A polysilicon stripping method without damaging the gate oxide

Abstract

A polysilicon stripping method without damaging the gate oxide. It relates to the field of semiconductor manufacturing technology, and particularly to a polysilicon stripping method without damaging the gate oxide. In the present invention, 29% ammonia water is used to remove Poly (polysilicon), replacing the original silicon etching solution (HNO3 + HF + HAc + H2O) for removing the Poly layer. While removing the Poly layer with ammonia water, SiO2 is not corroded, and the rework risk is extremely low. It has a good effect of removing the Poly layer and retaining SiO2. The present invention has the characteristics of not corroding SiO2, reducing the rework risk, and improving the quality of polysilicon layer removal, etc.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, and particularly to a method for stripping polysilicon without damaging the gate oxide. Background Art

[0002] During the manufacturing process of trench Schottky products (generally including the following steps: a. growing an oxide layer on the epitaxial layer; b. trench lithography and etching; c. growing a gate oxide layer in the trench; d. filling the trench with polysilicon; e. performing polysilicon back-etching, etc.), the gate oxide deposition (step c) and Poly (polysilicon) deposition (step d) are time-consuming and important processes. When the processing program is interrupted due to other abnormal reasons during the manufacturing process (the polysilicon surface is contaminated when the machine program is interrupted, so the corresponding layer needs to be removed), currently, a silicon etching solution (HNO3 + HF + HAc + H2O) is used to remove Poly (polysilicon), and the reaction equation is:

[0003] 1. 3Si + 18HF + 4HNO3 = 3H2SiF6 + 4NO↑ + 8H2O

[0004] 2. SiO2 + 6HF = H2SiF6 + 2H2O

[0005] HF in the silicon etching solution corrodes SiO2. The higher the HF concentration, the faster the SiO2 corrosion rate. The SiO2 under the gate oxide is thinner, and the corrosion uniformity of Poly by the silicon etching solution is poor. The SiO2 is easily corroded clean, and then it will continue to corrode the silicon substrate, damaging the device and resulting in product scrapping. Summary of the Invention

[0006] In view of the above problems, the present invention provides a method for stripping polysilicon without damaging the gate oxide, which does not corrode SiO2, reduces the risk of rework, and improves the quality of polysilicon layer removal.

[0007] The technical solution of the present invention is: a method for stripping polysilicon without damaging the gate oxide, comprising the following steps:

[0008] S1. Measuring the thickness of the polysilicon layer of the device to be reworked, and the measured thickness value is T1;

[0009] S2. Calculating the corrosion time of the polysilicon layer according to the polysilicon corrosion rate, and the corrosion time t1 of the polysilicon layer = T1 * 1.3 / polysilicon corrosion rate;

[0010] S3. Corroding the polysilicon layer

[0011] Putting the device with the polysilicon layer thickness measured in step S1 into a container tank filled with 29% ammonia water, taking it out after reacting for t1 time, and cleaning the residual acid solution on the device surface;

[0012] S4. Measure the thickness of the gate oxide layer, and the measured thickness is T2;

[0013] S5. Calculate the gate oxide layer etching time, where the gate oxide layer etching time t2 = T2 / SiO2 etching rate;

[0014] S6. Place the device in a 20:1 BOE etching solution for an etching time of t2 to remove the remaining gate oxide layer.

[0015] The measurement of the polysilicon etching rate in step S2 includes the following steps:

[0016] S2.1. Select a polysilicon monitoring wafer;

[0017] S2.2. Use a film thickness gauge to measure the actual thickness value of the polysilicon monitoring wafer in step S2.1 as A;

[0018] S2.3. Place the measured polysilicon monitoring wafer in a 29% ammonia water container for etching for 1 minute;

[0019] S2.4. Rinse with water and spin dry, and use a film thickness gauge to measure its thickness value as B;

[0020] S2.5. Calculate the etching rate through the formula E / R = (A - B) / 1 minute.

[0021] The calculation method of the SiO2 etching rate in step S5 is as follows:

[0022] S5.1. Take a SiO2 monitoring wafer and measure its thickness value as A1 with a film thickness tester;

[0023] S5.2. Place it in a 20:1 BOE etching solution for etching for 3 minutes, rinse with water and spin dry, and use a film thickness tester to measure its thickness value as B1;

[0024] S5.3. Through calculation, the SiO2 etching rate = (A1 - B1) / 3 minutes to obtain the SiO2 etching rate value.

[0025] The present invention uses 29% ammonia water to remove Poly (polysilicon), replacing the original silicon etching solution (HNO3 + HF + HAc + H2O) to remove the Poly layer. The ammonia water does not corrode SiO2 while removing the Poly layer, and the rework risk is extremely low. It has a good effect of removing the Poly layer and retaining SiO2. The present invention has the characteristics of not corroding SiO2, reducing the rework risk, and improving the quality of removing the polysilicon layer. Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of the trench Schottky product in the background art growing a gate oxide layer in the trench,

[0027] Figure 2 It is a schematic structural diagram of the polysilicon filling in the trench of the trench Schottky product in the background technology;

[0028] In the figure, 1 is the substrate layer, 2 is the epitaxial layer, 3 is the gate oxide layer, and 4 is the polysilicon layer. Detailed implementation manners

[0029] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation to the present invention.

[0030] As shown in the present invention Figure 1-2 A polysilicon stripping method without damaging the gate oxide includes the following steps:

[0031] S1. Measure the thickness of the polysilicon layer of the device to be reworked, and the measured thickness value is T1 (unit: Å);

[0032] S2. Calculate the etching time of the polysilicon layer according to the polysilicon etching rate. The etching time t1 of the polysilicon layer = T1 * 1.3 (over-etching amount) / polysilicon etching rate (unit: min);

[0033] There is a certain fluctuation in the etching rate. After calculating the etching time, an additional 30% etching is added to ensure that all unetched areas are etched clean. Therefore, the over-etching amount is taken as 1.3 in this case.

[0034] In the formula, the calculation method of the polysilicon etching rate uses a 10000 Å polysilicon monitoring wafer. Measure the previous value A with a film thickness meter, place the wafer in a 29% ammonia water container for etching for 1 min, rinse with water and spin dry, and measure the subsequent value B with a film thickness meter. The etching rate calculation is E / R = (A - B) / 1 min;

[0035] S3. Etch the polysilicon layer

[0036] Put the device with the polysilicon layer thickness measured in step S1 into a container filled with 29% ammonia water. After reacting for t1 time (the surface polysilicon is etched clean, and the color of the polysilicon changes from bright to dark of silicon dioxide, and the color change can be clearly seen), take it out and use pure water to clean the residual acid solution on the device surface;

[0037] Si + 4NH4OH = (NH4)4SiO4 + 2H2

[0038] S4. Measure the thickness of the gate oxide layer with a film thickness measuring instrument, and the measured thickness is T2 (unit: Å);

[0039] S5. Calculate the corrosion time of the gate oxide layer. The corrosion time t2 of the gate oxide layer = T2 / SiO2 corrosion rate (unit: min);

[0040] S6. Place the device into the BOE etching solution with a ratio of 20:1 for etching for a time of t2 to remove the remaining gate oxide layer.

[0041] The measurement of the polysilicon etching rate in step S2 includes the following steps:

[0042] S2.1. Select a polysilicon monitoring wafer with a thickness of 10000 Å;

[0043] S2.2. Use a film thickness meter to measure the actual thickness value of the polysilicon monitoring wafer in step S2.1 as A;

[0044] S2.3. Place the measured polysilicon monitoring wafer into a 29% ammonia water container for etching for 1 min;

[0045] S2.4. Rinse with water and spin dry, and use a film thickness meter to measure its thickness value as B;

[0046] S2.5. Calculate the etching rate through the formula E / R = (A - B) / 1 min. E / R represents the etching rate.

[0047] The calculation method of the SiO2 etching rate in step S5 is as follows:

[0048] S5.1. Take a SiO2 monitoring wafer and measure its thickness value as A1 with a film thickness tester;

[0049] S5.2. Place it into the BOE etching solution with a ratio of 20:1 for etching for 3 min, rinse with water and spin dry, and measure its thickness value as B1 with a film thickness tester;

[0050] S5.3. Through calculation, the SiO2 etching rate = (A1 - B1) / 3 min to obtain the SiO2 etching rate value.

[0051] The silicon etching solution will continue to etch the gate oxide after etching the polysilicon, and the gate oxide will become less and less. If the etching time is too long, the gate oxide will be etched clean, and the etching solution will continue to etch the silicon substrate, affecting the trench depth and morphology. If the etching time is too short, the polysilicon will not be etched clean. The ammonia water etching solution does not etch the gate oxide, which can ensure that after the polysilicon is etched clean, it will not continue to etch the silicon dioxide, and there is no over-etching situation. When using ammonia water to remove Poly (polysilicon), even if the etching time is long, it does not affect SiO2, ensuring sufficient etching time for Poly (polysilicon).

[0052] Regarding the content disclosed in this case, the following points need to be further explained:

[0053] (1). The accompanying drawings of the embodiments disclosed in this case only relate to the structures involved in the embodiments disclosed in this case, and other structures can refer to the general design;

[0054] (2). Without conflict, the embodiments disclosed in this case and the features in the embodiments can be combined with each other to obtain new embodiments;

[0055] The above is only the specific implementation manners disclosed in this case, but the protection scope of this disclosure is not limited thereto. The protection scope disclosed in this case shall be subject to the protection scope of the claims.

Claims

1. A polysilicon stripping method without damaging the gate oxide, characterized in that, It includes the following steps: S1. Measure the thickness of the polysilicon layer of the device to be reworked, and the measured thickness value is T1; S2. Calculate the corrosion time of the polysilicon layer according to the polysilicon corrosion rate. The polysilicon layer corrosion time t1 = T1 * 1.3 / polysilicon corrosion rate; There is a certain fluctuation in the corrosion rate. After calculating the corrosion time, add an additional 30% corrosion to ensure that all uncorroded areas are completely corroded. Therefore, the over-corrosion amount in this case is taken as 1.3; The polysilicon corrosion rate measurement in step S2 includes the following steps: S2.

1. Select a polysilicon monitoring wafer; S2.

2. Use a film thickness gauge to measure the actual thickness value of the polysilicon monitoring wafer in step S2.1 as A; S2.

3. Place the measured polysilicon monitoring wafer into a 29% ammonia water container tank and corrode it for 1 minute; S2.

4. Rinse with water and spin dry, and use a film thickness gauge to measure its thickness value as B; S2.

5. Calculate the corrosion rate through the formula E / R = (A - B) / 1min; S3. Corrode the polysilicon layer Place the device with the polysilicon layer thickness measured in step S1 into a container tank filled with 29% ammonia water. After reacting for t1 time, take it out and clean the residual acid solution on the device surface; S4. Measure the thickness of the gate oxide layer, and the measured thickness is T2; S5. Calculate the gate oxide layer corrosion time; the gate oxide layer corrosion time t2 = T2 / SiO2 corrosion rate; The SiO2 corrosion rate calculation method in step S5 is as follows: S5.

1. Take a SiO2 monitoring wafer and measure its thickness value as A1 with a film thickness tester; S5.

2. Place it into a 20:1 BOE etching solution and corrode it for 3 minutes. Rinse with water and spin dry, and measure its thickness value as B1 with a film thickness tester; S5.

3. Through calculation, the SiO2 corrosion rate = (A1 - B1) / 3min to obtain the SiO2 corrosion rate value; S6. Place the device into a 20:1 BOE etching solution, and the corrosion time is t2 to remove the remaining gate oxide layer.

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