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

Abstract

The invention provides a method for improving the thickness of an oxide on the side wall of a deep trench, and the method comprises the steps: providing a substrate, forming an epitaxial layer on the substrate, and sequentially forming a pad oxide layer, an etching stop layer, a polycrystalline silicon layer and a hard mask layer on the epitaxial layer; a photoresist layer is formed on the hard mask layer, the exposure focal length is adjusted to open the photoresist layer so as to define the forming position of the deep groove, the exposed hard mask layer is opened through etching to form an opening pattern, the side wall of the opening pattern is in an inclined shape, and the section of the opening pattern is in a trapezoid shape with the wide upper portion and the narrow lower portion; a deep groove is formed through etching, and the remaining photoresist layer is removed; forming a thermal oxide layer on the side walls of the polycrystalline silicon layer and the deep trench by using a thermal oxidation method, wherein the thermal oxide layer at the side wall of the polycrystalline silicon layer is in a convex shape; etching the thermal oxide layer to enable the thermal oxide layer to be reserved on the side wall of the deep groove; and forming a filling layer for filling the residual deep groove by using a deposition and grinding method. The method can improve the thickness of the oxide layer on the side wall of the deep trench.

Description

Technical Field

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

[0002] In the semiconductor field, great emphasis is placed on morphology control in the process. In the BCD deep trench (DTI, deep trench isolation) process, the trench is etched first, then the trench sidewalls are 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 substrate, and at the same time, the top sidewall oxide must have a certain thickness to meet the voltage resistance requirements; but during actual etching, the etching rate of the oxide at the top of the trench is always greater than that at the bottom. When etching through the bottom oxide, the top oxide is often etched very thinly, which ultimately leads to insufficient voltage resistance of the chip and leakage.

[0003] In order to solve the above problems, a new method for improving the oxide thickness of the deep trench sidewalls needs to be proposed. Summary of the invention

[0004] In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a method for improving the thickness of the oxide on the sidewalls of deep trenches, so as to solve the problem in the prior art that the etching rate of the oxide on the top of the trench is always greater than that on the bottom, and when etching through the bottom oxide, the top oxide is often etched very thin, which ultimately leads to insufficient voltage resistance and leakage of the chip.

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

[0006] Step 1: providing a substrate, forming an epitaxial layer on the substrate, and sequentially forming a pad oxide layer, an etch stop layer, a polysilicon layer and a hard mask layer on the epitaxial layer;

[0007] Step 2, forming a photoresist layer on the hard mask layer, adjusting the exposure focus to open the photoresist layer to define the formation position of the deep groove, and using etching to open the exposed hard mask layer to form an opening pattern, wherein the side wall of the opening pattern is an inclined morphology, and its cross-section is a trapezoidal shape that is wide at the top and narrow at the bottom;

[0008] Step 3: forming deep grooves by etching to remove the remaining photoresist layer;

[0009] Step 4: forming a thermal oxide layer on the polysilicon layer and the sidewalls of the deep trench by a thermal oxidation method, wherein the thermal oxide layer at the sidewalls of the polysilicon layer has a convex morphology;

[0010] Step 5, etching the thermal oxide layer so that it remains on the sidewall of the deep trench, and 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 remaining deep trenches by deposition and grinding methods.

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

[0013] Preferably, the material of the hard mask layer in step 1 is silicon dioxide.

[0014] Preferably, the range of the focal length of adjusting the exposure in step 2 is +0.4 to 1.4 microns.

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

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

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

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

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

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

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

[0022] Preferably, the chamber pressure in step five is 45 to 55 mtorr.

[0023] Preferably, the material of the filling layer in step six is ​​polycrystalline silicon.

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

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

[0026] The present invention can improve the thickness of the oxide layer on the side wall of the deep trench, thereby avoiding the problem of low breakdown voltage and easy chip failure caused by the thin side wall oxide layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Shown is a schematic diagram of the process flow of the present invention;

[0028] Figure 2 Shown is a schematic diagram of opening the hard mask layer of the present invention;

[0029] Figure 3 It is a schematic diagram of forming a deep trench according to the present invention;

[0030] Figure 4 Shown is a schematic diagram of forming a thermal oxide layer according to the present invention;

[0031] Figure 5 It is a schematic diagram of etching a thermal oxide layer according to the present invention. DETAILED DESCRIPTION

[0032] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0033] See also Figure 1 The present invention provides a method for improving the thickness of the oxide on the sidewall of a deep trench, comprising:

[0034] Step 1: providing a substrate 101, forming an epitaxial layer 102 on the substrate 101, and sequentially forming a pad oxide layer 103, an etch 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 etch stop layer 104 in step 1 is silicon nitride.

[0036] In some embodiments, the material of the hard mask layer 106 in step 1 is silicon dioxide.

[0037] Step 2: Form a photoresist layer (not shown) on the hard mask layer 106, adjust the exposure focus to open the photoresist layer to define the formation position of the deep trench, and use etching to open the exposed hard mask layer 106 to form an opening pattern. The sidewall of the opening pattern is inclined, and its cross-section is a trapezoidal shape that is wide at the top and narrow at the bottom, forming a Figure 2 The structure shown; due to the adjustment of the exposure focus, the opening slope of the hard mask layer 106 after etching will be different, and the polymer sidewall protection will be different when the bottom of the deep trench is etched later, which will make the sidewall oxide thickness different, thereby improving the sidewall oxide thickness;

[0038] In some embodiments, the range of the focal length of adjusting the exposure in step 2 is +0.4 to 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 3: Use etching to form deep trenches. During the etching process, the sidewalls of the polysilicon layer 105 will also be formed into an inclined morphology. Remove the remaining photoresist layer to form a Figure 3 The structure shown;

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

[0041] Step 4: Form a thermal oxide layer 107 on the polysilicon layer 105 and the sidewalls of the deep trench by thermal oxidation, wherein the thermal oxide layer 107 on the sidewalls of the polysilicon layer 105 is a protruding morphology, which has a blocking and protective effect on the sidewalls of the deep trench below, forming a Figure 4 The structure shown;

[0042] In some embodiments, the step of performing crystal edge etching is further included before step four.

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

[0044] Step 5: Etch the thermal oxide layer 107 so that it remains on the sidewall of the deep trench. The protruding thermal oxide layer 107 is used to protect the thermal oxide layer 107 on the top sidewall of the deep trench, forming a Figure 5 The structure shown;

[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 to O2 in step five is 1.2:1 to 1.4:1, for example 1.3:1. When etching the bottom of the deep trench, more polymers are formed on the sidewalls, which provides better protection for the sidewalls. 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 6: Form a filling layer to fill the remaining deep trenches by deposition and grinding.

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

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

[0053] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

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

[0055] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for improving the thickness of oxide on the sidewall of a deep trench, characterized in that: include: Step 1: providing a substrate, forming an epitaxial layer on the substrate, and sequentially forming a pad oxide layer, an etch stop layer, a polysilicon layer and a hard mask layer on the epitaxial layer; Step 2, forming a photoresist layer on the hard mask layer, adjusting the exposure focus to open the photoresist layer to define the formation position of the deep groove, and using etching to open the exposed hard mask layer to form an opening pattern, wherein the side wall of the opening pattern is an inclined morphology, and its cross-section is a trapezoidal shape that is wide at the top and narrow at the bottom; Step 3: forming deep grooves by etching to remove the remaining photoresist layer; Step 4: forming a thermal oxide layer on the polysilicon layer and the sidewalls of the deep trench by a thermal oxidation method, wherein the thermal oxide layer at the sidewalls of the polysilicon layer has a convex morphology; Step 5, etching the thermal oxide layer so that it remains on the sidewall of the deep trench, and the protruding thermal oxide layer is used to protect the thermal oxide layer on the top sidewall of the deep trench; Step six: forming a filling layer to fill the remaining deep trenches by deposition and grinding methods.

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

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

4. The method for improving the oxide thickness of the deep trench sidewall according to claim 1, characterized in that: The range of the focal length for adjusting the exposure in step 2 is +0.4 to 1.4 microns.

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

6. The method for improving the oxide thickness of the deep trench sidewall according to claim 1, characterized in that: Before step 4, a step of performing crystal edge etching is also included.

7. The method for improving the oxide thickness of the deep trench sidewall according to claim 1, characterized in that: In step 4, the photoresist layer is removed by using an ashing process and a wet cleaning method.

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

12. The method for improving the oxide thickness of the deep trench sidewall 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 the deep trench sidewall according to claim 1, characterized in that: The material of the filling layer in step six is ​​polysilicon.

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

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