Method for determining etching pressure of lamination of titanium and titanium nitride

Abstract

The invention relates to a method for determining the etching pressure of a lamination layer of titanium and titanium nitride. The method comprises the following steps: providing a semiconductor substrate; forming a lamination layer of titanium and titanium nitride on the semiconductor substrate, and determining the thickness ratio of titanium to titanium nitride in the lamination layer; determining the bias power of the plasma etching process; determining an etching pressure candidate range of the plasma etching process according to the bias power and the thickness ratio; in the determined etching pressure candidate range, the etching pressure is determined according to the protective gas flow and the etching temperature in the etching chamber; wherein the bias power is greater than an upper limit value of a process specification of a standard bias power when only plasma etching is carried out on the titanium nitride layer, and a pressure mean value in each etching pressure candidate range is smaller than a lower limit value of the process specification of a standard pressure when only plasma etching is carried out on the titanium nitride layer. According to the invention, better balance between improvement of parameter adjustment efficiency, improvement of etching efficiency and wafer protection can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor manufacturing, and in particular to a method for determining etching pressure of a stack of titanium and titanium nitride. Background Art

[0002] In the semiconductor manufacturing process, it may be necessary to use an adhesion barrier layer, for example, to bond a metal layer to a dielectric layer.

[0003] In a specific application, the adhesion barrier layer may include a two-layer structure, one layer is a metal titanium layer, and the other layer is a titanium nitride layer, so that the good adhesion of the titanium nitride layer can be used to enhance the connection effect of metal wires with very small sizes.

[0004] However, in the prior art, since the etching rate of titanium is faster than that of titanium nitride, the titanium metal layer is easily etched laterally during the top-down etching process. In severe cases, the titanium metal layer may even be completely hollowed out, causing the metal wire to collapse.

[0005] There is an urgent need for a method for determining etching process parameters of a stack of titanium and titanium nitride to improve the etching effect of the stack of titanium and titanium nitride. Summary of the invention

[0006] The technical problem solved by the present invention is to provide a method for determining the etching pressure of a stack of titanium and titanium nitride, which can determine an appropriate etching pressure that meets the requirements of other set parameters, and help to achieve a better balance between improving parameter adjustment efficiency, improving etching efficiency and protecting wafers.

[0007] To solve the above technical problems, an embodiment of the present invention provides a method for determining the etching pressure of a stack of titanium and titanium nitride, comprising: providing a semiconductor substrate; forming a stack of titanium and titanium nitride on the semiconductor substrate, and determining the thickness ratio of titanium and titanium nitride in the stack; determining the bias power of a plasma etching process; determining a candidate range of etching pressure for the plasma etching process according to the bias power and the thickness ratio; determining the etching pressure within the determined candidate range of etching pressure according to the flow rate of protective gas and the etching temperature in an etching chamber; wherein the bias power is greater than the upper limit value of the process specification of the standard bias power when only the titanium nitride layer is plasma etched, and the average pressure in each candidate range of etching pressure is less than the lower limit value of the process specification of the standard pressure when only the titanium nitride layer is plasma etched.

[0008] Optionally, the process specification of the etching pressure is pre-divided into multiple levels, each level has its own etching pressure range, the higher the level, the smaller the difference between the lower limit value of the process specification of the standard pressure and the pressure average in the etching pressure range; determining the etching pressure candidate range of the plasma etching process according to the bias power and the thickness ratio, including: determining the level according to the bias power, wherein the greater the bias power, the higher the level; determining the etching pressure candidate range according to the thickness ratio in the etching pressure range corresponding to the determined level, wherein the smaller the thickness ratio, the greater the pressure average in the etching pressure candidate range.

[0009] Optionally, each etching pressure range is pre-divided into multiple sub-levels, each sub-level has its own etching pressure selection range, the higher the sub-level, the smaller the difference between the lower limit value of the process specification of the standard pressure and the pressure average in the etching pressure selection range; the etching pressure selection range is determined according to the thickness ratio, including: determining the sub-level according to the thickness ratio, wherein the smaller the thickness ratio, the higher the sub-level.

[0010] Optionally, the bias power is selected from: 400W to 500W.

[0011] Optionally, the etching pressure is determined according to the protective gas flow rate and the etching temperature in the etching chamber, including: determining the protective gas flow rate in the etching chamber and the percentage of the protective gas flow rate in the process specification, recorded as a first percentage; determining the etching temperature in the etching chamber and the percentage of the protective gas flow rate in the process specification, recorded as a second percentage; determining the etching pressure according to a weighted operation result of the first percentage and the second percentage; wherein, the larger the first percentage is and the smaller the second percentage is, the greater the etching pressure is.

[0012] Optionally, the etching pressure is determined by the following formula:

[0013]

[0014] P≤P u ;

[0015] Wherein, P is used to represent the etching pressure, P u is used to indicate the upper limit of the determined etching pressure selection range, f is used to indicate the flow rate of the protective gas in the etching chamber, and f l Used to indicate the lower limit of the process specification of the protective gas flow rate, f u It is used to indicate the upper limit of the process specification of the protective gas flow rate, w1 is used to indicate the preset first weight, T is used to indicate the etching temperature in the etching chamber, T lUsed to indicate the lower limit of the process specification of etching temperature, T u It is used to indicate the upper limit of the process specification of the protective etching temperature, w2 is used to indicate the preset second weight, P m It is used to represent the average value of the determined etching pressure candidate range, and offset is used to represent the offset.

[0016] Optionally, the offset is determined using the following formula:

[0017] offset=0, when P≤P u ;

[0018]

[0019] Optionally, the protective gas is nitrogen; the process specification of the protective gas flow rate is 20sccm-30sccm.

[0020] Optionally, the lower limit value of the process specification of the standard pressure is selected from: 12mT to 15mT.

[0021] Optionally, a patterned tungsten material layer is formed on the stack of titanium and titanium nitride; wherein the ratio of the smallest pattern width in the tungsten material layer to the depth of the tungsten material layer is greater than or equal to 10:1.

[0022] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects:

[0023] In the embodiment of the present invention, by selecting a bias power greater than that when only the titanium nitride layer is plasma-etched, the deviation of the etching direction from the vertical direction can be reduced to a certain extent, and the lateral etching of the titanium layer can be alleviated. Then, the etching pressure candidate range of the plasma etching process is determined in combination with the thickness ratio of titanium and titanium nitride in the stack, so that the selection range of the etching pressure is narrowed through the first round of determination steps, and the pressure average value in each etching pressure candidate range is less than the process specification lower limit value of the standard pressure when only the titanium nitride layer is plasma-etched. Therefore, the etching pressure can be effectively controlled after the first round of determination steps. Within a certain low range, it helps to reduce the situation where excessive etching pressure damages the wafer, and achieves a better balance between improving parameter adjustment efficiency and protecting the wafer; further, the etching pressure is determined according to the protective gas flow rate and etching temperature in the etching chamber. The two parameters of protective gas flow rate and etching temperature can be combined to determine the available etching pressure within the narrowed range of etching pressure candidates through a second round of determination steps, thereby making the selection of etching pressure more suitable for the current environment and other predetermined parameters, and compared with relying on manual experience, the accuracy and efficiency of etching pressure selection can be effectively improved.

[0024] Further, the process specification of the etching pressure is pre-divided into multiple levels, each level has its own etching pressure range, the higher the level, the smaller the difference between the process specification lower limit of the standard pressure and the pressure mean value in the etching pressure range, in other words, the higher the level, the larger the etching pressure value, the shorter the adjustment time required to adjust from the standard pressure to the etching pressure, the higher the adjustment efficiency, and the smaller the process cost consumed in the adjustment process. In addition, the level is determined according to the bias power, wherein the greater the bias power, the higher the level; in the etching pressure range corresponding to the determined level, the etching pressure candidate range is determined according to the thickness ratio, wherein the smaller the thickness ratio, the greater the pressure mean value in the etching pressure candidate range, so that the thickness ratio of titanium and titanium nitride in the stack can be combined with this parameter, for the case where the proportion of titanium is smaller, a larger etching pressure can be used without worrying about the excessive lateral etching of titanium due to the large etching pressure, and conversely, for the case where the proportion of titanium is larger, a smaller etching pressure can be used to reduce the severity of the lateral etching of titanium.

[0025] Furthermore, each etching pressure range is pre-divided into multiple sub-levels, each sub-level has its own etching pressure selection range, the higher the sub-level, the smaller the difference between the process specification lower limit of the standard pressure and the pressure mean in the etching pressure selection range; the sub-level is determined according to the thickness ratio, wherein the smaller the thickness ratio, the higher the sub-level. By adopting the above scheme, the etching pressure selection sub-range can be set in combination with the thickness ratio, and then by selecting the sub-range, a more appropriate etching pressure range can be determined, which can further narrow the selection range of the etching pressure while effectively improving the accuracy and efficiency of the etching pressure selection.

[0026] Furthermore, the bias power is selected from: 400W to 500W. Compared with the process specification upper limit of the standard bias power when only the titanium nitride layer is plasma etched, such as 100W to 200W, the higher 400W to 500W is selected as the bias power. It can reduce the deviation of the etching direction from the vertical direction to a greater and more appropriate extent and reduce the lateral etching of the titanium layer.

[0027] Further, the flow rate of the protective gas in the etching chamber and the percentage of the protective gas in the process specification are determined, which is recorded as the first percentage; the etching temperature in the etching chamber and the percentage of the protective gas in the process specification are determined, which is recorded as the second percentage; the etching pressure is determined according to the weighted calculation result of the first percentage and the second percentage; wherein, the larger the first percentage is, the smaller the second percentage is, and the larger the etching pressure is. By adopting the above scheme, the higher the position of the protective gas flow in the process specification is, the more helpful it is to reduce the etching rate; the lower the position of the etching temperature in the process specification is, the more helpful it is to reduce the etching rate. Thus, when there are existing parameters for reducing the etching rate, the etching rate can be increased by increasing the etching pressure, and the value of the etching pressure can be quickly determined by quantitative calculation, so as to achieve a better balance between increasing the etching rate and adjusting the etching direction, so as to better protect the wafer.

[0028] Furthermore, by using an appropriate formula to determine the value of offset, P≤P u Specifically, when the etching pressure exceeds the upper limit value of the selected range, it is reduced to the upper limit value, thereby achieving the effect of reducing the etching pressure to a certain extent and protecting the wafer.

[0029] Furthermore, the protective gas is nitrogen, and the process specification of the protective gas flow rate is 20sccm-30sccm. Compared with selecting other inert gases as the protective gas, in the embodiment of the present invention, selecting nitrogen can reduce production costs and make it easier to keep the pressure in the etching chamber stable.

[0030] Furthermore, the lower limit value of the process specification of the standard pressure is set to be selected from: 12mT to 15mT, so as to avoid the problem of too low etching rate caused by unlimited reduction of the standard pressure. By controlling the lower limit value of the process specification, it helps to improve production efficiency and reduce process costs.

[0031] Furthermore, a patterned tungsten material layer is formed on the stack of titanium and titanium nitride; wherein the ratio of the smallest pattern width in the tungsten material layer to the depth of the tungsten material layer is greater than or equal to 10:1, that is, when the etching requirement of the tungsten material layer is a very large aspect ratio (exceeding one order of magnitude) and the complexity of selecting the etching pressure is very large, by adopting the solution of the embodiment of the present invention, while etching the tungsten material layer, by selecting an appropriate bias power and two rounds of determination steps, an appropriate etching pressure that meets the requirements of other predetermined parameters is determined, which helps to achieve a better balance between improving parameter adjustment efficiency, improving etching efficiency and protecting wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1It is a schematic diagram of a wafer cross-sectional structure corresponding to a stacked etching method of titanium and titanium nitride in the prior art;

[0033] Figure 2 is a flow chart of a method for determining etching pressure of a stack of titanium and titanium nitride in an embodiment of the present invention;

[0034] Figure 3 to Figure 4 It is a schematic diagram of the device cross-sectional structure corresponding to each step in a method for determining etching pressure of a stack of titanium and titanium nitride in an embodiment of the present invention.

[0035] Description of reference numerals:

[0036] Semiconductor substrate 100 , titanium layer 111 , titanium nitride layer 112 , stack 110 of titanium and titanium nitride, metal layer 120 , etch mask layer 130 , semiconductor substrate 200 , titanium layer 211 , titanium nitride layer 212 , stack 210 of titanium and titanium nitride, metal layer 220 , etch mask layer 230 . DETAILED DESCRIPTION

[0037] As mentioned above, in the prior art, since the etching rate of titanium is faster than that of titanium nitride, the titanium metal layer is easily etched sideways during the top-down etching process, and in severe cases, it may even be completely hollowed out, causing the metal wire to collapse.

[0038] Reference Figure 1 , Figure 1 The present invention is a schematic diagram of a wafer cross-sectional structure corresponding to a stacked etching method of titanium and titanium nitride in the prior art.

[0039] As shown in the figure, a semiconductor substrate 100 is provided, which may include structures located on the surface of the semiconductor substrate 100, such as gate structures, metal interconnect structures, etc., and is not limited to the part within the surface of the semiconductor substrate 100.

[0040] A stacked layer 110 of titanium and titanium nitride is formed on the semiconductor substrate 100 , and a metal layer 120 is formed on the stacked layer 110 of titanium and titanium nitride.

[0041] The stacked layer 110 of titanium and titanium nitride may include a titanium layer 111 and a titanium nitride layer 112 .

[0042] An etching mask layer 130 is formed, and the metal layer 120 is etched from the front surface of the semiconductor substrate 100 .

[0043] However, since the etching rate of the titanium layer 111 is faster than that of the titanium nitride layer 112, the titanium layer 111 is easily etched laterally during the top-down etching process (eg, Figure 1 In severe cases, the wire may be completely hollowed out, causing the wire to collapse.

[0044] After research, it is found that in the prior art, a single parameter that is beneficial to controlling the etching direction is often set and then the single parameter is adjusted, or multiple parameters that are beneficial to controlling the etching direction are set and then multiple parameters are adjusted based on manual experience.

[0045] However, in a specific implementation, the parameters that affect the control of etching direction may include the bias power of the plasma etching process, the flow rate of the protective gas in the etching chamber, the etching temperature and the etching pressure, etc. The adjustment of the above parameters depends on manual experience, and a large number of wafers need to be tested in batches (split), which takes a long time and has a high test cost.

[0046] Further research has found that among the above parameters, the etching pressure is more complicated to adjust. Specifically, the etching pressure has a greater impact on the wafer. Too much or too little etching pressure will cause the etching angle to deviate from the vertical downward direction, making the lateral etching of the titanium metal layer more serious. Excessive etching pressure will also damage the wafer. Furthermore, the above parameters often affect each other, making it difficult to adjust them in real time through manual experience.

[0047] In the embodiment of the present invention, by selecting a bias power greater than that when only the titanium nitride layer is plasma etched, the deviation of the etching direction from the vertical direction can be reduced to a certain extent, and the lateral etching of the titanium layer can be alleviated. Then, the etching pressure candidate range of the plasma etching process is determined in combination with the thickness ratio of titanium and titanium nitride in the stack, so that the selection range of the etching pressure is narrowed through the first round of determination steps. Since the pressure average value in each etching pressure candidate range is less than the process specification lower limit value of the standard pressure when only the titanium nitride layer is plasma etched, the etching pressure candidate range can be determined in the first round of determination steps. After that, the situation of excessive etching pressure damaging the wafer is effectively reduced, and a better balance is achieved between improving parameter adjustment efficiency and protecting the wafer; further, the etching pressure is determined according to the protective gas flow rate and etching temperature in the etching chamber. The two parameters of protective gas flow rate and etching temperature can be combined to determine the available etching pressure within the narrowed range of etching pressure candidates through a second round of determination steps, so that the selection of etching pressure is more suitable for the current environment and other predetermined parameters, and compared with relying on manual experience, the accuracy and efficiency of etching pressure selection can be effectively improved.

[0048] In order to make the above-mentioned objects, features and beneficial effects of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0049] Reference Figure 2 , Figure 21 is a flow chart of a method for determining etching pressure of a stack of titanium and titanium nitride in an embodiment of the present invention. The method for determining etching pressure of a stack of titanium and titanium nitride may include steps S21 to S25:

[0050] Step S21: providing a semiconductor substrate;

[0051] Step S22: forming a stack of titanium and titanium nitride on the semiconductor substrate, and determining a thickness ratio of titanium to titanium nitride in the stack;

[0052] Step S23: determining the bias power of the plasma etching process;

[0053] Step S24: determining a candidate range of etching pressure for the plasma etching process according to the bias power and the thickness ratio;

[0054] Step S25: determining the etching pressure within the determined etching pressure candidate range according to the protective gas flow rate and the etching temperature in the etching chamber.

[0055] The bias power is greater than the upper limit of the process specification of the standard bias power when only the titanium nitride layer is subjected to plasma etching, and the average pressure in each selected etching pressure range is less than the lower limit of the process specification of the standard pressure when only the titanium nitride layer is subjected to plasma etching.

[0056] Combine the following Figure 3 to Figure 4 Each of the above steps is described below.

[0057] Figure 3 to Figure 4 It is a schematic diagram of the device cross-sectional structure corresponding to each step in a method for determining etching pressure of a stack of titanium and titanium nitride in an embodiment of the present invention.

[0058] Reference Figure 3 , a semiconductor substrate 200 is provided, and a stacked layer 210 of titanium and titanium nitride is formed on the semiconductor substrate 200. The stacked layer 210 of titanium and titanium nitride may include a titanium layer 211 and a titanium nitride layer 212.

[0059] The material of the semiconductor substrate 200 may include silicon, germanium, silicon germanium, silicon carbide, gallium arsenide or indium gallium.

[0060] The semiconductor substrate 200 may also include structures located on the surface of the semiconductor substrate 200, such as a gate structure, a metal interconnect structure, etc., and is not limited to the portion within the surface of the semiconductor substrate 200. Figure 2 The semiconductor substrate 200 shown may have a dielectric layer thereon, such as tetraethyl orthosilicate (TEOS).

[0061] A stacked layer 210 of titanium and titanium nitride is formed on the semiconductor substrate 200 , and a metal layer 220 is formed on the stacked layer 210 of titanium and titanium nitride.

[0062] It should be pointed out that a patterned etching mask layer 230 can also be formed to etch the metal layer 220 from the front side of the semiconductor substrate 200 to obtain a patterned metal layer 220. The patterned etching mask layer 230 can also be used as a mask to etch the stack 210 of titanium and titanium nitride.

[0063] It should be noted that in the process of etching the stacked layer 210 of titanium and titanium nitride, it is necessary to use Figure 2 Shown is a method for determining etching parameters.

[0064] In step S22 , after forming the stack 210 of titanium and titanium nitride, the thickness ratio of the titanium layer 211 and the titanium nitride layer 212 in the stack can be determined, and the thickness ratio is objective and unchangeable for a single wafer.

[0065] In step S23 , the bias power of the plasma etching process may be determined.

[0066] In a specific implementation, the bias power of the plasma etching process may also be referred to as the lower RF power, which is often used to accelerate positive ions and provide vertical physical bombardment.

[0067] Specifically, the bias power may be greater than the upper limit of the process specification of the standard bias power when plasma etching is performed only on the titanium nitride layer 212 .

[0068] In the embodiment of the present invention, by selecting a suitable bias power, the deviation between the etching direction and the vertical direction can be reduced to a certain extent, thereby alleviating the problem of lateral etching of the titanium layer 211 .

[0069] Furthermore, the bias power can be selected from: 400W to 500W.

[0070] It should be noted that the ratio of the bias power to the upper limit of the process specification of the standard bias power may be ≥2 times, that is, the bias power may be set to double the upper limit of the process specification of the standard bias power.

[0071] In a specific implementation, the upper limit of the process specification of the standard bias power when only the titanium nitride layer 212 is plasma etched can be selected from 100 W to 200 W. The bias power is selected from 400 W to 500 W, which is greater than or equal to twice.

[0072] It should be pointed out that by selecting double the bias power, the deviation between the etching direction and the vertical direction can be reduced to a greater extent, and the problem of lateral etching of the titanium layer 211 can be alleviated. Then, the detailed etching pressure can be determined according to the specific conditions of other parameters, thereby balancing the effect of the bias power.

[0073] In an embodiment of the present invention, the bias power is selected from: 400W to 500W. Compared with the process specification upper limit value of the standard bias power when only plasma etching is performed on the titanium nitride layer 212, such as 100W to 200W, the higher 400W to 500W is selected as the bias power. It can reduce the deviation of the etching direction from the vertical direction and reduce the lateral etching of the titanium layer to a greater and more appropriate extent.

[0074] In step S24, a candidate range of etching pressure for the plasma etching process may be determined according to the bias power and the thickness ratio.

[0075] Furthermore, the process specifications of the etching pressure are pre-divided into multiple levels, each level has its own etching pressure range, and the higher the level, the smaller the difference between the lower limit value of the process specification of the standard pressure and the pressure average in the etching pressure range; the step of determining the etching pressure candidate range of the plasma etching process according to the bias power and the thickness ratio may include: determining the level according to the bias power, wherein the greater the bias power, the higher the level; in the etching pressure range corresponding to the determined level, determining the etching pressure candidate range according to the thickness ratio, wherein the smaller the thickness ratio, the greater the pressure average in the etching pressure candidate range.

[0076] It should be pointed out that the pressure average in each etching pressure selection range is lower than the process specification lower limit of the standard pressure when only plasma etching is performed on the titanium nitride layer 212. The etching pressure can be controlled within a certain low range, which helps to reduce the situation where excessive etching pressure damages the wafer.

[0077] Furthermore, the process specification lower limit value of the standard pressure can be selected from: 12mT to 15mT.

[0078] In an embodiment of the present invention, the lower limit value of the process specification of the standard pressure is set to be selected from: 12mT to 15mT, so as to avoid the problem of excessively low etching rate caused by unlimited reduction of the standard pressure. By controlling the lower limit value of the process specification, it helps to improve production efficiency and reduce process costs.

[0079] Furthermore, since the pressure average in each etching pressure selected range is lower than the process specification lower limit of the standard pressure when only the titanium nitride layer 212 is subjected to plasma etching, the smaller the difference between the process specification lower limit of the standard pressure and the pressure average in the etching pressure range, the greater the etching pressure is based on the process specification lower limit of the standard pressure.

[0080] Refer to Table 1, which is a correspondence table between level, thickness ratio, difference and pressure average.

[0081] Table 1

[0082]

[0083]

[0084] In Table 1, level 1 > level 2 > level 3.

[0085] Further, the level is determined according to the bias power, wherein the greater the bias power is, the higher the level is.

[0086] That is, the bias power of level 1 is greater than the bias power of level 2, and the bias power of level 2 is greater than the bias power of level 3.

[0087] Further, in the etching pressure range corresponding to the determined level, the etching pressure candidate range is determined according to the thickness ratio, wherein the smaller the thickness ratio is, the greater the pressure average in the etching pressure candidate range is.

[0088] Taking level 1 as an example, it can be understood that within the range corresponding to level 1, the smaller the thickness ratio, the smaller the difference (that is, the difference between the lower limit value of the process specification of the standard pressure and the pressure average in the etching pressure range), and the greater the etching pressure (indicated by the pressure average).

[0089] It should be noted that in Table 1, the number of levels is taken as 3 for illustration. In a specific implementation, the setting of the above number is not limited to this.

[0090] In an embodiment of the present invention, the process specifications of the etching pressure are pre-divided into multiple levels, each level has its own etching pressure range, and the higher the level, the smaller the difference between the lower limit value of the process specification of the standard pressure and the pressure mean in the etching pressure range. In other words, the higher the level, the greater the value of the etching pressure, the shorter the adjustment time required to adjust from the standard pressure to the etching pressure, the higher the adjustment efficiency, and the smaller the process cost consumed during the adjustment process.

[0091] In addition, the level is determined according to the bias power, wherein the greater the bias power, the higher the level; in the etching pressure range corresponding to the determined level, the etching pressure candidate range is determined according to the thickness ratio, wherein the smaller the thickness ratio, the greater the pressure average in the etching pressure candidate range, so that the parameter of the thickness ratio of titanium and titanium nitride in the stack can be combined. For the case where the titanium accounts for a smaller proportion, a larger etching pressure can be used without worrying about excessive lateral etching of titanium due to excessive etching pressure. Conversely, for the case where the titanium accounts for a larger proportion, a smaller etching pressure can be used to reduce the severity of the lateral etching of titanium.

[0092] Furthermore, each etching pressure range is pre-divided into multiple sub-levels, each sub-level has its own etching pressure selection range, the higher the sub-level, the smaller the difference between the lower limit value of the process specification of the standard pressure and the pressure average in the etching pressure selection range; according to the thickness ratio, the step of determining the etching pressure selection range may include: determining the sub-level according to the thickness ratio, wherein the smaller the thickness ratio, the higher the sub-level.

[0093] Refer to Table 2, which is a correspondence table between levels, sub-levels, thickness ratios, differences and pressure averages.

[0094] Table 2

[0095]

[0096] In Table 1, level 1 > level 2 > level 3, and sub-level 1 > sub-level 2.

[0097] Further, the sub-level is determined according to the thickness ratio, wherein the smaller the thickness ratio is, the higher the sub-level is.

[0098] That is, in each level, the thickness ratio of sub-level 1 is less than the thickness ratio of sub-level 2.

[0099] The higher the sub-level is, the smaller the difference between the lower limit of the process specification of the standard pressure and the average pressure in the selected range of etching pressure is, which means that on the basis of the lower limit of the process specification being less than the standard pressure, the higher the sub-level is, the greater the etching pressure is.

[0100] Taking level 1 as an example, it can be understood that within the range corresponding to level 1, the thickness ratio is a smaller value, the difference (that is, the difference between the lower limit value of the process specification of the standard pressure and the pressure mean in the etching pressure range) is a smaller value, and the etching pressure (indicated by the pressure mean) is a larger value; conversely, the thickness ratio is a larger value, the difference is a larger value, and the etching pressure is a smaller value.

[0101] It should be pointed out that in Table 1, an example is used in which the number of levels is 3, the number of sub-levels is 2 and corresponds to 2 thickness ratios, so min is used to represent the smaller value of the two, and max is used to represent the larger value of the two.

[0102] Furthermore, in a specific implementation, specific values ​​may be pre-configured so that the sub-level and its corresponding etching pressure range may be quickly determined by looking up a table.

[0103] However, in a specific implementation, the setting of the above number is not limited thereto, and an intermediate value may also be set according to the specific number.

[0104] In an embodiment of the present invention, each etching pressure range is pre-divided into a plurality of sub-levels, each sub-level has its own etching pressure selection range, the higher the sub-level, the smaller the difference between the process specification lower limit value of the standard pressure and the pressure mean value in the etching pressure selection range; the sub-level is determined according to the thickness ratio, wherein the smaller the thickness ratio, the higher the sub-level. By adopting the above scheme, the etching pressure selection sub-range can be set in combination with the thickness ratio, and then by selecting the sub-range, a more appropriate etching pressure range can be determined, which can further narrow the etching pressure selection range while effectively improving the accuracy and efficiency of etching pressure selection.

[0105] It should be particularly pointed out that the specific implementation of step S24 is not limited to the above content, and a weight value may be pre-set to determine the etching pressure candidate range by weighted calculation.

[0106] For example, multiple etching pressure selection ranges are pre-divided, and the following formula is used:

[0107] P1=w 11 ×P 偏置 +w 12 ×R 厚度比 ;

[0108] Among them, P1 is used to represent the etching pressure, w 11 Used to indicate bias power P 偏置 The preset weight value, P 偏置 Used to indicate bias power, w 12 Used to indicate thickness ratio R 厚度比 The preset weight value, R 厚度比 Used to express thickness ratio.

[0109] Among them, w 11 and w 12 The bias power P 偏置 and thickness ratio R 厚度比 become the same order of magnitude so that w 11 ×P偏置 and w 11 ×P 偏置 It is comparable and calculable, and can be determined based on historical experience data or test data of similar process platforms.

[0110] Furthermore, the etching pressure candidate range is determined according to which pre-divided etching pressure candidate range the calculated etching pressure P1 belongs to.

[0111] In the specific implementation of step S25, within the determined etching pressure candidate range, the etching pressure is determined according to the flow rate of the protective gas in the etching chamber and the etching temperature.

[0112] Furthermore, the step of determining the etching pressure according to the protective gas flow rate and the etching temperature in the etching chamber may include: determining the protective gas flow rate in the etching chamber and the percentage it occupies in its process specifications, recorded as a first percentage; determining the etching temperature in the etching chamber and the percentage it occupies in its process specifications, recorded as a second percentage; determining the etching pressure according to the weighted operation result of the first percentage and the second percentage; wherein, the larger the first percentage is, the smaller the second percentage is, and the greater the etching pressure is.

[0113] In an embodiment of the present invention, the above-mentioned scheme is adopted, and the characteristics that the higher the position of the protective gas flow rate in its process specifications, the more helpful it is to reduce the etching rate; the lower the position of the etching temperature in its process specifications, the more helpful it is to reduce the etching rate can be utilized. Therefore, when there are existing parameters for reducing the etching rate, the etching rate can be increased by increasing the etching pressure, and a better balance can be achieved between increasing the etching rate and adjusting the etching direction, so as to better protect the wafer.

[0114] Furthermore, the value of the etching pressure can be quickly determined through quantitative calculation.

[0115] Specifically, the etching pressure can be determined by using the following formula:

[0116]

[0117] P≤P u ;

[0118] Wherein, P is used to represent the etching pressure, P u is used to indicate the upper limit of the determined etching pressure selection range, f is used to indicate the flow rate of the protective gas in the etching chamber, and f l Used to indicate the lower limit of the process specification of the protective gas flow rate, f u It is used to indicate the upper limit of the process specification of the protective gas flow rate, w1 is used to indicate the preset first weight, T is used to indicate the etching temperature in the etching chamber, Tl Used to indicate the lower limit of the process specification of etching temperature, T u It is used to indicate the upper limit of the process specification of the protective etching temperature, w2 is used to indicate the preset second weight, P m It is used to represent the average value of the determined etching pressure candidate range, and offset is used to represent the offset.

[0119] Understandably, Can be used to express the first percentage, It can be used to represent the second percentage. The preset first weight w1 and the preset second weight w2 can be determined by historical experience data or by test data of similar processes.

[0120] The larger the first percentage is and the smaller the second percentage is, the more helpful it is to reduce the etching rate. When there are existing parameters for reducing the etching rate, in order to increase the etching rate, the calculated etching pressure is greater.

[0121] Furthermore, the following formula may be used to determine the offset so that P≤P u :

[0122] offset=0, when P≤P u ;

[0123] When P>P u .

[0124] In other words, when P>P u By adopting an appropriate offset, P = P u .

[0125] In the embodiment of the present invention, by using the above formula to determine the value of offset, P≤P u Specifically, when the etching pressure exceeds the upper limit value of the selected range, it is reduced to the upper limit value, thereby achieving the effect of reducing the etching pressure to a certain extent and protecting the wafer.

[0126] It should be particularly pointed out that the specific implementation of step S25 is not limited to the above content, and the etching pressure can also be determined by presetting the weight value of the protective gas flow and the weight value of the etching temperature and using a linear weighted operation.

[0127] For example, using the following formula:

[0128] P2=w 21 ×F 保护气体流量 +w 22 ×T 刻蚀温度 ;

[0129] Among them, P2 is used to represent the etching pressure, w 21 Used to indicate the protective gas flow rate F 保护气体流量 The preset weight value, F 保护气体流量 Used to indicate the protective gas flow rate, w 22 Used to indicate the etching temperature T 刻蚀温度 The preset weight value, T 刻蚀温度 Used to indicate etching temperature.

[0130] Among them, w 21 and w 22 It can make the protective gas flow F 保护气体流量 and etching temperature T 刻蚀温度 become the same order of magnitude so that w 21 ×F 保护气体流量 and w 21 ×T 刻蚀温度 It is comparable and calculable, and can be determined based on historical experience data or test data of similar process platforms.

[0131] It should be noted that if the calculated P2 exceeds the etching pressure selection range determined in step S24, the upper limit value or the lower limit value of the etching pressure selection range may be used as the finally selected etching pressure.

[0132] Furthermore, the protective gas is nitrogen; and the process specification of the protective gas flow rate is 20sccm-30sccm.

[0133] It should be pointed out that, in a specific implementation, other inert gases, such as helium, argon, neon, etc., may also be selected as protective gases.

[0134] In the embodiment of the present invention, compared with selecting other inert gases as the protective gas, in the embodiment of the present invention, selecting nitrogen can reduce production costs and is easier to keep the pressure in the etching chamber stable.

[0135] Reference Figure 4 The metal layer 220 and the stacked layer 210 of titanium and titanium nitride are etched to obtain the etched titanium layer 211 and the titanium nitride layer 212, wherein the lateral etching of the titanium layer 211 is relatively slight and is not likely to cause the collapse of the metal line.

[0136] In a specific application scenario, a complementary metal oxide semiconductor image sensor (CMOS Image Sensors, CIS) wafer can be formed, and the metal layer 220 formed on the stack 210 of titanium and titanium nitride can be a tungsten material layer. From the front side of the semiconductor substrate 200, the step of plasma etching the tungsten material layer is used to form a metal grid to reduce the optical crosstalk between adjacent pixel units in the image sensor.

[0137] Furthermore, a patterned tungsten material layer is formed on the stacked layer 210 of titanium and titanium nitride; wherein the ratio of the smallest pattern width in the tungsten material layer to the depth of the tungsten material layer is greater than or equal to 10:1.

[0138] Among them, the ratio of the minimum pattern width in the tungsten material layer to the depth of the tungsten material layer is greater than or equal to 10:1, that is, the etching requirement of the tungsten material layer is a very large aspect ratio (exceeding one order of magnitude), and the selection complexity of the etching pressure is very large.

[0139] It should be pointed out that in the scenario described above, the density of the metal grid is often large, the etching depth is often deep, and the aspect ratio requirement is very high. For example, the ratio of the minimum width of the pattern to be etched to the depth to be etched can exceed an order of magnitude, such as dozens or hundreds of times.

[0140] Since a multi-layer structure, such as a gate structure, a metal interconnect structure, a high-K material layer, etc., is often formed in the CIS wafer when the metal grid is formed, it is necessary to control the parameters of the production process to protect the formed structure, such as the need for better control of the etching pressure of plasma etching.

[0141] By adopting the solution of the embodiment of the present invention, while etching the tungsten material layer, an appropriate etching pressure that meets the requirements of other predetermined parameters is determined by selecting an appropriate bias power and two rounds of determination steps, which helps to achieve a better balance between improving parameter adjustment efficiency, improving etching efficiency and protecting the wafer.

[0142] In the embodiment of the present invention, by selecting a bias power greater than that when only the titanium nitride layer is plasma-etched, the deviation of the etching direction from the vertical direction can be reduced to a certain extent, and the lateral etching of the titanium layer can be alleviated. Then, the etching pressure candidate range of the plasma etching process is determined in combination with the thickness ratio of titanium and titanium nitride in the stack, so that the selection range of the etching pressure is narrowed through the first round of determination steps, and the pressure average value in each etching pressure candidate range is less than the process specification lower limit value of the standard pressure when only the titanium nitride layer is plasma-etched. Therefore, the etching pressure can be effectively controlled after the first round of determination steps. Within a certain low range, it helps to reduce the situation where excessive etching pressure damages the wafer, and achieves a better balance between improving parameter adjustment efficiency and protecting the wafer; further, the etching pressure is determined according to the protective gas flow rate and etching temperature in the etching chamber. The two parameters of protective gas flow rate and etching temperature can be combined to determine the available etching pressure within the narrowed range of etching pressure candidates through a second round of determination steps, thereby making the selection of etching pressure more suitable for the current environment and other predetermined parameters, and compared with relying on manual experience, the accuracy and efficiency of etching pressure selection can be effectively improved.

[0143] It should be understood that the term "and / or" in this article is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article indicates that the associated objects before and after are in an "or" relationship.

[0144] The "plurality" appearing in the embodiments of the present application refers to two or more.

[0145] The first, second, etc. descriptions appearing in the embodiments of the present application are only used for illustration and distinction of the description objects. There is no order, nor do they indicate any special limitation on the number of devices in the embodiments of the present application, and cannot constitute any limitation on the embodiments of the present application.

[0146] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for determining the etching pressure of a stack of titanium and titanium nitride, characterized in that: include: providing a semiconductor substrate; forming a stack of titanium and titanium nitride on the semiconductor substrate, and determining a thickness ratio of titanium to titanium nitride in the stack; Determine the bias power of the plasma etching process; Determining a candidate range of etching pressure for the plasma etching process according to the bias power and the thickness ratio; Determining the etching pressure within the determined etching pressure selection range according to the protective gas flow rate and the etching temperature in the etching chamber; The bias power is greater than the upper limit of the process specification of the standard bias power when only the titanium nitride layer is subjected to plasma etching, and the average pressure in each selected etching pressure range is less than the lower limit of the process specification of the standard pressure when only the titanium nitride layer is subjected to plasma etching.

2. The method according to claim 1, characterized in that The process specification of the etching pressure is pre-divided into a plurality of levels, each level having its own etching pressure range, and the higher the level, the smaller the difference between the lower limit value of the process specification of the standard pressure and the pressure mean value in the etching pressure range; Determining a candidate range of etching pressure for the plasma etching process according to the bias power and the thickness ratio includes: determining the level according to the bias power, wherein the greater the bias power, the higher the level; In the etching pressure range corresponding to the determined level, the etching pressure candidate range is determined according to the thickness ratio, wherein the smaller the thickness ratio is, the greater the pressure average in the etching pressure candidate range is.

3. The method according to claim 2, characterized in that Each etching pressure range is pre-divided into a plurality of sub-levels, each sub-level having its own etching pressure candidate range, and the higher the sub-level, the smaller the difference between the process specification lower limit value of the standard pressure and the pressure mean value in the etching pressure candidate range; According to the thickness ratio, determining the etching pressure candidate range includes: The sub-level is determined according to the thickness ratio, wherein the smaller the thickness ratio is, the higher the sub-level is.

4. The method according to any one of claims 1 to 3, characterized in that: The bias power is selected from: 400W to 500W.

5. The method according to claim 1, characterized in that: The etching pressure is determined according to the protective gas flow rate and etching temperature in the etching chamber, including: Determine the flow rate of the protective gas in the etching chamber and the percentage of the protective gas in the process specification, recorded as a first percentage; Determine the etching temperature in the etching chamber and the percentage of the etching temperature in the process specification, recorded as a second percentage; The etching pressure is determined according to a weighted calculation result of the first percentage and the second percentage; wherein, the larger the first percentage is, the smaller the second percentage is, and the larger the etching pressure is.

6. The method according to claim 5, characterized in that The etching pressure is determined using the following formula: P≤P u ; Wherein, P is used to represent the etching pressure, P u is used to indicate the upper limit of the determined etching pressure selection range, f is used to indicate the flow rate of the protective gas in the etching chamber, and f l Used to indicate the lower limit of the process specification of the protective gas flow rate, f u It is used to indicate the upper limit of the process specification of the protective gas flow rate, w1 is used to indicate the preset first weight, T is used to indicate the etching temperature in the etching chamber, T l Used to indicate the lower limit of the process specification of etching temperature, T u It is used to indicate the upper limit of the process specification of the protective etching temperature, w2 is used to indicate the preset second weight, P m It is used to represent the average value of the determined etching pressure candidate range, and offset is used to represent the offset.

7. The method according to claim 6, characterized in that The offset is determined using the following formula: offset=0, when P≤P u ; When P>P u .

8. The method according to any one of claims 5 to 7, characterized in that: The protective gas is nitrogen; The process specification of the protective gas flow rate is 20sccm-30sccm.

9. The method according to claim 1, characterized in that: The process specification lower limit value of the standard pressure is selected from: 12mT to 15mT.

10. The method according to claim 1, characterized in that A patterned tungsten material layer is formed on the stack of titanium and titanium nitride; Wherein, the ratio of the smallest pattern width in the tungsten material layer to the depth of the tungsten material layer is greater than or equal to 10:1.

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