A PECVD PSG / BPSG film preparation process without annealing to improve the reflow angle

Abstract

The invention discloses a PECVD PSG / BPSG film preparation process for improving the reflux angle without annealing, and belongs to the field of semiconductor technology. The invention optimizes the BPSG / PSG process temperature (450-500°C), pressure (3-5 torr), plate spacing (500-550 mils), and power (700-800 W), and each key condition works together to achieve the effect of reducing the reaction rate, improving the filling performance, and reducing the reflux angle, thereby achieving the purpose of removing the annealing process and significantly reducing the production cost.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors, and in particular relates to a PECVD PSG / BPSG film preparation process for improving the reflow angle without annealing. Background Art

[0002] As the size of semiconductor devices decreases, the width of the holes to be filled by the first layer of pre-metal dielectric (PMD) is getting smaller and smaller, and the aspect ratio is getting larger and larger. The hole filling ability has become the main consideration parameter for selecting PMD films. Silicon oxide is widely used as an insulating layer in the manufacture of semiconductor devices. For many years, boron and phosphorus doped silicate films, such as borophosphosilicate (BPSG) films or phosphosilicate (PSG) films, deposited from liquid sources such as tetraethylorthosilicate (TEOS), have become the first choice among silicon oxide films because of their excellent gap filling ability during glass reflow.

[0003] PSG / BPSG films are widely used as PMD films in advanced semiconductor devices, especially dynamic random access memory (DRAM) products. However, in order to improve the flatness of the trench after hole filling, high-temperature annealing is generally performed after the PSG / BPSG film is grown, but high-temperature annealing will increase the thermal budget, and some front layers will fail in high-temperature environments (front-layer metal silicides, etc. will fail at high temperatures, and high temperatures will also cause channel doping ion drift, etc.), so reducing the thermal budget has become an extremely important issue for semiconductor devices. Boron and phosphorus are introduced into the silicate glass layer to form doped silicate glass (BPSG) to improve the reflow and impurity absorption behavior of the BPSG film. For example, the existing Chinese patent document CN105826185A reports that the reflow process is improved and the reflow angle is reduced by increasing the content of dopants (such as boron source substances, phosphorus source substances, etc.), but it is still unavoidable to go through a high-temperature annealing process. Summary of the invention

[0004] In order to solve the above problems, the present invention optimizes the temperature, pressure, power and other conditions in the plasma enhanced chemical vapor deposition (PECVD) process for preparing PSG / BPSG thin films, so as to reduce the reaction rate (it is generally believed that after the reaction rate is reduced, the atomic nuclei have a longer time to flow on the surface during the continuous film formation process, which is more conducive to filling), improve the filling performance, and reduce the reflow angle, thereby eliminating the annealing process and significantly reducing the production cost.

[0005] The present invention provides a PECVD PSG / BPSG film preparation process without annealing and improving the reflow angle, comprising the following steps:

[0006] S1. Set the temperature of the heater in the PECVD system to 450-500°C and place the wafer on the heater;

[0007] S2, introducing a liquid source precursor into the cavity; the liquid source precursor is a combination of a silicon liquid source precursor and a phosphorus liquid source precursor, or a combination of a silicon liquid source precursor, a phosphorus liquid source precursor and a boron liquid source precursor;

[0008] S3, deposition: set the pressure to 3-5 torr, the plate spacing to 500-550 mils, and the power to 700-800 W for deposition;

[0009] S4. After the deposition is completed, nitrogen (N2) is introduced into the chamber for purging;

[0010] S5. After the purge is completed, the residual gas in the chamber is extracted to restore the chamber to a vacuum state, and the corresponding PSG / BPSG thin film product is taken out.

[0011] In one embodiment of the present invention, the temperature of the heater may be 470°C-490°C.

[0012] In one embodiment of the present invention, the silicon liquid source precursor may be TEOS.

[0013] In one embodiment of the present invention, the phosphorus liquid source precursor may be TEPO.

[0014] In one embodiment of the present invention, the boron liquid source precursor may be TEB.

[0015] In one embodiment of the present invention, when the liquid source precursor is a combination of a silicon liquid source precursor and a phosphorus liquid source precursor, the molar ratio of the silicon liquid source precursor to the phosphorus liquid source precursor is (10-20):1; specifically, 15:1 may be selected.

[0016] In one embodiment of the present invention, when the liquid source precursor is a combination of a silicon liquid source precursor and a phosphorus liquid source precursor, the flow rate of the silicon liquid source precursor introduced into the cavity is controlled to be 800-1000 mg / min, specifically 900 mg / min.

[0017] In one embodiment of the present invention, when the liquid source precursor is a combination of a silicon liquid source precursor and a phosphorus liquid source precursor, the flow rate of the phosphorus liquid source precursor introduced into the cavity is controlled to be 40-60 mg / min, specifically 50 mg / min.

[0018] In one embodiment of the present invention, when the liquid source precursor is a combination of a silicon liquid source precursor, a phosphorus liquid source precursor, and a boron liquid source precursor, the molar ratio of the boron liquid source precursor, the phosphorus liquid source precursor, and the silicon liquid source precursor is (2-5):1:(10-15); specifically, 3.5:1:13 can be selected.

[0019] In one embodiment of the present invention, when the liquid source precursor is a combination of a silicon liquid source precursor, a phosphorus liquid source precursor, and a boron liquid source precursor, the flow rate of the boron liquid source precursor introduced into the cavity is controlled to be 120-150 mg / min, specifically 140 mg / min.

[0020] In one embodiment of the present invention, when the liquid source precursor is a combination of a silicon liquid source precursor, a phosphorus liquid source precursor, and a boron liquid source precursor, the flow rate of the phosphorus liquid source precursor introduced into the cavity is controlled to be 40-60 mg / min, specifically 50 mg / min.

[0021] In one embodiment of the present invention, when the liquid source precursor is a combination of a silicon liquid source precursor, a phosphorus liquid source precursor, and a boron liquid source precursor, the flow rate of the silicon liquid source precursor introduced into the cavity is controlled to be 700-800 mg / min, specifically 750 mg / min.

[0022] In one embodiment of the present invention, in S3, the pressure is specifically set to 3 torr, the plate spacing is 500 mils, and the power is 700 W.

[0023] In one embodiment of the present invention, in S4, the flow rate of N2 entering the chamber is 3000-5000 sccm; specifically, 4000 sccm may be selected.

[0024] The present invention provides a pre-metal dielectric film based on the above method.

[0025] Beneficial effects:

[0026] Currently in the field of chemical vapor deposition (CVD) PMD film preparation, there is no pure process improvement solution to remove the annealing step. The solution of the present invention optimizes the process recipe (also known as recipe, including detailed settings of various process steps, parameters and conditions) of semiconductor devices, and multiple factors work together to achieve the effect of reducing the reflow angle while removing annealing without affecting its filling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a process flow chart of the PECVD PSG / BPSG film preparation process of the present invention.

[0028] Figure 2 This is a scanning electron microscope (SEM) image of the PSG film after the optimized recipe in Example 1. DETAILED DESCRIPTION

[0029] The meanings of some terms involved in the present invention are explained as follows:

[0030] Terms / Abbreviations meaning TEOS Tetraethyl orthosilicate TEPO Triethyl phosphate TEB Triethyl borate PSG Phospho-silicate Glass BPSG Boro-phospho-silicate Glass wafer Wafer heater Hot plate, heating the wafer SHD Showerhead, air distribution plate spacing Plate spacing, distance between wafer and SHD

[0031] Performance Test:

[0032] The reaction rate involved in the present invention refers to the ratio of the deposition film thickness to the deposition time.

[0033] The test process of the uniformity of the film thickness involved in the present invention is as follows: a 6-inch wafer is selected, 5 mm of the edge is removed, and the thickness of 49 points on the surface is tested by an ellipsometer to calculate the uniformity. The measured uniformity of the film thickness (U%) = sample standard deviation / average value × 100%.

[0034] The reflow angle involved in the present invention refers to the angle (tilt angle) formed when the film layer attempts to planarize on the topographic structure. If the topography of the underlying structure is fully compensated, the angle will be zero degrees.

[0035] Example 1 Preparation of PSG thin film based on PECVD

[0036] The process flow of preparing PSG film based on PECVD of the present invention is as follows: Figure 1 shown.

[0037] The plasma enhanced chemical vapor deposition (PECVD) system used in the method of the present invention mainly includes: a ceramic heater (different from the aluminum heater of the original process, it can provide a higher temperature for the wafer, up to 520°C), a SHD (a uniform gas disk, which evenly diffuses the precursor into the chamber), and a radio frequency system (provides dissociation energy to dissociate the precursor into an ion state).

[0038] S1, preheating step: the ceramic heater is set at 480°C, the wafer is placed on the heater for 10 s, and preheated to 300°C;

[0039] S2, liquid source stabilization step: stabilize the flow of TEOS and TEPO liquid source precursors for 30 seconds before entering the cavity, and then introduce them into the cavity after the flow rate is stable; wherein, the molar ratio of TEOS to TEPO is 15:1, and the flow rates of TEOS and TEPO liquid source precursors introduced into the cavity are controlled to be 900 mg / min and 50 mg / min, respectively;

[0040] S3, deposition step: pressure is set to 3 torr, plate spacing is set to 500 mils, power is set to 700 W (frequency is 13.56 MHz), ambient temperature is about 480 ° C, deposition is carried out under this process environment for 60 s;

[0041] S4, purge step: after the deposition is completed, N2 is introduced into the chamber at a flow rate of 4000 sccm and a constant pressure is maintained for 10 s;

[0042] S5, exhaust step: after stopping the introduction of N2, the residual gas in the chamber is extracted by the exhaust device, so that the chamber is restored to a vacuum state, and the PSG thin film product is taken out.

[0043] Example 2 Preparation of BPSG thin film based on PECVD

[0044] The process flow of preparing BPSG film based on PECVD of the present invention is as follows: Figure 1 shown.

[0045] The plasma enhanced chemical vapor deposition (PECVD) system used in the method of the present invention mainly includes: a ceramic heater (different from the aluminum heater of the original process, it can provide a higher temperature for the wafer, up to 520°C), a SHD (a uniform gas disk, which evenly diffuses the precursor into the chamber), and a radio frequency system (provides dissociation energy to dissociate the precursor into an ion state).

[0046] S1, preheating step: the ceramic heater is set at 480°C, the wafer is placed on the heater for 10 s, and preheated to 300°C;

[0047] S2, liquid source stabilization step: stabilize the flow of TEB, TEPO, and TEOS liquid source precursors for 30 seconds before entering the cavity, and then introduce them into the cavity after the flow rate is stable; wherein, the molar ratio of TEB, TEPO, and TEOS is 3.5:1:13, and the flow rates of TEB, TEPO, and TEOS liquid source precursors introduced into the cavity are controlled to be 140 mg / min, 50 mg / min, and 750 mg / min, respectively;

[0048] S3, deposition step: pressure is set to 3 torr, plate spacing is set to 500 mils, power is set to 700 W (frequency is 13.56 MHz), ambient temperature is about 480 ° C, deposition is carried out under this process environment for 60 s;

[0049] S4, purge step: after the deposition is completed, N2 is introduced into the chamber at a flow rate of 4000 sccm and a constant pressure is maintained for 10 s;

[0050] S5, exhaust step: after stopping the introduction of N2, the residual gas in the chamber is extracted by an exhaust device, so that the chamber is restored to a vacuum state, and the BPSG thin film product is taken out.

[0051] The reaction rate during the deposition process of this embodiment is 5400 A / min, the film thickness uniformity of the obtained BPSG thin film product is 1.02%, and the reflux angle is 45°.

[0052] Comparative Example 1

[0053] The PECVD system mainly includes: an aluminum heater (providing a temperature of 400°C for the wafer), a SHD (a uniform gas disk that evenly diffuses the precursor into the chamber), and a radio frequency system (providing dissociation energy to dissociate the precursor into an ion state).

[0054] Specific process steps:

[0055] S1, preheating step: the heater is set at 400°C, the wafer is placed on the heater for 10 s, and preheated to 380°C;

[0056] S2, liquid source stabilization step: the TEOS / TEPO liquid source precursor is first stabilized for 30 seconds before entering the cavity, and then introduced into the cavity after the flow rate is stabilized; the molar ratio of TEOS to TEPO in the TEOS / TEPO liquid source precursor is 15:1, and the flow rates of the TEOS / TEPO liquid source precursor introduced into the cavity are controlled to be 900 mg / min and 50 mg / min respectively;

[0057] S3, deposition step: pressure is set to 6.3 torr, spacing is set to 320 mils, power is set to 800 W, and deposition is performed for 30 s under this process environment;

[0058] S4, purge step: after the deposition is completed, N2 is introduced into the chamber at a flow rate of 4000 sccm and a constant pressure is maintained for 10 s;

[0059] S5, vacuum step: stop introducing nitrogen, and use the vacuum device to extract the residual gas in the chamber, so that the chamber returns to a vacuum state, and the PSG film product is taken out.

[0060] Comparative Example 2

[0061] Referring to Example 1, the temperature of the heater in S1 was adjusted to 350° C., and other conditions and other steps remained unchanged.

[0062] Comparative Example 3

[0063] Referring to Example 1, the temperature of the heater in S1 was adjusted to 550° C., and other conditions and other steps remained unchanged.

[0064] Comparative Example 4

[0065] Referring to Example 1, the pressure in S3 was adjusted to 2 torr; other conditions and other steps remained unchanged.

[0066] Comparative Example 5

[0067] Referring to Example 1, the pressure in S3 was adjusted to 6 torr; other conditions and other steps remained unchanged.

[0068] Comparative Example 6

[0069] Referring to Example 1, the spacing in S3 is set to 300 mils; other conditions and other steps remain unchanged.

[0070] Comparative Example 7

[0071] Referring to Example 1, the spacing in S3 is set to 600 mils; other conditions and other steps remain unchanged.

[0072] Comparative Example 8

[0073] Referring to Example 1, the power in S3 is adjusted to 500 W; other conditions and other steps remain unchanged.

[0074] Comparative Example 9

[0075] Referring to Example 1, the power in S3 is adjusted to 1000 W; other conditions and other steps remain unchanged.

[0076] The reaction rate, film thickness uniformity, and reflow angle of the products obtained in Example 1 and Comparative Examples 1-9 were tested. The results are shown in Table 1.

[0077] Table 1 Comparison of results of Example 1 and Comparative Examples 1-9

[0078]

[0079] Functions and effects of the embodiments:

[0080] Figure 2 This is the PSG SEM image after the recipe is optimized in Example 1. It can be seen that the reflux angle is approximately 40°, which is relatively smooth and is conducive to subsequent metal deposition.

[0081] It can be seen from Example 1 and Comparative Example 1 that the method of the embodiment of the present invention optimizes and improves the process menu, and the various working conditions cooperate and work together to significantly reduce the reaction rate, improve the PSG / BPSG hole filling property and reflux angle; at the same time, the process method of the present invention can remove the annealing step, save the process flow, reduce costs, and obtain the corresponding.

[0082] Further,

[0083] Combining Comparative Example 2 and Example 1, it can be seen that if the ambient temperature during the deposition process is too low, the surface mobility will be slow, resulting in a large reflow angle; and if the ambient temperature is too high, as shown in Comparative Example 3, the reflow angle cannot be effectively improved, and the reaction rate will be higher, which is not conducive to filling the hole.

[0084] Combining Comparative Example 4 and Example 1, it can be seen that if the pressure during the deposition process is too low, the film uniformity will be poor, and the reaction rate will be too slow, which will also lead to low wafer output per hour (WPH), both of which are not conducive to production; and if the pressure is too high, as shown in Comparative Example 5, the reaction rate is too large, turbulence is prone to occur, resulting in unstable uniformity, and the reflow angle is not improved.

[0085] Combining Comparative Example 6 and Example 1, it can be seen that when the distance between the electrodes during the deposition process is small, there will be an uneven phenomenon in which the inner circle is low and the outer circle is high, the film uniformity is poor, and the reflux angle is not improved; when the distance between the electrodes is large, as shown in Comparative Example 7, the reactant concentration is low, the plasma density is low, the liquid source dissociation is insufficient, and the final film uniformity is also poor.

[0086] Combining Comparative Examples 8-9 with Example 1, it can be seen that the RF power during the deposition process is inappropriate, such as when it is too small or too large, the reaction rate is relatively large, which is not conducive to sufficient hole filling and cannot effectively improve the reflow angle.

[0087] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A PECVD PSG / BPSG film preparation process without annealing to improve the reflow angle, characterized in that: The steps include: S1. Set the temperature of the heater in the PECVD system to 450-500°C and place the wafer on the heater; S2, introducing a liquid source precursor into the cavity; the liquid source precursor is a combination of a silicon liquid source precursor and a phosphorus liquid source precursor, or a combination of a silicon liquid source precursor, a phosphorus liquid source precursor and a boron liquid source precursor; S3, deposition: set the pressure to 3-5 torr, the plate spacing to 500-550 mils, and the power to 700-800 W for deposition; S4. After the deposition is completed, nitrogen (N2) is introduced into the chamber for purging; S5. After the purge is completed, the residual gas in the chamber is extracted to restore the chamber to a vacuum state, and the corresponding PSG / BPSG thin film product is taken out; When the liquid source precursor is a combination of a silicon liquid source precursor and a phosphorus liquid source precursor, the flow rate of the silicon liquid source precursor introduced into the cavity is controlled to be 800-1000 mg / min, and the flow rate of the phosphorus liquid source precursor introduced into the cavity is controlled to be 40-60 mg / min; When the liquid source precursor is a combination of a silicon liquid source precursor, a phosphorus liquid source precursor, and a boron liquid source precursor, the flow rate of the boron liquid source precursor introduced into the cavity is controlled to be 120-150 mg / mi, the flow rate of the phosphorus liquid source precursor introduced into the cavity is controlled to be 40-60 mg / min, and the flow rate of the silicon liquid source precursor introduced into the cavity is controlled to be 700-800 mg / min.

2. The PECVD PSG / BPSG film preparation process without annealing and improving the reflux angle according to claim 1, characterized in that: The silicon liquid source precursor is TEOS, the phosphorus liquid source precursor is TEPO, and the boron liquid source precursor is TEB.

3. The PECVD PSG / BPSG film preparation process without annealing and improving the reflux angle according to claim 1, characterized in that: When the liquid source precursor is a combination of a silicon liquid source precursor and a phosphorus liquid source precursor, the molar ratio of the silicon liquid source precursor to the phosphorus liquid source precursor is (10-20):

1.

4. The PECVD PSG / BPSG film preparation process without annealing and improving the reflux angle according to claim 1, characterized in that: When the liquid source precursor is a combination of a silicon liquid source precursor, a phosphorus liquid source precursor, and a boron liquid source precursor, the molar ratio of the boron liquid source precursor, the phosphorus liquid source precursor, and the silicon liquid source precursor is (2-5):1:(10-15).

5. A PECVD PSG / BPSG film preparation process without annealing and improving reflux angle according to any one of claims 1 to 4, characterized in that: In S1, the temperature of the heater is 470℃-490℃; in S3, the specific settings are pressure of 3 torr, plate spacing of 500 mils, and power of 700 W.

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