JP2006131954A - Plasma etching method, plasma etching system, molding die for optical element, and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma etching method and a plasma etching system which can improve the reproducibility of plasma etching machining while keeping a device stability during the practice of plasma etching, to provide a molding die capable of producing an optical element at high precision with high reproducibility by using the plasma etching method, and to provide the optical element. <P>SOLUTION: In the plasma etching method, high frequency electric power is controlled based on the electric potential of the base material to be worked measured in plasma etching, thus the electric potential of the base material to be worked under plasma etching is controlled to a prescribed range. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plasma etching method for processing a substrate such as silicon, a plasma etching apparatus, a molding die for an optical element obtained by using the plasma etching method, and an optical element.

  Conventionally, plasma etching, which is dry etching using plasma, has been used as a method for processing a substrate such as silicon (see Patent Document 1 below). In order to improve the performance of semiconductor elements and to manufacture molds for high-density integrated elements, more complicated and high-precision substrate processing is required. In particular, silicon may have good etching processability. Plasma etching has been widely applied (see Patent Document 2 below).

  Plasma etching is a silicon substrate against a plasma composed of positive ions, electrons, and neutral particles when electrons accelerated by introducing a reactive gas into a vacuum and applying a high-frequency electric field collide with gas molecules. This is a method of processing using positive ions or neutral particles by introducing a substrate to be processed such as. For example, as shown in Patent Document 2, plasma etching is performed in a plasma etching apparatus in which a substrate electrode connected to a high frequency generator is disposed in an etching chamber and plasma is excited by a resonator.

  However, conventionally, dry etching equipment such as plasma etching has a black box for the stability of the equipment, and the stability of the equipment cannot be monitored from the outside. The stability of the device could not be known until the material was evaluated. For this reason, it has been difficult to immediately stabilize the apparatus so that there is no error during plasma etching.

  In addition, under low-density plasma conditions when a fine periodic structure is formed on a substrate to be processed such as silicon by plasma etching, the plasma state becomes unstable, and the uniformity from batch to batch is particularly deteriorated. In addition, due to instability of the plasma state, variations in etching occur due to subtle changes in the shape of the object to be processed and the plasma state during continuous operation, and the reproducibility of the etching process decreases.

In plasma etching (generally dry etching), apparatus stability is evaluated by batch-to-batch uniformity and in-plane uniformity. In general, the batch-to-batch uniformity and the in-plane uniformity are good at ± 3% or less. However, it has been found by experiments by the present inventors that the batch-to-batch uniformity is about 7% at the maximum when etching a fine structure having a periodicity on the order of submicrons. Thus, conventionally, it has been difficult to process a substrate to be processed such as silicon with high accuracy and reproducibility by plasma etching.
Japanese Patent No. 2918892 JP 07-503815 A

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the prior art, and it is an object of the present invention to provide a plasma etching method and a plasma etching apparatus capable of maintaining apparatus stability during plasma etching and improving reproducibility of plasma etching processing. And It is another object of the present invention to provide an optical element molding die and an optical element that can be manufactured with high accuracy and reproducibility using a plasma etching method.

  In order to achieve the above object, the plasma etching method according to the present invention controls the potential of the substrate to be processed during the plasma etching by controlling the high frequency power based on the potential of the substrate to be processed measured in the plasma etching. Is controlled within a predetermined range.

  According to this plasma etching method, by measuring the potential of the substrate to be processed during plasma etching, by controlling the high-frequency power based on the measured value to control the potential of the substrate to be processed within a predetermined range, The apparatus stability can be maintained during the plasma etching, and the reproducibility of the plasma etching process can be improved. Thereby, when the plasma etching is repeatedly performed under the same conditions, the plasma etching process can be performed with high accuracy and reproducibility.

  In the plasma etching method, the potential of the workpiece substrate can be easily controlled by controlling the potential of the workpiece substrate based on the potential change of the workpiece substrate in the plasma etching acquired in advance.

  Further, by controlling the potential of the substrate to be processed within a predetermined range, the etching rate in the substrate to be processed can be controlled to be substantially constant, and plasma etching can be performed with high accuracy and reproducibility. .

  A plasma etching apparatus according to the present invention includes a vacuum chamber that holds a workpiece substrate therein, a potential measurement unit that measures the potential of the workpiece substrate held in the vacuum chamber, and plasma in the vacuum chamber. A high-frequency power source for generating, a bias high-frequency power source for applying a high-frequency bias power to the substrate to be processed, and a high-frequency power in the high-frequency power source based on the potential of the substrate to be processed measured by the potential measuring unit And a control unit capable of controlling the potential of the substrate to be processed during plasma etching within a predetermined range.

  According to this plasma etching apparatus, the plasma etching method can be executed, the potential of the substrate to be processed is measured during the plasma etching, and the potential of the substrate to be processed is determined by controlling the high frequency power based on the measured value. By controlling within the range, it is possible to maintain the stability of the apparatus during execution of the plasma etching and improve the reproducibility of the plasma etching process. Thereby, when the plasma etching is repeatedly performed under the same conditions, the plasma etching process can be performed with high accuracy and reproducibility.

  In the plasma etching apparatus, the control unit easily controls the potential of the substrate to be processed by controlling the potential of the substrate to be processed based on a potential change of the substrate to be processed in the plasma etching acquired in advance. it can.

  In addition, the control unit can control the etching rate of the substrate to be processed to be substantially constant by controlling the potential of the substrate to be processed within a predetermined range, thereby accurately and reproducibly performing plasma etching processing. Can be done well.

  The optical element molding die according to the present invention can be manufactured from a silicon substrate processed by the above-described plasma etching method. Thereby, a molding die for optical elements with high accuracy and good reproducibility can be obtained.

  The optical element according to the present invention can be manufactured using the molding die described above. Thereby, it can be set as the optical element which can be mass-produced with high quality by a shaping die.

  According to the plasma etching method and the plasma etching apparatus of the present invention, it is possible to maintain the apparatus stability and improve the reproducibility of the plasma etching process during the plasma etching.

  Further, it is possible to provide a molding die for optical elements that can be manufactured with high accuracy and reproducibility using a plasma etching method. It is possible to provide an optical element with high accuracy and high quality that can be mass-produced.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 schematically shows an ICP (inductively coupled plasma) etching apparatus capable of performing a plasma etching method according to the present embodiment. FIG. 2 is a block diagram showing the main part of the control system of the ICP etching apparatus of FIG.

  As shown in FIG. 1, an ICP (inductively coupled plasma) etching apparatus 200 includes a pair of high frequency electrodes 213 and 214 connected to a plasma generating high frequency power supply 212 in a vacuum plasma chamber 211. A substrate holder 215 for holding a silicon substrate 210 as a workpiece base is disposed on the side facing 214. When a high frequency voltage is applied from the high frequency power source 212 to the high frequency electrodes 213 and 214, plasma is formed in the plasma generation region AA in the vacuum plasma chamber 211, and the silicon substrate 210 is dry etched while flowing an etching gas into the chamber 211. be able to.

  A bias high frequency power source 216 is connected to the substrate holder 215 in the vacuum plasma chamber 211, and applies high frequency bias power to the bottom surface 210 b of the silicon substrate 210 held by the substrate holder 215. The potential difference (Vpp) with respect to the ground of the bottom surface 210 b of the silicon substrate 210 held by the substrate holder 215 is measured by the potential measuring device 230.

  A vacuum device 221 is connected to the vacuum plasma chamber 211 via a switching valve 222. Further, an etching gas source 223 is connected via a control valve 224. By controlling the gas flow rate with the control valve 224, the gas pressure can be changed within a predetermined range. It is possible to provide a plurality of etching gas sources 223 and flow a plurality of types of gases.

  As shown in FIG. 2, the ICP etching apparatus 200 of FIG. 1 includes a control unit 100 including a central processing unit (CPU). The control unit 100 includes a plasma generating high-frequency power source 212, a bias high-frequency power source 216, and a vacuum. The device 221, the vacuum device switching valve 222, and the etching gas source control valve 224 are controlled according to a predetermined sequence.

  That is, the controller 100 depressurizes the vacuum plasma chamber 211 with the vacuum device 221, controls the control valve 224 to flow the etching gas while controlling the gas flow rate, and inputs from the input setting unit 220. Based on the set conditions, high frequency power for plasma generation is set for the high frequency power supply 212, high frequency bias power is set for the bias high frequency power supply 216, and the high frequency power supply 212 is operated to generate plasma. Control to do.

  The control unit 100 further controls the potential difference (Vpp) with respect to the ground of the bottom surface 210b of the silicon substrate 210 measured by the potential measuring device 230 so as to have a constant relationship during plasma etching.

  Next, a method of controlling the potential difference (Vpp) with respect to the ground of the bottom surface 210b of the silicon substrate 210 in the control unit 100 of FIG. 2 will be described with reference to FIGS.

  FIG. 3 is a graph showing an example of the relationship between the potential difference (Vpp) and the etching rate of the substrate to be processed (silicon substrate) in order to explain the plasma etching method of the present embodiment. FIG. 4 is a graph showing an example of the relationship between the high frequency power (RF) and the potential difference (Vpp) from the high frequency power source for plasma generation. FIG. 5 is a diagram schematically showing a change with time of the potential difference (Vpp) in the plasma etching of the present embodiment.

  According to experiments and research conducted by the present inventors, it has been clarified that there is a certain relationship between the potential difference (Vpp) with respect to the ground of the bottom surface 210b of the silicon substrate 210 and the etching rate in the silicon substrate 210. That is, as shown in FIG. 3, when the potential difference (Vpp) between the substrate and ground increases, the etching rate tends to decrease. By monitoring the potential difference (Vpp) between the substrate and ground, the etching rate between batches is monitored. It is possible to quantify the error.

  The relationship of FIG. 3 can also be explained from the equation (1) described later. When the potential difference (Vpp) increases with respect to a constant high-frequency bias power W, the current value I decreases. The related etching rate is also reduced.

  As described above, since there is a fixed relationship between the potential difference (Vpp) between the substrate and ground and the etching rate, parameter control is performed in the control unit 100 so that the potential difference (Vpp) has a fixed relationship. The etching rate can always be kept constant.

  When a high frequency bias power W (constant) is applied from the bias high frequency power source 216 to the bottom surface 210b of the silicon substrate 210, the relationship between the potential difference Vpp between the substrate and ground and the current I is expressed by the following equation (1).

  I∝1 / Vpp (1)

  Here, the current value I is an amount related to the exchange of charges between the plasma ions and the surface of the silicon substrate 210, is an amount related to the etching rate, and the etching rate can be controlled by making the current amount constant. Can be constant. Thus, the etching rate can be made constant by performing parameter control that makes the potential difference (Vpp) a constant relationship.

  According to further experiments and researches by the present inventors, the potential difference (Vpp) between the substrate and the ground is approximately proportional to the high frequency power (RF) from the high frequency power supply 212 for plasma generation as shown in FIG. Turned out to be. Therefore, the etching rate can be stabilized by controlling the high frequency power (RF) as a parameter so that the potential difference (Vpp) is always constant, or the change over time of the potential difference (Vpp) always takes the same profile. .

  As described above, high-frequency bias power is applied to the bottom surface 210b of the silicon substrate 210. At this time, the potential difference (Vpp) with respect to the ground of the bottom surface 210b of the silicon substrate 210 is measured by the potential measuring device 230, and the control unit 100 detects the potential difference ( The etching rate can be stabilized by controlling the high-frequency power (RF) of the high-frequency power supply 212 so that Vpp) has a certain relationship.

  Here, the fact that the potential difference (Vpp) has a constant relationship means that even if the plasma etching is repeatedly performed under the same conditions, the change in the potential difference (Vpp) with time does not vary in each etching. For example, if the potential difference (Vpp) does not change with time as shown by the straight line B shown by the broken line in FIG. 5, the potential difference (Vpp) is substantially constant with respect to the straight line B even if the plasma etching is repeated under the same conditions. It is. Further, when the potential difference (Vpp) changes with time as shown by curve A in FIG. 5, the potential difference (Vpp) does not vary with respect to curve A even if plasma etching is repeatedly performed under the same conditions. It is to be.

  For example, when the potential difference (Vpp) changes with time as shown by curve A in FIG. 5 during plasma etching, the measured value of the potential difference (Vpp) at a certain time during plasma etching under the same conditions as follows is shown in FIG. When there is a difference by a difference value ΔVpp with respect to the value of curve A as shown at point m, the control unit 100 causes the high-frequency power of the high-frequency power supply 212 to follow the relationship between the high-frequency power (RF) and the potential difference (Vpp) as shown in FIG. By controlling (RF), the potential difference (Vpp) is controlled so as to approach the value of curve A (so that the difference value ΔVpp becomes zero). Specifically, when the difference value ΔVpp in FIG. 5 exceeds a predetermined value, the above-described high-frequency power (RF) control can be performed.

  As described above, by controlling the potential difference (Vpp) to a fixed relationship, the etching rate can be stabilized and plasma etching can be performed with high accuracy and reproducibility.

  Next, a plasma etching method according to this embodiment performed using the ICP etching apparatus shown in FIGS. 1 to 5 will be described with reference to FIGS.

  FIG. 6 is a flowchart for explaining the steps S01 to S13 of the plasma etching method according to the present embodiment. FIG. 7 is a cross-sectional view schematically showing steps (a) and (b) for forming a concavo-convex shape on a silicon substrate by the plasma etching method of FIG.

  The plasma etching method of FIG. 6 performs plasma etching on a silicon substrate 210 having an etching mask 15 on which a predetermined fine pattern is formed by electron beam drawing / development as shown in FIG. As shown in b), a high aspect ratio concavo-convex shape having the concavo-convex portion 10 having a depth T and a width W is processed.

  First, after a resist is uniformly applied to the silicon substrate 210 (S01), a predetermined fine pattern is drawn on the resist surface with an electron beam (S02), and development is performed with a predetermined developing material (S03). As shown in FIG. 7A, an etching mask 15 having a fine pattern with a thickness t is formed on the surface 210a of the silicon substrate 210.

  In addition, the electron beam drawing in step S02 is performed by the present inventors together with other inventors by using an electron beam drawing apparatus proposed in, for example, Japanese Patent Application Laid-Open No. 2004-107793 and Japanese Patent Application Laid-Open No. 2004-54218. Can do. Thereby, a desired drawing pattern can be formed on the resist film with high accuracy on the order of submicrons by three-dimensional drawing with an electron beam.

  Next, the silicon substrate 210 on which the etching mask 15 is formed is held on the substrate holder 215 in the vacuum plasma chamber 211 of FIG. 1 and set in the ICP etching apparatus 200 (S04). Various conditions such as high-frequency power, high-frequency bias power, and gas flow rate are input from the input setting unit 220 in FIG. 2 and set in the ICP etching apparatus 200 in FIG. 1 (S05).

  Next, after the vacuum plasma chamber 211 is evacuated and depressurized (S06), an etching gas is introduced into the vacuum plasma chamber 211, a high frequency voltage is applied to the electrodes 213 and 214 to generate plasma, and a bias voltage is applied. This is applied to the silicon substrate 210 to start etching the silicon substrate 210 (S07).

  Then, the control unit 100 measures the potential difference (Vpp) with the potential measuring device 230 (S08), and when the difference value ΔVpp in FIG. 5 of the measured value of the potential difference (Vpp) exceeds a predetermined value (S09), the high frequency power ( RF) is controlled so that the potential difference (Vpp) does not vary and has a constant relationship (S10).

  As described above, plasma etching is performed while controlling the potential difference (Vpp) by controlling the high-frequency power (RF). When the etching is completed (S11), the ICP etching apparatus 200 is stopped (S12), and the silicon substrate 210 is vacuum plasma. The chamber 211 is moved (S13). As a result, a concavo-convex shape having a high aspect ratio (T / W) having the concavo-convex portion 10 having a depth T and a width W as shown in FIG. 7B is formed on the surface 210a of the silicon substrate 210.

  As described above, according to the plasma etching method of the present embodiment, the potential difference (Vpp) of the silicon substrate is measured during the plasma etching, and the high-frequency power (RF) is controlled based on the measured value to control the potential difference (Vpp). ) Can be controlled within a predetermined range. For this reason, it is possible to maintain the apparatus stability during execution of the plasma etching and to improve the reproducibility of the plasma etching process. As a result, when the plasma etching is repeatedly performed under the same conditions to form a concavo-convex shape with a high aspect ratio as shown in FIG. 7B on the silicon substrate, the concavo-convex shape can be formed with high accuracy and reproducibility. The productivity of plasma etching is improved.

  Next, a method of manufacturing an optical element using a silicon substrate on which concave and convex shapes are formed by plasma etching in FIGS. 6 and 7 as a molding die will be described with reference to the flowchart of FIG. 8 and FIG.

  FIGS. 9A to 9C are schematic side views of the molding die and the optical element for explaining the steps of manufacturing the optical element by molding with the molding die in FIG.

  The silicon substrate 210 of FIG. 7 having the concavo-convex portion 10 processed into a concavo-convex shape by plasma etching as described above is formed into a molding die C for forming an optical element such as a wave plate or a diffraction grating as shown in FIG. 9A. (S21).

  As shown in FIG. 9A, the material M is set and fixed on the upper surface of the lower mold 31 made of stainless steel or the like, and the molding die C is set and fixed on the lower surface of the upper mold 32 made of stainless steel or the like (S22). ). The material M is preferably an optical element material such as PMMA, polycarbonate, or polyolefin.

  Next, the upper mold 32 is heated to the glass transition temperature of the material M or higher by energizing the heater provided in the upper mold 32 (S23). Next, the upper die 32 is moved downward and pressed against the lower die 31 (S24). As a result, the material M is rapidly heated to the glass transition temperature or higher and melted, and the uneven portion 10 of the molding die C is transferred to the surface (S25).

  Next, energization of the heater of the upper die 32 is stopped, the upper die 32 is naturally cooled (may be forced cooling), and cooling water is supplied to the piping provided in the lower die 31 to forcibly cool the lower die 31. (S26).

  Next, the upper mold 32 is moved upward so as to be separated from the material M (S27), thereby obtaining an optical element having the concavo-convex shape transferred thereto.

  As described above, according to the manufacturing method of the optical element shown in FIGS. 8 and 9, the silicon substrate 210 having the concavo-convex portion 10 in which the molding die C for molding the optical element is accurately formed by the above-described plasma etching method. Therefore, an optical element having an accurate uneven shape can be manufactured. For this reason, optical elements can be mass-produced with high quality using a molding die.

  Next, the plasma etching method according to the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

  As Examples 1, 2, and 3, plasma etching is performed while controlling the variation in potential difference (Vpp) between the substrate and the ground to deepen a groove with a line width of 100 nm on the silicon substrate, thereby forming an uneven shape. did. The plasma etching conditions are as shown in Table 1 below.

  As Comparative Examples 1, 2, and 3, the experiment date was changed by conventional plasma etching, and grooves having a line width of 100 nm were deeply formed under the same conditions as in Table 1 to form uneven shapes.

  FIG. 11 is a graph plotting changes with time in potential difference (Vpp) in each plasma etching of Examples 1, 2, and 3. Table 2 below shows the etching rates in Examples 1, 2, and 3.

  FIG. 10 is a graph plotting changes with time in potential difference (Vpp) in each plasma etching of Comparative Examples 1, 2, and 3. Table 3 below shows etching rates in Comparative Examples 1, 2, and 3.

  In Comparative Examples 1 to 3, as shown in Table 3, the etching rate varied due to the instability of the apparatus. At this plasma etching, as shown in FIG. 10, the potential difference (Vpp) between the substrate and the ground was You can see that it was quite scattered.

  On the other hand, in Examples 1 to 3, as a result of controlling the high frequency power and suppressing the variation in potential difference (Vpp) as shown in FIG. 11, the variation in the etching rate is 1.4% at the maximum as shown in Table 2. The target value was 3.0% or less.

  A scanning electron micrograph of the uneven shape formed on the surface of the silicon substrate in Example 1 is shown in FIG. An uneven shape with a high aspect ratio could be accurately formed on the silicon substrate.

  As described above, the best mode for carrying out the present invention has been described. However, the present invention is not limited to these, and various modifications are possible within the scope of the technical idea of the present invention. For example, the processed shape by the plasma etching method of the present embodiment is a concavo-convex shape, but may be other shapes such as a stepped shape and a sawtooth shape, and at least two of these shapes are mixed. It may be a thing. Further, the electron beam drawing in step S02 of FIG. 6 may draw a fine pattern by another exposure method.

  8 and 9 are for optical elements such as a wave plate having a binary structure and a diffraction grating. However, the present invention is not limited to this, and a stepped echelon diffraction grating is used. And an optical element having a sawtooth diffraction grating, and the optical surface may be a lens surface or a flat surface.

  Alternatively, a molding die mother die may be obtained from the silicon substrate processed by the above-described plasma etching method, and the molding die may be manufactured from the mother die by electroforming or the like.

It is a figure which shows roughly the ICP etching apparatus which can perform the plasma etching method of this Embodiment. It is a block diagram which shows the principal part of the control system of the ICP etching apparatus of FIG. It is a graph which shows an example of the relationship between a potential difference (Vpp) and the etching rate of a to-be-processed base material (silicon substrate) in order to demonstrate the plasma etching method of this Embodiment. It is a graph which shows an example of the relationship between the high frequency electric power (RF) and the potential difference (Vpp) by the high frequency power supply for plasma generation. It is a figure which shows typically the time-dependent change of a potential difference (Vpp) in the plasma etching of this Embodiment. It is a flowchart for demonstrating each step S01 thru | or S13 of the plasma etching method by this Embodiment. It is sectional drawing which shows typically the process (a) and (b) which form an uneven | corrugated shape in a silicon substrate by the plasma etching method of FIG. 6 and 7 are flowcharts for explaining steps S21 to S27 in which an optical element is manufactured using a silicon substrate on which concave and convex shapes are formed by performing plasma etching in FIGS. 6 and 7 as a molding die. FIGS. 9A to 9C are side views schematically showing a molding die and an optical element for explaining a process of manufacturing the optical element by molding with the molding die in FIG. It is the graph which plotted the time-dependent change of potential difference (Vpp) in each plasma etching of the comparative examples 1, 2, and 3. FIG. It is the graph which plotted the time-dependent change of electric potential difference (Vpp) in each plasma etching of Example 1, 2, and 3. FIG. It is a figure which shows the scanning electron micrograph about the uneven | corrugated shape formed in the surface of the silicon substrate in Example 1. FIG.

Explanation of symbols

210 Silicon substrate 210b Bottom surface 210a Surface 10 Concavity and convexity part 100 Control part 200 ICP (inductively coupled plasma) etching device 211 Vacuum plasma chamber 212 High frequency power source 215 for plasma generation Substrate holder 216 Bias high frequency power source 230 Potential measuring device C Mold M Material

Claims (8)

  A plasma etching method comprising controlling a potential of a substrate to be processed during the plasma etching within a predetermined range by controlling high-frequency power based on the potential of the substrate to be processed measured in plasma etching.   The plasma etching method according to claim 1, wherein the potential of the substrate to be processed is controlled based on a change in potential of the substrate to be processed in plasma etching acquired in advance.   3. The plasma etching method according to claim 1, wherein an etching rate of the substrate to be processed is controlled to be substantially constant by controlling a potential of the substrate to be processed within a predetermined range. A vacuum chamber for holding the workpiece substrate therein;
An electric potential measuring unit for measuring the electric potential of the workpiece substrate held in the vacuum chamber;
A high-frequency power source for generating plasma in the vacuum chamber;
A bias high-frequency power source for applying a high-frequency bias power to the workpiece substrate;
A control unit that controls high-frequency power in the high-frequency power source based on the potential of the substrate to be processed measured by the potential measuring unit, and can control the potential of the substrate to be processed during plasma etching within a predetermined range; A plasma etching apparatus comprising:   5. The plasma etching apparatus according to claim 4, wherein the control unit controls the potential of the substrate to be processed based on a potential change of the substrate to be processed in plasma etching acquired in advance.   6. The plasma etching according to claim 4, wherein the control unit controls the etching rate of the substrate to be processed to be substantially constant by controlling the potential of the substrate to be processed within a predetermined range. apparatus.   A molding die for an optical element that can be manufactured from a silicon substrate processed by the plasma etching method according to claim 1. An optical element that can be manufactured using the molding die according to claim 7.