Method for eliminating silicon wafer trail in LPCVD (Low Pressure Chemical Vapor Deposition) processing

Abstract

The invention relates to a method for eliminating silicon wafer boat traces in LPCVD (Low Pressure Chemical Vapor Deposition) processing, which belongs to the technical field of semiconductor manufacturing and comprises the following operation steps of: 1, carrying out plasma cleaning treatment on the surface of a silicon wafer before the silicon wafer is placed on a silicon boat; and 2, accurately controlling the reaction temperature, the reaction pressure and the reaction gas flow in the LPCVD (Low Pressure Chemical Vapor Deposition) process. And 3, after thin film deposition is completed, rapidly reducing the temperature of the supporting strip through a cooling medium circulation system, and rapidly and uniformly cooling the silicon wafer in a state of being in contact with the supporting strip. And 4, after cooling is completed, the silicon wafer is taken down from the silicon boat, and subsequent detection and processing are carried out. The method has the advantages of convenient operation and good operation stability. By optimizing the three links of preparation before deposition, deposition process control and deposition post-treatment, the common boat trace problem in the LPCVD process is systematically solved, and the uniformity of the thin film and the yield of the silicon wafer are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically to a method for eliminating boat tracks on silicon wafers during LPCVD processing. Background Technology

[0002] LPCVD (Liquid Permeable Chemical Vapor Deposition) reduces the reaction chamber pressure to below atmospheric pressure (typically 1–10 Torr, approximately 133–1330 Pa), allowing gaseous precursors to undergo a chemical reaction on the substrate surface under high-temperature conditions to generate a solid thin film. The low-pressure environment increases the mean free path of gas molecules, enhancing reaction uniformity and film quality, and reducing particulate contamination.

[0003] In the LPCVD (low-pressure chemical vapor deposition) process, silicon wafer boat marks (also known as boat imprints, contact marks, or wrap-around deposits) are significant defects affecting silicon wafer yield and film uniformity. Boat marks are typically caused by the contact points between the silicon wafer and the quartz boat, uneven airflow distribution, temperature gradients, or contamination on the boat surface.

[0004] In the LPCVD process, silicon wafers are typically placed on a silicon boat and fed into a reactor for thin film deposition. However, in actual production, it has been found that boat tracks often appear at the contact points between the silicon wafer and the silicon boat. These boat tracks manifest as significant differences in film thickness, quality, or electrical properties between the contact and non-contact areas on the silicon wafer, leading to decreased product performance, reduced yield, and consequently increased production costs. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for eliminating boat tracks on silicon wafers during LPCVD processing. This method offers advantages such as ease of operation and high stability. By optimizing three key aspects—pre-deposition preparation, deposition process control, and post-deposition treatment—it systematically solves the common boat track problem in LPCVD processes, significantly improving film uniformity and wafer yield.

[0006] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: A method for eliminating boat tracks on silicon wafers during LPCVD processing includes the following steps: Step 1: Before placing the silicon wafer onto the silicon boat, the surface of the silicon wafer is subjected to plasma cleaning. Plasma cleaning removes impurities, organic matter, and microparticles from the silicon wafer surface, improving the cleanliness and activity of the silicon wafer surface, resulting in more uniform subsequent thin film deposition.

[0007] The second step involves precisely controlling the reaction temperature, pressure, and reaction gas flow rate during the LPCVD process. The reaction temperature is controlled between 750 and 800°C, the reaction pressure is maintained between 10 and 20 Pa, and the flow rate of the silane reaction gas is optimized and adjusted according to the silicon wafer size and the required film thickness.

[0008] Step 3: After the thin film deposition is completed, the temperature of the support strip is rapidly reduced through the cooling medium circulation system, so that the silicon wafer can be cooled quickly and evenly while in contact with the support strip; the cooling rate is controlled at 5-10℃ / minute to avoid excessive thermal stress caused by excessive cooling.

[0009] Step 4: After cooling is complete, the silicon wafer is removed from the silicon boat for subsequent testing and processing.

[0010] Preferably, the parameters for plasma cleaning are: radio frequency power of 100-150W, cleaning time of 3-5 minutes, and working gas of argon and hydrogen in a ratio of argon:hydrogen = 3:1.

[0011] Preferably, a pulsed gas input method is adopted, which involves periodically opening and closing the reaction gas input valve, with a pulse period of 0.5 to 1 second and the opening time accounting for 30% to 50% of the pulse period. The pulsed gas input method can enhance the diffusion of gas on the silicon wafer surface and the uniformity of the reaction.

[0012] Preferably, for silicon wafers with a diameter of 12 inches, the silane flow rate is controlled at 50–80 sccm.

[0013] Preferably, before placing the silicon wafers onto the silicon boat, the silicon boat is cleaned by alkaline washing using a 35%–100% NaOH / KOH solution at a temperature of 60–70°C; the boat support is pretreated with H2 / N2O saturation treatment to reduce dust and debris contamination and improve cleanliness.

[0014] Preferably, the angle between the slot of the silicon boat and the vertical plane is ≤6° to enhance the adhesion of the silicon wafer and reduce the need for wrap-around plating; a silicon nitride coating is deposited on the quartz boat at a deposition temperature of 600~800℃ and an NH3 / DCS flow rate of 100~500 / 20~100SCCM to reduce contact stress and boat marks.

[0015] As a preferred method, the LPCVD process first involves loading and vacuuming. The substrate is placed on a quartz boat and sent into the reaction chamber, where it is evacuated to a low pressure using a vacuum pump. Next, the substrate is heated to a predetermined temperature of 500–900°C. Then, silane (SiH4) and ammonia (NH3) are introduced as precursor gases to carry out chemical reactions and deposition on the substrate surface, forming the desired thin film. Finally, unreacted gases and byproducts are removed.

[0016] The present invention can achieve the following effects: This invention provides a method for eliminating boat tracks on silicon wafers during LPCVD processing. Compared with existing technologies, it has the advantages of convenient operation and good operational stability. By optimizing three stages—pre-deposition preparation, deposition process control, and post-deposition treatment—it systematically solves the common boat track problem in LPCVD processes, significantly improving film uniformity and silicon wafer yield.

[0017] Prevention at the source: Through cleaning, coating and structural design, the physical and chemical causes of boat tracks are eliminated.

[0018] Process control: The kinetic environment for thin film growth was optimized through precise temperature and pressure control and innovative pulsed gas supply.

[0019] Result of curing: Rapid and uniform cooling protects the formed high-quality film and prevents defects from occurring during the cooling process. Detailed Implementation

[0020] The technical solution of the invention will be further described in detail below through examples.

[0021] Example: A method for eliminating boat tracks on silicon wafers during LPCVD processing, comprising the following steps: Step 1: Before placing the silicon wafers onto the silicon boat, the silicon boat is cleaned by alkaline washing using a 35%–100% NaOH / KOH solution at a temperature of 60–70℃. The boat support is pretreated with H2 / N2O saturation treatment, which forms a thin oxide layer on the surface of the boat support, effectively reducing the generation and adhesion of dust and debris and improving the overall cleanliness.

[0022] The angle between the slot of the silicon boat and the vertical plane is ≤6°, enhancing the adhesion of the silicon wafer and reducing the need for wrap-around plating. A silicon nitride coating is deposited on the quartz boat at a deposition temperature of 600–800℃ and an NH3 / DCS flow rate of 100–500 / 20–100 SCCM to reduce contact stress and boat marks. The deposition of the silicon nitride coating effectively buffers the difference in thermal expansion coefficients between the silicon wafer and the quartz boat, reducing contact stress, which is one of the fundamental reasons for boat marks.

[0023] The silicon wafer surface is subjected to plasma cleaning. The parameters for plasma cleaning are: radio frequency power 100-150W, cleaning time 3-5 minutes, and working gas is a mixture of argon and hydrogen in a ratio of argon:hydrogen = 3:1.

[0024] Step 2: During the LPCVD process, the reaction temperature, pressure, and reactant gas flow rate are precisely controlled. The reaction temperature is maintained between 750 and 800°C, the reaction pressure is maintained between 10 and 20 Pa, and the flow rate of the silane reactant gas is optimized and adjusted according to the silicon wafer size and the required film thickness. For a 12-inch diameter silicon wafer, the silane flow rate is controlled between 50 and 80 sccm.

[0025] The LPCVD process begins with loading and vacuuming. The substrate is placed on a quartz boat and sent into the reaction chamber, where it is evacuated to a low pressure using a vacuum pump. Next, the substrate is heated to a predetermined temperature, which is 500–900°C. Then, silane (SiH4) and ammonia (NH3) are introduced as precursor gases to carry out chemical reactions and deposition on the substrate surface to form the desired thin film. Finally, unreacted gases and byproducts are removed.

[0026] A pulsed gas input method is adopted, which involves periodically opening and closing the reaction gas input valve with a pulse period of 0.5 to 1 second and an opening time accounting for 30% to 50% of the pulse period. This creates an instantaneous concentration gradient in the reaction chamber, promoting uniform diffusion of gas molecules and effectively improving the problems of boat trails and film thickness unevenness caused by uneven gas flow field.

[0027] Step 3: After thin film deposition, the temperature of the support strip is rapidly reduced through a cooling medium circulation system, allowing the silicon wafer to cool quickly and uniformly while in contact with the support strip. The cooling rate is controlled at 5–10°C / minute to avoid excessive thermal stress caused by rapid cooling. This achieves rapid cooling while preventing excessive thermal stress at the contact point between the silicon wafer and the boat due to excessive cooling, thus preventing the "secondary formation" of boat tracks.

[0028] Step 4: After cooling, the silicon wafer is removed from the silicon boat and transferred to subsequent processes for thin film quality inspection (such as thickness, stress, uniformity) and other treatments.

[0029] In summary, this method for eliminating boat tracks on silicon wafers during LPCVD processing offers advantages such as ease of operation and high stability. By optimizing three key aspects—pre-deposition preparation, deposition process control, and post-deposition treatment—it systematically solves the common boat track problem in LPCVD processes, significantly improving film uniformity and wafer yield.

[0030] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for eliminating boat tracks on silicon wafers during LPCVD processing, characterized in that... The following steps are included: Step 1: Before placing the silicon wafer onto the silicon boat, perform plasma cleaning on the surface of the silicon wafer; Step 2: During the LPCVD process, the reaction temperature, pressure, and reaction gas flow rate are precisely controlled; the reaction temperature is controlled between 750 and 800°C, the reaction pressure is maintained between 10 and 20 Pa, and the flow rate of the reaction gas silane is optimized and adjusted according to the silicon wafer size and the required film thickness. Step 3: After the thin film deposition is completed, the temperature of the support strip is rapidly reduced through the cooling medium circulation system, so that the silicon wafer can be cooled quickly and evenly while in contact with the support strip; the cooling rate is controlled at 5-10℃ / minute to avoid excessive thermal stress caused by excessive cooling. Step 4: After cooling is complete, the silicon wafer is removed from the silicon boat for subsequent testing and processing.

2. The method for eliminating wafer boat tracks in LPCVD processing according to claim 1, characterized in that: The parameters for plasma cleaning are: radio frequency power 100-150W, cleaning time 3-5 minutes, and working gas is a mixture of argon and hydrogen in a ratio of argon:hydrogen = 3:

1.

3. The method for eliminating silicon wafer boat tracks in LPCVD processing according to claim 1, characterized in that: The gas input method is pulsed, which means that the reaction gas input valve is opened and closed periodically. The pulse period is 0.5 to 1 second, and the opening time accounts for 30% to 50% of the pulse period.

4. The method for eliminating silicon wafer boat tracks in LPCVD processing according to claim 1, characterized in that: For 12-inch diameter silicon wafers, the silane flow rate is controlled at 50–80 sccm.

5. The method for eliminating silicon wafer boat tracks in LPCVD processing according to claim 1, characterized in that: Before placing the silicon wafers onto the silicon boat, the silicon boat is cleaned by alkaline washing using a 35%–100% NaOH / KOH solution at a temperature of 60–70°C. The boat support is pretreated with H2 / N2O saturation treatment to reduce dust and debris contamination and improve cleanliness.

6. The method for eliminating silicon wafer boat tracks in LPCVD processing according to claim 1, characterized in that: The angle between the slot of the silicon boat and the vertical plane is ≤6°, which enhances the adhesion of the silicon wafer and reduces the need for wrap-around plating. A silicon nitride coating is deposited on the quartz boat at a deposition temperature of 600-800℃ and an NH3 / DCS flow rate of 100-500 / 20-100 SCCM to reduce contact stress and boat marks.

7. The method for eliminating silicon wafer boat tracks in LPCVD processing according to claim 1, characterized in that: The LPCVD process begins with loading and vacuuming. The substrate is placed on a quartz boat and sent into the reaction chamber, where it is evacuated to a low pressure using a vacuum pump. The substrate is then heated to a predetermined temperature of 500–900°C. Silane (SiH4) and ammonia (NH3) are then introduced as precursor gases to carry out a chemical reaction and deposition on the substrate surface, forming the desired thin film. Finally, unreacted gases and byproducts are removed.