CN102570018B - A Method of Making Integrated RF Patch Microstrip Antenna Based on BCB/Au - Google Patents

Abstract

The invention relates to a manufacturing method of an integrated patch antenna based on BCB/Au on a silicon base. It is characterized in that a deep groove is etched on the substrate silicon to increase the thickness of the dielectric material, thereby increasing the bandwidth of the antenna; the material filled in the groove is the same as the dielectric material of the transmission line, which is BCB with a low dielectric constant. The manufacturing process is as follows: first, etch a deep groove on the silicon base to increase the thickness of the dielectric material, sputter a layer of seed layer, and electroplate gold as the ground plane of the antenna; fill the groove with dielectric material, and control the temperature for curing ; Then drill Au pillars as via holes to lead out the ground wire; then coat a layer of BCB dielectric material, and perform CMP thinning and polishing after curing to increase surface flatness and expose the via holes; finally, photolithographically plate the antenna on the BCB graphics. This manufacturing method enables the antenna and the integrated circuit to be made together, which reduces the volume and improves the reliability, and at the same time reduces the transmission distance between the antenna transmitting module and the antenna, and reduces the transmission loss.

Description

A Method of Making Integrated RF Patch Microstrip Antenna Based on BCB/Au

technical field

The invention provides a microwave radio frequency antenna method manufactured by a microelectronic technology, which is used for wafer-level packaging and belongs to the technical field of wafer-level radio frequency packaging.

Background technique

Antennas are indispensable in the field of wireless radio frequency. The microstrip antenna is a new type of antenna successfully developed in the early 1970s. Compared with commonly used microwave antennas, it has the following advantages: small size, light weight, low profile, conformal to the carrier, simple manufacturing, and low cost; the electrical feature is that it can obtain a single-directional wide-lobe pattern, The maximum radiation direction is in the normal direction of the plane, easy to integrate with microstrip lines, and easy to realize linear polarization or circular polarization. Microstrip antennas with the same structure can form a microstrip antenna array to obtain higher gain and larger bandwidth. Therefore, microstrip antennas are getting more and more attention. The traditional radio frequency patch antenna is generally made on a PCB (printed circuit board) and connected to the transmitting circuit through a coaxial cable. Although this method has many of the above advantages, the dielectric constant, thickness of the substrate material, and the size consistency of the antenna are poor, especially in relatively high frequency bands, and these errors will have a great impact on the antenna parameters. After it comes out, it needs further debugging before it can be used, which reduces the production efficiency and increases the cost. In addition, the traditional patch antenna and integrated circuit are separated, and when they are connected together, they will be limited by the connector, which will cause some problems: such as impedance matching, parasitic inductance, parasitic capacitance and so on.

Due to the above shortcomings, the antenna made on the silicon chip came into being. Together with the integrated circuit, this kind of antenna has precise manufacturing process and good consistency, and has been widely used. However, this kind of antenna has a disadvantage, that is, the substrate is relatively thin, generally only tens of μm or even less than 1 μm, which greatly reduces the bandwidth. It is difficult to increase the thickness h of the substrate on silicon. The common method in literature reports is to etch grooves on silicon, fill the grooves with solid dielectric materials to make the height consistent with the surrounding, and then use liquid to make antenna patterns on it. This method makes the antenna substrate have at least two kinds of materials, the antenna loss increases, and the antenna pattern and the substrate material of the feeder are different, which is easy to cause impedance mismatch, and the simulation and process production are more troublesome; the other is to fill in the slot and The same dielectric material (usually liquid) in other areas, and then solidified, this method can also be used when the depth of the groove is relatively shallow, but when the depth is large, it often leads to poor flatness of the antenna surface, which is harmful to the antenna. cause adverse effects.

Contents of the invention

For the shortcomings of traditional patch antennas, the purpose of the present invention is to propose a method for making integrated radio frequency patch microstrip antennas based on BCB/Au, especially to improve the above-mentioned method of etching grooves, so that in the case of large depths, It is possible to use the same material and keep the flatness above and around the slot consistent. This method is fully compatible with the embedded wafer-level RF packaging process, and can be fabricated together with the MMIC (Monolithic Microwave Integrated Circuit) packaging process without additional steps.

The specific production scheme of the present invention: a) using silicon oxide as a mask, etch a deep groove with a depth of 200-400 μm on the silicon wafer with anisotropic etching solution KOH;

b) In the deep groove formed in step a, fill the BCB material with a relative dielectric constant <3.5, and use the surface tension of the liquid to make the liquid surface of BCB (benzocyclobutene benzocyclobutene) higher than the plane of the silicon wafer, higher than the Volume compensates for shrinkage of filled BCB upon curing;

c) The silicon wafer filled with BCB in the deep groove of step b is placed in a thermal reflow oven and cured in two stages. The first stage curing temperature is 170-190°C; Normal temperature; to ensure that the BCB dielectric material filled in the subsequent high temperature will no longer shrink; at the same time, the surface of the filled BCB after curing is not flat, and the middle depression is surrounded by protrusions;

d) After step c is solidified, the balls are planted to form Au solder balls, and the ground wire of the antenna is drawn out;

e) Coat a layer of BCB on the gluing machine, stand still for 2-4 hours after coating, then solidify, raise the temperature from normal temperature to 210-230°C for 20-40min, keep it warm for 40-60min, and finally cool down linearly. The time is 20-40min; to further improve the flatness of the surface;

f) After step e is completed, perform a CMP (Chemical Mechanical Planarization) process to make the surface smoother and expose the Au solder balls;

g) The method of photolithography electroplating makes the pattern of antenna above the deep groove, and its steps are:

① First, a layer of seed layer TiW/Au is sputtered on the surface of BCB with thicknesses of

② Then apply photoresist, photolithography, develop, expose the antenna pattern window above the groove, and then electroplate Au;

③Finally remove the glue and remove the seed layer, leaving the antenna pattern.

Its further characteristics are:

(1) In step e, another layer of BCB dielectric layer is coated with a thickness of 20-50 μm.

(2) In the step c, the curing temperature of the first stage is 180°C, and the curing temperature of the second stage is 230°C.

(3) The height of the Au solder balls described in step d is 20-50 μm.

(4) The height of the Au solder balls described in step d is 30-40 μm.

(5) In step e, another layer of BCB dielectric layer is coated with a thickness of 25-40 μm.

(6) The thickness of the electroplated Au in ② in the step g is 2-5 μm.

(7) The described method is characterized in that:

① In the first stage of step c, the temperature is raised from room temperature to 170-190°C for 60 minutes, so that the BCB is slowly solidified, the BCB is fully flowing, and the depression caused by shrinkage is as small as possible;

②Then raise the temperature to 210-250°C to make BCB fully solidified, and the whole process of the first and second stages is controlled within 120min.

(8) The material with a dielectric constant <3.5 described in step b is PI, which is also cured by heating.

The cross-sectional view and top view of the finished antenna are shown in f(a) and f(b) of Fig. 1 respectively. The antenna is integrated on the silicon substrate, and the thickness of the dielectric substrate is increased by digging deep grooves.

This kind of antenna overcomes the shortcoming of the thin substrate of the silicon-based integrated antenna. Compared with the traditional silicon-based integrated antenna, it can significantly increase the bandwidth of the antenna and improve the performance of the antenna. It can be seen from the production process that this production process is compatible with embedded chip packaging, and its production process is compatible with microelectronics technology. It can be carried out together with the MMCM (Microwave multichip module) packaging process, and at the wafer level Encapsulation is done on a basis. No additional process steps are required. Therefore, the antenna manufactured by this method can be packaged together with the chip. Compared with the traditional external antenna method, the transmission distance between the antenna transmitting module and the antenna is reduced, thereby reducing the loss. At the same time, the antenna is integrated with the chip, which improves the reliability and reduces the volume, which is in line with the trend of modern integrated circuit packaging.

Description of drawings

Figure 1: Microstrip patch antenna fabrication process.

a) Etching a deep groove on the silicon base with KOH etching solution;

b) filling the tank with excess BCB;

c) curing the BCB and planting balls on the substrate;

d) Coating a layer of BCB on the surface of the silicon substrate by spin coating;

e) CMP is performed to expose the Au solder balls, and the BCB reaches a suitable thickness and the surface is smooth;

f) Use the electroplating method to make antenna patterns on the upper surface of the BCB, where f (a) is a cross-sectional view of the finished antenna, f (b) is a top view, and 102 is the silicon-based surface stratum among the figures; 103 is the medium filled in the groove electrical material; 104 is a via hole on the surface dielectric material, that is, a solder ball; 105 is an antenna pattern on the upper side of the groove.

Figure 2: Temperature profile of BCB solidification in an etch bath.

Figure 3: Temperature profile of surface BCB curing.

Detailed ways

Embodiments of the present invention will be further specifically described below with reference to the accompanying drawings. The scope of the present invention is not limited to the following examples.

Example:

作为种子层，电镀Au大约3μm，作为天线的地平面(102)。(1) Etch a deep groove on the surface of silicon (101) with KOH, the depth is 200μm-400μm, this example is 300μm, sputter a layer of TiW/Au, the thickness is respectively

As a seed layer, about 3 μm of Au is plated, which serves as a ground plane (102) for the antenna.

(2) Fill the tank with a low dielectric constant material that is excessively filled with liquid. This example is BCB (103). Inject as much dielectric material as possible without overflowing the edge of the tank, and then cure it in a reflow oven. The temperature curve is shown in Figure 2. In the first 60 minutes, the BCB is cured slowly at a lower temperature (180°C) (i.e. room temperature or room temperature ~ 180°C), and at the same time, the BCB can flow fully, and the depression caused by shrinkage should be minimized, and then rise To 230°C, the BCB is completely cured, and then lowered to room temperature, the whole process takes 120 minutes. Described room temperature or normal temperature is 18-25 ℃.

(3) After solidification, the balls are planted (104), and the ground wire is drawn out. The height of the Au solder balls is about 30-40 μm.

(4) Coat BCB (103) on the gluing machine again with a thickness of 30 μm. After coating, let it stand for more than 2 hours to make the surface smoother, and then solidify. The solidification time curve is shown in Figure 3. In this embodiment The curing temperature of the middle surface BCB is 205°C, which makes the BCB basically cured but not completely, which is beneficial to the subsequent CMP process.

(5) Perform a CMP process to make the surface smoother, expose the Au solder balls (104), and make the thickness of the surface layer BCB be 25-40 μm.

(6) Making antenna patterns (105) on the surface by electroplating, and finally completing the manufacturing process of the antenna.

Claims (10)

1. A method for making a microstrip antenna of a radio frequency patch, characterized in that the steps of making are: a) Using silicon oxide as a mask, etch a deep groove with a depth of 200-400 μm on the silicon wafer with anisotropic etching solution KOH; b) In the deep groove formed in step a, fill the BCB material with a relative dielectric constant <3.5, and use the surface tension of the liquid to make the surface of the BCB liquid higher than the plane of the silicon wafer, and the higher volume compensates for the solidification of the filled BCB shrink; c) Put the silicon wafer filled with BCB in the deep groove in step b to cure in a thermal reflow oven, and slowly cure BCB at a lower temperature for the first 60 minutes. At the same time, BCB can flow sufficiently to minimize the depression caused by shrinkage, and then rise to 230°C to make the BCB fully cured, and then lower it to room temperature. The whole process takes 120 minutes to ensure that the BCB dielectric material filled in the subsequent high temperature will no longer shrink; at the same time, the surface of the BCB filled after curing is not flat, and the middle depression is surrounded by protrusions; d) After step c is solidified, the balls are planted to form Au solder balls, and the ground wire of the antenna is drawn out; e) Coat a layer of BCB on the gluing machine, stand still for 2-4 hours after coating, then solidify, raise the temperature from normal temperature to 210-230°C for 20-40min, keep it warm for 40-60min, and finally cool down linearly. The time is 20-40min; to further improve the flatness of the surface; f) After step e is completed, perform a CMP process to make the surface smoother and expose the Au solder balls; g) The method of photolithography electroplating makes the pattern of antenna above the deep groove, and its steps are: ① First, a layer of seed layer TiW/Au is sputtered on the surface of BCB with thicknesses of

② Then apply photoresist, photolithography, develop, expose the antenna pattern window above the groove, and then electroplate Au; ③Finally remove the glue and remove the seed layer, leaving the antenna pattern. 2. The method according to claim 1, characterized in that the thickness of one layer of BCB dielectric layer is recoated in step e and is 20-50 μm. 3. The method according to claim 1, wherein the curing temperature of the first stage in step c is 180° C., and the curing temperature of the second stage is 230° C. 4. The method according to claim 1, characterized in that the height of the Au solder balls described in step d is 20-50 μm. 5. The method according to claim 1 or 4, characterized in that the height of the Au solder balls described in step d is 30-40 μm. 6. The method according to claim 1 or 2, characterized in that the thickness of one layer of BCB dielectric layer is recoated in step e and is 25-40 μm. 7. The method according to claim 1, characterized in that the thickness of the Au plating described in step (2) in step g is 2-5 μm. 8. by the described method of claim 1, it is characterized in that: ① In the first stage of step c, the temperature is raised from room temperature to 170-190°C for 60 minutes, so that the BCB is slowly solidified, the BCB is fully flowing, and the depression caused by shrinkage is as small as possible; ②Then raise the temperature to 210-250°C to make the BCB fully solidified, and the whole process of the first stage and the second stage is controlled within 120min. 9. The method according to claim 1, characterized in that the dielectric constant<3.5 material described in step b is PI, which is solidified by heating. 10. The method according to any one of claims 1-4, characterized in that: ① The method described is compatible with the microelectronics process and carried out together with the MMCM packaging process, and is completed on the basis of wafer-level packaging; ② The bandwidth of the fabricated antenna increases significantly.

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