CN111403271A - Process method for depositing and doping silicon wafer surface - Google Patents

Abstract

The present invention provides a process method for depositing doping on a silicon surface, comprising a chamber capable of accommodating a silicon wafer and allowing the silicon to undergo surface deposition doping reaction therein, the chamber can be passed through for deposition doping impurities and/or gases conducive to deposition of doping, the chamber may be airtight, gas may be introduced or released in the chamber, temperature control or pressure regulation may be performed in the chamber, the chamber The process method in the chamber alternately passes different or the same gas during the reaction process of depositing doping. The present invention is beneficial for increasing the doping concentration and for increasing the uniform distribution of the doping sources.

Description

A process method for depositing doping on the surface of a silicon wafer

technical field

The present invention relates to the fields of solar photovoltaic and semiconductor manufacturing, and is particularly applicable to deposition and doping processes therein.

Background technique

In the field of solar photovoltaic and semiconductor manufacturing, diffusion equipment is mainly used for processes such as boron doping or phosphorus doping, and low pressure chemical vapor deposition (LPCVD) equipment is often used for silicon oxide, silicon nitride, amorphous silicon, polysilicon, phosphorus doped non- Thin films such as crystalline silicon and boron-doped amorphous silicon are grown; when the temperature and pressure of these conventional diffusion equipment reach the process conditions, the doping source gas, carrier gas, reaction gas, etc. enter the furnace body to participate in the reaction.

In the conventional LPCVD doping process, silane is used as the gas for growing silicon, and phosphine, diborane, etc. are used as the doping source gas. After the temperature and pressure are stable and meet the process requirements, silane and doping source gas are simultaneously introduced into the furnace, and a certain thickness and a certain concentration of doped amorphous silicon or doped polysilicon can be obtained after a certain period of time. Then go to the subsequent annealing process.

It is generally understood that in order to make the reaction more uniform or to make the results of the reaction such as film thickness and uniformity better, the gas will be mixed as uniformly as possible to achieve the above purpose, but the mixed gas is used for the reaction. On the contrary, it will lead to worse uniformity. The reasons are mainly as follows. First, silane and doping source gas enter the furnace body at the same time, and the gas concentration in each part is different, that is, the two gases react more quickly near the outlet of the furnace. In addition, due to the different decomposition rates of the impermeable gas, during the process of the gas running in the furnace tube, due to the different decomposition rates, the gas in the mixed gas decomposes relatively quickly and is easily consumed in the first half, and in the second half. The amount of the film is reduced, and the decomposition is relatively slow, and the reaction is mainly carried out in the second half. This method will cause the problem of uneven film thickness and uneven concentration. In fact, qi can not fundamentally solve the above problems.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention provides a process method for depositing doping on a silicon surface, which is beneficial to increase the doping concentration and improve the uniform distribution of doping sources.

In the process method adopted in the present invention, after the temperature and pressure reach stable process requirements, the reaction gas and the doping source gas are alternately injected into the cavity loaded with the silicon material, usually the sheet material, and the layered film is grown or doped. , so as to achieve the purpose of gradual generation and uniformity. When each reactive gas is introduced, there is no interference of other gases, and it is easy to form a uniform film thickness, and the doping concentration is higher than that of conventional products.

To this end, the process method used in the present invention includes a chamber capable of accommodating silicon wafers and allowing silicon to undergo surface deposition doping reactions therein, and the chamber can be passed through for deposition of doping and/or organic materials. In order to facilitate the deposition of doped gas, the chamber can be airtight, gas can be introduced or released in the chamber, temperature control or pressure regulation can be performed in the chamber, and the chamber can be During the reaction process of depositing doping, different or identical gases are introduced alternately at intervals.

Further, the gas includes a reactive gas that can be decomposed or adsorbed on the surface of the silicon wafer or react with substances on the surface of the silicon wafer. The reaction can include:

SiH ₄ (adsorption)=SiH ₂ (adsorption)+H ₂ ;

SiH ₂ (adsorption)=Si (solid)+H ₂ ;

PH ₃ (adsorption)=P (solid)+3/2H ₂

Further, the reaction gas can be introduced alone or by adding diluent gas or promoting gas.

On this basis, the diluent gas can be used to dilute the reactant gas without reacting or depositing with the reactant gas or the silicon wafer, and the diluent gas may include inert gas, nitrogen, hydrogen and the like.

The promoting gas can be used to promote the reaction gas to decompose or adsorb on the surface of the silicon wafer or react with substances on the surface of the silicon wafer, and the promoting gas can include hydrogen.

During the process, the main reaction gas and the doping source gas alternately flow into the cavity in which the silicon is placed to perform the process, and the main reaction gas and the doping source gas are introduced into the cavity in which the silicon is placed in different periods of time. process in the cavity.

In order to ensure the precision of the process, if conditions permit, the present invention preferably exhausts the main reaction or doping source gas injected in the previous injection before each gas injection, and then injects the next gas.

As an application scenario of the present invention, in the present invention, the cavity may adopt an LPCVD reaction furnace or a diffusion furnace. Taking the LPCVD reactor as an example, before the formal reaction, if necessary, pretreatment such as oxidation or annealing can be performed. After the pretreatment, when the doping coating process is started in LPCVD, the reaction conditions in the furnace are controlled in the temperature range of 530-650 degrees, and the process pressure range is 50mtorr-800mtorr. When the process conditions are reached, the main reaction is conducted alternately at intervals The gas and the doping source gas are put into the furnace body for the process, wherein the main reaction gas can be silane, and the doping source gas can be diluent gases including phosphine, diborane, borane, boron chloride, etc., After the process is over, the process gas is pumped and exhausted, and the temperature is lowered and the pressure is returned to the furnace.

In a technological process, the alternating ventilation can first introduce silane, stop and exhaust silane after a period of time; then introduce nitrogen, stop and exhaust nitrogen after a period of time; and then introduce doping source gas; After time, stop and exhaust the doping source gas, and then introduce nitrogen; and so on.

In a technological process, the alternate ventilation can first introduce silane and nitrogen, stop and exhaust the aforementioned gas after a period of time; then introduce nitrogen, stop and exhaust nitrogen after a period of time; and then introduce the doping source Gas and nitrogen, stop after a period of time and exhaust the aforesaid gas; re-introduce nitrogen; and so on.

In a process, the alternating ventilation can first introduce silane, stop and exhaust silane after a period of time; then introduce doping source gas, stop and exhaust doping source gas after a period of time; and so on. .

In a technological process, the alternate ventilation can first introduce silane and nitrogen, stop and exhaust the aforementioned gas after a period of time; then introduce doping source gas and nitrogen, stop and exhaust the aforementioned gas after a period of time; And so on.

Generally speaking, the passing time of silane is 1 second to 600 seconds, the passing time of doping source is 1 second to 600 seconds, and there can be a time interval of 0 to 120 seconds between passing silane and passing doping source gas; Enter a certain flow of nitrogen, or hydrogen or inert gas, which is used as a carrier gas, reducing pressure fluctuations during gas exchange, and diluting gas.

It should be noted that, in the process of the present invention, the time of the gas introduced each time should not be too long, to avoid that the reaction time of a certain gas is too long, and the generated material layer is too thick to achieve annealing uniformity, so it is necessary to strictly control the ventilation. time to control the thickness of each growth.

In practical applications, the way in which silane and doping source gas are introduced into the furnace body can be controlled directly into the furnace body through a preset on-off valve, or it can be pumped out first by the pump according to the set flow, and then discharged according to the set time. The process is carried out by switching the valve into the furnace tube in turn, that is, when a certain gas is not used in the furnace, it is directly discharged through the pump, and when a certain gas is needed, it is switched to the furnace through the valve. waiting time.

The beneficial effects of the present invention are: the present invention feeds one main reaction gas or doping source gas at a time, which is equivalent to only one reaction or doping at a time. After the current reaction or doping is completed, the current gas is discharged, and the The formation of layer-by-layer deposition growth in the reaction chamber is conducive to increasing the doping concentration and the uniform distribution of doping sources in the film. Interference can make the reaction consistent in the same time period, and the film thickness between sheets is uniform.

Description of drawings

FIG. 1 is a process flow diagram of Embodiment 1. FIG.

FIG. 2 is a process flow diagram of Embodiment 2. FIG.

FIG. 3 is a process flow diagram of Embodiment 3. FIG.

FIG. 4 is a process flow diagram of Embodiment 4. FIG.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with some specific implementation cases, or some comparisons and demonstrations of the results of the present invention will be made. It should be noted that the examples and comparative examples expressed in For those skilled in the art to better realize the technical solutions of the present invention and understand the technical effects of the present invention, the embodiments cannot be exhausted, so the protection scope of the present invention should not be limited to the contents described in the embodiments.

In addition, in some embodiments of the present invention, a method of arranging and arranging silicon wafers is adopted, which is mainly to verify the technical effect of the present invention. In actual production, the process can be carried out in a batch manner. .

Example 1

Take LPCVD doping as an example:

(1) 10 polishing sheets were prepared, 5 sheets in group A were grown with an oxide layer of 100 nm, and 5 sheets in group B were cleaned with hydrofluoric acid. (Group A is used to measure the film thickness of intrinsic silicon, and Group B is used to measure the doping concentration, the same below)

(2) In the LPCVD furnace chamber, place a quartz boat, and place one silicon wafer of group A and group B at 5 average intervals in the boat from the furnace mouth to the furnace tail (the positions are numbered 1, 2, 3, and 4 respectively). , 5).

(3) Oxygen is introduced into the LPCVD furnace, and an oxide layer of 1.5 nm is first grown on the surface of the silicon wafer.

(4) Evacuate oxygen and check for leaks.

(5) Control the temperature at 550°C and the pressure at 200mtorr, and start the ventilation reaction;

The specific ventilation steps are:

(5.1) pass 300sccm silane, the ventilation time is 60 seconds;

(5.2) 300sccm silane was introduced, and the ventilation time was 4 seconds;

(5.3) Phosphine diluted with nitrogen (the volume concentration of phosphine is 2%) is introduced, the flow rate is 300sccm, and the ventilation time is 3 seconds;

(5.4) loop to step (5.2).

The total aeration time throughout the process was 148 minutes.

After the process is completed, the temperature is lowered and the pressure is released, and the silicon wafers of groups A and B are taken out. After annealing, the doping film thickness of group A and the doping concentration of group B are tested. The test results are shown in Table 1:

Table 1

Wafer location 1 2 3 4 5 Film thickness (nm) 113 110 114 110 115 Concentration (/cm³) 8.2E20 8.5E20 8.1E20 8.0E20 8.4E20

It can be seen from Table 1 that through the above method, the obtained film thickness uniformity is 2.2%, the doping concentration uniformity is 3.0%, and the average concentration is 8.24E20/cm ³ .

Example 2

Take LPCVD doping as an example:

(1) 10 polishing sheets were prepared, 5 sheets in group A were grown with an oxide layer of 100 nm, and 5 sheets in group B were cleaned with hydrofluoric acid to remove the surface oxide layer.

(2) In the LPCVD boat, take 5 average intervals from the furnace mouth to the furnace tail and put down one silicon wafer of group A and group B respectively (the positions are 1, 2, 3, 4, and 5).

(3) The boat is pushed into the furnace tube, and oxygen is introduced to grow an oxide layer with a thickness of 1.5 nm.

(4) Evacuate oxygen and check for leaks.

(5) temperature control 570 degrees, pressure 450mtorr, start ventilation reaction;

The specific ventilation steps are:

(5.1) The total flow of silane is 380sccm, and the ventilation is 60 seconds;

(5.2) Introduce 200sccm of nitrogen gas, 300sccm of total flow of phosphine (diluted to 3% volume concentration), and ventilate for 4 seconds;

(5.3) Introduce nitrogen gas for 600sccm for 4 seconds;

(5.4) nitrogen 200sccm, silane total flow 380sccm, ventilation for 8 seconds;

(5.5) Nitrogen 600sccm, 4 seconds;

(5.6) loop to step (5.2).

The total ventilation step time was 180 minutes.

After the process is completed, take out group A and group B slices, after annealing, test the doping film thickness of group A and test the doping concentration of group B, the results are shown in Table 2:

Table 2

Wafer location 1 2 3 4 5 Thickness (nm) 108 107 110 112 108 Concentration (/cm3) 7.2E20 6.8E20 7.1E20 6.9E20 7.2E20

It can be seen that through the above method, the obtained film thickness uniformity is 2.3%, the doping concentration uniformity is 3.5%, and the average concentration is 7.0E20/cm ³ .

Example 3

Take LPCVD doping as an example:

(1) 10 polishing sheets were prepared, 5 sheets in group A were grown with 100 nm oxide layer, and 5 sheets in group B were cleaned with hydrofluoric acid.

(2) In the LPCVD furnace chamber, place a quartz boat, and place one silicon wafer of group A and group B at 5 average intervals in the boat from the furnace mouth to the furnace tail (the positions are numbered 1, 2, 3, and 4 respectively). , 5).

(3) The furnace tube was pushed forward, oxygen was introduced, and the oxidation process was carried out at 530° C., and the oxidation time was 10 minutes.

(4) Evacuate oxygen and check for leaks.

(5) The temperature is controlled to 580°C, the pressure is 500mtorr, the nitrogen flow rate is kept at 200sccm, and the nitrogen gas is still passed through the dopant source gas for 200sccm.

(6) Circulating and feeding silane, phosphine, silane and phosphine in turn (dilute the phosphine to a volume concentration of 3%), the total flow of silane is 430 sccm, the time of each feeding is 8 seconds, and the total flow of phosphine is 400 sccm , each time for 9 seconds, silane, phosphine ventilation interval of 10 seconds, the interval time to increase the nitrogen flow, the flow rate is 400sccm, the total circulation ventilation time 223 minutes.

After the process is completed, the temperature is lowered and the pressure is released, and the A and B groups are taken out. After annealing, the doping film thickness of the A group and the doping concentration of the B group are tested. The test results are shown in Table 3:

table 3

Wafer location 1 2 3 4 5 Film thickness (nm) 85 86 89 85 84 Concentration (/cm3) 7.3E20 7.1E20 7.4E20 7.5E20 7.3E20

It can be seen from Table 3 that through the above method, the obtained film thickness uniformity is 2.9%, and the doping concentration uniformity is 2.7%. And the average concentration was 7.38E20/cm ³ .

Comparative Example 1

In order to highlight the difference between the present invention and conventional ventilation methods in the prior art, a group of comparative examples is set up, taking LPCVD doping as an example:

1) Prepare 10 polishing sheets, 5 sheets in group A grow 100nm oxide layer, and 5 sheets in group B are cleaned with hydrofluoric acid.

2) Place one silicon wafer of Group A and Group B at 5 average intervals in the boat from the mouth of the furnace to the tail of the furnace (the positions are numbered 1, 2, 3, 4, and 5 respectively).

3) In the LPCVD furnace, after first oxidizing a layer of 1-2 nm oxide layer, stabilize the process temperature at 550 ° C and the pressure at 300 mtorr, and feed silane and phosphine at the same time. Time 90min.

After the process is completed, the temperature is reduced and the pressure is released, and the A and B groups are taken out. After annealing, the doping film thickness of the A group and the doping concentration of the B group are tested. The test results are shown in Table 4:

Table 4

Wafer location 1 2 3 4 5 Film thickness (A) 105 106 109 112 108 Concentration (B) 5.2E20 4.9E20 4.2E20 3.3E20 3.7E20

The uniformity of the film thickness obtained by the method in Table 3 was 3.2%, the uniformity of the doping concentration was 22.3%, and the average concentration was 4.26E20/cm3. Obviously, the performance of the conventional ventilation method in terms of film thickness uniformity and doping concentration is significantly different from that of the present invention, and it is difficult for this method to achieve uniform film thickness and uniform concentration at the same time. And the concentration is lower than the present invention.

Example 4

Take boron diffusion as an example:

1) Clean the N-type silicon wafer after texturing, place it in a quartz boat, and enter the furnace tube.

2) The temperature is increased to a constant temperature of 830°C, the pressure is controlled to 250mbar, and the ventilation reaction is started:

The specific ventilation steps are:

2.1) Pass nitrogen 1700sccm, oxygen 450sccm, ventilation time 30 seconds

2.2) Pour nitrogen 2100sccm, ventilation time 20 seconds

2.3) Pass nitrogen 1700sccm, boron trichloride 90sccm, ventilation time 30 seconds

2.4) Pour nitrogen 2100sccm, ventilation time 20 seconds

2.5) Loop to step 2.1)

20 cycles in total.

3) The temperature was raised to 1000°C, the pressure was 450 mbar, the nitrogen flow was 3000 sccm for 5 minutes, and the oxygen flow was 5000 sccm for 20 minutes.

4) Cooling down, back pressure and out of the oven.

Take 5 silicon wafers at an average interval from the furnace mouth to the furnace tail (the positions are marked as 1, 2, 3, 4, and 5), and test the square resistance. The results are shown in Table 5:

table 5

Cell 1 2 3 4 5 square resistance 109 107 106 105 108

It can be seen from Table 5 that the uniformity between the square resists of the silicon wafer obtained in Example 4 is 2.3%.

Example 5

Take boron diffusion as an example:

1) Clean the N-type silicon wafer after texturing, place it in a quartz boat, and enter the furnace tube.

2) Control the temperature to a constant temperature of 815°C, control the pressure to 150mbar, and start the ventilation reaction:

The specific ventilation steps are:

2.1) Pass nitrogen 1470sccm, oxygen 500sccm, ventilation time 45 seconds

2.2) Pass nitrogen for 1900sccm, ventilation time for 30 seconds

2.3) Pass nitrogen 1470sccm, boron trichloride 150sccm, ventilation time 40 seconds

2.4) Pass nitrogen for 1900sccm, ventilation time for 30 seconds

2.5) Loop to step 2.1)

18 cycles in total.

3) The temperature was raised to 1010° C., the pressure was 450 mbar, the nitrogen flow was 2500 sccm for 5 minutes, and the oxygen flow was 4500 sccm for 20 minutes.

4) Cooling down, back pressure and out of the oven.

Take 5 silicon wafers at an average interval from the furnace mouth to the furnace tail (the positions are marked as 1, 2, 3, 4, and 5) to test the square resistance. The results are shown in Table 6:

Table 6

Cell 1 2 3 4 5 square resistance 95 97 96 95 98

It can be seen from Table 6 that the uniformity between the square resists obtained by Example 5 is 1.6%.

Due to the high pressure in the furnace in the boron expansion process, the single ventilation time is relatively long.

Comparative Example 2

1) Clean the N-type silicon wafer after texturing, place it in a quartz boat, and enter the furnace tube.

2) The temperature is controlled to a constant temperature of 820°C, the pressure is controlled to 250mbar, and the ventilation reaction is started:

Through nitrogen 1700sccm, oxygen 450sccm, boron trichloride 150sccm, ventilation time 10 minutes.

3) The temperature was raised to 1000°C, the pressure was 450 mbar, the nitrogen flow was 3000 sccm for 5 minutes, and the oxygen flow was 5000 sccm for 20 minutes.

4) Cooling down, back pressure and out of the oven.

Take 5 silicon wafers at an average interval from the furnace mouth to the furnace tail (the positions are marked as 1, 2, 3, 4, and 5) to test the square resistance. The results are shown in Table 7:

Table 7

Cell 1 2 3 4 5 square resistance 106 102 97 94 97

In Comparative Example 2, a more traditional mixed ventilation method is adopted in order to adopt the method of alternating circulation ventilation. The alternate ventilation mode of the present invention can significantly improve the uniformity between the square resists of the silicon wafers prepared by the boron expansion process.

Claims (17)

1. A process method for depositing doping on a silicon surface, the process method comprising a chamber capable of accommodating a silicon wafer and allowing silicon to perform surface deposition doping reaction therein, wherein the chamber can be used for For the deposition of doping and/or the gas that is favorable for the deposition of doping, the process method is characterized in that different or the same gas is introduced alternately and at intervals during the reaction process of depositing doping. 2 . The method for depositing and doping on the surface of silicon according to claim 1 , wherein the gas comprises a reactive gas that can be decomposed or adsorbed on the surface of the silicon wafer or react with substances on the surface of the silicon wafer. 3 . 3 . The method for depositing and doping the silicon surface according to claim 2 , wherein the reaction gas can be introduced alone or by adding a dilution gas or a gas that promotes the reaction. 4 . 4 . The method for depositing doping on the surface of a silicon wafer according to claim 3 , wherein the dilution gas can be used to dilute the reactive gas, and does not react or deposit with the reactive gas or the silicon wafer. 5 . , the diluent gas can include inert gas, nitrogen, hydrogen, etc. 5. A process method for depositing doping on the surface of a silicon wafer according to claim 3, wherein the promoting gas can be used to promote the reaction gas to be decomposed or adsorbed on the surface of the silicon wafer or with the surface of the silicon wafer. The reaction of a substance, the promoting gas may include hydrogen. 6 . The method for depositing doping on a silicon surface according to claim 2 , wherein the reactive gas can include a main reactive gas and a doping source gas. 7 . 7 . The method for depositing and doping silicon surface according to claim 6 , wherein the main reaction gas can be silane, and the doping source gas can be phosphine, diborane, boron alkane, boron chloride gas. 8 . The method for depositing and doping silicon surface according to claim 6 , wherein the main reaction gas can be oxygen, and the doping source gas can be composed of boron chloride, nitrogen or argon. 9 . Gases such as phosphorus oxychloride carried, boron bromide carried by nitrogen or argon. 9 . The method for depositing doping on a silicon surface according to claim 6 or 7 , wherein the main reaction gas and the doping source gas alternately flow into the cavity in which the silicon wafer is placed. 10 . process. 10 . The method for depositing doping on a silicon surface according to claim 9 , wherein the main reaction gas and the doping source gas are passed into the cavity in which the silicon wafer is placed in different periods of time. 10 . craft. 11 . The method for depositing doping on the surface of a silicon wafer according to claim 1 , wherein the cavity can be an LPCVD reactor or a diffusion furnace. 12 . 12 . The method for depositing doping on the surface of a silicon wafer according to claim 1 , wherein the reaction conditions in the chamber are controlled within a temperature range of 500-800 degrees, and a process pressure range of 0-1200 mtorr. 13 . 13 . The process method for depositing doping on the surface of a silicon wafer according to claim 1 or 12 , wherein the reaction conditions in the chamber are controlled within a temperature range of 770-900 degrees, and a process pressure range of 20mbar～ normal pressure. 14. The process method for depositing and doping on the surface of a silicon wafer according to claim 1, wherein the alternate ventilation can first introduce silane, stop and exhaust silane after a period of time; Nitrogen, stop and exhaust nitrogen after a period of time; then feed the doping source gas; stop and exhaust the doping source gas after a period of time, and then feed nitrogen; and so on. 15. The process method for depositing and doping on the surface of a silicon wafer according to claim 1, wherein the alternate ventilation can first introduce silane and nitrogen, and stop and exhaust the aforementioned gas after a period of time; Then feed nitrogen, stop and exhaust nitrogen after a period of time; feed doping source gas and nitrogen again, stop and exhaust the aforementioned gases after a period of time; feed nitrogen again; and so on. 16 . The method for depositing doping on the surface of a silicon wafer according to claim 1 , wherein the alternate ventilation can first introduce silane, stop and exhaust silane after a period of time; Doping the source gas, stop and exhaust the doping source gas after a period of time; and so on. 17. A process method for depositing and doping on the surface of a silicon wafer according to claim 1, wherein the alternate ventilation can first introduce silane and nitrogen, and stop and exhaust the aforementioned gas after a period of time; The doping source gas and nitrogen gas are introduced again, and the gas is stopped and exhausted after a period of time; the cycle is repeated.

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