CN102095888B - Heat-type wind-speed and wind-direction sensor with heat insulation structure and preparation method thereof - Google Patents

Abstract

The invention discloses a thermal wind speed and direction sensor with a heat isolation structure, which comprises a silicon chip and a ceramic substrate. Sensing temperature measuring element, a heat insulation groove is arranged between the heating element and the heat sensing temperature measuring element, and a heat insulating cavity is arranged under the heat sensing temperature measuring element on the back of the silicon chip, the silicon chip and the ceramic substrate A gold-on-ceramic layer and a gold-on-silicon layer are arranged therebetween, and the gold-on-ceramic layer and the gold-on-silicon layer are connected through a gold-gold bonding process for thermal connection between the silicon chip and the ceramic substrate. The whole sensor preparation process uses a standard CMOS process, and the post-processing process is simple. The prepared heat insulation groove and heat insulation cavity can effectively enhance the sensitivity of the chip, reduce the heat conduction loss of the chip and the heat capacity of the sensor, and reduce the Response time of small sensors.

Description

Thermal wind speed and direction sensor with thermal isolation structure and preparation method thereof

technical field

The invention relates to a thermal wind speed and direction sensor with a heat isolation structure and is compatible with a standard CMOS process, in particular to an integrated wind speed and direction sensor with low power consumption and a preparation method thereof.

Background technique

In the design of CMOS integrated wind speed and direction sensor, there are two factors that limit its development. On the one hand, there is the problem of packaging. The sensor packaging material requires good thermal conductivity and protection for the sensor, and the design also needs to take into account the impact of the packaging material on sensor sensitivity, reliability, and price. This limits The degree of freedom of the sensor's own packaging design is limited, and the thermal flow sensor requires the sensitive part of the sensor to be exposed to the measurement environment, and at the same time requires the processing circuit to be isolated from the environment, so as not to affect the performance of the processing circuit. The two have conflicting requirements for packaging. . On the other hand, there is the problem of power consumption loss. The thermal wind speed and direction sensor senses changes in the wind through the heat exchange between the heat generated by the heating element on it and the external environment. It uses the forced convection effect, and the overall power consumption of the sensor is in addition to In addition to the heat loss caused by the forced convection effect, it also includes the power loss caused by the heat conduction effect. This part of the power consumption has no effect on the wind perception. Therefore, how to reduce the thermal wind speed and direction sensor caused by the heat conduction effect? The power loss of the sensor has become a big problem in the design of the sensor.

Most of the silicon wind speed and direction sensors reported in the past directly expose the sensitive surface of the silicon wafer to the natural environment, so as to be able to sense the change of the external wind speed. As a result, silicon wafers are easily subject to various contaminations, resulting in unstable performance and even damage. If a ceramic substrate with high thermal conductivity is used, and the silicon chip of the sensor is packaged by flip-chip packaging or thermally conductive adhesive, the above contradictions can be better avoided, but the heat generated by the sensor after packaging is extremely large. Part of it is dissipated from the silicon-based substrate in the form of heat conduction, and only a small part is heat-exchanged with the outside air through the ceramic, which greatly reduces the amplitude of the output sensitive signal, and the sensitive signal can be improved by increasing the power consumption of the sensor. Amplitude, but it causes a large power consumption of the whole sensor system.

Contents of the invention

The object of the present invention is to provide a thermal wind speed and direction sensor with thermal insulation structure and its preparation method. The designed sensor structure and packaging form are conducive to ensuring a large sensitive signal amplitude and at the same time, the sensor system has low power consumption.

The present invention adopts following technical scheme:

A thermal wind speed and direction sensor with a thermal isolation structure, including a silicon chip and a ceramic substrate, the silicon chip is located above the ceramic substrate, and four heating elements and four heat sensing sensors are arranged symmetrically on the four sides of the upper surface of the silicon chip The temperature element is characterized in that a heat-insulating groove is arranged between the heating element and the heat-sensing temperature-measuring element, and a heat-insulating cavity is arranged below the heat-sensing temperature-measuring element on the back of the silicon chip.

A preparation method of a thermal wind speed and direction sensor with a thermal isolation structure is as follows:

The first step, the preparation of the silicon chip

Step 1, thermally growing a first thermal oxide layer on the surface of the silicon chip;

Step 2, chemical vapor deposition of a silicon nitride layer on the first thermal oxide layer;

Step 3, using RIE technology to etch the silicon chip to define the active area;

Step 4, chemical vapor deposition of the second oxide layer;

Step 5, using CMP technology to polish the silicon chip;

Step 6, removing the silicon nitride layer by wet etching, and preparing the field oxide layer;

Step 7, P ion implantation to prepare N well;

Step 8, thermally growing the gate oxide layer;

Step 9, B ion implantation, preparing one end of the heating resistor and the temperature measuring thermocouple;

Step 10, chemical vapor deposition of the third oxide layer;

Step 11, using a dry etching process to prepare through holes on the thermocouple for temperature measurement and through holes on the heating resistor;

Step 12, using a sputtering process to prepare the aluminum pad for electrical lead-out, the other end (13) of the temperature measuring thermocouple, and the pad for electrical lead-out of the heating resistor;

Step 13, using a dry etching process to prepare a thermal insulation tank between the heating resistor and the temperature measuring thermocouple; and using a sputtering and stripping process to prepare a gold layer on silicon for bonding, and the gold layer on silicon is used for the isolation on the back of the silicon chip. A mask for the preparation of the thermal cavity and a gold layer for thermal connection to the ceramic substrate;

Step 14, using a wet etching process to prepare a thermal insulation cavity on the back of the silicon chip and below the temperature measuring thermocouple;

The second step, gold-gold bonding

Step 1, preparing a gold layer on the ceramic by sputtering and stripping on the back of the ceramic substrate;

Step 2, using the gold-gold bonding process to connect the gold layer on the ceramic and the gold layer on the silicon together to realize the thermal connection between the silicon chip and the ceramic substrate;

The third step is dicing to complete the preparation of the wind speed and direction sensor.

In the present invention, the heating element and the thermocouple temperature measuring element in the sensor are prepared in a silicon chip by using a standard CMOS process, and a heat insulation groove is arranged between the heating element and the thermocouple temperature measuring element, and a thermocouple temperature measuring element is placed under the thermocouple temperature measuring element. A heat-insulating cavity is provided, and a gold layer is prepared on the back of the silicon chip and the basic back of the ceramic. The silicon chip and the ceramic substrate are bonded together by gold-gold bonding technology, and the thermal connection between them is realized at the same time. package. Since both the gold layer bonded with gold and the ceramic substrate have certain heat conduction characteristics, the heat generated by the heating element on the silicon chip can be transferred to the ceramic substrate through the thermally conductive adhesive, so a temperature field can be established on the surface of the ceramic substrate. The surface is exposed to the external environment, and the temperature field established by the heating element on the upper surface of the ceramic substrate can sense the change of the wind, and the thermocouple temperature measuring element can measure the change of the temperature distribution of the temperature field through the thermal conductive glue. Under the condition of no wind outside, the distribution of temperature field presents a completely symmetrical state. When the outside wind blows over the upper surface of the ceramic substrate, the wind will take away part of the heat from the upper surface of the ceramic substrate in the form of heat convection, and the thermocouple temperature measuring element can measure the change of the temperature field through the heat conduction of the bonded gold layer. Furthermore, it can reflect the magnitude of the wind speed; the differential output of the symmetrically distributed upstream and downstream thermocouple temperature measuring elements reflects the change of the temperature gradient of the surface temperature field on the ceramic substrate, and can reflect the change information of the wind direction.

The thin-layer ceramic sheet used for packaging in the sensor structure is used as a packaging substrate for protecting the underlying silicon chip on the one hand, and on the other hand as a sensitive element that senses changes in the external wind. Only the upper surface of the whole sensor is in contact with the wind environment, and other components are isolated from the external environment through the ceramic substrate, so it can avoid being polluted by the external environment. Gold-gold bonding provides a thermal connection between the silicon chip and the ceramic substrate. The heat insulation groove is prepared between the heating element and the thermocouple temperature measuring element, which can isolate the heat conduction in the lateral direction of the silicon chip, strengthen the heat conduction in the vertical direction in the sensor chip, and increase the thermal resistance in the horizontal direction, so as to improve the sensitivity of the sensor. The thermal insulation cavity is prepared under the thermocouple temperature measuring element of the silicon chip, which can enhance the signal strength of the thermocouple temperature measuring element, reduce the heat conduction loss of the chip and the heat capacity of the chip, and then reduce the thermal response time of the chip. The design of the heat insulation structure can greatly reduce the useless power consumption caused by the heat conduction effect. The structure of the sensor of the invention is suitable for preparing a two-dimensional wind speed and direction sensor.

In this sensor design scheme, in the first step of silicon chip preparation, the heating element and thermocouple temperature measuring element use the standard CMOS process; in the second step of the preparation of the heat insulation tank, the MEMS dry etching process is used; the second step In the preparation of the thermal insulation cavity under the three-step thermocouple temperature measuring element, the MEMS anisotropic wet etching process is used.

The present invention obtains following effect:

1. The packaging process of the present invention belongs to sensor wafer level packaging. The process introduces a thin-layer ceramic wafer with a certain thermal conductivity as the packaging material of the sensor. The size of the ceramic wafer is exactly the same as that of the silicon chip. The gold layer between the silicon chip and the ceramic chip is used to realize the connection between the silicon chip and the ceramic chip through gold-gold bonding technology. The thermal connection between the silicon chip and the ceramic substrate is achieved by using this process, which can ensure that the thermal connection medium maintains a good geometric shape and material properties, and is more stable than the thermal connection method such as thermal conductive glue. Reliable and maintain good consistency between sensors. Compared with the traditional single-chip packaged wind speed and direction sensor, this form of wafer-level packaging greatly reduces the packaging cost of MEMS devices on the one hand, and on the other hand ensures the consistency of the deviation caused by the sensor package to a large extent. , reducing the cost of sensor back-end signal conditioning.

2. The present invention prepares a heat insulation groove between the heating element and the thermocouple temperature measuring element, which can isolate the heat conduction in the lateral direction of the silicon chip, strengthen the heat conduction in the vertical direction in the sensor chip, and increase the thermal resistance in the horizontal direction, so that the sensor can be improved. sensitivity.

3. The present invention adopts the MEMS anisotropic wet etching process to prepare a thermal insulation cavity under the thermocouple temperature measuring element of the silicon chip, which can enhance the signal strength of the thermocouple temperature measuring element, reduce the heat conduction loss of the chip and the heat capacity of the chip, Further reducing the thermal response time of the chip, it has the characteristics of low cost, good consistency, accurate shape control, and one-time process molding, which is very suitable for the back-end processing of MEMS sensors made by using CMOS standard process.

Description of drawings

FIG. 1 is a schematic diagram of steps 1 to 4 of the fabrication process of a silicon chip.

FIG. 2 is a schematic diagram of steps 5 to 9 of the silicon chip preparation process.

FIG. 3 is a schematic diagram of steps 10 to 14 of the silicon chip fabrication process.

Fig. 4 is a side view of the finished silicon chip.

Figure 5 is a top view of the fabricated silicon chip.

Fig. 6 is a side view of the prepared ceramic substrate.

Fig. 7 is a top view of the prepared ceramic substrate.

Fig. 8 is a thermal connection between a ceramic substrate and a silicon chip using gold-gold bonding.

FIG. 9 is a schematic cross-sectional view of the sensor after scribing.

Detailed ways

Example 1

The manufacturing process of a thermal wind speed and direction sensor with thermal isolation structure is as follows:

The first step, the preparation of the silicon chip, see Figure 1 to Figure 3

Step 1, thermally growing a first thermal oxide layer 2 on the surface of the silicon chip 1;

Step 2, chemical vapor deposition of a silicon nitride layer 3 on the first thermal oxide layer 1;

Step 3, using RIE technology to etch the silicon chip 1 to define the active region 4;

Step 4, chemical vapor deposition of the second oxide layer 5;

Step 5, using CMP technology to polish the silicon chip 1;

Step 6, removing the silicon nitride layer 3 by wet etching, and preparing the field oxide layer 6;

Step 7, P ion implantation to prepare N well 7;

Step 8, thermally growing the gate oxide layer 8;

Step 9, B ion implantation, preparing the heating resistor 9 and one end 10 of the temperature measuring thermocouple 15;

Step 10, chemical vapor deposition of the third oxide layer 11;

Step 11, using a dry etching process to prepare the through hole 12 on the temperature measuring thermocouple 15 and the through hole 20 on the heating resistor 9;

Step 12, using a sputtering process to prepare the aluminum pad 14 for electrical extraction, the other end 13 of the temperature measuring thermocouple 15, and the pad 21 for electrical extraction of the heating resistor 9;

Step 13, using a dry etching process to prepare a thermal insulation tank 16 between the heating resistor 9 and the temperature measuring thermocouple 15; A mask for the preparation of the thermal insulation cavity 17 on the back side of the silicon chip 1 and a gold layer for thermal connection with the ceramic substrate;

Step 14, using a wet etching process to prepare a thermal insulation cavity 17 on the back of the silicon chip 1 and below the temperature measuring thermocouple 15;

The second step is gold-gold bonding, see Figure 6 to Figure 8

Step 1, preparing the gold layer 18 on the ceramics by sputtering and stripping processes on the back of the ceramic substrate 20;

Step 2, using the gold-gold bonding process to connect the gold layer 18 on the ceramic and the gold layer 19 on the silicon together to realize the thermal connection between the silicon chip 1 and the ceramic substrate 20;

The third step is dicing to complete the preparation of the wind speed and direction sensor, as shown in Figure 9.

The invention is a scheme for realizing the preparation and packaging of a CMOS integrated wind speed and direction sensor. The side of the sensor chip that is in contact with the wind in the external environment is the upper surface of the ceramic substrate 20, and the gold layer 18 on the ceramics and the gold layer 19 on the silicon are connected by gold-gold bonding technology as the connection between the silicon chip 1 and the ceramic substrate 20. As the thermal connection medium, since the ceramic material has a certain thermal conductivity, a certain temperature field distribution can be established on the upper surface of the ceramic substrate 20 through the heat generated by the heating element 9 located on the silicon chip 1 . Under no wind conditions, the temperature field distribution is symmetrical around the center of the ceramic substrate 20; under the condition of a certain wind speed in the external environment, the symmetrical distribution is broken, and a temperature gradient field is generated, and the direction of the gradient is consistent with the direction of the wind direction. Four thermocouple temperature measuring elements are distributed around the heating element 9 in a symmetrical layout. The temperature field on the upper surface of the ceramic substrate 20 can be transmitted to the thermocouple temperature measuring element by utilizing the heat conduction characteristics of the gold layer 18 on the ceramic and the gold layer 19 on the silicon, and then the change of the temperature field on the upper surface of the ceramic substrate 20 can be measured. The information of wind speed and wind direction in the external environment can be obtained by processing the output signals of the four thermocouple temperature measuring elements.

In the traditional CMOS integrated wind speed and direction sensor, the heating element and temperature measuring element of the sensor are fabricated on the surface of the silicon chip, and then packaged with the ceramic substrate in the form of flip-chip flip-chip or heat-conducting glue. Since the thermal conductivity of silicon is much greater than that of ceramics, most of the heat generated by the heating element on the silicon after packaging is dissipated from the silicon substrate through heat conduction, and only a small amount of heat passes through the ceramic substrate and the air. Heat convection heat exchange is generated, which on the one hand greatly reduces the output signal of the sensor, on the other hand increases the working power of the sensor and reduces the efficiency of the sensor. Based on this problem, the predecessors proposed to make a cavity on the back of the silicon substrate or make a layer of porous silicon under the heating element to reduce the heat conduction of the silicon substrate, so that the sensor packaging or process consistency and CMOS process compatibility challenged.

In the present invention, a heat insulation groove is prepared between the heating element in the silicon chip and the thermocouple temperature measuring element, which can isolate the heat conduction in the lateral direction of the silicon chip, strengthen the heat conduction in the vertical direction in the sensor chip, and increase the thermal resistance in the horizontal direction , in order to increase the sensitivity of the sensor. The thermal insulation cavity is prepared under the thermocouple temperature measuring element of the silicon chip, which can enhance the signal strength of the thermocouple temperature measuring element, reduce the heat conduction loss of the chip and the heat capacity of the chip, and then reduce the thermal response time of the chip. The design of the heat insulation structure can greatly reduce the useless power consumption caused by the heat conduction effect. Realizing the thermal connection between the silicon chip and the ceramic chip by using the gold-gold bonding process can ensure the reliability of the geometry and material properties of the thermal connection medium and the consistency between the sensors.

Example 2

A thermal wind speed and direction sensor with a thermal isolation structure, comprising a silicon chip 1 and a ceramic substrate 20, the silicon chip 1 is located above the ceramic substrate 20, four heating elements 9 and 4 heat-sensing temperature-measuring elements 15, characterized in that a heat-insulating groove 16 is arranged between the heating element 9 and the heat-sensing temperature-measuring element 15, below the heat-sensing temperature-measuring element 15 on the back side of the silicon chip 1 A heat insulation cavity 17 is provided, and a gold layer 18 on ceramics and a gold layer 19 on silicon are provided between the silicon chip 1 and the ceramic substrate 20, and the gold layer 18 on ceramics and the gold layer 19 on silicon are connected through a gold-gold bonding process, It is used for thermal connection between the silicon chip 1 and the ceramic substrate 20 .

Claims (1)

1. preparation method with hot type wind speed wind direction sensor of heat insulation structure; Described hot type wind speed wind direction sensor with heat insulation structure; Comprise silicon (1) and ceramic substrate (20); Silicon (1) is positioned at the top of ceramic substrate (20), and being symmetrically distributed on upper surface four limits of silicon (1) is provided with 4 heating resistors (9) and 4 temperature thermocouples (15), it is characterized in that between heating resistor (9) and temperature thermocouple (15), being provided with heat dam (16); Below at silicon (1) back side, temperature thermocouple (15) is provided with heat insulation cavity (17), it is characterized in that:

The first step, the preparation of silicon

Step 1 is at silicon (1) surface heat first thermal oxide layer (2) of growing;

Step 2 goes up chemical vapor deposition silicon nitride layer (3) at first thermal oxide layer (1);

Step 3 utilizes the RIE technology that silicon (1) is carried out etching, definition active area (4);

Step 4, chemical vapor deposition second oxide layer (5);

Step 5 utilizes the CMP technology that silicon (1) is carried out polishing;

Step 6, wet etching is removed silicon nitride layer (3), and field oxide (6) is accomplished in preparation;

Step 7, the P ion injects, preparation N trap (7);

Step 8, heat growth gate oxide (8);

Step 9, the B ion injects, an end (10) of preparation heating resistor (9) and temperature thermocouple (15);

Step 10, chemical vapor deposition the 3rd oxide layer (11);

Step 11 utilizes dry etch process to prepare the last through hole (12) of temperature thermocouple (15) and heating resistor (9) is gone up through hole (20);

Step 12 is utilized sputtering technology to prepare electricity and is drawn with another end (13) and heating resistor (9) electricity of aluminum pad (14) and temperature thermocouple (15) and draw with pad (21);

Step 13 utilizes dry etch process between heating resistor (9) and temperature thermocouple (15), to prepare heat dam (16); And utilize sputter and stripping technology the preparation bonding with silicon on gold layer (19), gold layer (19) is used for the mask of the heat insulation cavity in silicon (1) back side (17) preparation and carries out hot tie-in with ceramic substrate on the silicon;

Step 14 utilizes wet corrosion technique at silicon (1) back side, temperature thermocouple (15) below preparation heat insulation cavity (17);

Second step, golden gold bonding

Step 1 utilizes sputter and stripping technology preparation pottery to go up gold layer (18) at the back side of ceramic substrate (20);

Step 2 utilizes golden gold bonding technology that gold layer (19) on gold layer (18) and the silicon on the pottery is linked together, and realizes the hot tie-in between silicon (1) and the ceramic substrate (20);

In the 3rd step, the preparation of wind speed wind direction sensor is accomplished in scribing.

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