Method for improving film thickness uniformity in diffusion oxidation process furnace

Abstract

The invention provides a method for improving film thickness uniformity in a diffusion oxidation process furnace. The method comprises the following steps: putting a silicon wafer into a wafer boat in a loading area; lifting the wafer boat into a furnace tube, and introducing normal-temperature nitrogen into the furnace tube in the process of lifting the wafer boat into the furnace tube; performing a diffusion oxidation process in the furnace tube; after the diffusion oxidation process is completed, the wafer boat descends, and normal-temperature nitrogen continues to be introduced into the furnace tube in the process that the wafer boat descends to leave the furnace tube; and taking out the silicon wafer from the wafer boat. One or more paths of normal-temperature nitrogen from bottom to top are added in the boat lifting process, convection is generated between the normal-temperature nitrogen and high-temperature nitrogen in the furnace tube, the temperature in the furnace tube is reduced, the temperature of a wafer boat area is increased, the temperature difference between the furnace inlet area and the furnace outlet area is decreased, and the uniformity in batch is optimized.

Description

Technical Field

[0001] The invention relates to the field of semiconductor integrated circuits, in particular to a diffusion oxidation process, and specifically to a method for improving the uniformity of film thickness in a diffusion oxidation process furnace. Background Art

[0002] In the semiconductor manufacturing process, the oxidation process has the following functions: 1) as the gate oxide film of the transistor; 2) as the separation of the transistor; 3) as the barrier layer and buffer layer for injection. The oxidation process often uses the furnace tube oxidation method to generate silicon dioxide on the silicon wafer by thermal oxidation growth. The furnace tube oxidation process is carried out in a furnace tube. The reaction chamber inside the furnace tube is at normal pressure and high temperature. The furnace tube oxidation process is a batch process, and the silicon wafer is placed on a silicon boat.

[0003] like Figures 1 to 3 As shown in the figure, during the process of the boat entering the tube (usually takes 20 minutes), a natural oxide film will be formed because the loading area is in the atmospheric state. At the same time, because the top position of the boat enters the furnace tube first and contacts the high temperature area, the thickness of the natural oxide film at the top position will be thicker than other positions, resulting in poor uniformity within the batch, and the thin film Gate Oxide process cannot meet the operating requirements. Summary of the invention

[0004] In view of this, the present invention provides a method for improving the uniformity of film thickness in a diffusion oxidation process furnace, so as to reduce the thickness difference of the natural oxide film in a batch and optimize the uniformity in the batch.

[0005] The present invention provides a method for improving the uniformity of film thickness in a diffusion oxidation process furnace, comprising the following steps:

[0006] Step 1: Place the silicon wafer into the wafer boat in the loading area;

[0007] Step 2, lifting the wafer boat into the furnace tube, and introducing nitrogen gas at room temperature into the furnace tube during the process of lifting the wafer boat into the furnace tube;

[0008] Step 3, performing a diffusion oxidation process in the furnace tube;

[0009] Step 4: after the diffusion oxidation process is completed, the wafer boat is lowered, and the normal temperature nitrogen is continuously introduced into the furnace tube during the process of the wafer boat being lowered away from the furnace tube;

[0010] Step 5: taking the silicon wafer out of the wafer boat.

[0011] Preferably, the direction of introducing the nitrogen in step 2 and step 4 is from bottom to top, along the direction in which the wafer boat rises.

[0012] Preferably, the nitrogen introduced in step 2 and step 4 is one or more ways.

[0013] Preferably, the nitrogen in step 2 and step 4 can be replaced by other inert gases.

[0014] Preferably, the inert gas is Ar or He.

[0015] Preferably, the environment in the furnace tube in step 2 and step 4 is high temperature nitrogen.

[0016] Preferably, the room temperature nitrogen introduced in step 2 and step 4 will generate convection with the high temperature nitrogen, so that the temperature in the furnace tube is reduced, the temperature of the wafer boat is increased, and the temperature difference is reduced.

[0017] The present invention provides a new operating method without modifying the equipment. By introducing a normal temperature N2 gas flow, the air temperature distribution in the wafer boat entry and exit area is changed, so that the temperature difference becomes smaller. This solves the problem that the top position of the boat enters the furnace tube first and contacts the high temperature area, and the thickness of the natural oxide film at the top position is thicker than that at other positions, resulting in poor uniformity within the batch and failure to meet the operating requirements. This achieves the purpose of optimizing the uniformity of the film thickness within the batch. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0019] Figures 1 to 3 The diagram shows the process of the boat entering the tube;

[0020] Figure 4 A schematic diagram showing an existing method for improving the uniformity of film thickness in a diffusion oxidation process furnace;

[0021] Figure 5 A schematic diagram showing another existing method for improving the uniformity of film thickness in a diffusion oxidation process furnace;

[0022] Figure 6 A flow chart showing a method for improving the uniformity of film thickness in a diffusion oxidation process furnace according to an embodiment of the present invention;

[0023] Figure 7 and Figure 8 Shown is a schematic diagram of an embodiment of the method of the present invention;

[0024] Fig. 9 A schematic diagram showing the film thickness in the furnace and the difference in the furnace before and after using the method of the embodiment of the present invention;

[0025] Fig.10 Displayed as per Fig. 9 A bar graph of the in-furnace differences was plotted;

[0026] Fig.11 and Fig.12 Displayed as per Fig. 9 A line graph of the film thickness inside the furnace is drawn. DETAILED DESCRIPTION

[0027] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the detailed description of the present invention below, some specific details are described in detail. It is possible for a person skilled in the art to fully understand the present invention without the description of these details. In order to avoid confusing the essence of the present invention, known methods, processes, flows, components and circuits are not described in detail.

[0028] In addition, persons of ordinary skill in the art will appreciate that the drawings provided herein are for illustration purposes and are not necessarily drawn to scale.

[0029] Unless the context clearly requires otherwise, the words "include", "including" and similar words throughout the application should be interpreted as including rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0030] In the description of the present invention, it should be understood that the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0031] Thermal oxide films are widely used in integrated circuit production, acting as stress buffer layers, ion implantation shielding layers, gate oxide layers, insulating layers or device surface passivation layers, etc., covering the entire wafer production process. Therefore, the particle condition of oxide film growth is very important to the electrical performance, yield and even reliability of the device.

[0032] In the prior art, in order to reduce the difference of natural oxide film within a batch and optimize the uniformity within the batch, the industry generally uses the following two methods: the first one, such as Figure 4 As shown in the figure, when N2 is always passed through the loading area, the atmospheric environment is changed to N2 environment, and the temperature difference between the top and bottom of the boat is large (28-800℃), there will be no natural oxide film growth, and the uniformity within the batch is optimized; the second type, such as Figure 5As shown, an exhaust line with a fan is added. When the fan is turned on, the high-temperature N2 in the furnace is quickly extracted from the tube. The temperature in the furnace is quickly cooled to 300°C and then the boat is lifted. The temperature difference is reduced (28-300°C) and the uniformity in the batch is optimized. At present, most FAB equipment cannot add the above two devices due to equipment model and cost issues. Therefore, the present invention proposes a new method for improving the uniformity of film thickness in the diffusion oxidation process furnace. The technical solution of the present invention is further explained below in conjunction with the accompanying drawings and through specific implementation methods.

[0033] Figure 6 The flowchart of the method for improving the uniformity of film thickness in a diffusion oxidation process furnace according to an embodiment of the present invention is shown. Figure 6 As shown, the following steps are included:

[0034] Step 1: Place the silicon wafers into the wafer boat in the loading area.

[0035] Step 2: Lift the wafer boat into the furnace tube, and introduce nitrogen gas at room temperature into the furnace tube during the process of lifting the wafer boat into the furnace tube.

[0036] In the embodiment of the present invention, the nitrogen is introduced from bottom to top, along the direction of the boat rising. And the nitrogen introduced is one or more ways. Nitrogen can be replaced by other inert gases, such as Ar or He. The environment in the tube is high-temperature nitrogen, and the introduced room-temperature nitrogen will generate convection with the high-temperature nitrogen, so that the temperature in the tube is reduced, the temperature of the boat is increased, and the temperature difference in the furnace area is reduced.

[0037] Figure 7 and Figure 8 The diagram is a schematic diagram of the boat lifting process according to an embodiment of the present invention. Figure 7 and Figure 8 As shown, during the boat lifting process, one or more routes of normal temperature N2 from bottom to top are added to generate convection with the high temperature N2 in the tube, the temperature in the tube is reduced, and the temperature in the boat area is increased, so that when the boat is lifted, the regional temperature difference becomes smaller and the uniformity in the batch is optimized.

[0038] Step 3: Perform a diffusion oxidation process in the furnace tube.

[0039] The film forming process is mainly carried out in the furnace tube, including a deposition process (especially a vapor phase chemical deposition CVD), a thermal oxidation growth process, etc. In the embodiment of the present invention, a diffusion oxidation process is carried out in the furnace tube.

[0040] Step 4: After the diffusion oxidation process is completed, the wafer boat is lowered, and room temperature nitrogen is continuously introduced into the furnace tube during the process of the wafer boat lowering out of the furnace tube.

[0041] Step 4 is the same as step 2 above. The direction of nitrogen introduction is from bottom to top, along the direction of the boat rising. And the nitrogen introduced is one or more ways. Nitrogen can be replaced by other inert gases, such as Ar or He. The environment in the tube is high-temperature nitrogen. The room-temperature nitrogen introduced will produce convection with the high-temperature nitrogen, making the temperature difference in the furnace exit area smaller.

[0042] Step 5: Take the silicon wafer out of the wafer boat.

[0043] In the embodiment of the present invention, without modifying the equipment, the air temperature distribution in the wafer boat inlet and outlet area is changed by introducing a normal temperature N2 gas flow, so that the temperature difference becomes smaller, thereby achieving the purpose of optimizing the uniformity of the film thickness within the batch.

[0044] Fig. 9 It is a schematic diagram showing the film thickness in the furnace and the difference in the furnace before and after using the method of the embodiment of the present invention. Fig. 9 As shown in the table, the film thickness at each position in the furnace, such as the top, center, and bottom, and its difference within the furnace are listed. Calculation shows that the average difference within the furnace is 0.8A before improvement, and the average difference within the furnace is 0.432A after improvement, and the uniformity within the batch is optimized.

[0045] Fig.10 Displayed as per Fig. 9 A bar graph of the furnace differences is drawn. Fig.10 As shown in the figure, the height of the columnar graph representing the difference in the furnace becomes lower and the height is uniform, which means that after adopting the method of the embodiment of the present invention, the difference in the furnace becomes smaller and the uniformity of the film thickness is improved.

[0046] Fig.11 and Fig.12 Displayed as per Fig. 9 The line graph of the film thickness in the furnace is drawn. By comparison, it can be seen that after adopting the method of the embodiment of the present invention, the film thickness trend at the top, center and bottom of the batch is more gentle, indicating that the embodiment of the present invention has achieved the purpose of reducing the temperature difference of the wafer boat entering and exiting the furnace and improving the uniformity of the film thickness in the diffusion oxidation process furnace.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for improving the uniformity of film thickness in a diffusion oxidation process furnace, characterized in that: The following steps are involved: Step 1: Place the silicon wafer into the wafer boat in the loading area; Step 2, lifting the wafer boat into the furnace tube, and introducing nitrogen gas at room temperature into the furnace tube during the process of lifting the wafer boat into the furnace tube; Step 3, performing a diffusion oxidation process in the furnace tube; Step 4: after the diffusion oxidation process is completed, the wafer boat is lowered, and the normal temperature nitrogen is continuously introduced into the furnace tube during the process of the wafer boat being lowered away from the furnace tube; Step 5: taking the silicon wafer out of the wafer boat.

2. The method for improving the uniformity of film thickness in a diffusion oxidation process furnace according to claim 1, characterized in that: The direction of introducing the nitrogen in step 2 and step 4 is from bottom to top, along the direction in which the wafer boat rises.

3. The method for improving the uniformity of film thickness in a diffusion oxidation process furnace according to claim 1, characterized in that: In step 2 and step 4, the nitrogen introduced is one or more ways.

4. The method for improving the uniformity of film thickness in a diffusion oxidation process furnace according to claim 1, characterized in that: The nitrogen in step 2 and step 4 can be replaced by other inert gases.

5. The method for improving the uniformity of film thickness in a diffusion oxidation process furnace according to claim 4, characterized in that: The inert gas is Ar or He.

6. The method for improving the uniformity of film thickness in a diffusion oxidation process furnace according to claim 1, characterized in that: The environment in the furnace tube in step 2 and step 4 is high temperature nitrogen.

7. The method for improving the uniformity of film thickness in a diffusion oxidation process furnace according to claim 6, characterized in that: The room temperature nitrogen introduced in step 2 and step 4 will generate convection with the high temperature nitrogen, so that the temperature in the furnace tube is reduced, the temperature of the wafer boat is increased, and the temperature difference is reduced.

Images