JP2011165722A - Ion implantation angle monitoring wafer and monitoring method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the reliability of a product, by providing an ion implantation angle monitoring wafer where change of ion implantation angle can be recognized in a short time by visual monitoring, and to provide a monitoring method which uses the product. <P>SOLUTION: A trench structure (constant depth, variable or constant width, variable depth) which depends upon a plurality of ion implantation angles is fabricated on the surface of an ion implantation region, and after performing ion implantation, at a certain angle to a wafer having a plurality of the trench structures; ion implantation region is etched by selective etching; and then the bottom and sidewall of front- and rear-trench structure patterns, corresponding to an assumed ion implantation angle are observed, thus conducting visual evaluation of the ion implantation angle. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wafer for monitoring an ion implantation angle and a monitoring method using the same.

  Currently, due to miniaturization of semiconductors, LDD (Lightly Doped Drain) structure for preventing deterioration of characteristics due to injection of hot carriers generated in a channel in a high electric field state in a MOS transistor into a gate oxide film, In the formation of a buffer layer for increasing the breakdown voltage of a next-generation IGBT (Insulated Gate Bipolar Transistor), ion implantation by ion angle implantation or channeling is used.

  When performing ion angle implantation as described above, the ion implantation angle is a very important parameter. For example, in ion implantation by channeling (ion implantation angle 0 °) used in the IGBT buffer layer, impurities may not be implanted deeply when tilted several degrees. An angle is set when it is desired to be implanted as shallow as the channel portion of a fine MOS transistor, but impurities may be implanted deeply when the ion implantation angle is reduced.

  Due to the deviation in the implantation angle, the amount of impurities changes, resulting in characteristic fluctuations such as a decrease in breakdown voltage and threshold fluctuation. In addition, in order to reduce the heat treatment temperature and shorten the processing time in a fine process, the ion implantation angle may be increased because shadowing is used.

  Therefore, by monitoring the implantation angle in the ion implantation step, it is possible to recognize and adjust the angle deviation, avoid the above-described characteristic variation due to the change in the impurity amount, and increase the reliability of the product.

  Patent Document 1 below describes an example of a monitoring method for an ion implantation process. FIG. 12 is a test pattern diagram for explaining the monitoring method disclosed in Patent Document 1. In FIG.

  A test pattern 91 shown in FIG. 12 is a pattern formed on a wafer, and has a line and space shape in which an oxide film and the surface of an ion implantation region are alternately shown. In addition, various patterns in which the inter-line distance d9 in the figure is changed can be created on one wafer.

  When ions are implanted into the test chip configured as shown in FIG. 12, the amount of impurities implanted into the test chip varies depending on the implantation angle. For example, when the ion implantation angle is close to a right angle (0 °) with respect to the test chip surface, the amount of implanted impurities increases, and the thermal conductivity and electrical resistance value decrease. On the contrary, if the test chip is tilted in the horizontal direction with respect to the surface of the test chip, the amount of implanted impurities decreases, and the thermal conductivity and the electrical resistance value increase.

  By monitoring the thermal conductivity and the electrical resistance value at the time of ion implantation in this way, the ion implantation angle can be monitored.

JP 2008-147402 A

  According to the method described in Patent Document 1, since the ion implantation angle can be monitored, even if the ion implantation angle deviates from the set ion implantation angle, it is recognized that it is defective, and the implantation angle is quickly readjusted to be defective. Product production ratio can be reduced and product reliability can be maintained.

  However, according to the method described in Patent Document 1, it is necessary to remove the oxide film in order to measure the electric resistance value, and then to perform annealing, so that a certain amount of time is required. At that time, if there is any failure in the annealing furnace, the reliability of the electrical resistance value is significantly reduced.

  Even if RTA (Rapid Thermal Annealing) is used as a method for shortening the time, if the amount of impurities is large, all impurities may not be activated, and this may also reduce the reliability of the electrical resistance value. There is. In addition, if you want to change to a different injection angle on the same model, it is necessary to test many times in advance and accumulate data results.

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a wafer for monitoring an ion implantation angle in a short time and visually without using only numerical data such as an electric resistance value and a monitoring method using the wafer. .

  A monitoring wafer according to the present invention for achieving the above object is for monitoring an ion implantation angle in an ion implantation process, and a plurality of trenches (grooves) corresponding to a plurality of ion implantation angles are formed on the wafer surface. It is characterized by forming.

  In the trench structure, the trench width or depth is determined by the ion implantation angle to be monitored.

  The monitoring method is characterized in that the ion implantation angle is visually evaluated by selectively etching a wafer implanted with ions from a certain angle and observing the bottom or side wall of the trench. At this time, since the activation of impurities is unnecessary, annealing is not necessary.

  Furthermore, if etching dimensions are accumulated and compared, it is possible to compare and judge changes in conditions more accurately.

  When trenches for a plurality of ion implantation angles exist in the wafer, ions implanted at an angle set on the apparatus side reach the entire trench sidewall corresponding to the set angle and the trench bottom corresponding to the set angle or more. When the ion implantation angle exceeds the set angle, the ions cannot reach the bottom of the trench corresponding to the set angle, and ions are implanted into a part of the side wall. In this case, the ion implantation angle can be obtained from the ion implantation region implanted in the side wall. When the implantation angle is smaller than the set angle, the ion implantation angle can be obtained from the ion implantation region that reaches the trench bottom corresponding to the set angle and is implanted into the trench bottom.

  That is, when the ion implantation angle is changed, if the angle is increased, a trace of ion implantation can be observed only at a part of the trench sidewall corresponding to the set angle, and a trace can be observed at the trench bottom corresponding to the set angle or more. there is a possibility. When the implantation angle is reduced, traces implanted into the trench bottom corresponding to the set angle can be observed, and traces of ion implantation may be observed at the end of the trench bottom corresponding to the set angle or less. .

  According to the configuration of the present invention, by forming trenches for a plurality of ion implantation angles on the wafer surface, it is possible to recognize an abnormal state of the ion implantation angle by a short time and visual monitoring.

1 is a schematic plan view of a monitoring wafer according to the present invention. The figure which shows the outline in the case of carrying out angle implantation with respect to the wafer for monitoring with constant trench depth. The figure which shows the outline in the case of carrying out angle implantation with respect to the wafer for monitoring with constant trench width. The figure which shows Example 1 at the time of ion-implanting from a different implantation angle to the trench of variable width. The figure which shows Example 2 at the time of ion-implanting from a different implantation angle to the trench of variable width. The figure which shows Example 3 at the time of ion-implanting from a different implantation angle to the trench of variable width. The figure which shows Example 4 at the time of ion-implanting from a different implantation angle to the variable width | variety trench. The figure which shows Example 1 at the time of ion-implanting from a different implantation angle to the trench of variable depth. The figure which shows Example 2 at the time of ion-implanting from a different implantation angle to the trench of variable depth. The figure which shows Example 3 at the time of ion-implanting from a different implantation angle to the trench of variable depth. The figure which shows Example 4 at the time of ion-implanting from a different implantation angle to the trench of variable depth. The schematic plan view which shows the test pattern used with the conventional monitoring method.

  Hereinafter, embodiments of a monitoring wafer and a monitoring method using the same according to the present invention (hereinafter referred to as a method of the present invention) will be described with reference to the drawings.

  FIG. 1 is a schematic plan view of a wafer used in the method of the present invention. The wafer 1 has a structure having a trench structure (hereinafter referred to as a trench) used for monitoring an ion implantation angle. The wafer 1 may be a wafer for ion implantation angle monitoring in which only a plurality of trenches 2 are formed, or may be a comprehensive monitoring / test wafer provided with a plurality of chips for monitoring and testing in other processes. The trenches 2 are arranged at various angles because this corresponds to various scanning methods at the time of ion implantation.

  2 and 3 are schematic cross-sectional views of a plurality of trenches 2 formed on the wafer 1. As shown in the figure, the trench structures in FIG. 2 have different widths and constant depths (here, w1 <w2 <w3). This is designed to allow monitoring with respect to a plurality of ion implantation angles. When the ion implantation angle θ to be monitored is determined, the ratio of the trench width w to the depth t is determined by the following equation.

  As shown in FIG. 2, when the ion implantation 3 is performed from the same angle, the trench 22 corresponding to the angle is ion-implanted into the entire sidewall and the bottom end, and in the trench 21 corresponding to a smaller angle, Ions do not reach the bottom of the trench, and ions are implanted only in part of the side walls. In the trench 23 corresponding to a large angle, ions are also implanted into the trench bottom.

  FIG. 4 to FIG. 7 show examples of ion implantation from different ion implantation angles (θ1, θ2, θ3, θ4) using the trench 2. 4 to 7 show cases where ion implantation 3 is performed from different ion implantation angles. The ion implantation angle θ is the tilt angle of the ion implantation line with respect to the normal of the wafer surface, and θ4 <θ3 <θ1 <θ2. It is.

Here, if the ion implantation conditions are ion: P +, energy: 125 keV, dose: 1.0E13 / cm ² , the beam diameter at this time is about 28-30 mm. This beam diameter is larger than the width and depth of the trench.

  Further, assuming that θ1 = 2 °, θ2 = 3 °, and θ3 = 1 °, the trench 21 corresponds to θ3, the trench 22 corresponds to θ1, and the trench 23 corresponds to θ2. 4 to 7, when t1 = 8 um, w1 = 0.15 um, w2 = 0.28 um, and w3 = 0.42 um according to Equation 1. As shown in FIG. 4, when ions are implanted at 2 °, ions are implanted into the entire side wall and bottom end of the trench 22 corresponding to the angle, and in the trench 23 corresponding to 3 °, ions are also implanted into the bottom. . However, in the trench 21 corresponding to 1 °, ions cannot reach the bottom, and an ion implantation trace can be observed on a partial side wall of the trench 21. At that time, the following relationship holds between θ and the depth t ′ of the ion implantation trace.

  For example, when ions are implanted into the trench 21 at θ = 2 ° as described above, the trench sidewall ion implantation region depth t ′ can be obtained from Equation 2 as t ′ = 3.7 μm. Also, the equation regarding the trench bottom ion-implanted region widths w ′ and θ is as follows.

  For example, when ions are implanted into the trench 23 at θ = 2 ° as described above, the ion implantation width at the bottom of the trench 23 can be obtained from Equation 3 as w ′ = 0.14 μm.

  As shown in FIG. 5, when the ion implantation angle is shifted from θ1 = 2 ° to θ2 = 3 °, ions are implanted into the entire sidewall of the trench 23. However, the ions do not reach the bottom in the trenches 21 and 22, and the ion implantation trace can be observed over the depth of about 5.14 μm from the number 2 on the side wall of the trench 21. It is considered that ions are implanted over the entire area.

  When the ion implantation angle is smaller, that is, θ3 = 1 ° as shown in FIG. 6, ions are implanted into the entire sidewall of the trench 21 and the bottom end, and the trenches 22 and 23 are also implanted into the bottom. In this case, using formula 3, the ion implantation width at the bottom of the trench 22 is about 0.14 μm, and the ion implantation width at the bottom of the trench 23 is about 0.28 μm. Even when the ion implantation angle is further reduced (FIG. 7)), w ′ can be obtained using Equation (3). Equations 2 and 3 can also be used to obtain the ion implantation angle θ from t ′ and w ′.

  From the above, when ions are implanted into the bottom of the trench, if the θ to be evaluated and w and t are determined, the dimension w ′ of the region implanted into the trench bottom or the region implanted into the side wall Dimension t ′ can be determined by Equations 2 and 3.

  When monitoring which trench is ion-implanted as described above, first, a chemical solution is used and etching is performed for a short time. As a result, by using the difference in etching rate between the ion-implanted portion and the non-implanted portion, only the ion-implanted portion is selectively etched. Then, the ion implantation angle is monitored by observing the trench bottom or side wall. For example, if an ion implantation trace can be observed on a partial side wall of the trench 21 and an ion implantation trace can be observed on the entire sidewall of the trench 22, the ion implantation angle is in the range of 1 ° <θ ≦ 2 °. Furthermore, the range of θ can be further reduced by the size of the ion implantation region on the side wall of the trench 21.

  Each trench structure in FIG. 3 has a different depth and a constant width (here, t4 <t3 <t2). This is designed to allow monitoring with respect to a plurality of ion implantation angles. When the ion implantation angle θ to be monitored is determined, the ratio of the trench width w to the depth t is determined by Equation 1 as in the first embodiment.

  As shown in FIG. 3, when the ion implantation 5 is performed from the same angle, the trench 25 corresponding to the angle is ion-implanted into the entire side wall, and the trench 24 corresponding to a smaller angle is implanted to the bottom of the trench. The ions do not reach and are implanted into a part of the side wall. In the trench 26 corresponding to a large angle, ions are also implanted into the trench bottom.

  8 to 11 show cases where ion implantation 5 is performed from different ion implantation angles. The ion implantation angle θ is the tilt angle of the ion implantation line with respect to the normal of the wafer surface, and θ8 <θ7 <θ5 <θ6. It is.

  The ion implantation conditions are the same as in the first embodiment, and θ5 = 2 °, θ6 = 3 °, and θ7 = 1 °. The trench 24 corresponds to θ7, the trench 25 corresponds to θ5, and the trench 26 corresponds to θ6. 8 to 11, when w4 = 0.15 μm, t2 = 8 μm, t3 = 4.3 μm, and t4 = 2.9 μm are obtained from Equation 1. As shown in FIG. 8, when ions are implanted at 2 °, ions are implanted into the entire sidewall of the trench 25 corresponding to the angle, and in the trench 26 corresponding to 3 °, the bottom portion is about 0.05 μm from Equation 3. Ions are implanted over a wide area and traces can be observed. However, in the trench 24 corresponding to 1 °, ions cannot reach the bottom, and from Equation 2, an ion implantation depth trace can be observed on the side wall of the trench 24 over about 3.7 μm.

  As shown in FIG. 9, when the ion implantation angle is shifted from θ5 = 2 ° to θ6 = 3 °, ions are implanted into the entire sidewall of the trench 26. However, the ions do not reach the bottom in the trenches 24 and 25, and from Equation 2, the ion implantation depth can be observed over about 5.14 um on the side wall of the trench 24, and the ion implantation depth is about 1.44 um on the side wall of the trench 25. Can be observed.

  As shown in FIG. 10, when the ion implantation angle is shifted to the smaller side, θ7 = 1 °, ions are implanted into the entire sidewall of the trench 26, and the trenches 24 and 25 are also implanted into the bottom. In this case, using formula 3, the ion implantation width at the bottom of the trench 24 is about 0.075 um, and the ion implantation width at the bottom of the trench 25 is about 0.10 um. Even when the ion implantation angle is further reduced (FIG. 11), w ′ can be obtained using Equation (3).

  When monitoring which trench is ion-implanted as described above, the same method as in Example 1 is used, and the observation method is also the same.

  In both practical examples 1 and 2, after performing ion implantation under the same conditions on this monitoring wafer together with the product at a constant rate and performing selective etching for a short time, the ion implantation angle can be determined by observing the trench bottom and sidewalls around the ion implantation angle. Even if changes due to some reason, it can be captured visually.

  Therefore, according to the feature of the monitoring wafer according to the present invention, it is possible to know the change of the ion implantation angle by directly observing the wafer without monitoring the transition of numerical data, and take measures based on the visual result. Therefore, it is possible to avoid the ion quantity deviating from being injected into the product, and it is possible to quickly prevent the generation of defective products. Further, since the monitoring method of the present invention directly observes the wafer, it is possible to quickly cope with the case of changing the implantation angle in the same model.

  By introducing the wafer having the trench structure at regular intervals in addition to the product, it is possible to periodically monitor changes in the ion implantation angle and recognize changes in the ion implantation conditions. If the image data at this time is stored, and further the etching dimensions are stored and compared, it is possible to compare and judge the change in the conditions more accurately.

  In addition, the monitoring wafer according to the present invention is mixed with the product as described above, and the wafer is observed after ion implantation under the same conditions as the product, so that a complicated process is not required for monitoring. Monitoring can be performed easily and quickly.

  Furthermore, in the monitoring method according to the present invention, after the ion implantation, the implanted portion is etched by short-time selective etching and the wafer is observed, so that an annealing step before measuring the electrical resistance value is not required, and the ions can be more quickly formed. Changes in injection angle can be recognized.

  Note that the ion implantation angle can be monitored more strictly by arranging a plurality of trench structures having the same width and depth in the same wafer and comparing the same trench pattern.

  Moreover, the structure which forms the trench structure mentioned above on the same wafer with the chip | tips other than the ion implantation angle monitoring use may be sufficient.

1 Wafer 2, 21, 22, 23, 24, 25, 26 Trench 3, 5 Ion implantation 4, 6 Ion implantation trace 91 Test pattern d9 Distance between lines t1, t2, t3, t4 Trench depths t ′, t ″, t ′ ″ trench side wall ion implantation region depth w1, w2, w3, w4 trench width w ′, w ″, w ′ ″ trench bottom ion implantation region width θ1, θ2, θ3, θ4, θ5, θ6 angle

Claims (4)

  A wafer for monitoring an ion implantation step of a semiconductor process, comprising a plurality of patterns of trench structures having a constant depth and a width determined by a plurality of ion implantation angles implanted into the wafer surface.   A wafer for monitoring an ion implantation process of a semiconductor process, comprising a plurality of patterns of trench structures having a fixed width and a depth determined by a plurality of ion implantation angles implanted on the wafer surface .   After performing ion implantation on the wafer according to claim 1 or 2, selectively etching and observing the bottom and side walls of the trench structure to visually evaluate the set ion implantation angle. A characteristic monitoring method.   The monitoring method according to claim 3, wherein after the ion implantation, the transition and comparison of the etching dimensions when the bottom and side walls of the trench structure are selectively etched are further performed.

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