Method of Deposition

Abstract

A hydrogenated silicon carbon nitride (SiCN:H) film is deposited onto a substrate by plasma enhanced chemical vapour deposition (PECVD) comprising: providing the substrate in a chamber; introducing silane (SiH.sub.4), a carbon-donating precursor, and nitrogen gas (N.sub.2) into the chamber; and sustaining a plasma in the chamber so as to deposit SiCN:H onto the substrate by PECVD, wherein the substrate is maintained at a temperature of less than about 250° C.

Claims

1. A method of depositing a hydrogenated silicon carbon nitride (SiCN:H) film onto a substrate by plasma enhanced chemical vapour deposition (PECVD) comprising: providing the substrate in a chamber; introducing silane (SiH.sub.4), a carbon-donating precursor, and nitrogen gas (N.sub.2) into the chamber; and sustaining a plasma in the chamber so as to deposit SiCN:H onto the substrate by PECVD, wherein the substrate is maintained at a temperature of less than about 250° C.

2. The method according to claim 1, wherein the carbon-donating precursor is an organosilane.

3. The method according to claim 2, wherein the organosilane is methylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, or a combination thereof.

4. The method according to claim 1, wherein the carbon donating precursor is a gaseous hydrocarbon.

5. The method according to claim 4, wherein the gaseous hydrocarbon is methane (CH.sub.4), acetylene (C.sub.2H.sub.2), or a combination thereof.

6. The method according to claim 1, wherein the silane (SiH.sub.4) is introduced into the chamber at a flow rate in the range of 100-500 sccm.

7. The method according to claim 1, wherein the carbon-donating precursor is introduced into the chamber at a flow rate in the range of 10-90 sccm.

8. The method according to claim 1, wherein the silane (SiH.sub.4) and the carbon-donating precursor are introduced into the chamber at flow rates (in sccm) in a ratio in the range of 3:1 to 30:1.

9. The method according to claim 8, wherein the ratio is about 10:1 to 12:1.

10. The method according to claim 1, wherein the nitrogen gas (N.sub.2) is introduced into the chamber at a flow rate in the range of 1000-10,000 sccm.

11. The method according to claim 1, wherein the substrate is maintained at a temperature of less than 225° C.

12. The method according to claim 1, wherein whilst the plasma is being sustained in the chamber, the chamber has a pressure in the range of 1-5 Torr.

13. The method according to claim 1, further comprising the subsequent step of performing a hydrogen plasma treatment comprising exposing the SiCN:H film to a hydrogen plasma.

14. The method according to claim 13, wherein during the hydrogen plasma treatment, the substrate is maintained at a temperature of less than about 200° C.

15. The method according to claim 1, wherein the hydrogenated silicon carbon nitride film is an amorphous hydrogenated silicon carbon nitride film (a-SiCN:H).

16. The method according to claim 1, wherein the substrate is a semiconductor substrate.

17. A substrate with a SiCN:H film deposited thereon using the method according to claim 1.

18. The substrate according to claim 17, wherein the SiCN:H film has a hydrogen content of more than about 2 at %.

19. A method of bonding two substrates comprising the steps of: providing a first substrate with the SiCN:H film and providing a second substrate with the SiCN:H film, wherein the first substrate with the SiCN:H film and the second substrate with the SiCN:H film are one of the substrate according to claim 17; and bonding the SiCN:H film of the first substrate to the SiCN:H film of the second substrate at a temperature of less than about 250° C.

20. A device comprising a stack of two or more substrates produced using the method according to claim 19.

Description

DESCRIPTION OF THE DRAWINGS

[0045] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0046] FIG. 1 is a schematic side view of two substrates ready to undergo a surface activated substrate-substrate bonding process;

[0047] FIG. 2 shows FTIR spectra of SiCN:H films deposited using comparative examples;

[0048] FIG. 3 shows FTIR spectra of SiCN:H films deposited using comparative examples;

[0049] FIG. 4 shows FTIR spectra of a SiCN:H films deposited using a method of the present invention, and a comparative example;

[0050] FIG. 5 is a plot showing carbon content in the as deposited SiCN:H layer as a function of the carbon-donating precursor to silane ratio;

[0051] FIG. 6 is a plot showing the change in refractive index (RI) after a period of six days as a function of the carbon-donating precursor to silane ratio;

[0052] FIG. 7 shows FTIR spectra of a SiCN:H film before and after a period of exposure to air for six days;

[0053] FIG. 8 is a plot showing the change in refractive index (RI) for a SiCN:H film deposited using an exemplary method of the invention;

[0054] FIG. 9 shows FTIR spectra of SiCN:H deposited using exemplary methods of the invention; and

[0055] FIG. 10 is a plot showing the change in refractive index of SiCN:H films deposited using exemplary methods of the invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0056] Although claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure. Accordingly, the scope of the disclosure is defined only by reference to the appended claims.

[0057] FIG. 1 shows a schematic of a surface activated bonding process used to bond two substrates together. The substrates 10a, 10b may comprise temperature sensitive features, such as device layers 12a, 12b. An adhesion layer 14a, 14b, such as a silicon carbon nitride (SiCN) layer, such as a hydrogenated silicon carbon nitride (SiCN:H) layer, is deposited on a surface of each substrate 10a, 10b. The two adhesion layers 14a, 14b can be smoothed, for example by chemical mechanical planarization (CMP), precisely aligned, pressed together at an elevated temperature, and annealed so as to bond the two substrates together via the adhesion layers 14a, 14b.

[0058] Apparatus suitable for depositing silicon carbon nitride (SiCN) films, such as SiCN:H films, according to exemplary methods of the present invention (and comparative examples) includes an SPTS Delta™ parallel plate PECVD apparatus, which is commercially available from SPTS Technologies Limited, located in Newport, South Wales, UK. All exemplary embodiments and comparative examples described below were performed using this apparatus.

Comparative Examples 1 and 2

[0059] SiCN:H adhesion layers are known to be deposited using high temperature (e.g. about 340-370° C.) plasma enhanced chemical vapour deposition (PECVD) using an organosilane and ammonia (NH.sub.3) as the reactive precursors. The organosilane acts as both a silicon and a carbon donating precursor, while ammonia serves as a nitrogen donating precursor.

[0060] As comparative examples (and with reference to FIG. 2), SiCN:H films were deposited onto a 300 mm silicon wafer at 350° C. by PECVD using an organosilane and ammonia (NH.sub.3) as the reactive precursors. The chamber pressure was maintained in the range of 1-5 Torr. In comparative example 1 (line 21 of FIG. 2), trimethylsilane (3MS) was used as the organosilane precursor. In comparative example 2 (line 22 of FIG. 2), tetramethylsilane (4MS) was used as the organosilane precursor.

[0061] A characteristic Si—CH.sub.3 stretching peak is visible at about 1257 cm.sup.−1 in both comparative examples 1 and 2 but is more pronounced when 3MS is used as the organosilane precursor (i.e. comparative example 1, line 21). Both spectra 21 and 22 show similar strength peaks at about 2133 cm.sup.−1 and about 2900 cm.sup.−1 corresponding to Si—H.sub.n (n=1-3) and CH.sub.m (m=1-3) stretching peaks respectively.

Comparative Examples 3 and 4

[0062] As further comparative examples (and with reference to FIG. 3), SiCN:H films were deposited onto a 300 mm silicon wafer by PECVD using trimethylsilane (3MS) and ammonia (NH.sub.3) as the reactive precursors. The plasma was sustained using a mixed frequency RF power. That is, a high frequency (HF) RF (operating at 13.56 Hz) and a low frequency (LF) RF (operating at 380 kHz) were used to sustain the plasma. Comparative example 3 (line 33 of FIG. 3) and comparative example 4 (line 34 of FIG. 3) use the same deposition parameters, except that comparative example 3 used a high deposition temperature of 370° C., whereas comparative example 4 used a low deposition temperature of 175° C.

[0063] The SiCN:H film deposited in comparative example 3 (line 33) exhibited acceptable properties as an adhesion layer and/or copper barrier layer. However, the high temperature required to deposit this film cannot be used on temperature sensitive substrates (i.e. substrates with a low thermal budget constraint).

[0064] The SiCN:H film deposited in comparative example 4 (i.e. at the lower temperature of 175° C., line 34) shows a significant increase in the Si—CH.sub.3 stretching peak (˜1257 cm.sup.−1), the Si—H.sub.n (n=1-3) stretching peak (˜2133 cm.sup.−1), and the CH.sub.m (m=1-3) stretching peak (˜2900 cm.sup.−1) compared to the film deposited at 370° C. (comparative example 3, line 30). Additionally, the peaks at 600-1200 cm.sup.−1 are more prominent for the SiCN:H film deposited at 175° C. These FTIR spectra indicate that the SiCN:H film deposited at 175° C. comprises more CH.sub.n, Si—CH.sub.n, Si—H.sub.n (n=1-3) terminated groups compared to the SiCN:H film deposited at 370° C.

[0065] The SiCN:H films deposited in comparative example 4 (i.e. at 175° C., using 3MS and NH.sub.3 as reactive precursors) have a lower density and a lower refractive index of ˜1.57. Due to the low density and porosity of the film, the SiCN:H film deposited in comparative example 4 absorbs moisture. The film of comparative example 4 is not viable as an adhesion layer. Additionally, due to the low density, the film would be a poor copper barrier layer and is likely to outgas during a bonding process, which would adversely affect the substrate-substrate bond strength. The unacceptable film formed in comparative example 4 shows that depositing acceptable SiCN:H films at low temperatures (e.g. <250° C.) is not a trivial modification.

EXEMPLARY EMBODIMENTS

[0066] The present invention provides a method of depositing hydrogenated silicon carbon nitride (SiCN:H) films that are acceptable for use as adhesion layers in a surface activated bonding process. In particular, acceptable SiCN:H films can be deposited onto substrates at temperatures of less than about 250° C., optionally less than 200° C., and optionally about 175° C. The substrate can be a semiconductor substrate, such as a silicon substrate or silicon wafer. The substrate can comprise a plurality of die. The substrate can comprise temperature sensitive features, such as device layers and interconnects, which may include copper layers embedded in a dielectric.

[0067] Exemplary embodiments of the invention comprise introducing a silicon donating precursor, a carbon-donating precursor, and a nitrogen donating precursor into a PECVD chamber. Optionally, one or more non-reactive carrier gases may also be introduced into the chamber. A plasma is sustained within the chamber so that a PECVD process can occur, which causes SiCN:H to deposit onto the substrate. The silicon donating precursor is silane (SiH.sub.4). The nitrogen donating precursor is nitrogen gas (N.sub.2). The carbon-donating precursor can be an organosilane, methane (CH.sub.4), acetylene (C.sub.2H.sub.2), or combinations thereof. The organosilane can be methylsilane, dimethylsilane, trimethylsilane (3MS), tetramethylsilane (4MS), or combinations thereof.

[0068] Table 1 shows exemplary PECVD process parameters suitable for achieving stable SiCN:H films at a deposition temperature in a range of 100−250° C.

TABLE-US-00001 TABLE 1 Process Parameters Range Preferred Range Chamber pressure mT 1000-5000 1400-3000 N.sub.2 flow rate Sccm   1000-10,000 2500-8000 Carbon-donating precursor Sccm 10-90 10-55 (e.g. 3 MS) flow rate SiH.sub.4 flow rate Sccm 100-500 200-300 HF RF power W  250-1250  500-1000 LF RF power W  0-400  0-200 Temperature ° C. 100-250   100-200° C.

Example 5

[0069] In one exemplary embodiment (Example 5), a SiCN:H film was deposited onto a 300 mm silicon wafer at 175° C. by PECVD. The reactive precursors were silane (SiH.sub.4), trimethylsilane (3MS) as the carbon-donating precursor, and nitrogen gas (N.sub.2).

[0070] Using the combination of a (non-carbon containing) silane, and a discrete carbon-containing precursor allows the carbon content of the SiCN:H films to be fine-tuned and varied in a controlled manner. This can also be more cost-effective than using a single organosilane precursor. The chamber pressure was in the range of 1-5 Torr. The plasma was sustained using a mixed frequency RF power. The mixed frequency RF power comprised a high frequency RF (operating at 13.56 Hz) and a low frequency RF (operating at 380 kHz).

[0071] FIG. 4 shows an FTIR spectrum of the as deposited SiCN:H film using the method of Example 5 (line 45). Line 43 (FIG. 4) corresponds to a SiCN:H film deposited at 370° C. using the same conditions as those used in comparative example 3. Comparative example 3 is used here as an exemplar spectrum of a SiCN:H film that is acceptable for use as an adhesion layer.

[0072] Table 2 shows the FTIR peak areas using the SiN peak to normalise the results.

TABLE-US-00002 TABLE 2 FTIR Peak Ratios SiC/SiN SiH/SiN SiCHx/SiN NH/SiN RI HT NH.sub.3 based SiCN:H 0.0042 0.0466 0.0042 0.0097 1.9762 (Comparative example 3) LT NH.sub.3 Based SiCN:H 0.0956 0.0512 0.0281 0.0757 1.5691 (Comparative example 4) LT N.sub.2 Based SiCN:H 0.0036 0.1230 0.0080 0.0179 1.9972 (Example 5)

[0073] The FTIR spectrum of the SiCN:H film deposited using the low temperature (LT) method of Example 5 (line 45) was similar to that of the deposited film in comparative example 3 (line 33, 43). However, the SiCN:H film of Example 5 exhibits a stronger Si—H peak (˜2120 cm.sup.−1) than the high temperature (HT) comparative example 3. This is a characteristic trait of SiCN:H films deposited using methods of the present invention.

[0074] Furthermore, based on Table 2, it is apparent the SiC/SiN, SiCH.sub.x/SiN, and NH/SiN ratios of Example 5 are a closer match with comparative example 3 than the results of comparative example 4. Additionally, the refractive indexes of comparative example 3 and Example 5 are closely matched. The low refractive index for comparative example 4 suggests this film has a very low density, and is not acceptable for use as an adhesion layer. Example 5 achieves a far superior film compared to comparative example 4 (also deposited at low temperature but using a known deposition recipe). Using a mixture of reactive precursors comprising the combination of silane (SiH.sub.4), a carbon-donating precursor, and nitrogen gas (N.sub.2) provide suitable conditions for depositing SiCN:H films that have improved qualities, whilst maintaining a low thermal budget. The SiCN:H films deposited using the present methods are acceptable for use as an adhesion layer in surface activated bonding processes, and can provide acceptable copper barrier layer characteristics.

[0075] Whilst Example 5 uses a 3MS carbon-donating precursor, acceptable results would be expected to occur if the 3MS precursor was substituted with other carbon-donating precursors, such as alternative organosilane precursors, e.g. tetramethylsilane (4MS).

[0076] The carbon-donating precursor to silane ratio can be varied by changing the flow rates of the reactive precursors. FIG. 5 shows how the ratio (as a percentage) of carbon-donating precursor (i.e. 3MS in this example) to silane (SiH.sub.4) affects the SiC/SiN (˜1250 cm.sup.−1) and SiCH.sub.x/SiN (˜2900 cm.sup.−1) FTIR peak area ratios (lines 50 and 52 respectively). The peak areas were ratioed to the major SiN peak area (at ˜840 cm.sup.−1) to normalise the results to variations in film thickness. Controlling the carbon-donating precursor to silane (SiH.sub.4) ratio allows the carbon content of the film to be varied in a controllable manner.

[0077] FIG. 6 shows how the ratio (as a percentage) of carbon-donating precursor (i.e. 3MS in this example) to silane (SiH.sub.4) affects the stability of the measured refractive index over a six day period. A lower 3MS/SiH.sub.4 flow rate ratio gave less of a change (reduction) in RI over time, which is indicative of a more stable film that is less moisture sensitive. Films with a 3MS/SiH.sub.4 ratio of ˜20% provided an acceptable change in RI of less than 0.14. However, a 3MS/SiH.sub.4 flow rate ratio of ˜10% provided a significant improvement in stability of the measured RI. Varying the carbon-donating precursor to silane flow rate ratio allows the carbon content in the SiCN:H films to be fine-tuned. Without wishing to be bound by any theory or conjecture, it is believed that a high carbon content in the films can provide an improved bonding strength. However, SiCN:H films with higher carbon content are also more susceptible to moisture absorption, and therefore are less stable.

[0078] FIG. 7 shows that the FTIR spectra of the SiCN:H films deposited using these methods show no significant change in their FTIR spectra over a six day period, indicating that the films are stable. In particular, there was no observable increase in an Si—O peak (˜1050 cm.sup.−1) and only a minimal increase in —OH peak (˜3350 cm.sup.−1) after six days of exposure to atmosphere. This indicates the film is stable and that only minimal water vapour absorption occurs after exposure to atmosphere at room temperature.

[0079] FIG. 8 shows how the refractive index varies over a six day period when exposed to atmosphere. An initial reduction in RI is observed within the first 24 hour period. However, thereafter, the RI remains stable at about 2.00.

[0080] Post-Deposition Treatment

[0081] An optional post-deposition treatment can be performed on the SiCN:H films deposited using methods of the present invention. The post-deposition treatment can improve the stability of the film, and further improve (reduce) the film's sensitivity to moisture. The post-deposition treatment can be a thermal anneal, a plasma treatment (such as a hydrogen plasma treatment), an e-beam treatment, an ultraviolet curing technique, or a combination thereof. Preferably, the post-deposition treatment is a hydrogen plasma treatment.

[0082] A hydrogen plasma treatment can comprise exposing the as deposited SiCN:H film to a hydrogen plasma, preferably without a break in vacuum and/or without exposure to water vapour/moisture. The hydrogen plasma treatment can comprise introducing a hydrogen gas precursor into the chamber and sustaining a plasma. The pressure in the chamber can be about 2 Torr. A high frequency RF power (e.g. operating at 13.56 MHz) of about 1 kW can be used to sustain the plasma. The hydrogen plasma treatment can be performed for a duration of about 30-300 s, optionally about 60 s. During the hydrogen plasma treatment, the substrate can be maintained at a temperature that is lower than the temperature used for the SiCN:H deposition step. For example, during the hydrogen plasma treatment, the substrate can be maintained at a temperature of about 200° C. or less, optionally about 175° C. or less, optionally about 150° C. or less, or optionally about 125° C. Performing the hydrogen plasma treatment at a low temperature (e.g. lower than the SiCN:H deposition step) can keep the substrate within low thermal budget constraints. This can help avoid damaging any temperature sensitive features of the substrate.

[0083] FIG. 9 shows how the FTIR spectrum changes over a six day period with and without a post-deposition hydrogen plasma treatment (lines 90 and 92 respectively).

[0084] FIG. 10 shows how a post-deposition hydrogen plasma treatment affects the stability of the RI of the deposited SiCN:H films over a six day period. Without a post-deposition hydrogen plasma treatment (line 100), an initial reduction in RI is observed within the first 24 hour period. However, thereafter, the RI remains stable at about 2.00. However, using a post-deposition hydrogen plasma treatment further improves the stability of the RI (line 102). Negligible changes in RI were observed over a six day period, with the RI retaining a value of about 2.02-2.03. Without wishing to be bound by any theory or conjecture, it is believed that the hydrogen plasma treatment passivates the SiCN:H surface so that it prevents the absorption of moisture. A post-deposition hydrogen plasma treatment can be used to improve the stability of the SiCN:H films.

[0085] Although the present disclosure has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the scope of the present disclosure. Hence, the present disclosure is deemed limited only by the appended claims and the reasonable interpretation thereof.