KR20010092868A - The method of wet etching an silicon nitride layer in semiconductor devices - Google Patents

Abstract

PURPOSE: A wet etching method of a silicon nitride layer is provided to prevent a dent phenomenon of a silicon liner and to improve an etch processing margin of the silicon nitride by constantly controlling a wet etching rate of the nitride liner and a pad nitride layer. CONSTITUTION: A variation of an etch quantity of a silicon nitride layer according to the number of times of wet etching processes carried out a batch unit is firstly calculated(11). Then, a standard batch and a standard etching time are determined(13). A constant time which can be addition and subtraction accumulated from the standard etching time of the standard batch is then determined(15). Finally, the wet etching of the silicon nitride layer is performed by application the constant time(17).

Description

Silicon nitride film wet etching method of semiconductor device {THE METHOD OF WET ETCHING AN SILICON NITRIDE LAYER IN SEMICONDUCTOR DEVICES}

The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a silicon nitride film wet etching method for a semiconductor device.

In general, a manufacturing process of a semiconductor device includes each unit process that is organically connected, and each unit process is performed continuously and repeatedly.

In particular, in the manufacture of semiconductor devices, the process of forming the device isolation film on the semiconductor substrate is an important process that determines the performance of the semiconductor device, and therefore, strict and precise process control is required. Conventionally, a LOCOS (LOCal Oxidation of Silicon) method for growing an insulating film by selectively thermally oxidizing a semiconductor substrate of an isolation pattern formed of a nitride film has been widely used. However, the bird's beak phenomenon generated in the above-described LOCOS method increases the width of the device isolation layer, thereby limiting the high integration of the semiconductor device. Various improvement methods have been proposed as a method of forming a device isolation film to solve the problem of the LOCOS method. Recently, shallow trench isolation is formed to form a trench in a semiconductor substrate and fill the trench with an insulating layer to isolate the semiconductor devices. Isolation (STI) method is widely used.

The shallow trench isolation method is briefly described as follows.

1 is a cross-sectional view illustrating a problem in a shallow trench isolation process of a semiconductor device according to a conventional method.

First, a pad oxide film (not shown) and a pad nitride film (not shown) are sequentially formed on the semiconductor substrate 100. The pad oxide film is formed using a thermal oxidation method, and has a thin thickness of 200 kPa to 500 kPa. The pad nitride layer is formed of a silicon nitride layer (Si ₃ N ₄ ), and is formed to a thickness of 1000 GPa to 2000 GPa using a Low Pressure Chemical Vapor Deposition (LPCVD) method.

Next, the pad nitride layer and the pad oxide layer are successively patterned to expose the device isolation layer forming region on the semiconductor substrate 100 to form an isolation pattern (not illustrated). Next, the trench 102 is formed by etching the semiconductor substrate 100 using the isolation pattern as an etch mask.

Next, a thin liner 104 is formed on the entire surface of the semiconductor substrate 100 including the trench 102. The liner 104 is formed of a silicon nitride film (Si ₃ N ₄ ), and has a thin thickness of about 50 kPa. In this case, sidewall oxide may be grown on the sidewall of the trench 102 by using a thermal oxidation method before forming the liner 104.

Next, an isolation layer 106 is formed on the semiconductor substrate 100 to fill the trench 102 including the liner 104. The device isolation layer 106 may be formed of an insulating material, and may be formed of an oxide film such as high temperature oxide (HTO), BoroPhosphor Silicate Glass (BPSG), or Undoped Silicate Glass (USG).

Next, the device isolation layer 106 exposed on the isolation pattern is removed and planarized using a chemical mechanical polishing (CMP) method.

Thereafter, the liner 104 and the pad nitride layer exposed on the semiconductor substrate 100 are wet etched using a strip process. The etching solution for wet etching uses a solution of phosphoric acid (H ₃ PO ₄ ) having a concentration of 85. The phosphoric acid solution concentration of 85 is known to exhibit the best etching rate under the same conditions. It is preferable that the temperature of the said phosphoric acid solution generally has a temperature of 160 to 170 degreeC.

In the above-described shallow trench isolation method of the semiconductor device, when the wet etching process is performed to continuously remove the liner and pad nitride film exposed on the semiconductor substrate, the silicon nitride film forming the liner and pad nitride film is a wet etching solution. Phosphoric acid (H ₃ PO ₄ ) solution is used. The etching rate of the phosphate solution decreases as the wet etching process is repeated and the wet etching throughput increases, that is, as the number of batches subjected to wet etching increases. In this case, one batch includes 50 wafers. In order to increase production in a semiconductor manufacturing process, a batch process is usually performed in a wet etching or chemical vapor deposition process.

As such, when the etching rate of the phosphate solution with respect to the silicon nitride film decreases as the number of wet etching batches increases, the etching amount is controlled when the wet etching process is performed to remove the silicon nitride film forming the liner and pad nitride film on the semiconductor substrate. Becomes difficult. For example, in the case where the entire wet etching process consists of 10 batches, if the process is performed based on the etch rate at the time of one batch, the etching batches after the predetermined number of batches may obtain an amount of etching below the target etching amount. When the process is performed based on the etching rate when the 10 batches are performed, the amount of etching below the target etching amount is obtained in the etching batches before the predetermined number of batches. As a result, overetching of the silicon nitride film is inevitable in order to obtain a target etching amount over the entire process batch, and in this case, as shown in part A of FIG. 1, the liners on both sides of the device isolation layer are overetched to dent. Silicon nitride film over-etching such as development or dipping occurs. In the process of removing the silicon nitride film exposed on the semiconductor substrate to complete the device isolation layer, as shown in part A of FIG. 1, when the dent or dipping of the liner occurs by silicon nitride film overetching, the threshold voltage of the semiconductor device ( Problems such as lowering of the threshold voltage, lowering the breakdown voltage of the subsequent gate oxide film, and the occurrence of the leakage current occur.

The present invention can maintain a constant etching rate and etching amount of the silicon nitride film exposed on the semiconductor substrate in the device isolation film forming process using the shallow trench isolation method in order to solve the problems caused by the conventional shallow trench isolation method described above. It is an object of the present invention to provide a shallow trench isolation method of a semiconductor device.

1 is a cross-sectional view illustrating a problem in a shallow trench isolation process of a semiconductor device according to a conventional method;

FIG. 2 is a graph showing a change in the etching amount of a silicon nitride film according to the number of processing batches in the silicon nitride film wet etching method according to the conventional method. A graph representing;

3 is a graph showing the silicon content in the phosphoric acid solution according to the number of treatment batches in the silicon nitride film wet etching process;

4 is a graph showing a change in the etching amount of the silicon nitride film according to the number of processing batches in the silicon nitride film wet etching method according to the present invention. Graph showing amount change;

5A-5G are cross-sectional views sequentially illustrating a shallow trench isolation process of a semiconductor device in accordance with the present invention;

6 is a flowchart sequentially illustrating a silicon nitride film wet etching method of a semiconductor device according to the present invention; And

7 is a graph showing the etching amount of the silicon nitride film in the case where the same etching time is applied for each number of treatment batches according to the conventional method and in the case of applying the etching process time addition / decrease method according to the present invention.

* Brief description of the main parts of the drawing

100, 300: semiconductor substrate 302: pad oxide film

304: pad nitride film 306: isolation pattern

102, 308: trench 310: sidewall oxide film

104, 312: nitride film liner 106, 314: device isolation film

According to an aspect of the present invention, there is provided a method of wet etching a silicon nitride film of a semiconductor device, the method comprising: measuring a change in etching amount of a film quality to be etched according to the number of times of a wet etching process performed in a batch unit; The first batch showing the etching amount closest to the target etching amount corresponding to the thickness of the film to be etched is determined as the reference batch, and the etching time of the reference batch is referred to as the reference etching time. Determining; For batches that undergo an etching process prior to the reference batch, a wet etching process is performed for a time that is cumulatively accumulated (or cumulatively added) for a predetermined time at the reference etching time, and the reference batch For the batches to be subjected to the etching process later than the step, the wet etching process may be performed during the cumulative addition (or cumulative difference) of the predetermined time period to the reference etching time.

The predetermined time is obtained by dividing the average etching change amount per batch by the etching rate of the reference batch, which increases or decreases every time the number of the wet etching processes increases by "1".

In a preferred embodiment of the present invention, the etching target film is a silicon nitride film (Si ₃ N ₄ ), the etching solution for the etching target film is a phosphoric acid (H ₃ PO ₄ ) solution.

Prior to the disclosure of the silicon nitride film wet etching method according to the present invention, the etching rate and the etching amount reduction of the silicon nitride film according to the increase in the wet etching throughput will be described in detail with reference to the experimental data.

FIG. 2 is a graph showing a change in etching amount of a silicon nitride film according to the number of etching treatment batches in the silicon nitride film wet etching method, and a graph showing an etching amount change when an etching process time of 10 minutes is applied to each etching treatment batch in the same manner. to be. The data shown in FIG. 2 are experimental values obtained by finishing the etching process under the same conditions as the actual process conditions and further performing the etching process for 10 minutes. In this case, the etching time of each batch is the same as 10 minutes, and as an etching solution, a phosphoric acid solution of 160 ° C. to 170 ° C. is used, and the phosphoric acid solution maintains a constant concentration of 85 in the process.

According to FIG. 2, the etching amount of the silicon nitride film tends to decrease as the number of processing batches increases. In more detail, when one batch is etched for 10 minutes, the etching amount of the silicon nitride film etched by the phosphate solution is about 595 kV, and when the 10 batches are etched for 10 minutes, the etching amount of about 565 kPa is applied to the phosphoric acid solution. Have Therefore, when each batch is etched for 10 minutes, it can be seen that the average etching amount of 2.9 kPa per batch is reduced.

The following table shows data indicating the etch rate of the oxide film and the silicon nitride film according to the increase in the number of etching treatment batches measured in the above process conditions, in units of μm / min.

TABLE 1

Comparison of Etch Rate of Oxide and Silicon Nitride According to Etching Amount

Membrane and etching process amount Immediately after wet etchant exchange After 5 batch etching treatment 10 batch after etching treatment Oxide film 2.0 dl / min. 1.2 Å / min. 0.8 dl / min. Silicon nitride film 60 Å / min. 58 dl / min. 56 dl / min.

As shown in Table 1, it can be seen that the oxide film has an etching rate of 2.0 kV / min. And the silicon nitride film has a etching rate of 60 kV / min. Immediately after the wet etching solution is replaced. However, as the number of etched batches increased, the etch rate of the wet etching solution for the oxide and silicon nitride film gradually decreased, and after the 10 batch etching process, the oxide film was 0.8 Å / min. And the silicon nitride film was 56 Å / min. Etch rate can be known.

The etching rate drop phenomenon of the phosphoric acid solution according to the increase in the number of treatment batches can be described as follows with reference to FIG. 3 and Scheme 1 below.

3 is a graph showing the silicon content in the phosphoric acid solution according to the number of treatment batches.

According to FIG. 3, the silicon content in the phosphoric acid solution gradually increases as the number of treatment batches increases. This increase in silicon content can be understood by the following reaction formula for the silicon nitride film and the silicon oxide film in the phosphoric acid solution.

Scheme 1

_{Si 3 N 4 + 4H 3 PO} 4 + 12H 2 O ↔3Si (OH) 4 + 4NH 4 · H 2 PO 4

SiO ₂ + 2H ₂ O ↔Si (OH) ₄

As can be seen in Scheme 1, a silicate (silicate, Si (OH) ₄ ) is formed as a reaction product of an etching reaction of a silicon nitride film and a silicon oxide film with respect to a phosphoric acid solution. As a result, the silicon content of the reaction product in the phosphoric acid solution is gradually increased, and as a result, the reaction rate and the reaction rate are gradually slowed, thereby reducing the etching rate of the phosphoric acid solution shown in FIG. 3.

Therefore, in order to compensate for the decrease in the silicon nitride film wet etch rate of the semiconductor device as described above, the etching process time per etching treatment batch is accumulated and increased by a predetermined time.

FIG. 4 is a graph showing an etching amount of a silicon nitride film when a process time of three seconds is accumulated and increased according to an increase in the number of etching process batches to correspond to the graph of FIG. 3. In this case, the data shown in FIG. 4 are experimental values obtained by performing an etching process after finishing the etching process under the same conditions as the actual process conditions, and the experimental conditions are the same as the experimental conditions for obtaining the data shown in FIG. 3.

According to FIG. 4, the etching amount of the silicon nitride film tends to remain constant or slightly increases as the number of processing batches increases. In more detail, the dispersion of the etching rate is about 13 μs between one batch for etching the silicon nitride film for 10 minutes and 10 batches for etching the silicon nitride film for 10 minutes and 30 seconds by accumulating the process time by 3 seconds depending on the number of processing batches. It shows a difference, and as the number of batches increases, there is a constant etching amount. From these results, even in a shallow trench isolation method of an actual semiconductor device, the etching rate and the etching amount of the etching solution with respect to the silicon nitride film can be kept constant by adding or subtracting a predetermined time for each etching treatment batch.

(Example)

Hereinafter, the silicon nitride film wet etching method of the semiconductor device according to the present invention will be described in detail with reference to the accompanying drawings.

5A through 5G are cross-sectional views sequentially illustrating a shallow trench isolation (STI) process of a semiconductor device according to the present invention.

Referring to FIG. 5A, a pad oxide film 302 and a pad nitride film 304 are sequentially formed on the semiconductor substrate 300. The pad oxide film 302 is formed using a thermal oxidation method, and is formed to a thin thickness of 200 kPa to 500 kPa. The pad nitride film 304 is formed of a silicon nitride film (Si ₃ N ₄ ), and has a low pressure. It is formed to a thickness of 1000 kPa to 2000 kPa using a Low Pressure Chemical Vapor Deposition (LPCVD) method.

Referring to FIG. 5B, the pad nitride layer 304 and the pad oxide layer 302 are successively patterned to expose the device isolation layer forming region on the semiconductor substrate 300 to form an isolation pattern 306.

Referring to FIG. 5C, the trench 308 is formed by etching the semiconductor substrate 300 using the isolation pattern 306 as an etch mask. In this case, the etching of the semiconductor substrate 300 is performed by anisotropic dry etching.

Referring to FIG. 5D, a thin side-wall oxide layer 310 is grown on an inner wall of the trench by using a thermal oxidation method, and then the semiconductor substrate 300 including the trench 308. ) And form a nitride liner 312 conformally. The nitride film liner 312 is formed of a silicon nitride film (Si ₃ N ₄ ), it is formed having a thin thickness of about 50Å.

Referring to FIG. 5E, an isolation layer 314 is formed on the semiconductor substrate 300 including the nitride film liner 312 to fill the trench 308. The device isolation layer 314 is formed of an oxide film such as high temperature oxide (HTO), BoroPhosphor Silicate Glass (BPSG), or Undoped Silicate Glass (USG). In this embodiment, a USG (Undoped Silicate Glass) oxide film is used as the device isolation film 314.

5F and 5G, the device isolation layer 314 exposed on the semiconductor substrate 300 is removed and planarized using a chemical mechanical polishing (CMP) method. Thereafter, the liner 312 and the pad nitride layer 304 exposed on the semiconductor substrate 300 are wet etched using a strip process. In this embodiment, the target etch amount of the liner to be etched is about 1440 kW, with a process tolerance of 1440 kW ± 80 kW. In the etching solution for wet etching, a phosphoric acid (H ₃ PO ₄ ) solution having a concentration of 85 is used in consideration of an optimal etching rate, and the temperature of the phosphoric acid solution generally has a temperature of 160 ° C to 170 ° C. Do.

In the silicon nitride film wet etching step of the method of shallow trench isolation of the semiconductor device as described above, maintaining the etching rate of the etching solution and the etching amount of the silicon nitride film with respect to the silicon nitride film is prevented from deteriorating the electrical characteristics of the semiconductor device. It is very important in that. Therefore, the silicon nitride film wet etching method of the semiconductor device according to the present invention maintains the etching rate of the etching solution and the etching amount of the silicon nitride film by accumulating or decreasing the etching process time per etching treatment batch by wet etching the silicon nitride film. do.

The wet etching method of the silicon nitride film forming the liner and pad nitride film exposed on the semiconductor substrate will be described in more detail as follows.

6 is a flowchart sequentially illustrating a silicon nitride film wet etching method of a semiconductor device according to the present invention.

In step 11, the change in the etching amount of the film to be etched according to the number of times of the wet etching process performed in batch units is measured. At this time, the etching time per each etching treatment batch of the wet etching process is kept constant. Accordingly, the etching amount change data according to the number of etching process batches can be obtained. In this embodiment, the etching amount according to the number of etching process batches gradually decreases.

In step 13, a reference batch and a reference etching time for determining whether to add or accumulate the etching time per each batch of processing of the film to be etched are determined. The reference batch may be obtained from the data obtained from the step 11, and is determined as the order in which the etching amount is closest to the target etching amount corresponding to the thickness of the film to be etched. Meanwhile, the reference etching time is determined by the etching time of the reference batch.

In step 15, a predetermined time to be cumulatively added or subtracted with respect to the etching time of each etching process batch is determined before and after the reference batch. The predetermined time may be obtained by dividing the average etching change amount per batch by the etching rate of the reference batch, which increases or decreases every time the number of the wet etching processes increases by "1".

In step 17, the predetermined time is added or subtracted to the etching time of each etching process batch to perform wet etching of the etch target membrane. For batches that undergo an etching process prior to the reference batch, a wet etching process is performed for a time that is cumulatively accumulated (or cumulatively added) for a predetermined time at the reference etching time, and the reference batch Batches that perform the etching process later than the wet etching process may be performed during a cumulative addition (or cumulative difference) for each predetermined time to the reference etching time.

7 is a silicon nitride film according to Process Condition 2, Process Condition 3, and Process Condition 4 when the same etching time is applied to each number of treatment batches according to the conventional method, and when the etching treatment time decrement method is applied according to the present invention. It is a graph which compares the etching amount of and shows. In this case, the process condition 1 is a graph showing the change in etching amount according to the number of etching treatment batches in the case of etching the target etching amount of 1440 Å in this embodiment by advancing the etching time of each batch in 35 minutes according to the conventional method. , Process Condition 2, Process Condition 3, and Process Condition 4 are graphs showing changes in etching amount according to the number of etching treatment batches when the etching time deceleration method is applied according to the present invention.

Referring to FIG. 7, a reference batch and a reference etching time are determined from the graph of process condition 1. In this embodiment, the etch amount target is 1440 kPa, and the batch showing the etch amount closest to the target etch amount is 7 batches. Therefore, in this embodiment, 7 batches are determined as the reference batch, and 35 minutes, which is the etching time of the 7 batches, is determined as the reference etching time. Next, a predetermined time to be cumulatively added or cumulatively added to the etching time of each etching processing batch is determined before and after the reference batch. The predetermined time is determined by dividing the average amount of etching change per batch by the etching rate of the reference batch from the graph of etching amount change of the process condition 1, which decreases each time the etching process batch is increased. It can be seen from this embodiment that the average etch change amount is obtained by obtaining an average slope of the process condition 1 graph, and has an average etch change amount of about 12 μs / batch. In addition, the etch rate of the reference batch can be determined as 1440 Å / 35 min. From the process condition 1 graph. Accordingly, when the average etch change is divided by the etch rate of the reference batch, the predetermined time to be accumulated or accumulated difference per batch is calculated on average. According to this calculation in this embodiment, (12 ms / batch) ÷ (1440 ms / 35 min.) = 0.29 min./batch, that is, a fixed time of 17.4 seconds per batch can be obtained. At this time, the predetermined time is determined to 20 seconds to secure the margin of the etching process. Thereafter, the wet etching process is performed for the batches 1 to 6 that perform the etching process prior to the reference batch, during the time of cumulatively subtracting the predetermined time 20 seconds at 35 minutes, which is the reference etching time, and the reference batch. Further, the wet etching process is performed for 7 to 10 batches which are subsequently subjected to the etching process for a period of cumulatively adding 20 seconds to 35 minutes, which is the reference etching time.

According to this, in the graph of process condition 1 of FIG. 7, the etching time per each etching batch is fixed at 35 minutes, and has an etching range of 1400 kPa to 1505 kPa, whereas in the graph of process condition 2, the difference per etching process batch or By applying a predetermined time of 20 seconds, one batch is etched for an etching time of 33 minutes and 10 batches are etched for an etching time of 36 minutes to have an etching amount range of 1419Å to 1440Å. From these results, it can be seen that more uniform etching amount and etching rate can be obtained in the case of the process condition 2 than in the case of the process condition 1.

Meanwhile, looking at the graphs of Process Condition 3 and Process Condition 4 obtained by proceeding at an etching process facility different from Process Condition 1 and Process Condition 2, first, in the graph of Process Condition 3, a predetermined time that is calculated or added per etching treatment batch is 10. If the etching process proceeds for 32 to 33.5 minutes with seconds, the etching amount ranges from 1440 Pa to 1471 Pa. In addition, in the graph of process condition 4, the etching process may be performed for 33 minutes to 36 minutes by setting a predetermined time to be added or added per etching treatment batch as 20 seconds, which is the same as process condition 2, thereby obtaining an etching amount range of 1419Å to 1440Å.

Table 2 below shows a case in which the same silicon nitride film etching time is maintained according to the number of etching process batches in the conventional method (process condition 1) and the etching process time is applied by accumulating a certain amount of etching process time according to the present invention. Data table showing the nitride film etching process time and the etching amount according to the cases (process conditions 2, process conditions 3, process conditions 4).

TABLE 2

Nitride Etching Process Time and Amount of Etching Process

Process time (min.) Etching amount Remarks 1 batch 10 batch range 1 batch 10 batch range One 35 35 --- 1505 1400 1400-1505 equal time per batch 2 33 36 33-36 1419 1440 1419-1440 20 seconds per batch 3 32 33.5 32 to 33.5 1440 1471 1440-1471 Add 10 seconds per batch 4 33 36 33-36 1436 1442 1436-1442 20 seconds per batch

As shown in FIG. 7 and Table 2, the cumulative addition or accumulation of a certain amount of etching time to the etching time of each etching treatment batch during the wet etching process for the removal of the silicon nitride film for the liner and pad nitride film of the semiconductor device. By performing the etching process by the difference, the problem of reducing the etching rate of the etching solution according to the increase in the number of etching treatment batches can be solved, and the etching rate and etching amount of the silicon nitride film liner can be obtained. In addition, as can be seen in Table 2, the etching range of the etching amount ranges from 21 kPa (process condition 2), 31 kPa (process condition 3) and 6 kPa (process condition 4), which is smaller than 105 kPa (process condition 1) of the conventional method. Since it can be reduced, the process margin of the etching process can be secured.

According to the present invention, in the shallow trench isolation method, when the etching process for removing the liner on the semiconductor substrate is performed, the wet etching process is performed by adding or subtracting the etching time according to the processing batch number, thereby increasing the number of processing batches. Even if it is possible to maintain a constant etching rate and etching amount. Accordingly, the etching amount can be precisely and strictly controlled when the liner in the trench opening is etched, thereby effectively preventing the dent or dipping of the liner occurring on the liner in the trench opening. It is possible to obtain an effect that can solve problems such as a cell threshold voltage drop. And since the etching amount range can be reduced, it is possible to improve the etching process margin of the liner made of a silicon nitride film.

Claims (3)

Measuring a change in the etching amount of the film to be etched according to the number of times of the wet etching process performed in a batch unit; The first batch showing the etching amount closest to the target etching amount corresponding to the thickness of the film to be etched is determined as the reference batch, and the etching time of the reference batch is referred to as the reference etching time. Making the decision, For batches that undergo an etching process prior to the reference batch, a wet etching process is performed for a time that is cumulatively accumulated (or cumulatively added) for a predetermined time at the reference etching time, and the reference batch (B) performing a wet etching process on the batches which are later subjected to the etching process during the cumulative addition (or cumulative difference) by the predetermined time at the reference etching time. Etching method. The method of claim 1, The predetermined time may be obtained by dividing an average amount of etching change per batch by an etching rate of the reference batch, which increases or decreases every time the number of the wet etching processes increases by "1". Silicon Nitride Wet Etching Method. The method of claim 1, The etching target film is a silicon nitride film (Si ₃ N ₄ ), The etching solution for the film to be etched is a silicon nitride film wet etching method of a semiconductor device, characterized in that the solution of phosphoric acid (H ₃ PO ₄ ).