA represents conversion efficiency, UOC represents open circuit voltage, Isc represents short circuit current, FF represents fill factor, Rs represents the series resistance of the solar cell, RSH represents the parallel resistance of the solar cell; in the table, the test quantity refers to the number of test battery pieces, and the electrical performance data in Table 2 is the average value.

[0106] Compared with the dry oxidation process in Comparative Example 1, the ECV curve of the present application has a shallower junction depth and a higher surface concentration due to the 60 min reduction in process time, but this brings about the improvement of FF and Isc, resulting in the final conversion efficiency being 0.08% higher than that of the oxidation process in Comparative Example 1.

[0107] 3. The uniformity data is as shown in Table 3.

[0108] Table 3

[0109]

[0110] From the data in Table 3, it can be seen that in the present application, the silicon sheet resistance uniformity and the resistance value are basically consistent with the dry oxidation process, so after shortening the process time and improving the growth rate, the uniformity of the oxidation layer and the resistance has not deteriorated.

[0111] ​Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the present application.

Claims

1. A novel boron diffusion wet oxygen process, characterized in that, Includes the following steps: (1) The boat carrying the silicon wafers is sent into the furnace tube; (2) Vacuum pump and leak check; (3) Heat to 800-810℃, introduce N2, and the furnace tube pressure is 150-180mbar; (4) At 800-810℃, N2 and O2 are introduced to carry out oxidation; (5) After heating to 800-810℃, introduce N2, O2 and boron sources, and the furnace tube pressure is 150-180mbar; (6) After heating to 830-840℃, introduce N2, O2 and boron sources, and the furnace tube pressure is 150-180mbar; (7) After heating to 850-860℃, introduce N2, O2 and boron sources, and the furnace tube pressure is 150-180mbar; (8) Heat to 950-960℃, introduce N2 during the heating process, and keep the furnace tube pressure at 400-450mbar; (9) The constant temperature propulsion is carried out at 950-960℃ for 20-23 minutes. N2 is introduced during the propulsion process and the furnace tube pressure is 400-450 mbar. (10) Heat to 1040-1050℃, and introduce N2 and O2 during the heating process. The furnace tube pressure is 600-650mbar. (11) Oxidize at 1040-1050℃ for 20-22 min, and introduce N2 and O2 during the oxidation process. The furnace tube pressure is 600-650 mbar. (12) Oxidize at 1040-1050℃ for 40-42 min, during which H2 and O2 are introduced and the furnace tube pressure is 250-300 mbar; (13) Cool down from 1040-1050℃ to 800℃, during which nitrogen and oxygen are introduced at a pressure of 600-650mbar. (14) Break the vacuum to normal pressure; (15) Get out of the boat.

2. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (3), the temperature is increased from 700℃-710℃ to 800-810℃ at a slope of 12-15 minutes.

3. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (4), the flow rates of N2 and O2 are 1000-1100 sccm and 2000-2100 sccm, respectively, and the flow time is 10-12 min.

4. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (5), the boron source is BCl3 or / and BBr3.

5. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (5), the flow rates of N2, O2 and boron source are 1500-1600 sccm, 540-560 sccm and 200-250 sccm, respectively, and the flow time is 2-3 min.

6. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (10), the temperature is increased from 950-960℃ to 1040-1050℃ at a slope, which takes 10-12 minutes.

7. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (10), the flow rates of N2 and O2 are 1000-1100 sccm and 10000-11000 sccm, respectively, and the flow time is 10-13 min.

8. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (11), the flow rates of N2 and O2 are 1000-1100 sccm and 10000-11000 sccm, respectively.

9. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (12), H2 and O2 are introduced at flow rates of 1500-1700 sccm and 3500-3700 sccm, respectively.

10. The novel boron diffusion wet oxygenation process according to claim 1, characterized in that, In step (13), the flow rates of nitrogen and oxygen are 100-500 sccm and 10000-11000 sccm, respectively, and the introduction time is 30-35 min.

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