Semiconductor device, cleaning method of shallow trench isolation structure

Abstract

The application discloses a kind of semiconductor device, shallow trench isolation structure's cleaning method, belong to semiconductor technical field, the method includes: providing a semiconductor device, semiconductor device includes silicon substrate, silicon substrate is stacked with multilayer semiconductor structure, in multilayer semiconductor structure, surface layer is silicon dioxide material, and the outer surface of surface layer exists the residue needing cleaning;Surface layer outer surface is handled using plasma nitriding method, so that surface layer outer surface is nitrided to form silicon oxynitride layer;Silicon oxynitride layer is etched using sulfuric acid hydrogen peroxide mixed solution, after silicon oxynitride layer is etched and removed, stop etching, to clean the outer surface residue of surface layer.The method can realize cleaning silicon dioxide under the premise that silicon dioxide loss is controllable.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a semiconductor device, a cleaning method for a shallow trench isolation structure, and the semiconductor device itself. Background Technology

[0002] In the semiconductor device manufacturing process, there may be a stage (such as the stage of producing shallow trench isolation structures) where the surface of the semiconductor device is silicon dioxide and there are serious residues on the silicon dioxide surface. It is necessary to clean these residues to improve the production yield of the semiconductor device.

[0003] In related technologies, hydrofluoric acid (HF) is typically used to clean residues on the surface of silica. For example, silica is immersed in a diluted hydrofluoric acid (DHF) solution to clean the residues on the silica surface.

[0004] However, the etching reaction endpoint of DHF is difficult to control, and DHF also reacts with silicon dioxide, which often results in a large loss of silicon dioxide when using DHF to clean the residue on the silicon dioxide surface. Summary of the Invention

[0005] This invention provides a cleaning method for semiconductor devices and shallow trench isolation structures, which can achieve silicon dioxide cleaning while keeping silicon dioxide loss under control. The technical solution includes at least the following:

[0006] In a first aspect, a method for cleaning a semiconductor device is provided, comprising: providing a semiconductor device, the semiconductor device including a silicon substrate, wherein a multilayer semiconductor structure is stacked on the silicon substrate, wherein a surface layer of the multilayer semiconductor structure is made of silicon dioxide, and the outer surface of the surface layer contains residues that need to be cleaned; treating the outer surface of the surface layer using a plasma nitriding method, thereby nitriding the outer surface of the surface layer to form a silicon oxynitride layer; etching the silicon oxynitride layer using a sulfuric acid-hydrogen peroxide mixture solution, and stopping the etching after the silicon oxynitride layer is etched away, in order to clean the residues on the outer surface of the surface layer.

[0007] Optionally, the thickness of the silicon oxynitride layer is in the range of 1. Up to 100 .

[0008] Optionally, the thickness of the silicon oxynitride layer is in the range of 5 mm. Up to 10 .

[0009] Optionally, during the treatment of the outer surface of the surface layer using plasma nitriding, the nitrogen concentration is greater than [missing information]. .

[0010] Optionally, in the sulfuric acid and hydrogen peroxide mixed solution, the ratio of sulfuric acid to hydrogen peroxide ranges from 10:1 to 1:10, and the temperature of the sulfuric acid ranges from 70°C to 200°C.

[0011] Optionally, the step of treating the outer surface of the surface layer with plasma nitriding to form a silicon oxynitride layer by nitriding the outer surface of the surface layer includes: using a plasma generator to perform the plasma nitriding, wherein the power range of the plasma generator is 500W to 3000W, the working time of the plasma generator is 5 seconds to 50 seconds, and the chamber pressure range of the plasma generator is 5 mTorr to 200 mTorr.

[0012] Optionally, after the steps of applying a sulfuric acid-hydrogen peroxide mixture to the silicon oxynitride layer and stopping the etching process after the silicon oxynitride layer has been etched away, the method further includes: removing the residual sulfuric acid-hydrogen peroxide mixture from the surface layer by water washing, thereby completing the cleaning of the surface layer.

[0013] Secondly, a method for cleaning a shallow trench isolation structure is also provided, comprising: sequentially depositing a first pad silicon oxide layer and a silicon nitride mask layer on a silicon substrate, and forming a photoresist layer with a shallow trench isolation structure pattern, wherein the first pad silicon oxide layer is made of silicon dioxide; using the photoresist layer as a mask, dry etching a portion of the silicon substrate to form a shallow trench; removing the photoresist layer; thermally oxidizing the sidewalls of the shallow trench to form a second pad silicon oxide layer, wherein the second pad silicon oxide layer is made of silicon dioxide; filling the shallow trench with silicon dioxide using chemical vapor deposition; removing the filled silicon dioxide using a chemical mechanical polishing process, wherein the chemical mechanical polishing process stops at the silicon nitride mask layer; removing the silicon nitride mask layer using a phosphoric acid wet etching process to obtain a first shallow trench isolation structure; and cleaning the residue on the outer surface of the first shallow trench isolation structure using the method described in the first aspect.

[0014] Optionally, the residues on the outer surface of the first shallow trench isolation structure include: silicon impurities left after removing the silicon nitride mask layer by phosphoric acid wet etching, and organic residues in the polishing slurry after removing the filled silicon dioxide by chemical mechanical polishing.

[0015] Thirdly, a semiconductor device is also provided, which is obtained by the cleaning method of the semiconductor device described in the first aspect, or by the cleaning method of the shallow trench isolation structure described in the second aspect.

[0016] The unexpected beneficial effects of the technical solution provided by this invention include at least the following:

[0017] Since the residue adheres to the outer surface of the surface layer, and the silicon oxynitride layer includes this outer surface, etching the silicon oxynitride layer with a sulfuric acid-hydrogen peroxide mixture can simultaneously remove the residue from the outer surface, thus achieving surface cleaning. The sulfuric acid-hydrogen peroxide mixture exhibits a significant difference in etching rate between SiON and SiO2. At room temperature, the etching rate of SiON with the sulfuric acid-hydrogen peroxide mixture is 25. The etching rate of SiO2 by the sulfuric acid-hydrogen peroxide mixture is almost zero.

[0018] In this case, after etching the silicon oxynitride layer with a sulfuric acid-hydrogen peroxide mixture, the etching rate of the sulfuric acid-hydrogen peroxide mixture on SiO2 is extremely low, so the reaction endpoint is easy to control (that is, after the sulfuric acid-hydrogen peroxide mixture etches the silicon oxynitride layer, the sulfuric acid-hydrogen peroxide mixture does not easily etch SiO2). There is sufficient time in the process flow to remove the remaining part of the sulfuric acid-hydrogen peroxide mixture on the surface layer, and the process of removing the remaining part of the sulfuric acid-hydrogen peroxide mixture on the surface layer after etching the silicon oxynitride layer is not likely to cause silicon dioxide loss.

[0019] During the cleaning process, some silica is lost. This lost silica is the nitrided silica, and only the nitrided silica is lost; no other silica is lost. Since the nitrided silica is determined by the plasma nitriding process, and this process can precisely control the nitrided portion of the silica, the silica loss during the cleaning process described in this invention is controllable. Thus, silica cleaning can be achieved while ensuring controllable silica loss. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart of a cleaning method for a semiconductor device provided by an exemplary embodiment of the present invention is shown;

[0022] Figure 2 A cross-sectional view of the structure formed by the relevant steps of a semiconductor device cleaning method provided as an exemplary embodiment of the present invention;

[0023] Figure 3A flowchart illustrating a cleaning method for a shallow trench isolation structure provided by an exemplary embodiment of the present invention is shown.

[0024] Figure 4 This is a schematic diagram of cleaning a shallow trench isolation structure using a semiconductor device cleaning method. Detailed Implementation

[0025] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” “third,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising” or “including” and similar terms mean that the elements or objects preceding “comprising” or “including” encompass the elements or objects listed following “comprising” or “including” and their equivalents, but do not exclude other elements or objects. “Above,” “below,” “left,” “right,” etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0027] Figure 1 A flowchart illustrating a semiconductor device cleaning method according to an exemplary embodiment of the present invention is shown. See also... Figure 1 The method includes:

[0028] In step 101, a semiconductor device is provided.

[0029] Semiconductor devices include a silicon substrate on which multiple semiconductor structures are stacked. In the multiple semiconductor structures, the surface layer is made of silicon dioxide (SiO2), and there are residues on the outer surface of the surface layer that need to be cleaned.

[0030] Here, the surface layer refers to the topmost layer in a multilayer semiconductor structure stacked on a silicon substrate, and the outer surface of the surface layer structure is in direct contact with the air.

[0031] Figure 2 A cross-sectional view of the structure formed by the relevant steps of a semiconductor device cleaning method provided as an exemplary embodiment of the present invention. Figure 2 Part (a) is a schematic diagram of the structure of a semiconductor device, such as Figure 2As shown in part (a), the semiconductor device includes a silicon substrate 201 on which a multilayer semiconductor structure 202 is stacked. The surface layer 203 of the multilayer semiconductor structure is made of silicon dioxide, and there are residues on the outer surface 204 of the surface layer 203 that need to be cleaned.

[0032] In step 102, the outer surface of the surface layer is treated by plasma nitriding, so that the outer surface of the surface layer is nitrided to form a silicon oxynitride layer.

[0033] Plasma nitriding is a nitriding process that diffuses nitrogen ions from the outer surface of a surface layer inwards, thereby altering the properties of a portion of the surface layer and forming a nitrided layer. In this embodiment of the invention, the surface layer is made of silicon dioxide; therefore, the nitrided layer formed by nitriding a portion of the surface layer is made of silicon oxynitride (SiON). That is, the outer surface of the surface layer is nitrided to form a silicon oxynitride layer.

[0034] In one possible implementation, the thickness of the silicon oxynitride layer ranges from 1. Up to 100 The silicon oxynitride layer is formed by nitriding a portion of the surface silicon dioxide (the nitrided silicon dioxide is equivalent to the lost silicon dioxide), and the silicon oxynitride layer needs to be etched away subsequently. If the thickness of the silicon oxynitride layer exceeds 100... This could lead to excessive loss of silicon dioxide. If the thickness of the silicon oxynitride layer is less than 1 mm... If the surface of the silica is uneven, some residue may not be completely cleaned.

[0035] In another possible implementation, the thickness of the silicon oxynitride layer ranges from 5 mm. Up to 10 The thickness of the silicon oxynitride layer is controlled within 5 mm. Up to 10 This ensures that the silica is not lost too much, and also avoids incomplete cleaning of residues due to an excessively thin silica oxynitride layer.

[0036] Optionally, during the treatment of the outer surface of the surface layer using plasma nitriding, the nitrogen concentration is greater than... During plasma nitriding to treat the outer surface of the surface layer, the nitrogen concentration affects the formation rate of silicon oxynitride and the final structural uniformity of the silicon oxynitride. By controlling the nitrogen concentration to be greater than... This can effectively improve the formation rate of silicon oxynitride layers and reduce the occurrence of unevenness or defects in the formed silicon oxynitride layers.

[0037] Optionally, step 102 includes: using a plasma generator to perform plasma nitriding.

[0038] The plasma generator has a power range of 500W to 3000W, an operating time range of 5 seconds to 50 seconds, and a chamber pressure range of 5 mTorr to 200 mTorr. This effectively improves the working efficiency of the plasma generator and the stability of the generated silicon oxynitride layer.

[0039] Figure 2 Part (b) is a schematic diagram of the outer surface treatment of the surface layer by plasma nitriding, as shown in the figure. Figure 2 As shown in part (b), the surface layer 203 was originally made of silicon dioxide. After nitriding, a part of the surface layer (including the outer surface 204) became a silicon oxynitride layer 205.

[0040] In step 103, the silicon oxynitride layer is etched using a sulfuric acid and hydrogen peroxide mixture. After the silicon oxynitride layer is etched away, the etching is stopped to clean the outer surface residue of the surface layer.

[0041] Since the residue is attached to the outer surface of the surface layer, and the silicon oxynitride layer includes the outer surface, the residue on the outer surface can be removed at the same time while the silicon oxynitride layer is etched using a sulfuric acid and hydrogen peroxide mixture, thus achieving the cleaning of the surface layer.

[0042] Optionally, in the sulfuric acid and hydrogen peroxide mixed solution, the sulfuric acid is concentrated sulfuric acid, and the hydrogen peroxide is electronic grade or reagent grade hydrogen peroxide, with the ratio of sulfuric acid to hydrogen peroxide ranging from 10:1 to 1:10 (volume ratio). When mixing sulfuric acid and hydrogen peroxide, the temperature of the sulfuric acid should be between 70°C and 200°C, and the hydrogen peroxide should be at room temperature before mixing.

[0043] The sulfuric acid-hydrogen peroxide mixed solution exhibits a significant difference in etching rate between SiON and SiO2. At room temperature, the etching rate of SiON with the sulfuric acid-hydrogen peroxide mixed solution is 25. The etching rate of SiO2 by the sulfuric acid-hydrogen peroxide mixture is almost zero.

[0044] In this case, after etching the silicon oxynitride layer with a sulfuric acid-hydrogen peroxide mixture, the etching rate of the sulfuric acid-hydrogen peroxide mixture on SiO2 is extremely low, so the reaction endpoint is easy to control (that is, after the sulfuric acid-hydrogen peroxide mixture etches the silicon oxynitride layer, the sulfuric acid-hydrogen peroxide mixture does not easily etch SiO2). There is sufficient time in the process flow to remove the remaining part of the sulfuric acid-hydrogen peroxide mixture on the surface layer, and the process of removing the remaining part of the sulfuric acid-hydrogen peroxide mixture on the surface layer after etching the silicon oxynitride layer is not likely to cause silicon dioxide loss.

[0045] During the cleaning process, some silica is lost. This lost silica is the nitrided silica, and only the nitrided silica is lost; no other silica is lost. Since the nitrided silica is determined by the plasma nitriding process, and this process can precisely control the nitrided portion of the silica, the silica loss during the cleaning process described in this embodiment is controllable. Thus, silica cleaning can be achieved while ensuring controllable silica loss.

[0046] Figure 2 Part (c) is a schematic diagram of the cleaned semiconductor device, such as... Figure 2 As shown in section (c), the silicon oxynitride layer 205 is removed, which is equivalent to the removal of residues, thereby achieving cleaning of the semiconductor device.

[0047] Optionally, after performing step 103, the method further includes: using a water washing method to remove the residual sulfuric acid and hydrogen peroxide mixture solution on the surface layer, thereby completing the cleaning of the surface layer.

[0048] Here, after etching the silicon oxynitride layer with a sulfuric acid and hydrogen peroxide mixture, some sulfuric acid and hydrogen peroxide mixture will remain on the surface layer. At this time, it is only necessary to wash away the residual sulfuric acid and hydrogen peroxide mixture with water.

[0049] For example, the semiconductor device can be a semiconductor device with a shallow trench isolation (STI) structure. The following is in conjunction with... Figure 3 The process flow of the cleaning method for semiconductor devices with STI.

[0050] Figure 3 A flowchart illustrating a cleaning method for a shallow trench isolation structure provided by an exemplary embodiment of the present invention is shown. See also: Figure 3 The method includes:

[0051] In step 301, a first pad silicon oxide layer and a silicon nitride mask layer are sequentially deposited on the silicon substrate, and a photoresist layer with a shallow trench isolation structure pattern is formed.

[0052] The first pad silicon oxide layer is made of silicon dioxide.

[0053] In step 302, using a photoresist layer as a mask, a portion of the silicon substrate is dry-etched to form shallow trenches.

[0054] In step 303, the photoresist layer is removed.

[0055] In step 304, the sidewalls of the shallow trench are thermally oxidized to form a second pad silicon oxide layer.

[0056] The second pad silicon oxide layer is made of silicon dioxide.

[0057] In step 305, silica is filled into the shallow trench using chemical vapor deposition.

[0058] In step 306, the filled silicon dioxide is removed by chemical mechanical polishing (CMP), and the CMP process stops at the silicon nitride mask layer.

[0059] In step 307, the silicon nitride mask layer is removed by wet etching with phosphoric acid to obtain the first shallow trench isolation structure.

[0060] As can be seen from 301 to 307 above, the oxide filled in the shallow trench isolation structure is silicon dioxide (i.e., step 305), and the oxide filled in the shallow trench isolation structure is equivalent to the surface layer in step 101.

[0061] During the fabrication of the shallow trench isolation structure, steps 306 and 307 result in a large amount of residue on the surface of the final shallow trench isolation structure. The chemical mechanical polishing (CMP) technique in step 306 requires the use of an polishing slurry, and organic matter in the polishing slurry will remain on the outer surface after step 306 is completed.

[0062] When wet etching silicon nitride with phosphoric acid, it is necessary to etch silicon nitride with high selectivity without damaging other materials. A high concentration of silicon ions can adjust the etching rate of phosphoric acid, thereby optimizing the selectivity and ensuring that phosphoric acid etches only silicon nitride without damaging other materials. Therefore, after the wet etching with phosphoric acid in step 307 is completed, silicon impurities will remain on the wafer inside the phosphoric acid tank.

[0063] In summary, the residues on the outer surface of the first shallow trench isolation structure include: silicon impurities left after removing the silicon nitride mask layer by phosphoric acid wet etching, and organic residues in the polishing slurry after removing the filled silicon dioxide by chemical mechanical polishing.

[0064] In step 308, residues on the outer surface of the first shallow trench isolation structure are cleaned.

[0065] In this embodiment of the invention, step 308 is implemented using the methods described in steps 101 to 103.

[0066] Figure 4 This is a schematic diagram of cleaning a shallow trench isolation structure using a semiconductor device cleaning method. Figure 4 Part (a) is a schematic diagram of the first shallow trench isolation structure. For example... Figure 4 As shown in part (a), the first shallow trench isolation structure includes: a silicon substrate 401, a shallow trench 402, and an oxide 403 (i.e., silicon dioxide) filling the shallow trench isolation structure. Here, the silicon substrate 401 is equivalent to... Figure 2 The silicon substrate 201 and the oxide 403 filled with the shallow trench isolation structure are equivalent to Figure 2 The surface layer 203 is in the middle. The outer surface 404 of the oxide 403 filled by the shallow trench isolation structure is equivalent to the outer surface 204 of the surface layer 203. There are residues on the outer surface 204 that need to be cleaned.

[0067] Furthermore, the first pad silicon oxide layer, the second pad silicon oxide layer, and the oxide filling the shallow trench isolation structure in steps 301-307 are all made of the same material, namely silicon dioxide. Figure 4 The oxide 403 filled with shallow trench isolation structure is uniformly represented.

[0068] When cleaning shallow trench isolation structures using semiconductor device cleaning methods, a silicon oxynitride layer is first formed on the surface layer (i.e., the oxide 403 filling the shallow trench isolation structure) by nitriding. For example... Figure 4 As shown in part (b), a silicon oxynitride layer 405 is formed on the oxide 403 filled with the shallow trench isolation structure by nitriding.

[0069] Then, a sulfuric acid-hydrogen peroxide mixture is used to etch the silicon oxynitride layer. After the silicon oxynitride layer is etched away, etching is stopped to clean any remaining residue on the outer surface of the surface layer. For example... Figure 4 As shown in part (c), while the silicon oxynitride layer is being etched, the outer surface 404, which originally had residues, is also removed, that is, the residues on the outer surface of the oxide 403 filled by the shallow trench isolation structure are cleaned.

[0070] The relevant content of step 308 is the same as that of steps 102 to 103 above. It is only necessary to replace the surface layer in steps 102 to 103 with the oxide of the first shallow trench isolation filling. The details are omitted here.

[0071] Since the thickness of the oxide filling in the shallow trench isolation structure is typically several thousand angstroms, while the silicon oxynitride layer is typically less than 100 angstroms, the loss of this portion of silicon dioxide is negligible compared to the total thickness of the oxide filling in the shallow trench isolation structure, meaning that this loss is acceptable.

[0072] This invention also provides a semiconductor device, which is obtained by a semiconductor device cleaning method or a shallow trench isolation structure cleaning method.

[0073] The above description is merely an optional embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for cleaning a semiconductor device, characterized in that, The method includes: A semiconductor device is provided, the semiconductor device including a silicon substrate, on which a multilayer semiconductor structure is stacked, wherein the surface layer of the multilayer semiconductor structure is made of silicon dioxide, the outer surface of the surface layer has residues that need to be cleaned, and the surface layer is an oxide filled with a shallow trench isolation structure; The outer surface of the surface layer is treated by plasma nitriding, so that the outer surface of the surface layer is nitrided to form a silicon oxynitride layer, and the thickness of the surface layer is much greater than the thickness of the silicon oxynitride layer. The silicon oxynitride layer is etched using a sulfuric acid and hydrogen peroxide mixture. After the silicon oxynitride layer is etched away, the etching is stopped to clean the outer surface residue of the surface layer.

2. The cleaning method for semiconductor devices according to claim 1, characterized in that, The thickness of the silicon oxynitride layer is in the range of 1. Up to 100 .

3. The cleaning method for semiconductor devices according to claim 1, characterized in that, The thickness of the silicon oxynitride layer is in the range of 5. Up to 10 .

4. The cleaning method for semiconductor devices according to claim 2 or 3, characterized in that, During the treatment of the outer surface of the surface layer using plasma nitriding, the nitrogen concentration is greater than... .

5. The method for cleaning semiconductor devices according to claim 1, characterized in that, In the sulfuric acid and hydrogen peroxide mixed solution, the volume ratio of sulfuric acid to hydrogen peroxide is 10:1 to 1:10, and the temperature range of the sulfuric acid is 70°C to 200°C.

6. The cleaning method for semiconductor devices according to claim 1, characterized in that, The step of treating the outer surface of the surface layer using plasma nitriding to form a silicon oxynitride layer includes: The plasma nitriding method is implemented using a plasma generator with a power range of 500W to 3000W, an operating time range of 5 seconds to 50 seconds, and a chamber pressure range of 5 mTorr to 200 mTorr.

7. The cleaning method for semiconductor devices according to claim 1, characterized in that, After the step of using a sulfuric acid-hydrogen peroxide mixture to etch the silicon oxynitride layer, and stopping the etching process after the silicon oxynitride layer has been etched away, the method further includes: The surface layer is cleaned by washing with water to remove the residual sulfuric acid and hydrogen peroxide mixture.

8. A cleaning method for a shallow trench isolation structure, characterized in that, The method includes: A first pad silicon oxide layer and a silicon nitride mask layer are sequentially deposited on a silicon substrate, and a photoresist layer with a shallow trench isolation structure pattern is formed. The first pad silicon oxide layer is made of silicon dioxide. Using the photoresist layer as a mask, a portion of the silicon substrate is dry-etched to form shallow trenches; Remove the photoresist layer; The sidewalls of the shallow trench are thermally oxidized to form a second pad silicon oxide layer, which is made of silicon dioxide. Silica was filled into the shallow trench using chemical vapor deposition. The filled silicon dioxide is removed by a chemical mechanical polishing process, which stops at the silicon nitride mask layer; The silicon nitride mask layer was removed by wet etching with phosphoric acid to obtain the first shallow trench isolation structure. The residue on the outer surface of the first shallow trench isolation structure is cleaned using the method described in any one of claims 1 to 7.

9. The cleaning method for the shallow trench isolation structure according to claim 8, characterized in that, The residues on the outer surface of the first shallow trench isolation structure include: silicon impurities left after removing the silicon nitride mask layer by phosphoric acid wet etching, and organic residues in the polishing slurry after removing the filled silicon dioxide by chemical mechanical polishing.

10. A semiconductor device, characterized in that, The semiconductor device is obtained by the cleaning method of any one of claims 1 to 7, or the semiconductor device is obtained by the cleaning method of the shallow trench isolation structure of any one of claims 8 to 9.

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