A four-time sequence pulse PECVD process with a weak oxidation buffer section embedded therein for inhibiting carbon deposition at the bottom of an APF heater

Abstract

The application discloses a four-time-sequential pulse PECVD process for inhibiting carbon deposition at the bottom of an APF heater by embedding a trace weak oxidation buffer section. The application adds a trace weak oxidation plasma buffer etching section between a deposition pulse and an inert purge cleaning pulse, and constructs a four-time-sequential cycle system including a deposition stage, a weak oxidation digestion buffer stage, a dilution transition stage and a large-flow purge cleaning stage. The low-concentration oxygen plasma selectively oxidizes and decomposes chamber free macromolecular carbon clusters and heavy carbon radicals, and converts them into gaseous CO and CO2 small molecules which are removed with the airflow. The application is combined with a staged helium flow to smoothly replace the residual carbon-containing gas in the chamber. The application does not need to modify the PECVD equipment hardware, can reduce the deposition rate of carbon deposition at the bottom of the heater by more than 50% compared with the traditional process, significantly reduces wafer carbon particle defects, and is suitable for seven to twenty-eight nanometer advanced process APF mass production.

Description

Technical Field

[0001] This invention belongs to the field of plasma-enhanced chemical vapor deposition (PECVD) semiconductor thin film preparation technology, and particularly relates to a four-time-sequence pulsed PECVD process for suppressing carbon deposition at the bottom of the APF heater by embedding a micro-amount weak oxidation buffer section. Background Technology

[0002] Amorphous carbon hard masks possess advantages such as high etching selectivity, dense and uniform film layers, and adjustable stress, making them an indispensable core masking layer in advanced multilayer thin film etching processes. Currently, the mainstream mass-production continuous APF process continuously supplies an acetylene carbon source throughout the entire process. Carbon free radicals, carbon ions, and large molecular carbon clusters continuously accumulate within the chamber. Excess heavy carbon particles settle downwards under the influence of gravity and the chamber's built-in electric field, accumulating over time at the bottom of the heater to form a loose, thick carbon layer. When the stress within the carbon layer becomes unbalanced, it flakes off, falling onto the wafer surface and creating fatal particle defects. This also causes heater temperature field shifts and plasma impedance drift, resulting in large batch-to-batch fluctuations in film thickness, refractive index, and film stress, and a narrow process window.

[0003] There are currently two main improvement approaches in the industry. The first is a hardware modification approach, which reduces the surface adsorption capacity of carbon particles by spraying an alumina or rare-earth zirconia ceramic coating onto the bottom surface of the heater. This approach requires modification of the heater, resulting in high hardware replacement costs. After long-term high-temperature cycling, the coating is prone to cracking and peeling, and it can only passively reduce carbon adsorption, failing to eliminate the source of carbon clusters in the chamber. The second approach is a pure pulse process optimization approach. Current technology uses a two-stage deposition and pure helium purging process, with no oxidizing gas involved throughout. It relies solely on high-flow-rate helium to physically dilute and entrain free carbon particles in the chamber. This approach can reduce the concentration of carbon particles, but it cannot decompose large molecular carbon clusters in the chamber that are large in size and have a strong tendency to settle. These carbon clusters are difficult to be carried away by the helium flow and will continue to settle to the bottom of the heater, resulting in a significant upper limit to the carbon accumulation inhibition effect.

[0004] Existing two-stage inert pulse solutions rely solely on physical dilution with inert gases, lacking methods for dissolving large carbon clusters. Hardware coating solutions depend on equipment modifications and have limited lifespans. Currently, there is no four-time-sequence APF deposition process that requires no hardware modifications, embeds a trace weak oxidation buffer within the pulse cycle, and decomposes suspended carbon clusters in situ. Summary of the Invention

[0005] This invention provides a four-time-sequence pulsed PECVD process for suppressing carbon deposition at the bottom of the APF heater, with an embedded micro-oxidation buffer stage. A single complete pulsed cycle unit sequentially executes a carbon deposition stage, a micro-oxidation digestion buffer stage, a helium dilution transition stage, and a high-flow-rate inert purging stage. Multiple pulsed cycle units run continuously until an amorphous carbon hard mask is deposited on the wafer surface to the target thickness. The complete process steps include:

[0006] S1. Transfer the silicon wafer into the PECVD reaction chamber and place it stably on the heater support platform. Evacuate the chamber to the process background vacuum. Heat the heater and keep it at a constant temperature of 300 to 500 degrees Celsius.

[0007] S2. Start the four-time pulse cycle process, repeat the cycle to complete the four-stage unit to complete thin film deposition. The operating logic of each stage of a single cycle unit is as follows:

[0008] Carbon deposition stage: Acetylene carbon source and helium carrier gas are introduced simultaneously, and the plasma is excited by the reference radio frequency power to deposit an amorphous carbon film on the wafer surface.

[0009] Trace weak oxidation digestion buffer stage: The acetylene carbon source is completely cut off, a mixture of low flow rate trace oxygen and medium flow rate helium is introduced, and the radio frequency power is reduced to 30% to 50% of the deposition power to form a weak oxidizing low intensity plasma, which selectively oxidizes and digests suspended macromolecular carbon clusters and heavy carbon free radicals in the chamber to generate gaseous carbon oxides.

[0010] Helium dilution transition stage: Cut off the oxygen supply and only introduce medium to high flow rate of high-purity helium to maintain low sustaining radio frequency power, so as to gradually dilute the residual gaseous oxidation products and unreacted trace carbon active groups in the chamber.

[0011] High-flow inertial purging and purification stage: Maintaining extremely low radio frequency sustaining power, increasing helium flow rate to the peak of the entire cycle, relying on high-speed inert airflow to carry away and extract residual carbon-containing gaseous products and tiny carbon particles from the downward cavity, and inhibiting carbon particle adsorption and deposition at the bottom of the heater.

[0012] S3. After the amorphous carbon film thickness on the wafer reaches the target process thickness, the RF power supply and all reactive gases are turned off, and a gradient multi-stage post-helium purging process is performed to remove the trace carbon groups remaining at the bottom of the cavity layer by layer, thus completing the APF thin film preparation.

[0013] Preferably, the total duration of a single complete four-time-sequence pulse cycle is 22 to 55 seconds; of which the carbon deposition stage lasts 7 to 26 seconds, the trace amount of weak oxidation digestion buffer stage lasts 4 to 10 seconds, the helium dilution transition stage lasts 5 to 13 seconds, and the high-flow-rate inert purging purification stage lasts 6 to 27 seconds; the effective carbon deposition duty cycle is controlled at 25% to 58%.

[0014] Preferably, the process parameters for the carbon deposition stage are: acetylene flow rate of 750 to 1600 sccm, helium flow rate of 250 to 800 sccm, radio frequency power of 400 to 1200 watts, and chamber stabilization pressure of 6 to 18 Torr.

[0015] Preferably, the process parameters for the trace weak oxidation digestion buffer stage are: oxygen flow rate of 5 to 40 sccm, helium flow rate of 700 to 1100 sccm, radio frequency power of 200 to 450 watts, and the pressure difference between the chamber and the deposition stage is controlled within ±1 Torr; the oxygen inlet is strictly controlled to be trace, which only digests the suspended free carbon particles in the chamber and does not etch the amorphous carbon film already formed on the wafer surface.

[0016] Preferably, the helium dilution transition stage is free of acetylene and oxygen, the helium flow rate is 900 to 1300 sccm, and the radio frequency sustaining power is 150 to 300 watts.

[0017] Preferably, the high-flow inertial purging purification stage is free of acetylene and oxygen, with a helium flow rate of 1100 to 1500 sccm and a radio frequency sustaining power of 100 to 220 watts.

[0018] Preferably, the gradient multi-stage post-helium purging is divided into two stages: first, purging at a medium flow rate for 18 to 28 seconds, and then purging at a peak flow rate for 12 to 30 seconds, to remove residual carbon active particles in the dead corner of the bottom chamber of the heater in layers.

[0019] Preferably, the entire process only requires adjusting the machine pulse timing, multi-component gas segmented flow rate, and stepped RF power parameters to suppress carbon buildup at the bottom of the heater. It does not require modification of the PECVD chamber hardware, spraying of alumina or YSZ ceramic anti-carbon coating on the bottom surface of the heater, or adding a dedicated bottom purge gas path and shielding structure.

[0020] Compared with related technologies, the present invention has the following beneficial effects.

[0021] First, zero hardware modification cost and convenient mass production deployment. Only the equipment pulse timing, gas segmented flow rate and stepped RF power are optimized. There is no need to spray ceramic coating on the heater, no need to add gas paths and shielding structures. Existing mass-produced PECVD machines can directly switch processes without hardware procurement and refurbishment costs.

[0022] Second, the dual carbon suppression mechanism significantly improves the suppression effect. A new trace-scale weak oxidation buffer stage decomposes large molecular carbon clusters in situ, reducing carbon particle deposition at the source. Compared to the traditional three-stage purely inert pulse process, the carbon deposition rate at the bottom of the heater is reduced by more than 50%, and wafer particle defects caused by carbon layer peeling are reduced by more than 65%.

[0023] Third, the process conditions are smooth, improving the batch stability of thin films. Four-stage gradient timing switches between gas and power, eliminating instantaneous changes in gas pressure and plasma. The heater temperature field and cavity plasma environment remain stable over the long term, reducing batch-to-batch variation in film thickness uniformity by more than 40%, and widening the APF process window. Trace amounts of oxygen act only on gaseous free carbon, without damaging the amorphous carbon film on the wafer surface. Thin film stress, density, and etching selectivity are superior to conventional pulse processes.

[0024] Fourth, it offers significant advantages in cost reduction and efficiency improvement. The overall consumption of acetylene carbon source is reduced by 25% to 35%. The cycle for wet maintenance with the chamber cover opened is extended from the conventional 300 pieces to over 2520 pieces, significantly reducing downtime, oxygen cleaning consumables, and wet cleaning chemical consumption, thereby increasing the effective production capacity of the machine.

[0025] Fifth, it has broad compatibility and adapts to multiple process nodes. The timing and parameter adjustment range is wide, and it can be matched with the mass production of APF hard masks for the full range of 7nm, 14nm and 28nm logic chips and memory chips, without process adaptation limitations. Detailed Implementation

[0026] The following embodiments further illustrate the present invention.

[0027] First Embodiment

[0028] This invention utilizes a four-times pulsed PECVD process with an embedded micro-aluminum weak oxidation buffer section, implemented on a standard mass-production APF PECVD deposition equipment. The entire process requires no modification to the heater or chamber hardware, and no ceramic anti-carbon deposition coating on the bottom surface. The complete process is divided into three main steps: chamber pretreatment, four-times pulsed cyclic deposition, and gradient multi-stage post-treatment purification.

[0029] Perform chamber pretreatment. The 300mm silicon wafer to be processed is transferred to the PECVD reaction chamber and stably placed on the graphite heater stage. The chamber vacuum pump is activated to evacuate to the process floor vacuum. The heater is started to raise the temperature and stabilize it at 380 degrees Celsius, maintaining a uniform temperature field across the entire stage without localized temperature differences.

[0030] Entering the core four-phase pulsed cyclic deposition process, the complete unit consists of a cyclic carbon deposition stage, a micro-amount weak oxidation digestion buffer stage, a helium dilution transition stage, and a high-flow-rate inert purging and purification stage, continuously growing amorphous carbon hard mask films on the wafer surface.

[0031] During the carbon deposition stage, acetylene flow rate of 1200 sccm and helium flow rate of 500 sccm are introduced, radio frequency power of 800 watts is maintained, and the cavity pressure is maintained at 12 Torr for 16 seconds. The ionized acetylene plasma completes the film deposition on the front side of the wafer.

[0032] In the trace-scale weak oxidation digestion buffer stage, acetylene is completely shut off, and oxygen flow rate is introduced at 20 sccm and helium flow rate at 900 sccm. The radio frequency is down-tuned to 320 watts for 7 seconds. The low-intensity weak oxidation plasma reacts with suspended carbon clusters in the chamber, decomposing them into small gaseous molecules of CO and CO2. The trace oxygen only acts on the gaseous free particles and does not corrode the solid carbon film on the wafer.

[0033] During the helium dilution transition phase, oxygen is cut off, and only helium is introduced at a flow rate of 1100 sccm, with the radio frequency maintained at 220 watts for 9 seconds. This gradually dilutes the oxidized waste gas in the chamber, buffering changes in operating conditions and preventing the sudden settling of residual carbon particles.

[0034] During the high-flow-rate inertial purging and purification phase, a carbon-free and oxygen-free environment is maintained, with the helium flow rate increased to 1300 sccm and the radio frequency maintained at 160 watts for 14 seconds. The high-speed helium flow carries away trace amounts of carbon oxides and tiny carbon particles from the bottom of the chamber and removes them simultaneously, reducing carbon adsorption on the bottom surface of the heater.

[0035] The wafer thin film thickness is monitored online in real time. Once the film layer reaches the target process thickness, the four-time pulse cycle is terminated, and a gradient multi-stage post-purification process is initiated. First, a medium-flow helium gas purging is performed for 22 seconds, followed by a peak helium gas purging for 20 seconds to remove residual trace carbon active groups in the dead corners at the bottom of the chamber in layers. After purification, the RF power supply and all process gases are turned off sequentially. After a slight depressurization of the chamber, the wafer is transferred out, and the single APF thin film fabrication process is completed.

[0036] This invention embeds a micro-scale weak oxidation digestion buffer segment within the pulse cycle, constructing a four-time-sequence synergistic control system. This solves the problems of continuous carbon particle enrichment and severe carbon buildup at the bottom of the heater in traditional continuous processes. It overcomes the shortcomings of existing two-stage pure inert pulses that only dilute but cannot decompose large molecular carbon clusters, and avoids the defects of high cost and poor reliability in hardware ceramic coating modification. While ensuring that the etching performance and film quality of the APF film meet the standards of advanced chip mass production, it significantly reduces the rate of ineffective carbon growth at the bottom of the heater, reduces wafer particle defects, extends the cavity maintenance cycle, and reduces the production cost of acetylene and cleaning consumables.

[0037] Second Embodiment

[0038] This embodiment provides another four-time-sequence pulsed PECVD process for suppressing carbon buildup at the bottom of the APF heater with an embedded micro-amount weak oxidation buffer section. The difference between this and the first embodiment lies in the adjustment of the process parameter window and the differentiated configuration of the duration allocation of each stage in a single cycle unit.

[0039] In this embodiment, the heater is kept at a constant temperature of 300 degrees Celsius. The chamber reference pressure is set to 6 Torr.

[0040] The total duration of a single complete four-phase pulse cycle is set to 22 seconds. The carbon deposition stage lasts 7 seconds, with an acetylene flow rate of 750 sccm, a helium flow rate of 250 sccm, an RF power of 400 W, and a chamber pressure maintained at 6 Torr. The trace oxidation digestion buffer stage lasts 4 seconds, with an oxygen flow rate of 5 sccm, a helium flow rate of 700 sccm, an RF power of 200 W, and the chamber pressure difference from the deposition stage controlled within ±1 Torr. The helium dilution transition stage lasts 5 seconds, with only a helium flow rate of 900 sccm and an RF maintenance power of 150 W. The high-flow-rate inert purging purification stage lasts 6 seconds, with only a helium flow rate of 1100 sccm and an RF maintenance power of 100 W.

[0041] This set of parameters is suitable for process scenarios with lower deposition rate requirements. By reducing the gas flow rate and RF power at each stage, the physical bombardment intensity of plasma on the wafer surface is further reduced, making it suitable for process nodes that are sensitive to thin film stress or have special requirements for film density.

[0042] In the gradient multi-stage post-helium purging process, the medium flow rate helium is first purged for 18 seconds, and then the peak flow rate helium is switched to purge for 12 seconds to remove residual carbon active particles in the dead corner of the bottom chamber of the heater in layers.

[0043] In this embodiment, the entire process also achieves carbon buildup suppression at the bottom of the heater simply by adjusting the machine pulse timing, multi-component gas segmented flow rate, and stepped radio frequency power parameters. There is no need to modify the PECVD cavity hardware, no need to spray alumina or YSZ ceramic anti-carbon coating on the bottom surface of the heater, and no need to add a dedicated bottom purge gas path and shielding structure.

[0044] This embodiment, together with the first embodiment, demonstrates that the technical solution of the present invention has a wide adjustable window for process parameters, and can flexibly configure the duration, gas flow rate and RF power of each stage according to different process requirements. It can be implemented in the mass production of APF hard masks for a full range of logic chips and memory chips from seven nanometers to twenty-eight nanometers, without process adaptation limitations.

[0045] Comparative Example

[0046] To verify the technical effectiveness of the present invention, a comparative experiment was conducted on a standard mass-production PECVD equipment. The experimental conditions were uniformly set as follows: 300 mm silicon wafer, heater constant temperature of 380 degrees Celsius, chamber reference pressure of 12 Torr, and target APF film thickness of 800 angstroms. The differences in process parameters and performance comparison results between the comparative examples and the first embodiment are as follows.

[0047] Comparative Example 1

[0048] This comparative example employs a two-stage inert pulse followed by batch offline oxygen plasma cleaning process. The two inert pulse cycles execute the carbon deposition stage and the high-flow-rate inert purging stage, excluding the trace weak oxidation digestion buffer stage and the helium dilution transition stage. After a certain number of deposition cycles, the wafer is removed from the chamber, and the chamber undergoes offline oxygen plasma cleaning. Deposition continues only after cleaning. The process parameters for the deposition stage are the same as in the first embodiment.

[0049] Under the above process conditions, the average carbon deposition thickness at the bottom of the heater is 10.2 micrometers, the number of carbon particles on the wafer surface is 50 to 100 per wafer (particle size greater than or equal to 0.1 micrometers), the batch variation of film thickness uniformity is ±3.8%, the relative consumption of acetylene gas is 100%, and the maintenance cycle of opening the cavity cover is 320 wafers.

[0050] Comparative Example 1 is compared with the first embodiment. The average carbon deposition thickness at the bottom of the heater in the first embodiment is 0.9 micrometers, which is 91.1% lower than that in Comparative Example 1; the number of carbon particles on the wafer surface is 0 to 10 per wafer, which is 85.4% lower than that in Comparative Example 1; the batch fluctuation of film thickness uniformity is ±1.7%, which is 55.3% lower than that in Comparative Example 1; the relative consumption of acetylene gas is 68%, which is 32% lower than that in Comparative Example 1; and the maintenance cycle for opening the cavity cover is 2520 wafers, which is 687% longer than that in Comparative Example 1.

[0051] Comparative Example 2

[0052] This comparative example was used to examine the changing trend of macromolecular carbon cluster concentration in the middle of the chamber, in order to verify the in-situ digestion effect of the trace weak oxidation digestion buffer section in the four-stage time sequence of this invention. The detection method employed was in-situ OES spectroscopy, with the relative intensity of the characteristic peak of the C2⁺ carbon cluster in the middle of the chamber used as the monitoring index.

[0053] Comparative Example 2 employed a two-stage inert pulse process scheme, excluding the trace weak oxidation digestion buffer section and the helium dilution transition section. At the 50th wafer cycle deposition, the relative intensity of the characteristic peak of the C2⁺ carbon cluster was 100 (baseline); as the number of wafers increased, the carbon cluster concentration continued to accumulate and rise, reaching 118.3 at the 150th wafer and 135.7 at the 300th wafer.

[0054] Under the four-stage sequential process conditions of the first embodiment, the relative intensity of the characteristic peak of the C2⁺ carbon cluster in the 50th piece was 42.6, in the 150th piece it was 44.1, and in the 300th piece it was 45.8. The carbon cluster concentration in the first embodiment remained stable at a low level for a long period without any cumulative effect, which contrasts sharply with the continuously increasing trend of carbon cluster concentration in Comparative Example 2. This data demonstrates from the gas-phase source that the present invention effectively suppresses carbon cluster concentration through cyclic embedded oxidation digestion.

[0055] Comparative Example 3

[0056] This comparative example is used to verify the synergistic effect of the four-stage timing sequence of the present invention. It involves performing a simple superposition of the individual effects of the two-stage pulse process and offline oxygen cleaning, and then comparing the calculation results with the measured values ​​of the first embodiment.

[0057] Comparative Example 3 is based on the two-stage inert pulse process scheme of Comparative Example 1. Regarding the bottom carbon deposit thickness, the individual effects of the two pulses are 22.8 micrometers, and the offline oxygen cleaning alone removes approximately 24.6%. The theoretically calculated value after simply combining the two is approximately 17.2 micrometers. The measured value of the first embodiment is 0.9 micrometers, which is 94.7% lower than the theoretical combined value.

[0058] Regarding the particle defect count, the individual effect of the two pulses was 245 particles per piece, and the offline oxygen cleaning alone removed approximately 24.1% of the particles. The theoretically calculated value for simple superposition was approximately 186 particles per piece. The actual measured value in the first embodiment was 27 particles per piece, which was 85.4% lower than the theoretical superposition value.

[0059] Regarding the chamber maintenance cycle index, the individual effect of the two pulses is 210 pieces, and the offline oxygen cleaning alone extends the removal rate by approximately 52%, with a theoretically calculated value of approximately 320 pieces when simply superimposed. The actual measured value in the first embodiment is 2520 pieces, which is 687% higher than the theoretical superimposed value.

[0060] The data in Comparative Example 3 above show that the four-time-sequence pulse process of the present invention is not a simple superposition of existing two-stage pulse processes plus offline oxygen cleaning. The four time stages produce a synergistic effect, and all core performance indicators significantly exceed the theoretical upper limit of superimposing individual technical means.

[0061] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A four-time-sequence pulsed PECVD process for suppressing carbon buildup at the bottom of an APF heater with an embedded trace amount of weak oxidation buffer section, characterized in that, A single complete pulse cycle unit sequentially executes the carbon deposition stage, the micro-oxidation and desorption buffer stage, the helium dilution transition stage, and the high-flow-rate inert purging stage. Multiple sets of pulse cycle units continue to run until the amorphous carbon hard mask is deposited on the wafer surface to the target thickness. The complete process steps include: S1. Transfer the silicon wafer into the PECVD reaction chamber and place it stably on the heater support platform. Evacuate the chamber to the process background vacuum. Heat the heater and keep it at a constant temperature of 300 to 500 degrees Celsius. S2. Start the four-time pulse cycle process, repeat the cycle to complete the four-stage unit to complete thin film deposition. The operating logic of each stage of a single cycle unit is as follows: Carbon deposition stage: Acetylene carbon source and helium carrier gas are introduced simultaneously, and the plasma is excited by the reference radio frequency power to deposit an amorphous carbon film on the wafer surface. Trace weak oxidation digestion buffer stage: The acetylene carbon source is completely cut off, a mixture of low flow rate trace oxygen and medium flow rate helium is introduced, and the radio frequency power is reduced to 30% to 50% of the deposition power to form a weak oxidizing low intensity plasma, which selectively oxidizes and digests suspended macromolecular carbon clusters and heavy carbon free radicals in the chamber to generate gaseous carbon oxides. Helium dilution transition stage: Cut off the oxygen supply and only introduce medium to high flow rate of high-purity helium to maintain low sustaining radio frequency power, so as to gradually dilute the residual gaseous oxidation products and unreacted trace carbon active groups in the chamber. High-flow inertial purging and purification stage: Maintaining extremely low radio frequency sustaining power, increasing helium flow rate to the peak of the entire cycle, relying on high-speed inert airflow to carry away and extract residual carbon-containing gaseous products and tiny carbon particles from the downward cavity, and inhibiting carbon particle adsorption and deposition at the bottom of the heater. S3. After the amorphous carbon film thickness on the wafer reaches the target process thickness, the RF power supply and all reactive gases are turned off, and a gradient multi-stage post-helium purging process is performed to remove the trace carbon groups remaining at the bottom of the cavity layer by layer, thus completing the APF thin film preparation.

2. The four-time-sequence pulsed PECVD process for suppressing carbon deposition at the bottom of the APF heater with an embedded micro-amount weak oxidation buffer section as described in claim 1, characterized in that: The total duration of a single complete four-time-sequence pulse cycle is 22 to 55 seconds; The carbon deposition stage lasts 7 to 26 seconds, the trace amount of weak oxidation and digestion buffer stage lasts 4 to 10 seconds, the helium dilution transition stage lasts 5 to 13 seconds, and the high-flow-rate inert purging and purification stage lasts 6 to 27 seconds; the effective carbon deposition duty cycle is controlled at 25% to 58%.

3. The four-time-sequence pulsed PECVD process for suppressing carbon buildup at the bottom of the APF heater with an embedded micro-amount weak oxidation buffer section as described in claim 1, characterized in that: The process parameters for the carbon deposition stage are: acetylene flow rate 750 to 1600 sccm, helium flow rate 250 to 800 sccm, radio frequency power 400 to 1200 watts, and chamber stabilization pressure 6 to 18 Torr.

4. The four-time-sequence pulsed PECVD process for suppressing carbon buildup at the bottom of the APF heater with an embedded trace amount of weak oxidation buffer section as described in claim 1, characterized in that: The process parameters for the trace-scale weak oxidation digestion buffer stage are: oxygen flow rate 5 to 40 sccm, helium flow rate 700 to 1100 sccm, RF power 200 to 450 watts, and the pressure difference between the chamber and the deposition stage is controlled within ±1 Torr. The oxygen flow rate is strictly controlled to be trace, which only digests the suspended free carbon particles in the chamber and does not etch the amorphous carbon film already formed on the wafer surface.

5. The four-time-sequence pulsed PECVD process for suppressing carbon buildup at the bottom of the APF heater with an embedded trace amount of weak oxidation buffer section as described in claim 1, characterized in that: During the helium dilution transition phase, there is no acetylene or oxygen, the helium flow rate is 900 to 1300 sccm, and the radio frequency sustaining power is 150 to 300 watts.

6. The four-time-sequence pulsed PECVD process for suppressing carbon buildup at the bottom of the APF heater with an embedded trace amount of weak oxidation buffer section as described in claim 1, characterized in that: The high-flow inertial purging purification stage is free of acetylene and oxygen, with a helium flow rate of 1100 to 1500 sccm and a radio frequency sustaining power of 100 to 220 watts.

7. The four-time-sequence pulsed PECVD process for suppressing carbon deposition at the bottom of the APF heater with an embedded micro-amount weak oxidation buffer section as described in claim 1, characterized in that: The gradient multi-stage post-helium purging is divided into two stages: first, a medium flow rate purging for 18 to 28 seconds, and then a peak flow rate purging for 12 to 30 seconds, to remove residual carbon active particles in the dead corner of the bottom chamber of the heater in layers.

8. The four-time-sequence pulsed PECVD process for suppressing carbon deposition at the bottom of the APF heater with an embedded trace amount of weak oxidation buffer section as described in claim 1, characterized in that: The entire process achieves carbon buildup suppression at the bottom of the heater simply by adjusting the machine pulse timing, multi-component gas segmented flow rate, and stepped RF power parameters. It does not require modification of the PECVD chamber hardware, spraying of alumina or YSZ ceramic anti-carbon coating on the bottom surface of the heater, or adding a dedicated bottom purge gas path and shielding structure.