Method for improving thickness uniformity of oxide on side wall of deep trench

Abstract

The invention provides a method for improving the thickness uniformity of oxide on the side wall of a deep groove, which comprises the following steps of: providing a substrate, depositing a hard mask layer on the substrate, coating photoresist with a certain thickness, then adjusting the focal length to be offset, and exposing and developing the photoresist to form a pattern etched by the deep groove; carrying out UVC glue solidification treatment on the photoresist; performing dry etching on the hard mask layer, and adjusting the proportion of etching gas and the etching pressure to form the hard mask layer with uniform and straight boundary morphology; and etching the deep groove, the side wall oxide and the bottom oxide by adopting a Bosch process so as to finally obtain the deep groove with the side wall oxide with uniform thickness and morphology. According to the method, the thickness uniformity of the oxide on the side wall of the DTI is adjusted and optimized through the photoresist thickness of DTI photoetching and the Focus, the Focus is adjusted to be biased, and the photoresist is subjected to UVC solidification treatment, so that the morphology of the photoresist is optimized; and meanwhile, the proportion and the pressure intensity of the etching gas during HM dry etching are finely adjusted, so that the morphology after etching is relatively uniform and straight, and the morphology of subsequent etching is prevented from being deteriorated.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor manufacturing, and in particular to a method for improving the uniformity of oxide thickness on a deep trench sidewall. Background Art

[0002] In the semiconductor field, the process technology pays great attention to morphology control. In the BCD deep trench isolation (DTI) process, the trench is etched first, then the trench sidewall is oxidized, and then the bottom of the trench oxide is etched to obtain a structure connected to the substrate (sub); this structure requires that the bottom of the DTI is connected to the sub, and the top sidewall oxide must have a certain thickness to meet the voltage resistance requirements; however, in actual production, the sidewall oxide may show serious uneven thickness, resulting in insufficient voltage resistance of the chip. Figure 1 As shown in the figure, after etching the bottom of DTI, the sidewall oxide (sidewall OX) of the platform vehicle product has obvious uneven thickness, curved lines, and thin Sidewall OX, which will lead to low breakdown voltage and easy chip failure. Therefore, it is urgent to improve the existing deep trench process to solve the problem that the existing deep trench sidewall oxide may show serious uneven thickness, resulting in insufficient voltage resistance and easy chip failure. Summary of the invention

[0003] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method for improving the uniformity of the oxide thickness of the sidewall of a deep trench, so as to optimize the deep trench process, thereby achieving the purpose of improving the uniformity of the oxide thickness of the sidewall and improving the pressure resistance of the chip.

[0004] The present invention provides a method for improving the uniformity of oxide thickness on the sidewall of a deep trench, comprising the following steps:

[0005] Step 1, providing a substrate, depositing a hard mask layer on the substrate, coating a photoresist of a certain thickness, then adjusting the focus and polarization, performing exposure and development, after which the photoresist has a deep groove etched pattern;

[0006] Step 2, performing UVC curing treatment on the photoresist;

[0007] Step 3, dry etching the hard mask layer under the patterned photoresist definition, and adjusting the proportion of etching gas and etching pressure to form a hard mask layer with a uniform and straight boundary morphology;

[0008] Step 4: Use the Bosch process to etch deep trenches, sidewall oxides and bottom oxides to finally obtain deep trenches with uniform sidewall oxide thickness and morphology.

[0009] Preferably, the substrate in step one is a silicon substrate.

[0010] Preferably, the material of the hard mask layer in step 1 is titanium nitride or silicon nitride.

[0011] Preferably, the thickness of the photoresist in step 1 is 2.6-2.9 um.

[0012] Preferably, the focal length in step 1 is adjusted to 0.8-1.0.

[0013] Preferably, the etching gas in step three is CF4, CHF3 and Ar.

[0014] Preferably, the flow rate of CF4 is adjusted to 40 sccm, the flow rate of CHF3 is adjusted to 20 sccm, and the flow rate of Ar is adjusted to 250 sccm.

[0015] Preferably, in step three, the etching pressure is adjusted to be lowered.

[0016] Preferably, the pressure is adjusted to 100 mT.

[0017] Preferably, step three also includes a step of removing the photoresist.

[0018] The present invention adjusts and optimizes the uniformity of the DTI sidewall oxide thickness through the DTI photolithography glue thickness and focus, adjusts the Focus to be positive, and performs UVC curing treatment on the photoresist to optimize the glue morphology; at the same time, by fine-tuning the hard mask layer (HM) dry etching, adjusting the proportion of etching gas (CF4 / CHF3 / AR) and etching pressure during dry etching, the morphology after etching is more uniform and straight, ensuring that the morphology of subsequent etching will not deteriorate, and achieving the purpose of optimizing the deep trench process, improving the uniformity of the sidewall oxide thickness, and improving the pressure resistance of the chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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:

[0020] Figure 1 A schematic diagram showing the morphology of the sidewall oxide after etching the bottom of the DTI process for existing platform vehicle products;

[0021] Figure 2 A flow chart showing a method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to an embodiment of the present invention;

[0022] Figure 3 A schematic diagram showing the deep trench morphology according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0023] 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.

[0024] 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.

[0025] Unless the context clearly requires otherwise, the words "include", "comprising" 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".

[0026] 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.

[0027] The existing DTI process method includes: DTI photolithography development: focus setting -0.1 to 0.3; NA; DTI hard mask (HM) etching: dry etching, etching gas is CF4 / CHF3 / AR (30 / 45 / 200sccm), pressure is 120mt; subsequent normal Bosch process etching deep trench, sidewall oxidation and bottom oxide etching to obtain the final morphology. However, after etching the HM layer, the HM morphology boundary is poor, there are more polymer residues, resulting in the concave side of the HM etching, so that the morphology of subsequent etching will deteriorate, and the sidewall oxide may show serious uneven thickness, resulting in insufficient chip withstand voltage performance. Therefore, the present invention proposes a method for improving the uniformity of the thickness of the sidewall oxide of the deep trench, which is used to optimize the deep trench process, and then achieve the purpose of improving the uniformity of the thickness of the sidewall oxide and improving the withstand voltage of the chip. The technical scheme of the present invention is further explained below in conjunction with the accompanying drawings and through specific implementation methods.

[0028] Figure 2 The flowchart of the method for improving the uniformity of the oxide thickness on the sidewall of a deep trench according to an embodiment of the present invention is shown. Figure 2 As shown, the method for improving the uniformity of the oxide thickness of the deep trench sidewall according to the embodiment of the present invention comprises the following steps:

[0029] Step 1: provide a substrate, deposit a hard mask layer on the substrate, and apply a certain thickness of photoresist, then adjust the focus and bias, perform exposure and development, and after exposure and development, the photoresist has a deep groove etched pattern.

[0030] The material of the substrate may be silicon, germanium, silicon germanium or silicon carbide, etc., or may be silicon on insulator (SOI) or germanium on insulator (GOI), or may be other materials, such as III and V group compounds such as gallium arsenide. The substrate in this embodiment is a silicon substrate, and further, it may be an undoped or lightly doped silicon substrate.

[0031] There are many materials for the hard mask layer. In the embodiment of the present invention, the material of the hard mask layer (HM) is titanium nitride or silicon nitride, usually silicon nitride (SiN), which can be formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0032] In the embodiment of the present invention, the thickness of the coated photoresist is 2.6-2.9um. The Focus setting needs to be adjusted from negative to positive, and further, the Focus setting is 0.8-1.0. After exposure and development, the photoresist morphology has a certain tap, the bottom of the photoresist is well coated and developed, and there is no undercut (undercut) and a photoresist with a deep groove etched pattern.

[0033] Step 2: Perform UVC curing treatment on the photoresist.

[0034] In the embodiment of the present invention, UVC glue curing treatment is performed to optimize the morphology of the glue.

[0035] Step 3: dry-etching the hard mask layer under the patterned photoresist definition, and adjusting the proportion of etching gas and etching pressure to form a hard mask layer with a uniform and straight boundary morphology.

[0036] In the embodiment of the present invention, the etching gas for dry etching the HM layer is CF4, CHF3 and Ar. The ratio of the etching gas is adjusted. Specifically, the flow rate of CF4 is adjusted to 40sccm, the flow rate of CHF3 is adjusted to 20sccm, and the flow rate of Ar is adjusted to 250sccm. The etching pressure is adjusted. Specifically, the etching pressure is adjusted to be lowered. The pressure in this embodiment is set to 100mT. By fine-tuning the dry etching during HM etching, adjusting the ratio of CF4 / CHF3 / AR and the etching pressure, the morphology after etching is made more uniform and straight, and the side of the HM etching is smooth, ensuring that the morphology of subsequent etching will not deteriorate.

[0037] In addition, step three also includes removing the photoresist. The photoresist can be removed by using a photoresist stripping process.

[0038] Step 4: Use the Bosch process to etch deep trenches, sidewall oxides and bottom oxides to finally obtain deep trenches with uniform sidewall oxide thickness and morphology.

[0039] like Figure 3 As shown, the final morphology shows that the sidewall oxide thickness is uniform and meets the requirements. Figure 1 Obviously, compared with the prior art, the embodiments of the present invention are helpful to improve the uniformity of the DTI sidewall oxide thickness, thereby achieving the purpose of improving the uniformity of the sidewall oxide thickness and improving the pressure resistance of the chip.

[0040] The embodiment of the present invention adjusts and optimizes the uniformity of the DTI sidewall oxide thickness through the DTI photolithography glue thickness and Focus, adjusts the Focus to be positive, and performs UVC curing treatment on the photoresist to optimize the glue morphology; at the same time, by fine-tuning the proportion of etching gas and etching pressure during HM dry etching, the morphology after etching is more uniform and straight, ensuring that the morphology of subsequent etching will not deteriorate, and finally obtaining a deep groove with uniform sidewall oxide thickness and thickness that meets the requirements, thereby achieving the purpose of optimizing the deep trench process, improving the uniformity of the sidewall oxide thickness, and improving the pressure resistance of the chip.

[0041] 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 oxide thickness on the sidewall of a deep trench, characterized in that: The following steps are involved: Step 1, providing a substrate, depositing a hard mask layer on the substrate, coating a photoresist of a certain thickness, then adjusting the focus and polarization, performing exposure and development, after which the photoresist has a deep groove etched pattern; Step 2, performing UVC curing treatment on the photoresist; Step 3, dry etching the hard mask layer under the patterned photoresist definition, and adjusting the proportion of etching gas and etching pressure to form a hard mask layer with a uniform and straight boundary morphology; Step 4: Use the Bosch process to etch deep trenches, sidewall oxides and bottom oxides to finally obtain deep trenches with uniform sidewall oxide thickness and morphology.

2. The method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to claim 1, characterized in that: The substrate in step 1 is a silicon substrate.

3. The method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to claim 1, characterized in that: The material of the hard mask layer in step 1 is titanium nitride or silicon nitride.

4. The method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to claim 1, characterized in that: The thickness of the photoresist in step 1 is 2.6-2.9 um.

5. The method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to claim 1, characterized in that: The focal length in step 1 is adjusted to 0.8-1.

0.

6. The method for improving the thickness uniformity of the oxide on the sidewall of a deep trench according to claim 1, characterized in that: The etching gases in step three are CF4, CHF3 and Ar.

7. The method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to claim 6, characterized in that: The flow rate of CF4 is adjusted to 40 sccm, the flow rate of CHF3 is adjusted to 20 sccm, and the flow rate of Ar is adjusted to 250 sccm.

8. The method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to claim 1, characterized in that: In step three, the etching pressure is adjusted to be lowered.

9. The method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to claim 8, characterized in that: The pressure was adjusted to 100 mT.

10. The method for improving the uniformity of oxide thickness on the sidewall of a deep trench according to claim 1, characterized in that: Step three also includes the step of removing the photoresist.

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