Aluminum Nitride Assemblage

Abstract

This invention relates to an assemblage of a semiconductor processing apparatus comprising a first aluminum nitride (AlN) component and a second aluminum nitride component, wherein the first and second aluminum nitride components are connected by a joint, said joint comprising a composite glass-ceramic comprising Y.sub.2O.sub.3Al.sub.2O.sub.3SiO.sub.2 (YAS) glass; and at least one of crystalline aluminosilicate and aluminum nitride.

Claims

1. An assemblage of a semiconductor processing apparatus comprising a first aluminum nitride (AlN) component and a second aluminum nitride component, wherein the first and second aluminum nitride components are connected by a joint, said joint comprising a composite glass-ceramic comprising: (a) Y.sub.2O.sub.3Al.sub.2O.sub.3SiO.sub.2 (YAS) glass; and (b) at least one of mullite and aluminum nitride.

2. The assemblage of claim 1 comprising: the Y.sub.2O.sub.3Al.sub.2O.sub.3SiO.sub.2 (YAS) glass, the mullite, and the aluminum nitride.

3. The assemblage of claim 1, wherein the at least one of the mullite and/or the aluminum nitride is encompassed by the YAS glass.

4. The assemblage of claim 1, wherein the joint comprises: 50 to 100 wt % Y.sub.2O.sub.3Al.sub.2O.sub.3SiO.sub.2 (YAS) glass; and 1 to 30 wt % mullite; and/or 2 to 50 wt % aluminum nitride;

5. The assemblage of claim 1, wherein the YAS glass comprises: 20-70 wt % Y.sub.2O.sub.3; 10-50 wt % Al.sub.2O.sub.3; and 1-50 wt % SiO.sub.2, wherein the sum of Y.sub.2O.sub.3+Al.sub.2O.sub.3+SiO.sub.2 is at least 95 wt %.

6. The assemblage according to claim 1, wherein the YAS glass comprises a peripheral region and a core region, said peripheral region interfacing with at least a portion of the first and/or second aluminum nitride components and the core region located in at least a central region of the joint.

7. The assemblage according to claim 6, where in the peripheral region comprises a YAS glass composition with an alumina content greater than the YAS glass of the core region.

8. The assemblage according to claim 6, wherein the YAS glass composition of the peripheral region comprises: 45-70 wt % Y.sub.2O.sub.3; 20-50 wt % Al.sub.2O.sub.3; and 1-20 wt % SiO.sub.2, wherein the sum of Y.sub.2O.sub.3+Al.sub.2O.sub.3+SiO.sub.2 is at least 95 wt %.

9. The assemblage according to claim 6, wherein the YAS glass composition of the core region comprises: 30-55 wt % Y.sub.2O.sub.3; 10-30 wt % Al.sub.2O.sub.3; and 15-50 wt % SiO.sub.2, wherein the sum of Y.sub.2O.sub.3+Al.sub.2O.sub.3+SiO.sub.2 is at least 95 wt %.

10. The assemblage according to claim 1, wherein the joint comprises 2 to 50 wt % AlN.

11. (canceled)

12. The assemblage of claim 10 or 11, wherein the joint comprises 1 to 30 wt % mullite.

13. The assemblage according to claim 1, wherein the first and/or the second AlN component comprises a Y.sub.2O.sub.3 rich phase comprising at least 30 wt % Y.sub.2O.sub.3.

14.-15. (canceled)

16. The assemblage of claim 1, wherein a thickness of the joint is no more than 150 m.

17. The assemblage of claim 1, comprising a He leakage rate of no more than 110.sup.7 mbar-l/sec determined in accordance with ASTM F19.

18. The assemblage of claim 1, wherein the first AlN component is an electrostatic chuck and the second AlN component is a pedestal shaft.

19. An assemblage of a semiconductor processing apparatus comprising a first aluminum nitride (AlN) component and a second aluminum nitride component, wherein the first and second aluminum nitride components are connected by a joint, said joint comprising a composite glass-ceramic comprising a Y.sub.2O.sub.3Al.sub.2O.sub.3SiO.sub.2 (YAS) glass phase comprising: 20-70 wt % Y.sub.2O.sub.3; 10-50 wt % Al.sub.2O.sub.3; and 1-50 wt % SiO.sub.2, wherein the sum of Y.sub.2O.sub.3+Al.sub.2O.sub.3+SiO.sub.2 is at least 95 wt %.

20. The assemblage of claim 19, wherein the first and/or the second AlN component comprises in a range of at least 1 to 7 wt % Y.sub.2O.sub.3.

21. The assemblage of claim 19, wherein the joint comprises one or both of 2 to 50 wt % AlN and 1 to 30 wt % mullite.

22.-32. (canceled)

33. A paste for use in forming the assemblage as defined claim 1, comprising a composite glass-ceramic or precursor thereof having a composition comprising, on a solvent free basis: 10-60 wt % Y.sub.2O.sub.3; 5-40 wt % Al.sub.2O.sub.3; 10-60 wt % SiO.sub.2; and 0-30 wt % AlN, wherein the sum of Y.sub.2O.sub.3+Al.sub.2O.sub.3+SiO.sub.2+AlN is at least 95 wt %.

34. The paste of claim 33, comprising: 20-40 wt % Y.sub.2O.sub.3; 20-40 wt % Al.sub.2O.sub.3; 20-40 wt % SiO.sub.2; and 1-20 wt % AlN.

35. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0072] FIG. 1 is a process flow diagram according to an exemplary embodiment of the current disclosure.

[0073] FIG. 2 is a cross-sectional diagram illustration of an aluminum nitride substrate which has been joined to an aluminum nitride shaft using the composite glass-ceramic joining material according to an exemplary embodiment of the current disclosure.

[0074] FIG. 3 is an SEM micrograph showing the microstructure of the composite glass-ceramic joining material disposed between aluminum nitride substrates according to Example 1 of the current disclosure.

[0075] FIG. 4 is a magnified SEM micrograph of FIG. 3 highlighting analysis points which are displayed in Table 2.

[0076] FIG. 5 is an SEM micrograph showing the microstructure of the joining material according to Example 2 disposed between aluminum nitride substrates.

[0077] FIG. 6 is a magnified SEM micrograph of a section of FIG. 5 showing the joint microstructure in more detail.

[0078] FIG. 7 is an SEM micrograph showing the microstructure of an alternative joining material according to Comparative Example #1 disposed between aluminum nitride substrates as a comparison to the current disclosure.

[0079] FIG. 8 is an SEM micrograph showing the microstructure of another alternative joining material according to Comparative Example #2 disposed between aluminum nitride substrates as a comparison to the current disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] Representative applications of glass ceramic joints and AlN assemblages comprising the same, and methods according to the presently described embodiments are provided in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the presently described embodiments can be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the presently described embodiments. Other applications are possible, such that the following examples should not be taken as limiting.

[0081] As illustrated in FIG. 1, the process of joining to AlN bodies together involves forming and sintering AlN bodies, followed by surface preparation involving grinding and polishing to obtain a smooth joining surfaces to which a joining paste, which has been prepared as a viscous past of joining materials, is applied. The two AlN bodies are then mated under load and then fired to produce the final assembly.

[0082] In reference to FIG. 2, shown is a cross-sectional diagram illustration of a final assembled part as joined according to an exemplary embodiment of the current disclosure. The assembly consists of a sintered AlN substrate 1 and a sintered AlN pedestal shaft 2, which have been joined using the composite glass-ceramic joining material of the present disclosure 3 disposed at the interface between 1 and 2. It is preferred that this assembly is retained in good geometrical constraints. Ideally, the process described in FIG. 1 does not significantly alter the microstructure, function or performances of the component pieces 1, 2.

[0083] In one embodiment, green AlN bodies with at least 1 wt % Y.sub.2O.sub.3 sintering aid are preferably formed into the desired shapes through dry-pressing or iso-pressing, such as the substrate and pedestal shaft of FIG. 2. The formed green AlN components are debinded using a slow and controlled ramp rate not greater than 2 C./min to 375 C. and held for at least 1 hr, followed by a slow controlled cool to room-temperature at a rate not greater than 4 C./min. The debinded AlN ceramics are then sintered using a ramp rate of no faster than 15 C./min to 1850 C., held at 1850 C. for at least 1 hr, and then cooled back down to room temperature at a rate not greater than 15 C./min. It is preferred that the sintered AlN components possess a density of at least 3.30 g/cm.sup.3 measured via the Archimedes method and a uniform microstructure with an average grain size not greater than 20 m. The sintered AlN ceramics are then ground and polished at their respective joining surfaces to achieve a flat and smooth interface for joining. It is preferred that the surface roughness (R.sub.a) is no greater than 45 m.

[0084] A paste containing components of the composite glass-ceramic joining materials is prepared to be applied at the joining interface. Raw powder materials of the joining material are preferably mixed in the following proportions: 50-100% of a Y.sub.2O.sub.3Al.sub.2O.sub.3SiO.sub.2 (YAS) glass forming component and 0-50 wt % of aluminum nitride raw powder. Wherein the YAS glass forming component contains 10-60 wt % Y.sub.2O.sub.3, 5-40 wt % Al.sub.2O.sub.3, and 10-60 wt % SiO.sub.2. Paste compositions within this range have a relatively low melting point and are able to generate crystalline aluminosilicate phases, such as mullite.

[0085] It is preferred that the raw powder materials used are of high purity (e.g. greater than 98 wt % or greater than 99 wt % or greater than 99.5 wt % purity). The component powder joining materials are then mixed and milled with a binder and solvent to form a viscous paste. It is preferred that the joining material paste exhibits a viscosity suitable for screen-printing applications with a solids-loading of at least 50 wt %, with the paste fully homogenized through thorough mixing of the components. The prepared paste is then applied to the joining surface of each sintered AlN body in a thin and uniform layer. Preferably the paste is applied using the screen-printing method at a thickness of less than 0.005 (127 m).

[0086] The sintered AlN bodies with the joining paste applied at their joining surfaces are then mated surface-to-surface and fired in N.sub.2 atmosphere to form a solid joint. It is preferred that a load is applied perpendicular to the joining interface during the firing process to force contact between the joined faces and promote flow and uniform distribution of the glass phase along the joint. It is preferred that the assembly be fired to a peak temperature between 1450 C.-1550 C. with a dwell time between 5 mins-2 hrs. It is further preferred that the heating and cooling rates during firing are between 10-30 C./min.

[0087] As seen in the SEM micrograph FIG. 3, which is a cross-section of the joint region of joined AlN ceramics prepared according to this preferred embodiment, the sintered AlN substrates 100, 105 have been joined between the composite glass-ceramic joining material, which comprises AlN particles 130 and mullite particles 140 embedded within a YAS glass matrix 110, 120. The YAS glass matrix comprises a lighter colored peripheral region 110 and a darker colored core region 120. The microstructure shows a thin, uniform, and continuous joint layer which is free of voids and defects. Additionally, the backscattered image enables the identification of a continuous yttria aluminosilicate glass-phase with a homogeneously distributed aluminosilicate (mullite) crystals and AlN filler particles.

Examples

[0088] Experiments were conducted to quantify the strength and hermeticity of AlN ceramics joined using the glass-ceramic composite joining material of the current disclosure as well as other joining materials which may be used in the semiconductor field as comparative examples using the ASTM F19 standardized procedure. AlN spray-dried powder containing 4 wt % Y.sub.2O.sub.3 sintering aid was used as the base powder material. AlN iso-pressed cylinders were formed, machined to the ASTM F19 sample specifications, and debinded at 375 C. for 2 hrs with a ramp and cool rate of 1.5 C./min and 3 C./min, respectively. The debinded ceramics were then sintered to 1850 C. for 3 hrs with a ramp and cool rate of 10 C./min to achieve a density of at least 3.30 g/cm.sup.3. The surfaces to be joined were then ground to flat and polished incrementally with a polishing wheel and diamond slurry up to a Roughness, Ra, of 9 m.

[0089] Joining pastes of varying compositions were prepared of approximately 65-70 wt % solids with remainder of binder and solvent to yield a viscous and screen-printable paste. For the composite glass-ceramic joining materials of the present disclosure, from hereafter referred to as: [0090] YAS+10% AlN (Example 1), the solids content of the paste was composed of 30 wt % Y.sub.2O.sub.3, 30 wt % Al.sub.2O.sub.3, 30 wt % SiO.sub.2, and 10 wt % AlN; [0091] YAS (1:1:1) (Example 2) the solids content of the paste was composed of 30 parts by weight (pbw) Y.sub.2O.sub.3, 30 pbw Al.sub.2O.sub.3, 30 pbw SiO.sub.2; and [0092] YAS (9:2:9) (Example 3) the solids content of the paste was composed of 9 pbw Y.sub.2O.sub.3, 2 pbw Al.sub.2O.sub.3, 9 pbw SiO.sub.2.

[0093] Example 2 differs from Example 1, in that sample contains no AlN (i.e. only the Y.sub.2O.sub.3, Al.sub.2O.sub.3 and SiO.sub.2 in a weight ratio of 1:1:1, such ratio being effective to yield crystalline aluminosilicate phases upon formation of the joint). Example 3, differed from Example 2, in that the weight ratio of Y.sub.2O.sub.3, Al.sub.2O.sub.3 and SiO.sub.2 was adjusted to 9:2:9, such that the no crystalline aluminosilicate phases were formed.

[0094] As an alternative joining solution, from hereafter referred to as Comparative Example #1 (CE #1), the solids content of the paste was composed of 40 wt % AlN, 15 wt % Al.sub.2O.sub.3, 8 wt % Y.sub.2O.sub.3, and 37 wt % CaCO.sub.3. As another alternative joining solution, from hereafter referred to as Comparative Example #2 (CE #2), the solids content of the paste was composed of 70 wt % AlN, 15 wt % Al.sub.2O.sub.3, and 15 wt % Y.sub.2O.sub.3.

[0095] Each joining paste was applied in a thin layer of approximately 0.003 (76 m) thickness to the joining surface of each respective AlN ASTM F19 part. The parts were then mated under an approximately 5 g load and fired under varying profiles depending on their composition. The samples (1 to 3) were fired at 1500 C. in N.sub.2 atmosphere for a 30 min dwell with a 10 C./min ramp and cool rate. For Comparative Example #1, the samples were fired in N.sub.2 atmosphere with a ramp rate of 10 C./min to 1400 C. for 2 hrs, followed by a second ramp at 10 C./min up to 1600 C. for another 2 hr dwell, and finally a 10 C./min cool to room-temperature. For Comparative Example #2, samples were fired in N.sub.2 atmosphere at 10 C./min to 1850 C. for a 1 hr dwell, followed by a 10 C./min cool to room-temperature.

[0096] The joined parts were then tested under the ASTM F19 standard procedure for hermeticity using a He spectrometer and for tensile strength using an Instron. The ASTM F19 testing results for each joining material of the present disclosure are shown in Table 1.

[0097] As indicated in Table 1, Example 1 achieved the combination of highest average strength at 23.64.6 MPa and lowest He leakage rate in the range of 110.sup.8-110.sup.9 mbar-l/sec (110.sup.9-110.sup.10 KPa-l/sec) across 5 samples. While Example 2, achieved a similar joint strength to Example 1, it had a reduced hermeticity performance. While Example 3, achieved a similar joint hermeticity performance to Example 1, it had a reduced joint strength. Comparative Example #1 (CE #1) achieved an average strength of only 10.83.9 MPa and a He leakage rate in the range of about 110.sup.3-110.sup.4 mbar-l/sec (110.sup.4-110.sup.5 KPa-l/sec) across 5 samples. Finally, the worst performing joining material was Comparative Example #2 (CE #2), which achieved an average strength of only 6.31.9 MPa and He leakage rate in the range of about 110.sup.1-110.sup.1 mbar-l/sec (110.sup.2-110.sup.3 KPa-l/sec) across 3 samples. This data suggests that the Example 1 (YAS+10%) AlN joining solution, followed by Examples 2 & 3, of the present disclosure possesses improved strength and hermeticity values when compared to other potential joining solutions of different compositions and joining conditions.

TABLE-US-00001 TABLE 1 Joining Average Temp. Strength Hermeticity Sample Joint material ( C.) (MPa) (mbar .Math. l/sec) size 1 1500 23.6 4.6.sup.& 1 10.sup.8 to 1 5 YAS (1:1:1) + 10.sup.9 10% AlN 2 1500 23.8 2.3 1 10.sup.5 to 1 5 YAS (1:1:1) 10.sup.6 3 1500 19.2 1 10.sup.8 to 1 1 YAS (9:2:9) 10.sup.9 CE#1 1400, 1600 10.8 3.9 1 10.sup.3 to 1 5 (2 step) 10.sup.4 CE#2 1850 6.3 1.9 1 10.sup.1 to 1 3 10.sup.2 .sup.&represents one standard deviation within sample population

Joint Microstructure

[0098] To qualitatively analyze the microstructure of the composite glass-ceramic, dry-pressed AlN pellets were formed and then debinded, sintered, and ground/polished under the same conditions as the above AlN ASTM F19 samples. The same respective joining pastes and joining parameters as in the above example were then applied to join the sintered pellets. The sintered pellets were then cross-sectioned and incrementally polished using a polishing wheel and diamond suspension up to 1 m. The polished samples were then analyzed for microstructure via SEM. The microstructure of joint corresponding to the YAS+10% AlN paste (Example 1) is presented in FIGS. 3 & 4 and shows that there is a uniform and consistent joint layer formed at 1500 C. for 30 mins consisting of 4 distinct phases: a yttria aluminosilicate glass (peripheral 110 and core regions 120), aluminosilicate (mullite) crystals 140, and AlN filler particles 130.

[0099] The composition of selected observed phases (FIG. 4) are provided in Table 2, using semi-quantitative EDS analysis. A Y.sub.2O.sub.3 rich phase 210 (light phase) was also identified in the AlN component 100. The peripheral glass phase located 110 at the interface of the AlN components may be at least partially derived from the Y.sub.2O.sub.3 sintering additive in the AlN components 100, 105.

TABLE-US-00002 TABLE 2 Phase (wt %) Al.sub.2O.sub.3 SiO.sub.2 Y.sub.2O.sub.3 YAS glass (core) #001 21 35 44 YAS glass (core) #002 21 36 43 YAS glass (peripheral) 36 3 61 #003 YAS glass (peripheral) 36 3 61 #004 Crystalline Al.sub.2O.sub.3 #005 85 15 Crystalline Al.sub.2O.sub.3 #006 87 13 Crystalline Al.sub.2O.sub.3 #007 55 45

[0100] The % surface area of the YAS glass, mullite and AlN phases was calculated through measuring the relative surface areas of four joint, each having a surface area of about 2000 m.sup.2. Buehler OmniMet software was used to measure the features on the images, which had been identified as YAS glass, AlN particles and mullite particles, through XRD and EDS analysis. The area measurement tool of the software was used to measure the number of pixels of the AlN and mullite phases. The % surface area of the AlN and mullite phase were determined by comparing the number of pixels relative to the total number of pixels in the joint area being measured. The % wt YAS glass was determined by difference (totalmulliteAlN). For the purposes of the present invention, the proportion of the % surface area of a phase is assumed to equal its wt % proportion (or its volume % proportion). For example, a 10% joint surface area of YAS glass is deemed to equate to 10 wt % of YAS glass in the joint.

[0101] The range of the relative portion of the phases is presented in Table 3 from the four joints produced from the paste comprising the abovementioned YAS+10 wt % AlN. For the purposes of the present invention, the % surface area of each of the phases may be regarded as the wt % of each of the phases.

TABLE-US-00003 TABLE 3 phase YAS glass Mullite AlN % wt 68-76 16-22 8-10

Effect of AlN Addition Phases

[0102] In general, the YAS glass phase should flow and fill in gaps, creating a dense and hermetic seal. However, in Example 2 the joint has a low hermetic value (Table 1). Visually analyzing the joint during its formation, it is observed that there is some overflow of the glass onto the sides of the sample. The resultant joint, as illustrated in FIG. 5 shows a first AlN substrate 300 and a second AlN substrate 310 connected by a joint 320, which comprised a number of voids 330.

[0103] Upon increased magnification (FIG. 6), the joint 320 comprises a peripheral glass phase 340 and a core glass phase 350, although there is a relatively lower proportion of the peripheral glass phase to core glass phase compared to Example 1. The angular darker grains 360 correspond to a crystalline aluminosilicate phase. The peripheral glass phase 340 is located in a peripheral region that interfaces with at least a portion of the first and/or second aluminum nitride substrates 300, 310. The core glass phase 350 is located in at least a central region of the joint. In one or more embodiments, the core glass phase 350 spans from the first aluminum nitride substrate to the second aluminum nitride substrate 300, 310.

[0104] While not wanting to be bound by theory, it is thought that, in Example 2, the glass was too fluid at the firing temperature and amounts of molten glass were forced out of the joint substrate interface. This resulted in insufficient reaction between the joint material and substrate at the substrate interface, with the migrated glass phase leaving behind voids at the joint interface. The lower proportion of the peripheral glass phase to the core glass phase may be a reflective of this lower level of reaction.

[0105] It is thought that by adding a small amount of AlN powder, there is an increase in glass viscosity at the application temperature, which enables the glass to be contained within the joint region, thereby preventing YAS glass migration away from the joint substrate interface and ensuring a sufficiently dense and hermetic joint. The AlN particles also reduce the differences in the coefficient of thermal expansion across the joint. Without AlN particles, the joint is also more susceptible to thermal shock and, as a result, micro-cracking may occur which provides gaseous pathways through the joint thereby also affecting the hermeticity value over time.

Effect of Crystalline Aluminosilicate

[0106] The effect of crystalline aluminosilicate is illustrated in comparative Example 3 (Table 1), with the absence of this component within the joint resulting in a reduction joint strength by about 20%. The crystalline phase is thought to function as a crack inhibitor, thereby interrupting crack propagation and improving joint strength and fracture toughness.

Comparative Examples

[0107] In FIG. 7, the microstructure of the Comparative Example #1 joining material, 6, is shown disposed between sintered AlN bodies, 4, following firing at 1400 C. and 1600 C. for 2 hrs each. FIG. 7 shows evidence of less flow of the CaO-based glass phase, leaving behind a not fully homogenized and uniform joint layer. In FIG. 8, the microstructure of Comparative Example #2 joining material, 7, is shown disposed between sintered AlN substrates, 4, following firing at 1850 C. for 1 hr. FIG. 8 presents a joint layer which has a highly non-uniform joining interface, additionally, the high temperatures required for bonding have significantly affected the distribution of the liquid-phase at the adjacent AlN substrates, which could potentially impact the properties and performance of the base AlN material. Overall, the results in Table 3 and the microstructure analysis indicate that the joints of Examples 1, 2 & 3 of the present disclosure exhibits (relative to CE #1 and CE #2) improved hermeticity and strength. Additionally, the assemblies of the present invention possess good joint homogeneity; uniform distribution and controlled formation of distinct glass and crystalline phases, when present.

[0108] Although the foregoing disclosure has been described in detail by way of illustration and example for purposes of clarity and understanding, it will be recognized that the above-described disclosure may be embodied in numerous other specific variations and embodiments without departing from the spirit or essential characteristics of the disclosure. Certain changes and modifications may be practiced, and it is understood that the disclosure is not to be limited by the foregoing details, but rather is to be defined by the scope of the appended claims.