Method for improving deep trench sidewall oxide thickness

Abstract

The application provides a method for improving the thickness of the oxide layer on the sidewall of a deep trench, and comprises the following steps: providing a substrate, forming an epitaxial layer on the substrate, and sequentially forming a pad oxide layer, an etching stop layer, a polysilicon layer and a hard mask layer on the epitaxial layer; forming a photoresist layer on the hard mask layer, adjusting the focal length of exposure to open the photoresist layer to define the forming position of the deep trench, and using etching to open the exposed hard mask layer to form an opening pattern, wherein the sidewall of the opening pattern is in an inclined shape, and the cross section of the opening pattern is in a trapezoidal shape with the upper part being wide and the lower part being narrow; forming a deep trench by etching, and removing the remaining photoresist layer; forming a thermal oxidation layer on the sidewall of the deep trench and the polysilicon layer by using a thermal oxidation method, wherein the thermal oxidation layer on the sidewall of the polysilicon layer is in a convex shape; etching the thermal oxidation layer to retain it on the sidewall of the deep trench; and forming a filling layer to fill the remaining deep trench by using a deposition and polishing method. The application can improve the thickness of the oxide layer on the sidewall of the deep trench.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to a method for improving the thickness of deep trench sidewall oxide. BACKGROUND

[0002] In the field of semiconductor, the morphology control is very important in the process. In the deep trench (DTI) process of BCD, the trench etching is firstly performed, then the trench sidewall is oxidized, and then the trench oxide bottom is etched to obtain a structure communicating with the substrate. The structure requires that the bottom of the DTI communicates with the substrate, and the sidewall oxide at the top has a certain thickness to meet the requirement of voltage resistance. However, in actual etching, the etching rate of the oxide at the top of the trench is always greater than that at the bottom. When the bottom oxide is etched through, the oxide at the top is often etched very thin, which finally leads to insufficient voltage resistance of the chip and leakage.

[0003] In order to solve the above problems, a new method for improving the thickness of deep trench sidewall oxide is needed. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a method for improving the thickness of deep trench sidewall oxide, which is used to solve the problem that in the prior art, the etching rate of the oxide at the top of the trench is always greater than that at the bottom. When the bottom oxide is etched through, the oxide at the top is often etched very thin, which finally leads to insufficient voltage resistance of the chip and leakage.

[0005] To achieve the above-mentioned purposes and other related purposes, the present application provides a method for improving the thickness of deep trench sidewall oxide, comprising:

[0006] Step one, providing a substrate, forming an epitaxial layer on the substrate, and sequentially forming a pad oxide layer, an etching stop layer, a polysilicon layer and a hard mask layer on the epitaxial layer;

[0007] Step two, forming a photoresist layer on the hard mask layer, adjusting the focal length of exposure to open the photoresist layer to define the formation position of the deep trench, and using etching to open the exposed hard mask layer to form an opening pattern, the sidewall of the opening pattern being an inclined morphology, and the cross section being a trapezoidal shape with the upper part being wide and the lower part being narrow;

[0008] Step three, forming a deep trench by etching and removing the remaining photoresist layer;

[0009] Step four, forming a thermal oxidation layer on the polysilicon layer and the sidewall of the deep trench by using thermal oxidation method, wherein the thermal oxidation layer at the sidewall of the polysilicon layer is a convex morphology;

[0010] Step five, etching the thermal oxide layer to keep it on the sidewall of the deep trench, the protruding thermal oxide layer is used to protect the thermal oxide layer on the top sidewall of the deep trench;

[0011] Step six, forming a filling layer to fill the rest of the deep trench by depositing and grinding.

[0012] Preferably, the material of the etching stop layer in step one is silicon nitride.

[0013] Preferably, the material of the hard mask layer in step one is silicon dioxide.

[0014] Preferably, the range of the focal length of the exposure adjustment in step two is +0.4-1.4 microns.

[0015] Preferably, the deep trench is formed by Bosch etching in step three.

[0016] Preferably, the step of performing edge etching is further included before step four.

[0017] Preferably, the photoresist layer is removed by ashing process and wet cleaning in step four.

[0018] Preferably, the etching in step five is dry etching, and the etching gas is C5F8 and O2.

[0019] Preferably, the ratio of C5F8 and O2 in step five is 1.2:1 to 1.4:1.

[0020] Preferably, the etching in step five further includes a carrier gas.

[0021] Preferably, the carrier gas in step five is Ar.

[0022] Preferably, the cavity pressure in step five is 45-55mtorr.

[0023] Preferably, the material of the filling layer in step six is polysilicon.

[0024] Preferably, the grinding method in step six is chemical mechanical planarization grinding.

[0025] As described above, the method for improving the thickness of the oxide layer on the sidewall of the deep trench has the following beneficial effects:

[0026] The present application can improve the thickness of the oxide layer on the sidewall of the deep trench, and avoid the problem of low breakdown voltage and chip failure caused by thin sidewall oxide layer. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The figure shows the process flow diagram of the present application;

[0028] Figure 2 An open hard mask layer of the present application is shown in the schematic diagram;

[0029] Figure 3 A deep trench formation of the present application is shown in the schematic diagram;

[0030] Figure 4 A thermal oxide layer formation of the present application is shown in the schematic diagram;

[0031] Figure 5 An etching thermal oxide layer of the present application is shown in the schematic diagram. DETAILED DESCRIPTION

[0032] The present application is described herein with reference to particular specific embodiments thereof, which provide an excellent understanding of the advantages and utilities of the present application. The present application can be practiced with other embodiments as well, and the scope of the present application is not limited to the specific embodiments described herein. Various modifications and changes can be made as would be obvious to a person skilled in the art having the benefit of this disclosure, without departing from the spirit of the present application.

[0033] Referring to Figure 1 The present application provides a method for improving the thickness of the sidewall oxide of a deep trench, comprising:

[0034] Step one, providing a substrate 101, forming an epitaxial layer 102 on the substrate 101, and sequentially forming a pad oxide layer 103, an etching stop layer 104, a polysilicon layer 105 and a hard mask layer 106 on the epitaxial layer 102;

[0035] In some embodiments, the material of the etching stop layer 104 in step one is silicon nitride.

[0036] In some embodiments, the material of the hard mask layer 106 in step one is silicon dioxide.

[0037] Step two, forming a photoresist layer (not shown in the figure) on the hard mask layer 106, adjusting the focal length of exposure to open the photoresist layer to define the formation position of the deep trench, and using etching to open the exposed hard mask layer 106 to form an opening pattern, the sidewall of the opening pattern is in an inclined shape, and the cross section is in a trapezoidal shape with the upper part being wide and the lower part being narrow, forming a structure as shown in Figure 2 Due to the adjustment of the focal length of exposure, the opening slope of the hard mask layer 106 after etching is different, which causes the protection of the polymer sidewall to be different during the etching of the bottom of the deep trench, and thus the thickness of the sidewall oxide is different, improving the thickness of the sidewall oxide;

[0038] In some embodiments, the range of the focal length of the adjusted exposure in step two is +0.4-1.4 microns. To obtain a good quality sidewall oxide layer thickness, the focal length should be positive, and the focal length can be fine-tuned according to specific requirements.

[0039] Step three, forming a deep trench by etching, the polysilicon layer 105 is also formed into an inclined shape during the etching process, and the remaining photoresist layer is removed to form a structure as shown in Figure 3 .

[0040] In some embodiments, the deep trench is formed by Bosch etching in step three. This process first uses fluorine-based active groups to etch silicon, and then performs sidewall passivation. The two-step process of etching and protection is alternated. It is achieved by alternating etching gas and passivation gas to achieve etching and sidewall passivation. After a short period of isotropic etching, the just-etched silicon surface is passivated. Due to the physical sputtering bombardment of ions in the depth direction, the passivation film can be retained, so that the next cycle of etching will not occur. Through this periodic "etching-passivation-etching", etching only occurs along the depth direction.

[0041] Step four, forming a thermal oxide layer 107 on the polysilicon layer 105 and the sidewall of the deep trench by a thermal oxidation method, wherein the thermal oxide layer 107 on the sidewall of the polysilicon layer 105 is convex, which has a protective effect on the sidewall of the underlying deep trench, and forms a structure as shown in Figure 4 .

[0042] In some embodiments, step four further includes a step of performing crystal edge etching.

[0043] In some embodiments, the photoresist layer is removed by a gray ash process and a wet cleaning method in step four.

[0044] Step five, etching the thermal oxide layer 107 to retain it on the sidewall of the deep trench, and the convex thermal oxide layer 107 is used to protect the thermal oxide layer 107 on the sidewall of the top of the deep trench, forming a structure as shown in Figure 5 .

[0045] In some embodiments, the etching in step five is dry etching, and the etching gas is C5F8 and O2.

[0046] In some embodiments, the ratio of C5F8 and O2 in step five is 1.2:1 to 1.4:1, for example 1.3:1. The sidewall formed by etching the bottom of the deep trench has more polymer, which is better for sidewall protection; at the same time, the thermal oxide layer 107 at the bottom can be etched through.

[0047] In some embodiments, the etching in step five further includes a carrier gas.

[0048] In some embodiments, the carrier gas in step five is Ar.

[0049] In some embodiments, the chamber pressure in step five is 45 to 55 mtorr, such as 50 mtorr.

[0050] Step six, forming a fill layer to fill the remaining deep trenches using deposition and polishing.

[0051] In some embodiments, the material of the fill layer in step six is polysilicon.

[0052] In some embodiments, the polishing method in step six is chemical mechanical planarization polishing.

[0053] It is to be understood that the figures provided in the present embodiments are merely schematic and that the actual number, shape and size of the components in the figures are not drawn according to the actual implementation, and the actual implementation of each component can be arbitrarily changed, and the component layout pattern can be more complex.

[0054] In summary, the present application can improve the thickness of the oxide layer on the sidewall of the deep trench, and avoid the problem of low breakdown voltage and chip failure caused by thin sidewall oxide layer. Therefore, the present application effectively overcomes the shortcomings of the prior art and has high industrial utilization value.

[0055] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea of the present application should be covered by the claims of the present application.

Claims

1. A method for improving the oxide thickness of deep trench sidewalls, characterized in that, include: Step 1: Provide a substrate, form an epitaxial layer on the substrate, and sequentially form a pad oxide layer, an etch stop layer, a polysilicon layer and a hard mask layer on the epitaxial layer; Step 2: Form a photoresist layer on the hard mask layer, adjust the exposure focal length to open the photoresist layer to define the formation position of the deep trench, and use etching to open the exposed hard mask layer to form an opening pattern. The sidewalls of the opening pattern are inclined and its cross-section is a trapezoidal shape that is wider at the top and narrower at the bottom. Step 3: Use etching to form deep trenches and remove the remaining photoresist layer; Step 4: A thermal oxide layer is formed on the polysilicon layer and the sidewalls of the deep trench using a thermal oxidation method, wherein the thermal oxide layer on the sidewalls of the polysilicon layer has a convex morphology. Step 5: Etch the thermal oxide layer to retain it on the sidewall of the deep trench. The protruding thermal oxide layer is used to protect the thermal oxide layer on the top sidewall of the deep trench. Step 6: Use deposition and grinding methods to form a filling layer that fills the remaining deep trenches.

2. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: The material of the etching stop layer in step one is silicon nitride.

3. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: The material of the hard mask layer in step one is silicon dioxide.

4. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: The range of focal length for adjusting the exposure in step two is +0.4 to 1.4 micrometers.

5. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: In step three, the deep trenches are formed using the Bosch etching method.

6. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: Step four includes a step of edge etching.

7. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: In step four, the photoresist layer is removed using an ashing process and a wet cleaning method.

8. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: The etching in step five is dry etching, and the etching gases are C5F8 and O2.

9. The method for improving the oxide thickness of deep trench sidewalls according to claim 8, characterized in that: The ratio of C5F8 to O2 in step five is 1.2:1 to 1.4:

1.

10. The method for improving the oxide thickness of deep trench sidewalls according to claim 8, characterized in that: The etching in step five also includes a carrier gas.

11. The method for improving the oxide thickness of deep trench sidewalls according to claim 10, characterized in that: The carrier gas mentioned in step five is Ar.

12. The method for improving the oxide thickness of deep trench sidewalls according to claim 8, characterized in that: The chamber pressure in step five is 45 to 55 mtorr.

13. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: The filling layer in step six is ​​made of polycrystalline silicon.

14. The method for improving the oxide thickness of deep trench sidewalls according to claim 1, characterized in that: The grinding method described in step six is ​​chemical mechanical planarization grinding.

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