Heat dissipation structure for deep groove etching process

Abstract

The invention discloses a heat dissipation structure for a deep groove etching process, belongs to the technical field of chip manufacturing, and particularly relates to a heat dissipation structure which is characterized in that after an MEMS structural layer is isolated into a peripheral structure and a suspended MEMS functional structure by an isolation trench, the MEMS functional structure needs to be continuously etched to form a gap for isolating the MEMS functional structure into each movable functional unit; heat generated in the etching process cannot be dissipated, the micro-load effect of etching is utilized, a heat dissipation structure is arranged in an isolation trench, a deep groove with a large depth-to-width ratio is formed between the heat dissipation structure and an MEMS functional structure, and a channel for the MEMS functional structure to dissipate heat to a peripheral area anchor point is reserved, so that the heat generated during etching of the MEMS functional structure can be dissipated through the peripheral area anchor point, and the heat dissipation efficiency of the MEMS functional structure is improved. The etching process is ensured to be normally completed, the heat dissipation problem of the suspended structure in the etching process is effectively solved, the process capability is improved, and the etching morphology meets the design requirement.

Description

Technical Field

[0001] The invention belongs to the technical field of chip manufacturing, and in particular relates to a heat dissipation structure used in a deep groove etching process. Background Art

[0002] MEMS (Micro-Electro-Mechanical Systems) is the abbreviation of micro-electromechanical systems. MEMS manufacturing technology uses micro-machining technology, especially semiconductor wafer manufacturing technology, to manufacture various micro-mechanical structures, combined with application-specific control integrated circuits (ASICs), to form intelligent micro-sensors, micro-actuators, micro-optical devices and other MEMS components. MEMS components have the advantages of small size, low cost, high reliability, strong resistance to harsh environments, low power consumption, high intelligence, easy calibration, and easy integration. They are widely used in consumer electronic products represented by smartphones. Taking smartphones as an example, they use MEMS components such as gyroscopes, accelerometers, altimeters, microphones, electronic compasses, tuned antennas, filters, etc. MEMS accelerometers are the most widely used among them. Every smartphone, even feature phones, are equipped with MEMS accelerometers as standard. In order to improve the accuracy of MEMS accelerometers, it is necessary to ensure that the etching morphology and size of key structures are within the specifications.

[0003] High aspect ratio etching process is an important process step in the processing of MEMS devices. For silicon materials, high aspect ratio etching process usually adopts Bosch process, which is an etching-passivation cycle process using octafluorocyclobutane (C 4 F 8 ) decomposition byproducts (i.e. polymers) as a passivation layer, with sulfur hexafluoride (SF 6 ) is used as the main etching gas, among which octafluorocyclobutane is a non-toxic and stable di-polytetrafluoroethylene. The byproducts decomposed in the plasma reaction chamber can be easily removed from the bottom of the etching by low-energy ion bombardment without leaving any residue. 6 ) and octafluorocyclobutane (C 4 F 8 ) exist in the plasma at the same time, the two substances will merge and disappear together. In order to solve the problem that the mixture makes the etching process difficult to control, the etching and passivation gases are alternately introduced into the process chamber separately to form a passivation cycle and an etching cycle. In the passivation cycle, C 4 F 8 The formed Teflon-like polymer film is deposited on the sidewalls and bottom. In the following etching cycle, the polymer at the bottom of the trench is bombarded by ions and reacts with the SF 6The fluorocarbons formed by the generated plasma radicals are removed, while the F ions and radicals will etch the silicon at the bottom, while the polymer on the sidewalls is not bombarded by ions and remains on the sidewalls, preventing the F ions from etching the sidewalls of the MEMS structure during the etching cycle. By alternating passivation and etching, sulfur hexafluoride and octafluorocyclobutane can etch and passivate the substrate under high concentration conditions, respectively, reducing the loss caused by the carbon fluoride polymerization reaction caused by the mixing of the two gases, greatly improving the selectivity of anisotropic etching, and the polymer on the sidewalls is easy to remove.

[0004] The heat generated during the etching process is conducted to the wafer substrate through the MEMS structure, anchor points and peripheral structures. The wafer substrate contacts the chuck of the etching equipment, and the heat is finally conducted out of the etching cavity by the chuck. As the etching process of the MEMS structure proceeds, the grooves of the MEMS structure are gradually formed, and the heat conduction cross-sectional area between the anchor points and the peripheral structure gradually decreases, that is, the thermal resistance gradually increases. When the MEMS structure is completely separated from the peripheral structure, the heat can only be conducted to the substrate through the spring or connecting rod connected to the anchor point. Since the spring or connecting rod is slender in shape, has a small cross-sectional area, and has a small number of anchor points, the thermal resistance is very large at this time. The heat accumulates in the etching area, which will cause the local temperature to rise, which will not only increase the etching rate of the photoresist protecting the MEMS pattern, but also affect the formation of the polymer (Polymer) protecting the sidewall, thereby increasing the lateral corrosion rate of the MEMS structure and seriously deforming the etching morphology.

[0005] The patent (CN112723298B) shows a heat dissipation compensation microstructure for etching MEMS micromirror devices. The heat dissipation structure connects the MEMS structural layer and the substrate layer. Before the structural layer is etched through, the heat generated by the etching is transferred to the substrate through the heat dissipation structure; after the structural layer is etched through, the reactive ions will continue to etch the heat dissipation column. In this patent, the heat dissipation column is actually a vertical driving electrode, so this method is not suitable for MEMS structures without vertical driving electrodes. Summary of the invention

[0006] The technical problem to be solved by the present invention is that when the MEMS structure is a suspended structure and the isolation groove is etched clean first, the heat generated by the MEMS functional structure during deep groove etching to form a gap cannot be efficiently conducted to the substrate through the anchor point and dissipated through the equipment chuck, resulting in a temperature increase in the local area and causing abnormal etching morphology. A heat dissipation structure for deep groove etching process is proposed.

[0007] In order to solve the above technical problems, the present invention provides a heat dissipation structure suitable for all MEMS structures, especially suspended MEMS structures without vertical driving electrodes in the deep groove etching process. By arranging the heat dissipation structure in the isolation groove, the depth-to-width ratio of the deep groove between the heat dissipation structure and the MEMS functional structure is greater than the depth-to-width ratio of the gap to be etched of the MEMS functional structure. Before the etching of the gap to be etched of the MEMS functional structure is completed, the heat dissipation structure can be used to transfer heat to the anchor points and the substrate in the peripheral area, and finally the etching cavity is guided out by the chuck, so that the etching process is completed normally and a morphology that meets the requirements is formed.

[0008] The heat dissipation structure for deep groove etching of the MEMS structure includes a MEMS structure layer, an anchor point layer and a substrate arranged in sequence from top to bottom. The MEMS structure layer is isolated by an isolation groove into a peripheral structure and a suspended MEMS functional structure. There is a lower cavity between the MEM functional structure and the substrate. The peripheral structure is connected to the substrate through a peripheral area anchor point, and the MEMS functional structure is connected to the substrate through a functional area anchor point. The MEMS functional structure includes a plurality of functional units, each of which has a gap between them, and the width of the gap is greater than the width of the isolation groove. A heat dissipation structure is provided in the isolation groove for transferring the heat generated when the MEMS functional structure is etched to the peripheral area anchor point. A deep groove is formed between the heat dissipation structure and the MEMS functional structure, and the depth-to-width ratio of the deep groove is greater than the depth-to-width ratio of the gap.

[0009] When the MEMS structure layer is etched through a mask to form an isolation groove and the MEMS structure layer is isolated into a peripheral structure and a MEMS functional structure, the peripheral structure serves as a protection zone to prevent overflow of the sealing solder and limit excessive displacement of the movable structure, and forms a sealing ring with the cover plate. It has a large bonding area with the substrate, has high thermal conductivity, and strong heat dissipation capability. During the etching process, the area near the anchor point in the peripheral area is etched clean first, and then the MEMS functional structure needs to be etched deep to form a gap, isolating the MEMS functional structure into active MEMS functional units, such as springs, connecting beams, comb teeth, mass blocks, anchor points, etc. When the MEMS functional structure is etched deep, due to the isolation of the isolation groove, the heat generated by the etching can only be transferred to the substrate through the anchor points in the functional area for heat dissipation. However, the number of anchor points in the functional area is small and the cross-sectional area is small. The large amount of heat generated by the deep groove etching cannot be conducted to the substrate, resulting in local heating inside the gap. When the temperature is too high, the etching rate of the photoresist mask used to protect the MEMS pattern will increase, and at the same time, the octafluorocyclobutane (C 4 F 8), thereby increasing the etching rate of the MEMS functional structure in all directions, and the final morphology is seriously deformed. Therefore, in order to ensure the accuracy of the structural dimensions and the perfection of the cross-sectional morphology after etching, an effective method is to conduct the heat generated during the etching process through the peripheral area anchor point connected to the peripheral structure. The specific solution is to use the micro-load effect of etching (that is, the smaller the area of ​​the local pattern to be etched, the slower the etching rate), and add a heat dissipation structure in the etching area close to the peripheral area anchor point. A deep groove with a large aspect ratio can be formed between the heat dissipation structure and the MEMS functional structure to reduce the etching rate, retaining the path for the MEMS functional structure to dissipate heat to the peripheral area anchor point, and ensuring that the etching process is completed normally. It can effectively solve the heat dissipation problem of the suspended structure during the etching process and improve the process capability. The present invention arranges a heat dissipation structure in the isolation groove, and forms a deep groove between the heat dissipation structure and the MEMS functional structure. Since the aspect ratio of the deep groove is greater than the aspect ratio of the gap, the deep groove will not be etched through before the gap is etched through. The heat generated by etching the deep groove of the MEMS functional structure can be transferred to the anchor point of the peripheral area through the heat dissipation structure, and then transferred to the substrate through the anchor point of the peripheral area for heat dissipation, thereby solving the problem of abnormal morphology caused by the inability to dissipate heat when etching the deep groove of the MEMS functional structure, and the etching morphology meets the design requirements.

[0010] Furthermore, the product of the number and area of ​​the functional area anchor points is smaller than the product of the number and area of ​​the peripheral area anchor points, so that the MEMS functional units formed by etching can move freely, reducing the constraints of the anchor points on the MEMS functional units.

[0011] Furthermore, the etching rate of the deep groove is lower than the etching rate of the gap, ensuring that the deep groove is not etched through before the gap is etched through, that is, part of the heat dissipation structure is still retained and not etched away, thereby forming a heat dissipation path.

[0012] Furthermore, the functional unit is a comb tooth, a resonant beam, a spring and / or a micromirror.

[0013] Furthermore, the cross-section of the heat dissipation structure is rectangular or trapezoidal, and the shape, size and number of the heat dissipation structure are related to the heat dissipation requirements and the width of the isolation trench.

[0014] Furthermore, the material of the MEMS functional structure is the same as that of the peripheral structure, which facilitates the manufacture of the device and makes it easy to control the etching degree of the isolation trench and the gap.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) The heat dissipation structure is located in the isolation trench, and there is a deep groove between it and the MEMS functional structure, which does not change the MEMS functional structure and does not affect the performance of the MEMS device;

[0017] (2) The heat generated by deep trench etching of MEMS functional structures can be transferred in time, solving the problem of abnormal morphology caused by the inability to dissipate heat during deep trench etching of MEMS functional structures. The etching morphology meets the design requirements.

[0018] (3) The heat dissipation structure is located in the isolation trench and is suitable for all MEMS structures, especially the heat dissipation of deep trench etching of suspended MEMS structures without vertical driving electrodes, and has strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a cross-sectional view of the MEMS structure to be processed.

[0020] Figure 2 It is a cross-sectional view of the MEMS structure after the isolation trench is etched through.

[0021] Figure 3 This is a cross-sectional view of the MEMS structure after the gap is etched through.

[0022] Figure 4 It is a structural diagram of the peripheral structure and the MEMS functional structure;

[0023] Figure 5 It is another structural diagram of the peripheral structure and the MEMS functional structure;

[0024] Figure 6 This is a schematic diagram of heat conduction during etching of MEMS functional structures.

[0025] Figure 7 This is the etching morphology of the gap when no heat dissipation structure is used.

[0026] Figure 8 It is a schematic diagram of the heat dissipation structure.

[0027] Fig. 9 This is a schematic diagram of heat conduction during etching of MEMS functional structures when a heat dissipation structure is used.

[0028] Fig.10 This is the etching morphology of the gap when using a heat dissipation structure.

[0029] Fig.11 It is a shape of heat dissipation structure.

[0030] Fig.12 It is another shape of heat dissipation structure. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0032] A heat dissipation structure for a deep trench etching process includes a MEMS structure layer 101, an anchor layer 102 and a substrate 103 arranged in sequence from top to bottom. The MEMS structure layer 101 and the anchor layer 102 are bonded by silicon-silicon bonding or gold-silicon bonding, and the anchor layer 102 is bonded to the substrate 103. The substrate 103 can be a silicon wafer, a glass wafer or an SOI (Silicon-on-Insulator) silicon wafer material. The MEMS structure layer 101 is isolated by the isolation groove 105 into a peripheral structure 205 and a suspended MEMS functional structure 206. The MEMS functional structure 206 is made of the same material as the peripheral structure 205. There is a lower cavity 104 between the MEMS functional structure 205 and the substrate 103. The peripheral structure 205 is connected to the substrate 103 via the peripheral region anchor point 204. The MEMS functional structure 206 is connected to the substrate 103 via the functional region anchor point 201. The product of the number and area of ​​the functional region anchor points 201 is less than the product of the number and area of ​​the peripheral region anchor points 204. The MEMS functional structure 206 is connected to the substrate 103 via the functional region anchor point 201. 06 includes several functional units, such as comb teeth, resonant beams, springs and / or micromirrors, etc., and there is a gap 106 between each functional unit, and the width of the gap 106 is greater than the width of the isolation groove 105; a heat dissipation structure 207 is provided in the isolation groove 105, which is used to transfer the heat generated during the etching of the MEMS functional structure 206 to the peripheral area anchor point 204, and a deep groove 208 is formed between the heat dissipation structure 207 and the MEMS functional structure 206, and the depth-to-width ratio of the deep groove 208 is greater than the depth-to-width ratio of the gap 106, and the etching rate of the heat dissipation structure 207 is lower than the etching rate of the MEMS functional structure 206.

[0033] The MEMS structure to be processed is a suspended structure, such as Figure 1 As shown, from top to bottom it is composed of a MEMS structure layer 101, an anchor layer 102 and a substrate 103. The MEMS structure layer 101 is connected to the substrate 103 through the anchor layer 102. There is a lower cavity 104 between the MEMS structure layer 101 and the substrate 103. The lower cavity 104 and the upper cavity on the MEMS device cover can form a sealed cavity for the activity of the MEMS functional structure. The sealed cavity is generally a vacuum cavity.

[0034] In the process of etching the MEMS structure layer 101, an isolation trench 105 is formed by deep trench etching to isolate the MEMS structure layer 101 into a peripheral structure 205 and a MEMS functional structure 206. Figure 2 As shown, the MEMS functional structure 206 is connected to the substrate through the functional region anchor 201, and the peripheral structure 205 is connected to the substrate through the peripheral region anchor 204. When the isolation trench 105 is etched, the MEMS functional structure 206 is also etched to form the gap 106. However, since the width of the isolation trench 105 is smaller than the width of the gap 106 to be etched, when the isolation trench 105 is etched through, the gap 106 is not etched through. Figure 2 As shown, it is necessary to continue to perform deep trench etching on the MEMS functional structure 206 to form a gap 106, which is used to isolate the MEMS functional structure 206 into various functional units that can move, such as comb teeth, resonant beams, springs, micromirrors, etc. Figure 3 shown.

[0035] In the plan view, Figure 4 or Figure 5 As shown, the isolation groove 105 is used to electrically isolate the peripheral structure 205 from the MEMS functional structure 206, and the gap 106 is used to form different functional units. The width of the gap 106 is greater than the width of the isolation groove 105. Therefore, the etching rate of the isolation groove 105 is faster than the etching rate of the gap 106. When the isolation groove 105 has not been completely etched, the heat generated by the gap 106 during the etching process is mainly dissipated by Figure 6 The heat is conducted to the peripheral region anchor point 204 through the path shown, and finally conducted to the device chuck through the substrate 103 for heat dissipation. When the isolation groove 105 is completely etched, the heat dissipation path to the peripheral region anchor point 204 is disconnected, and heat can only be transferred to the substrate 103 through the functional region anchor point 201. However, the functional region anchor points 201 are small in area and few in number, and the large amount of heat generated by etching the gap 106 cannot be conducted to the substrate 103, resulting in local heating of the gap 106. When the temperature is too high, the etching rate of the photoresist mask used to protect the MEMS pattern will increase, and at the same time, the protective octafluorocyclobutane (C 2+) layer cannot be formed on the sidewall of the gap 106. 4 F 8 ), so the etched morphology is as follows Figure 7 As shown, this morphology obviously cannot meet the design requirements.

[0036] In order to solve the problem of abnormal etching morphology of the gap 106, a heat dissipation structure 207 is added in the isolation trench 105, such as Figure 8 As shown, a deep groove 208 with a high aspect ratio is formed between the heat dissipation structure 207 and the MEMS functional structure 206. Since the aspect ratio of the deep groove 208 is greater than the aspect ratio of the gap 106, the etching rate of the deep groove 208 is lower than that of the gap 106. After the isolation groove 105 is etched, the heat generated by etching the gap 106 can still be conducted to the peripheral region anchor point 204 through the heat dissipation structure 207 that has not been etched, and finally conducted to the device chuck through the substrate 103 for heat dissipation, as shown in FIG. Fig. 9 Finally, the gap 106 is etched before the deep groove 208 is etched through, which solves the problem of abnormal morphology of the gap 106 due to the inability to dissipate heat after the isolation groove 105 is etched open. After adding the heat dissipation structure 207, the etching morphology of the MEMS functional structure 206 is as follows: Fig.10 As shown, it meets the design requirements.

[0037] The heat dissipation structure 207 is a structure designed in the isolation trench 105, which locally forms a higher aspect ratio than other structures (such as the gap 106). According to the heat dissipation requirements and the width of the isolation trench 105, the heat dissipation structure can also be other shapes, such as Fig.11 The rectangle shown or Fig.12 Trapezoid shown.

[0038] The heat dissipation structure 207 is a method for adjusting the deep groove etching morphology. By adjusting the aspect ratio of some areas, the etching rate is reduced to ensure that the heat generated during etching of other areas can be extracted from the heat dissipation structure. When all structures are etched, the heat dissipation structure 207 is completely etched.

[0039] The above is only the best embodiment of the present invention. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several modifications or equivalent substitutions can be made to the technical solution of the present invention, which should also be regarded as falling within the protection scope of the present invention.

Claims

1. A heat dissipation structure for a deep trench etching process, comprising a MEMS structure layer, an anchor layer and a substrate arranged in sequence from top to bottom, characterized in that: The MEMS structural layer is isolated by an isolation groove into a peripheral structure and a suspended MEMS functional structure. There is a lower cavity between the MEM functional structure and the substrate. The peripheral structure is connected to the substrate through a peripheral area anchor point, and the MEMS functional structure is connected to the substrate through a functional area anchor point. The MEMS functional structure includes a plurality of functional units, each of which has a gap between them, and the width of the gap is greater than the width of the isolation groove. A heat dissipation structure is provided in the isolation groove for transferring the heat generated during the etching of the MEMS functional structure to the peripheral area anchor point. A deep groove is formed between the heat dissipation structure and the MEMS functional structure, and the depth-to-width ratio of the deep groove is greater than the depth-to-width ratio of the gap.

2. The heat dissipation structure for deep trench etching process according to claim 1, characterized in that: The product of the number of anchor points and the area of ​​the functional area is smaller than the product of the number of anchor points and the area of ​​the peripheral area.

3. The heat dissipation structure for deep trench etching process according to claim 1 or 2, characterized in that: The etching rate of deep trenches is lower than that of gaps.

4. The heat dissipation structure for deep trench etching process according to claim 1, characterized in that: The functional units are comb teeth, resonant beams, springs and / or micromirrors.

5. The heat dissipation structure for deep trench etching process according to claim 1 or 2, characterized in that: The cross section of the heat dissipation structure is rectangular.

6. The heat dissipation structure for deep trench etching process according to claim 1 or 2, characterized in that: The cross section of the heat dissipation structure is trapezoidal.

7. The heat dissipation structure for deep trench etching process according to claim 1, characterized in that: The material of the MEMS functional structure is the same as that of the peripheral structure.

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